Shear jamming in highly strained granular system without shear banding
Zhao, Yiqiu; Barés, Jonathan; Zheng, Hu; Behringer, Robert
2016-11-01
Bi et al. have shown that, if sheared, a granular material can jam even if its packing fraction (ϕ) is lower than the critical isotropic jamming point ϕJ. They have introduced a new critical packing fraction value ϕS such that for ϕSjams if sheared. Nevertheless, the value of ϕS as a function of the shear profile or the strain necessary to observe jamming remain poorly understood because of the experimental complexity to access high strain without shear band. We present a novel 2D periodic shear apparatus made of 21 independent, aligned and mirrored glass rings. Each ring can be moved independently which permits us to impose any desired shear profile. The circular geometry allows access to any strain value. The forces between grains are measured using reflective photoelasticity. By performing different shear profiles for different packing fractions we explored the details of jamming diagram including the location of the yield surface. This work is supported by NSF No.DMR1206351, NASA No.NNX15AD38G and W. M. Keck Foundation.
Cosmic shear measurement with maximum likelihood and maximum a posteriori inference
Hall, Alex
2016-01-01
We investigate the problem of noise bias in maximum likelihood and maximum a posteriori estimators for cosmic shear. We derive the leading and next-to-leading order biases and compute them in the context of galaxy ellipticity measurements, extending previous work on maximum likelihood inference for weak lensing. We show that a large part of the bias on these point estimators can be removed using information already contained in the likelihood when a galaxy model is specified, without the need for external calibration. We test these bias-corrected estimators on simulated galaxy images similar to those expected from planned space-based weak lensing surveys, with very promising results. We find that the introduction of an intrinsic shape prior mitigates noise bias, such that the maximum a posteriori estimate can be made less biased than the maximum likelihood estimate. Second-order terms offer a check on the convergence of the estimators, but are largely sub-dominant. We show how biases propagate to shear estima...
In vivo vascular wall shear rate and circumferential strain of renal disease patients.
Park, Dae Woo; Kruger, Grant H; Rubin, Jonathan M; Hamilton, James; Gottschalk, Paul; Dodde, Robert E; Shih, Albert J; Weitzel, William F
2013-02-01
This study measures the vascular wall shear rate at the vessel edge using decorrelation based ultrasound speckle tracking. Results for nine healthy and eight renal disease subjects are presented. Additionally, the vascular wall shear rate and circumferential strain during physiologic pressure, pressure equalization and hyperemia are compared for five healthy and three renal disease subjects. The mean and maximum wall shear rates were measured during the cardiac cycle at the top and bottom wall edges. The healthy subjects had significantly higher mean and maximum vascular wall shear rate than the renal disease subjects. The key findings of this research were that the mean vascular wall shear rates and circumferential strain changes between physiologic pressure and hyperemia that was significantly different between healthy and renal disease subjects.
2007-01-01
The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-medium- angles. This ductile shear zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone, a brittle fault and a gouge zone. All these zones share similar planar attitudes, but contain different linear attitudes and kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These meas- urements yield Fulin indexes of 1.25―3.30, Lode’s parameters of -0.535―-0.112 and strain parameters of 0.41―0.75 for the protomylonite, respectively. These data are plotted within the apparent constric- tional field in Fulin and Hossack diagrams. In contrast, for the mylonite, corresponding parameters are 0.99―1.43, -0.176―-0.004 and 0.63―0.82, respectively, and located in the apparent constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67―0.95, suggesting that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so the lineation in the ductile shear zone could not deflect 90° in the progressively deformation.
An octahedral shear strain-based measure of SNR for 3D MR elastography
McGarry, M D J; Perrinez, P R; Pattison, A J; Weaver, J B; Paulsen, K D [Thayer School of Engineering, Dartmouth College, Hanover, NH 03755 (United States); Van Houten, E E W, E-mail: matthew.d.mcgarry@dartmouth.edu [Department of Mechanical Engineering, University of Canterbury, Christchurch (New Zealand)
2011-07-07
A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, {gamma}, is directly related to the shear modulus, {mu}, through the definition of shear stress, {tau} = {mu}{gamma}. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects. (note)
An Octahedral Shear Strain Based measure of SNR for 3D MR Elastography
McGarry, MDJ; Van Houten, EEW; Perriñez, PR; Pattison, AJ; Weaver, JB; Paulsen, KD
2011-01-01
A signal to noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for MR elastography, where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects. PMID:21654044
An octahedral shear strain-based measure of SNR for 3D MR elastography.
McGarry, M D J; Van Houten, E E W; Perriñez, P R; Pattison, A J; Weaver, J B; Paulsen, K D
2011-07-07
A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects.
Computer modelling of bone's adaptation: the role of normal strain, shear strain and fluid flow.
Tiwari, Abhishek Kumar; Prasad, Jitendra
2017-04-01
Bone loss is a serious health problem. In vivo studies have found that mechanical stimulation may inhibit bone loss as elevated strain in bone induces osteogenesis, i.e. new bone formation. However, the exact relationship between mechanical environment and osteogenesis is less clear. Normal strain is considered as a prime stimulus of osteogenic activity; however, there are some instances in the literature where osteogenesis is observed in the vicinity of minimal normal strain, specifically near the neutral axis of bending in long bones. It suggests that osteogenesis may also be induced by other or secondary components of mechanical environment such as shear strain or canalicular fluid flow. As it is evident from the literature, shear strain and fluid flow can be potent stimuli of osteogenesis. This study presents a computational model to investigate the roles of these stimuli in bone adaptation. The model assumes that bone formation rate is roughly proportional to the normal, shear and fluid shear strain energy density above their osteogenic thresholds. In vivo osteogenesis due to cyclic cantilever bending of a murine tibia has been simulated. The model predicts results close to experimental findings when normal strain, and shear strain or fluid shear were combined. This study also gives a new perspective on the relation between osteogenic potential of micro-level fluid shear and that of macro-level bending shear. Attempts to establish such relations among the components of mechanical environment and corresponding osteogenesis may ultimately aid in the development of effective approaches to mitigating bone loss.
Lesuer, D R; Syn, C K; Sherby, O D
2004-07-06
The mechanical response of a pearlitic UHCS-1.3C steel deformed at approximately 4000 s{sup -1} to large strains ({var_epsilon} = -0.9) has been studied. Failure, at both the macroscopic and the microscopic levels has been evaluated, and the ability of the material to absorb energy in compression has been examined. Failure occurred by the development of a shear band. However before failure, extensive buckling of the carbide plates was observed and the UHCS-1.3C material exhibited significant potential for compressive ductility and energy absorption due to the distributed buckling of these plates. Strain localization during adiabatic shear band development resulted in the formation of austenite. Subsequent cooling produced a divorced-eutectoid transformation with associated deformation, which resulted in a microstructure consisting of 50 to 100 nm sized grains. The stress-strain behavior within the shear band has also been determined. The results are used to critically evaluate the maximum shear stress criterion of shear band development. New criteria for the development of shear bands are developed based on a strain energy concept.
The importance of strain localisation in shear zones
Bons, Paul D.; Finch, Melanie; Gomez-Rivas, Enrique; Griera, Albert; Llorens, Maria-Gema; Steinbach, Florian; Weikusat, Ilka
2016-04-01
The occurrence of various types of shear bands (C, C', C'') in shear zones indicate that heterogeneity of strain is common in strongly deformed rocks. However, the importance of strain localisation is difficult to ascertain if suitable strain markers are lacking, which is usually the case. Numerical modelling with the finite-element method has so far not given much insight in the development of shear bands. We suggest that this is not only because the modelled strains are often not high enough, but also because this technique (that usually assumes isotropic material properties within elements) does not properly incorporate mineral deformation behaviour. We simulated high-strain, simple-shear deformation in single- and polyphase materials with a full-field theory (FFT) model coupled to the Elle modelling platform (www.elle.ws; Lebensohn 2001; Bons et al. 2008). The FFT-approach simulates visco-plastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses in relations to the applied stresses. Griera et al. (2011; 2013) have shown that this approach is particularly well suited for strongly anisotropic minerals, such as mica and ice Ih (Llorens 2015). We modelled single- and polyphase composites of minerals with different anisotropies and strengths, roughly equivalent to minerals such as ice Ih, mica, quartz and feldspar. Single-phase polycrystalline aggregates show distinct heterogeneity of strain rate, especially in case of ice Ih, which is mechanically close to mica (see also Griera et al. 2015). Finite strain distributions are heterogeneous as well, but the patterns may differ from that of the strain rate distribution. Dynamic recrystallisation, however, usually masks any strain and strain rate localisation (Llorens 2015). In case of polyphase aggregates, equivalent to e.g. a granite, we observe extensive localisation in both syn- and antithetic shear bands. The antithetic shear bands
Constitutive relations for the shear band evolution in granular matter under large strain
无
2008-01-01
A so-called "split-bottom ring shear cell" leads to wide shear bands under slow, quasi-static deformation. Unlike normal cylindrical Couette shear cells or rheometers, the bottom plate is split such that the outer part of it can move with the outer wail, while the other part (inner disk) is immobile. From discrete element simulations (DEM), several continuum fields like the density, velocity, deformation gradient and stress are computed and evaluated with the goal to formulate objective constitutive relations for the powder flow behavior. From a single simulation, by applying time-and (local) space-averaging, a non-linear yield surface is obtained with peculiar stress dependence.The anisotropy is always smaller than the macroscopic friction coefficient. However, the lower bound of anisotropy increases with the strain rate, approaching the maximum according to a stretched exponential with a specific rate that is consistent with a shear path of about one particle diameter.
Strain Rate Sensitivity of Epoxy Resin in Tensile and Shear Loading
Gilat, Amos; Goldberg, Robert K.; Roberts, Gary D.
2005-01-01
The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5x10(exp 5), 2, and 450 to 700 /s. In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear both resins show a ductile response with maximum stress that is increasing with strain rate. In tension a ductile response is observed at low strain rate (approx. 5x10(exp 5) /s), and brittle response is observed at the medium and high strain rates (2, and 700 /s). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.
Theory and Practice of Shear/Stress Strain Gage Hygrometry
Shams, Qamar A.; Fenner, Ralph L.
2006-01-01
Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.
Evolution of displacements and strains in sheared amorphous solids
Maloney, Craig E [Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA (United States); Robbins, Mark O [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)], E-mail: craigmaloney@cmu.edu, E-mail: mr@pha.jhu.edu
2008-06-18
The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Both the mean squared displacement and mean squared strain rise linearly with the length of the strain interval {delta}{gamma} over which they are measured. However, the increase in displacement does not represent single-particle diffusion. There are long-range spatial correlations in displacement associated with slip lines with an amplitude of order the particle size. Strong dependence on system size is also observed. The probability distributions of displacement and strain are very different. For small {delta}{gamma} the distribution of displacement has a plateau followed by an exponential tail. The distribution becomes Gaussian as {delta}{gamma} increases to about 0.03. The strain distributions consist of sharp central peaks associated with elastic regions, and long exponential tails associated with plastic regions. The latter persist to the largest {delta}{gamma} studied.
Maximum twin shear stress factor criterion for sliding mode fracture initiation
黎振兹; 李慧剑; 黎晓峰; 周洪彬; 郝圣旺
2002-01-01
Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is the maximum twin shear stress factor criterion. The authors studied a finite width plate with central slant crack, subject to a far-field uniform uniaxial tensile or compressive stress.
吴志荣; 胡绪腾; 宋迎东
2013-01-01
工程中的大多构件承受着复杂的载荷形式,将单轴疲劳模型应用到多轴载荷情况已不能满足工程精度的要求,多轴载荷下的疲劳寿命计算日益引起人们的重视.基于临界平面的思想,结合Fatemi-Socie(FS)模型和Smith-Watson-Topper(SWT)参数各自的优点,提出一种新的多轴疲劳寿命预测模型.该模型以最大切应变幅与最大切应变幅平面上修正SWT参数的和作为多轴疲劳损伤控制参量,此参量可以同时考虑非比例附加循环硬化和平均应力对材料多轴疲劳寿命的影响,能同时适用于比例和非比例加载下的多轴疲劳问题.采用纯钛Ti、BT9钛合金、304不锈钢、S45C钢和1045HR钢5种材料多轴疲劳试验数据对提出的模型进行评估和验证,对几种材料比例和非比例加载下的多轴疲劳寿命预测结果大都分布在试验结果的2倍分散带之内,结果表明提出的多轴疲劳寿命模型具有较高的预测精度.%The most components of engineering structures are usually subjected to a complex loading. It is unable to meet the requirements of engineering precision if a uniaxial fatigue model is used under multi-axial loading. The calculation of fatigue life prediction under multiaxial loading causes people's attention more and more. A new multiaxial fatigue life prediction model is proposed based on the critical plane criteria. The model integrates the respective advantages of Fatemi-Socie(FS) model and Smith-Watson-Topper(SWT) parameter. The damage parameter in this model takes the sum of the maximum shear strain amplitude and the modified SWT parameter on the maximum shear strain amplitude plain. It can consider the effects of additional cyclic hardening due to non-proportional loading and mean stress on the multi-axial fatigue life of material. The proposed model can be applied to proportional and non-proportional loading. The model is evaluated by the multiaxial fatigue test data of pure titanium, BT9
Hooyer, T.S.; Iverson, N.R.; Lagroix, F.; Thomason, J.F.
2008-01-01
Wet-based portions of ice sheets may move primarily by shearing their till beds, resting in high sediment fluxes and the development of subglacial landforms. This model of glacier movement, which requires high bed shear strains, can be tested using till microstructural characteristics that evolve during till deformation. Here we examine the development of magnetic fabric using a ring shear device to defom two Wisconsin-age basal tills to shear strains as high as 70. Hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility (AMS) develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller. At moderate shear strains (???6-25), principal axes of maximum magnetic susceptibility develop a strong fabric (S1 eignevalues of 0.83-0.96), without further strengthening at higher strains, During deformation, directions of maximum susceptibility cluster strongly in the direction of shear and plunge 'up-glacier,' consistent with the behavior of pebbles and sand particles studied in earlier experiments. In contrast, the magnitude of AMS does not vary systematically with strain and is small relative to its variability among samples; this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear. Although processes other than pervasive bed deformation may result in strong flow parallel fabrics, AMS fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model. Copyright 2008 by the American Geophysical Union.
Effect of consolidation ratios on maximum dynamic shear modulus of sands
Yuan Xiaoming; Sun Jing; Sun Rui
2005-01-01
The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field or in the laboratory. The effect of consolidation ratios on the maximum DSM for two types of sand is investigated by using resonant column tests. And, an increment formula to obtain the maximum DSM for cases of consolidation ratio kc＞1 is presented. The results indicate that the maximum DSM rises rapidly when kc is near 1 and then slows down, which means that the power function of the consolidation ratio increment kc-1 can be used to describe the variation of the maximum DSM due to kc＞1. The results also indicate that the increase in the maximum DSM due to kc＞1 is significantly larger than that predicted by Hardin and Black's formula.
COMPRESSIVE AND SHEAR ANALYSIS OF RUBBER BLOCK UNDER LARGE STRAIN
K. Sridharan
2013-01-01
Full Text Available The Elastomeric materials have found use in a wide range of applications, including hoses, tires, gaskets, seals, vibration isolators, bearings and dock fenders. The analysis of rubber blocks for its compression and shear behavior has been carried out using the imaging techniques. The dynamic stressing and its associated change in shape of the rubber blocks during large compression are very limited as their measurements were difficult. A newly developed Machine Vision based image processing test has been effectively used to study the deformation characteristics of the rubber blocks under large strains. An extended analysis on the rubber blocks has been carried out to understand the compression and deformation behavior in static and dynamic condition and the nonlinear behavior were also characterized. The rubber blocks of distinguished geometries have shown diverse change in shape and nonlinear deformation behavior under compression/shear loading.
Strain and shear types of the Louzidian ductile shear zone in southern Chifeng,Inner Mongolia,China
WANG XinShe; ZHENG YaDong; WANG Tao
2007-01-01
The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-mediumangles. This ductile shear zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone, a brittle fault and a gouge zone. All these zones share similar planar attitudes. But contain different linear attitudes and kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These measurements yield Fulin indexes of 1.25-3.30,Lode's parameters of-0.535-0.112 and strain parameters of 0.41-0.75 for the protomylonite, respectively. These data are plotted within the apparent constrictional field in Fulin and Hossack diagrams. In contrast, for the mylonite, corresponding parameters are 0.99-1.43,-0.176--0.004 and 0.63-0.82,respectively,and located in the apparent constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67-0.95,suggesting that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so the lineation in the ductile shear zone could not deflect 90.in the progressively deformation.
Monitoring dyke injection and strain field evolution using shear-wave splitting.
Kendall, J.-M.; Verdon, J. P.; Keir, D.; Baird, A.
2012-04-01
Magma storage and dyke injection in the shallow crust is a fundamental process in rifting and volcanic environments. The dyking will tend to align with directions of maximum compressive stress, and the associated aligned fracturing and melt migration provides a very effective means of generating seismic anisotropy. Observations of shear-wave splitting provide one of the most unambiguous indicators of such anisotropy. As such, shear-wave splitting can be used to monitor the evolving strain field in volcanic and rifting environments. Here we apply lessons learned from monitoring fracture propagation during the hydraulic stimulation of tight-gas reservoirs. In a number of experiments we observe spatial and temporal variations in shear-wave splitting magnitude and orientation. We invert shear-wave observations for fracture properties, including the tangential and normal compliance, the ratio of which is a good indicator of fluid flow and permeability. Frequency dependent affects can be also used to indicate the length scales of the causative cracks or fractures. We apply these insights to microseismic data recently acquired across the volcanically active Afar triple junction in Ethiopia. The pattern of S-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The results help in our understanding of the role of melt in strain accommodation in rifting and volcanic environments.
Tat, Jimmy; Kociolek, Aaron M; Keir, Peter J
2013-10-01
Non-inflammatory fibrosis and thickening of the subsynovial connective tissue (SSCT) are characteristic in carpal tunnel syndrome (CTS) patients. These pathological changes have been linked to repetitive hand tasks that create shear forces between the flexor tendons and SSCT. We measured the relative motion of the flexor digitorum superficialis tendon and SSCT during two repetitive finger tasks using color Doppler ultrasound. Twelve participants performed flexion-extension cycles for 30 min with the long finger alone (differential movement) and with all four fingers together (concurrent movement). Shear strain index (SSI, a relative measure of excursion in flexion and extension) and maximum velocity ratio (MVR, the ratio of SSCT versus tendon during flexion and extension) were used to represent shear. A linear effect of exertion time was significant and corresponded with larger tendon shear in differential motion. The flexion SSI increased 20.4% from the first to the 30th minute, while MVR decreased 8.9% in flexion and 8.7% in extension. No significant changes were found during concurrent motion. These results suggest that exposure to repetitive differential finger tasks may increase the risk of shear injury in the carpal tunnel. Copyright © 2013 Orthopaedic Research Society.
王志; 饶秋华; 谢海峰
2008-01-01
Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τmax at the crack tip is much larger than the maximum tensile stress σ1 and the ratio of τmax/σ1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain-time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ1 and τmax are increased as the load increases,but the slope of τmax is larger than that of σ1 and the value of τmax is always larger than that of σ1.Therefore,τmax reaches its limited value at peak load before σ1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear) test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.
孙宗颀
2001-01-01
When a crack is subjected to shear force, crack branching usually occurs. Theoretical study shows that the crack branching under shear loading is caused by tensile stress, but not caused by shear fracture. The co-plane shear fracture could be obtained if compressive stress with given direction is applied to the specimen, subsequently, calculated shear fracture toughness, KⅡ C, is larger than KⅠ C. A prerequisite of possible occurrence of mode Ⅱ fracture was proposed. The study of shear fracture shows that the maximum circumferential stress theory considered its criterion as a parametric equation of a curve in KⅠ, KⅡ plane is incorrect; the predicted ratio KⅡ C/KⅠ C=0.866 is incorrect too.
International Organization for Standardization. Geneva
1997-01-01
Fibre-reinforced plastic composites - Determination of the in-plane shear stress/shear strain response, including the in-plane shear modulus and strength, by the plus or minus 45 degree tension test method
Effects of texture on shear band formation in plane strain tension/compression and bending
Kuroda, M.; Tvergaard, Viggo
2007-01-01
model analysis. Third, shear band developments in plane strain pure bending of a sheet specimen with the typical textures are studied. Regions near the surfaces in a bent sheet specimen are approximately subjected to plane strain tension or compression. From this viewpoint, the bendability of a sheet......In this study, effects of typical texture components observed in rolled aluminum alloy sheets on shear band formation in plane strain tension/compression and bending are systematically studied. The material response is described by a generalized Taylor-type polycrystal model, in which each grain...... are obtained: i.e. the critical strain at the onset of shear banding and the corresponding orientation of shear band. Second, the shear band development in plane strain tension/compression is analyzed by the finite element method. Predictability of the finite element analysis is compared to that of the simple...
无
2010-01-01
The Louzidian low-angle ductile shear detachment zone at the south of Chifeng is a SE-dipping, low-angle normal fault system. It is composed mainly of ductile shear zone, ductile-brittle shear zone and brittle fault zone. The ductile shear zone consists of, from bottom to top, mylonitic rocks, protomylonites and mylonites. Finite strain measurement of feldspar strain markers from those rocks using the Rf /φ method shows that strain intensities (Es) of the mylonite at core of the ductile shear zone (Es=0.65-0.96) are higher than those of the mylonitic rocks close to the granite intrusions (Es=0.59-0.62) and of the protomylonites at top of the ductile shear zone (Es= 0.47-0.70), and the strain types of the protomylonites and mylonties are elongate strain and plane-flattening strain, respectively. The kinematic vorticity values (Wk) estimated by the Polar Mohr diagram and the Rigid Grain Net range from 0.81 to 0.90 with an average of 0.85 for the protomylonites, and from 0.53 to 0.80 with 0.66 on average for the mylonites; Wk values of the extensional crenulation cleavage, i.e., C′, estimated by C′ method range from 0.63 to 0.37 with an average of 0.50. The angles between the maximum principal stress and shearing direction determined using the Maximum effective moment criterion evolved from 61° to 69° and to 75°, and finally normal to shearing direction. The results of strain and kinematic vorticity measurements suggest that high strain corresponds to low kinematic vorticity. Kinematic vorticity measurements show that the Louzidian low-angle ductile shear detachment zone is a result of a combination of simple-dominated general shearing at the early stage and pure-dominated general shearing at the late stage. All these, together with isotope geochronology and regional tectonic background, suggest that the Louzidian ductile shear detachment zone resulted from a combination of crust extension and magma intrusion. The model of simple shear at the early stage and
Evaluation of stresses in a combined plane strain-simple shear test
Boogaard, van den A.H.; Riel, van M.; Huetink, J.
2005-01-01
A biaxial testing device for sheet metal has been developed that can impose a combination of plane strain and simple shear deformation. The specimen has a large width to height ratio and a small height to thickness ratio. The forces in tensile and shear direction are easily measured and the tensile
Analysis of strain paths of sheared edges during hole expansion tests
Koebel, Philipp; Van Tyne, Chester J.; Hora, Pavel; Manopulo, Niko
2013-12-01
One of the limitations to the widespread use of advanced high strength steel (AHSS) sheets is the cracking of sheared edges during subsequent stretching operations, as nearly all stamped parts are sheared prior to sheet forming. Cracking at the edge occurs at levels below the conventional forming limit criteria. Understanding the strain path of the sheared edge during a hole expansion test should provide insight into the strain path of a sheared edge when it is stretched during production. As a result, experimental as well as finite element simulations are used for analyzing the strain path behavior of a sheared edge during hole expansion tests. The shearing process changes the global behavior in the sheet during a hole expansion, and the finite element results indicate that the strain paths for points near the edge of the hole during expansion are non-linear due to the presence of the shear affected zone (SAZ). These results are consistent with previously measured experimental values for the strain path.
Ott, Kyle A; Armiger, Robert S; Wickwire, Alexis C; Carneal, Catherine M; Trexler, Morgana M; Lennon, Andrew M; Zhang, Jiangyue; Merkle, Andrew C
2012-01-01
Predicting spinal injury under high rates of vertical loading is of interest, but the success of computational models in modeling this type of loading scenario is highly dependent on the material models employed. Understanding the response of these biological materials at high strain rates is critical to accurately model mechanical response of tissue and predict injury. While data exists at lower strain rates, there is a lack of the high strain rate material data that are needed to develop constitutive models. The Split Hopkinson Pressure Bar (SHPB) has been used for many years to obtain properties of various materials at high strain rates. However, this apparatus has mainly been used for characterizing metals and ceramics and is difficult to apply to softer materials such as biological tissue. Recently, studies have shown that modifications to the traditional SHPB setup allow for the successful characterization of mechanical properties of biological materials at strain rates and peak strain values that exceed alternate soft tissue testing techniques. In this paper, the previously-reported modified SHPB technique is applied to characterize human intervertebral disc material under simple shear. The strain rates achieved range from 5 to 250 strain s-1. The results demonstrate the sensitivity to the disc composition and structure, with the nucleus pulposus and annulus fibrosus exhibiting different behavior under shear loading. Shear tangent moduli are approximated at varying strain levels from 5 to 20% strain. This data and technique facilitates determination of mechanical properties of intervertebral disc materials under shear loading, for eventual use in constitutive models.
A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.
Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan
2015-06-01
In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.
Dynamical properties of the brain tissue under oscillatory shear stresses at large strain range
Boudjema, F.; Khelidj, B.; Lounis, M.
2017-01-01
In this experimental work, we study the viscoelastic behaviour of in vitro brain tissue, particularly the white matter, under oscillatory shear strain. The selective vulnerability of this tissue is the anisotropic mechanical properties of theirs different regions lead to a sensitivity to the angular shear rate and magnitude of strain. For this aim, shear storage modulus (G‧) and loss modulus (G″) were measured over a range of frequencies (1 to 100 Hz), for different levels of strain (1 %, to 50 %). The mechanical responses of the brain matter samples showed a viscoelastic behaviour that depend on the correlated strain level and frequency range and old age sample. The samples have been showed evolution behaviour by increasing then decreasing the strain level. Also, the stiffness anisotropy of brain matter was showed between regions and species.
Small breast lesion classification performance using the normalized axial-shear strain area feature.
Thittai, Arun K; Yamal, Jose-Miguel; Ophir, Jonathan
2013-03-01
Breast cancers that are found and confirmed because they are causing symptoms tend to be larger and are more likely to have already spread to the lymph nodes and beyond. Thus, early detection and confirmation are of paramount importance. The normalized axial-shear strain area (NASSA) feature from the axial-shear strain elastogram (ASSE) has been shown to be a feature that can identify the boundary-bonding conditions that are indicative of the presence of cancer. Recently, we investigated and reported on the potential of the NASSA feature for breast lesion classification into fibroadenomas and cancers. In this article, we investigate the size distribution of the lesions that were part of the previous study and analyze classification performance specifically on small lesions (BIRADS) ultrasound scores. The observers outlined the lesions on the sonograms and the lesion size (maximum circle-equivalent diameter in millimeters) was computed from this outline. The ASSE was automatically segmented and color-overlaid on the sonogram, and the NASSA feature from ASSE was computed semi-automatically. Receiver operating characteristic curves were then generated for the subset of cases involving small lesions. Box plots were produced for the two different lesion size groups, small and large, from a logistic regression classifier that was built previously. The results of our study show that approximately 38% and 22% of the fibroadenomas and cancers, respectively, were small. Furthermore, it was found that the NASSA feature resulted in a perfect classification of the small lesions, both in the training data and in the cross-validation. For lesions 10 mm had a difference of 0.52 ± 0.24 (p 10 mm). These results suggest that the ASSE feature can work equally well, even on small lesions, to improve the standard ultrasound BIRADS-based breast lesion classification of fibroadenoma and malignant tumors.
SMALL BREAST LESION CLASSIFICATION PERFORMANCE USING THE NORMALIZED AXIAL-SHEAR STRAIN AREA FEATURE
Thittai, Arun K.; Yamal, Jose-Miguel; Ophir, Jonathan
2013-01-01
Breast cancers that are found and confirmed because they are causing symptoms tend to be larger and are more likely to have already spread into the lymph nodes and beyond. Thus early detection and confirmation are of paramount importance. The normalized axial–shear strain area (NASSA) feature from the axial-shear strain elastogram (ASSE) has been shown to be a feature that can identify the boundary bonding conditions that are indicative of the presence of cancer. Recently, we investigated and reported on the potential of the NASSA feature for breast lesion classification into fibroadenomas and cancers. In this paper, we investigate the size distribution of the lesions that were part of the previous study and analyze classification performance specifically on small lesions (BIRADS® ultrasound scores. The observers outlined the lesions on the sonograms and the lesion size (maximum circle-equivalent diameter in mm) was computed from this outline. The ASSE was automatically segmented and color overlaid on the sonogram, and the NASSA feature from ASSE was computed semi–automatically. Receiver operating characteristic (ROC) curves were then generated for the subset of cases involving small lesions. Box-plots were produced for the two different lesion size groups, small and large, from a logistic regression classifier that was built previously. The results of our study show that approximately 38% and 22% of the fibroadenomas and cancers respectively were small. Further, it was found that the NASSA feature resulted in a perfect classification of the small lesions, both in the training data and in the cross-validation. For lesions 10 mm had a difference of 0.52 ± 0.24 (p10 mm). These results suggest that the ASSE feature can work equally well even on small lesions to improve the standard US BIRADS–based breast lesion classification of fibroadenoma and malignant tumors. PMID:23312961
Determination of Modulus of Elasticity and Shear Modulus by the Measurement of Relative Strains
Labašová, Eva
2016-12-01
This contribution is focused on determining the material properties (Young modulus and shear modulus) of the testing samples. The theoretical basis for determining material properties are the knowledge of linear elasticity and strength. The starting points are dependencies among the modulus of elasticity, shear modulus, normal stress and relative strain. The relative strains of the testing samples were obtained by measuring predefined load conditions using a strain-gauge bridge and the universal measurement system Quantum X MX 840. The integration of these tasks into the teaching process enhances practical and intellectual skills of students at secondary level technical universities.
WANG Xue-bin
2006-01-01
By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstmctural effect beyond the occurrence of shear strain localization, the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB) were analyzed. The peak local plastic shear strain is proportional to the average plastic shear strain, while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress. The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain. A parametric study was carried out to study the influence of constitutive parameters on shear strain localization. Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain. Higher values of strain-hardening exponent, strain rate sensitive coefficient, melting point,thermal capacity and mass density result in higher critical plastic shear strain, leading to less apparent shear localization at the same average plastic shear strain. The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain, the distributions of local plastic shear strain and deformation in ASB. The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous. When the maximum critical plastic shear strain is reached, the least apparent shear localization occurs.
Effect of bone-soft tissue friction on ultrasound axial shear strain elastography
Tang, Songyuan; Chaudhry, Anuj; Kim, Namhee; Reddy, J. N.; Righetti, Raffaella
2017-08-01
Bone-soft tissue friction is an important factor affecting several musculoskeletal disorders, frictional syndromes and the ability of a bone fracture to heal. However, this parameter is difficult to determine using non-invasive imaging modalities, especially in clinical settings. Ultrasound axial shear strain elastography is a non-invasive imaging modality that has been used in the recent past to estimate the bonding between different tissue layers. As most elastography methods, axial shear strain elastography is primarily used in soft tissues. More recently, this technique has been proposed to assess the bone-soft tissue interface. In this paper, we investigate the effect of a variation in bone-soft tissue friction coefficient in the resulting axial shear strain elastograms. Finite element poroelastic models of bone specimens exhibiting different bone-soft tissue friction coefficients were created and mechanically analyzed. These models were then imported to an ultrasound elastography simulation module to assess the presence of axial shear strain patterns. In vitro experiments were performed to corroborate selected simulation results. The results of this study show that the normalized axial shear strain estimated at the bone-soft tissue interface is statistically correlated to the bone-soft tissue coefficient of friction. This information may prove useful to better interpret ultrasound elastography results obtained in bone-related applications and, possibly, monitor bone healing.
Effects of relative density and accumulated shear strain on post-liquefaction residual deformation
J. Kim
2013-10-01
Full Text Available The damage caused by liquefaction, which occurs following an earthquake, is usually because of settlement and lateral spreading. Generally, the evaluation of liquefaction has been centered on settlement, that is, residual volumetric strain. However, in actual soil, residual shear and residual volumetric deformations occur simultaneously after an earthquake. Therefore, the simultaneous evaluation of the two phenomena and the clarification of their relationship are likely to evaluate post-liquefaction soil behaviors more accurately. Hence, a quantitative evaluation of post-liquefaction damage will also be possible. In this study, the effects of relative density and accumulated shear strain on post-liquefaction residual deformations were reviewed through a series of lateral constrained-control hollow cylindrical torsion tests under undrained conditions. In order to identify the relationship between residual shear and residual volumetric strains, this study proposed a new test method that integrates monotonic loading after cyclic loading, and K0-drain after cyclic loading – in other words, the combination of cyclic loading, monotonic loading, and the K0 drain. In addition, a control that maintained the lateral constrained condition across all the processes of consolidation, cyclic loading, monotonic loading, and drainage was used to reproduce the anisotropy of in situ ground. This lateral constrain control was performed by controlling the axial strain, based on the assumption that under undrained conditions, axial and lateral strains occur simultaneously, and unless axial strain occurs, lateral strain does not occur. The test results confirmed that the recovery of effective stresses, which occur during monotonic loading and drainage after cyclic loading, respectively, result from mutually different structural restoration characteristics. In addition, in the ranges of 40–60% relative density and 50–100% accumulated shear strain, relative
Reduced thoracolumbar fascia shear strain in human chronic low back pain
2011-01-01
Background The role played by the thoracolumbar fascia in chronic low back pain (LBP) is poorly understood. The thoracolumbar fascia is composed of dense connective tissue layers separated by layers of loose connective tissue that normally allow the dense layers to glide past one another during trunk motion. The goal of this study was to quantify shear plane motion within the thoracolumbar fascia using ultrasound elasticity imaging in human subjects with and without chronic low back pain (LBP). Methods We tested 121 human subjects, 50 without LBP and 71 with LBP of greater than 12 months duration. In each subject, an ultrasound cine-recording was acquired on the right and left sides of the back during passive trunk flexion using a motorized articulated table with the hinge point of the table at L4-5 and the ultrasound probe located longitudinally 2 cm lateral to the midline at the level of the L2-3 interspace. Tissue displacement within the thoracolumbar fascia was calculated using cross correlation techniques and shear strain was derived from this displacement data. Additional measures included standard range of motion and physical performance evaluations as well as ultrasound measurement of perimuscular connective tissue thickness and echogenicity. Results Thoracolumbar fascia shear strain was reduced in the LBP group compared with the No-LBP group (56.4% ± 3.1% vs. 70.2% ± 3.6% respectively, p fascia shear strain and the following variables: perimuscular connective tissue thickness (r = -0.45, p fascia shear strain was ~20% lower in human subjects with chronic low back pain. This reduction of shear plane motion may be due to abnormal trunk movement patterns and/or intrinsic connective tissue pathology. There appears to be some sex-related differences in thoracolumbar fascia shear strain that may also play a role in altered connective tissue function. PMID:21929806
The plane strain shear fracture of the advanced high strength steels
Sun, Li
2013-12-01
The "shear fracture" which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of "shear fracture" phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a "shear fracture" in the component.
The plane strain shear fracture of the advanced high strength steels
Sun, Li, E-mail: li.sun@gm.com [General Motors China Science Lab, No.56 Jinwan Road, Shanghai, 201206 (China)
2013-12-16
The “shear fracture” which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of “shear fracture” phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a “shear fracture” in the component.
无
2006-01-01
Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stress- strain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial compression were presented, respectively. The three derived stress- strain curves were generalized as a unified formula. Beyond the onset of strain localization, a linear strain-softening constitutive relation for localized band was assigned. The size of the band was controlled by internal or characteristic length according to gradient-dependent plasticity. Elastic strain within the entire specimen was assumed to be uniform and decreased with the increase of plastic strain in localized band. Total strain of the specimen was decomposed into elastic and plastic parts. Plastic strain of the specimen was the average value of plastic strains in localized band over the entire specimen. For different heights, the predicted softening branches of the relative stress - strain curves in uniaxial compression are consistent with the previously experimental results for normal concrete specimens. The present expressions for the post-peak stress - deformation curves in uniaxial tension and direct shear agree with the previously numerical results based on gradient-dependent plasticity.
Analysis of Maximum Shear Stress of Asphalt Pavement%沥青路面最大剪应力分析
陈光伟; 费国新; 陈荣生
2012-01-01
Factors and variation of the maximum shear stress of the typical semi-rigid asphalt pavement and bridge deck pavement in Jiangsu were calculated and analyzed using ABAQUS software. The maximum shear stress distribution was consistent with the semi-rigid asphalt pavement and bridge deck pavement and the maximum shear stress level was close under the level. The maximum shear stress showed a positive correlation with the verticaland horizontal vehicle loads and was significantly affected by the loads. The maximum shear stress decreased as the pavement thickness and modulus increase, and increased as the semi-rigid base thickness and modulus increase, but the increase value was small. Thereby these analysis above would provides an academic basis for solving the rutting problem.%采用ABAQUS软件对典型半刚性基层沥青路面及桥面铺装层中最大剪应力影响因素及变化规律进行了计算与分析。分析表明：半刚性基层沥青路面与水泥混凝土桥面铺装层最大剪应力分布与变化规律基本一致，在相同荷载条件作用下，最大剪应力水平亦接近；最大剪应力与车辆垂直荷载和水平荷载作用呈正比关系，最大剪应力受其影响显著；最大剪应力随着面层或铺装层厚度、模量的增加而相应地变小，随着半刚性基层厚度与模量的增加而变大。以上抗剪影响因素及变化规律的研究为解决车辙问题提供了一定的理论基础。
Cleber Granato de Faria
2015-07-01
Full Text Available ECAP (Equal Channel Angular Pressing involves the pressing of a prismatic specimen through two channels with the cross-section identical to that of the specimen and intercepting at a certain angle. The specimen undergoes shearing over a single plane but no dimensional changes, leading to a possible anisotropy in the mechanical properties of the processed specimen. In addition, multiple ECAP passes lead to a severe refinement of the material structure, which is a function of the angle between the channels and the rotation of the sample in successive passes (the so-called “processing route”. An analysis is presented of the mechanical and microstructural anisotropy along three orthogonal axes in an aluminum alloy specimen processed along three different processing routes. The mechanical properties were evaluated through shearing tests, and the stress–strain curves thus determined indicated that the mechanical behavior of the commercial purity aluminum after ECAP depends on the processing route. The analysis of the specimen surfaces after testing revealed the presence of shearing bands whose orientation also depended on the processing route.
Martin, A.; Bos, M.; Stuart, M.C.; Vliet, T. van
2002-01-01
Interfacial shear properties of adsorbed protein layers at the air/water interface were determined using a Couette-type surface shear rheometer. Such experiments are often used to determine a steady-state ratio between stress and rate of strain, which is then denoted as "surface shear viscosity". Ho
Adiabatic Shear Band Formation in Intermetallic WHA at High Strain Rates and Elevated Temperatures
Duprey, K. E.; Clifton, R. J.; Griffo, A.; German, R. M.
1997-07-01
A novel tungsten-based composite is being developed at The Pennsylvania State University to enhance shear banding by introducing a strong thermo-plastic instability. This liquid phase sintered composite consists of tungsten grains embedded in an intermetallic alloy matrix which has the property that its flow stress increases with increasing temperature up to a critical temperature at which rapid thermal softening begins. Pressure-shear plate impact experiments are being used to subject thin plates of this composite to shearing at strain rates of 10^5 s-1 to 10^6 s-1 at pressures of 6 - 8 GPa, and temperatures up to 650 ^o C. The experiments, combined with computer simulation, are being conducted to determine the effects of the thermal properties of the matrix on the initiation and propagation of adiabatic shear bands.
Suppression of repeated adiabatic shear banding by dynamic large strain extrusion machining
Cai, S. L.; Dai, L. H.
2014-12-01
High speed machining (HSM) is an advanced production technology with great future potential. Chip serration or segmentation is a commonly observed phenomenon during high speed machining of metals, which is found to be ascribed to a repeated shear band formation fueled by thermo-plastic instability occurring within the primary shear zone. The occurrence of serrated chips leads to the cutting force fluctuation, decreased tool life, degradation of the surface finish and less accuracy in machine parts during high speed machining. Hence, understanding and controlling serrated chip formation in HSM are extremely important. In this work, a novel dynamic large strain extrusion machining (DLSEM) technique is developed for suppressing formation of serrated chips. The systematic DLSEM experiments of Ti-6Al-4V and Inconel 718 alloy with varying degrees of imposed extrusion constraint were carried out. It is found that there is a prominent chip morphology transition from serrated to continuous state and shear band spacing decreases with the constraint degree increasing. In order to uncover underlying mechanism of the imposed extrusion constraint suppressing repeated adiabatic shear banding in DLSEM, new theoretical models are developed where the effects of extrusion constraint, material convection due to chip flow and momentum diffusion during shear band propagation are included. The analytical expressions for the onset criterion of adiabatic shear band and shear band spacing in DLSEM are obtained. The theoretical predictions are in agreement with the experimental results.
Ring, Uwe; Bernet, Matthias; Tulloch, Andy
2015-04-01
The Sisters Shear Zone (SSZ) on Stewart Island, New Zealand, is a greenschist-facies extensional shear zone active prior to and possibly during the development of the Pacific-Antarctica spreading ridge at ˜76 Ma. We report quantitative kinematic and rotation data as well as apatite fission-track (AFT) ages from the SSZ. Early kinematic indicators associated with the NNE-trending stretching lineation formed under upper greenschist-facies metamorphism and show alternating top-to-the-NNW and top-to-the-SSE senses of shear. During progressive exhumation lowermost greenschist-facies and brittle-ductile kinematic indicators depict a more uniform top-to-the-SSE sense of shear in the topmost SSZ just below the detachment plane. Deformed metagranites in the SSZ allow the reconstruction of deformation and flow parameters. The mean kinematic vorticity number (Wm) ranges from 0.10 to 0.89; smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone (deeper and upper parts relate to present geometry). High finite strain intensity correlates with low Wm and high Wm numbers near the detachment correlate with relatively weak strain intensity. Finite strain shows oblate geometries. Overall, our data indicate vertical and possibly temporal variations in deformation of the SSZ. Most AFT ages cluster around 85-75 Ma. We interpret the AFT ages to reflect the final stages of continental break-up just before and possibly during the initiation of sea-floor spreading between New Zealand and Antarctica.
The growth and coalescence of ellipsoidal voids in plane strain under combined shear and tension
Scheyvaerts, F.; Onck, P. R.; Tekoglu, C.; Pardoen, T.
2011-01-01
New extensions of a model for the growth and coalescence of ellipsoidal voids based on the Gurson formalism are proposed in order to treat problems involving shear and/or voids axis not necessarily aligned with the main loading direction, under plane strain loading conditions. These extensions are m
Reduced thoracolumbar fascia shear strain in human chronic low back pain
Konofagou Elisa E
2011-09-01
Full Text Available Abstract Background The role played by the thoracolumbar fascia in chronic low back pain (LBP is poorly understood. The thoracolumbar fascia is composed of dense connective tissue layers separated by layers of loose connective tissue that normally allow the dense layers to glide past one another during trunk motion. The goal of this study was to quantify shear plane motion within the thoracolumbar fascia using ultrasound elasticity imaging in human subjects with and without chronic low back pain (LBP. Methods We tested 121 human subjects, 50 without LBP and 71 with LBP of greater than 12 months duration. In each subject, an ultrasound cine-recording was acquired on the right and left sides of the back during passive trunk flexion using a motorized articulated table with the hinge point of the table at L4-5 and the ultrasound probe located longitudinally 2 cm lateral to the midline at the level of the L2-3 interspace. Tissue displacement within the thoracolumbar fascia was calculated using cross correlation techniques and shear strain was derived from this displacement data. Additional measures included standard range of motion and physical performance evaluations as well as ultrasound measurement of perimuscular connective tissue thickness and echogenicity. Results Thoracolumbar fascia shear strain was reduced in the LBP group compared with the No-LBP group (56.4% ± 3.1% vs. 70.2% ± 3.6% respectively, p Conclusion Thoracolumbar fascia shear strain was ~20% lower in human subjects with chronic low back pain. This reduction of shear plane motion may be due to abnormal trunk movement patterns and/or intrinsic connective tissue pathology. There appears to be some sex-related differences in thoracolumbar fascia shear strain that may also play a role in altered connective tissue function.
Strain localization in shear zones during exhumation: a graphical approach to facies interpretation
Cardello, Giovanni Luca; Augier, Romain; Laurent, Valentin; Roche, Vincent; Jolivet, Laurent
2015-04-01
Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shear zones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailed characterization and processes comprehension are far to be fully addressed. In this work, a graphic approach to tectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), which is mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite. Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, from syn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphic reactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frame of smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5 tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved within large boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetric boudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed by chlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture is progressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequence of stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage. In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formed glaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tension gashes that gradually evolve to blueschist shear bands. This process determinates the
Shear-coupled grain-boundary migration dependence on normal strain/stress
Combe, N.; Mompiou, F.; Legros, M.
2017-08-01
In specific conditions, grain-boundary (GB) migration occurs in polycrystalline materials as an alternative vector of plasticity compared to the usual dislocation activity. The shear-coupled GB migration, the expected most efficient GB based mechanism, couples the GB motion to an applied shear stress. Stresses on GB in polycrystalline materials seldom have, however, a unique pure shear component. This work investigates the influence of a normal strain on the shear coupled migration of a Σ 13 (320 )[001 ] GB in a copper bicrystal using atomistic simulations. We show that the yield shear stress inducing the GB migration strongly depends on the applied normal stress. Beyond, the application of a normal stress on this GB qualitatively modifies the GB migration: while the Σ 13 (320 )[001 ] GB shear couples following the 〈110 〉 migration mode without normal stress, we report the observation of the 〈010 〉 mode under a sufficiently high tensile normal stress. Using the nudge elastic band method, we uncover the atomistic mechanism of this 〈010 〉 migration mode and energetically characterize it.
Kinugasa, Ryuta; Oda, Toshiaki; Komatsu, Toshihiko; Edgerton, V Reggie; Sinha, Shantanu
2013-11-01
Muscle fascicles insert into a sheet-like aponeurosis. Adjacent aponeuroses are structurally in contact with each other, and ultimately merge into a common tendon. Consequently, fascicle shortening in planes of tissue layers in adjacent compartments must cause sliding between aponeuroses parallel to the acting forces. In this study, we used velocity-encoded, phase-contrast, and water-saturated spin-lattice relaxation time-weighted imaging to identify and track fascicle and aponeurosis behaviors of human medial gastrocnemius (MG) and soleus (Sol) during 15° dorsiflexion to 30° plantarflexion contractions of the ankle. Interaponeurosis shear strain, which was defined as the relative displacement of the aponeurosis at the fascicle end points (insertion) of the MG and Sol, was an average of 1.35 ± 0.27% (range 1.12 ∼ 1.87%), indicating that the strain is greater in the aponeurosis of MG fascicle insertion than the Sol. The myotendinous junction (MTJ) displacement increased significantly with decreasing interaponeurosis shear strain (P < 0.05). The magnitude of interaponeurosis shear strain had significant correlation with the temporal difference between the time at which the peak aponeurosis displacement of the MG and Sol occurred (P < 0.05). Our model also indicated that theoretical MTJ displacement varies in relation to temporal difference: no temporal difference caused the largest MTJ displacement and presence of temporal differences indicated a reduction in MTJ displacement. Therefore, we concluded that interaponeurosis shear strain is a mechanism enabling individual muscle contraction and thus specific loading of the tendon and joint.
Philipsen, Kirsten Riber; Christiansen, Lasse Engbo; Mandsberg, Lotte Frigaard
2008-01-01
that best describes data is a model taking into account the full covariance structure. An inference study is made in order to determine whether the growth rate of the five bacteria strains is the same. After applying a likelihood-ratio test to models with a full covariance structure, it is concluded...... that the specific growth rate is the same for all bacteria strains. This study highlights the importance of carrying out an explorative examination of residuals in order to make a correct parametrization of a model including the covariance structure. The ML method is shown to be a strong tool as it enables......The specific growth rate for P. aeruginosa and four mutator strains mutT, mutY, mutM and mutY–mutM is estimated by a suggested Maximum Likelihood, ML, method which takes the autocorrelation of the observation into account. For each bacteria strain, six wells of optical density, OD, measurements...
Rahmaan Taamjeed
2015-01-01
Full Text Available Shear tests were performed at strain rates ranging from quasi-static (.01 s−1 to 600 s−1 for DP600 steel and AA5182-O sheet metal alloys at room temperature. A miniature sized shear specimen was modified and validated in this work to perform high strain rate shear testing. Digital image correlation (DIC techniques were employed to measure the strains in the experiments, and a criterion to detect the onset of fracture based on the hardening rate of the materials is proposed. At equivalent strains greater than 20%, the DP600 and AA5182 alloys demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the DP600 shows positive rate sensitivity while the AA5182 was not sensitive to strain rate. For both alloys, the equivalent fracture strain and elongation to failure decreased with strain rate. A conversion of the shear stress to an equivalent stress using the von Mises yield criterion provided excellent agreement with the results from tensile tests at elevated strain rates. Unlike the tensile test, the shear test is not limited by the onset of necking so the equivalent stress can be determined over a larger range of strain.
Rajagopal, K. R.
2011-01-06
This paper is the first part of an extended program to develop a theory of fracture in the context of strain-limiting theories of elasticity. This program exploits a novel approach to modeling the mechanical response of elastic, that is non-dissipative, materials through implicit constitutive relations. The particular class of models studied here can also be viewed as arising from an explicit theory in which the displacement gradient is specified to be a nonlinear function of stress. This modeling construct generalizes the classical Cauchy and Green theories of elasticity which are included as special cases. It was conjectured that special forms of these implicit theories that limit strains to physically realistic maximum levels even for arbitrarily large stresses would be ideal for modeling fracture by offering a modeling paradigm that avoids the crack-tip strain singularities characteristic of classical fracture theories. The simplest fracture setting in which to explore this conjecture is anti-plane shear. It is demonstrated herein that for a specific choice of strain-limiting elasticity theory, crack-tip strains do indeed remain bounded. Moreover, the theory predicts a bounded stress field in the neighborhood of a crack-tip and a cusp-shaped opening displacement. The results confirm the conjecture that use of a strain limiting explicit theory in which the displacement gradient is given as a function of stress for modeling the bulk constitutive behavior obviates the necessity of introducing ad hoc modeling constructs such as crack-tip cohesive or process zones in order to correct the unphysical stress and strain singularities predicted by classical linear elastic fracture mechanics. © 2011 Springer Science+Business Media B.V.
Tanabe, Yuki; Kido, Teruhito; Kurata, Akira; Sawada, Shun; Suekuni, Hiroshi; Kido, Tomoyuki; Yokoi, Takahiro; Miyagawa, Masao; Mochizuki, Teruhito [Ehime University Graduate School of Medicine, Department of Radiology, Toon City, Ehime (Japan); Uetani, Teruyoshi; Inoue, Katsuji [Ehime University Graduate School of Medicine, Department of Cardiology, Pulmonology, Hypertension and Nephrology, Toon City, Ehime (Japan)
2017-04-15
To evaluate the feasibility of three-dimensional (3D) maximum principal strain (MP-strain) derived from cardiac computed tomography (CT) for detecting myocardial infarction (MI). Forty-three patients who underwent cardiac CT and magnetic resonance imaging (MRI) were retrospectively selected. Using the voxel tracking of motion coherence algorithm, the peak CT MP-strain was measured using the 16-segment model. With the trans-mural extent of late gadolinium enhancement (LGE) and the distance from MI, all segments were classified into four groups (infarcted, border, adjacent, and remote segments); infarcted and border segments were defined as MI with LGE positive. Diagnostic performance of MP-strain for detecting MI was compared with per cent systolic wall thickening (%SWT) assessed by MRI using receiver-operating characteristic curve analysis at a segment level. Of 672 segments excluding16 segments influenced by artefacts, 193 were diagnosed as MI. Sensitivity and specificity of peak MP-strain to identify MI were 81 % [95 % confidence interval (95 % CI): 74-88 %] and 86 % (81-92 %) compared with %SWT: 76 % (60-95 %) and 68 % (48-84 %), respectively. The area under the curve of peak MP-strain was superior to %SWT [0.90 (0.87-0.93) vs. 0.80 (0.76-0.83), p < 0.05]. CT MP-strain has a potential to provide incremental value to coronary CT angiography for detecting MI. (orig.)
Large-Strain Softening of Aluminum in Shear at Elevated Temperature: Influence of Dislocation Climb
Kassner, M. E.; Campbell, C. S.; Ermagan, R.
2017-09-01
This communication complements an earlier publication in this journal by the authors describing the basis for large-strain softening in aluminum under pure shear at elevated temperatures. Earlier work by the authors and the materials community only considered changes in the dislocation glide stress with the evolving texture as an explanation for the softening. New analysis finds that changes in the dislocation climb stress with texture development can explain the softening trends.
1992-12-01
Dugundji (12) have developed a theory to predict large deflections of laminated beams. Minguet and Dugundji assume transverse shear strains are constant...nine elements as shown in figure 3.3. 3.2 Cantilevered Composite Beam The next problem considered is one considered by Minguet and Dugundji (12) in...in figure 3.4. Minguet and Dugundji (M&D) formulated an updated Lagrangian displacement scheme based on Euler angles which track the rigid body motion
Javanbakht, Mahdi; Levitas, Valery I.
2016-12-01
Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions
The growth and coalescence of ellipsoidal voids in plane strain under combined shear and tension
Scheyvaerts, F.; Onck, P. R.; Tekogˇlu, C.; Pardoen, T.
2011-02-01
New extensions of a model for the growth and coalescence of ellipsoidal voids based on the Gurson formalism are proposed in order to treat problems involving shear and/or voids axis not necessarily aligned with the main loading direction, under plane strain loading conditions. These extensions are motivated and validated using 3D finite element void cell calculations with overall plane strain enforced in one direction. The starting point is the Gologanu model dealing with spheroidal void shape. A void rotation law based on homogenization theory is coupled to this damage model. The predictions of the model closely agree with the 3D cell calculations, capturing the effect of the initial void shape and orientation on the void rotation rate. An empirical correction is also introduced for the change of the void aspect ratio in the plane transverse to the main axis of the void departing from its initially circular shape. This correction is needed for an accurate prediction of the onset of coalescence. Next, a new approach is proposed to take strain hardening into account within the Thomason criterion for internal necking, avoiding the use of strain hardening-dependent fitting parameters. The coalescence criterion is generalized to any possible direction of the coalescence plane and void orientation. Finally, the model is supplemented by a mathematical description of the final drop of the stress carrying capacity during coalescence. The entire model is developed for plane strain conditions, setting the path to a 3D extension. After validation of the model, a parametric study addresses the effect of shear on the ductility of metallic alloys for a range of microstructural and flow parameters, under different stress states. In general, the presence of shear, for identical stress triaxiality, decreases the ductility, partly explaining recent experimental results obtained in the low stress triaxiality regime.
McKnight, G. P.; Henry, C. P.
2008-03-01
Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than
Curiale, Ariel H; Vegas-Sánchez-Ferrero, Gonzalo; Bosch, Johan G; Aja-Fernández, Santiago
2015-08-01
The strain and strain-rate measures are commonly used for the analysis and assessment of regional myocardial function. In echocardiography (EC), the strain analysis became possible using Tissue Doppler Imaging (TDI). Unfortunately, this modality shows an important limitation: the angle between the myocardial movement and the ultrasound beam should be small to provide reliable measures. This constraint makes it difficult to provide strain measures of the entire myocardium. Alternative non-Doppler techniques such as Speckle Tracking (ST) can provide strain measures without angle constraints. However, the spatial resolution and the noisy appearance of speckle still make the strain estimation a challenging task in EC. Several maximum likelihood approaches have been proposed to statistically characterize the behavior of speckle, which results in a better performance of speckle tracking. However, those models do not consider common transformations to achieve the final B-mode image (e.g. interpolation). This paper proposes a new maximum likelihood approach for speckle tracking which effectively characterizes speckle of the final B-mode image. Its formulation provides a diffeomorphic scheme than can be efficiently optimized with a second-order method. The novelty of the method is threefold: First, the statistical characterization of speckle generalizes conventional speckle models (Rayleigh, Nakagami and Gamma) to a more versatile model for real data. Second, the formulation includes local correlation to increase the efficiency of frame-to-frame speckle tracking. Third, a probabilistic myocardial tissue characterization is used to automatically identify more reliable myocardial motions. The accuracy and agreement assessment was evaluated on a set of 16 synthetic image sequences for three different scenarios: normal, acute ischemia and acute dyssynchrony. The proposed method was compared to six speckle tracking methods. Results revealed that the proposed method is the most
Numerical modelling of the evolution of conglomerate deformation up to high simple-shear strain
Ran, Hao; Bons, Paul D.; Wang, Genhou; Steinbach, Florian; Finch, Melanie; Ran, Shuming; Liang, Xiao; Zhou, Jie
2017-04-01
Deformed conglomerates have been widely used to investigate deformation history and structural analysis, using strain analyses techniques, such as the Rf-Φ and Fry methods on deformed pebbles. Although geologists have focused on the study of deformed conglomerates for several decades, some problems of the process and mechanism of deformation, such as the development of structures in pebbles and matrix, are still not understand well. Numerical modelling provides a method to investigate the process of deformation, as a function of different controlling parameters, up to high strains at conditions that cannot be achieved in the laboratory. We use the 2D numerical modelling platform Elle coupled to the full field crystal visco-plasticity code (VPFFT) to simulate the deformation of conglomerates under simple shear conditions, achieving high finite strains of ≥10. Probably for the first time, we included the effect of an anisotropy, i.e. mica-rich matrix. Our simulations show the deformation of pebbles not only depends on the viscosity contrast between pebbles and matrix but emphasises the importance of interaction between neighbouring pebbles. Under the same finite strain shearing the pebbles of conglomerates with high pebble densities show higher Rf and lower Φ than those of conglomerates with a low density pebbles. Strain localisation can be observed at both the margin of strong pebbles and in the bridging area between the pebbles. At low to medium finite strain, local areas show the opposite (antithetic) shear sense because of the different relative rotation and movement of pebbles or clusters of pebbles. Very hard pebbles retain their original shape and may rotate, depending on the anisotropy of the matrix. σ-clasts are formed by pebbles with moderate viscosity contrast between pebble and a softer matrix. By contrast, δ-clasts are not observed in our simulations with both isotropic and anisotropic matrices, which is consistent with their relative scarcity in
In-situ shear stress indicator using heated strain gages at the flow boundary
Yeh, Chi-An; Yang, Fuling
2011-11-01
This work borrows the concept of hot-wire anemometry and sketch a technique that uses local heat transfer to infer the flow field and the corresponding stress. Conventional strain gages were mounted at the flow solid boundary as the heat source and acrylic boundary was chosen for its low thermal conductivity ensuring heat accumulation when a gage is energized. The gage would now work in slightly overheated state and its self-heating leads to an additional thermal strain. When exposed to a flow field, heat is brought away by local forced convection, resulting in deviations in gage signal from that developed in quiescent liquid. We have developed a facility to achieve synchronous gage measurements at different locations on a solid boundary. Three steady flow motions were considered: circular Couette flow, rectilinear uniform flow, and rectilinear oscillating flow. Preliminary tests show the gage reading does respond to the imposed flow through thermal effects and greater deviation was measured in flows of higher shear strain rates. The correlation between the gage signals and the imposed flow field is further examined by theoretical analysis. We also introduced a second solid boundary to the vicinity of the gage in the two rectilinear flows. The gage readings demonstrate rises in its magnitudes indicating wall amplification effect on the local shear strain, agreeing to the drag augmentation by a second solid boundary reported in many multiphase flow literatures.
Deformation and failure of OFHC copper under high strain rate shear compression
Ruggiero, Andrew; Testa, Gabriel; Bonora, Nicola; Iannitti, Gianluca; Persechino, Italo; Colliander, Magnus Hörnqvist
2017-01-01
Hat-shaped specimen geometries were developed to generate high strain, high-strain-rates deformation under prescribed conditions. These geometries offer also the possibility to investigate the occurrence of ductile rupture under low or negative stress triaxiality, where most failure models fail. In this work, three tophat geometries were designed, by means of extensive numerical simulation, to obtain desired stress triaxiality values within the shear region that develops across the ligament. Material failure was simulated using the Continuum Damage Model (CDM) formulation with a unilateral condition for damage accumulation and validated by comparing with quasi-static and high strain rate compression tests results on OFHC copper. Preliminary results seem to indicate that ductile tearing initiates at the specimen corner location where positive stress triaxiality occurs because of local rotation and eventually propagates along the ligament.
无
2009-01-01
This work deals with the preliminary relationship between strain path and strain partitioning pattern in a sinistral transpressional zone,Lancangjiang shear zone,located to the southeast of Tibet.Various ductile rocks provide an opportunity to investigate quantitative finite strain(Rs),kinematic vorticity values(Wm),and proportions of simple and pure shear components.The mean kinematic vorticity values(Wm) were evaluated based on three methods,such as Rs-θ,prophyroclast hyperbolic distribution method(PHD),and polar Mohr diagram construction(PMD).Wm for mylonitic metasediments of the low-grade schist belt ranged from 0.19 to 0.54.Protomylonites,mylonites,and ultramylonites recorded differential Wm values,0.19―0.73,0.11―0.8,and 0.84―0.95(even 0.99) respectively in the high-grade gneiss belt.Based on classical strain analysis and these kinematic vorticity evaluations,the shear zone is classified as a preliminarily bulk monoclinic symmetry.The pattern of vorticity path suggests that a previously undocumented transpressional setting and strain partitioning pattern in the southeast region of Tibet Plateau,characterized by steep-narrow domain of simple-shearing(Tertiary strike-slip shearing) deformation and wider domain of mostly pure-shearing(Tertiary contraction) to accommo-date intracontinental deformation.
ZHANG Bo; ZHANG JinJiang; ZHONG DaLai; GUO Lei
2009-01-01
This work deals with the preliminary relationship between strain path and strain partitioning pattern in a sinistral transpressional zone, Lancangjiang shear zone, located to the southeast of Tibet. Various ductile rocks provide an opportunity to investigate quantitative finite strain (Rs), kinematic vorticity values (Wm), and proportions of simple and pure shear components. The mean kinematic vorticity val-ues (Wm) were evaluated based on three methods, such as Rs-θ, prophyroclast hyperbolic distribution method (PHD), and polar Mohr diagram construction (PMD). Wm for mylonitic metasediments of the low-grade schist belt ranged from 0.19 to 0.54. Protomylonites, mylonites, and ultramylonitea recorded differential Wm values, 0.19-0.73, 0.11-0.8, and 0.84-0.95 (even 0.99) respectively in the high-grade gneiss belt. Based on classical strain analysis and these kinematic vorticity evaluations, the shear zone Is classified as a preliminarily bulk monoclinic symmetry. The pattern of vorticity path suggests that a previously undocumented transpressional setting and strain partitioning pattern in the southeast re-gion of Tibet Plateau, characterized by steep-narrow domain of simple-shearing (Tertiary strike-slip shearing) deformation and wider domain of mostly pure-shearing (Tertiary contraction) to accommo-date intracontinental deformation.
Ganau, Sergi, E-mail: sganau@tauli.cat [Women' s Imaging Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); Andreu, Francisco Javier, E-mail: xandreu@tauli.cat [Pathology Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); Escribano, Fernanda, E-mail: fescribano@tauli.cat [Women' s Imaging Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); Martín, Amaya, E-mail: amartino@tauli.cat [Women' s Imaging Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); Tortajada, Lidia, E-mail: ltortajada@tauli.cat [Women' s Imaging Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); Villajos, Maite, E-mail: mvillajos@tauli.cat [Women' s Imaging Department, UDIAT-Centre Diagnòstic, Institut Universitari Parc Taulí – UAB, Parc Taulí, 1, 08205 Sabadell, Barcelona (Spain); and others
2015-04-15
Highlights: •Shear wave elastography provides a quantitative assessment of the hardness of breast lesions. •The hardness of breast lesions correlates with lesion size: larger lesions are harder than smaller ones. •Histologic type and grade do not correlate clearly with elastography parameters. •HER2, luminal B HER2+, and triple-negative tumors have lower maximum hardness and mean hardness than other tumor types. •Half the tumors classified as BI-RADS 3 were luminal A and half were HER2. -- Abstract: Purpose: To evaluate the correlations of maximum stiffness (Emax) and mean stiffness (Emean) of invasive carcinomas on shear-wave elastography (SWE) with St. Gallen consensus tumor phenotypes. Methods: We used an ultrasound system with SWE capabilities to prospectively study 190 women with 216 histologically confirmed invasive breast cancers. We obtained one elastogram for each lesion. We correlated Emax and Emean with tumor size, histologic type and grade, estrogen and progesterone receptors, HER2 expression, the Ki67 proliferation index, and the five St. Gallen molecular subtypes: luminal A, luminal B without HER2 overexpression (luminal B HER2−), luminal B with HER2 overexpression (luminal B HER2+), HER2, and triple negative. Results: Lesions larger than 20 mm had significantly higher Emax (148.04 kPa) and Emean (118.32 kPa) (P = 0.005) than smaller lesions. We found no statistically significant correlations between elasticity parameters and histologic type and grade or molecular subtypes, although tumors with HER2 overexpression regardless whether they expressed hormone receptors (luminal B HER2+ and HER2 phenotypes) and triple-negative tumors had lower Emax and Emean than the others. We assessed the B-mode ultrasound findings of the lesions with some of the Emax or Emean values less than or equal to 80 kPa; only four of these had ultrasound findings suggestive of a benign lesion (two with luminal A phenotype and two with HER2 phenotype). Conclusions: We
Brands, D W; Bovendeerd, P H; Peters, G W; Wismans, J S
2000-11-01
The large strain dynamic behaviour of brain tissue and silicone gel, a brain substitute material used in mechanical head models, was compared. The non-linear shear strain behaviour was characterised using stress relaxation experiments. Brain tissue showed significant shear softening for strains above 1% (approximately 30% softening for shear strains up to 20%) while the time relaxation behaviour was nearly strain independent. Silicone gel behaved as a linear viscoelastic solid for all strains tested (up to 50%) and frequencies up to 461 Hz. As a result, the large strain time dependent behaviour of both materials could be derived for frequencies up to 1000 Hz from small strain oscillatory experiments and application of Time Temperature Superpositioning. It was concluded that silicone gel material parameters are in the same range as those of brain tissue. Nevertheless the brain tissue response will not be captured exactly due to increased viscous damping at high frequencies and the absence of shear softening in the silicone gel. For trend studies and benchmarking of numerical models the gel can be a good model material.
ZHOU Yan-guo; CHEN Yun-min; HUANG Bo
2005-01-01
The seismic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil-particle structure, which may both lead to a degradation in undrained stiffness and strength of soils. Only the effective stress influence on small strain shear modulus Gmax is considered in seismic response analysis nowadays, and the cyclic shearing induced fabric changes of the soil-particle structure are neglected. In this paper, undrained cyclic triaxial tests were conducted on saturated sands with the shear wave velocity measured by bender element, to study the influences of seismic loading on Gmax. And Gmax of samples without cyclic loading effects was also investigated for comparison. The test results indicated that Gmax under cyclic loading effects is lower than that without such effects at the same effective stress, and also well correlated with the effective stress variation. Hence it is necessary to reinvestigate the determination of Gmax in seismic response analysis carefully to predict the ground responses during earthquake more reasonably.
Zhan, Hongyi, E-mail: h.zhan@uq.edu.au [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Zeng, Weidong [State Key Laboratory of Solidification Processing, School of Materials, Northwestern Polytechnical University, Xi' an 710072 (China); Wang, Gui [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Defence Material Technology Centre, Level 2, 24 Wakefield St, Hawthorn, VIC 3122 (Australia); Kent, Damon [School of Science and Engineering, University of the Sunshine Coast, Sippy Downs, Queensland 4575 (Australia); Dargusch, Matthew [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Defence Material Technology Centre, Level 2, 24 Wakefield St, Hawthorn, VIC 3122 (Australia)
2015-04-15
The microstructural evolution and grain refinement within adiabatic shear bands in the Ti6554 alloy deformed at high strain rates and elevated temperatures have been characterized using transmission electron microscopy. No stress drops were observed in the corresponding stress–strain curve, indicating that the initiation of adiabatic shear bands does not lead to the loss of load capacity for the Ti6554 alloy. The outer region of the shear bands mainly consists of cell structures bounded by dislocation clusters. Equiaxed subgrains in the core area of the shear band can be evolved from the subdivision of cell structures or reconstruction and transverse segmentation of dislocation clusters. It is proposed that dislocation activity dominates the grain refinement process. The rotational recrystallization mechanism may operate as the kinetic requirements for it are fulfilled. The coexistence of different substructures across the shear bands implies that the microstructural evolution inside the shear bands is not homogeneous and different grain refinement mechanisms may operate simultaneously to refine the structure. - Graphical abstract: Display Omitted - Highlights: • The microstructure within the adiabatic shear band was characterized by TEM. • No stress drops were observed in the corresponding stress–strain curve. • Dislocation activity dominated the grain refinement process. • The kinetic requirements for rotational recrystallization mechanism were fulfilled. • Different grain refinement mechanisms operated simultaneously to refine the structure.
Perepelyuk, Maryna; Chin, LiKang; Cao, Xuan; van Oosten, Anne; Shenoy, Vivek B; Janmey, Paul A; Wells, Rebecca G
2016-01-01
Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G' and G" and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver.
Axial-shear strain elastography for breast lesion classification: further results from in vivo data.
Thittai, Arun K; Yamal, Jose-Miguel; Mobbs, Louise M; Kraemer-Chant, Christina M; Chekuri, Srinivasa; Garra, Brian S; Ophir, Jonathan
2011-02-01
The purpose of this work was to investigate the potential of the normalized axial-shear strain area (NASSA) feature, derived from axial-shear strain elastograms (ASSE), for breast lesion classification of fibroadenoma and cancer. This study consisted of previously acquired in vivo digital radiofrequency data of breast lesions. A total of 33 biopsy-proven malignant tumors and 30 fibroadenoma cases were included in the study, which involved three observers blinded to the original BIRADS-ultrasound scores. The observers outlined the lesions on the sonograms. The ASSEs were segmented and color-overlaid on the sonograms, and the NASSA feature from the ASSE was computed semi-automatically. Receiver operating characteristic (ROC) curves were then generated and the area under the curve (AUC) was calculated for each observer performance. A logistic regression classifier was built to compare the improvement in the AUC when using BIRADS scores plus NASSA values as opposed to BIRADS scores alone. BIRADS score ROC had an AUC of 0.89 (95% CI = 0.81 to 0.97). In comparison, the average of the AUC for all the three observers using ASSE feature alone was 0.84. However, the AUC increased to 0.94 (average of 3 observers) when BIRADS score and ASSE feature were combined. The results demonstrate that the NASSA feature derived from ASSE has the potential to improve BIRADS breast lesion classification of fibroadenoma and malignant tumors.
Pesin Alexander
2017-01-01
Full Text Available A three-roll rolling process is a significant technique in the production of wire rod, round bars and hexagonal profiles for structural applications. Better mechanical properties of wire rod, round bars and hexagonal profiles can be achieved due to large plastic deformation by the three-roll rolling process. Asymmetric rolling is a novel technique characterized by a kinematic asymmetry linked to the difference in peripheral speed of the rolls, able to introduce additional shear strains through the bar thickness. Physical simulation of shear strain, which is similar to that occurring in asymmetric three-roll rolling process, is very important for design of technology of producing ultrafine grain materials. Shear testing is complicated by the fact that a state of large shear is not easily achievable in most specimen geometries. Application of the shear-compression testing and specimen geometry to physical simulation of asymmetric three-roll rolling process is discussed in the paper. FEM simulation and comparison of the stress-strain state during shear-compression testing and asymmetric three-roll rolling process is presented. The results of investigation can be used to optimize the physical simulation of asymmetric three-roll rolling processes and for design of technology of producing ultrafine grain materials by severe plastic deformation.
Shear strain in Nd0.5Ca0.5MnO3 at high pressures.
Arulraj, Anthony; Dinnebier, Robert E; Carlson, Stefan; Hanfland, Michael; van Smaalen, Sander
2005-04-29
High-pressure x-ray powder diffraction has been measured on the half doped rare earth manganite Nd0.5Ca0.5MnO3 up to a pressure of 15 GPa. We report the presence of a quantifiable amount of shear distortion of the MnO6 octahedra in Nd0.5Ca0.5MnO3 at high pressures. The lattice strain of Nd0.5Ca0.5MnO3 is minimal at a crossover pressure of p* approximately 7 GPa, with the same lattice strain above and below this pressure achieved by shear and Jahn-Teller-type distortions, respectively. The increase in shear strain with increasing pressure provides a mechanism for the insulating behavior of manganites at high pressures that has not been considered before.
Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.
2004-01-01
A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.
Cao, Y.; Wang, Y.B. [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Figueiredo, R.B. [Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais, Belo Horizonte, MG 31270-901 (Brazil); Chang, L. [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Liao, X.Z., E-mail: xiaozhou.liao@sydney.edu.au [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Kawasaki, M. [Departments of Aerospace and Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453 (United States); Zheng, W.L. [Shanghai Research Institute of Materials, 99 Handan Road, Shanghai 200437 (China); Ringer, S.P. [Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006 (Australia); Langdon, T.G. [Departments of Aerospace and Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453 (United States); Materials Research Group, School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ (United Kingdom); Zhu, Y.T. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 (United States)
2011-06-15
Highlights: > Three-dimensional shear strain patterns were evaluated during high-pressure torsion. > Double-swirl patterns are visible on the top surfaces of discs in early stages of HPT. > Double-swirls ultimately evolve into a single swirl with increasing revolutions. > Microstructural evolution in HPT may deviate initially from rigid-body situation - Abstract: The shear strain imposed on austenite/ferrite duplex stainless steel discs at different stages of high-pressure torsion (HPT) processing was imaged in plan-view and cross-section using optical microscopy and scanning electron microscopy. The effect of the shear strain was correlated to the hardness evolution of the discs. The shear-strain patterns are complex and are different on the top and bottom surfaces of the discs. A double-swirl pattern emerged on the top surface in the early stages of HPT. These two centres of the swirl moved towards the centre of the disc as the numbers of HPT revolutions was increased and ultimately the double-swirl evolved into a single-swirl. Less regular shear-strain patterns were observed on the bottom surfaces of the discs. Multiple ring-like patterns with mirror symmetry over the central axes of the discs were visible from cross-sectional observations. Nanoindentation testing on the two surfaces and a cross-section of HPT discs showed that the hardness is insensitive to specific shear-strain patterns, but is closely related to the widths of the austenite and ferrite phase domains. Late in the deformation process, the hardness in the interior of an HPT disc may be higher than at either of the disc surfaces because of the development of finer microstructural phase distributions.
Mechanical anisotropy control on strain localization in upper mantle shear zones
Herwegh, Marco; Mercolli, Ivan; Linckens, Jolien; Müntener, Othmar
2016-05-01
Mantle rocks at oceanic spreading centers reveal dramatic rheological changes from partially molten to solid-state ductile to brittle deformation with progressive cooling. Using the crustal-scale Wadi al Wasit mantle shear zone (SZ, Semail ophiolite, Oman), we monitor such changes based on quantitative field and microstructural investigations combined with petrological and geochemical analyses. The spatial distribution of magmatic dikes and high strain zones gives important information on the location of magmatic and tectonic activity. In the SZ, dikes derived from primitive melts (websterites) are distributed over the entire SZ but are more abundant in the center; dikes from more evolved, plagioclase saturated melts (gabbronorites) are restricted to the SZ center. Accordingly, harzburgite deformation fabrics show a transition from protomylonite (1100°C), mylonite (900-800°C) to ultramylonite (dikes) and solid-state deformation (protomylonites-mylonites; 1100-900°C), (ii) dominant solid-state deformation in harzburgite mylonites (900-800°C) with some last melt injections (gabbronorites) and ultramylonites (dike-related ridge-parallel deformation controls the onset of the entire strain localization history promoting nucleation sites for different strain weakening processes as a consequence of changing physicochemical conditions.
Im, Jooeun; Kim, Mihyun; Choi, Ki-Sun; Hwang, Tae-Kyung; Kwon, Il-Bum
2014-06-10
In this paper, new fiber Bragg grating (FBG) sensor probes are designed to intermittently detect the maximum tensile strain of composite materials, so as to evaluate the structural health status. This probe is fabricated by two thin Al films bonded to an FBG optical fiber and two supporting brackets, which are fixed on the surface of composite materials. The residual strain of the Al packaged FBG sensor probe is induced by the strain of composite materials. This residual strain can indicate the maximum strain of composite materials. Two types of sensor probes are prepared-one is an FBG with 18 μm thick Al films, and the other is an FBG with 36 μm thick Al films-to compare the thickness effect on the detection sensitivity. These sensor probes are bonded on the surfaces of carbon fiber reinforced plastics composite specimens. In order to determine the strain sensitivity between the residual strain of the FBG sensor probe and the maximum strain of the composite specimen, tensile tests are performed by universal testing machine, under the loading-unloading test condition. The strain sensitivities of the probes, which have the Al thicknesses of 18 and 36 μm, are determined as 0.13 and 0.23, respectively.
Regan, S.; Williams, M. L.; Mahan, K. H.; Orlandini, O. F.; Jercinovic, M. J.; Leslie, S. R.; Holland, M.
2012-12-01
Ultramylonitic shear zones typically involve intense strain localization, and when developed over large regions can introduce considerable heterogeneity into the crust. The Cora Lake shear zone (CLsz) displays several 10's to 100's of meters-wide zones of ultramylonite distributed throughout its full 3-5 km mylonitized width. Detailed mapping, petrography, thermobarometry, and in-situ monazite geochronology suggest that it formed during the waning phases of granulite grade metamorphism and deformation, within one of North America's largest exposures of polydeformed lower continental crust. Anastomosing zones of ultramylonite contain recrystallized grain-sizes approaching the micron scale and might appear to suggest lower temperature mylonitization. However, feldspar and even clinopyroxene are dynamically recrystallized, and quantitative thermobarometry of syn-deformational assemblages indicate high P and T conditions ranging from 0.9 -10.6 GPa and 775-850 °C. Even at these high T's, dynamic recovery and recrystallization were extremely limited. Rocks with low modal quartz have extremely small equilibrium volumes. This is likely the result of inefficient diffusion, which is further supported by the unannealed nature of the crystals. Local carbonate veins suggests that H2O poor, CO2 rich conditions may have aided in the preservation of fine grain sizes, and may have inhibited dynamic recovery and recrystallization. The Cora Lake shear zone is interpreted to have been relatively strong and to have hardened during progressive deformation. Garnet is commonly fractured perpendicular to host rock fabric, and statically replaced by both biotite and muscovite. Pseudotachylite, with the same sense of shear, occurs in several ultramylonitized mafic granulites. Thus, cataclasis and frictional melt are interpreted to have been produced in the lower continental crust, not during later reactivation. We suggest that strengthening of rheologically stiffer lithologies led to
Xia, Rongmin; Thittai, Arun K
2014-03-01
Axial strain elastograms (ASEs) have been found to help visualize sonographically invisible thermal lesions. However, in most studies involving high-intensity focused ultrasound (HIFU)-induced thermal lesions, elastography imaging was performed separately later, after the lesion was formed. In this article, the feasibility of monitoring, in real time, tissue elasticity variation during HIFU treatment and immediately thereafter is explored using quasi-static elastography. Further, in addition to ASEs, we also explore the use of simultaneously acquired axial-shear strain elastograms (ASSEs) for HIFU lesion visualization. Experiments were performed on commercial porcine liver samples in vitro. The HIFU experiments were conducted at two applied acoustic power settings, 35 and 20 W. The experimental setup allowed us to interrupt the HIFU pulse momentarily several different times during treatment to perform elastographic compression and data acquisition. At the end of the experiments, the samples were cut along the imaging plane and photographed to compare size and location of the formed lesion with those visualized on ASEs and ASSEs. Single-lesion and multiple-lesion experiments were performed to assess the contribution of ASEs and ASSEs to lesion visualization and treatment monitoring tasks. At both power settings, ASEs and ASSEs provided accurate location information during HIFU treatment. At the low-power setting case, ASEs and ASSEs provide accurate lesion size in real-time monitoring. Lesion appearance in ASEs and ASSEs was affected by the cavitation bubbles produced at the high-power setting. The results further indicate that the cavitation bubbles influence lesion appearance more in ASEs than in ASSEs. Both ASEs and ASSEs provided accurate size information after a waiting period that allowed the cavitation bubbles to disappear. The results indicate that ASSEs not only improve lesion visualization and size measurement of a single lesion, but, under certain
Nestorović, M. D.; Triantafyllidis, N.
2004-04-01
A limiting factor in the design of fiber-reinforced composites is their failure under axial compression along the fiber direction. These critical axial stresses are significantly reduced in the presence of shear stresses. This investigation is motivated by the desire to study the onset of failure in fiber-reinforced composites under arbitrary multi-axial loading and in the absence of the experimentally inevitable imperfections and finite boundaries. By using a finite strain continuum mechanics formulation for the bifurcation (buckling) problem of a rate-independent, perfectly periodic (layered) solid of infinite extent, we are able to study the influence of load orientation, material properties and fiber volume fraction on the onset of instability in fiber-reinforced composites. Two applications of the general theory are presented in detail, one for a finitely strained elastic rubber composite and another for a graphite-epoxy composite, whose constitutive properties have been determined experimentally. For the latter case, extensive comparisons are made between the predictions of our general theory and the available experimental results as well as to the existing approximate structural theories. It is found that the load orientation, material properties and fiber volume fraction have substantial effects on the onset of failure stresses as well as on the type of the corresponding mode (local or global).
Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.; Mainprice, David; Clément, Maxime
2016-04-01
has not been previously reported and offers an unique opportunity to estimate a lower bound for the strain rates and local shear stresses generated during the grain growth and coeval compaction. Estimated values based on experimental creep rates on pyroxene aggregates [3] result in strain rates in the order of 10-12 to 10-13 s-1 and shear stresses of 60-70 MPa. Lower shear stress values (20-40 MPa) are retrieved using the thermodynamic model clinoenstatite inversion of Coe [4] in combination with the hydrostatic high-pressure experimental data on the stability of low clinoenstatite (P21/c). These data suggest that, under low deviatoric stress, fluid extraction and compaction near equilibrium in natural systems are only marginally higher than the strain rate of the solid matrix. These observations support the relatively long residence time of fluids in dehydration fronts and the necessity to further explore and quantify the feedback between mineral grain growth and fluid migration. [1] Connolly (2010) Elements 6(3):165-172; [2] Padrón-Navarta et al. (2015). Contrib Miner Petrol 169:35 [3] Raleigh et al. (1971). J Geophys Res 76(17): 4011-4022; [4] Coe (1970). Contrib Miner Petrol 26(3):247-264
Chowdhury, Sugata; Simpson, Jeffrey; Einstein, T. L.; Walker, Angela R. Hight
2D-materials with controllable optical, electronic and magnetic properties are desirable for novel nanodevices. Here we studied these properties for both pristine and hydrogenated TaSe2 (TaSe2-H) monolayer (ML) in the framework of DFT using the PAW method. We considered uniaxial and biaxial tensile strain, as well as shear strain along the basal planes in the range between 1% and 16%. Previous theoretical works (e.g.) considered only symmetrical biaxial tensile. Pristine ML is ferromagnetic for uniaxial tensile strain along ◯ or ŷ. For tensile strain in ŷ, the calculated magnetic moments of the Ta atoms are twice those for the same strain in ◯. Under pure shear strain (expansion along ŷ and compression along ◯), a pristine ML is ferromagnetic, but becomes non-magnetic when the strain directions are interchanged. Due to carrier-mediated double-exchange, the pristine ML is ferromagnetic when the Se-Ta-Se bond angle is < 82° and the ML thickness is < 3.25Å. We find that all Raman-active phonon modes show obvious red-shifting due to bond elongation and the E2 modes degeneracy is lifted as strain increases. For a TaSe2-H ML, the same trends were observed. Results show the ability to tune the properties of 2D-materials.
Sung Woo Park
2015-03-01
Full Text Available The safety of a multi-span waler beam subjected simultaneously to a distributed load and deflections at its supports can be secured by limiting the maximum stress of the beam to a specific value to prevent the beam from reaching a limit state for failure or collapse. Despite the fact that the vast majority of accidents on construction sites occur at waler beams in retaining wall systems, no safety monitoring model that can consider deflections at the supports of the beam is available. In this paper, a maximum stress estimation model for a waler beam based on average strains measured from vibrating wire strain gauges (VWSGs, the most frequently used sensors in construction field, is presented. The model is derived by defining the relationship between the maximum stress and the average strains measured from VWSGs. In addition to the maximum stress, support reactions, deflections at supports, and the magnitudes of distributed loads for the beam structure can be identified by the estimation model using the average strains. Using simulation tests on two multi-span beams, the performance of the model is evaluated by estimating maximum stress, deflections at supports, support reactions, and the magnitudes of distributed loads.
A.H. Curiale (Ariel H.); G. Vegas-Sanchez-Ferrero (Gonzalo); J.G. Bosch (Hans); S. Aja-Fernández (Santiago)
2015-01-01
textabstractThe strain and strain-rate measures are commonly used for the analysis and assessment of regional myocardial function. In echocardiography (EC), the strain analysis became possible using Tissue Doppler Imaging (TDI). Unfortunately, this modality shows an important limitation: the angle
A.H. Curiale (Ariel H.); G. Vegas-Sanchez-Ferrero (Gonzalo); J.G. Bosch (Johan); S. Aja-Fernández (Santiago)
2015-01-01
textabstractThe strain and strain-rate measures are commonly used for the analysis and assessment of regional myocardial function. In echocardiography (EC), the strain analysis became possible using Tissue Doppler Imaging (TDI). Unfortunately, this modality shows an important limitation: the angle b
Wright, W J; Samale, M; Hufnagel, T; LeBlanc, M; Florando, J
2009-06-15
We have made measurements of the temporal and spatial features of the evolution of strain during the serrated flow of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass tested under quasistatic, room temperature, uniaxial compression. Strain and load data were acquired at rates of up to 400 kHz using strain gages affixed to all four sides of the specimen and a piezoelectric load cell located near the specimen. Calculation of the displacement rate requires an assumption about the nature of the shear displacement. If one assumes that the entire shear plane displaces simultaneously, the displacement rate is approximately 0.002 m/s. If instead one assumes that the displacement occurs as a localized propagating front, the velocity of the front is approximately 2.8 m/s. In either case, the velocity is orders of magnitude less than the shear wave speed ({approx}2000 m/s). The significance of these measurements for estimates of heating in shear bands is discussed.
L. Spruzeniece
2015-04-01
Full Text Available This study focuses on physiochemical processes occurring in a brittle-ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia, a coarse-grained two feldspar-quartz-biotite granite is transformed into a medium grained orthogneiss at the shear zone margins and a fine-grained quartz-muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized showing distinct crystallographic preferred orientation (CPO. Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts, in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data shows a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high and low strain fabrics represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. We suggest that the fabrics and mineralogical changes in the shear zone centre have formed due to fluid influx probably along an initially brittle fracture. Here, hydration reactions dramatically changed the rheological properties of the rock. In the newly produced muscovite-quartz layers creep cavitation associated with grain
Baumgartner, L. J. [New South Wales Department of Primary Industries, Narrandera Fisheries Centre, Narrandera NSW Australia; Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Thorncraft, G. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Phonekhampheng, O. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Boys, C. [New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, Nelson Bay NSW Australia; Navarro, A. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Robinson, W. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Brown, R. [Pacific Northwest National Laboratory, Richland WA USA; Deng, Z. D. [Pacific Northwest National Laboratory, Richland WA USA
2017-02-09
Fluid shear arises when two bodies of water, travelling at different velocities, intersect. Fish entrained at the interface of these two water masses will experience shear stress; which can be harmful. The stress magnitude is dependent on waterbody mass and velocity; with the fish impact largely related to body size. Elevated shear stress occurs where rapidly flowing water passes near spillways, across screens, within turbine draft tubes or other passage routes. A flume was used to determine critical tolerances of silver shark (Balantiocheilos melanopterus) to different shear stress rates generated by a high velocity jet. Fish experienced higher levels of injury and mortality as shear stress was increased. Excessive shear forces had damaging impacts on fish. Mortality occurred at shear levels higher that 600/s. It is important that developers should attempt to model potential shear profiles expected during turbine passage in selected designs. These data will be critical to determine potential impacts on fish. If the likelihood of adverse impact is high, then alternative designs which have lower shear stress could be explored.
Khosravi Ali
2016-01-01
Full Text Available Experimental studies have indicated that the small strain shear modulus, Gmax, of unsaturated silt and clay has a greater amount during imbibition than during drainage, when presented as a function of matric suction. However, due to material properties and inter-particle forces, different behavior is expected in the case of sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drainage, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during imbibition. In the study presented herein, an effort has been made to compare the Gmax behavior of specimens of silt and sand during hydraulic hysteresis. In this regard, a series of bender element tests were carried out in a modified triaxial test device with suction-saturation control to evaluate the impact of hydraulic hysteresis on Gmax for specimens of silt and sand. Trends between the Gmax and matric suction for unsaturated sand were found to be different from those for silty specimens. The variations in Gmax showed an up and down trend in both drainage and imbibition paths for sandy specimens, where plotted as a function of matric suction. Results also indicated smaller magnitudes of Gmax upon imbibition than those during drainage; a behavior which is believed to be attributed to variations in suction stress with matric suction. In silty specimens, a stiffer response was measured during imbibition which was hypothesized to be due to drainage-induced hardening experienced by the specimens that was not fully recovered during imbibition.
Jastrzebska M.
2010-06-01
Full Text Available The paper deals with comparison of tangent shear moduli Gs of kaolin from Tułowice obtained from cyclic triaxial tests on the basis of external and internal reading in the small strains range (10-5÷10-3. The tests were carried out on a modernised test bed, enabling full saturation of specimens using the back pressure method as well as a precise internal measurement of strains by means of contactless microdisplacements sensors. The value of linearity factor L is one of adopted quality criteria for two measuring methods. Maintaining a constant deformation rate the influence of various cyclic process parameters (deviator stress amplitude – constant or variable; high or low; initial level of stress and strain, at which the unloading and reloading cycles were started; overconsolidation ratio OCR as well as cycles’ number and arrangement on the "shear modulus – axial strain" characteristic was studied. The obtained values of Gint and Gext (or Lint and Lext clearly show an underestimation (even 5 times of Gs value within the range 10-5÷10-3 when using an external measurement. In addition, the differences between Gint and Gext, which develop differently depending on specified cyclic process parameters, gradually decrease with increasing axial strains.
Torvela, Taija; Ehlers, Carl
2010-07-01
This study demonstrates the impact of variations in overall crustal rheology on crustal strength in relatively high P- T conditions at mid- to lower mid-crustal levels. In a crustal-scale shear zone, along-strike variations in the rheological competence result in large-scale deformation partitioning and differences in the deformation style and strain distribution. The structural behaviour of the crustal-scale Sottunga-Jurmo shear zone (SJSZ) in SW Finland is described. The shear zone represents a discontinuity between the amphibolite-to-granulite facies, dome-and-basin style crustal block to the north and the amphibolite facies rocks with dominantly steeply dipping structures to the south. The overall deformation style and resulting strains along the shear zone are greatly affected by the local lithology. The results of this study also have implications for the current tectonic models of the Palaeoproterozoic Fennoscandia. The most important implication is that the SJSZ, together with other structurally related shear zones, compartmentalised the far-field stresses, so that the late ductile structures within and south of the SJSZ can be allocated to a convergence from the south as late as ~1.79 Ga rather than to the Nordic orogeny from the west-northwest. It is further suggested that at ~1.79 Ga the stress regime was still compressive/transpressive and that the ~1.79 Ga magmatism in Åland at least initiated in a compressive setting. No extension or orogenic collapse, therefore, occurred in the Åland area while the rocks still were within the ductile regime.
Sumi, Chikayoshi; Nakayama, Kiyoshi; Kubota, Mitsuhiro
2000-06-01
An effective shear modulus reconstruction technique is described which uses ultrasonic strain measurements for diagnosis of superficial tissues, i.e. our previously developed ultrasonic strain measurement and shear modulus reconstruction methods are combined and enhanced. The technique realizes very low computational load, yet yields fairly high quantitativeness, high stability and spatial resolution, and large dynamic range. The suitability of the method is demonstrated on in vitro pork ribs and in vivo human breast tissues (fibroadenoma and scirrhous carcinoma).
Rainone, Corrado; Urbani, Pierfrancesco; Yoshino, Hajime; Zamponi, Francesco
2015-01-01
We consider the adiabatic evolution of glassy states under external perturbations. The formalism we use is very general. Here we use it for infinite-dimensional hard spheres where an exact analysis is possible. We consider perturbations of the boundary, i.e., compression or (volume preserving) shear strain, and we compute the response of glassy states to such perturbations: pressure and shear stress. We find that both quantities overshoot before the glass state becomes unstable at a spinodal point where it melts into a liquid (or yields). We also estimate the yield stress of the glass. Finally, we study the stability of the glass basins towards breaking into sub-basins, corresponding to a Gardner transition. We find that close to the dynamical transition, glasses undergo a Gardner transition after an infinitesimal perturbation.
Prediction of Maximum Strain in Finocyl Port Case-bonded Solid Propellants under Pressure Loading
Himanshu Shekhar
2006-07-01
Full Text Available Finite element analysis of case-bonded solid propellants in finocyl port configuration hasbeen carried out using finite element method. The parametric studies have also been conductedfor loading conditions, material properties, and geometrical configurations. The results arepresented in the form of a universal power law, which can be utilised for primary assessmentof peak strain in any finocyl port propellant configuration without using finite element software.This eliminates dependence on finite element software for structural integrity analysis of solidpropellants in finocyl port configuration under port pressurisation. The results obtained by finiteelement analysis and power law are in close agreement.
Moreno, V.; Vázquez-Vázquez, C.; Gallas, M.; Crespo, J.
2011-05-01
Electronic Speckle Pattern Interferometry (ESPI) has been used in experiments to measure displacement on the surface of bones undergoing external forces. However in order to asses directly the derivative of the displacements a related technique, Shearography, is used. This technique has been applied in biomechanical experiments although limited to small pieces of bone to determine their elastic properties. In this work we propose the use of Shearing Speckle Interferometry to evaluate the mechanical behaviour of the human mandible under compressive stress, simulating masticatory forces or impacts, in order to analyze the strain distribution on mandibular bone.
A New Accurate yet Simple Shear Flexible Triangular Plate Element with Linear Bending Strains
Damkilde, Lars; Pedersen, Ronnie
2010-01-01
The paper describes a new shear flexible triangular element. The formulation is based on displacement interpolation of the transverse displacement of the midsurface and the rotations of the cross-sections, and the element is fully compatible. The basic principle is to use a so-called balanced...
A New Accurate Yet Simple Shear Flexible Triangular Plate Element With Linear Bending Strains
Damkilde, Lars
2008-01-01
Plate bending elements have been and still are the subject of many papers. Zienkiewicz, given a very good overview of the historical development dating back to around 1965. In this paper focus will entirely be on plate elements taking the shear flexibility into account i.e. using Reissner- Mindlin...... plate theory...
Influence of Particle Morphology on 3D Kinematic Behavior and Strain Localization of Sheared Sand
Alshibli, Khalid A.; Jarrar, Maha F.; Druckrey, Andrew M.; Al-Raoush, Riyadh I.
2017-02-01
The constitutive behavior of sheared sand is highly influenced by particle morphology, gradation, mineralogy, specimen density, loading condition, stress path, and boundary conditions. The current literature lacks a three-dimensional (3D) systematic experimental study that investigates the influence of particle morphology, confining pressure, and specimen density on the failure mode of sheared sand. In this paper, surface texture, roundness, and sphericity of three uniform sands and glass beads with similar grain size were quantified by using 3D images of particles. In situ nondestructive 3D synchrotron microcomputed tomography (SMT) was used to monitor the deformation of medium-dense and very dense dry sand specimens that were tested under axisymmetric triaxial loading condition at 15 and 400 kPa confining pressures. The particles were identified and tracked in 3D as shearing progressed within the specimens, and maps of incremental particle translation and rotation were developed and used to uncover the relationship between particle morphology, specimen density, and confining pressure on the deformation and failure mode of sheared sand. This paper discusses the relationship between the failure mode and particle morphology, specimen density, and confining pressure.
Philipsen, Kirsten Riber; Christiansen, Lasse Engbo; Mandsberg, Lotte Frigaard
2008-01-01
with an exponentially decaying function of the time between observations is suggested. A model with a full covariance structure containing OD-dependent variance and an autocorrelation structure is compared to a model with variance only and with no variance or correlation implemented. It is shown that the model...... are used for parameter estimation. The data is log-transformed such that a linear model can be applied. The transformation changes the variance structure, and hence an OD-dependent variance is implemented in the model. The autocorrelation in the data is demonstrated, and a correlation model...... that best describes data is a model taking into account the full covariance structure. An inference study is made in order to determine whether the growth rate of the five bacteria strains is the same. After applying a likelihood-ratio test to models with a full covariance structure, it is concluded...
Ewertsen, Caroline; Carlsen, Jonathan Frederik; Christiansen, Iben Riishede
2016-01-01
and methods: Ten healthy volunteers (five males and five females) had their biceps brachii, gastrocnemius, and quadriceps muscle examined with strain- and shear wave elastography at three different depths and in regions located above bone and beside bone. Strain ratios were averaged from cine-loops of 10 s...
PREDICTION OF MAXIMUM CREEP STRAIN OF HIGH PERFORMANCE STEEL FIBER REINFORCED CONCRETE
Mishina Alexandra Vasil'evna
2012-12-01
Full Text Available The strongest research potential is demonstrated by the areas of application of high performance steel fiber reinforced concrete (HPSFRC. The research of its rheological characteristics is very important for the purposes of understanding its behaviour. This article is an overview of an experimental study of UHSSFRC. The study was carried out in the form of lasting creep tests of HPSFRC prism specimen, loaded by stresses of varied intensity. The loading was performed at different ages: 7, 14, 28 and 90 days after concreting. The stress intensity was 0.3 and 0.6 Rb; it was identified on the basis of short-term crush tests of similar prism-shaped specimen, performed on the same day. As a result, values of ultimate creep strains and ultimate specific creep of HPSFRC were identified. The data was used to construct an experimental diagramme of the ultimate specific creep on the basis of the HPSFRC loading age if exposed to various stresses. The research has resulted in the identification of a theoretical relationship that may serve as the basis for the high-precision projection of the pattern of changes in the ultimate specific creep of HPSFRC, depending on the age of loading and the stress intensity.
Aswani, Karan
The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in Arizona State University by Dr. Barzin Mobasher and Dr. Chote Soranakom. Intrinsic material property of moment-curvature response for SHCC was used to derive the relationship between applied load and deflection in a two-step process involving the limit state analysis and kinematically admissible displacements. For application of SHCC in structures such as shear walls, tensile and shear properties are necessary for design. Lot of research has already been done to study the tensile properties and therefore shear property study was undertaken to prepare a design guide. Shear response of textile reinforced concrete was investigated based on picture frame shear test method. The effects of orientation, volume of cement paste per layer, planar cross-section and volume fraction of textiles were investigated. Pultrusion was used for the production of textile reinforced concrete. It is an automated set-up with low equipment cost which provides uniform production and smooth final surface of the TRC. A 3-D optical non-contacting deformation measurement technique of digital image correlation (DIC) was used to conduct the image analysis on the shear samples by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-field strain distribution, displacement and strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and gave a relation between shear angle and shear strain.
Analysis of damage localization for ductile metal in process of shear band propagation
无
2006-01-01
Distribution of localized damage in shear band can' t be predicted theoretically based on classical elastoplastic theory. The average damage variable in shear band was considered to be a non-local variable. Based on non-local theory, an analytical expression for the localized damage in strain-softening region of shear band in the process of shear band propagation was presented using boundary condition and symmetry of local damage variable, etc. The results show that dynamic shear softening modulus, dynamic shear strength and shear elastic modulus influence the distribution of the localized damage in shear band. Internal length of ductile metal only governs the thickness of shear band. In the strain-softening region of shear band, the local damage variable along shear band's tangential and normal directions is non-linear and highly non-uniform. The non-uniformities in the normal and tangential directions of shear band stem from the interactions and interplaying among microstructures and the non-uniform distribution of shear stress, respectively. At the tail of the strain-softening region, the maximum value of local damage variable reaches 1. This means that material at this position fractures completely. At the tip of shear band and upper as well as lower boundaries, no damage occurs. Local damage variable increases as dynamic shear softening modulus decreases or shear elastic modulus increases, leading to difficulty in identification or detection of damage for less ductile metal material at higher strain rates.
Nonuniform Shear Strains in Torsional Kolsky Bar Tests on Soft Specimens
2015-02-01
for the ramp-up portion of the loading pulse (see [ Fitzpatrick and Scheidler 2013]): H5(x)= 10x3− 15x4+ 6x5, 0≤ x ≤ 1. (B-1) This function increases...from 0 at x = 0 to 1 at x = 1 and has zero first and second derivatives at both of these end points. Following [ Fitzpatrick and Scheidler 2013], one can...B. R. Donnelly and J. Medige, “Shear properties of human brain tissue”, J. Biomech. Eng. (ASME) 119:4 (1997), 423–432. [ Fitzpatrick and Scheidler
Amenzade, R. Yu.; Kiiko, I. A.
2007-06-01
It is commonly assumed that the theory based on the Kirchhoff hypotheses describes the properties inherent in the wave processes occurring in shells filled with fluids. But there are several new effects that cannot be described by this theory (in particular, the appearance of new types of waves). In this paper, we present a linearized description of axisymmetric wave motion of a perfect incompressible fluid in a multilayered cylindrical shell with allowance for shear strain; the shell is assumed to be infinite and simply supported. This description is aimed at finding new mechanical effects and hence at estimating the influence of the multiple layers and the shear strain on the wave characteristics. In a sense, it generalizes and develops well-known studies of this type. Practice necessitates deriving equations constructed under the assumption that the physical and mechanical properties of the shell material are inhomogeneous along the thickness direction or the shell is multilayered; the development of refined theories (compared with the classical theory based on the Kirchhoff—Love straight normal hypothesis) is also inspired by practice. This is primarily related to the fact that multilayered thin-walled shells made of composite materials are used in various fields of technology. It is of interest to note that, as a result of long evolution, the phenomenon of being multilayered also predominates in living organisms. For example, this is typical of big blood vessels [1] (arteries and veins). In [2], on the basis of a three-dimensional variational principle of mixed type, the equations of motion and physical relations for elastic anisotropic shells rigidly inhomogeneous in the thickness direction are derived under the assumptions of the theory of thin shells and with shear strains taken into account. It is also noted that the case of multilayered shells can be modeled by introducing functions with integrable singularities. When studying wave propagation in
Analysis of localized shear deformation of ductile metal based on gradient-dependent plasticity
王学滨; 代树红; 海龙; 潘一山
2003-01-01
Shear localization in linear strain softening heterogeneous material under simple shear was investigated analytically.The closed-form solutions obtained based on gradient plasticity theory considering interactions and interplaying among microstructures due to heterogeneity of metal material show that in the normal direction of shear band,elastic shear displacement is linear; while plastic and total shear displacement are non-linear.Elastic shear strain in the band is uniform and the non-uniformity of total shear displacement stems from localized plastic shear displacement.In the center of the band,plastic and total shear displacement all reach their maximum values.In strain-softening process,elastic displacement decreases as flow shear stress decreases.Contrarily,plastic and total shear displacement increase and manifest shear localization occurs progressively.Under the same shear stress level,plastic and total shear displacement increase as strain softening modulus and elastic shear modulus decrease.The present analytical solutions were compared with many experimental results and the agreement is good.
Gerstein, Gregory; Klusemann, Benjamin; Bargmann, Swantje; Schaper, Mirko
2015-01-15
In the current work, the evolutions of grain and dislocation microstructures are investigated on the basis of plane strain tension and simple shear tests for an interstitial free steel (DC06) and a 6000 series aluminum alloy (AA6016-T4). Both materials are commonly-used materials in the automobile industry. The focus of this contribution is on the characterization and comparison of the microstructure formation in DC06 and AA6016-T4. Our observations shed light on the active mechanisms at the micro scale governing the macroscopic response. This knowledge is of great importance to understand the physical deformation mechanisms, allowing the control and design of new, tailor-made materials with the desired material behavior.
De Oliveira, G N [Pos-graduacao em Engenharia Mecanica, TEM/PGMEC, Universidade Federal Fluminense, Rua Passo da Patria, 156, Niteroi, R.J., Brazil, Cep.: 24.210-240 (Brazil); Nunes, L C S [Laboratorio de Mecanica Teorica e Aplicada, Departamento de Engenharia Mecanica, Universidade Federal Fluminense, Rua Passo da Patria, 156, Niteroi, R.J., Brazil, Cep.: 24.210-240 (Brazil); Dos Santos, P A M, E-mail: pams@if.uff.br [Instituto de Fisica, Laboratorio de Optica Nao-linear e Aplicada, Universidade Federal Fluminense, Av. Gal. Nilton Tavares de Souza, s/n, Gragoata, Niteroi, R.J., Brazil, Cep.:24.210-346 (Brazil)
2011-01-01
In the present work a digital image correlation (DIC) method is used in order to analyze the adhesive shear modulus of poly-dimethylsiloxane (PDMS) submitted to different loads and temperatures. This is an optical-numerical full-field surface displacement measurement method. It is based on a comparison between two images of a specimen coated by a random speckled pattern in the undeformed and in the deformed states. A single lap joint testing is performed. This is a standard test specimen for characterizing adhesive properties and it is considered the simplest form of adhesive joints. For the single lap joint specimen, steel adherends are bonded using a flexible rubber elastic polymer (PDMS), which is a commercially available silicone elastic rubber.
Amaya, Ronny; Pierides, Alexis; Tarbell, John M
2015-01-01
Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle - SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4%) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease.
Ronny Amaya
Full Text Available Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS and circumferential stress (CS that can be characterized by the temporal phase angle between WSS and CS (stress phase angle - SPA. Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180° such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0° are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 ° and synchronous hemodynamics (SPA=0 °. This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2 and CS (4 ± 4% over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 ° can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease.
Befus, M; Mukherjee, D V; Herzig, C T A; Lowy, F D; Larson, E
2017-07-01
Prisons/jails are thought to amplify the transmission of Staphylococcus aureus (SA) particularly methicillin-resistant SA infection and colonisation. Two independently pooled cross-sectional samples of detainees being admitted or discharged from two New York State maximum-security prisons were used to explore this concept. Private interviews of participants were conducted, during which the anterior nares and oropharynx were sampled and assessed for SA colonisation. Log-binomial regression and correspondence analysis (CA) were used to evaluate the prevalence of colonisation at entry as compared with discharge. Approximately 51% of admitted (N = 404) and 41% of discharged (N = 439) female detainees were colonised with SA. Among males, 59% of those admitted (N = 427) and 49% of those discharged (N = 393) were colonised. Females had a statistically significant higher prevalence (1·26: P = 0·003) whereas males showed no significant difference (1·06; P = 0·003) in SA prevalence between entry and discharge. CA demonstrated that some strains, such as spa types t571 and t002, might have an affinity for certain mucosal sites. Contrary to our hypothesis, the prison setting did not amplify SA transmission, and CA proved to be a useful tool in describing the population structure of strains according to time and/or mucosal site.
Sawko, Robert; Thompson, Chris P.
2010-09-01
This paper presents a series of numerical simulations of non-Newtonian fluids in high Reynolds number flows in circular pipes. The fluids studied in the computations have shear-thinning and yield stress properties. Turbulence is described using the Reynolds-Averaged Navier-Stokes (RANS) equations with the Boussinesq eddy viscosity hypothesis. The evaluation of standard, two-equation models led to some observations regarding the order of magnitude as well as probabilistic information about the rate of strain. We argue that an accurate estimate of the rate of strain tensor is essential in capturing important flow features. It is first recognised that an apparent viscosity comprises two flow dependant components: one originating from rheology and the other from the turbulence model. To establish the relative significance of the terms involved, an order of magnitude analysis has been performed. The main observation supporting further discussion is that in high Reynolds number regimes the magnitudes of fluctuating rates of strain and fluctuating vorticity dominate the magnitudes of their respective averages. Since these quantities are included in the rheological law, the values of viscosity obtained from the fluctuating and mean velocity fields are different. Validation against Direct Numerical Simulation data shows at least an order of magnitude discrepancy in some regions of the flow. Moreover, the predictions of the probabilistic analysis show a favourable agreement with statistics computed from DNS data. A variety of experimental, as well as computational data has been collected. Data come from the latest experiments by Escudier et al. [1], DNS from Rudman et al. [2] and zeroth-order turbulence models of Pinho [3]. The fluid rheologies are described by standard power-law and Herschel-Bulkley models which make them suitable for steady state calculations of shear flows. Suitable regularisations are utilised to secure numerical stability. Two new models have been
Sample Disturbance in Resonant Column Test Measurement of Small-Strain Shear-Wave Velocity
Chiara, Nicola; Stokoe, K. H.
The accurate assessment of dynamic soil properties is a crucial step in the solution process of geotechnical earthquake engineering problems. The resonant column test is one of the ordinary procedures for dynamic characterization of soil. In this paper, the impact of sample disturbance on the resonant column test measurement of small-strain S-wave velocity is examined. Sample disturbance is shown to be a function of the ratio of the laboratory to field S-wave velocities: Vs, lab/Vs,field. The influence of four parameters - soil stiffness, soil plasticity index, in-situ sample depth and in-situ effective mean confining pressure - on sample disturbance is investigated both qualitatively and quantitatively. The relative importance of each parameter in predicting the small-strain field S-wave velocity from the resonant column test values is illustrated and predictive equations are presented.
Jean Didier Koffi Kouassi; Vlad Muresan; Sophie Nadège Gnangui; Elena Mudura; Lucien Patrice Kouame
2014-01-01
The objective of this work was to study the effects of wheat flour dough’s viscoelastic level by adding glucose oxidase (Gox) on its rheological properties at dynamic shear strain mode to predict the final product quality. Dough does display a linear viscoelastic domain. Glucose oxidase (Gox) was added to dough in order to enhance its viscoelasticity and to take into account the possible effects of this viscoelasticity on the results. Whatever the types of dough strain used G’ increased, tan ...
Kirby, S.H.
1985-01-01
the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere. ?? 1985.
Manickam, Kavitha; Machireddy, Ramasubba Reddy; Raghavan, Bagyam
2016-04-01
It has been observed that many pathological process increase the elastic modulus of soft tissue compared to normal. In order to image tissue stiffness using ultrasound, a mechanical compression is applied to tissues of interest and local tissue deformation is measured. Based on the mechanical excitation, ultrasound stiffness imaging methods are classified as compression or strain imaging which is based on external compression and Acoustic Radiation Force Impulse (ARFI) imaging which is based on force generated by focused ultrasound. When ultrasound is focused on tissue, shear wave is generated in lateral direction and shear wave velocity is proportional to stiffness of tissues. The work presented in this paper investigates strain elastography and ARFI imaging in clinical cancer diagnostics using real time patient data. Ultrasound B-mode imaging, strain imaging, ARFI displacement and ARFI shear wave velocity imaging were conducted on 50 patients (31 Benign and 23 malignant categories) using Siemens S2000 machine. True modulus contrast values were calculated from the measured shear wave velocities. For ultrasound B-mode, ARFI displacement imaging and strain imaging, observed image contrast and Contrast to Noise Ratio were calculated for benign and malignant cancers. Observed contrast values were compared based on the true modulus contrast values calculated from shear wave velocity imaging. In addition to that, student unpaired t-test was conducted for all the four techniques and box plots are presented. Results show that, strain imaging is better for malignant cancers whereas ARFI imaging is superior than strain imaging and B-mode for benign lesions representations.
Scale dependence of the alignment between strain rate and rotation in turbulent shear flow
Fiscaletti, D.
2016-10-24
The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor e(i), with the vorticity vector omega, is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and the probability density functions of the magnitude of the alignment cosines between the two unit vectors vertical bar e(i) . (omega) over cap vertical bar are examined. It is observed that the alignment tendencies are insensitive to the concurrent large-scale velocity fluctuations, but are quantitatively affected by the nature of the concurrent large-scale velocity-gradient fluctuations. It is confirmed that the small-scale (local) vorticity vector is preferentially aligned in parallel with the large-scale (background) extensive strain-rate eigenvector e(1), in contrast to the global tendency for omega to be aligned in parallelwith the intermediate strain-rate eigenvector [Hamlington et al., Phys. Fluids 20, 111703 (2008)]. When only data from regions of the flow that exhibit strong swirling are included, the so-called high-enstrophy worms, the alignment tendencies are exaggerated with respect to the global picture. These findings support the notion that the production of enstrophy, responsible for a net cascade of turbulent kinetic energy from large scales to small scales, is driven by vorticity stretching due to the preferential parallel alignment between omega and nonlocal e(1) and that the strongly swirling worms are kinematically significant to this process.
Garber, Joshua M.; Roeske, Sarah M.; Warren, Jessica; Mulcahy, Sean R.; McClelland, William C.; Austin, Lauren J.; Renne, Paul R.; Vujovich, Graciela I.
2014-07-01
The Bajo Pequeño Shear Zone (BPSZ) is a lower-crustal shear zone that records shortening and exhumation associated with the establishment of a new plate boundary, and its placement in a regional structural context suggests that local- to regional-scale strain localization occurred with progressive deformation. A kilometer-scale field and analytical cross section through the ~80 m thick BPSZ and its adjacent rocks indicates an early Devonian (405-400 Ma) phase of deformation on the western margin of Gondwanan continental crust. The earliest stages of the BPSZ, recorded by metamorphic and microstructural data, involved thrusting of a hotter orthogneiss over a relatively cool pelitic unit, which resulted in footwall garnet growth and reset footwall white mica 40Ar/39Ar ages in proximity to the shear zone. Later stages of BPSZ activity, as recorded by additional microstructures and quartz c-axis opening angles, were characterized by strain localization to the center of the shear zone coincident with cooling and exhumation. These and other data suggest that significant regional tectonism persisted in the Famatinian orogenic system for 60-70 million years after one microplate collision (the Precordillera) but ceased 5-10 million years prior to another (Chilenia). A survey of other synchronous structures shows that strain was accommodated on progressively narrower structures with time, indicating a regional pattern of strain localization and broad thermal relaxation as the Precordillera collision evolved.
Yongbo XU; Yilong BAI; M.A.Meyers
2006-01-01
α-titanium and its alloys with a dual-phase structure (α+β) were deformed dynamically under strain rate of about 104 s-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate (9×105 s-1) deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations inthe bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products (α2) had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10μm in diameter observed within the bands are proposed to be the results of recrystallization.
Length Scaling of Shear Zones at the Frictional-Viscous Transition (FVT)
Schrank, C. E.; Handy, M. R.; Fusseis, F.
2005-12-01
We present a new method for determining the characteristic length scales of strain localization in crustal scale shear zones. This entails determining two parameters that describe the degree of strain heterogeneity in natural shear zones: (1) the strain localization factor, LfRA, defined as the ratio of the shear zone area to a chosen reference area, ARA, and (2) the relative localization intensity, Iloc, a function of the ratio of the mean shear strain to the maximum shear strain measured in a transect of the shear zone. ARA is a geometric homogenization scale determined from autocorrelation functions (ACF) of 2-D images (thin sections, foliation maps and aerial photographs) of shear zone networks on different scales that formed during a single deformational event. When applied to shear zones from a well exposed segment of the frictional-to-viscous transition (FVT) in NE Spain, we found that maxima in LfRA on the mm, cm, m and km scales coincided with the length scales of existing mineralogical and lithological heterogeneities. On any of these characteristic length scales, Iloc increased both along and across the length of the shear zones, suggesting that the shear zones weakening as a function of time and strain. This is consistent with structural evidence for progressive weakening of the crust on the characteristic length scales of strain heterogeneity.
Hendrikson, Wim J; Deegan, Anthony J; Yang, Ying; van Blitterswijk, Clemens A; Verdonschot, Nico; Moroni, Lorenzo; Rouwkema, Jeroen
2017-01-01
Scaffolds for regenerative medicine applications should instruct cells with the appropriate signals, including biophysical stimuli such as stress and strain, to form the desired tissue. Apart from that, scaffolds, especially for load-bearing applications, should be capable of providing mechanical stability. Since both scaffold strength and stress-strain distributions throughout the scaffold depend on the scaffold's internal architecture, it is important to understand how changes in architecture influence these parameters. In this study, four scaffold designs with different architectures were produced using additive manufacturing. The designs varied in fiber orientation, while fiber diameter, spacing, and layer height remained constant. Based on micro-CT (μCT) scans, finite element models (FEMs) were derived for finite element analysis (FEA) and computational fluid dynamics (CFD). FEA of scaffold compression was validated using μCT scan data of compressed scaffolds. Results of the FEA and CFD showed a significant impact of scaffold architecture on fluid shear stress and mechanical strain distribution. The average fluid shear stress ranged from 3.6 mPa for a 0/90 architecture to 6.8 mPa for a 0/90 offset architecture, and the surface shear strain from 0.0096 for a 0/90 offset architecture to 0.0214 for a 0/90 architecture. This subsequently resulted in variations of the predicted cell differentiation stimulus values on the scaffold surface. Fluid shear stress was mainly influenced by pore shape and size, while mechanical strain distribution depended mainly on the presence or absence of supportive columns in the scaffold architecture. Together, these results corroborate that scaffold architecture can be exploited to design scaffolds with regions that guide specific tissue development under compression and perfusion. In conjunction with optimization of stimulation regimes during bioreactor cultures, scaffold architecture optimization can be used to improve
Hendrikson, Wim J.; Deegan, Anthony J.; Yang, Ying; van Blitterswijk, Clemens A.; Verdonschot, Nico; Moroni, Lorenzo; Rouwkema, Jeroen
2017-01-01
Scaffolds for regenerative medicine applications should instruct cells with the appropriate signals, including biophysical stimuli such as stress and strain, to form the desired tissue. Apart from that, scaffolds, especially for load-bearing applications, should be capable of providing mechanical stability. Since both scaffold strength and stress–strain distributions throughout the scaffold depend on the scaffold’s internal architecture, it is important to understand how changes in architecture influence these parameters. In this study, four scaffold designs with different architectures were produced using additive manufacturing. The designs varied in fiber orientation, while fiber diameter, spacing, and layer height remained constant. Based on micro-CT (μCT) scans, finite element models (FEMs) were derived for finite element analysis (FEA) and computational fluid dynamics (CFD). FEA of scaffold compression was validated using μCT scan data of compressed scaffolds. Results of the FEA and CFD showed a significant impact of scaffold architecture on fluid shear stress and mechanical strain distribution. The average fluid shear stress ranged from 3.6 mPa for a 0/90 architecture to 6.8 mPa for a 0/90 offset architecture, and the surface shear strain from 0.0096 for a 0/90 offset architecture to 0.0214 for a 0/90 architecture. This subsequently resulted in variations of the predicted cell differentiation stimulus values on the scaffold surface. Fluid shear stress was mainly influenced by pore shape and size, while mechanical strain distribution depended mainly on the presence or absence of supportive columns in the scaffold architecture. Together, these results corroborate that scaffold architecture can be exploited to design scaffolds with regions that guide specific tissue development under compression and perfusion. In conjunction with optimization of stimulation regimes during bioreactor cultures, scaffold architecture optimization can be used to improve
Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik (Clay Technology AB, Lund (Sweden))
2010-12-15
This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed
Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik (Clay Technology AB, Lund (Sweden))
2010-12-15
This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed
Cepeda-Jiménez, C.M., E-mail: carmen.cepeda@imdea.org [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain); Orozco-Caballero, A.; García-Infanta, J.M. [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain); Zhilyaev, A.P. [Institute for Metals Superplasticity Problems, Russian Academy of Science, 39 Khalturina, 450001 Ufa (Russian Federation); Ruano, O.A.; Carreño, F. [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain)
2014-03-01
An as-cast Al–7 wt%Si alloy was subjected to processing by high-pressure torsion (HPT) at room temperature, through 1/4, 1/2, 1 and 5 turns at a pressure of 6 GPa and two rotation speeds, 0.1 and 1 rpm. Vickers microhardness was measured along diameters of HPT disk surfaces. The final hardness values were higher than in the initial as-cast condition and, unexpectedly, nearly constant under all different processing conditions, and along the disk diameter. The microstructure was characterised by optical and scanning electron microscopy. The as-cast microstructure comprises equiaxed primary α dendrite cells embedded in the Al–Si eutectic constituent. The morphology and distribution of the eutectic constituent in the HPT processed materials is used to delineate the shear strain, which was analysed in the cross-section planes of the disks. A high degree of homogeneity in the imposed shear strain throughout the samples was observed, being congruent with the ideal rigid-body torsion. In addition, the high compressive pressure applied, causing compressive strain prior to the torsional strain, is responsible for the deformation-induced precipitation of small Si particles and for the (sub)grain refinement in the primary Al constituent. The role of torsional strain is that of increasing monothonically the redistribution of the eutectic silicon and the misorientation of the (sub)grains.
Macente, Alice; Fusseis, Florian; Menegon, Luca; John, Timm
2016-04-01
Synkinematic reaction microfabrics carry important information on the kinetics, timing and rheology of tectonometamorphic processes. Despite being routinely interpreted in metamorphic and structural studies, reaction and deformation microfabrics are usually described in two dimensions. We applied Synchrotron-based x-ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite-garnet eclogite in 3D. In the investigated samples, which cover a strain gradient into a shear zone from the Western Gneiss Region (Norway) previously described by John et al., (2009), we focused on the spatial transformation of garnet coronas into elongated clusters of garnets. Our microtomographic data allowed us to quantify changes to the garnet volume, their shapes and their spatial arrangement. We combined microtomographic observations with light microscope- and backscatter electron images as well as electron microprobe- (EMPA) and electron backscatter diffraction (EBSD) analyses to correlate mineral composition and orientation data with the x-ray absorption signal of the same mineral grains. This allowed us to extrapolate our interpretation of the metamorphic microfabric evolution to the third dimension, effectively yielding a 4-dimensional dataset. We found that: - The x-ray absorption contrast between individual mineral phases in our microtomographic data is sufficient to allow the same petrographic observations than in light- and electron microscopy, but extended to 3D. - Amongst the major constituents of the synkinematic reactions, garnet is the only phase that can be segmented confidently from the microtomographic data. - With increasing deformation, the garnet volume increases from about 9% to 25%. - Garnet coronas in the gabbros never completely encapsulate olivine grains. This may indicate that the reaction progressed preferentially in some directions, but also leaves pathways for element transport to and from the olivines that are
Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio
2013-04-01
The Badajoz-Córdoba Shear Zone is a is 30-40 km wide and 400 km long, NW-SE trending structure located at the boundary between the Ossa-Morena and Central-Iberian Zones of the Iberian Massif. Two elongated domains can be differentiated inside: the Obejo-Valsequillo domain to the NE and the Ductile Shear Belt (DSB) to the SW. The former exhibits Precambrian to Cambrian volcano-sedimentary rocks unconformably overlaying a Neoproterozoic basement formed by the "Serie Negra". The latter, 5-15 km wide, is composed mainly of metamorphic tectonites including the "Serie Negra" and other units located structurally under it. The petrofabric of "Serie Negra" black quartzites from the DSB is analyzed in this study with the Electron Back-Scattered Diffraction technique (EBSD). Black quartzites represent originally siliceous, chemical-biochemical shallow-water marine deposits, currently composed almost exclusively of quartz and graphite. Macroscopically they exhibit an outstanding planolinear tectonic fabric. Petrographically, coarse- and fine-grained dynamically recrystallized quartz bands alternate. The former contain quartz grains with irregular shapes, mica inclusions and "pinning" grain boundaries. Oriented mica grains and graphite particles constrain irregular quartz grain shapes. Quartz ribbons with chessboard microstructures also occur, indicating recrystallization under elevated temperatures coeval with extreme stretching. Fine-grained recrystallized quartz bands are dominated by quartz grains with straight boundaries, triple junctions, a scarcer evidence of bulging, and a higher concentration of dispersed, minute graphite grains. Quartz lattice-preferred orientation (LPO) patterns permit to identify two well-developed maxima for [c] axes: one close to the Y structural direction and the other one around Z, and -axes girdles normal to Y and Z. Although both [c] axis maxima appear in the coarse- and fine-grained bands, subsets can be isolated with grain cluster
Jean Didier Koffi Kouassi
2014-05-01
Full Text Available The objective of this work was to study the effects of wheat flour dough’s viscoelastic level by adding glucose oxidase (Gox on its rheological properties at dynamic shear strain mode to predict the final product quality. Dough does display a linear viscoelastic domain. Glucose oxidase (Gox was added to dough in order to enhance its viscoelasticity and to take into account the possible effects of this viscoelasticity on the results. Whatever the types of dough strain used G’ increased, tan δ decreased and led to less sticky dough. Wheat flour dough, an increase in G’ with extension may be associated to a strain-hardening phenomenon but the role of dough viscoelasticity is discussed.
王学滨
2004-01-01
A method for calculation of temperature distribution in adiabatic shear band is proposed in terms of gradient-dependent plasticity where the characteristic length describes the interactions and interplaying among microstructures. First, the increment of the plastic shear strain distribution in adiabatic shear band is obtained based on gradient-dependent plasticity. Then, the plastic work distribution is derived according to the current flow shear stress and the obtained increment of plastic shear strain distribution. In the light of the well-known assumption that 90% of plastic work is converted into the heat resulting in increase in temperature in adiabatic shear band, the increment of the temperature distribution is presented. Next, the average temperature increment in the shear band is calculated to compute the change in flow shear stress due to the thermal softening effect. After the actual flow shear stress considering the thermal softening effect is obtained according to the Johnson-Cook constitutive relation, the increment of the plastic shear strain distribution, the plastic work and the temperature in the next time step are recalculated until the total time is consumed. Summing the temperature distribution leads to rise in the total temperature distribution. The present calculated maximum temperature in adiabatic shear band in titanium agrees with the experimental observations. Moreover, the temperature profiles for different flow shear stresses are qualitatively consistent with experimental and numerical results. Effects of some related parameters on the temperature distribution are also predicted.
Sung Woo Park; Byung Kwan Oh; Hyo Seon Park
2015-01-01
The safety of a multi-span waler beam subjected simultaneously to a distributed load and deflections at its supports can be secured by limiting the maximum stress of the beam to a specific value to prevent the beam from reaching a limit state for failure or collapse. Despite the fact that the vast majority of accidents on construction sites occur at waler beams in retaining wall systems, no safety monitoring model that can consider deflections at the supports of the beam is available. In this...
岩石剪切破坏全应力-应变性状%COMPLETE STRESS-STRAIN BEHAVIOR FOR SHEAR FAILURE OF ROCKS
无
2001-01-01
The investigation of complete stress-strain behavior andcompressive failure behavior of some Hong Kong rocks are carried out. A large number of tests have been conducted to study the deformation and failure features of rocks. Some interesting test results have been obtained. These results show that localized deformation and failure strongly affect the deformation and failure process of the specimens just prior to the peak stress and in the post-peak stage. The two types of failure modes, namely exfoliation and shear failure have been investigated in detail. For the exfoliation failure mode, an experiment method has been proposed to observe the exfoliating process. A proposed model has been used to explain the influence of exfoliation on the gross stress-strain curve. It is found that the exfoliation during loading may be one of the reasons that a granite specimen exhibits Class Ⅱ behavior. The influences of machine stiffness control modes, end constraints, loading rate and confining pressure on the test results have been discussed and investigated. A new classification method of rock failure has been proposed. Special attention has been devoted to the investigation of the localized deformation and failure process of intact rock in the shear failure mode. A test method is proposed to detect the process. It is found that the deformation of rock material may be divided into three stages: namely uniform stage, pre-peak bifurcation stage and post-peak bifurcation stage. This phenomenon has been explained by a proposed qualitative analysis. It is further found that this localized process will significantly influence the shape of stress-strain curves, that is, the localized deformation is one of reasons that rock displays the effect of length to diameter ratio. A constitutive model is proposed to simulate the localized deformation and failure process. It can simulate the strain softening, strain localization, effect of length to diameter(L/D) ratio， unloading
Quantitative calculation of local shear deformation in adiabatic shear band for Ti-6Al-4V
无
2007-01-01
JOHNSON-COOK(J-C) model was used to calculate flow shear stress-shear strain curve for Ti-6Al-4V in dynamic torsion test. The predicted curve was compared with experimental result. Gradient-dependent plasticity(GDP) was introduced into J-C model and GDP was involved in the measured flow shear stress-shear strain curve, respectively, to calculate the distribution of local total shear deformation(LTSD) in adiabatic shear band(ASB). The predicted LTSDs at different flow shear stresses were compared with experimental measurements. J-C model can well predict the flow shear stress-shear strain curve in strain-hardening stage and in strain-softening stage where flow shear stress slowly decreases. Beyond the occurrence of ASB, with a decrease of flow shear stress, the increase of local plastic shear deformation in ASB is faster than the decrease of elastic shear deformation, leading to more and more apparent shear localization. According to the measured flow shear stress-shear strain curve and GDP, the calculated LTSDs in ASB are lower than experimental results. At earlier stage of ASB, though J-C model overestimates the flow shear stress at the same shear strain, the model can reasonably assess the LTSDs in ASB. According to the measured flow shear stress-shear strain curve and GDP, the calculated local plastic shear strains in ASB agree with experimental results except for the vicinity of shear fracture surface. In the strain-softening stage where flow shear stress sharply decreases, J-C model cannot be used. When flow shear stress decreases to a certain value, shear fracture takes place so that GDP cannot be used.
Shear Yielding and Shear Jamming of Dense Hard Sphere Glasses
Urbani, Pierfrancesco; Zamponi, Francesco
2017-01-01
We investigate the response of dense hard sphere glasses to a shear strain in a wide range of pressures ranging from the glass transition to the infinite-pressure jamming point. The phase diagram in the density-shear strain plane is calculated analytically using the mean-field infinite-dimensional solution. We find that just above the glass transition, the glass generically yields at a finite shear strain. The yielding transition in the mean-field picture is a spinodal point in presence of disorder. At higher densities, instead, we find that the glass generically jams at a finite shear strain: the jamming transition prevents yielding. The shear yielding and shear jamming lines merge in a critical point, close to which the system yields at extremely large shear stress. Around this point, highly nontrivial yielding dynamics, characterized by system-spanning disordered fractures, is expected.
1976-03-01
17. DISTRIBSUTION STATEMENT (of the absltact enteped In BItk 20, It ditferentt hora Repat) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue or r’everse...above, it is not possible to determine T2 unambiguously, because of the absence of a well- defined yield point; AT is clearly very small, if not zero ...letter F) except in some of the dynamic tests where the strain-hardening rate becomes zero at large strains. The considerable temperature sensitivity
Wang, Lu; Liu, Hongji; Li, Fanzhu; Shen, Jianxiang; Zheng, Zijian; Gao, Yangyang; Liu, Jun; Wu, Youping; Zhang, Liqun
2016-10-05
Although numerous research studies have been focused on studying the self-assembled morphologies of block-copolymers (BCPs) and their nanocomposites, little attention has been directed to explore the relation between their ordered structures and the resulting mechanical properties. We adopt coarse-grained molecular dynamics simulation to study the influence of the morphologies on the stress-strain behavior of pure block copolymers and block copolymers filled with uniform or Janus nanoparticles (NPs). At first, we examine the effect of the arrangement (di-block, tri-block, alternating-block) and the components of the pure block copolymers, and by varying the component ratio between A and B blocks, spherical, cylindrical and lamellar phases are all formed, showing that spherical domains bring the largest reinforcing effect. Then by studying BCPs filled with NPs, the Janus NPs induce stronger bond orientation of polymer chains and greater mechanical properties than the uniform NPs, when these two kinds of NPs are both located in the interface region. Meanwhile, some other anisotropic Janus NPs, such as Janus rods and Janus sheets, are incorporated to examine the effect on the morphology and the stress-strain behavior. These findings deepen our understanding of the morphology-mechanics relation of BCPs and their nanocomposites, opening up a vast number of approaches such as designing the arrangement and components of BCPs, positioning uniform or Janus NPs with different shapes and shear flow to tailor their stress-strain performance.
degli Alessandrini, Giulia; Menegon, Luca; Malaspina, Nadia; Dijkstra, Arjan; Anderson, Mark
2016-04-01
This study investigates the deformation mechanisms of a metagabbroic dyke experiencing syn-kinematic melt-rock interaction in a continental lower-crustal shear zone in the Seiland Igneous Province (northern Norway). Solid state shearing occurred at T ≈750-820 °C, P ≈0.75-0.95 GPa and was coeval with melt infiltration from dehydration melting of adjacent metasediments, as evident from thin leucosome veinlets within the dykes. The mylonite consists of cpx [Ca0.47,Mg0.35,Fe0.18]SiO3 + opx [Ca0.1,Mg0.5,Fe0.4]SiO3 + pl (An77Ab22Or1) porphyroclasts with localized grt and ilm coronas, embedded in a fine grained matrix of cpx + opx + pl + qtz + ilm ± kfs. Porphyroclasts range in size (diameter) between 25 to 650 μm, whereas the fine grain matrix is consistently below 10 μm (average 4-7 μm). Porphyroclasts show varying degrees of elongation, with the opx reaching aspect ratios of 1:16 and the cpx reaching rare maxima of 1:7. Cpx and pl porphyroclasts are micro-fractured and micro-boudinaged with fine-grained material infill. Texturally, opx porphyroclasts display a marked crystallographic preferred orientation (CPO) and activity of the {100} and minor {100} slip systems, whereas cpx and pl porphyroclasts are randomly oriented. All porphyroclasts have strong internal misorientations (undulatory and sweeping extinction) and lack recovery features (subgrains). The fine-grained polyphase matrix wrapping the porphyroclasts displays weak to absent CPO, with the exception of opx that shows a {100} poles-to-planes maxima perpendicular to the foliation. Based on the microstructure, we argue that a large part of the matrix is the product of metamorphic reactions in the presence of melt. To test this hypothesis, the interaction between the studied mafic dyke and an adjacent felsic leucosome was modelled using PerpleX for P-T conditions ranging between 7-9 kbar and 700-1000°C. Results show that the syn-kinematic mineral assemblage (opx + cpx + pl + qtz + ilm ± kfs) can be
WANG Xue-bin
2006-01-01
Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and average temperatures as well as their evolutions. The differential local plastic shear strain was derived to calculate the differential local plastic work and the temperature rise due to the microstructural effect. The total temperature in ASB is the sum of initial temperature, temperature rise at strain-hardening stage and non-uniform temperature due to the microstructural effect beyond the peak shear stress. The flow shear stress-average plastic shear strain curve, the temperature distribution, the peak and average temperatures in ASB are computed for Ti-6Al-4V. When the imposed shear strain is less than 2 and the shear strain rate is 1 000 s-1, the dynamic recovery and recrystallization processes occur. However, without the microstructural effect, the processes might have not occurred since heat diffusion decreases the temperature in ASB. The calculated maximum temperature approaches 1 500 K so that phase transformation might take place. The present predictions support the previously experimental results showing that the transformed and deformed ASBs are observed in Ti-6Al-4V. Higher shear strain rate enhances the possibility of dynamic recrystallization and phase transformation.
Amann, Christian P., E-mail: Christian.2.Amann@uni-konstanz.de; Fuchs, Matthias, E-mail: Matthias.Fuchs@uni-konstanz.de [Fachbereich Physik, Universität Konstanz, 78457 Konstanz (Germany); Denisov, Dmitry; Dang, Minh Triet; Schall, Peter [Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam (Netherlands); Struth, Bernd [Deutsches Elektronen-Synchrotron, Hamburg (Germany)
2015-07-21
We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses.
The influence of water and LPO on the initiation and evolution of mantle shear zones
Skemer, Philip; Warren, Jessica M.; Hansen, Lars N.; Hirth, Greg; Kelemen, Peter B.
2013-08-01
We present data from the Josephine Peridotite (SW Oregon, USA) that constrain the underlying physical processes responsible for the initiation of shear localization and the evolution of ductile shear zones in Earth's mantle. Field measurements of narrow (2-60 m wide) ductile shear zones in harzburgite were used to construct strain profiles, which have maximum shear strains ranging from γ=5.25 to γ>20. Measurements of pyroxene water concentrations from harzburgite samples within and immediately adjacent to the shear zones indicate that gradients in water concentration exist on a 10-100 m scale, even after exhumation. Water concentration measurements are correlated with olivine lattice-preferred orientation (LPO), corroborating experimental results on the influence of water on slip system activity. Using empirical olivine flow laws and the diffusivity of water in olivine, we model initiation of a ductile shear zone through localized water weakening. We demonstrate that this mechanism can readily generate spatial perturbations in both effective viscosity and strain. However this model is not able to reproduce both the observed shear strain gradients and water concentration data from the Josephine shear zones. We evaluate other plausible localization mechanisms, which may amplify this initial strain perturbation. The most relevant at these conditions is the development of viscous anisotropy associated with the evolution of olivine LPO. Using recent experimental results, we demonstrate that progressive rotation of olivine LPO into the shear plane enhances deformation within a shear zone. We conclude that feedback between at least two microphysical processes is needed to account for observed outcrop-scale shear localization.
Jungkyu ePark
2015-03-01
Full Text Available Shape memory composites (SMCs based on shape memory alloys (SMAs and shape memory polymers (SMPs allow many design possibilities due to their controllable temperature-dependent mechanical properties. The complementary characteristics of SMAs and SMPs can be utilized in systems with shape recovery created by the SMA and shape fixity provided by the SMP. In this research, three SMC operating regimes are identified and the behavior of SMC structures is analyzed by focusing on composite shape fixity and interfacial stresses. Analytical models show that SMPs can be used to adequately fix the shape of SMA actuators and springs. COMSOL finite element simulations are in agreement with analytical expressions for shape fixity and interfacial stresses. Analytical models are developed for an end-coupled linear SMP-SMA two-way actuator and the predicted strain is shown to be in good agreement with experimental test results.
郑为为; 杨王玥; 孙祖庆
2002-01-01
B2-ordered Fe3Al single crystals with various orientations were deformed in tension at room temperature in vacuum. The shape of shear stress-strain curves and work hardening rates were found to be strongly dependent on the orientation. The formation of the five different work hardening stages were considered to be related to the number of operative slip systems, the effect of secondary slip systems and the dissociation of the twofold superdislocation. Stage I is an easy glide stage corresponding to single slip. Stage II, with high hardening rate, often corresponds to the existence of conjugate slip systems. Stage III, with relatively low hardening rate, corresponds to the weaker hardening of secondary slip systems. Stage IV, with the highest hardening rate, is not only related to multiple slip but also the dissociation of twofold superdislocations and the moving of superpartials with an antiphase boundary (APB) trap. Stages V, with a negative hardening rate, may be caused by the cross slip of single dissociated superdislocation. The number of stages and the work hardening rate of the same stage were also found to change significantly, when the tensile orientation lies in different orientation regions.
Constantinescu, E.; Oanta, E.; Panait, C.
2017-08-01
The paper presents an initial study concerning the form factors for shear, for a rectangular and for a circular cross section, being used an analytical method and a numerical study. The numerical study considers a division of the cross section in small areas and uses the power of the definitions in order to compute the according integrals. The accurate values of the form factors are increasing the accuracy of the displacements computed by the use of the strain energy methods. The knowledge resulted from this study will be used for several directions of development: calculus of the form factors for a ring-type cross section of variable ratio of the inner and outer diameters, calculus of the geometrical characteristics of an inclined circular segment and, using a Bool algebra that operates with geometrical shapes, for an inclined circular ring segment. These shapes may be used to analytically define the geometrical model of a complex composite section, i.e. a ship hull cross section. The according calculus relations are also useful for the development of customized design commands in CAD commercial applications. The paper is a result of the long run development of original computer based instruments in engineering of the authors.
Gourmelen, Noel; Amelung, Falk; Lanari, Riccardo
2010-09-01
The principal limitations of interferometric synthetic aperture radar (InSAR) to measure subtle, long-wavelength deformation are uncertainties associated with the satellite orbits. We propose a method to remove orbital phase errors from the InSAR data by integrating InSAR and continuous GPS time series. We model the along-track variation of the baseline errors as second-order polynomials and estimate the coefficients using the continuous GPS measurements. We apply this method to a 600 km long region encompassing the Basin and Range and the eastern California shear zone. Comparison of the corrected InSAR velocities with independent GPS data shows that this method removes the long-wavelength InSAR errors. The InSAR data reveal a region of sharp variation in the line-of-sight velocity across the Hunter Mountain fault. We model the deformation as interseismic elastic strain accumulation across a strike-slip fault. The modeling suggests a fault slip rate of 4.9 ± 0.8 mm/yr and a locking depth of 2 ± 0.4 km. The shallow locking depth suggests that the Hunter Mountain fault is a transfer fault between low angle normal faults in the area.
Youk, Ji Hyun; Son, Eun Ju; Gweon, Hye Mi; Kim, Hana; Park, Yun Joo; Kim, Jeong-Ah
2014-10-01
Our aim was to compare the diagnostic performance of strain elastography (SE) and shear-wave elastography (SWE), combined with B-mode ultrasonography (US), in breast cancer. For 79 breast lesions that underwent SE and SWE, two radiologists reviewed five data sets (B-mode US, SWE, SE and two combined sets). Qualitative and quantitative elastographic data and Breast Imaging Reporting and Data System (BI-RADS) categories were recorded. The area under the receiver operating characteristic curve (AUC) was evaluated. No significant difference in the AUC between the two elastography methods was noted. After subjective assessment by reviewers, the AUC for the combined sets was improved (SWE, 0.987; SE, 0.982; B-mode US, 0.970; p < 0.05). When SE and SWE were added, 38% and 56% of benign BI-RADS category 4a lesions with a low suspicion of cancer were downgraded without false-negative results, respectively. SE and SWE performed similarly. Therefore, addition of SE or SWE improved the diagnostic performance of B-mode US, potentially reducing unnecessary biopsies. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Analysis of fracture process zone in brittle rock subjected to shear-compressive loading
ZHOU De-quan; CHEN Feng; CAO Ping; MA Chun-de
2005-01-01
An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of KⅡ to KⅠ . The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.
王学滨; 杨梅; 于海军; 海龙; 潘一山
2004-01-01
Closed-form analytical solutions of plastic shear strain and relative plastic shear displacement during shear band propagation are proposed under dynamic loadings based on gradient-dependent plasticity considering the effect of microstructures due to heterogeneous texture of Ti. According to the differences in shear stress levels, Ti specimen is divided into three regions. residual region, strain-softening region and elastic region. Well-developed shear band is formed in the residual region and the relative plastic shear displacement no longer increases. In the normal and tangential directions, the plastic strain and the displacement are nonuniform in the strain-softening region.At the tip of shear band, the shear stress acting on the band is increased to shear strength from the elastic state and the shear localization just occurs. Prior to the tip, Ti remains elastic. At higher strain rates, the extent of plastic strain concentration is greater than that under static loading. Higher strain rate increases the relative plastic shear displacement. The present analytical solution for evolution or propagation of shear localization under nonuniform shear stress can better reproduce the observed localized characteristics for many kinds of ductile metals.
干砂最大剪切模量的共振柱与弯曲元试验%Resonant column and bender element tests on maximum shear modulus of dry sand
柏立懂; 项伟; SAVIDIS A Stavros; RACKWITZ Frank
2012-01-01
对德国4种干砂试样进行了共振柱与弯曲元对比试验，旨在分析弯曲元法测定砂土最大剪切模量时存在问题和解决方法。研究表明：时域初达法判定的剪切波传播时间较其他方法具有更好的稳定性；弯曲元试验测定最大剪切模量输入电压脉冲频率的减小而减小，衰减程度因砂土类型而异，该影响随围压的增大而减弱；对比分析表明，弯曲元与共振柱试验测定的最大剪切模量具有良好的线性关系，对柏林砂和不伦瑞克砂，存在一个临界最大剪切模量，小于该临界值时，弯曲元测值大于共振柱测值，而大于该临界值时，前者小于后者，两者差值随土样刚度增大而增大。对比研究指出，弯曲元试验尽可能采用合适高频脉冲电压作为激发电压，实践中应事先与共振柱试验进行对比。%The problems and solutions of applying the bender element method to determine the maximum shear modulus （Gmax） of sand are investigated by conducting resonant column （RC） and bender element （BE） tests on four dry sands obtained from Germany. The study indicates that the start-to-start method is more reliable to identify the time of shear wave propagation in specimens compared to other methods. In BE tests, the excitation frequency of input waves has influence on the tested Gmax, and this influence is dependent on soil types and reduced by increasing confining pressure. A comparison between RC and BE tests shows that Gmax by both methods may be well expressed as a linear equation; for the Berlin sand and Braunschweig coarse sand, there exists a threshold Gmax below which Gmax by BE tests （Gmax （BE）） is greater than that by RC tests （Gmax （RC））, however beyond which the Gmax （BE） is smaller than Gmax （RC） and the distance between both increases with increasing stiffness soil. In practice, it is suggested that the input voltage with proper high
Failure During Sheared Edge Stretching
Levy, B. S.; van Tyne, C. J.
2008-12-01
Failure during sheared edge stretching of sheet steels is a serious concern, especially in advanced high-strength steel (AHSS) grades. The shearing process produces a shear face and a zone of deformation behind the shear face, which is the shear-affected zone (SAZ). A failure during sheared edge stretching depends on prior deformation in the sheet, the shearing process, and the subsequent strain path in the SAZ during stretching. Data from laboratory hole expansion tests and hole extrusion tests for multiple lots of fourteen grades of steel were analyzed. The forming limit curve (FLC), regression equations, measurement uncertainty calculations, and difference calculations were used in the analyses. From these analyses, an assessment of the primary factors that contribute to the fracture during sheared edge stretching was made. It was found that the forming limit strain with consideration of strain path in the SAZ is a major factor that contributes to the failure of a sheared edge during stretching. Although metallurgical factors are important, they appear to play a somewhat lesser role.
Nie, Guanjun; Shan, Yehua
2014-09-01
Quartz c-axis fabrics are widely used to determine the shear plane in ductile shear zones, based upon an assumption that the shear plane is perpendicular to both the central segment of quartz c-axis crossed girdle and single girdle. In this paper the development of quartz c-axis fabric under simple-pure shear deformation is simulated using the visco-plastic self-consistent (VPSC) model so as to re-examine this assumption. In the case of no or weak dynamic recrystallization, the simulated crossed girdles have a central segment perpendicular or nearly perpendicular to the maximum principal finite strain direction (X) and the XY finite strain plane, and at a variable angle relative to the imposed kinematic framework that is dependent on the modeled flow vorticity and finite strain. These crossed girdles have a symmetrical skeleton with respect to the finite strain axes, regardless of the bulk strain and the kinematic vorticity, and rotate in a way similar to the shear sense with increasing bulk strain ratio. The larger the vorticity number the more asymmetrical their legs tend to be. In the case of strong dynamic recrystallization and large bulk strain, under simple shear the crossed girdle switches into single girdles, sub-perpendicular to the shear plane, by losing the weak legs. The numerical results in our models do not confirm the above-mentioned assumption.
Akira Onuki; Akira Furukawa; Akihiko Minami
2005-05-01
We present a time-dependent Ginzburg–Landau model of nonlinear elasticity in solid materials. We assume that the elastic energy density is a periodic function of the shear and tetragonal strains owing to the underlying lattice structure. With this new ingredient, solving the equations yields formation of dislocation dipoles or slips. In plastic flow high-density dislocations emerge at large strains to accumulate and grow into shear bands where the strains are localized. In addition to the elastic displacement, we also introduce the local free volume . For very small the defect structures are metastable and long-lived where the dislocations are pinned by the Peierls potential barrier. However, if the shear modulus decreases with increasing , accumulation of around dislocation cores eventually breaks the Peierls potential leading to slow relaxations in the stress and the free energy (aging). As another application of our scheme, we also study dislocation formation in two-phase alloys (coherency loss) under shear strains, where dislocations glide preferentially in the softer regions and are trapped at the interfaces.
Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges
Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Lacroute, Y.; Markey, L.; Salazar, M.; Vignal, V. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France)
2011-05-15
Research highlights: > Surface strains measured using nanogauge were compared to the texture obtained by EBSD. > Statistics of the principal strain discern the grains according to the Schmid factor. > Strain hotspots were localized near a triple junction of alloy 600 under tensile loading. > Asymetrical profile of the GB strains is a criterion for surface cracking initiation. - Abstract: A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.
Morales, L. F. G.; Rybacki, E.; Dresen, G. H.; Kilian, R.
2015-12-01
In the Earth's middle to lower crust, strain is frequently localized along ductile shear zones, which commonly nucleate at structural and material heterogeneities. To investigate shear zone nucleation and development due to heterogeneities, we performed constant strain-rate (CSR) and constant stress (CS) simple shear (torsion) deformation experiments on Carrara marble samples containing weak (limestone) inclusions. The experiments were conducted in a Paterson-type gas deformation apparatus at 900 °C temperature and 400 MPa confining pressure and maximum bulk shear strains of 3. Peak shear stress was about 20 MPa for all the samples, followed by smooth weakening and steady state behavior. The strain is predominantly localized in the host marble within the process zone in front of the inclusion, defined by a zone of intense grain size reduction due to dynamic recrystallization. In CS tests a narrow shear zone developed in front of the inclusion, whereas in CSR experiments the deformation is more heterogeneously distributed, up to g=3.. In the later, secondary foliations oblique to the process zone and alternating thin, high-strain layers are common. In samples deformed at the same shear strain (g=1), the average recrystallized grain size in the process zone is similar for CS and CSR conditions. Crystallographic preferred orientation (CPO) measurements shows that different grain sizes have slightly different CPO patterns. CPO strength varies for different grain sizes, with a CPO strength peak between 40-50 μm, decreasing progressively within smaller grain size, but with secondary peaks for different coarse-grained sizes. Our observations suggest that the initial formation and transient deformation of shear zones is strongly affected by loading conditions.
Strength and behavior in shear of reinforced concrete deep beams under dynamic loading conditions
Adhikary, Satadru Das [School of Civil and Environmental Engineering, Nanyang Technological University, 639798 (Singapore); Li, Bing, E-mail: cbli@ntu.edu.sg [School of Civil and Environmental Engineering, Nanyang Technological University, 639798 (Singapore); Fujikake, Kazunori [Department of Civil and Environmental Engineering, National Defense Academy, Yokosuka 239 8686 (Japan)
2013-06-15
Highlights: ► Effects of wider range of loading rates on dynamic shear behavior of RC deep beams. ► Experimental investigation of RC deep beam with and without shear reinforcements. ► Verification of experimental results with truss model and FE simulation results. ► Empirical equations are proposed to predict the dynamic increase factor of maximum resistance. -- Abstract: Research on reinforced concrete (RC) deep beams has seen considerable headway over the past three decades; however, information on the dynamic shear strength and behavior of RC deep beams under varying rates of loads remains limited. This paper describes the experimental results of 24 RC deep beams with and without shear reinforcements under varying rates of concentrated loading. Results obtained serve as useful data on shear resistance, failure patterns and strain rates corresponding to varying loading rates. An analytical truss model approach proves its efficacy in predicting the dynamic shear resistance under varying loading rates. Furthermore, three-dimensional nonlinear finite element (FE) model is described and the simulation results are verified with the experimental results. A parametric study is then conducted to investigate the influence of longitudinal reinforcement ratio, transverse reinforcement ratio and shear span to effective depth ratio on shear behavior. Subsequently, two empirical equations were proposed by integrating the various parameters to assess the dynamic increase factor (DIF) of maximum resistance under varying rates of concentrated loading.
张涛; 刘松玉; 蔡国军
2015-01-01
小应变剪切模量和无侧限抗压强度是表征固化土刚度和强度特性的两个重要参数.简要介绍了弯曲元测试技术的原理及其在试验中存在的问题,采用压电陶瓷弯曲元测试技术对水泥和木质素固化剂固化粉土试样在不同养护龄期下的小应变剪切模量进行了测试,同时对相应龄期下试样进行了常规无侧限抗压强度试验,通过引入归一化参数G28和 UCS28对不同固化土的小应变剪切模量和无侧限抗压强度之间的相关关系进行分析,提出了固化土刚度与强度的相关性模型,可为地基处理中固化土的无损测试与加固效果评价提供新的方法.结果表明,水泥、木质素固化粉土的小应变剪切模量随养护龄期增加而增加,养护龄期28 d内增长显著,28 d后增长趋于平稳;相同类型固化土不论固化剂掺量多少,其小应变剪切模量随养护时间的发展在本质上是相同的;固化土归一化无侧限抗压强度表现出与小应变剪切模量相似的发展趋势;提出的固化土归一化模型可作为一种土体强度无损检测的新方法.%The small-strain shear modulus and unconfined compressive strength are two important parameters to characterize the stiffness and strength of stabilized soils. The fundamental and the main problems existing in the experiment of bender element technique are briefly reviewed. The small-strain shear modulus of cement and lignin stabilized silt are tested under different curing time by piezoelectric bender element technique. The conventional unconfined compressive strength test is also carried out on stabilized samples under different curing time. The relationships between the small-strain shear modulus and unconfined compressive strength of different stabilized soils are analyzed by introducing the normalized parametersG28 and UCS28. A stabilization model for the stiffness and strength of stabilized soils is proposed to provide a new method for
Two-state shear diagrams for complex fluids in shear flow
1999-01-01
The possible "phase diagrams'' for shear-induced phase transitions between two phases are collected. We consider shear-thickening and shear-thinning fluids, under conditions of both common strain rate and common stress in the two phases, and present the four fundamental shear stress vs. strain rate curves and discuss their concentration dependence. We outline how to construct more complicated phase diagrams, discuss in which class various experimental systems fall, and sketch how to reconstru...
Rotational tumbling of Escherichia coli aggregates under shear
Portela, R; Almeida, P L; Sobral, R G; Franco, J M; Leal, C R
2016-01-01
Growing living cultures of Escherichia coli bacteria were investigated using real-time in situ rheology and rheo-imaging measurements. In the early stages of growth (lag phase), and when subjected to a constant stationary shear, the viscosity slowly increases with the cell's population. As the bacteria reach the exponential phase of growth, the viscosity increases rapidly, with sudden and temporary abrupt decreases and recoveries. At a certain stage, corresponding grossly to the late phase of growth, when the population stabilises, the viscosity also keeps its maximum constant value, with drops and recoveries, for a long period of time. This complex rheological behaviour, which was observed to be shear strain dependent, is a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. Particular attention was given to the late phase of growth of E. coli populations under shear. Rheo-imaging measurements revealed, near the static plate, a rotational motion o...
Modeling dynamic recrystallization of olivine aggregates deformed in simple shear
Wenk, H.-R. [Department of Geology and Geophysics, University of California, Berkeley (United States); Tome, C. N. [Materials, Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
1999-11-10
Experiments by Zhang and Karato [1995] have shown that in simple shear dislocation creep of olivine at low strains, an asymmetric texture develops with a [100] maximum rotated away from the shear direction against the sense of shear. At large strain where recrystallization is pervasive, the texture pattern is symmetrical, and [100] is parallel to the shear direction. The deformation texture can be adequately modeled with a viscoplastic self-consistent polycrystal plasticity theory. This model can be expanded to include recrystallization, treating the process as a balance of boundary migration (growth of relatively underformed grains at the expense of highly deformed grains) and nucleation (strain-free nuclei replacing highly deformed grains). If nucleation dominates over growth, the model predicts a change from the asymmetric to the symmetric texture as recrystallization proceeds and stabilization in the ''easy slip'' orientation for the dominant (010)[100] slip system. This result is in accordance with the experiments and suggests that the most highly deformed orientation components dominate the recrystallization texture. The empirical model will be useful to simulate more adequately the development of anisotropy in the mantle where olivine is largely recrystallized. (c) 1999 American Geophysical Union.
Bestmann, Michel; Kunze, Karsten; Matthews, Alan
2000-11-01
The deformation history of a monophase calcite marble shear zone complex on Thassos Island, Northern Greece, is reconstructed by detailed geometric studies of the textural and microstructural patterns relative to a fixed reference system (shear zone boundary, SZB). Strain localization within the massive marble complex is linked to decreasing P- T conditions during the exhumation process of the metamorphic core complex. Solvus thermometry indicates that temperatures of 300-350°C prevailed during part of the shear zone deformation history. The coarse-grained marble protolith outside the shear zone is characterized by symmetrically oriented twin sets due to early coaxial deformation. A component of heterogeneous non-coaxial deformation is first recorded within the adjacent protomylonite. Enhanced strain weakening by dynamic recrystallization promoted strong localization of plastic deformation in the ultramylonite of the calcite shear zone, where high strain was accommodated by non-coaxial flow. This study demonstrates that both a pure shear and a simple shear strain path can result in similar crystallographic preferred orientations (single c-axis maximum perpendicular to the SZB) by different dominant deformation mechanisms. Separated a-axis pole figures (+ a- and - a-axis) show different density distributions with orthorhombic texture symmetry in the protolith marble and monoclinic symmetry in the ultramylonite marble consistently with the observed grain fabric symmetry.
Viscous shear heating instabilities in a 1-D viscoelastic shear zone
Homburg, J. M.; Coon, E. T.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.
2010-12-01
instabilities can occur. The instability is enhanced by the development of a self-localizing thermal perturbation in the fine grained zone that is narrower than the original width of the fine-grained zone. To examine the effect of melting, we include a parameterization of partially molten rock viscosity as a function of temperature assuming a simple relationship between melt fraction and temperature. At T > ~1400°C, all other deformation mechanisms are deactivated but shear heating continues, allowing for continued temperature evolution. In addition a strain rate cap proportional to the shear wave velocity in olivine has been imposed, reflecting the maximum rate that changes in stress can be communicated through the system. While Kelemen and Hirth (2007) allowed for grain size evolution, this has not yet been implemented in our model. Adding grain size evolution as an additional strain softening mechanism would probably allow instabilities to develop at more geologically reasonable applied strain rates. In addition to discussing the stability of the olivine only system, we will explore grain size evolution during system evolution and evaluate the consequences that the grain size evolution and lithology have on the stability of the system.
Mao Liangjie
Full Text Available A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.
Statistical data generated through CFD to aid in the scale-up of shear sensitive processes
Khan, Irfan; Das, Shankhadeep; Cloeter, Mike; Gillis, Paul; Poindexter, Michael
2016-11-01
A number of industrial processes are considered shear-sensitive, where the product quality depends on achieving the right balance between mixing energy input and the resulting strain rate distribution in the process. Examples of such industrial processes are crystallization, flocculation and suspension polymerization. Scale-up of such processes are prone to a number of challenges including the optimization of mixing and shear rate distribution in the process. Computational Fluid Dynamics (CFD) can be a valuable tool to aid in the process scale-up; however for modeling purpose, the process will often need to be simplified appropriately to reduce the computational complexity. Commercial CFD tools with appropriate Lagrangian particle tracking models can be used to gather statistical data such as maximum strain rate distribution and maximum number of passes through a specific strain rate. This presentation will discuss such statistical tools and their application to a model scale-up problem.
Micromechanics of shear banding
Gilman, J.J.
1992-08-01
Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.
Kinkhabwala, Ali
2013-01-01
The most fundamental problem in statistics is the inference of an unknown probability distribution from a finite number of samples. For a specific observed data set, answers to the following questions would be desirable: (1) Estimation: Which candidate distribution provides the best fit to the observed data?, (2) Goodness-of-fit: How concordant is this distribution with the observed data?, and (3) Uncertainty: How concordant are other candidate distributions with the observed data? A simple unified approach for univariate data that addresses these traditionally distinct statistical notions is presented called "maximum fidelity". Maximum fidelity is a strict frequentist approach that is fundamentally based on model concordance with the observed data. The fidelity statistic is a general information measure based on the coordinate-independent cumulative distribution and critical yet previously neglected symmetry considerations. An approximation for the null distribution of the fidelity allows its direct conversi...
Effects of loading history on small-strain shear modulus of saturated clays%循环应力历史对饱和软黏土小应变剪切模量的影响
谷川; 蔡袁强; 王军; 杨芳; 胡秀青
2012-01-01
饱和软黏土的小应变剪切模量Gmax是其基本力学参数。在进行饱和软黏土的有效应力动力分析时，往往认为小应变剪切模量Gmax只随着有效应力的降低而衰减，而不受动荷载应力历史的影响，因此基本采用静力状态下得到的小应变剪切模量代替相同有效应力时动力状态下的小应变剪切模量。但是，对于饱和软黏土，目前并没有足够多的试验数据证明这一假设。基于这一考虑，通过GDS动三轴及弯曲元测试系统，研究了循环应力历史对饱和软黏土小应变剪切模量的影响，试验结果表明循环应力历史对Gmax的影响较大，采用静力状态下得到的Gmax代替动力状态下的Gmax并不可取。同时，发现可以使用小应变剪切模量的突变来表征饱和软黏土的结构破坏。%The small-strain shear modulus is the main physical index of saturated clays. In the methods for the effective stress analysis, the mall-strain shear modulus obtained from static tests is often used in the dynamic analysis without regard to the influence of loading history. However, for saturated clays, this assumption has not been proved by enough test data. Based on this consideration, a few cyclic triaxial and bender element tests were conducted to study the influence of loading history on the small-strain shear modulus of saturated clays. The test results indicate that the influence is great and the above assumption is not correct. Meanwhile, it is also found that the small-strain shear modulus can be used to determine the failure criterion of saturated clays under cyclic loading.
Capacitive Extensometer Particularly Suited for Measuring in Vivo Bone Strain
Perusek, Gail P. (Inventor)
2000-01-01
The present invention provides for in vivo measurements of the principal strain magnitudes and directions, and maximum shear strain that occurs in a material, such as human bone, when it is loaded (or subjected to a load). In one embodiment the invention includes a capacitive delta extensometer arranged with six sensors in a three piece configuration, with each sensor of each pair spaced apart from each other by 120 degrees.
Ritter, Malte C.; Rosenau, Matthias; Leever, Karen; Oncken, Onno
2014-05-01
. Therefore simultaneous monitoring and analysis of strain weakening and strain localisation becomes feasible. Here we present results from first tests of this setup demonstrating its capability and limits. Various granular analogue materials with differing mechanical properties are tested and compared to results in ring shear and axial tests. Preliminary results show a principal pattern of correlated strain weakening and localisation that is characterized by a phase shift between stress and strain evolution during shear zone formation: Strain localisation has its maximum when the weakening rate is highest. Strain then delocalises, however, and reaches a steady state when the material strength reaches a stable value. References: Lohrmann, J., Kukowski, N., Adam, J., and Oncken, O., 2003, The impact of analogue material properties on the geometry, kinematics, and dynamics of convergent sand wedges: Journal of Structural Geology, v. 25, no. 10, p. 1691-1711, doi: 10.1016/S0191-8141(03)00005-1. Schrank, C.E., Boutelier, D.A., and Cruden, A.R., 2008, The analogue shear zone: From rheology to associated geometry: Journal of Structural Geology, v. 30, no. 2, p. 177-193, doi: 10.1016/j.jsg.2007.11.002.
Localization in inelastic rate dependent shearing deformations
Katsaounis, Theodoros
2016-09-04
Metals deformed at high strain rates can exhibit failure through formation of shear bands, a phenomenon often attributed to Hadamard instability and localization of the strain into an emerging coherent structure. We verify formation of shear bands for a nonlinear model exhibiting strain softening and strain rate sensitivity. The effects of strain softening and strain rate sensitivity are first assessed by linearized analysis, indicating that the combined effect leads to Turing instability. For the nonlinear model a class of self-similar solutions is constructed, that depicts a coherent localizing structure and the formation of a shear band. This solution is associated to a heteroclinic orbit of a dynamical system. The orbit is constructed numerically and yields explicit shear localizing solutions. © 2016 Elsevier Ltd
Compaction and shear settlement of granular materials
Morland, L. W.
1993-03-01
S HEARING of granular materials causes rearrangement of the granular structure which induces irreversible volume decrease and shear strain, in addition to reversible strain. A model is presented which describes the reversible strain by a hypoelastic law, and the irreversible compaction and shear by evolutionary laws. The latter are differential relations defining the progress of irreversible strain as an appropriate time-independent monotonic loading parameter increases, which incorporate dependence on the current state, and which require a direction for the irreversible shear strain increment. Such a model allows a variety of choices and combinations for the loading parameter, shear increment direction and arguments reflecting the current state. A wide selection of possible choices is incorporated in a systematic analysis of the initial shearing response of an unstressed material. It is shown that a physically sensible response restricts the choice to essentially two forms of dependence, and further restricts the initial shapes of the constitutive functions. The simpler model form reduces to three coupled non-linear differential equations for shearing, from which some general conclusions can be drawn, and numerical illustrations for shear stress and shear strain cycling are presented for simple valid model functions.
Finite Element Modeling of the Behavior of Armor Materials Under High Strain Rates and Large Strains
Polyzois, Ioannis
For years high strength steels and alloys have been widely used by the military for making armor plates. Advances in technology have led to the development of materials with improved resistance to penetration and deformation. Until recently, the behavior of these materials under high strain rates and large strains has been primarily based on laboratory testing using the Split Hopkinson Pressure Bar apparatus. With the advent of sophisticated computer programs, computer modeling and finite element simulations are being developed to predict the deformation behavior of these metals for a variety of conditions similar to those experienced during combat. In the present investigation, a modified direct impact Split Hopkinson Pressure Bar apparatus was modeled using the finite element software ABAQUS 6.8 for the purpose of simulating high strain rate compression of specimens of three armor materials: maraging steel 300, high hardness armor (HHA), and aluminum alloy 5083. These armor materials, provided by the Canadian Department of National Defence, were tested at the University of Manitoba by others. In this study, the empirical Johnson-Cook visco-plastic and damage models were used to simulate the deformation behavior obtained experimentally. A series of stress-time plots at various projectile impact momenta were produced and verified by comparison with experimental data. The impact momentum parameter was chosen rather than projectile velocity to normalize the initial conditions for each simulation. Phenomena such as the formation of adiabatic shear bands caused by deformation at high strains and strain rates were investigated through simulations. It was found that the Johnson-Cook model can accurately simulate the behavior of body-centered cubic (BCC) metals such as steels. The maximum shear stress was calculated for each simulation at various impact momenta. The finite element model showed that shear failure first occurred in the center of the cylindrical specimen and
Seismic anisotropy of the crust in Yunnan,China: Polarizations of fast shear-waves
SHI Yu-tao; GAO Yuan; WU Jing; LUO Yan; SU You-jin
2006-01-01
Using seismic data recorded by Yunnan Telemetry Seismic Network from January 1, 2000 to December 31, 2003,the dominant polarization directions of fast shear-waves are obtained at l0 digital seismic stations by SAM technique, a systematic analysis method on shear-wave splitting, in this study. The results show that dominant directions of polarizations of fast shear-waves at most stations are mainly at nearly N-S or NNW direction in Yunnan.The dominant polarization directions of fast shear-waves at stations located on the active faults are consistent with the strike of active faults, directions of regional principal compressive strains measured from GPS data, and basically consistent with regional principal compressive stress. Only a few of stations show complicated polarization pattern of fast shear-waves, or are not consistent with the strike of active faults and the directions of principal GPS compressive strains, which are always located at junction of several faults. The result reflects complicated fault distribution and stress field. The dominant polarization direction of fast shear-wave indicates the direction of the in-situ maximum principal compressive stress is controlled by multiple tectonic aspects such as the regional stress field and faults.
Guelorget, Bruno [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)]. E-mail: bruno.guelorget@utt.fr; Francois, Manuel [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Vial-Edwards, Cristian [Departemento de Ingenieria Mecanica y Metalurgica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, 6904411 Santiago (Chile); Montay, Guillaume [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Daniel, Laurent [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Lu, Jian [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)
2006-01-15
In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order to measure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force ({epsilon} {sup t} {approx_equal} 19.4 and 25.4%, respectively). Thus, a localization phenomenon occurs before the classic Considere's criterion (dF = 0) for the diffuse neck initiation. On the other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, then strain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the total strain and the strain rate measurements.
Cyclic Shearing Deformation Behavior of Saturated Clays
无
2007-01-01
The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay's strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The deformations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deformation and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used.
Dynamic shear deformation in high purity Fe
Cerreta, Ellen K [Los Alamos National Laboratory; Bingert, John F [Los Alamos National Laboratory; Trujillo, Carl P [Los Alamos National Laboratory; Lopez, Mike F [Los Alamos National Laboratory; Gray, George T [Los Alamos National Laboratory
2009-01-01
The forced shear test specimen, first developed by Meyer et al. [Meyer L. et al., Critical Adiabatic Shear Strength of Low Alloyed Steel Under Compressive Loading, Metallurgical Applications of Shock Wave and High Strain Rate Phenomena (Marcel Decker, 1986), 657; Hartmann K. et al., Metallurgical Effects on Impact Loaded Materials, Shock Waves and High Strain rate Phenomena in Metals (Plenum, 1981), 325-337.], has been utilized in a number of studies. While the geometry of this specimen does not allow for the microstructure to exactly define the location of shear band formation and the overall mechanical response of a specimen is highly sensitive to the geometry utilized, the forced shear specimen is useful for characterizing the influence of parameters such as strain rate, temperature, strain, and load on the microstructural evolution within a shear band. Additionally, many studies have utilized this geometry to advance the understanding of shear band development. In this study, by varying the geometry, specifically the ratio of the inner hole to the outer hat diameter, the dynamic shear localization response of high purity Fe was examined. Post mortem characterization was performed to quantify the width of the localizations and examine the microstructural and textural evolution of shear deformation in a bcc metal. Increased instability in mechanical response is strongly linked with development of enhanced intergranular misorientations, high angle boundaries, and classical shear textures characterized through orientation distribution functions.
Kiatgamolchai, S
2000-01-01
gamma has the bowl shape with the minimum at x approx 0.25-0.3. These characteristics suggest a possible influence of alloy disorder scattering. The mobilities and activation energies of the carriers in the boron-doped cap vary between samples and this is believed to be due to boron-spike near the Si/Si-substrate interface, in some samples. The source of electron-like carrier is presently unknown. Magnetotransport properties of modulation-doped p-type Si sub 1 sub - sub x Ge sub x /Si and Si sub 1 sub - sub x Ge sub x /Si sub 1 sub - sub y Ge sub y heterostructures were studied, in the magnetic field range 0-12 T, and in the temperature range 0.35-300 K. The experimental data within the classical regime have been analysed by mobility spectrum analysis, in order to separate the influences of different parallel conduction paths. A new method of mobility spectrum analysis has been developed by the based on the concept of maximum-entropy, and this computation has been shown to overcome several drawbacks or limita...
WANG Xue-bin
2006-01-01
Patterns of shear band, precursors to shear failure occurring in strain-softening stage, axial, lateral and volumetric strains as well as Poisson's ratio of plane strain rock specimens in compression for different heights were investigated by use of Fast Lagrangian Analysis of Continua(FLAC). A material imperfection closer to the lower-left comer of the specimen was prescribed. For finer mesh, the imperfection was modeled by four null elements, while it was modeled by a null element for coarser mesh. FISH functions were written to calculate the entire deformational characteristics of the specimen. In elastic stage, the adopted constitutive relation was linear elastic; in strain-softening stage, a composite Mohr-Coulomb criterion with tension cut-off and a post-peak linear constitutive relation were adopted. Height of rock specimen does not influence shear band's pattern (including the thickness and inclination angle of shear band). The slopes of the post-peak stress-axial strain curve, stress-lateral strain curve,lateral strain-axial strain curve, Poisson's ratio-axial strain curve and volumetric strain-axial strain curve depend on the height. Hence, the slopes of these curves cannot be considered as material properties. Nonlinear deformation prior to the peak stress is a kind of precursors to shear failure, which is less apparent for shorter specimen. For the same axial strain, lower lateral expansion is reached for shorter specimen, leading to lower Poisson's ratio and higher volumetric strain. The maximum volumetric strain of longer specimen is less than that of shorter specimen. The conclusions drawn from numerical results using finer mesh qualitatively agree with those using coarser mesh.
Shear Thickening Behaviour of Composite Propellant Suspension under Oscillatory Shear
D. Singh
2016-04-01
Full Text Available Composite propellant suspensions consist of highly filled polymeric system wherein solid particles of different sizes and shapes are dispersed in a polymeric matrix. The rheological behaviour of a propellant suspension is characterised by viscoplasticity and shear rate and time dependant viscosity. The behaviour of composite propellant suspension has been studied under amplitude sweep test where tests were performed by continuously varying strain amplitude (strain in %, γ by keeping the frequency and temperature constant and results are plotted in terms of log γ (strain amplitude vs logGʹ and logGʺ (Storage modulus and loss modulus, respectively. It is clear from amplitude sweep test that dynamic moduli and complex viscosity show marked increase at critical strain amplitude after a plateau region, infering a shear thickening behaviour.
Xuebin Wang
2006-01-01
Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect (interactions and interplay among microstructures) due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate.Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.
Lateral shear interferometry with holo shear lens
Joenathan, C.; Mohanty, R. K.; Sirohi, R. S.
1984-12-01
A simple method for obtaining lateral shear using holo shear lenses (HSL) has been discussed. This simple device which produces lateral shears in the orthogonal directions has been used for lens testing. The holo shear lens is placed at or near the focus of the lens to be tested. It has also been shown that HSL can be used in speckle shear interferometry as it performs both the functions of shearing and imaging.
高英俊; 全四龙; 邓芊芊; 罗志荣; 黄创高; 林葵
2015-01-01
针对刃型位错的滑移运动，构建包含外力场与晶格原子密度耦合作用的体系自由能密度函数，建立剪切应变作用体系的晶体相场模型。模拟了双相双晶体系的位错攀移和滑移运动，计算了位错滑移的Peierls势垒和滑移速度。结果表明：施加较大的剪切应变率作用，体系能量变化为单调光滑曲线，位错以恒定速度做连续运动，具有刚性运动特征；剪切应变率较小时，体系能量变化出现周期波动特征，位错运动是处于低速不连续运动状态，运动出现周期“颠簸”式滑移运动，具有黏滞运动特征；位错启动运动，存在临界的势垒。位错启动攀移运动的Peierls势垒要比启动滑移Peierls势垒大几倍。位错攀移和滑移运动特征与实验结果相符合。%Structural kinetics in crystalline solids is driven heterogeneously at an atomic level by localized defects, which in turn drive mesoscopic and macroscopic phenomena such as structural phase transformation, fracture, and other forms of plastic flows. A complete description of such processes therefore requires a multiscale approach. Existing modeling methods typically operate exclusively either on an atomic scale or on a mesoscopic scale and macroscopic scale. Phase-field-crystal model, on the other hand, provides a framework that combines atomic length scale and mesoacpoic/diffusive time scale, with the potential reaching a mesoacpoic length through systemic multiscale expansion method. In order to study the dislocation movement under shear strain, the free energy density functional including the exerting shear force term is constructed and also the phase field crystal model for system of shear stain is established. The climb and glide of single dislocation in two-grain system are simulated, and the glide velocity of dislocation and the Peierls potential for dislocation gliding are calculated. The results show that the energy curve changing
Butler, B.D.; Hanley, H.J.M.; Straty, G.C. [National Institute of Standards and Technology, Boulder, CO (United States); Muzny, C.D. [Univ. of Colorado, Boulder, CO (United States)
1995-12-31
An experimental small angle neutron scattering (SANS) study of dense silica gels, prepared from suspensions of 24 nm colloidal silica particles at several volume fractions {theta} is discussed. Provided that {theta}{approx_lt}0.18, the scattered intensity at small wave vectors q increases as the gelation proceeds, and the structure factor S(q, t {yields} {infinity}) of the gel exhibits apparent power law behavior. Power law behavior is also observed, even for samples with {theta}>0.18, when the gel is formed under an applied shear. Shear also enhances the diffraction maximum corresponding to the inter-particle contact distance of the gel. Difficulties encountered when trying to interpret SANS data from these dense systems are outlined. Results of computer simulations intended to mimic gel formation, including computations of S(q, t), are discussed. Comments on a method to extract a fractal dimension characterizing the gel are included.
Strain localization and damage development in 2060 alloy during bending
Xiao Jin; Bao-qin Fu; Cheng-lu Zhang; Wei Liu
2015-01-01
The microstructure evolution and damage development of the third-generation Al–Li alloy 2060 (T8) were studied using in situ bending tests. Specimens were loaded with a series of punches of different radii, and the microstructure evolution was studied by scanning electron microscopy, electron backscatter diffraction, and digital image correlation (DIC) methods. The evolution of the microscopic fracture strain distribution and microstructure in 2060 alloy during bending was characterized, where the dispersion distribution of precipitates was recorded by backscattered electron imaging and later inputted into a DIC system for strain calculations. The experimental results showed that strain localization in the free surface of bent specimens induced damage to the microstructure. The region of crack initiation lies on the free surface with maximum strain, and the shear crack propagates along the macro-shear band in the early stages of bending. Crack propagation in the later stages was interpreted on the basis of the conventional mechanism of ductile fracture.
Patrício, P; Almeida, P L; Portela, R; Sobral, R G; Grilo, I R; Cidade, T; Leal, C R
2014-08-01
The activity of growing living bacteria was investigated using real-time and in situ rheology-in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus-strain COL and its isogenic cell wall autolysis mutant, RUSAL9-were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of the cultures of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the cultures of the two strains follows different and rich behaviors, with no counterpart in the optical density or in the population's colony-forming units measurements. While the viscosity of strain COL culture keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain culture decreases steeply, still in the exponential phase, remains constant for some time, and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviors, which were observed to be shear-stress-dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL culture, obtained with oscillatory shear, exhibit power-law behaviors whose exponents are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant culture have complex behaviors, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. Nevertheless, these behaviors reflect the bacteria growth stage.
Mesoscale Elucidation of Biofilm Shear Behavior
Barai, Pallab; Mukherjee, Partha P
2015-01-01
Formation of bacterial colonies as biofilm on the surface/interface of various objects has the potential to impact not only human health and disease but also energy and environmental considerations. Biofilms can be regarded as soft materials, and comprehension of their shear response to external forces is a key element to the fundamental understanding. A mesoscale model has been presented in this article based on digitization of a biofilm microstructure. Its response under externally applied shear load is analyzed. Strain stiffening type behavior is readily observed under high strain loads due to the unfolding of chains within soft polymeric substrate. Sustained shear loading of the biofilm network results in strain localization along the diagonal direction. Rupture of the soft polymeric matrix can potentially reduce the intercellular interaction between the bacterial cells. Evolution of stiffness within the biofilm network under shear reveals two regions: a) initial increase in stiffness due to strain stiffe...
Continuous shear - a method for studying material elements passing a stationary shear plane
Lindegren, Maria; Wiwe, Birgitte; Wanheim, Tarras
2003-01-01
Traditionally, material response to shear deformation has been studied with methods where the shear is gradually increasing from zero to the final value over a certain fixed deformation zone, e.g. in the well-known torsion test of a tube with a defined shear zone established by a machined...... circumferential groove. Normally shear in metal forming processes is of another nature, namely where the material elements move through a stationary shear zone, often of small width. In this paper a method enabling the simulation of this situation is presented. A tool for continuous shear has beeen manufactured...... and tested with AlMgSil and copper. The sheared material has thereafter been tested n plane strain compression with different orientation concerning the angle between the shear plane and the compression direction....
Rotational tumbling of Escherichia coli aggregates under shear
Portela, R.; Patrício, P.; Almeida, P. L.; Sobral, R. G.; Franco, J. M.; Leal, C. R.
2016-12-01
Growing living cultures of Escherichia coli bacteria are investigated using real-time in situ rheology and rheoimaging measurements. In the early stages of growth (lag phase) and when subjected to a constant stationary shear, the viscosity slowly increases with the cell's population. As the bacteria reach the exponential phase of growth, the viscosity increases rapidly, with sudden and temporary abrupt decreases and recoveries. At a certain stage, corresponding grossly to the late phase of growth, when the population stabilizes, the viscosity also keeps its maximum constant value, with drops and recoveries, for a long period of time. This complex rheological behavior, which is observed to be shear strain dependent, is a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. Particular attention is given to the late phase of growth of E. coli populations under shear. Rheoimaging measurements reveal, near the static plate, a rotational motion of E. coli aggregates, collectively tumbling and flowing in the shear direction. This behavior is interpreted in the light of a simple theoretical approach based on simple rigid body mechanics.
Continuous shear - a method for studying material elements passing a stationary shear plane
Lindegren, Maria; Wiwe, Birgitte; Wanheim, Tarras
2003-01-01
Traditionally, material response to shear deformation has been studied with methods where the shear is gradually increasing from zero to the final value over a certain fixed deformation zone, e.g. in the well-known torsion test of a tube with a defined shear zone established by a machined circumf...... and tested with AlMgSil and copper. The sheared material has thereafter been tested n plane strain compression with different orientation concerning the angle between the shear plane and the compression direction....
Syed, Sammiuddin [Department of Civil, Construction and Environmental Engineering, North Carolina State University, Campus Box 7908, Raleigh, NC 27695-7908 (United States); Gupta, Abhinav, E-mail: agupta1@ncsu.edu [Department of Civil, Construction and Environmental Engineering, North Carolina State University, Campus Box 7908, Raleigh, NC 27695-7908 (United States)
2015-12-15
Highlights: • A simulation-based fragility evaluation framework is presented. • The framework incorporates uncertainties and randomness in damage plasticity model of RC shear walls. • The framework also incorporates randomness in earthquake time histories. • Performance of RC shear walls is characterized in terms of two different limit states. • Significance of considering uncertainties in material constitutive model is illustrated. - Abstract: Part 2 of this two-part manuscript builds upon the conclusions from Part 1 by evaluating whether or not it is important to considering uncertainties in material constitutive model parameters in the fragility assessment of concrete shear walls. A particular application of a box-shaped shear wall is considered because this particular specimen was tested in the past under the JNES/NUPEC program in Japan and has been used extensively by various researchers around the world to conduct studies on reconciliation of experimental and analytical results. A simulation-based fragility evaluation framework is presented in this paper. The uniqueness of this framework lies in incorporation of the uncertainties and randomness associated with the parameters of damage plasticity model as well as earthquake input motions, which are essential for estimating the demands. Unlike most of the previous studies that focus mostly on shear capacity, two different performance limit states based on maximum shear strains and maximum shear force are considered in the fragility assessment. For each performance limit state, variation in the probability of failure due to uncertainties in the material constitutive model is determined for illustrating the significance of considering such uncertainties.
A novel limiting strain energy strength theory
LIU Guang-lian
2009-01-01
With applied dislocation theory,the effects of shear and normal stresses on the slide and climb motions at the same section of a crystal were analyzed.And,based on the synergetic effect of both normal and shear strain specific energies,the concept of the total equivalent strain specific energy (TESSE) at an oblique section and a new strength theory named as limiting strain energy strength theory (LSEST) were proposed.As for isotropic materials,the plastic yielding or brittle fracture of under uniaxial stress state would occur when the maximum TESSE reached the strain specific energy,also the expressions on the equivalent stresses and a function of failure of the LSEST under different principal stress states were obtained.Relationship formulas among the tensile,compressive and shear yield strengths for plastic metals were derived.These theoretical predictions,according to the LSEST,were consistent very well with experiment results of tensile,compressive and torsion tests of three plastic metals and other experiment results from open literatures.This novel LSEST might also help for strength calculation of other materials.
Haptic Edge Detection Through Shear
Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent
2016-01-01
Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals. PMID:27009331
Yuan Xiaoming; Sun Jing; Sun Rui
2006-01-01
An error analysis of the dynamic shear modulus of stiff specimens from tests performed by a new resonant column device developed by the Institute of Engineering Mechanics, China was conducted. A modified approach for calculating the dynamic shear modulus of the stiff specimens is presented. The error formula of the tests was deduced and parameters that impact the accuracy of the test were identified. Using six steel specimens with known standard stiffness as a base, a revised dynamic shear modulus calculation for stiff specimens was formulated by comparing three of the models.The maximum error between the test results and the calculated results shown by curves from both the free-vibration and the resonant-vibration tests is less than 6%. The free-vibration and resonant-vibration tests for three types of stiff samples with a known modulus indicate that the maximum deviation between the actual and the tested value using the modified approach were less than 10%. As a result, the modified approach presented here is shown to be reliable and the new device can be used for testing dynamic shear modulus of any stiff materials at low shear strain levels
Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography.
Yamakoshi, Yoshiki; Nakajima, Takahito; Kasahara, Toshihiro; Yamazaki, Mayuko; Koda, Ren; Sunaguchi, Naoki
2017-02-01
Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is [Formula: see text] for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.
Strain localization in carbonate rocks experimentally deformed in the ductile field
Rybacki, E.; Morales, L. F. G.; Dresen, G.
2012-04-01
The deformation of rocks in the Earth's crust is often localized, varying from brittle fault gauges in shallow environments to mylonites in ductile shear zones at greater depth. A number of theoretical, experimental, and field studies focused on the evolution and extend of brittle fault zones, but little is known so far about initiation of ductile shear zones. Strain localization in rocks deforming at high temperature and pressure may be induced by several physical, chemical, or structurally-related mechanisms. We performed simple and pure shear deformation experiments on carbonate rocks containing structural inhomogenities in the ductile deformation regime. The results may help to gain insight into the evolution of high temperature shear zones. As starting material we used cylindrical samples of coarse-grained Carrara marble containing one or two 1 mm thin artificially prepared sheets of fine-grained Solnhofen limestone, which act as soft inclusions under the applied experimental conditions. Length and diameter of the investigated solid and hollow cylinders were 10-20 mm and 10-15 mm, respectively. Samples were deformed in a Paterson-type gas deformation apparatus at 900° C temperature and confining pressures of 300 and 400 MPa. Three samples were deformed in axial compression at a bulk strain rate of 8x10-5 s-1to axial strains between 0.02 and 0.21 and 15 samples were twisted in torsion at a bulk shear strain rate of 2x10-4 s-1 to shear strains between 0.01 and 3.74. At low strain, specimens deformed axially and in torsion show minor strain hardening that is replaced by strain weakening at shear strains in excess of about 0.2. Peak shear stress at the imposed condition is about 20 MPa. Strain localized strongly within the weak inclusions as indicated by inhomogeneous bending of initially straight strain markers on sample jackets. Maximum strain concentration within inclusions with respect to the adjacent matrix was between 4 and 40, depending on total strain and
Simple shear of deformable square objects
Treagus, Susan H.; Lan, Labao
2003-12-01
Finite element models of square objects in a contrasting matrix in simple shear show that the objects deform to a variety of shapes. For a range of viscosity contrasts, we catalogue the changing shapes and orientations of objects in progressive simple shear. At moderate simple shear ( γ=1.5), the shapes are virtually indistinguishable from those in equivalent pure shear models with the same bulk strain ( RS=4), examined in a previous study. In theory, differences would be expected, especially for very stiff objects or at very large strain. In all our simple shear models, relatively competent square objects become asymmetric barrel shapes with concave shortened edges, similar to some types of boudin. Incompetent objects develop shapes surprisingly similar to mica fish described in mylonites.
ON WALL SHEAR STRESS OF ARTERY
Liu Zhao-rong; Liu Bao-yu; Qin Kai-rong
2003-01-01
In this paper, a method was proposed that the wall shear stress of artery could be determined by measuring the centerline axial velocity and radial motion of arterial wall simultaneously.The method is simple in application and can get higher precision when it is used to determine the shear stress of arterial wall in vivo.As an example, the shear stress distribution in periodic oscillatory flow of human carotid was calculated and discussed.The computed results show that the shear stress distribution at any given instant is almost uniform and will be zero at the centerline and tends to maximum at the vessel wall.
Novel shear mechanism in nanolayered composites
Mara, Nathan [Los Alamos National Laboratory; Bhattacharyya, Dhriti [Los Alamos National Laboratory; Hirth, John P [Los Alamos National Laboratory; Dickerson, Patricia O [Los Alamos National Laboratory; Misra, Amit [Los Alamos National Laboratory
2009-01-01
Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bi-metal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Previous work investigating shear band formation in nanocrystalline materials has shown a connection between insufficient strain hardening and the onset of shear banding in Fe and Fe-10% Cu, but has also shown that hardening does not necessarily offset shear banding in Pd nanomaterials. Therefore, the mechanisms behind shear localization in nanocrystalline materials are not completely understood. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.
Graham, Rodney
2017-04-01
temperature shear zones with flaser gabbro and amphibolitization must have been developed at deeper levels in the shear zone and 'dragged upwards'. An attempt to justify these assertions will made using outcrop exsmples and some deep Seismic data John Ramsay was always cautious about up-scaling and indulging in large scale tectonic speculations, but without his geometric acumen the big scale picture would have been even less clear. Ramsay, J.G. and Graham, R.H., 1970. Strain variation in shear belts. Canadian Journal of Earth Sciences, 7(3), pp.786-813.
Oscillatory shear response of moisture barrier coatings containing clay of different shape factor.
Kugge, C; Vanderhoek, N; Bousfield, D W
2011-06-01
Oscillatory shear rheology of barrier coatings based on dispersed styrene-butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25-100 Pa s.
Micromechanical modeling of damage in periodic composites using strain gradient plasticity
Azizi, Reza
2012-01-01
Damage evolution at the fiber matrix interface in Metal Matrix Composites (MMCs) is studied using strain gradient theory of plasticity. The study includes the rate independent formulation of energetic strain gradient plasticity for the matrix, purely elastic model for the fiber and cohesive zone...... model under simple shear and transverse uniaxial tension using plane strain and periodic boundary conditions. The result of the overall response curve, effective plastic strain, effective stress and higher order stress distributions are shown. The effect of the material length scale, maximum stress...
Feng, Xiaojun; Jessell, Mark Walter; Amponsah, Prince Ofori; Martin, Roland; Ganne, Jérôme; Liu, Daqing; Batt, Geoffrey E.
2016-10-01
Tectonic inheritance acquired from past geological events can control the formation of new plate boundaries. The aim of this paper is to explore the role of inherited NE and NW trending fabrics and their rheological influence on the propagation of Oligocene-Miocene strike-slip faulting that matured to become the Australian-Pacific plate boundary fault in southern New Zealand. Strain weakening plays a significant role in controlling the formation, growth and evolution of strain localization. In this study, three-dimensional thermo-mechanical models have been used to explore the effect of strain weakening on the Oligocene-Miocene self-organization of strain localization. Strain weakening is simulated through decreasing either the coefficient of friction of upper crust, its cohesion, or the rheological viscosity contrast between the inherited structures and their surrounding wall rocks. Viscosity contrast is obtained by varying the viscosity of inherited structures. Softening coefficient (α) is a measure of strain weakening. Our experiments robustly demonstrate that a primary boundary shear zone becomes mature quicker when softening coefficients are increased. Deformation is focused along narrow high-strain shear zones in the centre of the model when the softening coefficients are high, whereas the strain is more diffuse with many shear zones spread over the model and possibly some high-strain shear zones focused near one border at lower softening coefficients. Varying the viscosity contrast has less effect on the distribution of maximum finite strain. Under simple-shear boundary conditions, NW trending inherited structures make a major contribution to forming early zones of highly focused strain, up to a shear strain of about γ = 3.7. During this process, most NE-trending structures move and rotate passively, accommodate less strain, or even be abandoned through time.
2017-09-13
Activation of a slip system requires that it is critically stressed , i.e. that the shear stress resolved on the slip system exceeds a threshold...increment. A direct way of investigating which slip systemsmay be active in each grain is to investigate the stress state of the grain. From...correlation (DIC) system [29] and a load cell. The stress - strain curve in Fig. 1b) presents the maximum stress reading after each loading step. Relaxation
ANALYSIS OF SIMPLE SHEAR ENDOCHRONIC EQUATIONS FOR FINITE PLASTIC DEFORMATION
江五贵; 黄明挥
2005-01-01
Jaumann rate, generalized Jaumann rate, Fu rate and Wu rate were incorporated into endochronic equations forfinite plastic deformation to analyze simple shear finite deformation. The results show that an oscillatory shear stress and normal stress response to a monotonically increasing shear strain occurs when Jaumann rate objective model is adopted for hypoelastic or endochronic materials. The oscillatory response is dependent on objective rate adopted, independent on elastoplastic models. Normal stress is unequal to zero during simple shear finite deformation.
Empirical paths of poles to planes (eppps) constrain the kinematics of geological shear zones
Talbot, Christopher J.
2014-09-01
Ductile shear zones are tabular bodies of deformed rocks bound by less deformed wall rocks. This work introduces a simple empirical approach to analysing the 3D kinematics of shear zones. The orientations of pre-shear planar markers distorted across natural shear zones by local strains are systematically measured and plotted as poles on lower hemisphere equal area projections that constrain smooth empiricalpaths ofpoles toplanes (eppps). Such eppps recording local strain gradients are used to fix a reference frame to the plane of greatest shear in any homogeneous bulk strain. Assuming that space can be taken as a proxy for time, the curvatures of pre-shear planar markers across shear zones are interpreted as the records of the 3D bulk strain histories of shear zones. The sig- or zig-moidal symmetries of sheared markers record different amounts of the same general strain within the same overall movement pattern (i.e. in a constant flow field) whatever its geometry or history. In effect eppps represent the strain memories of shear zones with successively inward readings recording successively younger shearing. In planes other than the bulk XY, great circle eppps indicate simple shear while hyperbolic eppps indicate pure shear. Eppps for suites of shear zones in Proterozoic gneisses in Sweden exhibit the parabolic shapes indicative of pure rather than simple shear.
Shear Reinforcement Requirements for High-Strength Concrete Bridge Girders
Ramirez, J. A.; Aguilar, Gerardo
2005-01-01
A research program was conducted on the shear strength of high-strength concrete members. The objective was to evaluate the shear behavior and strength of concrete bridge members with compressive strengths in the range of 10 000 to 15 000 psi. The goal was to determine if the current minimum amount of shear reinforcement together with maximum spacing limits in the 2004 AASHTO LRFD Specifications, and the upper limit on the nominal shear strength were applicable to concrete compressive strengt...
Shear zone junctions: Of zippers and freeways
Passchier, Cees W.; Platt, John P.
2017-02-01
Ductile shear zones are commonly treated as straight high-strain domains with uniform shear sense and characteristic curved foliation trails, bounded by non-deforming wall rock. Many shear zones, however, are branched, and if movement on such branches is contemporaneous, the resulting shape can be complicated and lead to unusual shear sense arrangement and foliation geometries in the wall rock. For Y-shaped shear zone triple junctions with three joining branches and transport direction at a high angle to the branchline, only eight basic types of junction are thought to be stable and to produce significant displacement. The simplest type, called freeway junctions, have similar shear sense in all three branches. The other types show joining or separating behaviour of shear zone branches similar to the action of a zipper. Such junctions may have shear zone branches that join to form a single branch (closing zipper junction), or a single shear zone that splits to form two branches, (opening zipper junction). All categories of shear zone junctions show characteristic foliation patterns and deflection of markers in the wall rock. Closing zipper junctions are unusual, since they form a non-active zone with opposite deflection of foliations in the wall rock known as an extraction fault or wake. Shear zipper junctions can form domains of overprinting shear sense along their flanks. A small and large field example are given from NE Spain and Eastern Anatolia. The geometry of more complex, 3D shear zone junctions with slip parallel and oblique to the branchline is briefly discussed.
顾晓强; 杨峻; 黄茂松; 高广运
2016-01-01
利用弯曲元、共振柱和循环扭剪试验联合测定了不同围压和密实度条件下干砂的小应变剪切模量，研究了弯曲元试验中输出信号的特性和各种信号分析方法确定剪切波传播时间的可靠性，并对比了不同试验的结果。研究结果表明，在共振柱试验时，需要考虑系统刚度对试验结果的影响，特别当试样刚度较大时。弯曲元输出信号中最先到达的是近场效应，其初始极化方向跟剪切波相反。近场效应随着输入频率的增加有一定程度的减小，但不会消失。实际试验中建议输入频率不断增加，直至输出信号比较稳定。值得注意的是，剪切初达波的振幅可能远小于后续振动，因此容易造成初达波的误判。时域初达波法能比较可靠准确地确定剪切波的传播时间，波峰法、交互相关法和交互功率法结果均随输入频率有较大波动，不能可靠地确定剪切波的传播时间。对比试验表明，弯曲元、共振柱和循环扭剪试验确定小应变剪切模量对细砂和粗砂均吻合良好，初步表明砂土粒径对不同试验方法结果的一致性没有影响。%Bender element (BE), resonant column (RC) and cyclic torsional shear (TS) tests are performed to measure the small strain shear modulus of dry sands. Thecharacteristics of the received signals in BE tests are investigated, and different interpretation methods are used to determine the travel time of shear waves.The results indicate that it is important to account for the compliance of the testing system in RC tests, especially when the specimen is stiff. In BE tests, the near fieldcomponent arrives first and its initial polarization is opposite to that of the input signal. The near flied decreases as the input frequency increases, but it always exists. Inpractice, it isrecommended that the input frequency should increase continuously until the output signal becomes stable. Note that
Initiation and Propagation of Shear Bands in Antiplane Shear Deformation.
1984-03-01
hypoelastic ), and they examined the differences between the uniform deformation field under rising load and the nonuniform field due to the imperfection...approach to the study of the criteria for the onset of shear localization in one dimensional models has been considered by some authors, including...to simulate the phenomenon of thermal softening due to adiabatic heating, a material model is selected which shows a local maximum in the dependence
Shear-stress relaxation and ensemble transformation of shear-stress autocorrelation functions
Wittmer, J. P.; Xu, H.; Baschnagel, J.
2015-02-01
We revisit the relation between the shear-stress relaxation modulus G (t ) , computed at finite shear strain 0 0 with Geq being the static equilibrium shear modulus. G (t ) and C(t ) | γ thus must become different for solids and it is impossible to obtain Geq alone from C(t ) | γ as often assumed. We comment briefly on self-assembled transient networks where Geq(f ) must vanish for a finite scission-recombination frequency f . We argue that G(t ) =C (t ) | τ=C(t ) | γ should reveal an intermediate plateau set by the shear modulus Geq(f =0 ) of the quenched network.
Origins of Shear Jamming for Frictional Grains
Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert
2016-11-01
Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.
Three dimensional fabric evolution of sheared sand
Hasan, Alsidqi; Alshibli, Khalid (UWA)
2012-10-24
Granular particles undergo translation and rolling when they are sheared. This paper presents a three-dimensional (3D) experimental assessment of fabric evolution of sheared sand at the particle level. F-75 Ottawa sand specimen was tested under an axisymmetric triaxial loading condition. It measured 9.5 mm in diameter and 20 mm in height. The quantitative evaluation was conducted by analyzing 3D high-resolution x-ray synchrotron micro-tomography images of the specimen at eight axial strain levels. The analyses included visualization of particle translation and rotation, and quantification of fabric orientation as shearing continued. Representative individual particles were successfully tracked and visualized to assess the mode of interaction between them. This paper discusses fabric evolution and compares the evolution of particles within and outside the shear band as shearing continues. Changes in particle orientation distributions are presented using fabric histograms and fabric tensor.
Mohammad Derikvand; Ghanbar Ebrahimi
2014-01-01
We studied the effect of loose tenon dimensions on stress and strain distributions in T-shaped mortise and loose tenon (M<) furni-ture joints under uniaxial bending loads, and determined the effects of loose tenon length (30, 45, 60, and 90 mm) and loose tenon thickness (6 and 8 mm) on bending moment capacity of M< joints constructed with polyvinyl acetate (PVAc) adhesive. Stress and strain distributions in joint elements were then estimated for each joint using ANSYS finite element (FE) software. The bending moment capacity of joints increased significantly with thickness and length of the tenon. Based on the FE analysis results, under uniaxial bending, the highest shear stress values were obtained in the middle parts of the tenon, while the highest shear elastic strain values were estimated in glue lines between the tenon sur-faces and walls of the mortise. Shear stress and shear elastic strain values in joint elements generally increased with tenon dimensions and corre-sponding bending moment capacities. There was consistency between predicted maximum shear stress values and failure modes of the joints.
Mechanical mechanism analysis of tension type anchor based on shear displacement method
XIAO Shu-jun; CHEN Chang-fu
2008-01-01
Based on the fact that the shear stress along anchorage segment is neither linearly nor uniformly distributed, the load transfer mechanism of the tension type anchor was studied and the mechanical characteristic of anchorage segment was analyzed. Shear stress-strain relationship of soil surrounding anchorage body was simplified into three-folding-lines model consisting of elastic phase, elasto-plastic phase and residual phase considering its softening eharaeteristic. Meanwhile, shear displacement method that has been extensively used in the analysis of pile foundation was introduced. Based on elasto-plastic theory, the distributions of displacement, shear stress and axial force along the anchorage segment of tension type anchor were obtained, and the formula for calculating the elastic limit load was also developed accordingly. Finally, an example was given to discuss the variation of stress and displacement in the anchorage segment with the loads exerted on the anchor, and a program was worked out to calculate the anchor maximum bearing capacity. The influence of some parameters on the anchor bearing capacity was discussed, and effective anchorage length was obtained simultaneously. The results show that the shear stress first increases and then decreases and finally trends to theresidual strength with increase of distance from bottom of the anchorage body, the displacement increases all the time with theincrease of distance from bottom of the anchorage body, and the increase of velocity gradually becomes greater.
Shear bands in a bulk metallic glass after large plastic deformation
Qu, D.D.; Wang, Y.B.; Liao, X.Z.; Shen, J. (Harbin); (Sydney)
2012-10-23
A transmission electron microscopy investigation is conducted to trace shear bands in a Zr{sub 53}Cu{sub 18.7}Ni{sub 12}Al{sub 16.3} bulk metallic glass after experiencing 4% plastic deformation. Shear band initiation, secondary shear band interactions, mature shear band broadening and the interactions of shear bands with shear-induced nanocrystals are captured. Results suggest that the plasticity of the bulk metallic glass is enhanced by complex shear bands and their interactions which accommodate large plastic strain and prevent catastrophic shear band propagation.
Wittmer, J. P.; Xu, H.; Polińska, P.; Weysser, F.; Baschnagel, J.
2013-03-01
The shear modulus G of two glass-forming colloidal model systems in d = 3 and d = 2 dimensions is investigated by means of, respectively, molecular dynamics and Monte Carlo simulations. Comparing ensembles where either the shear strain γ or the conjugated (mean) shear stress τ are imposed, we compute G from the respective stress and strain fluctuations as a function of temperature T while keeping a constant normal pressure P. The choice of the ensemble is seen to be highly relevant for the shear stress fluctuations μF(T) which at constant τ decay monotonously with T following the affine shear elasticity μA(T), i.e., a simple two-point correlation function. At variance, non-monotonous behavior with a maximum at the glass transition temperature Tg is demonstrated for μF(T) at constant γ. The increase of G below Tg is reasonably fitted for both models by a continuous cusp singularity, G(T)∝(1 - T/Tg)1/2, in qualitative agreement with recent theoretical predictions. It is argued, however, that longer sampling times may lead to a sharper transition.
Experimental study of shear rate dependence in perpetually sheared granular matter
Liu Sophie Yang
2017-01-01
Full Text Available We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called “3D Stadium Shear Device” which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10−6 to 10−2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.
Modelling to very high strains
Bons, P. D.; Jessell, M. W.; Griera, A.; Evans, L. A.; Wilson, C. J. L.
2009-04-01
Ductile strains in shear zones often reach extreme values, resulting in typical structures, such as winged porphyroclasts and several types of shear bands. The numerical simulation of the development of such structures has so far been inhibited by the low maximum strains that numerical models can normally achieve. Typical numerical models collapse at shear strains in the order of one to three. We have implemented a number of new functionalities in the numerical platform "Elle" (Jessell et al. 2001), which significantly increases the amount of strain that can be achieved and simultaneously reduces boundary effects that become increasingly disturbing at higher strain. Constant remeshing, while maintaining the polygonal phase regions, is the first step to avoid collapse of the finite-element grid required by finite-element solvers, such as Basil (Houseman et al. 2008). The second step is to apply a grain-growth routine to the boundaries of polygons that represent phase regions. This way, the development of sharp angles is avoided. A second advantage is that phase regions may merge or become separated (boudinage). Such topological changes are normally not possible in finite element deformation codes. The third step is the use of wrapping vertical model boundaries, with which optimal and unchanging model boundaries are maintained for the application of stress or velocity boundary conditions. The fourth step is to shift the model by a random amount in the vertical direction every time step. This way, the fixed horizontal boundary conditions are applied to different material points within the model every time step. Disturbing boundary effects are thus averaged out over the whole model and not localised to e.g. top and bottom of the model. Reduction of boundary effects has the additional advantage that model can be smaller and, therefore, numerically more efficient. Owing to the combination of these existing and new functionalities it is now possible to simulate the
Disentangling the role of structure and friction in shear jamming
Vinutha, H. A.; Sastry, Srikanth
2016-06-01
Amorphous sphere packings have been intensely investigated to understand mechanical and flow behaviour of dense granular matter and to explore universal aspects of the jamming transition, from fluid to structurally arrested states. Considerable recent research has focused on anisotropic packings of frictional grains generated by shear deformation leading to shear jamming, occurring below the jamming density for isotropic packings of frictionless grains. Here, with the aim of disentangling the role of shear-deformation-induced structures and friction in generating shear jamming, we computationally study sheared assemblies of frictionless spheres, over a wide range of densities. We demonstrate that shear deformation alone leads to the emergence of geometric features characteristic of jammed packings, with the increase of shear strain. We also show that such emergent geometry, together with friction, leads to mechanically stable, shear-jammed, packings above a threshold density that lies well below the isotropic jamming point.
刘军; 周飞航; 刘飞
2016-01-01
In order to ensure the high-efficiency and stable operation of the wind turbines, this paper presents compensation torque of fuzzy variable gain in torque control. The influence of mechanical torque fluctuation of wind turbines caused by random dither component of the tower shadow effect, wind shear, wind speed and reference rotation fluctuation calculated via optimal tip speed ratio on permanent magnet synchronous wind power system is alleviated effectively, the low frequency oscillation of wind power system is suppressed, and the stability of the system is ensured. It calculates accurate reference speed of maximum electromagnetic power by modifying the optimal tip speed ratio, and makes the unit run at the corresponding working point of maximum electromagnetic power. It truly achieves the maximum wind power tracking, by calculating the optimal tip speed ratio, considering the shafting friction loss. A direct-driven permanent magnet synchronous wind power system simulation platform is built in detail under Matlab/Simulink, and the correctness and effectiveness of the method is proved.%为了保证风电机组高效稳定运行，通过在转矩控制环节中引入模糊变增益的转速补偿转矩，有效地减轻了由塔影效应、风切变、风速中的随机脉动分量引起的风力机输出的机械转矩波动与按照最优叶尖速比法计算的参考转速的波动对永磁同步风力发电系统的影响，抑制了风电系统的低频震荡并保证了系统的稳定性。当考虑到轴系的摩擦损耗时，为了真正地实现最大风能跟踪，通过对最优叶尖速比进行修正，得出最大电磁功率所对应的准确的参考转速，使得机组运行在最大电磁功率对应的工作点处。在Matlab/Simulink下构建了直驱永磁同步风电系统的详细仿真平台，验证了该方法的正确性与有效性。
Shear System Debugging and Shear Test
YANG; Dong-xue; JIAO; Hai-yang
2015-01-01
Shear system is the essential equipment of head-end processing in the spent fuel reprocessing process,with the aim of cutting spent fuels into appropriate lengths for dissolve,separatingspent fuel core from jacket.Shear system of CRARL is mainly set in 01Bhot cell,element rods will be cut into short lengths of 10-30mm
Little, Timothy A.; Prior, David J.; Toy, Virginia G.
2016-03-01
The Alpine fault self-exhumes its own ductile shear zone roots and has a known slip kinematics. Within ˜1 km of the fault, the mylonitic foliation is subparallel to the boundary of the amphibolite-facies ductile shear zone in which it formed. Using EBSD, we analyzed quartz Lattice Preferred Orientations [LPOs) of mylonites along a central part of the Alpine Fault. All LPOs feature a strongest girdle of [c]-axes that is forward-inclined ˜28 ± 4° away from the pole to the fault. A maximum of axes is inclined at the same angle relative the fault. The [c]-axis girdle is perpendicular to extensional (C') shear bands and the maximum is parallel to their slip direction. [c]-axis girdles do not form perpendicular to the SZB. Schmid factor analysis suggests that σ1 was arranged at 60-80° to the Alpine Fault. These observations indicate ductile transpression in the shear zone. The inclined arrangement of [c]-axis girdles, axes, and C' planes relative to the fault can be explained by their alignment relative to planes of maximum shear-strain-rate in a general shear zone, a significant new insight regarding shear zones and how LPO fabrics may generally develop within them. For the Alpine mylonite zone, our data imply a kinematic vorticity number (Wk) of ˜0.7 to ˜0.85. Inversions of seismic focal mechanisms in the brittle crust of the Southern Alps indicate that σ1 is oriented ˜60° to the Alpine Fault; that shear bands form at ˜30° to this direction, and that σ2 and σ3 flip positions between the brittle and ductile parts of the crust.
Esfandiar, Habib; KoraYem, Moharam Habibnejad [Islamic Azad University, Tehran (Iran, Islamic Republic of)
2015-09-15
In this study, the researchers try to examine nonlinear dynamic analysis and determine Dynamic load carrying capacity (DLCC) in flexible manipulators. Manipulator modeling is based on Timoshenko beam theory (TBT) considering the effects of shear and rotational inertia. To get rid of the risk of shear locking, a new procedure is presented based on mixed finite element formulation. In the method proposed, shear deformation is free from the risk of shear locking and independent of the number of integration points along the element axis. Dynamic modeling of manipulators will be done by taking into account small and large deformation models and using extended Hamilton method. System motion equations are obtained by using nonlinear relationship between displacements-strain and 2nd PiolaKirchoff stress tensor. In addition, a comprehensive formulation will be developed to calculate DLCC of the flexible manipulators during the path determined considering the constraints end effector accuracy, maximum torque in motors and maximum stress in manipulators. Simulation studies are conducted to evaluate the efficiency of the method proposed taking two-link flexible and fixed base manipulators for linear and circular paths into consideration. Experimental results are also provided to validate the theoretical model. The findings represent the efficiency and appropriate performance of the method proposed.
Stress, strain rate and anisotropy in Kyushu, Japan
Savage, M. K.; Aoki, Y.; Unglert, K.; Ohkura, T.; Umakoshi, K.; Shimizu, H.; Iguchi, M.; Tameguri, T.; Ohminato, T.; Mori, J.
2016-04-01
Seismic anisotropy, the directional dependence of wave speeds, may be caused by stress-oriented cracks or by strain-oriented minerals, yet few studies have quantitatively compared anisotropy to stress and strain over large regions. Here we compare crustal stress and strain rates on the Island of Kyushu, Japan, as measured from inversions of focal mechanisms, GPS and shear wave splitting. Over 85,000 shear wave splitting measurements from local and regional earthquakes are obtained from the NIED network between 2004 and 2012, and on Aso, Sakurajima, Kirishima and Unzen volcano networks. Strain rate measurements are made from the Japanese Geonet stations. JMA-determined S arrival times processed with the MFAST shear wave splitting code measure fast polarisations (Φ), related to the orientation of the anisotropic medium and time delays (dt), related to the path length and the percent anisotropy. We apply the TESSA 2-D delay time tomography and spatial averaging code to the highest quality events, which have nearly vertical incidence angles, separating the 3455 shallow (depth = 40 km) earthquakes. Using square grids with 30 km sides for all the inversions, the best correlations are observed between splitting from shallow earthquakes and stress. Axes of maximum horizontal stress (SHmax) and Φ correlate with a coefficient c of 0.56, significant at the 99% confidence level. Their mean difference is 31.9°. Axes of maximum compressional strain rate and SHmax are also well aligned, with an average difference of 28°, but they do not correlate with each other, meaning that where they differ, the difference is not systematic. Anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion (c = - 0.64; significant at the 99% confidence level). The anisotropy and stress results are consistent with stress-aligned microcracks in the crust in a dominantly strike-slip regime. Eigenvalues of maximum horizontal strain rate
Chong, Song Hun
2016-08-09
Geosystems often experience numerous loading cycles. Plastic strain accumulation during repetitive mechanical loads can lead to shear shakedown or continued shear ratcheting; in all cases, volumetric strains diminish as the specimen evolves towards terminal density. Previously suggested models and new functions are identified to fit plastic strain accumulation data. All accumulation models are formulated to capture terminal density (volumetric strain) and either shakedown or ratcheting (shear strain). Repetitive vertical loading tests under zero lateral strain conditions are conducted using three different sands packed at initially low and high densities. Test results show that plastic strain accumulation for all sands and density conditions can be captured in the same dimensionless plot defined in terms of the initial relative density, terminal density, and ratio between the amplitude of the repetitive load and the initial static load. This observation allows us to advance a simple but robust procedure to estimate the maximum one-dimensional settlement that a foundation could experience if subjected to repetitive loads. © 2016, Canadian Science Publishing. All rights reserved.
Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Northwestern U.; Shapiro, Charles; /Chicago U. /KICP, Chicago; White, Martin J.; /UC, Berkeley, Astron.
2005-08-01
Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.
Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Northwestern U.; Shapiro, Charles; /Chicago U. /KICP, Chicago; White, Martin J.; /UC, Berkeley, Astron.
2005-08-01
Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.
Assessment of Deformation of Shear Localized Chip in High Speed Machining
T; C; LEE; W; S; LAU; S; K; CHAN
2002-01-01
As the cutting speed goes higher, the mechanism of chip deformation will be changed significantly, i.e., continuous chip in low cutting speed will shift to serrated chip with shear localization. For the shear localized chip, the parameters used to assess the chip deformation for continuous chip, such as shorten coefficient ξ, shear angle φ and shear strain ε, can not describe the chip deformation correctly or comprehensively. This paper deals with the assessment of chip deformation of shear localization. Th...
Shabbir, Aamir; Huang, Qian; P. Baeza, Guilhem
2017-01-01
(ethylene oxide) (PEO) along the backbone in the coionomer with poly ( tetramethylene glycol) PTMO, increases the maximum Hencky strain at fracture thus adding ductility to the brittle PTMO-Na ionomer. As a result, the coionomer deforms much more compared to PTMO-Na but both fracture eventually...... to formation of strong ionic aggre-gates. These ionomer melts exhibit viscoelastic properties similar to well-entangled melts with an extended rubbery plateau. To evaluate the effects of nonlinear deforma-tion, the rheology of these ionomers was investigated using uniaxial extension and shear. The measurements...
A void coalescence model for combined tension and shear
Butcher, C.; Chen, Z. T.
2009-03-01
The influence of shear loading on damage development in Gurson-based models has long been neglected resulting in inadequate fracture strain predictions at low triaxiality where shear effects become significant. The plastic limit-load fracture criterion used in advanced Gurson models neglects the influence of shear loading and overestimates the fracture strain and porosity at low triaxiality. In this paper, we extend the recently proposed shear damage model of Xue [1] to provide a stronger physical foundation by removing the simplifying assumptions. Then we directly modify the plastic limit-load fracture criterion by coupling with the extended shear damage model to account for shear weakening and failure of the intervoid ligament in void coalescence. We apply the modified plastic limit-load criterion to predict the necking of sheet tensile specimens and find very good agreement with the available experimental results.
Maximum Autocorrelation Factorial Kriging
Nielsen, Allan Aasbjerg; Conradsen, Knut; Pedersen, John L.
2000-01-01
This paper describes maximum autocorrelation factor (MAF) analysis, maximum autocorrelation factorial kriging, and its application to irregularly sampled stream sediment geochemical data from South Greenland. Kriged MAF images are compared with kriged images of varimax rotated factors from...
Atomic structure of amorphous shear bands in boron carbide.
Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W
2013-01-01
Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.
Shear-accelerated crystallization in a supercooled atomic liquid.
Shao, Zhen; Singer, Jonathan P; Liu, Yanhui; Liu, Ze; Li, Huiping; Gopinadhan, Manesh; O'Hern, Corey S; Schroers, Jan; Osuji, Chinedum O
2015-02-01
A bulk metallic glass forming alloy is subjected to shear flow in its supercooled state by compression of a short rod to produce a flat disk. The resulting material exhibits enhanced crystallization kinetics during isothermal annealing as reflected in the decrease of the crystallization time relative to the nondeformed case. The transition from quiescent to shear-accelerated crystallization is linked to strain accumulated during shear flow above a critical shear rate γ̇(c)≈0.3 s(-1) which corresponds to Péclet number, Pe∼O(1). The observation of shear-accelerated crystallization in an atomic system at modest shear rates is uncommon. It is made possible here by the substantial viscosity of the supercooled liquid which increases strongly with temperature in the approach to the glass transition. We may therefore anticipate the encounter of nontrivial shear-related effects during thermoplastic deformation of similar systems.
Shear crack propagation in MBC strengthened concrete beams”
Täljsten, Björn; Blanksvärd, Thomas; Carolin, Anders
2008-01-01
study of MBC systems. Emphasis is placed on the cracking behavior of the MBC system used for shear strengthening of RC beams. Traditional foil strain gauges and photometric measurements have been used for monitoring of the cracking behavior. In this study it is shown that the use of mineral based shear...
Three-dimensional finite element analysis of critical pre-twist strain angle for torsional axis
ZHOU Guo-feng; LI Xiao-yan; SHI Yao-wu; XU Bin-shi
2005-01-01
A three-dimensional elasto-plastic finite element analysis of pre-twist process for a torsional axis made of 45GrNiMoVA steel, was carried out using a commercial finite element analysis code, MSC MARC 2001. The results show that the critical pre-twist strain angle is 0. 027 rad and the maximum elastic shear stress after pre-twist is 1 694 MPa for the torsional axis.
Rock avalanche deposits store quantitative evidence on internal shear during runout
Zhang, M.; McSaveney, M. J.
2017-09-01
We investigated the quantitative effect of internal shear on grain breakage during rock avalanche runout, by means of 38 ring-shear experiments on identical sand samples at different normal stresses, shear strains and shear strain rates. We compared sample grain-size characteristics before and after shearing. We found that grain size decreased with increase in normal stress and shear strain. Reduction in grain size was inferred to occur through grain breakage associated with grain interactions in strong force chains during strain. The results were consistent with observations of both inverse-grading structure in deep rock avalanche exposures, and fining and grading of particles with increasing rock avalanche travel distance. Our study suggested that with appropriate calibration, variations in grain-size distributions within a rock avalanche deposit would provide quantitative information on the distribution of internal shear during its runout.
System size dependence of the structure and rheology in a sheared lamellar liquid crystalline medium
Jaju, S. J.; Kumaran, V.
2016-12-01
The structural and rheological evolution of an initially disordered lamellar phase system under a shear flow is examined using a mesoscale model based on a free energy functional for the concentration field, which is the scaled difference in the concentration between the hydrophilic and hydrophobic components. The dimensionless numbers which affect the shear evolution are the Reynolds number (γ ˙ ¯ L2 /ν ) , the Schmidt number (ν /D ) , a dimensionless parameter Σ =(A λ2 /ρ ν2 ) , a parameter μr which represents the viscosity contrast between the hydrophilic and hydrophobic components, and (L /λ ) , the ratio of system size and layer spacing. Here, ρ, ν, and D are the density, kinematic viscosity (ratio of viscosity and density), and the mass diffusivity, and A is the energy density in the free energy functional which is proportional to the compression modulus. Two distinct modes of structural evolution are observed for moderate values of the parameter Σ depending only on the combination ScΣ and independent of system size. For ScΣ less than about 10, the layers tend to form before they are deformed by the mean shear, and layered but misaligned domains are initially formed, and these are deformed and rotated by the flow. In this case, the excess viscosity (difference between the viscosity and that for an aligned state) does not decrease to zero even after 1000 strain units, but appears to plateau to a steady state value. For ScΣ greater than about 10, layers are deformed by the mean shear before they are fully formed, and a well aligned lamellar phase with edge dislocation orders completely due to the cancellation of dislocations. The excess viscosity scales as t-1 in the long time limit. The maximum macroscopic viscosity (ratio of total stress and average strain rate over the entire sample) during the alignment process increases with the system size proportional to (L/λ ) 3 /2. For large values of Σ, there is localisation of shear at the walls
Michels, M.H.A.; Goot, van der A.J.; Vermuë, M.H.; Wijffels, R.H.
2016-01-01
The tolerance to shear stress of Tetraselmis suecica, Isochrysis galbana, Skeletonema costatum, and Chaetoceros muelleri was determined in shear cylinders. The shear tolerance of the microalgae species strongly depends on the strain. I. galbana, S. costatum, and C. muelleri exposed to shear stress b
Measurement and modeling of bed shear stress under solitary waves
Jayakumar, S.; Guard, P.A.; Baldock, T.E.
convolution integration methods forced with the free stream velocity and incorporating a range of eddy viscosity models. Wave friction factors were estimated from skin shear stress at different instances over the wave (viz., time of maximum positive total...
无
2000-01-01
The main problem,in determining the shear displacement of a general shear zone with volume change using the available formula,is that it is hard to know the initial angle between the planes (or lines) in the plane of shear.A planar deformation analysis of this kind of ductile shear zone is carried out with the polar Mohr diagram.If the volume change is induced by homogeneous contraction in the Z direction of the shear zone,there are sufficient conditions for constructing a polar Mohr diagram regardless of sequence of the simple shear and volume change.Therefore,the angle between a line and the shear direction before and after the deformation can be measured.Making use of these lines the shear strain and the volume change can be calculated and the shear displacement can be determined.
李海; 郭召杰; 刘瑞洵; 刘树文; 张志诚
2000-01-01
The main problem, in determining the shear displacement of a general shear zone with volume change using the available formula, is that it is hard to know the initial angle between the planes (or lines) in the plane of shear. A planar deformation analysis of this kind of ductile shear zone is carried out with the polar Mohr diagram. If the volume change is induced by homogeneous contraction in the Z direction of the shear zone, there are sufficient conditions for constructing a polar Mohr diagram regardless of sequence of the simple shear and volume change. Therefore, the angle between a line and the shear direction before and after the deformation can be measured. Making use of these lines the shear strain and the volume change can be calculated and the shear displacement can be determined.
Shearing stability of lubricants
Shiba, Y.; Gijyutsu, G.
1984-01-01
Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.
Shearing stability of lubricants
Shiba, Y.; Gijyutsu, G.
1984-03-01
Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.
The effect of shearing rate and slope angle on the simple shear response of marine clays
Biscontin, G.; Rutherford, C.
2010-12-01
The response of submarine slopes to seismic or storm loading has become an important element in the risk assessment for offshore structures and local tsunami hazard. Evaluation of submarine slope stability requires characterization of soil behavior and relies on the selection of appropriate parameter values. Although the traditional simple shear device has been used to investigate cyclic loading effects on marine clay, it does not allow for complex loading conditions which often contribute to the failure on submarine slopes. Understanding the interaction between the initial shear stress, the slope angle, and the multi-directional shaking due to earthquakes or storm loading is an important aspect to understanding the failure mechanisms of submarine slope failures. The initial static driving force on the slope is combined with the dynamic loading by storms and earthquakes to create complex loading paths. Therefore, the ability to apply complex stress or strain paths is important to fully study the shear response of marine clays on submarine slopes. A new multi-directional simple shear device developed at Texas A&M University allows loading along three independent axes, two perpendicular horizontal directions to allow any stress or strain paths in the horizontal plane, and a third in the vertical direction. This device is used to investigate the response of Gulf of Mexico marine deposits to different loading conditions. To study the effect of slope angle on the shear response of the soil, samples are subjected to a shear stress during consolidation, Kα consolidation. One-dimensional monotonic and cyclic shearing of Ko consolidated specimens is used to simulate level ground conditions, whereas sloping surfaces were simulated using Kα consolidation for both monotonic and cyclic tests. The effects of shearing rate on the soil response are investigated using strain controlled tests at varying frequencies.
Compression Enhanced Shear Yield Stress of Electrorheological Fluid
ZHANG Min-Liang; TIAN Yu; JIANG Ji-Le; ZHU Xu-Li; MENG Yong-Gang; WEN Shi-Zhu
2009-01-01
@@ Shear tests of an electrorheological fluid with pre-applied electric field and compression along the field direction are carried out. The results show that pre-compressions can increase the shear yield stress up to ten times. Under the same external electric field strength, a higher compressive strain corresponds to a larger shear yield stress enhancement but with slight current density decrease, which shows that the particle interaction potentials are not increased by compressions but the compression-induced chain aggregation dominates the shear yield stress improvement. This pre-compression technique might be useful [or developing high performance flexible ER or magnetorheological couplings.
Shear resistance properties of TPS modified bitumen binders and asphalt mixtures
曹庭维; 吴少鹏; 刘聪慧; 张涛
2008-01-01
Shear resistance properties of the virgin bitumen and modified bitumen binders with Tafpack Super(TPS) modifier and SBS modified bitumen were discussed.Dynamic shear rheometer(DSR) was used to measure the laboratory creep data for these binders over a wide range of constant shear stresses at 20 ℃ to characterize the shear creep behaviors of all kinds of asphalt binders,and the rutting test system was used to investigate the permanent deformation of porous asphalt mixtures using the above bitumen binders for a fixed compressive stress.The shear strain rate and shear creep modulus were used to characterize the shear creep behavior of the TPS modified bitumen,and the rutting test results were used to show the consistency of porous asphalt mixtures with the bitumen binders.Results indicate that a distinction of shear creep strain can be made among different contents of TPS modified bitumen at the same stress level,where the shear creep strain-time response curve of the SBS modified bitumen binder is between the curves of the 8% TPS and 12% TPS modified bitumen binders.The shear strain rate and the shear creep modulus of the TPS modified bitumen binders are obtained to compare with those of the SBS modified bitumen binder which results in the same trend as the shear creep strain-time response curve.Permanent deformation results of all the porous asphalt mixtures from the rutting test show reasonable agreement with the findings of the shear strain rates and shear creep modulus over the range of shear stress levels.
Domino boudinage under layer-parallel simple shear
Dabrowski, Marcin; Grasemann, Bernhard
2014-11-01
The boudin segments of a torn competent layer experience synthetic rotation in layer-parallel simple shear. As long as the individual segments in a boudin train are constrained by their neighbors, even a highly viscous boudin deforms internally to create the necessary space for rotation. The rotation rate is then much smaller compared to the case of an isolated segment. Hence, a small tilt of boudin segments is not indicative of low strain. The rotation rate at this stage largely depends on the aspect ratio of the boudin segments and the scaled gap width. Once the tilted boudins are no longer constrained by their neighbors, the rotation rate greatly accelerates. In the case of a low viscosity ratio between the boudins and the host, the boudin segments develop complex shapes, which may give an impression of shear-band boudins forming under the opposite shear sense. We furthermore investigate the behavior of boudin trains of finite length. The terminal segments are displaced out of the shear plane, deforming into isoclinal folds, and separate into groups of boudin segments that rotate into the shear direction and eventually lead to an overall chaotic appearance of the structure. Natural examples of domino boudinage from a high shear -strain detachment zone in the Western Cyclades (Greece) show many similarities with the modeled structures suggesting that, under simple shear deformation, the rotation and separation of boudin segments is an indicator for high shear strain.
Comment on shear-rotation mechanism for martensitic transformations
CHEN Zi; GUO Zhenghong
2004-01-01
The "shear-rotation mechanism" for f.c.c.→b.c.c.(b.c.t.) martensitic transformation is further discussed in this paper. Although "shear-rotation mechanism" involves some valuable ideas which is based on the Nishiyama's model, the concept of "rotation" in "shear-rotation mechanism" may not be consistent with the general definition in crystallography. In addition, the mathematical expression of this mechanism is questionable. Furthermore, a detailed mathematical analysis given in the present paper indicates that the nature of "shear-rotation mechanism" is equivalent to the first two steps of Nishiyama's model, I.e. It is an invariant line strain (ILS) rather than an invariant plane strain (IPS). In other words, it is difficult to obtain the IPS based on the "shear-rotation mechanism" even though the isotropic contraction is involved. Therefore, a new method should be developed to explain the IPS based on Nishiyama's model.
Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)
Paegle, Ieva; Fischer, Gregor
2012-01-01
and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...
Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)
Paegle, Ieva; Fischer, Gregor
2011-01-01
and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...
Crystallography of shear transformations in zirconium hydrides
Cassidy, Michael Philip [Univ. of Illinois, Urbana-Champaign, IL (United States)
1978-01-01
The crystallography and substructure of the transformations which have been hypothesized as involving a martensitic shear, and which occur between zirconium hydrides were investigated. Specifically, the formation of gamma zirconium hydride from delta hydride and the delta hydride to epsilon hydride transformation were studied. The habit planes, orientation relationships, lattice invariant shears, and interface structures were determined by transmission electron microscopy and diffraction. Surface tilts were observed and measured with an interference microscope. The direction and magnitude of the shape strain produced by the formation of gamma were determined by the measurement of fiducial scratch displacements. These results were compared with the phenomenological crystallographic theory of martensitic transformations.
Enhancing Rotational Diffusion Using Oscillatory Shear
Leahy, Brian D.
2013-05-29
Taylor dispersion - shear-induced enhancement of translational diffusion - is an important phenomenon with applications ranging from pharmacology to geology. Through experiments and simulations, we show that rotational diffusion is also enhanced for anisotropic particles in oscillatory shear. This enhancement arises from variations in the particle\\'s rotation (Jeffery orbit) and depends on the strain amplitude, rate, and particle aspect ratio in a manner that is distinct from the translational diffusion. This separate tunability of translational and rotational diffusion opens the door to new techniques for controlling positions and orientations of suspended anisotropic colloids. © 2013 American Physical Society.
Enhancing Rotational Diffusion Using Oscillatory Shear
Leahy, Brian D.; Cheng, Xiang; Ong, Desmond C.; Liddell-Watson, Chekesha; Cohen, Itai
2013-05-01
Taylor dispersion—shear-induced enhancement of translational diffusion—is an important phenomenon with applications ranging from pharmacology to geology. Through experiments and simulations, we show that rotational diffusion is also enhanced for anisotropic particles in oscillatory shear. This enhancement arises from variations in the particle’s rotation (Jeffery orbit) and depends on the strain amplitude, rate, and particle aspect ratio in a manner that is distinct from the translational diffusion. This separate tunability of translational and rotational diffusion opens the door to new techniques for controlling positions and orientations of suspended anisotropic colloids.
Constant load and constant volume response of municipal solid waste in simple shear.
Zekkos, Dimitrios; Fei, Xunchang
2017-05-01
Constant load and constant volume simple shear testing was conducted on relatively fresh municipal solid waste (MSW) from two landfills in the United States, one in Michigan and a second in Texas, at respective natural moisture content below field capacity. The results were assessed in terms of two failure strain criteria, at 10% and 30% shear strain, and two interpretations of effective friction angle. Overall, friction angle obtained assuming that the failure plane is horizontal and at 10% shear strain resulted in a conservative estimation of shear strength of MSW. Comparisons between constant volume and constant load simple shear testing results indicated significant differences in the shear response of MSW with the shear resistance in constant volume being lower than the shear resistance in constant load. The majority of specimens were nearly uncompacted during specimen preparation to reproduce the state of MSW in bioreactor landfills or in uncontrolled waste dumps. The specimens had identical percentage of waste. The results of these tests suggest the possibility of significantly lower shear strength of MSW in bioreactor landfills where waste is placed with low compaction effort and constant volume, i.e., "undrained", conditions may occur. Compacted MSW specimens resulted in shear strength parameters that are higher than uncompacted specimens and closer to values reported in the literature. However, the normalized undrained shear strength in simple shear for uncompacted and compacted MSW was still higher than the normalized undrained shear strength reported in the literature for clayey and silty soils. Copyright © 2016 Elsevier Ltd. All rights reserved.
The Maximum Effective Moment Criterion (MEMC) and Its Implications in Structural Geology
无
2006-01-01
The Mohr-Coulomb criterion has been widely used to explain formation of fractures.However, it fails to explain large strain deformation that widely occurs in nature. There is presently a σ1-σ3 represents the yield strength of the related rock, L is a unit length and α is the angle between σ1and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to σ1 and there is a slight difference in the moment in the range of 55°±10°. The range covers the whole observations available from nature and experiments. Its major implications include: (1) it can be used to determine the stress state when the related deformation features formed; (2) it provides a new approach to determine the Wk of the related ductile shear zone if only the ratio of the vorticity and strain rate remains fixed; (3) It can be used to explain (a) the obtuse angle in the contraction direction of conjugate kink-bands and extensional crenulation cleavages, (b) formation of low-angle normal faults and high-angle reverse faults, (c) lozenge ductile shear zones in basement terranes, (d) some crocodile structures in seismic profiles and (e) detachment folds in foreland basins.
Engineering piezoresistivity using biaxially strained silicon
Pedersen, Jesper Goor; Richter, Jacob; Brandbyge, Mads;
2008-01-01
We calculate the shear piezocoefficient of p-type silicon with grown-in biaxial strain using a 66 k·p method. We find a significant increase in the value of the shear piezocoefficient for compressive grown-in biaxial strain, while tensile strain decreases the piezocoefficient. The dependence...... of the piezocoefficient on temperature and dopant density is altered qualitatively for strained silicon. In particular, we find that a vanishing temperature coefficient may result for silicon with grown-in biaxial tensile strain. These results suggest that strained silicon may be used to engineer the iezoresistivity...
Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands
1980-05-01
Thompson, Met. Trans., 2, 1970, p. 219. 1 0F. P. Bowden and P. H. Thomas, "The Sur’faoe Temrperature of SUding SoZida," P-oc. Roy. Soo., Ser. A, VoZ ...transformations that occur in steel at temperatures near Tcr are listed in Table II. 12M.taZ. Handbook., Ninth Edition, VoZ . 1, Ed. Bngae P. Bardas, Amorioan
MENG Guo-jie; REN Jin-wei; WU Ji-cang; SHEN Xu-hui
2008-01-01
Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of the formulae, we also derive expressions of strain components and Euler vector uncertainties respectively for subnets using the law of error propagation. Taking GPS velocity field in Sichuan-Yunnan area as an example, we compute dilation rate and maximum shear strain rate field using the above procedure, and their characteristics are preliminarily carried on. Limits of the strain model for small array are also discussed. We make detailed explanations on small array method and the choice of small arrays. How to set weights of GPS observations are further discussed. Moreover relationship between strain and radius of GPS subnets is also analyzed.
Alix-Williams, Darius; Falk, Michael L.
2015-03-01
We examine the general framework of the effective temperature formalism of the shear transformation zone (STZ) theory of plasticity via molecular dynamics simulation of two distinct amorphous systems - Silicon and Cu-Zr. In both systems strain localization is observed during simple shear loading. The shear bands differ in the rate of broadening and the sharpness of the interface between the flowing and jammed material. We examine both systems for scaling expected to arise between effective temperature and shear rate. For each system a local dimensionless effective temperature that quantifies structural disorder is extracted by assuming a linear relation to the local potential energy per atom. Research possible through support from National Science Foundation Grant No. 0801471.
Antony, S. J.; Kruyt, N. P.
2009-03-01
The interlink between particle-scale properties and macroscopic behavior of three-dimensional granular media subjected to mechanical loading is studied intensively by scientists and engineers, but not yet well understood. Here we study the role of key particle-scale properties, such as interparticle friction and particle elastic modulus, in the functioning of dual contact force networks, viz., strong and weak contacts, in mobilizing shear strength in dense granular media subjected to quasistatic shearing. The study is based on three-dimensional discrete element method in which particle-scale constitutive relations are based on well-established nonlinear theories of contact mechanics. The underlying distinctive contributions of these force networks to the macroscopic stress tensor of sheared granular media are examined here in detail to find out how particle-scale friction and particle-scale elasticity (or particle-scale stiffness) affect the mechanism of mobilization of macroscopic shear strength and other related properties. We reveal that interparticle friction mobilizes shear strength through bimodal contribution, i.e., through both major and minor principal stresses. However, against expectation, the contribution of particle-scale elasticity is mostly unimodal, i.e., through the minor principal stress component, but hardly by the major principal stress. The packing fraction and the geometric stability of the assemblies (expressed by the mechanical coordination number) increase for decrease in interparticle friction and elasticity of particles. Although peak shear strength increases with interparticle friction, the deviator strain level at which granular systems attain peak shear strength is mostly independent of interparticle friction. Granular assemblies attain peak shear strength (and maximum fabric anisotropy of strong contacts) when a critical value of the mechanical coordination number is attained. Irrespective of the interparticle friction and elasticity
FE Analysis on Shear Deformation for Asymmetrically Hot-Rolled High-Manganese Steel Strip
Sui, Feng-Li; Wang, Xin; Li, Chang-Sheng; Zhao, Jun
2016-09-01
Shear deformation along the longitudinal cross section of the high-manganese steel strip has been analyzed in hot asymmetrical rolling process using rigid-plastic finite element model. The friction coefficient between the rolls and the strip surfaces, the diameter of the work rolls, the speed ratio for the lower/upper rolls, the reduction rate and the initial temperature of the billet were all taken into account. Influence of these process parameters on the shear stress, the shear strain and the related shear strain energy in the center layer of the hot-rolled strip was analyzed. It is indicated that increasing the speed ratio, the reduction rate and the work roll diameter is an effective way to accumulate more shear strain energy in the strip center. A mathematical model reflecting the relationship between the shear strain energy and the process parameters has been established.
Negative pressure in shear thickening band of a dilatant fluid
Nagahiro, Shin-ichiro
2015-01-01
We perform experiments and numerical simulations to investigate spatial distribution of pressure in a sheared dilatant fluid of the Taylor-Couette flow under a constant external shear stress. In a certain range of shear stress, the flow undergoes the shear thickening oscillation around 20 Hz. The pressure measurement during the oscillation at the wall of the outer cylinder indicates that a localized negative pressure region rotates around the axis with the flow. The maximum negative pressure is close to the Laplace pressure of the grain radius and nearly independent of the applied shear stress. Simulations of a phenomenological model reveal that the thickened region is dominated by a negative pressure band, which extends along the tensile direction in the flow. Such shear thickening with negative pressure contradicts a naive picture of jamming mechanism, where thickening is expected in the compressing direction with the positive pressure.
Geometric aspects of shear jamming induced by deformation of frictionless sphere packings
Vinutha, H. A.; Sastry, Srikanth
2016-09-01
It has recently been demonstrated that shear deformation of frictionless sphere packings leads to structures that will undergo jamming in the presence of friction, at densities well below the isotropic jamming point {φj}≈ 0.64 , and at high enough strains. Here, we show that the geometric features induced by strain are robust with respect to finite size effects, and include the feature of hyperuniformity, previously studied in the context of jamming, and more recently in driven systems. We study the approach to jamming as strain is increased, by evolving frictionless sheared configurations through frictional dynamics, and thereby identify a critical, or jamming, strain for each density, for a chosen value of the coefficient of friction. In the presence of friction above a certain strain value the sheared frictionless packings begin to develop finite stresses, which marks the onset of shear jamming. At a higher strain value, the shear stress reaches a saturation value after rising rapidly above the onset of shear jamming, which permits identification of the shear jamming transition. The onset of shear jamming and shear jamming are found to occur when the coordination number Z reaches values of Z = 3 and Z = 4 respectively. By considering percolation probabilities for the contact network, clusters of four coordinated and six coordinated spheres, we show that the percolation of four coordinated spheres corresponds to the onset of shear jamming behaviour, whereas the percolation of six coordinated spheres corresponds to shear jamming, for the chosen friction coefficients. At the onset of shear jamming, the force distribution begins to develop a peak at finite value and the force network is anisotropic and heterogeneous. And at the shear jamming transition, the force distribution has a well defined peak close to and the force network is less anisotropic and homogeneous. We briefly discuss mechanical aspects of the jamming behaviour by performing
Akhras, G.; Cheung, M. S.; Li, W.
1994-08-01
In the present study, a finite strip method for the elastic analysis of anisotropic laminated composite plates is developed according to higher-order shear deformation theory. This theory accounts for the parabolic distribution of the transverse shear strains through the thickness of the plate and for zero transverse shear stresses on the plate surfaces. In comparison with the finite strip method based on first-order shear deformation theory, the present method gives improved results while using approximately the same number of degrees of freedom. It also eliminates the need for shear correction factors in calculating the transverse shear stiffness.
Maximum Autocorrelation Factorial Kriging
Nielsen, Allan Aasbjerg; Conradsen, Knut; Pedersen, John L.; Steenfelt, Agnete
2000-01-01
This paper describes maximum autocorrelation factor (MAF) analysis, maximum autocorrelation factorial kriging, and its application to irregularly sampled stream sediment geochemical data from South Greenland. Kriged MAF images are compared with kriged images of varimax rotated factors from an ordinary non-spatial factor analysis, and they are interpreted in a geological context. It is demonstrated that MAF analysis contrary to ordinary non-spatial factor analysis gives an objective discrimina...
Structural Evidence for Fluid-Assisted Shear Failure within a Ductile Shear Zone
Compton, K.; Kirkpatrick, J. D.
2014-12-01
Recent observations of seismic slip occurring below the seismogenic zone of large fault zones have emphasized the significance of coeval ductile and brittle processes at high temperatures. We present observations of a shear zone contained within the Saddlebag Lake pendant of the eastern Sierra Nevada, CA, where Triassic and Jurassic metavolcanics and metasediments are highly strained in a high-temperature shear zone. Transposed bedding and cleavage that define a flattening fabric, dextrally rotated porphyroclasts, and a steep, pervasive lineation together suggest an overall transpressive kinematic regime for the ductile deformation. The high-strain rocks exhibit multiple episodes of vein formation, indicating a prolonged migration of hydrothermal fluids throughout the system. Crosscutting relationships and mineral assemblages define discrete sets of differently oriented veins. The veins form by fracture, but many veins are folded and boudinaged, showing synkinematic brittle and ductile deformation. We document foliation-parallel quartz veins that show shear displacement from the geometry of pull-apart structures and offsets of earlier veins. Synkinematic equilibrium mineral assemblages within the host rock and dynamic recrystallization of the quartz veins show they formed at temperatures around 400 to 500°C. The shear fractures have horizontal trace lengths of up to a few meters and displacements range from 2-3 mm to ~3 cm, with 1-5 mm of opening. Assuming the observed offset in the fractures occurred in a single event, these measurements are consistent with stress drops of 1 to 10 MPa. We interpret these observations to show that the veins formed as a result of high pore fluid pressure that caused shear failure at low effective stresses. Because foliated rocks are mechanically anisotropic, the foliation provided planes of weakness for failure with a preferred orientation. Evidence for shear failure occurring within crystal-plastic shear zones at high temperatures
Arnal, Bastien; Pernot, Mathieu; Tanter, Mickael
2011-08-01
The clinical applicability of high-intensity focused ultrasound (HIFU) for noninvasive therapy is currently hampered by the lack of robust and real-time monitoring of tissue damage during treatment. The goal of this study is to show that the estimation of local tissue elasticity from shear wave imaging (SWI) can lead to a precise mapping of the lesion. HIFU treatment and monitoring were respectively performed using a confocal setup consisting of a 2.5-MHz single element transducer focused at 34 mm on ex vivo samples and an 8-MHz ultrasound diagnostic probe. Ultrasound-based strain imaging was combined with shear wave imaging on the same device. The SWI sequences consisted of 2 successive shear waves induced at different lateral positions. Each wave was created with pushing beams of 100 μs at 3 depths. The shear wave propagation was acquired at 17,000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions, allowing a duty cycle of more than 90%. Thus, elasticity and strain mapping was achieved every 3 s, leading to real-time monitoring of the treatment. When thermal damage occurs, tissue stiffness was found to increase up to 4-fold and strain imaging showed strong shrinkages that blur the temperature information. We show that strain imaging elastograms are not easy to interpret for accurate lesion characterization, but SWI provides a quantitative mapping of the thermal lesion. Moreover, the concept of shear wave thermometry (SWT) developed in the companion paper allows mapping temperature with the same method. Combined SWT and shear wave imaging can map the lesion stiffening and temperature outside the lesion, which could be used to predict the eventual lesion growth by thermal dose calculation. Finally, SWI is shown to be robust to motion and reliable in vivo on sheep muscle.
Bay, Niels; Bjerregaard, Henrik; Petersen, Søren. B;
1994-01-01
The present paper describes an investigation of roll bonding an AlZn alloy to mild steel. Application of cross shear roll bonding, where the two equal sized rolls run with different peripheral speed, is shown to give better bond strength than conventional roll bonding. Improvements of up to 20......-23% in bond strength are found and full bond strength is obtained at a reduction of 50% whereas 65% is required in case of conventional roll bonding. Pseudo cross shear roll bonding, where the cross shear effect is obtained by running two equal sized rolls with different speed, gives the same results....
Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ
2009-07-14
One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.
Evidence for Triassic sinistral shear along the Altyn Tagh fault, northern Tibet (China)
Li, H.; Yang, J.; Wu, C.; Xu, Z.; Tapponnier, P.; Arnaud, N.
2005-12-01
The strike-slip faults of north Tibet accommodate part of the Cenozoic convergence between India and Asia. Along the Xorkol basin west-north of Qaidam, the active traces of the Altyn Tagh fault follow narrow belts of granitic and amphibolitic mylonites. The deformation recorded in those mylonites is sinistral strike-slip. Three types of zircon may be sorted out from the mylonites: anatectic (magmatic), long columnar zircons, magmatic columnar zircons, and residual, metamorphic, sub-rounded zircon. Three groups of U-Pb ages measured by ion microprobe (SHRIMP) on single zircon were obtained: 530-550Ma for the columnar, magmatic zircon, 460-510Ma for the sub-rounded, residual metamorphic zircon, and 235-245Ma for the long-columnar anatectic (magmatic) zircon. The latter type of zircon is well oriented with the crystal long axis parallel to the stretching lineation. Mineral inclusions in the oriented zircons are also parallel to the stretching lineation, which coincides with the direction of maximum tectonic stress in the process of the strike-slip. Raman spectrum study indicates that the inclusion minerals show the melting phase feature, and cathodoluminescence images show that this type of zircon has a relatively homogeneous internal structure. Therefore, the long columnar zircons resulted from rapid oriented growth in a partial melting regime in the ductile shear process. It not only denotes the direction of shear strain in the strike-slip shear, but the growth age (crystallization age) of this type of zircon denotes the age of strike-slip shear. 40Ar/39Ar ages of directionaly grown hornblendes and biotite in the same samples are 220-230Ma and 190-200Ma, respectively. This suggest syntectonic anatexis and cooling occurred during strike-slip shear along the Altyn Tagh fault in Triassic time (to Early Jurassic). The Triassic shear may be related to oblique collision between the Bayan Har and the Kunlun- Qaidam blocks. 120Ma (Arnaud, et al., 2003) and 90Ma (Liu, et al
Meng, Fanzhen; Zhou, Hui; Wang, Zaiquan; Zhang, Liming; Kong, Liang; Li, Shaojun; Zhang, Chuanqing
2017-08-01
Filled joints, which are characterized by high deformability and low shear strength, are among the most critical discontinuities in rock mass and may be sheared repeatedly when subject to cyclic loading. Shear tests were carried out on tension splitting joints, with soil and granular cement mortar particles used as infillings, and the effects of the shear history on the mechanical behavior and acoustic emission (AE) of clean and filled joints were studied. The maximum strength in the subsequent shears was approximately 60% of the peak strength of the first shear for a clean joint, and the friction angle degraded from 63° to 45° after the first shear. The maximum shear strength of the filled joints was lower than 35% of the peak strength of the clean joint under the same normal stress. The change in the shear strength of filled joints with the number of shearing cycles was closely related to the transformation of the shear medium. Rolling friction occurred and the shear strength was low for the granular particle-filled joint, but the strength was elevated when the particles were crushed and sliding friction occurred. The AEs were significantly reduced during the second shear for the clean joint, and the peak AEs were mainly obtained at or near the turning point of the shear stress curve for the filled joint. The AEs were the highest for the cement particle-filled joint and lowest for the dry soil-filled joint; when subjected to repeated shears, the AEs were more complex because of the continuous changes to the shear medium. The evolution of the AEs with the shear displacement can accurately reflect the shear failure mechanism during a single shear process.
WANG Xue-bin
2004-01-01
The paper was numerically focused on investigation of deformation, failure and instability of shear band-surrounding elastic rock system in plane strain direct shear test considering shear dilatancy according to fast lagrangian analysis of continua (FLAC). The adopted failure criterion was a composite Mohr-Coulomb criterion with tension cut-off and post-peak constitutive relation of rock, i.e. linear strain-softening. Numerical results show that dilation angle affects the responses of elements, the number and the position of yielded elements. Increasing dilation angle results in higher load-carrying capability of elements, higher deformation or strain corresponding to peak stress, less brittle post-peak stress-deformation curve. Strain-hardening behavior can occur if dilation angle is high.Therefore, shear band-elastic rock body system tends to be stable and rock burst does not occur as dilation angle is increased. Moreover, the number of yielded elements is increased with dilation angle increase and two parallel plastic zones initially generated in the middle of two loading ends of specimen no longer remain collinear, reflecting increase in deformation resistant of the system. Evolution of volumetric strain rate was investigated based on three-dimensional curved surface diagrams. Approximately, volumetric strain rate concentration regions coincide with plastic zones. Volumetric strain rate in yielded elements is very evident. However, in elastic zones volumetric strain has not been nearly changed throughout the numerical tests.
Current horizontal strain field in Chinese mainland derived from GPS data
杨国华; 李延兴; 韩月萍; 胡新康; 巩曰沐
2002-01-01
The current crustal horizontal strain field is given in the paper based on the horizontal movement rates obtained from about 400 GPS stations located in Chinese mainland and its surrounding areas. The results show: a) The horizontal strain in Chinese mainland is "strong in the west and weak in the east" and the shear strain is larger than the normal strain (absolute magnitude). The general strain magnitude is 10-8/a and in local regions is 10-7/a, but the strain distribution is not homogeneous; b) The regions with the most significant NS-trending strains are the Himalayas belt along the western segment of Chinese southern boundary, the segment of 36°N～42°N along the western boundary and the northern margin of Qaidam block; c) The EW-trending strain variation along the western margin is the maximum and it is characterized by the alternatively positive and negative variations from the west to the east; d) The regions with larger magnitudes of REN (NE-trending shear strain) and Rmax (maximum shear strain) are Himalayas belt, the segment of 36°N～42°N along the western boundary, the western part of Qaidam block, Sichuan-Yunnan (Chuan-Dian) rhombic block and the border area of Alxa, Qilian and Tarim blocks; e) The surrounding area of Qinghai-Xizang (Qingzang) block is mainly superfacial contraction and its interior is basically superfacial expansion. The area to its north is mainly superfacial contraction with the maximum magnitude along the western boundary and the minimum magnitude in the eastern part (except Yanshan tectonic zone); f) In the west of the western part, the principal compressive strain is in the SN direction and the principal tensile strain is in the EW direction, while in the eastern margin area of the western part, the principal compressive strain is proximate EW and the principal tensile strain is about SN. The principal strain direction of Chuan-Dian rhombic block has changed greatly. In the northern part, it is compression in the EW and
Maximum-biomass prediction of homofermentative Lactobacillus.
Cui, Shumao; Zhao, Jianxin; Liu, Xiaoming; Chen, Yong Q; Zhang, Hao; Chen, Wei
2016-07-01
Fed-batch and pH-controlled cultures have been widely used for industrial production of probiotics. The aim of this study was to systematically investigate the relationship between the maximum biomass of different homofermentative Lactobacillus and lactate accumulation, and to develop a prediction equation for the maximum biomass concentration in such cultures. The accumulation of the end products and the depletion of nutrients by various strains were evaluated. In addition, the minimum inhibitory concentrations (MICs) of acid anions for various strains at pH 7.0 were examined. The lactate concentration at the point of complete inhibition was not significantly different from the MIC of lactate for all of the strains, although the inhibition mechanism of lactate and acetate on Lactobacillus rhamnosus was different from the other strains which were inhibited by the osmotic pressure caused by acid anions at pH 7.0. When the lactate concentration accumulated to the MIC, the strains stopped growing. The maximum biomass was closely related to the biomass yield per unit of lactate produced (YX/P) and the MIC (C) of lactate for different homofermentative Lactobacillus. Based on the experimental data obtained using different homofermentative Lactobacillus, a prediction equation was established as follows: Xmax - X0 = (0.59 ± 0.02)·YX/P·C.
DYNAMIC EFFECTIVE SHEAR STRENGTH OF SATURATED SAND
邵生俊; 谢定义
2002-01-01
The dynamic effective shear strength of saturated sand under cyclic loading is discussed in this paper. The discussion includes the transient time dependency behaviors based on the analysis of the results obtained in conventional cyclic triaxial tests and cyclic torsional shear triaxial tests. It has been found that the dynamic effective shear strength is composed of effective frictional resistance and viscous resistance, which are characterized by the strain rate dependent feature of strength magnitude, the coupling of consolidation stress with cyclic stress and the dependency of time needed to make the soil strength suffciently mobilized, and can also be expressed by the extended Mohr-Coulomb's law. The two strength parameters of the dynamic effective internal frictional angle φd and the dynamic viscosity coefficient η are determined. The former is unvaried for different number of cyclic loading, dynamic stress form and consolidation stress ratio. And the later is unvaried for the different dynamic shear strain rate γt developed during the sand liquefaction, but increases with the increase of initial density of sand. The generalization of dynamic effective stress strength criterion in the 3-dimensional effective stress space is studied in detail for the purpose of its practical use.
Magnetohydrodynamic Shearing Waves
Johnson, B M
2006-01-01
I consider the nonaxisymmetric linear theory of an isothermal magnetohydrodynamic (MHD) shear flow. The analysis is performed in the shearing box, a local model appropriate for a thin disk geometry. Linear perturbations in this model can be decomposed in terms of shearing waves (shwaves), which appear spatially as plane waves in a frame comoving with the shear. The time dependence of these waves cannot in general be expressed in terms of a frequency eigenvalue as in a normal mode decomposition, and numerical integration of a set of first-order amplitude equations is required for a complete characterization of their behavior. Their generic time dependence, however, is oscillatory with slowly-varying frequency and amplitude, and one can construct accurate analytic solutions by applying the Wentzel-Kramers-Brillouin method to the full set of amplitude equations. For the bulk of wavenumber space, therefore, the shwaves are well-approximated as modes with time-dependent frequencies and amplitudes. The incompressiv...
Laboratory Investigation on Shear Behavior of Rock Joints and a New Peak Shear Strength Criterion
Zhang, Xiaobo; Jiang, Qinghui; Chen, Na; Wei, Wei; Feng, Xixia
2016-09-01
In this study, shear tests on artificial rock joints with different roughness were conducted under five normal stress levels. Test results showed that the shear strength of rock joints had a positive correlation with roughness and the applied normal stress. Observation of joint specimens after shear tests indicated that asperity damage was mainly located in the steep areas facing the shear direction. The damaged joint surfaces tend to be rough, which implies that tensile failure plays an important role in shear behavior. As a result of the anisotropic characteristic of joint roughness, two quantitative 2D roughness parameters, i.e., the revised root-mean-square of asperity angle tan-1( Z 2r) and the maximum contact coefficient C m, were proposed considering the shear direction. The proposed roughness parameters can capture the difference of roughness in forward and reverse directions along a single joint profile. The normalized tensile strength and the proposed roughness parameters were used to perform a rational derivation of peak dilatancy angle. A negative exponential-type function was found to be appropriate to model the peak dilatancy angle. Using the new model of peak dilatancy angle, we obtained a new criterion for peak shear strength of rock joints. The good agreement between test results and predicted results by the new criterion indicated that the proposed criterion is capable of estimating the peak shear strength of rock joints. Comparisons between the new criterion and published models from available literature revealed that the proposed criterion has a good accuracy for predicting the peak shear strength of joints investigated in this study.
Kim, Jong-Woong; Jung, Seung-Boo
2004-04-25
An experimental investigation was combined with a non-linear finite element analysis using an elastic-viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of BGA solder joints. Two solder compositions were examined in this work: Sn-3.5Ag and Sn-3.5Ag-0.75Cu. The Cu substrates had been surface finished electrolytically with a 7 {mu}m thick Ni diffusion barrier followed by an 0.5 {mu}m thick Au layer to enhance solderability. Ag{sub 3}Sn and a few AuSn{sub 4} intermetallic compound (IMC) particles were found inside the two solders. Only a continuous Ni{sub 3}Sn{sub 4} layer was observed at the interface between the Au/Ni plated layer and the Sn-3.5Ag, while a continuous (Ni{sub 1-x}Cu{sub x}){sub 3}Sn{sub 4} layer and a small amount of discontinuous (Cu{sub 1-y}Ni{sub y}){sub 6}Sn{sub 5} particles were formed at the interface between the substrate and the Sn-3.5Ag-0.75Cu. The IMC was identified using energy dispersive spectrometer (EDS) and electron probe micro analysis (EPMA). Shear tests were carried out over a shear speed range from 10 to 700 {mu}m/s at a shear ram height of 50 {mu}m. The shear force was observed to linearly increase with shear speed and reach a maximum value at the highest shear speed in both the experimental and the computational results. All test specimens fractured in a ductile mode. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions.
Shear-resistant behavior of light composite shear wall
李升才; 董毓利
2015-01-01
Shear test results for a composite wall panel in a light composite structure system are compared with test results for shear walls in Japan. The analysis results show that this kind of composite wall panel works very well, and can be regarded as a solid panel. The composite wall panel with a hidden frame is essential for bringing its effect on shear resistance into full play. Comprehensive analysis of the shear-resistant behavior of the composite wall panel suggests that the shear of the composite shear wall panel can be controlled by the cracking strength of the web shearing diagonal crack.
Shear-Resistant Behavior Analysis of Light Composite Shear Walls
李升才; 江见鲸; 于庆荣
2002-01-01
Shear test results for a composite wall panel in a light composite structure system are compared with test results for shear walls in Japan in this paper. The analysis results show that this kind of composite wall panel works very well, and can be regarded as a solid panel. The composite wall panel with a hidden frame is essential for bringing its effect on shear resistance into full play. Comprehensive analysis of the shear-resistant behavior of the composite wall panel suggests that the shear of the composite shear wall panel can be controlled by the cracking strength of the web shearing diagonal crack.
Direct Shear Tests with Evaluation of Variable Shearing Area
Šarūnas Skuodis
2014-12-01
Full Text Available Investigations of soil shear strength properties for Baltic Sea shore sand along Klaipėda city are presented. Investigated sand angle of internal friction (φ and cohesion (c is determined via two different direct shear tests procedures. First procedure is standard and ordinary in geotechnical practice, when direct shear test is provided using constant shearing area A0. Second test procedure is different because shearing area according to horizontal displacement each test second is recalculated. This recalculated shearing area author’s call corrected shearing area A. Obtained normal and tangential stresses’ difference via two different testing procedures was 10%.
Strain Pattern in Supercooled Liquids
Illing, Bernd; Fritschi, Sebastian; Hajnal, David; Klix, Christian; Keim, Peter; Fuchs, Matthias
2016-11-01
Investigations of strain correlations at the glass transition reveal unexpected phenomena. The shear strain fluctuations show an Eshelby-strain pattern [˜cos (4 θ ) /r2 ], characteristic of elastic response, even in liquids, at long times. We address this using a mode-coupling theory for the strain fluctuations in supercooled liquids and data from both video microscopy of a two-dimensional colloidal glass former and simulations of Brownian hard disks. We show that the long-ranged and long-lived strain signatures follow a scaling law valid close to the glass transition. For large enough viscosities, the Eshelby-strain pattern is visible even on time scales longer than the structural relaxation time τ and after the shear modulus has relaxed to zero.
Interfacial shear behavior of composite flanged concrete beams
Moataz Awry Mahmoud
2014-08-01
Full Text Available Composite concrete decks are commonly used in the construction of highway bridges due to their rapid constructability. The interfacial shear transfer between the top slab and the supporting beams is of great significance to the overall deck load carrying capacity and performance. Interfacial shear capacity is directly influenced by the distribution and the percentage of shear connectors. Research and design guidelines suggest the use of two different approaches to quantify the required interfacial shear strength, namely based on the maximum compressive forces in the flange at mid span or the maximum shear flow at the supports. This paper investigates the performance of flanged reinforced concrete composite beams with different shear connector’s distribution and reinforcing ratios. The study incorporated both experimental and analytical programs for beams. Key experimental findings suggest that concentrating the connectors at the vicinity of the supports enhances the ductility of the beam. The paper proposes a simple and straight forward approach to estimate the interfacial shear capacity that was proven to give good correlation with the experimental results and selected code provisions. The paper presents a method to predict the horizontal shear force between precast beams and cast in-situ slabs.
The experimental basis for interpreting particle and magnetic fabrics of sheared till
Iverson, N.R.; Hooyer, T.S.; Thomason, J.F.; Graesch, M.; Shumway, J.R.
2008-01-01
Particle fabrics of basal tills may allow testing of the bed-deformation model of glacier flow, which requires high bed shear strains (>100). Field studies, however, have not yielded a systematic relationship between shear-strain magnitude and fabric development. To isolate this relationship four basal tills and viscous putty were sheared in a ring-shear device to strains as high as 714. Fabric was characterized within a zone of shear deformation using the long-axis orientations of fine-gravel and sand particles and the anisotropy of magnetic susceptibility (AMS) of small (???5-8 cm3) intact samples. Results indicate that till particles rotate toward the plane of shearing with long-axis orientations that become tightly clustered in the direction of shear (0??78 particle-size fraction under consideration. These results do not support the Jeffery model of particle rotation, which correctly describes particle rotation in the viscous putty but not in the tills, owing to fluid-mechanical assumptions of the model that are violated in till. The sensitivity of fabric development to shear-strain magnitude indicates that, for most till units where shear-strain magnitude is poorly known, attributing fabric variations to spatial differences in other variables, such as till thickness or water content, will be inherently speculative. Attributing fabric characteristics to particular basal till facies is uncertain because shear-strain magnitude is unlikely to be closely correlated to till facies. Weak or spatially variable fabrics, in the absence of post-depositional disturbance or major deviations from unidirectional simple shear, indicate that till has not been pervasively sheared to the high strains required by the bed-deformation model. Strong flow-parallel fabrics are a necessary but insufficient criterion for confirming the model. Copyright ?? 2008 John Wiley & Sons, Ltd.
Maximum likely scale estimation
Loog, Marco; Pedersen, Kim Steenstrup; Markussen, Bo
2005-01-01
A maximum likelihood local scale estimation principle is presented. An actual implementation of the estimation principle uses second order moments of multiple measurements at a fixed location in the image. These measurements consist of Gaussian derivatives possibly taken at several scales and/or ...
Shear wall ultimate drift limits
Duffey, T.A. [Duffy, (T.A.) Tijeras, NM (United States); Goldman, A. [Goldman, (A.), Sandia, Los Alamos, NM (United States); Farrar, C.R. [Los Alamos National Lab., NM (United States)
1994-04-01
Drift limits for reinforced-concrete shear walls are investigated by reviewing the open literature for appropriate experimental data. Drift values at ultimate are determined for walls with aspect ratios ranging up to a maximum of 3.53 and undergoing different types of lateral loading (cyclic static, monotonic static, and dynamic). Based on the geometry of actual nuclear power plant structures exclusive of containments and concerns regarding their response during seismic (i.e.,cyclic) loading, data are obtained from pertinent references for which the wall aspect ratio is less than or equal to approximately 1, and for which testing is cyclic in nature (typically displacement controlled). In particular, lateral deflections at ultimate load, and at points in the softening region beyond ultimate for which the load has dropped to 90, 80, 70, 60, and 50 percent of its ultimate value, are obtained and converted to drift information. The statistical nature of the data is also investigated. These data are shown to be lognormally distributed, and an analysis of variance is performed. The use of statistics to estimate Probability of Failure for a shear wall structure is illustrated.
Shear wave elastography with a new reliability indicator
Christoph F. Dietrich
2016-09-01
Full Text Available Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s. The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed. The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France, point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France. More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.
Turbulent flows over superhydrophobic surfaces with shear-dependent slip length
Khosh Aghdam, Sohrab; Seddighi, Mehdi; Ricco, Pierre
2015-11-01
Motivated by recent experimental evidence, shear-dependent slip length superhydrophobic surfaces are studied. Lyapunov stability analysis is applied in a 3D turbulent channel flow and extended to the shear-dependent slip-length case. The feedback law extracted is recognized for the first time to coincide with the constant-slip-length model widely used in simulations of hydrophobic surfaces. The condition for the slip parameters is found to be consistent with the experimental data and with values from DNS. The theoretical approach by Fukagata (PoF 18.5: 051703) is employed to model the drag-reduction effect engendered by the shear-dependent slip-length surfaces. The estimated drag-reduction values are in very good agreement with our DNS data. For slip parameters and flow conditions which are potentially realizable in the lab, the maximum computed drag reduction reaches 50%. The power spent by the turbulent flow on the walls is computed, thereby recognizing the hydrophobic surfaces as a passive-absorbing drag-reduction method, as opposed to geometrically-modifying techniques that do not consume energy, e.g. riblets, hence named passive-neutral. The flow is investigated by visualizations, statistical analysis of vorticity and strain rates, and quadrants of the Reynolds stresses. Part of this work was funded by Airbus Group. Simulations were performed on the ARCHER Supercomputer (UKTC Grant).
Direct shear of olivine single crystals
Tielke, Jacob A.; Zimmerman, Mark E.; Kohlstedt, David L.
2016-12-01
Knowledge of the strengths of the individual dislocation slip systems in olivine is fundamental to understanding the flow behavior and the development of lattice-preferred orientation in olivine-rich rocks. The most direct measurements of the strengths of individual slip systems are from triaxial compression experiments on olivine single crystals. However, such experiments only allow for determination of flow laws for two of the four dominant slip systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip systems independently, we performed deformation experiments on single crystals of San Carlos olivine in a direct shear geometry. Experiments were carried out at temperatures of 1000 ° to 1300 °C, a confining pressure of 300 MPa, shear stresses of 60 to 334 MPa, and resultant shear strain rates of 7.4 × 10-6 to 2.1 × 10-3 s-1. At high-temperature (≥1200 °C) and low-stress (≤200 MPa) conditions, the strain rate of crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system follows a power law relationship with stress, whereas at lower temperatures and higher stresses, strain rate depends exponentially on stress. The flow laws derived from the mechanical data in this study are consistent with a transition from the operation of a climb-controlled dislocation mechanism during power-law creep to the operation of a glide-controlled dislocation mechanism during exponential creep. In the climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker than crystals orientated for shear on the (100)[001] slip system. In contrast, in the glide-controlled regime the opposite is observed. Extrapolation of flow laws determined for crystals sheared in orientations favorable for slip on these two slip systems to upper mantle conditions reveals that the (001)[100] slip system is weaker at temperatures and stresses that are typical of the asthenospheric mantle, whereas the (100
Localization and instability in sheared granular materials: Role of friction and vibration
Kothari, Konik R
2016-01-01
Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies and variability under different loading conditions have not been fully explored. Here, we use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as presence and absence of acoustic vibrations. Our results suggest that at low and intermediate strain rates, persistent shear bands develop only in the absence of vibrations. Vibrations tend to fluidize the granular network and de-localize slip at these rates. Stick-slip is only observed for frictional grains and it is confined to the shear band. At high strain rates, stick-slip disappears and the different systems exhibit similar stress-slip response. Changing the vibration intensity, duration or time of...
Maximum information photoelectron metrology
Hockett, P; Wollenhaupt, M; Baumert, T
2015-01-01
Photoelectron interferograms, manifested in photoelectron angular distributions (PADs), are a high-information, coherent observable. In order to obtain the maximum information from angle-resolved photoionization experiments it is desirable to record the full, 3D, photoelectron momentum distribution. Here we apply tomographic reconstruction techniques to obtain such 3D distributions from multiphoton ionization of potassium atoms, and fully analyse the energy and angular content of the 3D data. The PADs obtained as a function of energy indicate good agreement with previous 2D data and detailed analysis [Hockett et. al., Phys. Rev. Lett. 112, 223001 (2014)] over the main spectral features, but also indicate unexpected symmetry-breaking in certain regions of momentum space, thus revealing additional continuum interferences which cannot otherwise be observed. These observations reflect the presence of additional ionization pathways and, most generally, illustrate the power of maximum information measurements of th...
Shear band in sand with spatially varying density
Borja, Ronaldo I.; Song, Xiaoyu; Rechenmacher, Amy L.; Abedi, Sara; Wu, Wei
2013-01-01
Bifurcation theory is often used to investigate the inception of a shear band in a homogeneously deforming body. The theory predicts conjugate shear bands that have the same likelihood of triggering. For structures loaded symmetrically the choice of which of the two conjugate shear bands will persist is arbitrary. In this paper we show that spatial density variation could be a determining factor for the selection of the persistent shear band in a symmetrically loaded localizing sand body. We combine experimental imaging on rectangular sand specimens loaded in plane strain compression with mesoscale finite element modeling on symmetrically loaded sand specimens to show that spatial heterogeneity in density does have a profound impact on the persistent shear band.
Plastic response and correlations in athermally sheared amorphous solids
Puosi, F.; Rottler, J.; Barrat, J.-L.
2016-09-01
The onset of irreversible deformation in low-temperature amorphous solids is due to the accumulation of elementary events, consisting of spatially and temporally localized atomic rearrangements involving only a few tens of atoms. Recently, numerical and experimental work addressed the issue of spatiotemporal correlations between these plastic events. Here, we provide further insight into these correlations by investigating, via molecular dynamics (MD) simulations, the plastic response of a two-dimensional amorphous solid to artificially triggered local shear transformations. We show that while the plastic response is virtually absent in as-quenched configurations, it becomes apparent if a shear strain was previously imposed on the system. Plastic response has a fourfold symmetry, which is characteristic of the shear stress redistribution following the local transformation. At high shear rate we report evidence for a fluctuation-dissipation relation, connecting plastic response and correlation, which seems to break down if lower shear rates are considered.
Shear induced phase transitions induced in edible fats
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.
Maj, M; Oliferuk, W, E-mail: mimaj@ippt.gov.p [Institute of Fundamental Technological Research Polish Academy of Sciences, Pawinskiego 5b, 02-106 Warsaw (Poland)
2010-07-01
In the present paper the influence of pre-strain direction on energy balance during deformation of austenitic steel was investigated and the analysis of microscopic phenomena responsible for this influence was performed. The specimens with different pre-strain directions were prepared and the ratio of the stored energy increment to plastic work increment, called energy storage rate, as a function of plastic strain was experimentally determined. At the initial stage of plastic deformation of annealed materials this quantity vs. plastic strain has a maximum. It has been shown that for specimens strained in the same direction as pre-strain the energy storage rate decreases monotonically with deformation while for specimens where strain path was changed, the maximum of the energy storage rate is observed (as in case of annealed material). The study of slip and microstructure evolution at meso- and micro-scales have shown that the change in pre-strain direction leads to the redistribution of internal stresses generated by incompatible slip in neighbouring grains of different orientation. Just after change in strain direction the accommodation of these stresses takes place not only by generation of geometrically necessary dislocations but also by micro-shear banding.
Mellema, Daniel C; Song, Pengfei; Kinnick, Randall R; Urban, Matthew W; Greenleaf, James F; Manduca, Armando; Chen, Shigao
2016-09-01
Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a "strain-like" compression artifact that is coupled with the observed shear waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate shear wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300 Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥ 19 dB) between the target and
High Resolution Shear Profile Measurements in Entangled Polymers
Hayes, Keesha A.
2008-11-17
We use confocal microscopy and particle image velocimetry to visualize motion of 250-300 nm. fluorescent tracer particles in entangled polymers subject to a rectilinear shear flow. Our results show linear velocity profiles in polymer solutions spanning a wide range of molecular weights and number of entanglements (8≤Z≤56), but reveal large differences between the imposed and measured shear rates. These findings disagree with recent reports that shear banding is a characteristic flow response of entangled polymers, and instead point to interfacial slip as an important source of strain loss. © 2008 The American Physical Society.
Maiti, Moumita; Vinutha, H. A.; Sastry, Srikanth; Heussinger, Claus
2015-10-01
Using an athermal quasistatic simulation protocol, we study the distribution of free volumes in sheared hard-particle packings close to, but below, the random-close packing threshold. We show that under shear, and independent of volume fraction, the free volumes develop features similar to close-packed systems — particles self-organize in a manner as to mimick the isotropically jammed state. We compare athermally sheared packings with thermalized packings and show that thermalization leads to an erasure of these structural features. The temporal evolution in particular the opening-up and the closing of free-volume patches is associated with the single-particle dynamics, showing a crossover from ballistic to diffusive behavior.
ESTIMATION OF EFFECTIVE SHEAR STRESS WORKING ON FLAT SHEET MEMBRANE USING FLUIDIZED MEDIA IN MBRs
Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi; Mishima, Iori
This study was aimed at estimating effective shear stress working on flat sheet membrane by the addition of fluidized media in MBRs. In both of laboratory-scale aeration tanks with and without fluidized media, shear stress variations on membrane surface and water phase velocity variations were measured and MBR operation was conducted. For the evaluation of the effective shear stress working on membrane surface to mitigate membrane surface, simulation of trans-membrane pressure increase was conducted. It was shown that the time-averaged absolute value of shear stress was smaller in the reactor with fluidized media than without fluidized media. However, due to strong turbulence in the reactor with fluidized media caused by interaction between water-phase and media and also due to the direct interaction between membrane surface and fluidized media, standard deviation of shear stress on membrane surface was larger in the reactor with fluidized media than without media. Histograms of shear stress variation data were fitted well to normal distribution curves and mean plus three times of standard deviation was defined to be a maximum shear stress value. By applying the defined maximum shear stress to a membrane fouling model, trans-membrane pressure curve in the MBR experiment was simulated well by the fouling model indicting that the maximum shear stress, not time-averaged shear stress, can be regarded as an effective shear stress to prevent membrane fouling in submerged flat-sheet MBRs.
Forming limit strains of interstitial free-IF steel sheet
Bressan, José Divo; Moreira, Luciano Pessanha; Freitas, Maria Carolina dos Santos
2016-10-01
Present work examines mathematical models to predict the onset of localized necking in sheet metal forming of interstitial free steel, such as biaxial stretching and deep drawing. Forming Limit Curve, FLC, which is an essential material parameter necessary to numerical simulation by FEM, of IF steel sheet was assessed experimentally by Nakajima testing and ASAME software. The "Map of Principal Surface Limit Strains - MPLS", shows the experimental FLC which is the plot of principal true strains in the sheet metal surface (ɛ1, ɛ2), occurring at critical points obtained in laboratory formability tests or in the fabrication process of parts. Two types of undesirable rupture mechanisms can occur in sheet metal forming products: localized necking and rupture by induced shear stress. Therefore, two kinds of limit strain curves can be plotted in the forming map: the local necking limit curve FLC-N and the shear stress rupture limit curve FLC-S. Localized necking is theoretically anticipated to occur by two mathematical models: Marciniak-Kuczynski modeling, hereafter named M-K approach, and D-Bressan modeling. In the M-K approach, local necking originates at an initial sheet thickness heterogeneity or defect fo = tob/toa. The strain state inside the evolving groove moves to plane strain and the limit strain ɛ1* is attained when the strain ɛ1a outside the groove or neck stop to increase. In the D-Bressan model, local necking is proposed to initiate at the instability point of maximum load, at a thickness defect (λ/μ)diffuse inside the grooved sheet thickness. The inception of visible grooving on the sheet surface evolves from instability point to localized (λ/μ)crit and final rupture, during further sheet metal straining. Work hardening law is defined for a strain and strain-rate material by the effective current stress. The average experimental hardening law curve for tensile tests at 0°, 45° and 90°, assuming normal anisotropy, was used to analyze the plasticity
Risk of shear failure and extensional failure around over-stressed excavations in brittle rock
Nick Barton
2017-04-01
Full Text Available The authors investigate the failure modes surrounding over-stressed tunnels in rock. Three lines of investigation are employed: failure in over-stressed three-dimensional (3D models of tunnels bored under 3D stress, failure modes in two-dimensional (2D numerical simulations of 1000 m and 2000 m deep tunnels using FRACOD, both in intact rock and in rock masses with one or two joint sets, and finally, observations in TBM (tunnel boring machine tunnels in hard and medium hard massive rocks. The reason for ‘stress-induced’ failure to initiate, when the assumed maximum tangential stress is approximately (0.4–0.5σc (UCS, uniaxial compressive strength in massive rock, is now known to be due to exceedance of a critical extensional strain which is generated by a Poisson's ratio effect. However, because similar ‘stress/strength’ failure limits are found in mining, nuclear waste research excavations, and deep road tunnels in Norway, one is easily misled into thinking of compressive stress induced failure. Because of this, the empirical SRF (stress reduction factor in the Q-system is set to accelerate as the estimated ratio σθmax/σc >> 0.4. In mining, similar ‘stress/strength’ ratios are used to suggest depth of break-out. The reality behind the fracture initiation stress/strength ratio of ‘0.4’ is actually because of combinations of familiar tensile and compressive strength ratios (such as 10 with Poisson's ratio (say 0.25. We exceed the extensional strain limits and start to see acoustic emission (AE when tangential stress σθ ≈ 0.4σc, due to simple arithmetic. The combination of 2D theoretical FRACOD models and actual tunnelling suggests frequent initiation of failure by ‘stable’ extensional strain fracturing, but propagation in ‘unstable’ and therefore dynamic shearing. In the case of very deep tunnels (and 3D physical simulations, compressive stresses may be too high for extensional strain fracturing, and
Liu, Xianfeng; Zhang, Chonglei; Yuan, Shengyang; Fityus, Stephen; Sloan, Scott William; Buzzi, Olivier
2016-09-01
This study aims at providing quality experimental data on the effects of temperature on tensile strength and small strain shear stiffness of two Australian mudstones. The objective is to provide multiscale data in view of developing a numerical model that can capture and simulate the complex multiphysics of underground coal fire propagation. Two mudstones were collected in the Hunter Valley, close to a known underground coal fire, referred to as "Burning Mountain." The rock specimens were heated to a range of temperatures (maximum of 900 °C) for 24 h, and the materials were comprehensively characterized by X-ray diffraction, thermal gravimetric analyses, optical microscopy and scanning electron microscopy. In addition, mercury intrusion porosimetry was used in order to track changes in pore size distribution with temperature. Investigations at microscale were complemented by testing at the macroscale. In particular, the paper focuses on the evolution of the tensile strength and small strain shear stiffness as the materials are subjected to heating treatment. Results show that both parameters evolve in a non-monotonic manner with temperature. The observed mechanical responses are fully explained and corroborated by microstructural observations.
Mixing through shear instabilities
Brüggen, M
2000-01-01
In this paper we present the results of numerical simulations of the Kelvin-Helmholtz instability in a stratified shear layer. This shear instability is believed to be responsible for extra mixing in differentially rotating stellar interiors and is the prime candidate to explain the abundance anomalies observed in many rotating stars. All mixing prescriptions currently in use are based on phenomenological and heuristic estimates whose validity is often unclear. Using three-dimensional numerical simulations, we study the mixing efficiency as a function of the Richardson number and compare our results with some semi-analytical formalisms of mixing.
Maximum Likelihood Associative Memories
Gripon, Vincent; Rabbat, Michael
2013-01-01
Associative memories are structures that store data in such a way that it can later be retrieved given only a part of its content -- a sort-of error/erasure-resilience property. They are used in applications ranging from caches and memory management in CPUs to database engines. In this work we study associative memories built on the maximum likelihood principle. We derive minimum residual error rates when the data stored comes from a uniform binary source. Second, we determine the minimum amo...
Maximum likely scale estimation
Loog, Marco; Pedersen, Kim Steenstrup; Markussen, Bo
2005-01-01
A maximum likelihood local scale estimation principle is presented. An actual implementation of the estimation principle uses second order moments of multiple measurements at a fixed location in the image. These measurements consist of Gaussian derivatives possibly taken at several scales and....../or having different derivative orders. Although the principle is applicable to a wide variety of image models, the main focus here is on the Brownian model and its use for scale selection in natural images. Furthermore, in the examples provided, the simplifying assumption is made that the behavior...... of the measurements is completely characterized by all moments up to second order....
Stimulated bioluminescence by fluid shear stress associated with pipe flow
Cao Jing; Wang Jiangan; Wu Ronghua, E-mail: caojing981@126.com [Col. of Electronic Eng., Naval University of Engineering, Wuhan 430033 (China)
2011-01-01
Dinoflagellate can be stimulated bioluminescence by hydrodynamic agitation. Two typical dinoflagellate (Lingulodinium polyedrum and Pyrocystis noctiluca) was choosed to research stimulated bioluminescence. The bioluminescence intensity and shear stress intensity were measured using fully developed pipe flow. There is shear stress threshold to agitate organism bioluminescence. From these experiment, the response thresholds of the stimulated bioluminscence always occurred in laminar flows at a shear stress level of 0.6-3 dyn/cm{sup 2}. At the same time, the spectral characteristc of dinoflagellate was recorded, the wavelength of them is about 470nm, and the full width at half maximum is approximate 30nm.
Zhang, Rui; Gao, Peifeng; Wang, Xingzhe
2017-09-01
A semi-phenomenological approach, which combined the microscopic properties calculated by first-principles and macroscopic critical characteristics determined from empirical relations, is suggested to investigate the superconducting critical properties of the low temperature superconductor Nb3Sn with different intrinsic strain modes like uniaxial tension, shear and torsion deformations. Firstly, the microscopic properties of the electronic structure and density of state for Nb3Sn are numerically obtained by first-principles calculations using density-functional theory in the generalized gradient approximation. These are further incorporate with the macroscopic empirical relation of the unified scaling law for predicting critical parameters of the strained Nb3Sn superconductor. The superconducting critical profiles of critical temperature, magnetic field and current, in such a way, are achieved for Nb3Sn under different strains. The predictions on the critical parameters of the superconductor bulk in uniaxial tension/compression state exhibit obvious degradations and bell-shaped curves with maximum critical values at zero strain and a slight asymmetry between the tensile and compressive strains, which show quite good agreements with the experimental data. As for Nb3Sn under shear and torsion deformations, the similar degradations on critical parameters also are presented which are monotonously decreased with the applied strains. The first-principles calculations and results in this work are based on an assumption which the superconducting critical properties from the strain-induced variations in the electronic density of states. Furthermore, the modified critical surfaces of Nb3Sn, determined by the critical temperature, current and magnetic field dependence upon the applied different strains are depicted. The present study will be helpful to identify the scaling relation for the critical parameters and understanding the origin of strain sensitivity in Nb3Sn
Torsional shear flow of granular materials: shear localization and minimum energy principle
Artoni, Riccardo; Richard, Patrick
2016-10-01
The rheological properties of granular matter submitted to torsional shear are investigated numerically by means of discrete element method. The shear cell is made of a cylinder filled by grains which are sheared by a bumpy bottom and submitted to a vertical pressure which is applied at the top. Regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. The effects of the (i) the applied pressure, (ii) sidewall friction, and (iii) angular velocity are investigated. A model, based on the purely local μ (I) -rheology and a minimum energy principle is able to capture the effect of the two former quantities but unable to account the effect of the latter. Although, an ad hoc modification of the model allows to reproduce all the numerical results, our results point out the need for an alternative rheology.
Evolution of shear banding flows in metallic glasses characterized by molecular dynamics
Yao, Li, E-mail: yltiger@sjtu.edu.cn [Shanghai Institute of Space Power-Sources, 2965 Dongchuan Rd., Shanghai 200245 (China); Luan, Yingwei [School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240 (China)
2016-06-21
To reveal the evolution of shear banding flows, one-dimensional nanostructure metallic glass composites have been studied with molecular dynamics. The inherent size determines the initial thickness of shear bands, and the subsequent broadening can be restricted to some extent. The vortex-like flows evoke the atomic motion perpendicular to the shear plane, which accelerates the interatomic diffusion. The reduction of local strain rate causes the flow softening for monolithic Cu-Zr glass, but the participation of Cu-atoms in the shear banding flow gradually leads to the shear hardening for the composites.
Korjenic Sinan
2015-11-01
Full Text Available This paper is about the shear capacity of partition walls in old buildings based on shear tests which were carried out under real conditions in an existing building. There were experiments conducted on different floors and in each case, the maximum recordable horizontal force and the horizontal displacement of the respective mortar were measured. At the same time material studies and material investigations were carried out in the laboratory. The material parameters were used for the calculation of the precise shear capacity of each joint. In the shear tests, the maximum displacement of a mortar joint was determined at a maximum of two to four millimetres. Furthermore, no direct linear relationship between the theoretical load (wall above it and the shear stress occurred could be detected in the analysis of the experiment, as it was previously assumed.
Interaction of monopoles, dipoles, and turbulence with a shear flow
Marques Rosas Fernandes, V. H.; Kamp, L. P. J.; van Heijst, G. J. F.; Clercx, H. J. H.
2016-09-01
Direct numerical simulations have been conducted to examine the evolution of eddies in the presence of large-scale shear flows. The numerical experiments consist of initial-value-problems in which monopolar and dipolar vortices as well as driven turbulence are superposed on a plane Couette or Poiseuille flow in a periodic two-dimensional channel. The evolution of the flow has been examined for different shear rates of the background flow and different widths of the channel. Results found for retro-grade and pro-grade monopolar vortices are consistent with those found in the literature. Boundary layer vorticity, however, can significantly modify the straining and erosion of monopolar vortices normally seen for unbounded domains. Dipolar vortices are shown to be much more robust coherent structures in a large-scale shear flow than monopolar eddies. An analytical model for their trajectories, which are determined by self-advection and advection and rotation by the shear flow, is presented. Turbulent kinetic energy is effectively suppressed by the shearing action of the background flow provided that the shear is linear (Couette flow) and of sufficient strength. Nonlinear shear as present in the Poiseuille flow seems to even increase the turbulence strength especially for high shear rates.
Hansen, Klaus
This report gives a summary of the present information on the behaviour of vertical keyed shear joints in large panel structures. An attemp is made to outline the implications which this information might have on the analysis and design of a complete wall. The publications also gives a short...
Shear behavior of reinforced Engineered Cementitious Composites (ECC) beams
Paegle, Ieva; Fischer, Gregor
2010-01-01
This paper describes an experimental investigation of the shear behavior of beams consisting of steel reinforced Engineered Cementitious Composites (ECC). Based on the strain hardening and multiple cracking behavior of ECC, this study investigates the extent to which ECC can improve the shear...... randomly distributed PVA (polyvinyl alcohol) fiber beams with different stirrup spacing and reinforced concrete (RC) beams for comparison. Displacement and strain measurements taken using the ARAMIS photogrammetric data acquisition system by means of processing at high frame rate captured images of applied...
F. TopsÃƒÂ¸e
2001-09-01
Full Text Available Abstract: In its modern formulation, the Maximum Entropy Principle was promoted by E.T. Jaynes, starting in the mid-fifties. The principle dictates that one should look for a distribution, consistent with available information, which maximizes the entropy. However, this principle focuses only on distributions and it appears advantageous to bring information theoretical thinking more prominently into play by also focusing on the "observer" and on coding. This view was brought forward by the second named author in the late seventies and is the view we will follow-up on here. It leads to the consideration of a certain game, the Code Length Game and, via standard game theoretical thinking, to a principle of Game Theoretical Equilibrium. This principle is more basic than the Maximum Entropy Principle in the sense that the search for one type of optimal strategies in the Code Length Game translates directly into the search for distributions with maximum entropy. In the present paper we offer a self-contained and comprehensive treatment of fundamentals of both principles mentioned, based on a study of the Code Length Game. Though new concepts and results are presented, the reading should be instructional and accessible to a rather wide audience, at least if certain mathematical details are left aside at a rst reading. The most frequently studied instance of entropy maximization pertains to the Mean Energy Model which involves a moment constraint related to a given function, here taken to represent "energy". This type of application is very well known from the literature with hundreds of applications pertaining to several different elds and will also here serve as important illustration of the theory. But our approach reaches further, especially regarding the study of continuity properties of the entropy function, and this leads to new results which allow a discussion of models with so-called entropy loss. These results have tempted us to speculate over
Electrorheological Effects at High Shear Rate
无
2006-01-01
Much attention has been given to electrorheological (ER) fluids because of the ER effect, which has been described by a large number of researchers as a notable increase in the apparent viscosity of a fluid upon the application of an electric field. The description of ER effects is, however, not accurate at high shear rates. To clarify the discrepancy, we analyze and compute the apparent viscosity as a function of shear rate for ER fluid flow between rotating coaxial cylinders in the presence of an electric field. The theoretical predictions show that the increase of electric intensity contributes little to the apparent viscosity enhancement at high shear rates, while ER effects for ER fluids with a higher polarization rate still exist and ER devices possess controllability in this regime. Description of the ER effect by the apparent viscosity leads to an unrealistic conclusion that ER effects disappear at high shear rates, because the apparent viscosity of ER fluids approaches the value for Newtonian fluids. Therefore, it is concluded that the proper description of ER effects, i.e., one that holds uniformly for any strain rate when ER effects exist, is manifested by a remarkable increase in the extra stress rather than in the apparent viscosity of ER fluids.
Shear Thinning of Noncolloidal Suspensions
Vázquez-Quesada, Adolfo; Tanner, Roger I.; Ellero, Marco
2016-09-01
Shear thinning—a reduction in suspension viscosity with increasing shear rates—is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.
Regularized maximum correntropy machine
Wang, Jim Jing-Yan
2015-02-12
In this paper we investigate the usage of regularized correntropy framework for learning of classifiers from noisy labels. The class label predictors learned by minimizing transitional loss functions are sensitive to the noisy and outlying labels of training samples, because the transitional loss functions are equally applied to all the samples. To solve this problem, we propose to learn the class label predictors by maximizing the correntropy between the predicted labels and the true labels of the training samples, under the regularized Maximum Correntropy Criteria (MCC) framework. Moreover, we regularize the predictor parameter to control the complexity of the predictor. The learning problem is formulated by an objective function considering the parameter regularization and MCC simultaneously. By optimizing the objective function alternately, we develop a novel predictor learning algorithm. The experiments on two challenging pattern classification tasks show that it significantly outperforms the machines with transitional loss functions.
Shear strength of non-shear reinforced concrete elements
Hoang, Cao linh
1997-01-01
The paper deals with the plastic shear strength of non shear reinforced T-beams.The influence of an un-reinforced flange on the shear capacity is investigated by considering a failure mechanism involving crack sliding in the web and a kind of membrane action over an effective width of the flange...
Rheological responses of fumed silica suspensions under steady and oscillatory shear
无
2009-01-01
Rheological experiments under steady and oscillatory shear were conducted for fumed silica suspen- sions in polyethylene glycol. Under steady shear the shear-thinning and thickening response were exhibited and the flow exponent N was determined. With the increase of concentration the flow exponent N showed a rapid increase, and it increased dramatically when the discontinuous shear-thickening took place. Oscillatory shear experiments were conducted at constant frequency and constant amplitude strain, respectively. The shear-thinning and the discontinuous shear-thickening behavior were observed under different constant frequencies from 10 to 80 rad/s. The correlation between complex modulus (G*) and sweep frequency (ω) was illuminated at γ =750%. It was found that the correlation between G* and ω could be fitted by equation: G*∝ωn. The indexes in shear-thinning region and shear-thickening were determined. The indexes were similar to some extent at shear-thinning region and increased dramati- cally to a much higher value when the shear-thickening occurred,especially at higher weight fractions. The behaviors can be qualitatively explained as follows: the shear-thinning owes to decrease of viscos- ity, which results from disruption of the aggregates; the cluster theory attributes the shear-thickening to the formation of metastable, flow induced clusters, which block the system.
Rheological responses of fumed silica suspensions under steady and oscillatory shear
YANG HaiLin; RUAN JianMing; ZOU JianPeng; WU QiuMei; ZHOU ZhongCheng; ZHOU ZhiHua
2009-01-01
Rheological experiments under steady and oscillatory shear were conducted for fumed silica suspensions in polyethylene glycol. Under steady shear the shear-thinning and thickening response were exhibited and the flow exponent Nwas determined. With the increase of concentration the flow exponent N showed a rapid increase, and it increased dramatically when the discontinuous shear-thickening took place. Oscillatory shear experiments were conducted at constant frequency and constant amplitude strain, respectively. The shear-thinning and the discontinuous shear-thickening behavior were observed under different constant frequencies from 10 to 80 rad/s. The correlation between complex modulus (G*)and sweep frequency (ω) was illuminated atγ=750%. It was found that the correlation between G* and ω could be fitted by equation: G*∝ωn. The indexes in shear-thinning region and shear-thickening were determined. The indexes were similar to some extent at shear-thinning region end increased dramatically to a much higher value when the shear-thickening occurred, especially at higher weight fractions. The behaviors can be qualitatively explained as follows: the shear-thinning owes to decrease of viscosity, which results from disruption of the aggregates; the cluster theory attributes the shear-thickening to the formation of metastable, flow induced clusters, which block the system.
Analysis of a high intensity shear zone between overlapping fiber ends in a polymer matrix composite
Lindgreen, Britta
2008-01-01
The formation of high intensity shear zones in a glass fiber reinforced thermoplast is studied numerically. The thermoplast is characterized by a finite strain elastic-viscoplastic constitutive relation and the calculations are carried out using a dynamic finite element program where plane strain...... conditions are assumed to prevail in the direction of the thickness. Different ratios of the elongation strain and the transverse strain are studied to consider the effect of different levels of stress triaxiality and the effect of these states on the shear zone development and emerging strain and stress...
Guelorget, Bruno [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)], E-mail: bruno.guelorget@utt.fr; Francois, Manuel; Montay, Guillaume [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)
2009-04-15
In this paper, electronic speckle pattern interferometry strain rate measurements are used to quantify the width of the strain localization band, which occurs when a sheet specimen is submitted to tension. It is shown that the width of this band decreases with increasing strain. Just before fracture, this measured width is about five times wider than the shear band and the initial sheet thickness.
Shear Behavior of Concrete Beams Reinforced with GFRP Shear Reinforcement
Heecheul Kim; Min Sook Kim; Myung Joon Ko; Young Hak Lee
2015-01-01
This paper presents the shear capacities of concrete beams reinforced with glass fiber reinforced polymer (GFRP) plates as shear reinforcement. To examine the shear performance, we manufactured and tested a total of eight specimens. Test variables included the GFRP strip-width-to-spacing ratio and type of opening array. The specimen with a GFRP plate with a 3×2 opening array showed the highest shear strength. From the test results, the shear strength increased as the strip-width-to-strip-spac...
MECHANICAL BEHAVIOR OF AMORPHOUS POLYMERS IN SHEAR
张赟; 黄筑平
2004-01-01
Based on the non-equilibrium thermodynamic theory, a new thermo-viscoelastic constitutive model for an incompressible material is proposed. This model can be considered as a kind of generalization of the non-Gaussian network theory in rubber elasticity to include the viscous and the thermal effects. A set of second rank tensorial internal variables was introduced, and in order to adequately describe the evolution of these internal variables, a new expression of the Helmholtz free energy was suggested. The mechanical behavior of the thermo-viscoelastic material under simple shear deformation was studied, and the "viscous dissipation induced" anisotropy due to the change of orientation distribution of molecular chains was examined. Influences of strain rate and thermal softening produced by the viscous dissipation on the shear stress were also discussed. Finally, the model predictions were compared with the experimental results performed by G'Sell et al., thus the validity of the proposed model is verified.
Jeřábek, Petr; Bukovská, Zita
2015-04-01
recrystallization along thin shear bands records strain rates of ~10^-14 whereas the recrystallization along thick shear bands records strain rates of ~10^-15. The contemporaneous operation of solution-precipitation creep in shear bands and dislocation creep in quartz along the shear band boundary suggests low viscosity contrast between the mixed phase shear band matrix and pure quartz aggregate implying that the solution-precipitation creep reflect similar stress and strain rate conditions as the dislocation creep in quartz. Stage III of shear band evolution is characterized by interconnection of dispersed muscovite grains and the deformation becomes accommodated by dislocation creep in thin muscovite bands separating the inactive domains of stage II microstructure. References: Holyoke III, C. W., & Kronenberg, A. K. (2010). Accurate differential stress measurement using the molten salt cell and solid salt assemblies in the Griggs apparatus with applications to strength, piezometers and rheology. Tectonophysics, 494(1-2), 17-31. Paterson, M. S., & Luan, F. C. (1990). Quartzite rheology under geological conditions. In R. J. Knipe & E. H. Rutter (Eds.), Deformation Mechanisms, Rheology and Tectonics (pp. 299-307). London: Geological Society Special Publications. Stipp, M., & Tullis, J. (2003). The recrystallized grain size piezometer for quartz. Geophysical Research Letters, 30(21), 1-5.
Equalized near maximum likelihood detector
2012-01-01
This paper presents new detector that is used to mitigate intersymbol interference introduced by bandlimited channels. This detector is named equalized near maximum likelihood detector which combines nonlinear equalizer and near maximum likelihood detector. Simulation results show that the performance of equalized near maximum likelihood detector is better than the performance of nonlinear equalizer but worse than near maximum likelihood detector.
Cheeseman, Peter; Stutz, John
2005-01-01
A long standing mystery in using Maximum Entropy (MaxEnt) is how to deal with constraints whose values are uncertain. This situation arises when constraint values are estimated from data, because of finite sample sizes. One approach to this problem, advocated by E.T. Jaynes [1], is to ignore this uncertainty, and treat the empirically observed values as exact. We refer to this as the classic MaxEnt approach. Classic MaxEnt gives point probabilities (subject to the given constraints), rather than probability densities. We develop an alternative approach that assumes that the uncertain constraint values are represented by a probability density {e.g: a Gaussian), and this uncertainty yields a MaxEnt posterior probability density. That is, the classic MaxEnt point probabilities are regarded as a multidimensional function of the given constraint values, and uncertainty on these values is transmitted through the MaxEnt function to give uncertainty over the MaXEnt probabilities. We illustrate this approach by explicitly calculating the generalized MaxEnt density for a simple but common case, then show how this can be extended numerically to the general case. This paper expands the generalized MaxEnt concept introduced in a previous paper [3].
Fiber bundle models for stress release and energy bursts during granular shearing
Michlmayr, Gernot; Or, Dani; Cohen, Denis
2012-12-01
Fiber bundle models (FBMs) offer a versatile framework for representing transitions from progressive to abrupt failure in disordered material. We report a FBM-based description of mechanical interactions and associated energy bursts during shear deformation of granular materials. For strain-controlled shearing, where elements fail in a sequential order, we present analytical expressions for strain energy release and failure statistics. Results suggest that frequency-magnitude characteristics of fiber failure vary considerably throughout progressive shearing. Predicted failure distributions were in good agreement with experimentally observed shear stress fluctuations and associated bursts of acoustic emissions. Experiments also confirm a delayed release of acoustic emission energy relative to shear stress buildup, as anticipated by the model. Combined with data-rich acoustic emission measurements, the modified FBM offers highly resolved contact-scale insights into granular media dynamics of shearing processes.
Anisotropic shear melting and recrystallization of a two-dimensional complex plasma.
Nosenko, V; Ivlev, A V; Morfill, G E
2013-04-01
A two-dimensional plasma crystal was melted by suddenly applying localized shear stress. A stripe of particles in the crystal was pushed by the radiation pressure force of a laser beam. We found that the response of the plasma crystal to stress and the eventual shear melting depended strongly on the crystal's angular orientation relative to the laser beam. Shear stress and strain rate were measured, from which the spatially resolved shear viscosity was calculated. The latter was shown to have minima in the regions with highest strain rate, thus demonstrating shear thinning. Shear-induced reordering was observed in the steady-state flow, where particles formed strings aligned in the flow direction.
Shear Behavior of Concrete Beams Reinforced with GFRP Shear Reinforcement
Heecheul Kim
2015-01-01
Full Text Available This paper presents the shear capacities of concrete beams reinforced with glass fiber reinforced polymer (GFRP plates as shear reinforcement. To examine the shear performance, we manufactured and tested a total of eight specimens. Test variables included the GFRP strip-width-to-spacing ratio and type of opening array. The specimen with a GFRP plate with a 3×2 opening array showed the highest shear strength. From the test results, the shear strength increased as the strip-width-to-strip-spacing ratio increased. Also, we used the experimental results to evaluate whether the shear strength equations of ACI 318-14 and ACI 440.1R can be applied to the design of GFRP shear reinforcement. In the results, the ACI 440 equation underestimated the experimental results more than that of ACI 318.
Mechanical characterization of hyperelastic polydimethylsiloxane by simple shear test
Nunes, L.C.S., E-mail: luizcsn@mec.uff.br [Laboratory of Opto-Mechanics (LOM/LMTA), Department of Mechanical Engineering (PGMEC-TEM), Universidade Federal Fluminense - UFF, Rua Passo da Patria, 156, Bloco E, Sala 216, Niteroi, RJ CEP 24210-240 (Brazil)
2011-01-25
Graphical abstract: Display Omitted Research highlights: {yields} Mechanical characterization of Polydimethylsiloxane under large shear deformations {yields} Non-linear shear stress-strain relationship is achieved in simple shear tests {yields} Constitutive modeling of large shear deformations in rubber-like materials is proposed. - Abstract: Polydimethylsiloxane (PDMS) is a commercially silicone rubber widely used in mechanical sensors, electronic products and medical devices. This paper describes and analyzes the mechanical behavior of polymer PDMS under large shear deformations. The goal of this work is to estimate experimentally the angular distortions associated with different applied forces, considering a simple shear test based on single lap joints. The experimental procedure to obtain the displacement field is carried out using the digital image correlation (DIC) method, which is an optical-numerical experimental approach developed for full-field and non-contact measurements. The material parameters, associated with classical Mooney-Rivlin model, are estimated from experimental data by means of Levenberg-Marquardt method. Furthermore, due to nonlinear stress-strain behavior observed in experimental data, it is proposed a new nonlinear model and two new parameters are determined in the same way.
Numerical Simulation of Systems of Shear Bands in Ductile Metal with Inclusions
Plohr, JeeYeon N. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division
2016-08-11
These are slides for a presentation on numerical simulation of systems of shear bands in ductile metal with inclusions, performed at Los Alamos National Laboratory. The conclusions are the following: A shear band is much thinner (0.1 μm) than the spacing between inclusions (100μm). Therefore fully resolved simulation is not feasible; asymptotic analysis allows modeling of a shear band as a velocity discontinuity within a moderately sized cell; formation criterion (critical strain) is determined by rate-dependent viscoplastic flow rule; inclusions cause shear bands to form at smaller strain; under expansion, shear bands form at the same strain than under compression; this can be applied to crystal plasticity.
MM98.57 Quantification of Combined Strain Paths
Nielsen, Morten Sturgård; Wanheim, Tarras
1998-01-01
is to describe the total strain history as a curve in the 6-dimensional shear strain, normal strain space. In order to be able to use these experimental data for calculation, the development of this strain curve must be transformed into a set of scalar relations that may be used for predicting the yield surface...
2012-09-13
accommodate a trial run of inert single base pellet feed for use in a twin screw extruder. 15. SUBJECT TERMS INIT248, Advanced Propellant Technology...Bldg. 4909-5 – Shear Roll Mill Pilot Plant at the Radford Army Ammunition Plant (RFAAP) in order to produce pellet feed for a twin screw extruder used...propellant to simulate feed for a twin screw extruder. Preventive maintenance procedures were in progress in final preparation for running with
Parker, S. D.
2016-12-01
The kinematic evolution of the eastern Snake River Plain (ESRP) remains highly contested. A lack of strike-slip faults bounding the ESRP serves as a primary assumption in many leading kinematic models. Recent GPS geodesy has highlighted possible shear zones along the ESRP yet regional strike-slip faults remain unidentified. Oblique movement within dense arrays of high-angle conjugate normal faults, paralleling the ESRP, occur within a discrete zone of 50 km on both margins of the ESRP. These features have long been attributed to progressive crustal flexure and subsidence within the ESRP, but are capable of accommodating the observed strain without necessitating large scale strike-slip faults. Deformation features within an extensive Neogene conglomerate provide field evidence for dextral shear in a transtensional system along the northern margin of the ESRP. Pressure-solution pits and cobble striations provide evidence for a horizontal ENE/WSW maximum principal stress orientation, consistent with the hypothesis of a dextral Centennial shear zone. Fold hinges, erosional surfaces and stratigraphic datums plunging perpendicular into the ESRP have been attributed to crustal flexure and subsidence of the ESRP. Similar Quaternary folds plunge obliquely into the ESRP along its margins where diminishing offset along active normal faults trends into linear volcanic features. In all cases, orientations and distributions of plunging fold structures display a correlation to the terminus of active Basin and Range faults and linear volcanic features of the ESRP. An alternative kinematic model, rooted in kinematic disparities between Basin and Range faults and parallelling volcanic features may explain the observed downwarping as well as provide a mechanism for the observed shear along the margins of the ESRP. By integrating field observations with seismic, geodetic and geomorphic observations this study attempts to decipher the signatures of crustal flexure and shear along the
The effect analysis of strain rate on power transmission tower-line system under seismic excitation.
Tian, Li; Wang, Wenming; Qian, Hui
2014-01-01
The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results show that the effect of strain rate on the transmission tower generally decreases the maximum top displacements, but it would increase the maximum base shear forces, and thus it is necessary to consider the effect of strain rate on the seismic analysis of the transmission tower. The effect of strain rate could be ignored for the seismic analysis of the conductors and ground lines, but the responses of the ground lines considering strain rate effect are larger than those of the conductors. The results could provide a reference for the seismic design of the transmission tower-line system.
WANG Xue-bin
2005-01-01
The distributed shear stress and the displacement across shear band, the evolution of plastic zones, and the load-carrying capacity of rock specimen were investigated in plane strain direct shear test according to Fast Lagrangian Analysis of Continua (FLAC). And then the shear displacement distribution in normal direction of system composed of localized shear band and elastic rock was analyzed based on gradient-dependent plasticity. The adopted failure criterion was a composite of Mohr-Coulomb criterion, that is, the relation between tension cut-off and post-peak constitutive of rock was linear strain-softening. Numerical results show that shear stress field approximately undergoes three different stages. At first, shear stress is only concentrated in the middle of top and base of specimen. Next, shear stress in the middle of specimen tends to increase, owing to superposition of shear stresses. Interestingly, two peaks of shear stress appear far from the loading ends of specimen, and the peaks approach with the increase in timestep until elements at the center of specimen yield. Finally, relatively lower shear stress level is reached in large part of specimen except in the regions near the two ends. As flow stress decreases, the analytical shear displacement distribution in shear band based on gradient-dependent plasticity becomes steep; outside the band, it is linear and its slope tends to decrease. These theoretical results qualitatively agree with that of the present numerical predicted results. Main advantage of the analytical solution over the numerical results according to FLAC is that it is continuous, smooth and non-linear (except at elastic stage).
Large-scale ordering of nanoparticles using viscoelastic shear processing
Zhao, Qibin; Finlayson, Chris E.; Snoswell, David R. E.; Haines, Andrew; Schäfer, Christian; Spahn, Peter; Hellmann, Goetz P.; Petukhov, Andrei V.; Herrmann, Lars; Burdet, Pierre; Midgley, Paul A.; Butler, Simon; Mackley, Malcolm; Guo, Qixin; Baumberg, Jeremy J.
2016-06-01
Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.
Interfacial stresses in strengthened beam with shear cohesive zone model
Zergua Abdesselam
2015-02-01
The failure of strengthened beams with fibre-reinforced polymer (FRP) materials is due to high stress concentration of FRP–concrete interface. Understanding the cause and mechanism of the debonding of the FRP plate and the prediction of the stress distribution at the concrete–FRP interface are important for more effective strengthening technique. This paper presents an analytical solution, based on Smith and Teng’s equations, for interfacial shear and normal stresses in reinforced concrete (RC) beams strengthened with a fibre reinforced polymer (FRP) plate. However, the shear stress–strain relationship is considered to be bilinear curve. The effects of the shear deformations are calculated in an RC beam, an adhesive layer, and an FRP plate. The results of parametric study are compared with those of Smith and Teng. They confirm the accuracy of the proposed approach in predicting both interfacial shear and normal stresses.
Shear-banding Induced Indentation Size Effect in Metallic Glasses
Lu, Y. M.; Sun, B. A.; Zhao, L. Z.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.
2016-06-01
Shear-banding is commonly regarded as the “plasticity carrier” of metallic glasses (MGs), which usually causes severe strain localization and catastrophic failure if unhindered. However, through the use of the high-throughput dynamic nanoindentation technique, here we reveal that nano-scale shear-banding in different MGs evolves from a “distributed” fashion to a “localized” mode when the resultant plastic flow extends over a critical length scale. Consequently, a pronounced indentation size effect arises from the distributed shear-banding but vanishes when shear-banding becomes localized. Based on the critical length scales obtained for a variety of MGs, we unveil an intrinsic interplay between elasticity and fragility that governs the nanoscale plasticity transition in MGs. Our current findings provide a quantitative insight into the indentation size effect and transition mechanisms of nano-scale plasticity in MGs.
Ab initio study of Ni2MnGa under shear deformation
Zelený Martin
2015-01-01
Full Text Available The effect of shear deformation on Ni2MnGa magnetic shape memory alloy has been investigated using ab initio electronic structure calculations. We used the projector-augmented wave method for the calculations of total energies and stresses as functions of applied affine shear deformation. The studied nonmodulated martensite (NM phase exhibits a tetragonally distorted L21 structure with c/a > 1. A large strain corresponding to simple shears in {001}, {100} and {100} systems was applied to describe a full path between two equivalent NM lattices. We also studied {101} shear which is related to twining of NM phase. Twin reorientation in this system is possible, because applied positive shear results in path with significantly smaller energetic barrier than for negative shear and for shears in other studied systems. When the full relaxation of lattice parameters is allowed, the barriers further strongly decrease and the structures along the twinning path can be considered as orthorhombic.
Second harmonic generation of shear waves in crystals.
Jiang, Wenhua; Cao, Wenwu
2004-02-01
Nonlinear self-interaction of shear waves in electro-elastic crystals is investigated based on the rotationally invariant state function. Theoretical analyses are conducted for cubic, hexagonal, and trigonal crystals. The calculations show that nonlinear self-interaction of shear waves has some characteristics distinctly different from that of longitudinal waves. First, the process of self-interaction to generate its own second harmonic wave is permitted only in some special wave propagation directions for a shear wave. Second, the geometrical nonlinearity originated from finite strain does not contribute to the second harmonic generation (SHG) of shear waves. Therefore, unlike the case of longitudinal wave, the second-order elastic constants do not involve in the nonlinear parameter of the second harmonic generation of shear waves. Third, unlike the nonlinearity parameter of the longitudinal waves, the nonlinear parameter of the shear wave exhibits strong anisotropy, which is directly related to the symmetry of the crystal. In the calculations, the electromechanical coupling nonlinearity is considered for the 6 mm and 3 m symmetry crystals. Complement to the SHG of longitudinal waves already in use, the SHG of shear waves provides more measurements for the determination of third-order elastic constants of solids. The method is applied to a Z-cut lithium niobate (LiNbO3) crystal, and its third-order elastic constant c444 is determined.
Paegle, Ieva; Fischer, Gregor
2016-01-01
This paper describes an experimental investigation of the shear behavior of beams consisting of steel Reinforced Engineered Cementitious Composites (R/ECC). This study investigates and quantifies the effect of ECC's strain hardening and multiple cracking behavior on the shear capacity of beams lo...
A comparative evaluation of in-plane shear test methods for laminated graphite-epoxy composites
Morton, John; Ho, Henjen
1992-01-01
The objectives were to evaluate popular shear test methods for various forms of graphite-epoxy composite materials and to determine the shear response of graphite-epoxy composites with various forms of fiber architecture. Numerical and full-field experimental stress analyses were performed on four shear test configurations for unidirectional and bidirectional graphite-epoxy laminates to assess the uniformity and purity of the shear stress (strain) fields produced in the specimen test section and to determine the material in-plane shear modulus and shear response. The test methods were the 10 deg off-axis, the +/- 45 deg tension, the Iosipescu V-notch, and a compact U-notch specimen. Specimens were prepared from AS4/3501-6 graphite-epoxy panels, instrumented with conventional strain gage rosettes and with a cross-line moire grating, and loaded in a convenient testing machine. The shear responses obtained for each test method and the two methods of specimen instrumentation were compared. In a second phase of the program the shear responses obtained from Iosipescu V-notch beam specimens were determined for woven fabric geometries of different weave and fiber architectures. Again the responses of specimens obtained from strain gage rosettes and moire interferometry were compared. Additional experiments were performed on a bidirectional cruciform specimen which was also instrumented with strain gages and a moire grating.
CRACK PROBLEM UNDER SHEAR LOADING IN CUBIC QUASICRYSTAL
周旺民; 范天佑; 尹姝媛
2003-01-01
The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function. Based on the work, the analytic solutions of elastic field of cubic quasicrystal with a penny-shaped crack under the shear loading are found, and the stress intensity factor and strain energy release rate are determined.
Price, Nancy A.; Song, Won Joon; Johnson, Scott E.; Gerbi, Christopher C.; Beane, Rachel J.; West, David P.
2016-07-01
Microstructural investigations were carried out on quartz veins in schist, protomylonite, and mylonite samples from an ancient seismogenic strike-slip shear zone (Sandhill Corner shear zone, Norumbega fault system, Maine, USA). We interpret complexities in the microstructural record to show that: (1) pre-existing crystallographic preferred orientations (CPO) in the host rock may persist in the new CPO patterns of the shear zone and (2) the inner and outer parts of the shear zone followed diverging paths of fabric development. The host rocks bounding the shear zone contain asymmetrically-folded quartz veins with a strong CPO. These veins are increasingly deformed and recrystallized with proximity to the shear zone core. Matrix-accommodated rotation and recrystallization may position an inherited c-axis maximum in an orientation coincident with rhomb or basal slip. This inherited CPO likely persists in the shear zone fabric as a higher concentration of poles in one hemisphere of the c-axis pole figure, leading to asymmetric crossed girdle or paired maxima c-axis patterns about the foliation plane. Three observed quartz grain types indicate a general trend of localization with decreasing temperature: (1) large (> 100 μm), low aspect ratio (<~5) and (2) high aspect ratio (~ 5-20) grains overprinted by (3) smaller (<~80 μm), low aspect ratio (<~4) grains through subgrain rotation-dominated recrystallization. In the outer shear zone, subgrain rotation recrystallization led to a well-developed c-axis crossed girdle pattern. In the inner shear zone, the larger grains are completely overprinted by smaller grains, but the CPO patterns are relatively poorly developed and are associated with distinctively different misorientation angle histogram profiles ("flat" neighbor-pair profile with similar number fraction for angles from 10 to 90°). This may reflect the preferential activation of grain size sensitive deformation processes in the inner-most part of the shear zone
Bodaghi, M.; Damanpack, A. R.; Liao, W. H.
2016-07-01
The aim of this article is to develop a robust macroscopic bi-axial model to capture self-accommodation, martensitic transformation/orientation/reorientation, normal-shear deformation coupling and asymmetric/anisotropic strain generation in polycrystalline shape memory alloys. By considering the volume fraction of martensite and its preferred direction as scalar and directional internal variables, constitutive relations are derived to describe basic mechanisms of accommodation, transformation and orientation/reorientation of martensite variants. A new definition is introduced for maximum recoverable strain, which allows the model to capture the effects of tension-compression asymmetry and transformation anisotropy. Furthermore, the coupling effects between normal and shear deformation modes are considered by merging inelastic strain components together. By introducing a calibration approach, material and kinetic parameters of the model are recast in terms of common quantities that characterize a uniaxial phase kinetic diagram. The solution algorithm of the model is presented based on an elastic-predictor inelastic-corrector return mapping process. In order to explore and demonstrate capabilities of the proposed model, theoretical predictions are first compared with existing experimental results on uniaxial tension, compression, torsion and combined tension-torsion tests. Afterwards, experimental results of uniaxial tension, compression, pure bending and buckling tests on {{NiTi}} rods and tubes are replicated by implementing a finite element method along with the Newton-Raphson and Riks techniques to trace non-linear equilibrium path. A good qualitative and quantitative correlation is observed between numerical and experimental results, which verifies the accuracy of the model and the solution procedure.
Nucleation of amorphous shear bands at nanotwins in boron suboxide
An, Qi; Reddy, K. Madhav; Qian, Jin; Hemker, Kevin J.; Chen, Ming-Wei; Goddard, William A., III
2016-03-01
The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics.
Macro and meso characteristics evolution on shear behavior of rock joints
李凯辉; 曹平; 张科; 钟涌芳
2015-01-01
Direct shear tests were conducted on the rock joints under constant normal load (CNL), while the acoustic emission (AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress−shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface,Sp (the maximum height of joint surface),N (number of islands),A (projection area) andV (volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient (JRC) and joint matching coefficient (JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.
Computational strain gradient crystal plasticity
Niordson, Christian Frithiof; Kysar, Jeffrey W.
2014-01-01
of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically...
Numerical simulation of systems of shear bands in ductile metal with inclusions
Plohr, JeeYeon N.; Plohr, Bradley J.
2016-02-01
We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands). This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127-139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31-41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211-220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.
Numerical simulation of systems of shear bands in ductile metal with inclusions
Plohr, JeeYeon N., E-mail: jplohr@lanl.gov; Plohr, Bradley J. [Los Alamos National Laboratory, Theoretical Division, Los Alamos, NM 87545 (United States)
2016-02-15
We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands). This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127–139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31–41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211–220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.
Powers, Philip S.
1983-01-01
This report is intended to provide internal documentation for the U.S. Geological Survey laboratory's automatic data acquisition system. The operating procedures for each type of test are designed to independently lead a first-time user through the various stages of using the computer to control the test. Continuing advances in computer technology and the availability of desktop microcomputers with a wide variety of peripheral equipment at a reasonable cost can create an efficient automated geotechnical testing environment. A geotechnical testing environment is shown in figure 1. Using an automatic data acquisition system, laboratory test data from a variety of sensors can be collected, and manually or automatically recorded on a magnetic device at the same apparent time. The responses of a test can be displayed graphically on a CRT in a matter of seconds, giving the investigator an opportunity to evaluate the test data, and to make timely, informed decisions on such matters as whether to continue testing, abandon a test, or modify procedures. Data can be retrieved and results reported in tabular form, or graphic plots, suitable for publication. Thermistors, thermocouples, load cells, pressure transducers, and linear variable differential transformers are typical sensors which are incorporated in automated systems. The geotechnical tests which are most practical to automate are the long-term tests which often require readings to be recorded outside normal work hours and on weekends. Automation applications include incremental load consolidation tests, constant-rate-of-strain consolidation tests, direct shear tests, ring shear tests, and triaxial shear tests.
Fillingham, Patrick; Murali, Harikrishnan
2016-11-01
Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field and the wall shear stress resulted from normally impinging axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle, while varying height to diameter ratio (H/D) and inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. The Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize the shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP2). Due to the jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime, wall shear stress is limited to a finite value. Additionally, formation of shock structures in the wall flow were observed for DJP>2 resulting in difficulties with dimensionless analysis. In the subsonic impingement and transitional regimes equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships wall shear stress can be predicted at all locations along the impingement surface.
Plasticity Approach to Shear Design
Hoang, Cao Linh; Nielsen, Mogens Peter
1998-01-01
The paper presents some plastic models for shear design of reinforced concrete beams. Distinction is made between two shear failure modes, namely web crushing and crack sliding. The first mentioned mode is met in beams with large shear reinforcement degrees. The mode of crack sliding is met in no...... in uncracked concrete. Good agree between theory and tests has been found.Keywords: dsign, plasticity, reinforced concrete, reinforcement, shear, web crushing.......The paper presents some plastic models for shear design of reinforced concrete beams. Distinction is made between two shear failure modes, namely web crushing and crack sliding. The first mentioned mode is met in beams with large shear reinforcement degrees. The mode of crack sliding is met in non......-shear reinforced beams as well as in lightly shear reinforced beams. For such beams the shear strength is determined by the recently developed crack sliding model. This model is based upon the hypothesis that cracks can be transformed into yield lines, which have lower sliding resistance than yield lines formed...
Research on the seismic performance of the low-yield-strength steel shear panel damper
山下, 友樹; 張, 超鋒; 青木, 徹彦
2012-01-01
A low-yield-strength steel shear panel damper (LYSPD) with 70% shear strain is developed and verified by static incremental cyclic tests in previous research. The mechanical properties and fatigue performance of the LYSPD deteriorate with the high temperature caused by high strain speed and internal friction in constant cyclic dynamic tests. To compare with the earthquake response wave, the deterioration mentioned above may be overestimated. Thus, this study is also seeking to develop a scien...
Comparison Of Direct Simple Shear Confinement Methods On Clay And Silt Specimens
2011-12-20
methods performed in the Marine Geomechanics Laboratory at the University of Rhode Island. In this chapter sample preparation, storage, equipment, and... Geomechanics Laboratory at the University of Rhode Island. Direct simple shear tests allow for the measurement of maximum horizontal shear stress of
Yielding of glass under shear: A directed percolation transition precedes shear-band formation
Shrivastav, Gaurav Prakash; Chaudhuri, Pinaki; Horbach, Jürgen
2016-10-01
Under external mechanical loading, glassy materials, ranging from soft matter systems to metallic alloys, often respond via formation of inhomogeneous flow patterns, during yielding. These inhomogeneities can be precursors to catastrophic failure, implying that a better understanding of their underlying mechanisms could lead to the design of smarter materials. Here, extensive molecular dynamics simulations are used to reveal the emergence of heterogeneous dynamics in a binary Lennard-Jones glass, subjected to a constant strain rate. At a critical strain, this system exhibits for all considered strain rates a transition towards the formation of a percolating cluster of mobile regions. We give evidence that this transition belongs to the universality class of directed percolation. Only at low shear rates, the percolating cluster subsequently evolves into a transient (but long-lived) shear band with a diffusive growth of its width. Finally, the steady state with a homogeneous flow pattern is reached. In the steady state, percolation transitions also do occur constantly, albeit over smaller strain intervals, to maintain the stationary plastic flow in the system.
Miao, Hongchen; Huan, Qiang; Li, Faxin
2016-11-01
The fundamental shear horizontal (SH0) wave in plate-like structures is of great importance in non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive, while excitation or reception of SH0 waves using piezoelectrics is always a challenge. In this work, we firstly demonstrate via finite element simulations that face-shear piezoelectrics is superior to thickness-shear piezoelectrics in driving SH waves. Next, by using a newly defined face-shear d24 PZT wafer as an actuator and face-shear d36 PMN-PT wafers as sensors, pure SH0 wave was successfully excited in an aluminum plate from 130 to 180 kHz. Then, it was shown that the face-shear d24 PZT wafer could receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120-230 kHz). The directionality of the excited SH0 wave was also investigated using face-shear d24 PZT wafers as both actuators and sensors. Results show that pure SH0 wave can be excited symmetrically along two orthogonal directions (0° and 90°) and the amplitude of the excited SH0 wave can keep over 90% of the maximum amplitude when the deviate angle is within 30°. This work could greatly promote the applications of SH0 wave in NDT and SHM.
Hansen, Christian Skodborg
-plane loaded walls and disks is however not included in any guidelines, and only a small fraction of scientists have initiated research within this topic. Furthermore, studies of the principal behavior and response of a strengthened disk has not yet been investigated satisfactorily, and this is the principal...... be altered to fit the surrounding boundary conditions. The effective cohesive law will then become a function of the investigated structural geometry. A simplified approach for the latter topic was used to predict the load capacity of concrete beams in shear. Results obtained were acceptable, but the model...
Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon
2017-01-25
Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12-16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications.
Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon
2017-01-01
Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12–16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications. PMID:28120921
Nonlinear Absolute Nodal Coordinate Formulation of a Flexible Beam Considering Shear Effect
LIU Jin-yang; SHEN Ling-jie; HONG Jia-zhen
2005-01-01
Nonlinear modeling of a flexible beam with large deformation was investigated. Absolute nodal cooridnate formulation is employed to describe the motion, and Lagrange equations of motion of a flexible beam are derived based on the geometric nonlinear theory. Different from the previous nonlinear formulation with EulerBernoulli assumption, the shear strain and transverse normal strain are taken into account. Computational example of a flexible pendulum with a tip mass is given to show the effects of the shear strain and transverse normal strain. The constant total energy verifies the correctness of the present formulation.
The genesis of adiabatic shear bands
Landau, P.; Osovski, S.; Venkert, A.; Gärtnerová, V.; Rittel, D.
2016-11-01
Adiabatic shear banding (ASB) is a unique dynamic failure mechanism that results in an unpredicted catastrophic failure due to a concentrated shear deformation mode. It is universally considered as a material or structural instability and as such, ASB is hardly controllable or predictable to some extent. ASB is modeled on the premise of stability analyses. The leading paradigm is that a competition between strain (rate) hardening and thermal softening determines the onset of the failure. It was recently shown that microstructural softening transformations, such as dynamic recrystallization, are responsible for adiabatic shear failure. These are dictated by the stored energy of cold work, so that energy considerations can be used to macroscopically model the failure mechanism. The initial mechanisms that lead to final failure are still unknown, as well as the ASB formation mechanism(s). Most of all - is ASB an abrupt instability or rather a gradual transition as would be dictated by microstructural evolutions? This paper reports thorough microstructural characterizations that clearly show the gradual character of the phenomenon, best described as a nucleation and growth failure mechanism, and not as an abrupt instability as previously thought. These observations are coupled to a simple numerical model that illustrates them.
Fluid migration in ductile shear zones
Fusseis, Florian; Menegon, Luca
2014-05-01
Fluid migration in metamorphic environments depends on a dynamically evolving permeable pore space, which was rarely characterised in detail. The data-base behind our understanding of the 4-dimensional transport properties of metamorphic rocks is therefore fragmentary at best, which leaves conceptual models poorly supported. Generally, it seems established that deformation is a major driver of permeability generation during regional metamorphism, and evidence for metamorphic fluids being channelled in large scale shear zones has been found in all depth segments of the continental crust. When strain localizes in ductile shear zones, the microfabric is modified until a steady state mylonite is formed that supports large deformations. A dynamic porosity that evolves during mylonitisation controls the distinct transport pathways along which fluid interacts with the rock. This dynamic porosity is controlled by a limited number of mechanisms, which are intrinsically linked to the metamorphic evolution of the rock during its deformational overprint. Many mid- and lower-crustal mylonites comprise polyphase mixtures of micron-sized grains that show evidence for deformation by dissolution/precipitation-assisted viscous grain boundary sliding. The establishment of these mineral mixtures is a critical process, where monomineralic layers are dispersed and grain growth is inhibited by the heterogeneous nucleation of secondary mineral phases at triple junctions. Here we show evidence from three different mid- and lower-crustal shear zones indicating that heterogeneous nucleation occurs in creep cavities. Micro- and nanotomographic observations show that creep cavities provide the dominant form of porosity in these ultramylonites. They control a "granular fluid pump" that directs fluid migration and hence mass transport. The granular fluid pump operates on the grain scale driven by viscous grain boundary sliding, and requires only small amounts of fluid. The spatial arrangement of
Techniques for forecasting and detecting a type of wind shear called microbursts are being tested this month in an operational program at Denver's Stapleton International Airport as part of an effort to reduce hazards to airplanes and passengers.Wind shear, which can be spawned by convective storms, can occur as a microburst. These downbursts of cool air are usually recognizable as a visible rain shaft beneath a thundercloud. Sometimes, however, the rain shaft evaporates before reaching the ground, leaving the downdraft invisible. Although thunderstorms are traditionally avoided by airplane pilots, these invisible downdrafts also harbor hazards in what usually appear to be safe skies. When the downdraft reaches the earth's surface, the downdraft spreads out horizontally, much like a stream of water gushing from a garden hose on a concrete surface, explained John McCarthy, director of the operational program. Airplanes can encounter trouble when the downdraft from the microburst causes sudden shifts in wind direction, which may reduce lift on the wing, an especially dangerous situation during takeoff.
In-shoe plantar tri-axial stress profiles during maximum-effort cutting maneuvers.
Cong, Yan; Lam, Wing Kai; Cheung, Jason Tak-Man; Zhang, Ming
2014-12-18
Soft tissue injuries, such as anterior cruciate ligament rupture, ankle sprain and foot skin problems, frequently occur during cutting maneuvers. These injuries are often regarded as associated with abnormal joint torque and interfacial friction caused by excessive external and in-shoe shear forces. This study simultaneously investigated the dynamic in-shoe localized plantar pressure and shear stress during lateral shuffling and 45° sidestep cutting maneuvers. Tri-axial force transducers were affixed at the first and second metatarsal heads, lateral forefoot, and heel regions in the midsole of a basketball shoe. Seventeen basketball players executed both cutting maneuvers with maximum efforts. Lateral shuffling cutting had a larger mediolateral braking force than 45° sidestep cutting. This large braking force was concentrated at the first metatarsal head, as indicated by its maximum medial shear stress (312.2 ± 157.0 kPa). During propulsion phase, peak shear stress occurred at the second metatarsal head (271.3 ± 124.3 kPa). Compared with lateral shuffling cutting, 45° sidestep cutting produced larger peak propulsion shear stress (463.0 ± 272.6 kPa) but smaller peak braking shear stress (184.8 ± 181.7 kPa), of which both were found at the first metatarsal head. During both cutting maneuvers, maximum medial and posterior shear stress occurred at the first metatarsal head, whereas maximum pressure occurred at the second metatarsal head. The first and second metatarsal heads sustained relatively high pressure and shear stress and were expected to be susceptible to plantar tissue discomfort or injury. Due to different stress distribution, distinct pressure and shear cushioning mechanisms in basketball footwear might be considered over different foot regions.
On strain and stress in living cells
Cox, Brian N.; Smith, David W.
2014-11-01
in detail. However, estimates can be inferred from the known relative velocities of the cells' centers of mass. When averaged over a volume comparable to the cell size, representative values of the strain are, to order of magnitude, ɛ0≈0.1 and γ0≈0.1. The shape distortions of cells seen, for example, in Fig. 1c, imply peak strains in minor segments of a cell of magnitude unity, ɛ0≈1 and γ0≈1; these values represent the upper bound of plausible values and are included for discussion of the extremes of attainable strain energy rates.Given the strain magnitudes, the strain rates follow from the fact that a cell switches from one contacting neighbor in the adjacent row to the next in approximately 0.25 d, during which motion the strains might vary from zero to their maximum values and back again. Thus the most probable shear strain rate is inferred to be γ˙0=10-6 s-1 and the most probable tensile strain rate is inferred to be ɛ˙0≈10-6 s-1, with high bounds γ˙0=10-5 s-1 and ɛ˙0=10-5 s-1.
Effects of induced shear deformation on microstructure and texture evolution in CP-Ti rolled sheets
Milner, Justin L. [Department of Automotive Engineering, Clemson University, Greenville, SC 29607 (United States); Abu-Farha, Fadi, E-mail: FADI@clemson.edu [Department of Automotive Engineering, Clemson University, Greenville, SC 29607 (United States); Kurfess, Thomas [School of Mechanical Engineering, Georgia Institute of Technology, GA 30332 (United States); Hammond, Vincent H. [US Army Research Laboratory, Aberdeen Proving Ground, MD 21005 (United States)
2014-12-01
Commercial pure titanium sheets were deformed by shear rolling at 400 °C with subsequent annealing to investigate microstructure and texture evolution along with its effects on the mechanical properties. A four sheet multilayer rolling scheme was used to isolate shear strains within the outer sheets, termed isolated shear rolling (ISR), thus allowing for direct comparison between shear strained material (outer sheets) and plane-strained material under similar conditions. Microstructure and texture evolution were investigated by electron backscatter diffraction analysis, while mechanical properties were evaluated through tensile testing aided by digital image correlation (DIC). Texture was seen to evolve from a ±30° transverse direction (TD) split basal texture to primarily basal texture (〈0001〉//Normal Direction) for the shear-strained sheets, in comparison with a slight rotation to a ±20° TD-split for the plane-strained sheets. After short-term annealing at 600 °C for 15 min, texture remained similar to that of the as-processed material yet at lower intensity levels. Compared to the base material, shear-rolled material showed much higher Lankford Coefficient values, with a significant boost attributed to shear deformation. The greater stretch formability is achieved in the shear-rolled material by rotation of the basal poles to become parallel to the sheet thickness. The results obtained here with ISR in regards to the effects of inducing higher shear strains on the rolled material are comparable to those reported in the literature by differential speed rolling (DSR)
Inductive shearing of drilling pipe
Ludtka, Gerard M.; Wilgen, John; Kisner, Roger; Mcintyre, Timothy
2016-04-19
Induction shearing may be used to cut a drillpipe at an undersea well. Electromagnetic rings may be built into a blow-out preventer (BOP) at the seafloor. The electromagnetic rings create a magnetic field through the drillpipe and may transfer sufficient energy to change the state of the metal drillpipe to shear the drillpipe. After shearing the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.
Inductive shearing of drilling pipe
Ludtka, Gerard M.; Wilgen, John; Kisner, Roger; Mcintyre, Timothy
2016-04-19
Induction shearing may be used to cut a drillpipe at an undersea well. Electromagnetic rings may be built into a blow-out preventer (BOP) at the seafloor. The electromagnetic rings create a magnetic field through the drillpipe and may transfer sufficient energy to change the state of the metal drillpipe to shear the drillpipe. After shearing the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.
Optimal disturbances in shearing and swirling flows
Daly, Conor
2011-11-01
Over the past twenty years transient energy density growth of linearly stable disturbances has shown to be the likely instigator for transition to turbulence in parallel shear flows. In this vein, optimal linear perturbations are calculated for two flows which have a mixture of forces acting on the fluid body. These are; rotating plane Couette flow (RPCF), which combines pressure-driven shear and swirl, and cylindrical Couette-Poiseuille flow (CCPF), which combines pressure-driven and Couette shear. Contours are presented of the maximum achievable linear transient growth, G, over the full range of wavenumbers within the linearly stable parameter regimes. Reference is made to experimental works on each flow and we examine the role that optimal disturbances have in the different transition phenomena that are observed. It is found that the contours of G fall qualitatively alongside the points of transition in the two flows, in support of the notion that large linear transient growth can act a precursor to transition. Despite the combination of effects acting on each fluid, transition in both flows falls in the range 102 flows the same mechanism may be at work. This work is funded by EPSRC.
Dyess, Jonathan
This dissertation is a multi-scale structural and kinematic analysis of the Shagawa Lake shear zone in northeastern Minnesota (USA). The Neoarchean Shagawa Lake shear zone is an ~70 km long ~7 km wide subvertical package of L-S tectonites located within the Wawa Subprovince of the Archean Superior Province. In this dissertation, I (1) discuss a new method for mapping regional tectonic fabrics using high-resolution LiDAR altimetry data; (2) examine the geometric relationships between metamorphic foliation, elongation lineation, vorticity, and non-coaxial shear direction within individual L-S tectonites; and (3) incorporate LiDAR, field, and microstructural data sets into a comprehensive structural and kinematic analysis of the Western Shagawa Lake shear zone. Lastly, I discuss implications for assembly of the southern Superior Province. In Chapter one I examine an Archean granite-greenstone terrane in NE Minnesota to illustrate the application of high-resolution LiDAR altimetry to mapping regional tectonic fabrics in forested, glaciated areas. I describe the recognition of lineaments and distinguishing between tectonic and glacial lineament fabrics. I use a 1-m posted LiDAR derived bare-earth digital elevation model (DEM) to construct multiple shaded-relief images for lineament mapping with sun elevation of 45˚ and varying sun azimuth in 45˚ intervals. Two suites of lineaments are apparent. Suite A has a unimodal orientation, mean trend of 035, and consists of short (> 2 km long) lineaments within sediment deposits and bedrock. Suite B lineaments, which are longer (1-30 km) than those of suite A, have a quasi-bimodal orientation distribution, with maximum trends of 065 and 090. Only one lineament suite is visible in areas where suites A and B are parallel. I interpret suite A as a surficial geomorphologic fabric related to recent glaciation, and suite B as a proxy for the regional tectonic fabric. In Chapter two I present a detailed kinematic study of seven
Correa-Gomes, Luiz Cesar [Centro Federal de Educacao Tecnologica da Bahia, Salvador, BA (Brazil). Dept. de Ciencias Aplicadas; Universidade Federal da Bahia (UFBA), Salvador (Brazil). Inst. de Geociencias. Dept. de Geologia]. E-mails: gomes@cefetba.br, lccgomes@ufba.br; Dominguez, Jose Maria Landim; Barbosa, Johildo Salomao Figueiredo; Silva, Idney Cavalcanti da; Pinto, Moises Vieira [Universidade Federal da Bahia (UFBA), Campus de Ondina, Salvador (Brazil). Inst. de Geociencias. Dept. de Geologia]. E-mails: jose_landim@uol.com.br; johildo@cpgg.ufba.br; idney25@ig.com.br; geofisica.ufba@gmail.com
2005-12-15
The Almada Basin is a geometric out-pattern member in the group the onshore coastline sedimentary basins of the Bahia State and neighborhoods. This basin differs from the traditional elongated-shape trending Camamu and Reconcavo-Tucano-Jatoba basins, and shows a compact rhombohedral arrangement following N45 deg, N90 deg, N120 deg e N-S structural lineaments. This shape directly or indirectly reflects a specific geological history influenced by the paleoproterozoic and neo proterozoic orogeny, neo proterozoic shear zones and mesozoic super continent break-up. Several sets of fault and fractures were kinematically studied inside and around the basin, and the main stress tensors obtained using inversion methods. The structural study of the Almada Basin allowed to recognize that: the initial tectonic activity was controlled by normal faults, with orthorhombic-rhombohedral 3-D extensional strain pattern, followed by trans tensional ones characterizing the Almada Basin as a poly phasic tectonic basin, and during the transtensive phase this basin was affected by at least two almost orthogonal extensional events, indicating a possible {sigma}{sub 1} orientation inversion during its formation and tectonic evolution. These data are crucial for prospecting groundwater and hydrocarbon in the basin onshore and offshore areas. (author)
Influence of shear velocity on frictional characteristics of rock surface
T N Singh; A K Verma; Tanmay Kumar; Avi Dutt
2011-02-01
Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate of strain under normal loads was observed. Friction at the interface of the rock samples was developed by increasing shear strain at a constant rate by applying constant velocity using the tribometer. For shaly sandstone, state parameters ( and ) played a major role in determining the friction values and roughness of the contact surfaces as well. Higher values of for shaly sandstone may be attributed to the fact that its surface had a greater number of pronounced asperities. Rubbing between the surfaces does not mean that surface becomes smoother. This is because of variation of friction between surfaces.
Behaviour of voids in a shear field
Tvergaard, Viggo
2009-01-01
to a plane connecting the ends of the micro-crack is used as an approximate representation of contact stresses during frictionless sliding. In a previous study of the same problem the author applied hydrostatic pressure inside the nearly closed micro-crack to approximate contact conditions. The transverse...... surface loads used in the present analyses avoid the tendency to unrealistically elongate the voids. It is found that even though the model applied here gives significantly later occurrence of a maximum overall shear stress than that found by using hydrostatic pressure, the present model does predict...... a maximum in all the cases analyzed and thus illustrates the micro-mechanism leading to failure of the material by localization of plastic flow....
Multiplicative earthquake likelihood models incorporating strain rates
Rhoades, D. A.; Christophersen, A.; Gerstenberger, M. C.
2017-01-01
SUMMARYWe examine the potential for strain-rate variables to improve long-term earthquake likelihood models. We derive a set of multiplicative hybrid earthquake likelihood models in which cell rates in a spatially uniform baseline model are scaled using combinations of covariates derived from earthquake catalogue data, fault data, and strain-rates for the New Zealand region. Three components of the strain rate estimated from GPS data over the period 1991-2011 are considered: the shear, rotational and dilatational strain rates. The hybrid model parameters are optimised for earthquakes of M 5 and greater over the period 1987-2006 and tested on earthquakes from the period 2012-2015, which is independent of the strain rate estimates. The shear strain rate is overall the most informative individual covariate, as indicated by Molchan error diagrams as well as multiplicative modelling. Most models including strain rates are significantly more informative than the best models excluding strain rates in both the fitting and testing period. A hybrid that combines the shear and dilatational strain rates with a smoothed seismicity covariate is the most informative model in the fitting period, and a simpler model without the dilatational strain rate is the most informative in the testing period. These results have implications for probabilistic seismic hazard analysis and can be used to improve the background model component of medium-term and short-term earthquake forecasting models.
An Experimental Study of Shear-Dominated Failure in the 2013 Sandia Fracture Challenge Specimen
Corona, Edmundo [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Deibler, Lisa Anne [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Reedlunn, Benjamin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ingraham, Mathew Duffy [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Williams, Shelley [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-04-01
This report presents an experimental study motivated by results obtained during the 2013 Sandia Fracture Challenge. The challenge involved A286 steel, shear-dominated compression specimens whose load-deflection response contained a load maximum fol- lowed by significant displacement under decreasing load, ending with a catastrophic fracture. Blind numerical simulations deviated from the experiments well before the maximum load and did not predict the failure displacement. A series of new tests were conducted on specimens machined from the original A286 steel stock to learn more about the deformation and failure processes in the specimen and potentially improve future numerical simulations. The study consisted of several uniaxial tension tests to explore anisotropy in the material, and a set of new tests on the compression speci- men. In some compression specimen tests, stereo digital image correlation (DIC) was used to measure the surface strain fields local to the region of interest. In others, the compression specimen was loaded to a given displacement prior to failure, unloaded, sectioned, and imaged under the microscope to determine when material damage first appeared and how it spread. The experiments brought the following observations to light. The tensile tests revealed that the plastic response of the material is anisotropic. DIC during the shear- dominated compression tests showed that all three in-plane surface strain components had maxima in the order of 50% at the maximum load. Sectioning of the specimens revealed no signs of material damage at the point where simulations deviated from the experiments. Cracks and other damage did start to form approximately when the max- imum load was reached, and they grew as the load decreased, eventually culminating in catastrophic failure of the specimens. In addition to the steel specimens, a similar study was carried out for aluminum 7075-T651 specimens. These specimens achieved much lower loads and displacements
Fahrudin Fahrudin
2012-02-01
Full Text Available The deformation mechanisme in ductile – transition zone show microfracture cataclasis activities,intracrystalline deformations, twinning, kinking, solid-sate diffusion creep, recovery and recrystallisation. Thatactivities to extend the sense shear indication. Sense shear can see i.e porfiroclast, mica fish, porfiroblast, veins,strain shadow, strain fringe and boudin. Commonly sense shear indications to get the form of ellipsoid geometry.That geometry experience to development the structure along progressive deformations process. Thedevelopment of inclusion and fabric also occur at that process.
Shear strength of non-shear reinforced concrete elements
Hoang, Cao linh
1997-01-01
The paper deals with the shear strength of prestressed hollow-core slabs determined by the theory of plasticity. Two failure mechanisms are considered in order to derive the solutions.In the case of sliding failure in a diagonal crack, the shear strength is determined by means of the crack sliding...
Shear strength of non-shear reinforced concrete elements
Hoang, Cao linh
1997-01-01
The report deals with the shear strength of statically indeterminate reinforced concrete beams without shear reinforcement. Solutions for a number of beams with different load and support conditions have been derived by means of the crack sliding model developed by Jin- Ping Zhang.This model...
WANG Xue-bin
2007-01-01
To consider the effects of the interactions and interplay among microstructures, gradient-dependent models of second- and fourth-order are included in the widely used phenomenological Johnson-Cook model where the effects of strain-hardening, strain rate sensitivity, and thermal-softening are successfully described. The various parameters for 1006 steel, 4340 steel and S-7 tool steel are assigned. The distributions and evolutions of the local plastic shear strain and deformation in adiabatic shear band (ASB) are predicted. The calculated results of the second- and fourth-order gradient plasticity models are compared. S-7 tool steel possesses the steepest profile of local plastic shear strain in ASB, whereas 1006 steel has the least profile. The peak local plastic shear strain in ASB for S-7 tool steel is slightly higher than that for 4340 steel and is higher than that for 1006 steel. The extent of the nonlinear distribution of the local plastic shear deformation in ASB is more apparent for the S-7 tool steel, whereas it is the least apparent for 1006 steel. In fourth-order gradient plasticity model, the profile of the local plastic shear strain in the middle of ASB has a pronounced plateau whose width decreases with increasing average plastic shear strain, leading to a shrink of the portion of linear distribution of the profile of the local plastic shear deformation. When compared with the second-order gradient plasticity model, the fourth-order gradient plasticity model shows a lower peak local plastic shear strain in ASB and a higher magnitude of plastic shear deformation at the top or base of ASB, which is due to wider ASB. The present numerical results of the second- and fourth-order gradient plasticity models are consistent with the previous numerical and experimental results at least qualitatively.
王学滨; 唐巨鹏; 张智慧
2004-01-01
The paper concerns the issue of size law, localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band, and based on gradient-dependent plasticity, an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen, the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain, the dilation and compaction within shear band are analyzed.Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.
Flexible Micropost Arrays for Shear Stress Measurement
Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.
2015-01-01
Increased fuel costs, heightened environmental protection requirements, and noise abatement continue to place drag reduction at the forefront of aerospace research priorities. Unfortunately, shortfalls still exist in the fundamental understanding of boundary-layer airflow over aerodynamic surfaces, especially regarding drag arising from skin friction. For example, there is insufficient availability of instrumentation to adequately characterize complex flows with strong pressure gradients, heat transfer, wall mass flux, three-dimensionality, separation, shock waves, and transient phenomena. One example is the acoustic liner efficacy on aircraft engine nacelle walls. Active measurement of shear stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current shear stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant shear stress data. The state-of-the-art for shear stress sensing uses indirect or direct measurement techniques. Indirect measurements (e.g., hot-wire, heat flux gages, oil interferometry, laser Doppler anemometry, small scale pressure drag surfaces, i.e., fences) require intricate knowledge of the studied flow, restrictive instrument arrangements, large surface areas, flow disruption, or seeding material; with smaller, higher bandwidth probes under development. Direct measurements involve strain displacement of a sensor element and require no prior knowledge of the flow. Unfortunately, conventional "floating" recessed components for direct measurements are mm to cm in size. Whispering gallery mode devices and Fiber Bragg Gratings are examples of recent additions to this type of sensor with much smaller (?m) sensor components. Direct detection techniques are often single point measurements and difficult to calibrate and implement in wind tunnel experiments. In addition, the wiring, packaging, and installation
Simulation of Random Waves and Associated Laminar Bottom Shear Stresses
Mao-Lin SHEN; Ching-Jer HUANG
2008-01-01
This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundary conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves are determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the numerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug's model (1995). The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.
The Critical Criterion on Runaway Shear Banding in Metallic Glasses
Sun, B. A.; Yang, Y.; Wang, W. H.; Liu, C. T.
2016-02-01
The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures.
Effect of different lateral occlusion schemes on peri-implant strain: A laboratory study
Lo, Jennifer; Palamara, Joseph
2017-01-01
PURPOSE This study aims to investigate the effects of four different lateral occlusion schemes and different excursions on peri-implant strains of a maxillary canine implant. MATERIALS AND METHODS Four metal crowns with different occlusion schemes were attached to an implant in the maxillary canine region of a resin model. The included schemes were canine-guided (CG) occlusion, group function (GF) occlusion, long centric (LC) occlusion, and implant-protected (IP) occlusion. Each crown was loaded in three sites that correspond to maximal intercuspation (MI), 1 mm excursion, and 2 mm excursion. A load of 140 N was applied on each site and was repeated 10 times. The peri-implant strain was recorded by a rosette strain gauge that was attached on the resin model buccal to the implant. For each loading condition, the maximum shear strain value was calculated. RESULTS The different schemes and excursive positions had impact on the peri-implant strains. At MI and 1 mm positions, the GF had the least strains, followed by IP, CG, and LC. At 2 mm, the least strains were associated with GF, followed by CG, LC, and IP. However, regardless of the occlusion scheme, as the excursion increases, a linear increase of peri-implant strains was detected. CONCLUSION The peri-implant strain is susceptible to occlusal factors. The eccentric location appears to be more influential on peri-implant strains than the occlusion scheme. Therefore, adopting an occlusion scheme that can reduce the occurrence of occlusal contacts laterally may be beneficial in reducing peri-implant strains. PMID:28243391
Microstructure evolution mechanism in adiabatic shear band in TA2
杨扬; 熊俊; 杨续跃
2004-01-01
The micro structure evolution mechanism in adiabatic shear band in commercial pure titanium (TA2) at high strain rates(γ≈105 - 106/s) were studied. The nanosized recrystallized grains (about 50 nm in diameter) within the center of adiabatic shear band (ASB) were observed by means of transmission electronic microscope (TEM). A Rotational Dynamic Recrystallization (RDR) mechanism can explain the microstructure evolution (i. e. nanosized grains were formed within 5 - 10μs) in ASB. Kinetics calculations indicate that the recrystallized small grains are formed during the deformation and don't undergo significant growth by grain boundary migration after deformation.
Electroosmotic shear flow in microchannels
Mampallil, Dileep; Ende, van den Dirk
2013-01-01
We generate and study electroosmotic shear flow in microchannels. By chemically or electrically modifying the surface potential of the channel walls a shear flow component with controllable velocity gradient can be added to the electroosmotic flow caused by double layer effects at the channel walls.
Dynamic material strength measurement utilizing magnetically applied pressure-shear
Alexander C.S.
2012-08-01
Full Text Available Magnetically applied pressure-shear (MAPS is a recently developed technique used to measure dynamic material strength developed at Sandia National Laboratories utilizing magneto-hydrodynamic (MHD drive pulsed power systems. MHD drive platforms generate high pressures by passing a large current through a pair of parallel plate conductors which, in essence, form a single turn magnet coil. Lorentz forces resulting from the interaction of the self-generated magnetic field and the drive current repel the plates and result in a high pressure ramp wave propagating in the conductors. This is the principle by which the Sandia Z Machine operates for dynamic material testing. MAPS relies on the addition of a second, external magnetic field applied orthogonally to both the drive current and the self-generated magnetic field. The interaction of the drive current and this external field results in a shear wave being induced directly in the conductors. Thus both longitudinal and shear stresses are generated. These stresses are coupled to a sample material of interest where shear strength is probed by determining the maximum transmissible shear stress in the state defined by the longitudinal compression. Both longitudinal and transverse velocities are measured via a specialized velocity interferometer system for any reflector (VISAR. Pressure and shear strength of the sample are calculated directly from the VISAR data. Results of tests on several materials at modest pressures (∼10GPa will be presented and discussed.
Mizuno, H; Yamamoto, R
2012-04-01
A steady shear flow can drive supercooled liquids into a non-equilibrium state. Using molecular dynamics simulations under steady shear flow superimposed with oscillatory shear strain for a probe, non-equilibrium mechanical responses are studied for a model supercooled liquid composed of binary soft spheres. We found that even in the strongly sheared situation, the supercooled liquid exhibits surprisingly isotropic responses to oscillating shear strains applied in three different components of the strain tensor. Based on this isotropic feature, we successfully constructed a simple two-mode Maxwell model that can capture the key features of the storage and loss moduli, even for highly non-equilibrium state. Furthermore, we examined the correlation functions of the shear stress fluctuations, which also exhibit isotropic relaxation behaviors in the sheared non-equilibrium situation. In contrast to the isotropic features, the supercooled liquid additionally demonstrates anisotropies in both its responses and its correlations to the shear stress fluctuations. Using the constitutive equation (a two-mode Maxwell model), we demonstrated that the anisotropic responses are caused by the coupling between the oscillating strain and the driving shear flow. Due to these anisotropic responses and fluctuations, the violation of the fluctuation-dissipation theorem (FDT) is distinct for different components. We measured the magnitude of this violation in terms of the effective temperature. It was demonstrated that the effective temperature is notably different between different components, which indicates that a simple scalar mapping, such as the concept of an effective temperature, oversimplifies the true nature of supercooled liquids under shear flow. An understanding of the mechanism of isotropies and anisotropies in the responses and fluctuations will lead to a better appreciation of these violations of the FDT, as well as certain consequent modifications to the concept of an
Effects of Magnetic Shear on Ion-Cyclotron Modes.
Ganguli, Gurudas
Effects of Magnetic Shear on electrostatic Ion -Bernstein Modes (IBM) are examined. Shear affects the mode structure in 3 principal ways: (i) Local effect, (ii) Global effect and (iii) Orbital effect. The role of shear at the above three levels is investigated for IBM in general and in the context of parametric instability of two Ion-Bernstein modes by a magnetosonic wave in a multispecies plasma in particular. An improved marginal stability criterion is presented at Local and Global levels and the region where the Orbital effects are influential is defined and discussed. An electron drift relative to the ions is introduced parallel to the external magnetic field giving rise to Current Driven Ion Cyclotron Instability (CDICI). An improved theory of CDICI in a sheared magnetic field is given. For temperature ratios (tau) = T(,i)/T(,e) > .25, the imaginary part of the local dispersion relation, (as a function of k(,(PARLL)) (('x)), the local parallel wavevector), can be approximated by a parabola, while for weaker (tau) it can be approximated by a pair of straight lines; in each case a second order differential equation is solved for complex roots, (omega). Growth rates ((gamma)/(OMEGA)), are plotted against the square of the normalized pependicular wavevector ((TURN)b) for various values of shear, temperature ratios and electron drift strengths. The main effect of shear is to localize this instability in x-space around some x(,0) such that k(,(PARLL))('0) = ('s)k(,y)x(,0), (('s) being inverse shear length), corresponds to the ((gamma)/(OMEGA))(,max) in the absence of shear. Shear also reduces the growth rate in general: however, ((gamma)/(OMEGA)) for the b values away from the value corresponding to the maximum growth rate are affected more than those which are closer, thereby making the instability more coherent in b. Operator methods employing the Vlasov operator to obtain orbits and velocities in external magnetic fields are studied. Particle orbits and
Shojaaee, Zahra; Roux, Jean-Noël; Chevoir, François; Wolf, Dietrich E
2012-07-01
We report on a numerical study of the shear flow of a simple two-dimensional model of a granular material under controlled normal stress between two parallel smooth frictional walls moving with opposite velocities ± V. Discrete simulations, which are carried out with the contact dynamics method in dense assemblies of disks, reveal that, unlike rough walls made of strands of particles, smooth ones can lead to shear strain localization in the boundary layer. Specifically, we observe, for decreasing V, first a fluidlike regime (A), in which the whole granular layer is sheared, with a homogeneous strain rate except near the walls, then (B) a symmetric velocity profile with a solid block in the middle and strain localized near the walls, and finally (C) a state with broken symmetry in which the shear rate is confined to one boundary layer, while the bulk of the material moves together with the opposite wall. Both transitions are independent of system size and occur for specific values of V. Transient times are discussed. We show that the first transition, between regimes A and B, can be deduced from constitutive laws identified for the bulk material and the boundary layer, while the second one could be associated with an instability in the behavior of the boundary layer. The boundary zone constitutive law, however, is observed to depend on the state of the bulk material nearby.
Leahy, Brian; Ong, Desmond; Cheng, Xiang; Cohen, Itai
2013-03-01
The idea of Taylor dispersion - enhancement of translational diffusion under shear - has found applications in fields from pharmacology to chemical engineering. Here, in a combination of experiment and simulations, we study the translational and rotational diffusion of colloidal dimers under triangle-wave oscillatory shear. We find that the rotational diffusion is enhanced, in addition to the enhanced translational diffusion. This ``rotational Taylor dispersion'' depends strongly on the strain rate (Peclet number), aspect ratio, and the shear strain, in contradistinction to translational Taylor dispersion in a shear flow, which depends only weakly on strain rate and aspect ratio. This separate tunability of translations and orientations promises important applications in mixing and self-assembly of solutions of anisometric colloids. We discuss the corresponding effect on the structure and rheology of denser suspensions of rod-like particles. B. L. acknowledges supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.
Maximum-likelihood cluster recontruction
Bartelmann, M; Seitz, S; Schneider, P J; Bartelmann, Matthias; Narayan, Ramesh; Seitz, Stella; Schneider, Peter
1996-01-01
We present a novel method to recontruct the mass distribution of galaxy clusters from their gravitational lens effect on background galaxies. The method is based on a least-chisquare fit of the two-dimensional gravitational cluster potential. The method combines information from shear and magnification by the cluster lens and is designed to easily incorporate possible additional information. We describe the technique and demonstrate its feasibility with simulated data. Both the cluster morphology and the total cluster mass are well reproduced.
A Piezoelectric Shear Stress Sensor
Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning
2016-01-01
In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry
Patricio, P; Portela, R; Sobral, R G; Grilo, I R; Cidade, T; Leal, C R
2014-01-01
The activity of growing living bacteria was investigated using real-time and in situ rheology -- in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell wall autolysis mutant -- were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the two strains follow different and rich behaviours, with no counterpart in the optical density or in the population's colony forming units measurements. While the viscosity of strain COL keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain ...
METHOD FOR CALCULATION OF STRESS-STRAIN STATE DUE TO SINGLE TWIN IN GRAIN OF VARIOUS FORMS
T. V. Drabysheuskaya
2016-01-01
Full Text Available The paper investigates a stress-strain state in a polycrystalline grain due to presence in its body of a single micro- twin in case of various grain boundary forms. A methodology for calculation of displacement and stress fields for the specified stress-strain state of a polygon-shaped grain has been developed in the paper. Nodal points in a polycrystalline grain that have a maximum stresses contributing to initiation of destruction have been revealed in the paper. The aim of this work has been to study the stress-strain state due to a single micro-twin in the polycrystalline grain and form of grain boundaries. The paper describes polycrystalline grains having a regular polygon shape and containing a single wedge twin in their body. Polycrystalline grain boundaries are presented as walls with complete dislocation. The investigated grains are located far from the surface of twinning material. The developed methodology for calculation of displacement and stresses created by wedge twin is based on the principle of superposition. Calculations on stress tensor components have been carried out for iron (Fe. The presented results of calculations for stress fields have indicated to validity of the used dislocation model. Twin and grain boundaries being stress concentrators are clearly visible on the obtained distributions of stress fields. Maximum normal stresses are observed on the twin boundaries; σxy maximum shear stresses are located at nodal points of the twin; σzy and σxz shear stresses are maximum on the grain boundaries. The conducted investigations have resulted in study of the stress-strain state due to a single wedge-shaped micro-twin in the polycrystalline grain and form of the grain boundaries. Zones of stress concentration in the polycrystalline grain have been identified in the presence of residual mechanical wedge twin. A method for evaluation of the given state has been developed in the paper.
2015-03-12
to connect to a signal conditioner 200 (See FIG. 6). The deformable ring 102 may be constructed from conventional materials (metal, composite...plastic etc.) or with piezoelectric ceramics. If the ring 102 is constructed with piezoelectric ceramics, the ring itself is the sensor; therefore...elements used (i.e., resistance strain gages, fiber optic Bragg grating or piezoelectric material ), an output is generated (i.e., resistance
MM98.83 Quantification of Combined Strain Paths
Nielsen, Morten Sturgård; Lindegren, Maria; Wanheim, Tarras
1998-01-01
When working with processes where large plastic deformation occurs, a way of desribing the deformation process is to view the whole deformation history as a curve in the 6-dimensional shear strain normal strain space, henceforth called a strain history curve (SHC). This paper focuses on the SHC...
What can we Learn From Small Non-Recoverable Strains at Plate Boundaries?
Lewis, J. C.; Pluhar, C. J.
2003-12-01
Background seismicity carries often overlooked information about how the crust responds to plate motions. Integrating focal mechanisms for background seismicity with (1) geologic observations, and (2) geodetic constraints, is critical to establishing a better understanding of both the rock record and contemporary deformation. Treating the crust as a micropolar continuum it is possible to constrain not only the orientations and relative magnitudes of the principal strains but also the vorticity of crustal blocks with respect to the large-scale continuum. We show the utility of this approach with examples from the Cascadia margin and the Coso Range (within the Eastern California shear zone). In the upper crust of the Cascadia margin, seismogenic strain appears to be dominated by accommodation of motion of the Oregon forearc block. This suggests that the shallow crust is responding to long-term motion of the Oregon forearc rather than the interseismic locking of the subduction megathrust. In the area west of Mt. Rainier, this response is marked by non-zero relative vorticity in a regime of N-S shortening and crustal thickening. To date, geologic studies necessary to evaluate the significance of this vorticity have not been completed. In contrast within the Coso Range of California, seismogenic strain at Wild Horse Mesa indicates a component of relative vorticity that is broadly consistent with paleomagnetically constrained finite rotations of the ca. 3 Ma lava flows that compose the mesa. This area is centered at a right-releasing step in the Eastern California shear zone and thus is experiencing active transtension. Stratigraphic constraints have been used to suggest that significant dextral shearing in this region initiated ca. 3.5-2 Ma. The seismogenic response to transtension is depth-dependent plane strain with crustal thinning above 5 km and horizontal dextral shearing from 5-8 km. Both structural levels indicate subhorizontal E-W maximum stretching. Relative
Fluid Effects on Shear for Seismic Waves in Finely Layered Porous Media
Berryman, J G
2004-07-22
Although there are five effective shear moduli for any layered VTI medium, one and only one effective shear modulus of the layered system (namely the uniaxial shear) contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized shear waves. Pore fluids can increase the magnitude the shear energy stored in this modulus by an amount that ranges from the smallest to the largest effective shear moduli of the VTI system. But, since there are five shear moduli in play, the overall increase in shear energy due to fluids is reduced by a factor of about 5 in general. We can therefore give definite bounds on the maximum increase of overall shear modulus, being about 20% of the allowed range as liquid is fully substituted for gas. An attendant increase of density (depending on porosity and fluid density) by approximately 5 to 10% decreases the shear wave speed and, thereby, partially offsets the effect of this shear modulus increase. The final result is an increase of shear wave speed on the order of 5 to 10%. This increase is shown to be possible under most favorable circumstances - i.e. when the shear modulus fluctuations are large (resulting in strong anisotropy) and the medium behaves in an undrained fashion due to fluid trapping. At frequencies higher than seismic (such as sonic and ultrasonic waves for well-logging or laboratory experiments), resulting short response times also produce the requisite undrained behavior and, therefore, fluids also affect shear waves at high frequencies by increasing rigidity.
彭凯; 朱俊高; 冯树荣; 蔡昌光; 朱晟
2013-01-01
The mechanical behaviors of the interface between coarse-grained soil and concrete are investigated by simple shear tests under conditions of cemented soil slurry (clay mixed with cement grout).The results show that the relation curve between shear stress and shear strain appears stress-strain softening and shear dilatation is significant.The point of peak strength and the position when the shear dilatation occurs are related to normal stress.In addition,shear dilatation occurs before the shear stress reaches peak value.In shear failure state,with the same height,the shear displacement increases as the normal stress increases.While with the same normal stress and at the same height,the shear displacement increases as the concrete content increases.A particle flow model of simple shear test between interface between coarse-grained soil and concrete is constructed by PFC (particle flow code).The disturbed height of the sample and the main influence factors are determined by analyzing the laws of particle motion at different heights inside the sample.The PFC results show disturbed height of the sample is related to maximum particle diameter of the soil,normal stress and roughness of the interface (with or without slurry) etc.In terms of the coarse-grained soil,the shear displacement is significant in the area which is close to the interface and about 3-4 times of the maximum particle diameter,and informed the obvious shear band.Further,the thickness of the interface can be regarded as the value.%采用大型单剪仪进行粗粒土与混凝土接触面在水泥土泥皮(粘土中掺入水泥)条件下的剪切试验,揭示泥皮条件下接触面的力学特性与机理.试验结果表明,峰值强度以及剪胀发生所对应的位置与法向应力大小有关,峰值强度所对应的剪应变滞后于产生剪胀的位置.剪切破坏时,在同一高度处,法向应力越大,切向位移也越大；同样的法向应力及高度处,切向位移随水泥含
A method for calculating damage evolution in adiabatic shear band of titanium alloy
WANG Xue-bin
2009-01-01
A method for calculating the evolution of the local damage variable at the adiabatic shear band (ASB) center was proposed. In the present method, the JOHNSON-COOK model and the nonlocal theory were adopted, and the damage variable formula applicable for the bilinear (linearly elastic and strain-softening) constitutive relation was further generalized to consider the plastic deformation occurring in the strain-hardening stage. Aiming at Ti-6Al-4V, the effect of strain rate on the evolution of the local damage variable at the ASB center was investigated. In addition, a parametric study was carried out, including the effects of strain-hardening exponent, strain rate sensitive coefficient, thermal-softening exponent, static shear strength, strain-hardening modulus, shear elastic modulus, work to heat conversion factor, melting temperature and initial temperature. The damage extent at the ASB center in the radial collapse experiment was assessed. It is found that at higher strain rates the damage in the ASB becomes more serious at the same average plastic shear strain of the ASB.
Shear Profiles and Velocity Distribution in Dense Shear Granular Flow
WANG Deng-Ming; ZHOU You-He
2009-01-01
We perform DEM simulations to investigate the influence of the packing fraction γ on the,shape of mean tan-gential velocity profile in a 2D annular dense shear granular flow. There is a critical packing fraction γc. For γ < γc, the mean tangential velocity profile shows a roughly exponential decay from the shearing boundary and is almost invariant to the imposed shear rate. However, for γ γc, the tangential velocity profile exhibits a rate-dependence feature and changes from linear to nonlinear gradually with the increasing shear rate. Fhrther-more, the distributions of normalized tangential velocities at different positions along radial direction exhibit the Gaussian or the composite Gaussian distributing features.
Stress-strain relationship with soil structural parameters of collapse loess
2008-01-01
Through the tri-axial shearing tests of unsaturated intact loess and based on the concept of comprehensive soil structural potential,this paper reveals the changing laws of soil structural property under the triaxial stress conditions and establishes a mathematical expression equation of structural parameters,whereby reflecting the effects of unsaturated loess water content,stress and strain states,which is introduced into the shearing stress and shearing strain relation to obtain the structural stress-strain relation.The tests reveal that the loess dilatancy is of shearing contraction and shearing expansion,whereby indicating that there is a good linear relation between the stress ratio and shearing expansion strain ratio.The larger consolidation confining pressure is,the larger the stress of shearing contraction and expansion critical point is;and the larger water content is,the smaller the strain ratio of shearing contraction and expansion critical point is.Finally,the constitutive model is established to reflect the variation in loess structure,stressstrain softening and hardening,and shearing contraction and shearing expansion features.Through the comparative analysis,the stress-strain curves described by the constitutive relationship are found to be in good conformity with test results,whereby testing the rationality of the model in this paper.
Fluid-Assisted Shear Failure Within a Ductile Shear Zone
Kirkpatrick, J. D.; Compton, K.; Holk, G. J.
2015-12-01
Exhumed shear zones often contain folded and/or dynamically recrystallized structures such as veins and pseudotachylytes that record contemporaneous brittle and ductile deformation representing mixed bulk rheology. Here, we constrain the conditions that promote the transitions between ductile and brittle deformation by investigating quartz veins with shear offsets in the Saddlebag Lake shear zone in the central Sierra Nevada, California. Mesozoic metasedimentary rocks within the shear zone contain transposed bedding, strong cleavage, dextrally rotated porphyroclasts, and a steep mineral lineation, which together suggest an overall transpressive kinematic regime for the ductile deformation. Foliation sub-parallel veins are one subset of the veins in the shear zone. They have observed horizontal trace lengths of up to around 5 meters, though most are obscured by limited exposure, and displacements range from ~3-30 mm, with 1-5 mm of opening. Foliation sub-parallel veins are folded with the foliation and quartz microstructures and fluid inclusion thermobarometry measurements from vein samples indicate temperatures during vein formation by fracture were between 300-680°C. Quartz δ18O values (+5.9 to +16.5) suggest extended fluid-rock interaction that involved magmatic (δ18O ~ +8 to +10) and meteoric (δ18O down to -1) fluids. Foliation sub-parallel veins are most abundant in relatively massive, quartz-rich rocks where they are boudinaged, indicating they were rigid inclusions after formation. Based on the orientation and spatial distribution of the veins, we infer that they formed under high differential stress with pore pressures sufficiently high for the rocks to be critically stressed for shear failure along mechanically weak foliation planes. These observations suggest high pore pressures and mechanical heterogeneity at a variety of scales are necessary conditions for nucleation of shear fractures within ductile shear zones.
Ideal shear strength and deformation behaviours of L1$_0$ TiAl from first-principles calculations
PING-YING TANG; GUO-HUA HUANG; QING-LIAN XIE; JIAN-YING LI
2016-10-01
The stress–strain relationships for four different shear processes of L1$_0$ TiAl have been investigated from first-principles calculations, and the peak shear stresses in these slip systems were obtained. By analysing the structural unit cell, bond length and charge density, the deformation modes under shear were elaborately discussed. Both of the peak shear stresses and the charge density indicate that the ideal shear strength of L10 TiAl occurs in the $\\langle 11\\bar{2}]${111} direction. It is shown that some bonds are enormously stretched accompanying with depletion of charge density as the strain increase. The density of states was studied in detail. It is indicated that strong hybridizationexists between Ti 3$d$ and Al 2$p$, and the structural stability would be lowered with increase of the strain.
Numerical simulation and optimization of clearance in sheet shearing process
秦泗吉; 李洪波; 彭加耕; 李硕本
2003-01-01
An analysis model to simplify the shearing and blanking process was developed. Based on the simplified model, the shearing process was simulated by FEM and analyzed for various clearances. An optimum clearance in the process was determined by new approach based on orientation of the maximum shearing stress on the characteristic line linking two blades, according to the law of crack propagation and experiments. The optimum clearance determined by this method can be used to dictate the range of reasonable clearance. By the new approach, the optimum clearance can be obtained conveniently and accurately even if there is some difference between the selected points, where the initial crack is assumed originated, and the actual one, where the initial crack occurs really.
OECD Maximum Residue Limit Calculator
With the goal of harmonizing the calculation of maximum residue limits (MRLs) across the Organisation for Economic Cooperation and Development, the OECD has developed an MRL Calculator. View the calculator.
Li, Weidong; Gao, Yanfei; Bei, Hongbin
2016-01-01
As a commonly used method to enhance the ductility in bulk metallic glasses (BMGs), the introduction of geometric constraints blocks and confines the propagation of the shear bands, reduces the degree of plastic strain on each shear band so that the catastrophic failure is prevented or delayed, and promotes the formation of multiple shear bands. The clustering of multiple shear bands near notches is often interpreted as the reason for improved ductility. Experimental works on the shear band arrangements in notched metallic glasses have been extensively carried out, but a systematic theoretical study is lacking. Using instability theory that predicts the onset of strain localization and the free-volume-based finite element simulations that predict the evolution of shear bands, this work reveals various categories of shear band arrangements in double edge notched BMGs with respect to the mode mixity of the applied stress fields. A mechanistic explanation is thus provided to a number of related experiments and especially the correlation between various types of shear bands and the stress state. PMID:27721462
Li, Weidong; Gao, Yanfei; Bei, Hongbin
2016-10-01
As a commonly used method to enhance the ductility in bulk metallic glasses (BMGs), the introduction of geometric constraints blocks and confines the propagation of the shear bands, reduces the degree of plastic strain on each shear band so that the catastrophic failure is prevented or delayed, and promotes the formation of multiple shear bands. The clustering of multiple shear bands near notches is often interpreted as the reason for improved ductility. Experimental works on the shear band arrangements in notched metallic glasses have been extensively carried out, but a systematic theoretical study is lacking. Using instability theory that predicts the onset of strain localization and the free-volume-based finite element simulations that predict the evolution of shear bands, this work reveals various categories of shear band arrangements in double edge notched BMGs with respect to the mode mixity of the applied stress fields. A mechanistic explanation is thus provided to a number of related experiments and especially the correlation between various types of shear bands and the stress state.
Composite Interlaminar Shear Fracture Toughness, G(sub 2c): Shear Measurement of Sheer Myth?
OBrien, T. Kevin
1997-01-01
The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.
Laboratory Studies on the Effects of Shear on Fish
Neitzel, Duane A.; Richmond, Marshall C.; Dauble, Dennis D.; Mueller, Robert P.; Moursund, Russell A.; Abernethy, Cary S.; Guensch, Greg R.
2000-09-20
The overall objective of our studies was to specify an index describing the hydraulic force that fish experience when subjected to a shear environment. Fluid shear is a phenomenon that is important to fish. However, elevated levels of shear may result in strain rates that injure or kill fish. At hydroelectric generating facilities, concerns have been expressed that strain rates associated with passage through turbines, spillways, and fish bypass systems may adversely affect migrating fish. Development of fish friendly hydroelectric turbines requires knowledge of the physical forces (injury mechanisms) that impact entrained fish and the fish's tolerance to these forces. It requires up-front, pre-design specifications for the environmental conditions that occur within the turbine system, in other words, determining or assuming that those conditions known to injure fish will provide the descriptions of conditions that engineers must consider in the design of a turbine system. These biological specifications must be carefully and thoroughly documented throughout the design of a fish friendly turbine. To address the development of biological specifications, we designed and built a test facility where juvenile fish could be subjected to a range of shear environments and quantified their biological response.
Grafted polymer under shear flow
Kumar, Sanjiv; Foster, Damien P.; Giri, Debaprasad; Kumar, Sanjay
2016-04-01
A self-attracting-self-avoiding walk model of polymer chain on a square lattice has been used to gain an insight into the behaviour of a polymer chain under shear flow in a slit of width L. Using exact enumeration technique, we show that at high temperature, the polymer acquires the extended state continuously increasing with shear stress. However, at low temperature the polymer exhibits two transitions: a transition from the coiled to the globule state and a transition to a stem-flower like state. For a chain of finite length, we obtained the exact monomer density distributions across the layers at different temperatures. The change in density profile with shear stress suggests that the polymer under shear flow can be used as a molecular gate with potential application as a sensor.
SEDflume - High Shear Stress Flume
Federal Laboratory Consortium — The U.S. Army Corps of Engineers High Shear Stress flume (SEDflume) is designed for estimating erosion rates of fine-grained and mixed fine/coarse grained sediments...
Mixing and chemical reaction in sheared and nonsheared homogeneous turbulence
Leonard, Andy D.; Hill, James C.
1992-01-01
Direct numerical simulations were made to examine the local structure of the reaction zone for a moderately fast reaction between unmixed species in decaying, homogeneous turbulence and in a homogeneous turbulent shear flow. Pseudospectral techniques were used in domains of 64 exp 3 and higher wavenumbers. A finite-rate, single step reaction between non-premixed reactants was considered, and in one case temperature-dependent Arrhenius kinetics was assumed. Locally intense reaction rates that tend to persist throughout the simulations occur in locations where the reactant concentration gradients are large and are amplified by the local rate of strain. The reaction zones are more organized in the case of a uniform mean shear than in isotropic turbulence, and regions of intense reaction rate appear to be associated with vortex structures such as horseshoe vortices and fingers seen in mixing layers. Concentration gradients tend to align with the direction of the most compressive principal strain rate, more so in the isotropic case.
Formation and dilatation of shear bands in a Cu-Zr metallic glass: A free volume perspective
Tang, Chunguang; Peng, Hailong; Chen, Yu; Ferry, Michael
2016-12-01
We report the tensile deformation behaviour of metallic glass Cu50Zr50 as a function of quenching rate using molecular dynamics simulations. The atomic-scale shearing is found to be independent of atomic free volume, and the macroscopic correlation between the yield strength and density (or average free volume) is a coincidence, whereby samples with large free volume also have a low density of shear-resistant local five-fold symmetry. In the relatively slowly quenched (≤1010 K/s) samples, shear bands have a dilatation about 0.5%, which compares well with recent experimental results. In contrast, although more active local shearing occurs in the rapidly quenched samples, shear banding is not observed. This is because the strain energy disperses into local atomic shearing at the macroscopically elastic stage and, hence, is not sufficient for shear band activation, resulting in homogeneous deformation and appreciable plasticity.
Shear strength behavior of geotextile/geomembrane interfaces
Belén M. Bacas
2015-12-01
Full Text Available This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces, the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A large direct shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strain softening behavior with a very small dilatancy (<0.5 mm and nonlinear failure envelopes at a normal stress range of 25–450 kPa. The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail. This study has generated several practical recommendations to help professionals to choose what materials are more adequate. From the three geotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength under high normal stress. For low normal stress, however, needle-punched monofilaments are recommended. For the regular textured geomembranes tested, the space between the asperities is an important factor. The closer these asperities are, the better the result achieves. For the irregular textured geomembranes tested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.
Shear strength behavior of geotextile/geomembrane interfaces
Belén M. Bacas; Jorge Cañizal; Heinz Konietzky
2015-01-01
This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces, the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A large direct shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strain softening behavior with a very small dilatancy (<0.5 mm) and nonlinear failure envelopes at a normal stress range of 25e450 kPa. The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail. This study has generated several practical recommendations to help professionals to choose what materials are more adequate. From the three geotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength under high normal stress. For low normal stress, however, needle-punched monofilaments are recommended. For the regular textured geomembranes tested, the space between the asperities is an important factor. The closer these asperities are, the better the result achieves. For the irregular textured geomembranes tested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.
Shear correction factors for layered plates and shells
Gruttmann, F.; Wagner, W.
2016-10-01
In this paper layered composite shells subjected to static loading are considered. The theory is based on a multi-field functional, where the associated Euler-Lagrange equations include besides the global shell equations formulated in stress resultants, the local in-plane equilibrium in terms of stresses and a constraint which enforces the correct shape of warping through the thickness. Within representative volume elements warping displacements are interpolated with layerwise cubic functions in thickness direction and constant shape throughout the reference surface. Elimination of warping and Lagrange parameters by static condensation leads to a material matrix for the stress resultants and to shear correction factors for layered plates and shells. For linear elasticity the computation can be done once in advance. The condensed material matrix is used in displacement based elements along with the enhanced strain method or in mixed hybrid elements with the usual 5 or 6 nodal degrees of freedom. This allows standard geometrical boundary conditions and the elements are applicable also to shell intersection problems. The interlaminar shear stresses are evaluated via the constitutive law by back substitution of the eliminated parameters. The computed transverse shear stresses are automatically continuous at the layer boundaries and zero at the outer surfaces. Furthermore, the integrals of the shear stresses coincide exactly with the shear forces without introduction of further constraints.
Shear correction factors for layered plates and shells
Gruttmann, F.; Wagner, W.
2017-01-01
In this paper layered composite shells subjected to static loading are considered. The theory is based on a multi-field functional, where the associated Euler-Lagrange equations include besides the global shell equations formulated in stress resultants, the local in-plane equilibrium in terms of stresses and a constraint which enforces the correct shape of warping through the thickness. Within representative volume elements warping displacements are interpolated with layerwise cubic functions in thickness direction and constant shape throughout the reference surface. Elimination of warping and Lagrange parameters by static condensation leads to a material matrix for the stress resultants and to shear correction factors for layered plates and shells. For linear elasticity the computation can be done once in advance. The condensed material matrix is used in displacement based elements along with the enhanced strain method or in mixed hybrid elements with the usual 5 or 6 nodal degrees of freedom. This allows standard geometrical boundary conditions and the elements are applicable also to shell intersection problems. The interlaminar shear stresses are evaluated via the constitutive law by back substitution of the eliminated parameters. The computed transverse shear stresses are automatically continuous at the layer boundaries and zero at the outer surfaces. Furthermore, the integrals of the shear stresses coincide exactly with the shear forces without introduction of further constraints.
Anisotropy and Heterogeneity Interaction in Shear Zones
Dabrowski, M.; Schmid, D. W.
2009-04-01
Rocks are heterogeneous on many different scales and deformation may introduce a coexistence of heterogeneity and anisotropy in shear zones. A competent inclusion embedded in a laminated matrix is a typical example. Indisputably, the presence of a mechanical heterogeneity leads to a flow perturbation and consequently to a deflection of the lamination in its vicinity. Assuming a passive response of the matrix phase, the pattern formation around rigid objects has been modeled in two and three dimensions using analytical solutions. Yet, the laminas may be mechanically distinct, leading to an effectively anisotropic rheology of the matrix. The feedback of an evolving matrix structure on the inclusion motion cannot be precluded in this case. In our study elliptical inclusions of varying aspect ratios are embedded in a laminated linear viscous host and subject to a large simple shear deformation in finite element numerical simulations. Increasing the viscosity ratio of the weak and strong lamina significantly changes the pattern characteristics in the matrix. The structural evolution around an inclusion proves to have a major impact on the inclusion motion, leading to the stabilization of elongated inclusions at antithetic orientations. We provide a comparison of two different modeling approaches. In the first approach discrete layers are introduced in the matrix and the large strain evolution of individual minute layers is resolved. Next, the matrix is modeled as an anisotropic medium using an evolving director field that locally describes the anisotropy direction. The length scale of layering can be restored in this model using the micropolar medium formulation.
Amador Carrascal, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F; Urban, Matthew
2017-01-11
Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver shear wave velocities values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue shear wave velocity values, such as food intake, body mass index (BMI), ultrasound scanners, scanning protocols, ultrasound image quality, etc. Time-to-peak (TTP) methods have been routinely used to measure the shear wave velocity. However, there is still a need for methods that can provide robust shear wave velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this study, two modified shear wave speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time (spatiotemporal peak, STP); the second method applies an amplitude filter (spatiotemporal thresholding, STTH) to select points with motion amplitude higher than a threshold for shear wave group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in shear wave velocity estimates compared to TTP in phantom. Moreover, in a cohort of 14 healthy subjects STP and STTH methods improved both the shear wave velocity measurement precision and the.
Juffer, P.; Bakker, A.D.; Klein-Nulend, J.; Jaspers, R.T.
2014-01-01
Skeletal muscle fibers have the ability to increase their size in response to a mechanical overload. Finite element modeling data suggest that mechanically loaded muscles in vivo may experience not only tensile strain but also shear stress. However, whether shear stress affects biological pathways i
Strain-accelerated dynamics of soft colloidal glasses
Agarwal, Praveen
2011-04-11
We have investigated strain-accelerated dynamics of soft glasses theoretically and experimentally. Mechanical rheology measurements performed on a variety of systems reveal evidence for the speeding-up of relaxation at modest shear strains in both step and oscillatory shear flows. Using the soft glassy rheology (SGR) model framework, we show that the observed behavior is a fundamental, but heretofore unexplored attribute of soft glasses. © 2011 American Physical Society.
Search for New Highly Energetic Phases under Compression and Shear
2015-05-01
diamond anvil cell. Europhysics Letters , 2009, Vol. 88, 16004, 1-6. IF: 2.753 4. Ji, C., Hou, D., Zhu, H., Wu, J., Chyu, M., Ma, Y., Pressure...I-2. The room temperature phase diagram of NaN3. Letters mark the material surrounding the sample as pressure transmitting media. (b) Shear...transitions at large strains: Phase-field theory and simulations. Physical Review Letters , 2009, Vol. 103, No. 2, 025702; selected and published by
Maximum margin Bayesian network classifiers.
Pernkopf, Franz; Wohlmayr, Michael; Tschiatschek, Sebastian
2012-03-01
We present a maximum margin parameter learning algorithm for Bayesian network classifiers using a conjugate gradient (CG) method for optimization. In contrast to previous approaches, we maintain the normalization constraints on the parameters of the Bayesian network during optimization, i.e., the probabilistic interpretation of the model is not lost. This enables us to handle missing features in discriminatively optimized Bayesian networks. In experiments, we compare the classification performance of maximum margin parameter learning to conditional likelihood and maximum likelihood learning approaches. Discriminative parameter learning significantly outperforms generative maximum likelihood estimation for naive Bayes and tree augmented naive Bayes structures on all considered data sets. Furthermore, maximizing the margin dominates the conditional likelihood approach in terms of classification performance in most cases. We provide results for a recently proposed maximum margin optimization approach based on convex relaxation. While the classification results are highly similar, our CG-based optimization is computationally up to orders of magnitude faster. Margin-optimized Bayesian network classifiers achieve classification performance comparable to support vector machines (SVMs) using fewer parameters. Moreover, we show that unanticipated missing feature values during classification can be easily processed by discriminatively optimized Bayesian network classifiers, a case where discriminative classifiers usually require mechanisms to complete unknown feature values in the data first.
Maximum Entropy in Drug Discovery
Chih-Yuan Tseng
2014-07-01
Full Text Available Drug discovery applies multidisciplinary approaches either experimentally, computationally or both ways to identify lead compounds to treat various diseases. While conventional approaches have yielded many US Food and Drug Administration (FDA-approved drugs, researchers continue investigating and designing better approaches to increase the success rate in the discovery process. In this article, we provide an overview of the current strategies and point out where and how the method of maximum entropy has been introduced in this area. The maximum entropy principle has its root in thermodynamics, yet since Jaynes’ pioneering work in the 1950s, the maximum entropy principle has not only been used as a physics law, but also as a reasoning tool that allows us to process information in hand with the least bias. Its applicability in various disciplines has been abundantly demonstrated. We give several examples of applications of maximum entropy in different stages of drug discovery. Finally, we discuss a promising new direction in drug discovery that is likely to hinge on the ways of utilizing maximum entropy.
Taylor's experiment in a periodically sheared particulate suspension
Souzy, Mathieu; Pham, Phong; Metzger, Bloen
2016-08-01
We revisit Taylor's experiment investigating the evolution of a blob of dye in a periodically sheared suspension of non-Brownian particles. Above a critical strain amplitude, particulate suspensions are subject to phase transition where reversibility is lost and particles fail to return to their original positions. We investigate the effect of this transition on the dispersion of a blob of dye. Beyond the critical strain, the dispersion of the blob is found to increase significantly. The dispersion coefficient of the blob of dye is measured and compared to the self-diffusivity coefficient of the particles.
Simulations of Reversed Shear Configuration in EAST
NIU Xingping; WU Bin
2007-01-01
The reversed shear (RS) mode is one of the advanced configurations being considered in EAST.Predictive simulations of EAST reversed shear configuration are carried out using an 1.5D equilibrium evolution code.In order to have the desired monotonic q-profile during a tokamak discharge,a successful preparation phase is required.In our simulation,the plasma current is ramped up from 100 kA to a flat-top maximum of 1.0 MA for four seconds.An ICRH power of 1 MW is applied until the plasma shape is formed at the moment of 4 s,and then the power is raised to 3 MW.A LHCD power of 3.5 MW is applied from is to optimize the plasma current density profile.A series of simulations are performed to study the influence of the time of applying the auxiliary heating on the plasma parameters.Based on these simulations,a scheme is proposed and tested for the control of the safety factor profile,which is very useful in real time profile control in tokamak experiments.
An Implementation of Bayesian Lensing Shear Measurement
Sheldon, Erin S
2014-01-01
The Bayesian gravitational shear estimation algorithm developed by Bernstein and Armstrong (2014) can potentially be used to overcome noise bias and recover shear using very low signal-to-noise ratio (S/N) galaxy images. In that work the authors confirmed the method is sufficiently unbiased for planned surveys (fractional error less than 2 x 10^{-3}) in a simplified demonstration, but no test was performed on images. Here I present a full implementation for fitting models to galaxy images, including the effects of a point spread function (PSF) and pixelization. I tested the implementation using simulated galaxy images modeled as Sersic profiles with n=1 (exponential) and n=4 (De Vaucouleurs'), convolved with a PSF and a flat pixel response function. I used a round Gaussian model for the PSF to avoid potential PSF-fitting errors. I simulated galaxies with mean observed, post-PSF full-width at half maximum equal to approximately 1.2 times that of the PSF, with log-normal scatter. I also drew fluxes from a log-n...
Vascular endothelium-leukocyte interaction; sticking shear force in venules.
Schmid-Schoenbein, G W; Fung, Y C; Zweifach, B W
1975-01-01
To determine the shear force acting on a white blood cell sticking to the endothelium of a blood vessel, the flow field about a single white blood cell in a venule was determined by hign-speed motion picture photomicrography. The force acting on the white blood cell was then calculated according to the principles of fluid mechanics. In this paper, the calculation was made using an experimentally determined dimensionless shear force coefficient obtained from a kinematically and dynamically similar model. The large physical model of the hemodynamic system could be easily instrumented, and the shear force acting on the model cell and the flow field around it were measured. The data were then used to calculate a shear force coefficient. On the basis of dynamic similarity, this shear force coefficient was applied to the white blood cell in the venule. The shear force coefficient was strongly influenced by the hematocrit, so in vivo hematocrits were measured from electron micrographs. It was found that in the venules of the rabbit omentum a white blood cell sticking to the endothelial wall was subjected to a shear force in the range of 4 times 10--5 dynes to 234 times 10--5 dynes; the exact value depended on the size and motion of the white blood cell, the size of the blood vessel, the velocity of the blood flow, and the local hematocrit, which varied between 20% and 40% in venules of about 40 mum in diameter. The contact area between the white blood cell and the endothelial cell was estimated, and the shear stress was found to range between 50 dynes/cm-2 and 1060 dynes/cm-2. The normal stress of interaction between the white blood cell and the endothelium had a maximum value that was of the same order of magnitude as the shear stress. The accumulated relative error of the experimental procedure was about 49%. The instantaneous shear force was a random function of time because of random fluctuations of the hematocrit.
Eruptive shearing of tube pumice: pure and simple
Dingwell, Donald B.; Lavallée, Yan; Hess, Kai-Uwe; Flaws, Asher; Marti, Joan; Nichols, Alexander R. L.; Gilg, H. Albert; Schillinger, Burkhard
2016-09-01
Understanding the physicochemical conditions extant and mechanisms operative during explosive volcanism is essential for reliable forecasting and mitigation of volcanic events. Rhyolitic pumices reflect highly vesiculated magma whose bubbles can serve as a strain indicator for inferring the state of stress operative immediately prior to eruptive fragmentation. Obtaining the full kinematic picture reflected in bubble population geometry has been extremely difficult, involving dissection of a small number of delicate samples. The advent of reliable high-resolution tomography has changed this situation radically. Here we demonstrate via the use of tomography how a statistically powerful picture of the shapes and connectivity of thousands of individual bubbles within a single sample of tube pumice emerges. The strain record of tube pumice is modelled using empirical models of bubble geometry and liquid rheology, reliant on a constraint of magmatic water concentration. FTIR analysis reveals an imbalance in water speciation, suggesting post-eruption hydration, further supported by hydrogen and oxygen isotope measurements. Our work demonstrates that the strain recorded in the tube pumice dominated by simple shear (not pure shear) in the late deformational history of vesicular magma before eruption. This constraint in turn implies that magma ascent is conditioned by a velocity gradient (across the conduit) at the point of origin of tube pumice. Magma ascent accompanied by simple shear should enhance high eruption rates inferred independently for these highly viscous systems.
Effective temperature dynamics of shear bands in metallic glasses
Daub, Eric G.; Klaumünzer, David; Löffler, Jörg F.
2014-12-01
We study the plastic deformation of bulk metallic glasses with shear transformation zone (STZ) theory, a physical model for plasticity in amorphous systems, and compare it with experimental data. In STZ theory, plastic deformation occurs when localized regions rearrange due to applied stress and the density of these regions is determined by a dynamically evolving effective disorder temperature. We compare the predictions of STZ theory to experiments that explore the low-temperature deformation of Zr-based bulk metallic glasses via shear bands at various thermal temperatures and strain rates. By following the evolution of effective temperature with time, strain rate, and temperature through a series of approximate and numerical solutions to the STZ equations, we successfully model a suite of experimentally observed phenomena, including shear-band aging as apparent from slide-hold-slide tests, a temperature-dependent steady-state flow stress, and a strain-rate- and temperature-dependent transition from stick-slip (serrated flow) to steady-sliding (nonserrated flow). We find that STZ theory quantitatively matches the observed experimental data and provides a framework for relating the experimentally measured energy scales to different types of atomic rearrangements.
Experimental observation of shear thickening oscillation
Nagahiro, Shin-ichiro; Nakanishi, Hiizu; Mitarai, Namiko
2013-01-01
We report experimental observations of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed...
Fracture Behavior of Dielectric Elastomer under Pure Shear Loading
Ahmad, D.; Patra, K.
2017-09-01
Dielectric elastomer has become a very important material for many emerging applications areas like optics, micro fluidics, sensors, actuators and energy harvesting. However, these elastomer components are prone to fracture or catastrophic failure because of defects likes notches, flaws, and fatigue crack, impurities which occur during production or during service. To make better use of this material, it is important to investigate fracture characteristics under different operating conditions. This study experimentally investigated the effects of notch length and strain rate on the fracture toughness, failure stretch and failure stress of acrylic elastomer under pure shear deformation mode. It is observed that failure stretch depends on notch length and independent of strain rate, but failure stress decreases with increasing notch length and increases with increasing strain rate. It is also found that fracture toughness is independent of notch lengths. However, fracture toughness is found to increase with strain rate.
First-principles study of the transport behavior of zigzag graphene nanoribbons tailored by strain
Jinying Wang
2012-03-01
Full Text Available The charge transport properties of zigzag graphene nanoribbons (ZGNRs under uniaxial and shear strains are theoretically studied. Although all strained ZGNRs have similar metallic band structures, they show four types of transport behavior under bias voltages that depend on the type of strain and the mirror symmetry of the ZGNR. Under an applied uniaxial strain, the current of symmetric ZGNRs is consistently small, while for asymmetric ZGNRs it is large. In contrast, the current increases with increasing shear strain for symmetric ZGNRs while it decreases for asymmetric ZGNRs. The current properties merge when the shear strain exceeds a critical value, and the two systems then show similar behavior. Our results suggest that strained ZGNRs with an appropriate applied shear are ideal conducting wires.
Helical propulsion in shear-thinning fluids
Gomez, Saul; Lauga, Eric; Zenit, Roberto
2016-01-01
Swimming microorganisms often have to propel in complex, non-Newtonian fluids. We carry out experiments with self-propelling helical swimmers driven by an externally rotating magnetic field in shear-thinning, inelastic fluids. Similarly to swimming in a Newtonian fluid, we obtain for each fluid a locomotion speed which scales linearly with the rotation frequency of the swimmer, but with a prefactor which depends on the power index of the fluid. The fluid is seen to always increase the swimming speed of the helix, up to 50% faster and thus the strongest of such type reported to date. The maximum relative increase for a fluid power index of around 0.6. Using simple scalings, we argue that the speed increase is not due to the local decrease of the flow viscosity around the helical filament but hypothesise instead that it originates from confinement-like effect due to viscosity stratification around the swimmer.
Shear elasticity of fluids at low-frequent shear influence.
Badmaev, Badma B; Budaev, Ochir R; Dembelova, Tuyana S; Damdinov, Bair B
2006-12-22
The visco-elastic properties of liquids have been investigated using acoustical resonance method. Piezoquatrz performed tangential oscillations on the main resonance frequency of 74 kHz contacts by the one end of horizontal surface with the studied liquid layer covered by quartz cover-plate. So the stagnant shear waves are installed in layer. The solution of interaction of piezoquartz-liquid layer-cover-plate gives three methods of determination of the real shear modulus (G) and the tangent of mechanical loss angle (tan theta) of liquid. The first method is realized at smaller thickness of liquid layer then the length of shear wave. Liquids of different classes have been studied using this method: polymer liquids, oils, glycols and alcohols. The second method is connected with the propagation of shear wave in liquid layer, parameters of which are determined the G and tan theta. And the third method is based on the determination of limit shift of resonance frequencies at completes damping of shear wave in thick layer of liquid. All these three methods give satisfactory agreement of results.
Experimental method for the evaluation of the susceptibility of materials to shear band formation
Tham R.
2012-08-01
Full Text Available In order to characterize materials with respect to their susceptibility to shear band formation at high strain rates, a modified Hopkinson pressure bar apparatus and hat-shaped steel specimens with a shear zone having a width significantly larger than the typical width of adiabatic bands are used. The sample is directly impacted by the striker. The force acting on the sample is measured with a PVDF-gauge between the sample and the output bar. The displacement is recorded with an electro-optical extensometer. The energy absorbed by the shearing process up to failure can be used as a reference for the susceptibility of materials to shear band formation. The method is demonstrated comparing the shear behavior of two high-strength steels with similar metallic structure and strength. Differences were found in the transition region between quasi-static and fully adiabatic shearing conditions where the energy up to rupture differs by 40 %. For fully adiabatic shear band formation, the deformation process of both materials equals. At extreme rates, shear processes are mainly governed by the thermodynamic properties of the materials. On the other hand, strength and structural properties play a role for low and intermediate rates where global and localized shear mechanisms occur in parallel.
Mondro, Claire A.; Fisher, Donald; Yeh, En-Chao
2017-05-01
In the eastern Central Range of Taiwan there is a regional variation in the orientation of maximum finite stretch across the slate belt, with down-dip maximum stretch found in the western Central Range and along-strike maximum stretch in the eastern Central Range. Incremental strain histories from syntectonic fibers in pyrite pressure shadows indicate a progressive change in extension direction from down dip to along strike during deformation, there is a corresponding temporal variation in stretching direction shown in samples from the eastern edge of the Central Range, a pattern that mimics the regional west-to-east spatial variation. These observed temporal and spatial strain distributions are used to evaluate the kinematics associated with slaty cleavage development during advection through the Taiwan orogenic system. The subduction zone beneath the island of Taiwan is influenced by two types of obliquity that have the potential to generate the observed along-strike stretching. First, the plate motion vector of the Philippine Sea plate relative to the Eurasian plate is slightly oblique to the regional strike of the mountain range, which could result in partitioning of strike slip shearing into the interior of the collision. Second, the north-south Luzon volcanic arc on the Philippine Sea Plate is obliquely oriented relative to the northeast-southwest edge of the Eurasian continental margin, which could result in lateral extrusion of the ductile core of the range. Incremental strain histories in cleavage-parallel samples represent a time-for-space equivalence where the stretching direction is fixed relative to the position within the mountain belt architecture (e.g., the topographic divide), and temporal variations in the eastern central Range reflect lateral advection through the strain field in response to accretionary and erosional fluxes. Incremental strain histories in cleavage perpendicular samples show both clockwise and counter-clockwise rotation of
Internal Shear Forging Processes for Missile Primary Structures.
1981-07-20
permissible for (A) 2024-T4 Al, (B) 6061 -T6 Al, (C) annealed copper, and (0) mild steel .. .. .. ... ... .. ... ... ..... 19 17 Maximum reduction in shear...spinnability tests, indicating degree of forward reduction permissible for (A) 2024-T4 Al, (B) 6061 -T Al, (C) annealed copper, (D) mild steel. Attempts were...rotationssymmetrisches Hohlkirper aus Aluminium ," Doctoral Dissertation, University of Stuttgart, 1961. J 23. S. Kalpakjian, "An Experimental Study of Plastic
Roles of nanoclusters in shear banding and plastic deformation of bulk metallic glasses
Nieh, T G
2012-07-31
During the course of this research we published 33 papers in various physics/material journals. We select four representing papers in this report and their results are summarized as follows. I. To study shear banding process, it is pertinent to know the intrinsic shear strain rate within a propagating shear band. To this aim, we used nanoindentation technique to probe the mechanical response of a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass in locality and found notable pop-in events associated with shear band emission. Using a free volume model and under the situation when temperature and stress/hardness are fixed result in an equation, which predicts that hardness serration caused by pop-in decreases exponentially with the strain rate. Our data are in good agreement with the prediction. The result also predicts that, when strain rate is higher than a critical strain rate of 1700 s^-1, there will be no hardness serration, thereby no pop-in. In other words, multiple shear bandings will take place and material will flow homogeneously. The critical strain rate of 1700 s^-1 can be treated as the intrinsic strain rate within a shear band. We subsequently carried out a simulation study and showed that, if the imposed strain rate was over , the shear band spacing would become so small that the entire sample would virtually behave like one major shear band. Using the datum strain rate =1700 s^-1 and based on a shear band nucleation model proposed by us, the size of a shear-band nucleus in Au-BMG was estimated to be 3 10^6 atoms, or a sphere of ~30 nm in diameter. II. Inspired by the peculiar result published in a Science article Super Plastic Bulk Metallic Glasses at Room Temperature, we synthesized the Zr-based bulk metallic glass with a composition identical to that in the paper (Zr64.13Cu15.75Ni10.12Al10) and, subsequently, tested in compression at the same slow strain rate (~10^-4 s^-1). We found that the dominant deformation mode is always single shear. The stress-strain
A new dedicated finite element for push-over analysis of reinforced concrete shear wall systems
Delal Doğru ORMANCI
2016-06-01
Full Text Available In this study, a finite element which has been analyzed based on anisotropic behavior of reinforced shear walls is developed. Element stiffness matrices were varied based on whether the element is in the tension or the compression zone of the cross-section. Nonlinear behavior of reinforced shear wall model is investigated under horizontal loads. This behavior is defined with a similar approach to plastic hinge assumption in frame structures that the finite element behaves lineer elastic between joints and plastic deformations are concentrated on joints as vertical plastic displacements. According to this acceptance, plastic behavior of reinforced shear wall occurs when the vertical strain reaches elastic strain limit. In the definition of finite element, displacement functions are chosen considering that the partition of shear walls just at floor levels, are enough for solution. Results of this study are compared with the solution obtained from a different computer programme and experimental results.
FRP-RC Beam in Shear: Mechanical Model and Assessment Procedure for Pseudo-Ductile Behavior
Floriana Petrone
2014-07-01
Full Text Available This work deals with the development of a mechanics-based shear model for reinforced concrete (RC elements strengthened in shear with fiber-reinforced polymer (FRP and a design/assessment procedure capable of predicting the failure sequence of resisting elements: the yielding of existing transverse steel ties and the debonding of FRP sheets/strips, while checking the corresponding compressive stress in concrete. The research aims at the definition of an accurate capacity equation, consistent with the requirement of the pseudo-ductile shear behavior of structural elements, that is, transverse steel ties yield before FRP debonding and concrete crushing. For the purpose of validating the proposed model, an extended parametric study and a comparison against experimental results have been conducted: it is proven that the common accepted rule of assuming the shear capacity of RC members strengthened in shear with FRP as the sum of the maximum contribution of both FRP and stirrups can lead to an unsafe overestimation of the shear capacity. This issue has been pointed out by some authors, when comparing experimental shear capacity values with the theoretical ones, but without giving a convincing explanation of that. In this sense, the proposed model represents also a valid instrument to better understand the mechanical behavior of FRP-RC beams in shear and to calculate their actual shear capacity.
Greenslade, Thomas B., Jr.
1985-01-01
Discusses a series of experiments performed by Thomas Hope in 1805 which show the temperature at which water has its maximum density. Early data cast into a modern form as well as guidelines and recent data collected from the author provide background for duplicating Hope's experiments in the classroom. (JN)
Abolishing the maximum tension principle
Dabrowski, Mariusz P
2015-01-01
We find the series of example theories for which the relativistic limit of maximum tension $F_{max} = c^2/4G$ represented by the entropic force can be abolished. Among them the varying constants theories, some generalized entropy models applied both for cosmological and black hole horizons as well as some generalized uncertainty principle models.
Abolishing the maximum tension principle
Mariusz P. Da̧browski
2015-09-01
Full Text Available We find the series of example theories for which the relativistic limit of maximum tension Fmax=c4/4G represented by the entropic force can be abolished. Among them the varying constants theories, some generalized entropy models applied both for cosmological and black hole horizons as well as some generalized uncertainty principle models.
Kalita, Viktor; Snarskii, Andrew; Shamonin, Mikhail; Zorinets, Denys
2017-01-01
The influence of an external magnetic field on the static shear strain and the effective shear modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al, Phys. Rev. E 93, 062503 (2016)]. The planar problem of magnetostriction in an MAE with soft magnetic inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is so...
Faris, Allison T.; Seed, Raymond B.; Kayen, Robert E.; Wu, Jiaer
2006-01-01
During the 1906 San Francisco Earthquake, liquefaction-induced lateral spreading and resultant ground displacements damaged bridges, buried utilities, and lifelines, conventional structures, and other developed works. This paper presents an improved engineering tool for the prediction of maximum displacement due to liquefaction-induced lateral spreading. A semi-empirical approach is employed, combining mechanistic understanding and data from laboratory testing with data and lessons from full-scale earthquake field case histories. The principle of strain potential index, based primary on correlation of cyclic simple shear laboratory testing results with in-situ Standard Penetration Test (SPT) results, is used as an index to characterized the deformation potential of soils after they liquefy. A Bayesian probabilistic approach is adopted for development of the final predictive model, in order to take fullest advantage of the data available and to deal with the inherent uncertainties intrinstiic to the back-analyses of field case histories. A case history from the 1906 San Francisco Earthquake is utilized to demonstrate the ability of the resultant semi-empirical model to estimate maximum horizontal displacement due to liquefaction-induced lateral spreading.
Barcos, L.; Balanyá, J. C.; Díaz-Azpiroz, M.; Expósito, I.; Jiménez-Bonilla, A.
2015-11-01
Complex strain patterns in the Gibraltar Arc derive from the interaction between the westward drift - and concomitant back-arc extension - of the arc hinterland (Alboran Domain) and the Europe-Africa convergence. In order to explore strain partitioning modes within the arc and the role played by large-scale oblique structures, we have studied the kinematics of the Torcal Shear Zone located at the northern branch of the Gibraltar Arc. The Torcal Shear Zone is a 70 km-long, E-W brittle-ductile shear zone that underwent overall dextral transpression during the Late Miocene to Quaternary time. Within the Torcal Shear Zone strain is highly partitioned at multiple scales into shortening, oblique, extensional and strike-slip structures. Moreover, strain partitioning is heterogeneous along-strike giving rise to four distinct structural domains. In the central sector the strain is pure-shear dominated, although narrow sectors parallel to the shear walls are simple-shear dominated. A single N99°E-N109°E trending horizontal velocity vector (V→) could explain the kinematics of the entire central sector of the Torcal Shear Zone. Lateral domains have different strain patterns and are comparable to splay-dominated and thrust-dominated strike-slip fault tips. The Torcal Shear Zone provokes the subvertical extrusion of the External Betics units against the Alboran Domain and a dextral deflection of the structural trend. Moreover, the estimated V→ points to the importance of the westward motion of the hinterland relative to the external wedge and fits well with the radial outward thrusting pattern identified in the arc.
Kaminski, K.; Mittelstaedt, E. L.; Warren, J. M.; Kurz, M. D.; Kumamoto, K.
2015-12-01
Recent studies of ductile peridotite shear zones in the Josephine Peridotite in SW Oregon find higher helium concentrations in whole rock samples located where total strain is greatest and recrystallized grain sizes are smallest. Based upon these results, previous workers suggest that dynamic recrystallization may lead to increased storage of He on grain boundaries. To assess the feasibility of this mechanism for enhanced He storage, we utilize a combined set of new and previous data from Shear Zone A (SZA) and B (SZB) of the Fresno Bench of the Josephine Peridotite to constrain a 1D numerical model of a ductile shear zone; the combined data set includes both He concentrations as well as measured total strain across the shear zone. Existing data within the region of highest strain (0 to ~2.5 m from the center of each shear zone) are sparse and, thus, we strategically sampled locations within this zone to maximize data resolution across a range of total strain. In each sample, we measure helium concentrations in unserpentinized harzburgite bulk rock using mass spectrometry. Analysis of the orientation of pyroxene foliation planes compared to shear planes provides an estimation of shear strain during deformation. Numerically, our model is discretized using finite differences and incorporates a non-linear, temperature-dependent viscosity, shear heating, and dynamic recrystallization. Here, we present our newly compiled collection of helium concentrations relative to total strain within SZA and SZB and measured grain sizes, which are used to constrain the modeled equilibrium grain size and quantitatively test dynamic recrystallization as a mechanism for concentrating He within peridotite shear zones.
Wang Sheng-zu
2006-01-01
According to the "Netlike Plastic-Flow (NPF)" continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous (plastic) flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogenic layer can be estimated using the "earthquake-recurrence-interval" method, in which the strain rate is calculated in terms of the recurrence interval of two sequential carthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the "conjugate-angle" method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10-15 ～ 10-14/s in this region. The strain rates within the plastic-flow belts,which control seismic activities in the seismogenic layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogenic layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogenic layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang (Tibet) plateau to the North China plain
High shear stress relates to intraplaque haemorrhage in asymptomatic carotid plaques
Tuenter, A.; Selwaness, M.; Arias Lorza, A.
2016-01-01
BACKGROUND AND AIMS: Carotid artery plaques with vulnerable plaque components are related to a higher risk of cerebrovascular accidents. It is unknown which factors drive vulnerable plaque development. Shear stress, the frictional force of blood at the vessel wall, is known to influence plaque...... estimating equations analysis, adjusting for age, sex and carotid wall thickness. RESULTS: The study group consisted of 93 atherosclerotic carotid arteries of 74 participants. In plaques with higher maximum shear stresses, IPH was more often present (OR per unit increase in maximum shear stress (log...... formation. We evaluated the association between shear stress and plaque components (intraplaque haemorrhage (IPH), lipid rich necrotic core (LRNC) and/or calcifications) in relatively small carotid artery plaques in asymptomatic persons. METHODS: Participants (n = 74) from the population-based Rotterdam...
The development of a tensile-shear punch correlation for yield properties of model austenitic alloys
Hankin, G.L.; Faulkner, R.G. [Loughborough Univ. (United Kingdom); Hamilton, M.L.; Garner, F.A. [Pacific Northwest National Lab., Richland, WA (United States)
1997-08-01
The effective shear yield and maximum strengths of a set of neutron-irradiated, isotopically tailored austentic alloys were evaluated using the shear punch test. The dependence on composition and neutron dose showed the same trends as were observed in the corresponding miniature tensile specimen study conducted earlier. A single tensile-shear punch correlation was developed for the three alloys in which the maximum shear stress or Tresca criterion was successfully applied to predict the slope. The correlation will predict the tensile yield strength of the three different austenitic alloys tested to within {+-}53 MPa. The accuracy of the correlation improves with increasing material strength, to within {+-} MPa for predicting tensile yield strengths in the range of 400-800 MPa.
Brittle-to-viscous behaviour of quartz gouge in shear experiments
Richter, Bettina; Stunitz, Holger; Heilbronner, Renée
2016-04-01
In order to study the microstructure development across the brittle-viscous transition and to derive the corresponding flow laws, we performed shear experiments on quartz gouge in a Griggs-type deformation apparatus. The starting material is a crushed quartz single crystal (sieved grain size water added. The experiments were conducted at temperatures between 500 ° C and 1000 ° C at confining pressures of 0.5 GPa, 1.0 GPa or 1.5 GPa. Four strain-rate-stepping experiments were conducted at strain rates between ˜2.5 x 10-6 s-1 and ˜2.5 x 10-4 s-1. Other experiments were conducted at constant strain rates of ˜2.5 x 10-6 s-1, ˜2.5 x 10-5 s-1, ˜2.5 x 10-4 s-1 and ˜2.5 x 10-3 s-1. At high confining pressure, the strength of the samples decreases with increasing temperature for all strain rates. The largest decrease occurred between 650 ° C and 700 ° C at shear strain rates of ˜2.5 x 10-5 s-1. At the same time, the pressure dependence of strength is positive for T ≤ 650 ° C while an inverse pressure dependence is observed at T > 650 ° C. For T one dominated by cataclastic flow to one dominated by crystal plasticity. The microstructure reveals a less abrupt transition in terms of operating processes, because brittle and viscous processes are equally active around 650 ° C. With increasing temperature the volume fraction of recrystallised grains increases, and at 900 ° C - 1000 ° C recrystallisation is nearly complete at strains of γ ˜ 3. The crystallographic preferred orientation of the c-axis evolves from a random distribution at low temperatures towards two peripheral maxima at intermediate temperatures. At high temperatures the c-axis show a single Y-maximum. At high temperature, the stress exponent is n = 2.1 ± 0.2. The activation energy Q is 193 ± 12 kJ/mol at strain rates of 10-5 s-1, at faster strain rates the activation energy drops down to Q = 119 ± 12 kJ/mol. This small stress exponent at high temperatures indicates a combination of
Size-independent shear band formation in amorphous nanowires made from simulated casting
Shi, Yunfeng
2010-03-01
Molecular dynamics simulations indicate that surfaces strongly influence the strain localization behavior of amorphous nanowires in tension. A sample preparation routine that simulates casting was employed to facilitate the relaxation of the sample surface. Samples as short as 15 nm (7.5 nm in diameter) form dominant shear bands during deformation. The elastic energy release during plastic deformation is sufficient to provide the excess potential energy required for the shear band nucleation at rather small sample sizes. The results show that shear band formation is almost size-independent and is bounded only by its own length scale.
Zhu, H.; Shan, G. C.; Shek, C. H.; Lee, J. E.-Y.
2012-07-01
The frequency response of a single crystal silicon resonator under nonlinear vibration is investigated and related to the shear property of the material. The shear stress-strain relation of bulk silicon is studied using a first-principles approach. By incorporating the calculated shear property into a device-level model, our simulation closely predicts the frequency response of the device obtained by experiments and further captures the nonlinear features. These results indicate that the observed nonlinearity stems from the material's mechanical property. Given the high quality factor (Q) of the device reported here (˜2 × 106), this makes it highly susceptible to such mechanical nonlinear effects.
A DEM investigation on simple shear behavior of dense granular assemblies
史旦达; 薛剑峰; 赵振营; 史跻宇
2015-01-01
A micromechanical investigation on simple shear behavior of dense granular assemblies was carried out by discrete element method. Three series of numerical tests were performed to examine the effects of initial porosity, vertical stress and particle shape on simple shear behavior of the samples, respectively. It was found that during simple shear the directions of principal stress and principal strain increment rotate differently with shear strain level. The non-coaxiality between the two directions decreases with strain level and may greatly affect the shear behavior of the assemblies, especially their peak friction angles. The numerical modelling also reveals that the rotation of the principal direction of fabric anisotropy lags behind that of the major principal stress direction during simple shear, which is described as fabric hyteresis effect. The degrees of fabric and interparticle contact force anisotropies increase as particle angularity increases, whereas the orientations of these anisotropies have not been significantly influenced by particle shape. An extended stress–dilatancy relationship based on ROWE-DAVIS framework was proposed to consider the non-coaxiality effect under principal stress rotation. The model was validated by present numerical results as well as some published physical test and numerical modelled data.
Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah
Katz, Yoram; Weinberger, Ram; Aydin, Atilla
2004-03-01
Riedel shear structures are common fault patterns identified within shear zones and related to the embryonic stages of fault formation. This study focuses on the geometry of outcrop-scale natural shear zones consisting of different generations of Riedel structures, exposed in the Jurassic Navajo sandstone, Capitol Reef National Park, Utah. Geometric analysis of different structures shows that the spacing of synthetic R-deformation bands increases with the spacing of antithetic R'-deformation bands. Systematic correlation is found between the R-band spacing and the angles formed between R- and R'-bands. Examination of young Riedel structures shows their tendency to localize along narrow, elongated domains sub-parallel to the shear direction and create denser Riedel networks. We suggest that the evolution of Riedel structures is dominated by two mechanisms: (1) discrete faulting in the form of conjugate deformation bands, generally complying with the Mohr-Coulomb criteria, and (2) granular flow, which rotates mainly the R'-deformation bands. Both mechanisms are intensified with progressive strain, decreasing the deformation-band spacing and increasing the R- to R'-angles. The tendency of young Riedel structures to organize in dense elongated networks is related to strain localization during the shear-zone evolution. We suggest a kinematic explanation for the evolution of Riedel-structure networks, which relates the network geometry to the progressive accumulation and localization of shear strain.
Shear Acceleration in Expanding Flows
Rieger, F M
2016-01-01
Shear flows are naturally expected to occur in astrophysical environments and potential sites of continuous non-thermal Fermi-type particle acceleration. Here we investigate the efficiency of expanding relativistic outflows to facilitate the acceleration of energetic charged particles to higher energies. To this end, the gradual shear acceleration coefficient is derived based on an analytical treatment. The results are applied to the context of the relativistic jets of active galactic nuclei. The inferred acceleration timescale is investigated for a variety of conical flow profiles (i.e., power law, Gaussian, Fermi-Dirac) and compared to the relevant radiative and non-radiative loss timescales. The results exemplify that relativistic shear flows are capable of boosting cosmic-rays to extreme energies. Efficient electron acceleration, on the other hand, requires weak magnetic fields and may thus be accompanied by a delayed onset of particle energization and affect the overall jet appearance (e.g., core, ridge ...
Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation
He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A. Lindsay
2016-01-01
At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands. PMID:27181922
Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation.
He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A Lindsay
2016-05-16
At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands.
van Opheusden, Joost H. J.; Molenaar, J.
2014-04-01
In this paper we describe a viscoelastic type of phase separation in a simulated binary fluid with a sticky and an inert component, without any external gradients. Phase segregation under simple shear occurs due to transient network formation of the sticky component, expelling the inert particles from the network. When model parameters are adjusted to reduce network formation and rearrangement, the segregation effect is significantly smaller or absent. The behavior is independent of shear rate; segregation increases mainly with shear strain. The model is applied to wheat dough. Recent experiments have shown that prolonged shear flow of wheat dough can even give macroscopic segregation.
Jezek, Josef; Gilder, Stuart A.
2006-12-01
We present a model that describes the rotation of ellipsoidal magnetic particles in a viscous fluid under the influence of hydrodynamic and magnetic forces, with an aim to better understand how sediments acquire their remanent magnetizations. Analyses of the governing equations elucidate how magnetic particles will rotate for different values of leading parameters including particle shape, remanent and induced magnetic intensity, magnetic field intensity and direction, strain rate, shear direction, and viscosity. Numerical solution of the governing equations makes it possible to visualize the rotation path and the magnetic direction of a particle through time. Thus the model can discern the timescales and trajectories of magnetic particles rotating due to torque of the magnetic field couple while simultaneously entrained in a velocity gradient. For example, in a layer of viscosity 104 Pa s, prolate magnetite starting at any initial orientation and subjected to simple shear with a strain rate of 3.17 × 10-8 s-1 needs 4 months to rotate within 3° of the Earth's field direction. Under the same conditions, hydrodynamic forces will govern the orientation of oblate hematite whose moment will be perpetually randomly oriented with respect to the magnetic field direction. When applied to laboratory experiments, the viscous model successfully matches the observed data, particularly after accounting for mechanical interaction and flocculation effects. Magnetic anisotropies calculated from multiparticle systems of hematite yield typical sedimentary fabrics with relatively low percentages of anisotropy (<5%) and maximum principal axes that lie in the sedimentation plane.
M.Q. Jiang
2015-08-01
Full Text Available A theoretical model that takes into account the free-volume aided cooperative shearing of shear transformation zones (STZs is developed to quantitatively understand the ductile-to-brittle transition (DBT of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-type rearrangements to dilatational processes (termed tension transformation zones (TTZs.
Water pumping in mantle shear zones
Précigout, Jacques; Prigent, Cécile; Palasse, Laurie; Pochon, Anthony
2017-06-01
Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is thus crucial to understanding how water impacts Earth's geodynamics. Here we demonstrate that ductile flow exerts a dynamic control on water-rich fluid circulation in mantle shear zones. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. We also give evidence of cracking induced by fluid pressure where the highest amount of water is expected. These results emphasize long-term fluid pumping attributed to creep cavitation and associated phase nucleation during grain size reduction. Considering the ubiquitous process of grain size reduction during strain localization, our findings shed light on multiple fluid reservoirs in the crust and mantle.
Suvorov, A. P.; Selvadurai, A. P. S.
2016-11-01
The paper examines the problem of the shear of a porous hyperelastic material, the pore space of which is saturated with an incompressible fluid. Poro-hyperelasticity provides a suitable approach for modelling the mechanical behaviour of highly deformable materials in engineering applications and particularly soft tissues encountered in biomechanical applications. Unlike with the infinitesimal theory of poroelasticity, the application of pure shear generates pore fluid pressures that dissipate with time as fluid migrates either from or into the pore space due to the generated fluid pressure gradients. The analytical results provide benchmark problems that can be used to examine the accuracy of computational approaches.
Shear loading of costal cartilage
Subit, Damien
2014-01-01
A series of tests were performed on a single post-mortem human subject at various length scales. First, tabletop tests were performed. Next, the ribs and intercostal muscles were tested with the view to characterize the load transfer between the ribs. Finally, the costal cartilage was tested under shear loading, as it plays an important in the transfer of the load between the ribs and the sternum. This paper reports the results of dynamic shear loading tests performed on three samples of costal cartilage harvested from a single post-mortem human subject, as well as the quantification of the effective Young's modulus estimated from the amount of cartilage calcification.
Shear strength of non-shear reinforced concrete elements
Hoang, Cao linh
1997-01-01
. The position of the crack in which sliding takes place is determined by the crack sliding model developed by Jin-Ping Zhang. The theoretical calculations are compared with test results reported in the literature. A good agreement has been found.A simplified method to calculate the shear capacity of T...
Shear resistance of beams based on the effective shear depth
Pruijssers, A.F.
1986-01-01
Despite extensive experimental and theoretical studies the shear resistance of beams with longitudinal reinforcement is described by empirical expressions. A reliable empirical formula is derived by Rafla [10]. This formula is based on 442 experimental results. In this report no experiments are
Cosmic Shear Bias and Calibration in Cosmic Shear Studies
Taylor, A N
2016-01-01
With the advent of large-scale weak lensing surveys there is a need to understand how realistic, scale-dependent systematics bias cosmic shear and dark energy measurements, and how they can be removed. Here we describe how spatial variations in the amplitude and orientation of realistic image distortions convolve with the measured shear field, mixing the even-parity convergence and odd-parity modes, and bias the shear power spectrum. Many of these biases can be removed by calibration to external data, the survey itself, or by modelling in simulations. The uncertainty in the calibration must be marginalised over and we calculate how this propagates into parameter estimation, degrading the dark energy Figure-of-Merit. We find that noise-like biases affect dark energy measurements the most, while spikes in the bias power have the least impact, reflecting their correlation with the effect of cosmological parameters. We argue that in order to remove systematic biases in cosmic shear surveys and maintain statistica...
Active Control of Shear Thickening in Suspensions
Lin, Neil Y C; Cates, Michael E; Sun, Jin; Cohen, Itai
2016-01-01
Shear thickening, an increase of viscosity with shear rate, is a ubiquitous phenomena in suspended materials that has implications for broad technological applications. Controlling this thickening behavior remains a major challenge and has led to empirical strategies ranging from altering the particle surfaces and shape to modifying the solvent properties. However, none of these methods allow for active control of flow properties during shear itself. Here, we demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate shear thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to two decades on demand. In a separate setup, we show that such effects can be induced by simply agitating the sample transversely to the primary shear direction. Overall, the ability of in situ manipulation of shear thickening paves a...
Shear wave splitting and subcontinental mantle deformation
Silver, Paul G.; Chan, W. Winston
1991-09-01
We have made measurements of shear wave splitting in the phases SKS and SKKS at 21 broadband stations in North America, South America, Europe, Asia, and Africa. Measurements are made using a retrieval scheme that yields the azimuth of the fast polarization direction ϕ and delay time δt of the split shear wave plus uncertainties. Detectable anisotropy was found at most stations, suggesting that it is a general feature of the subcontinental mantle. Delay times range from 0.65 s to 1.70 s and average about 1 s. Somewhat surprisingly, the largest delay time is found in the 2.7 b.y.-old Western Superior Province of the Canadian Shield. The splitting observations are interpreted in terms of the strain-induced lattice preferred orientation of mantle minerals, especially olivine. We consider three hypotheses concerning the origin of the continental anisotropy: (1) strain associated with absolute plate motion, as in the oceanic upper mantle, (2) crustal stress, and (3) the past and present internal deformation of the subcontinental upper mantle by tectonic episodes. It is found that the last hypothesis is the most successful, namely that the most recent significant episode of internal deformation appears to be the best predictor of ϕ. For stable continental regions, this is interpreted as "fossil" anisotropy, whereas for presently active regions, such as Alaska, the anisotropy reflects present-day tectonic activity. In the stable portion of North America there is a good correlation between delay time and lithospheric thickness; this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant. The acceptance of this hypothesis has several implications for subcontinental mantle deformation. First, it argues for coherent deformation of the continental lithosphere (crust and mantle) during orogenies. This implies that the anisotropic portion of the lithosphere was present since the
Maximum Genus of Strong Embeddings
Er-ling Wei; Yan-pei Liu; Han Ren
2003-01-01
The strong embedding conjecture states that any 2-connected graph has a strong embedding on some surface. It implies the circuit double cover conjecture: Any 2-connected graph has a circuit double cover.Conversely, it is not true. But for a 3-regular graph, the two conjectures are equivalent. In this paper, a characterization of graphs having a strong embedding with exactly 3 faces, which is the strong embedding of maximum genus, is given. In addition, some graphs with the property are provided. More generally, an upper bound of the maximum genus of strong embeddings of a graph is presented too. Lastly, it is shown that the interpolation theorem is true to planar Halin graph.
Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear
Rogers, Michael C.; Chen, Kui; Andrzejewski, Lukasz; Narayanan, Suresh; Ramakrishnan, Subramanian; Leheny, Robert L.; Harden, James L.
2014-12-22
We report x-ray photon correlation spectroscopy experiments on a concentrated nanocolloidal gel subject to in situ oscillatory shear strain. The strain causes periodic echoes in the speckle pattern that lead to peaks in the intensity autocorrelation function. Above a threshold strain that is near the first yield point of the gel, the peak amplitude decays exponentially with the number of shear cycles, signaling irreversible particle rearrangements. The wave-vector dependence of the decay rate reveals a power-law distribution in the size of regions undergoing shear-induced rearrangement. The gel also displays strain softening well below the threshold, indicating a range of strains at which the rheology is nonlinear but the microscopic deformations are reversible.
Ductility of Advanced High-Strength Steel in the Presence of a Sheared Edge
Ruggles, Tim; Cluff, Stephen; Miles, Michael; Fullwood, David; Daniels, Craig; Avila, Alex; Chen, Ming
2016-07-01
The ductility of dual-phase (DP) 980 and transformation-induced plasticity (TRIP) assisted bainitic ferritic (TBF) 980 steels was studied in the presence of a sheared edge. Specimens were tested in uniaxial tension in a standard test frame as well as in situ in the scanning electron microscope (SEM). Incremental tensile straining was done in the SEM with images taken at each strain increment. Then digital image correlation (DIC) was used to compute the effective strain at the level of the individual phases in the microstructure. Shear banding across multiple phases was seen in strained TBF specimens, while the DP specimens exhibited more of a patchwork strain pattern, with high strains concentrated in ferrite and low strains observed in the martensite. Two-point statistics were applied to the strain data from the DIC work and the corresponding microstructure images to evaluate the effect of phase hardness on localization and fracture. It was observed that the DP 980 material had a greater tendency for localization around hard phases compared to the TBF 980. This at least partially explains the greater ductility of the TBF material, especially in specimens where a sheared edge was present.
Remizov, Ivan D
2009-01-01
In this note, we represent a subdifferential of a maximum functional defined on the space of all real-valued continuous functions on a given metric compact set. For a given argument, $f$ it coincides with the set of all probability measures on the set of points maximizing $f$ on the initial compact set. This complete characterization lies in the heart of several important identities in microeconomics, such as Roy's identity, Sheppard's lemma, as well as duality theory in production and linear programming.
The Testability of Maximum Magnitude
Clements, R.; Schorlemmer, D.; Gonzalez, A.; Zoeller, G.; Schneider, M.
2012-12-01
Recent disasters caused by earthquakes of unexpectedly large magnitude (such as Tohoku) illustrate the need for reliable assessments of the seismic hazard. Estimates of the maximum possible magnitude M at a given fault or in a particular zone are essential parameters in probabilistic seismic hazard assessment (PSHA), but their accuracy remains untested. In this study, we discuss the testability of long-term and short-term M estimates and the limitations that arise from testing such rare events. Of considerable importance is whether or not those limitations imply a lack of testability of a useful maximum magnitude estimate, and whether this should have any influence on current PSHA methodology. We use a simple extreme value theory approach to derive a probability distribution for the expected maximum magnitude in a future time interval, and we perform a sensitivity analysis on this distribution to determine if there is a reasonable avenue available for testing M estimates as they are commonly reported today: devoid of an appropriate probability distribution of their own and estimated only for infinite time (or relatively large untestable periods). Our results imply that any attempt at testing such estimates is futile, and that the distribution is highly sensitive to M estimates only under certain optimal conditions that are rarely observed in practice. In the future we suggest that PSHA modelers be brutally honest about the uncertainty of M estimates, or must find a way to decrease its influence on the estimated hazard.
Alternative Multiview Maximum Entropy Discrimination.
Chao, Guoqing; Sun, Shiliang
2016-07-01
Maximum entropy discrimination (MED) is a general framework for discriminative estimation based on maximum entropy and maximum margin principles, and can produce hard-margin support vector machines under some assumptions. Recently, the multiview version of MED multiview MED (MVMED) was proposed. In this paper, we try to explore a more natural MVMED framework by assuming two separate distributions p1( Θ1) over the first-view classifier parameter Θ1 and p2( Θ2) over the second-view classifier parameter Θ2 . We name the new MVMED framework as alternative MVMED (AMVMED), which enforces the posteriors of two view margins to be equal. The proposed AMVMED is more flexible than the existing MVMED, because compared with MVMED, which optimizes one relative entropy, AMVMED assigns one relative entropy term to each of the two views, thus incorporating a tradeoff between the two views. We give the detailed solving procedure, which can be divided into two steps. The first step is solving our optimization problem without considering the equal margin posteriors from two views, and then, in the second step, we consider the equal posteriors. Experimental results on multiple real-world data sets verify the effectiveness of the AMVMED, and comparisons with MVMED are also reported.
Critical shear stress produced by interaction of edge dislocation with nanoscale inhomogeneity
Q H Fang; J M Chen; Y W Liu; P H Wen
2010-04-01
According to the Mott and Nabarro’s model, the contribution to the critical shear stress of the material caused by the interaction between edge dislocations and nanoscale cylindrical inhomogeneities with interface stresses is obtained. The influence of the radius and the volume fraction of the inhomogeneity as well as the interface stresses on the critical shear stress is investigated. The important result is that, if the interface stress is considered, a maximum of the contribution to the critical shear stress produced by this interaction may be obtained when the radius of the inhomogeneity reaches a critical value.
Estimation of the shear stress on the surface of an aortic valve leaflet.
Weston, M W; LaBorde, D V; Yoganathan, A P
1999-01-01
The limited durability of xenograft heart valves and the limited supply of allografts have sparked interest in tissue engineered replacement valves. A bioreactor for tissue engineered valves must operate at conditions that optimize the biosynthetic abilities of seeded cells while promoting their adherence to the leaflet matrix. An important parameter is shear stress, which is known to influence cellular behavior and may thus be crucial in bioreactor optimization. Therefore, an accurate estimate of the shear stress on the leaflet surface would not only improve our understanding of the mechanical environment of aortic valve leaflets, but it would also aid in bioreactor design. To estimate the shear stress on the leaflet surface, two-component laser-Doppler velocimetry measurements have been conducted inside a transparent polyurethane valve with a trileaflet structure similar to the native aortic valve. Steady flow rates of 7.5, 15.0, and 22.5 L/min were examined to cover the complete range possible during the cardiac cycle. The laminar shear stresses were calculated by linear regression of four axial velocity measurements near the surface of the leaflet. The maximum shear stress recorded was 79 dyne/cm2, in agreement with boundary layer theory and previous experimental and computational studies. This study has provided a range of shear stresses to be explored in bioreactor design and has defined a maximum shear stress at which cells must remain adherent upon a tissue engineered construct.
Laboratory studies on the effects of shear on fish: Final report
Neitzel, Duane A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Richmond, M. C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Dauble, D. D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Mueller, R. P. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Moursund, R. A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Abernethy, C. S. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Guensch, G. R. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Cada, G. F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2000-09-01
The overall objective of these studies was to specify an index describing the hydraulic force that fish experience when subjected to a shear environment. Fluid shear is a phenomenon that is important to fish. However, elevated levels of shear may result in strain rates that injure or kill fish. At hydroelectric generating facilities, concerns have been expressed that strain rates associated with passage through turbines, spillways, and fish bypass systems may adversely affect migrating fish. Development of fish-friendly hydroelectric turbines requires knowledge of the physical forces (injury mechanisms) that impact entrained fish and the fish’s tolerance to these forces. It requires up-front, pre-design specifications for the environmental conditions that occur within the turbine system; in other words, determining or assuming conditions known to injure fish will assist engineers in the design of a fish-friendly turbine system. To address the development of biological specifications, this experiment designed and built a test facility where juvenile fish could be subjected to a range of shear environments and quantified their biological response. The test data reported here provide quantified strain rates and the relationship of these forces to direct and indirect biological effects on fish. The study concludes that juvenile salmonids and American shad should survive shear environments where strain rates do not exceed 500 cm/s/cm at a Dy of 1.8 cm. Additional studies are planned with a sensor fish to better link hydraulic conditions found within the laboratory and field environments.
Prediction of shear bands in sand based on granular flow model and two-phase equilibrium
张义同; 齐德瑄; 杜如虚; 任述光
2008-01-01
In contrast to the traditional interpretation of shear bands in sand as a bifurcation problem in continuum mechanics,shear bands in sand are considered as high-strain phase(plastic phase) of sand and the materials outside the bands are still in low-strain phase(elastic phase),namely,the two phases of sand can coexist under certain condition.As a one-dimensional example,the results show that,for materials with strain-softening behavior,the two-phase solution is a stable branch of solutions,but the method to find two-phase solutions is very different from the one for bifurcation analysis.The theory of multi-phase equilibrium and the slow plastic flow model are applied to predict the formation and patterns of shear bands in sand specimens,discontinuity of deformation gradient and stress across interfaces between shear bands and other regions is considered,the continuity of displacements and traction across interfaces is imposed,and the Maxwell relation is satisfied.The governing equations are deduced.The critical stress for the formation of a shear band,both the stresses and strains inside the band and outside the band,and the inclination angle of the band can all be predicted.The predicted results are consistent with experimental measurements.
Pulsatile blood flow, shear force, energy dissipation and Murray's Law
Bengtsson Hans-Uno
2006-08-01
Full Text Available Abstract Background Murray's Law states that, when a parent blood vessel branches into daughter vessels, the cube of the radius of the parent vessel is equal to the sum of the cubes of the radii of daughter blood vessels. Murray derived this law by defining a cost function that is the sum of the energy cost of the blood in a vessel and the energy cost of pumping blood through the vessel. The cost is minimized when vessel radii are consistent with Murray's Law. This law has also been derived from the hypothesis that the shear force of moving blood on the inner walls of vessels is constant throughout the vascular system. However, this derivation, like Murray's earlier derivation, is based on the assumption of constant blood flow. Methods To determine the implications of the constant shear force hypothesis and to extend Murray's energy cost minimization to the pulsatile arterial system, a model of pulsatile flow in an elastic tube is analyzed. A new and exact solution for flow velocity, blood flow rate and shear force is derived. Results For medium and small arteries with pulsatile flow, Murray's energy minimization leads to Murray's Law. Furthermore, the hypothesis that the maximum shear force during the cycle of pulsatile flow is constant throughout the arterial system implies that Murray's Law is approximately true. The approximation is good for all but the largest vessels (aorta and its major branches of the arterial system. Conclusion A cellular mechanism that senses shear force at the inner wall of a blood vessel and triggers remodeling that increases the circumference of the wall when a shear force threshold is exceeded would result in the observed scaling of vessel radii described by Murray's Law.
Experimental observation of shear thickening oscillation
Nagahiro, Shin-ichiro; Mitarai, Namiko
2012-01-01
We report experimental observation of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. The shear thickening oscillation is caused by the interplay between the fluid dynamics and the shear thickening, and has been predicted theoretically by the present authors using a phenomenological fluid dynamics model for the dilatant fluid, but never been reported experimentally. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed strong vibrations of the frequency around 20 Hz, which is consistent with our theoretical prediction.
Unexpected shear strength change in magnetorheological fluids
Yu Tian
2014-09-01
Full Text Available Smart materials of magnetorheological (MR fluids could be turned from a liquid state into a solid state, which solidification extent or shear strength often increases monotonically with the applied magnetic field. In this study, the shear stress of a dilute MR fluid decreased with increasing applied magnetic field at a constant shear rate. The dynamic shear stress was significantly higher than the stable counterpart at medium magnetic fields. They are ascribed to the slow particle structure transformation. A higher shear rate and particle volume fraction could reduce the transient time and the shear strength difference.
Structural mechanisms of formation of adiabatic shear bands
Mikhail Sokovikov
2016-10-01
Full Text Available The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the
Richter, B.; Stünitz, H.; Heilbronner, R.
2016-11-01
Coesite was found in quartz aggregates, experimentally deformed at confining pressures of 1.0-1.5 GPa and temperatures between 600°C and 900°C. The confining pressure (Pc) and, in most cases, the mean stress (σm) of the experiments were below those of the quartz-to-coesite phase transformation. Yet coesite formed when the maximum principal stress (σ1) was within the P-T range of the coesite stability field. In one sample, the euhedral coesite grains were corroded indicating that coesite started to transform back to quartz. It is inferred that this sample started to deform with σ1 above the quartz-to-coesite phase transformation and, with ongoing deformation, σ1 decreased to values in the quartz stability field due to strain weakening. In all cases, σ1 triggered the quartz-to-coesite reaction as well as the reverse reaction, suggesting that σ1 is the critical parameter for the quartz-to-coesite transformation—not Pc or σm. With progressive deformation, the coesite laths rotated toward the shear plane as more rigid particles with the sense of shear. In case of back reaction, new quartz grains exhibit no systematic crystallographic relationship with respect to old coesite. The experiments cover different degrees of pressure "overstepping," different temperatures, and different experimental durations at P and T, and deformation always enhances the reaction kinetics. The observation that σ1 is critical for a pressure-dependent phase transformation (also for reversals) poses questions for the thermodynamic treatment of such phase transformations.
Investigation on Cracking of Concrete Shear Wall under Exceeded Temperature Differences Rate
无
2006-01-01
In situ, the changes of temperature, deformation, and stressing of steel bar of C40 reinforced concrete shear wall were measured, respectively. The results are obvious that the temperature change of climate is one of the most effective factors which could lead the concrete shear wall to cracking at earlier age. The temperature differences between inside and outside concrete shear wall are so large that the concrete will gain larger shrinkage. This larger shrinkage which is caused by the temperature reducing ratio will gain the strained action of head, end and reinforced steel bar of concrete shear wall. This action can lead to tensile stress on the surface and inside concrete shear wall. If the tensile stress would exceed the pull strength of concrete, the concrete shear wall would crack and cause deterioration. Thus, the enhancing curing of concrete shear wall in suit at earlier age, and controlling temperature reducing ratio and deform caused by shrinkage, will be available treatments which control occurring and developing of cracking on concrete shear wall.
JU; Yiwen; WANG; Guiliang; JIANG; Bo; HOU; Quanlin
2004-01-01
The ductile shearing zones of coal seams in a brittle deformation domain in superficial lithosphere are put forward based on the study on bedding shearing and ductile rheology of coal seams. The macrocosmic and microcosmic characteristics include wrinkle fold, mymonitized zones and ductile planar structure of coal seams, etc., while the microcosmic characteristics may also include different optic-axis fabrics and the anisotropy of vitrinite reflectance as well as the change of chemical structure and organic geochemistry components. The forming mechanism is analyzed and the strain environment of ductile shearing zones of coal seams discussed. The result indicates that, in the superficial brittle deformation domain, the coal seams are easy to be deformed, resulting in not only brittle deformation but also ductile shearing deformation under the action of force. Because of simple shearing stress, the interlayer gliding or ductile rheology may take place between coal seams and wall rocks. Therefore, many ductile shearing zones come into being in superficial lithosphere (<5 km). The research on ductile shearing zone of brittle deformation domain in superficial lithosphere is significant not only theoretically for the study of ductile shearing and ductile rheology of the lithosphere but also practically for the structural movement of coal seams, the formation and accumulation of coal-bed methane, and the prevention and harness of gas burst in coal mine.
Shear Melting and High Temperature Embrittlement: Theory and Application to Machining Titanium
Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J.
2015-04-01
We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.
Shear behavior of coarse aggregates for dam construction under varied stress paths
Liu Hanlong; Deng An; Shen Yang
2008-01-01
Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads. With the increase of dam height, high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates, and thus impede the high dam's proper construction, operation and maintenance. An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus. Through triaxial shear tests, the strain-stress behaviors of aggregates were observed under constant confining pressures: 300 kPa, 600 kPa, 900 kPa and 1200 kPa. Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed. Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states. In triaxial shear tests, it was found that peak deviator stresses increase along with confining pressures, whereas the peak principal stress ratios decrease as confining pressures increase. With increasing confining pressures, the dilation decreases and the contraction eventually prevails. Initial strength parameters (Poisson's ratio and tangent modulus) show a nonlinear relationship with confining pressures when the pressures are relatively low. Shear strength parameters decrease with increasing confining pressures. The failure envelope lines are convex curves, with clear curvature under low confining pressures. Under moderate confining pressures, dilation is offset by particle breakage. Under high confining pressures, dilation disappears.
Shear melting and high temperature embrittlement: theory and application to machining titanium.
Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J
2015-04-24
We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.
Maximum bubble pressure rheology of low molecular mass organogels.
Fei, Pengzhan; Wood, Steven J; Chen, Yan; Cavicchi, Kevin A
2015-01-13
Maximum bubble pressure rheology is used to characterize organogels of 0.25 wt % 12-hydroxystearic acid (12-HSA) in mineral oil, 3 wt % (1,3:2,4) dibenzylidene sorbitol (DBS) in poly(ethylene glycol), and 1 wt % 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) in poly(ethylene glycol). The maximum pressure required to inflate a bubble at the end of capillary inserted in a gel is measured. This pressure is related to the gel modulus in the case of elastic cavitation and the gel modulus and toughness in the case of irreversible fracture. The 12-HSA/mineral oil gels are used to demonstrate that this is a facile technique useful for studying time-dependent gel formation and aging and the thermal transition from a gel to a solution. Comparison is made to both qualitative gel tilting measurements and quantitative oscillatory shear rheology to highlight the utility of this measurement and its complementary nature to oscillatory shear rheology. The DBS and DMDBS demonstrate the generality of this measurement to measure gel transition temperatures.
Shear-affected depletion interaction
July, C.; Kleshchanok, D.; Lang, P.R.
2012-01-01
We investigate the influence of flow fields on the strength of the depletion interaction caused by disc-shaped depletants. At low mass concentration of discs, it is possible to continuously decrease the depth of the depletion potential by increasing the applied shear rate until the depletion force i
Grouted Connections with Shear Keys
Pedersen, Ronnie; Jørgensen, M. B.; Damkilde, Lars
2012-01-01
This paper presents a finite element model in the software package ABAQUS in which a reliable analysis of grouted pile-to-sleeve connections with shear keys is the particular purpose. The model is calibrated to experimental results and a consistent set of input parameters is estimated so...
A simplified four-unknown shear and normal deformations theory for bidirectional laminated plates
A M Zenkour
2015-02-01
This paper presents a simplified 4-unknown shear and normal deformations theory for the bending analysis of cross-ply laminated plates. The present theory accounts for an adequate distribution of transverse shear strains through the plate thickness and tangential stress-free on the plate surfaces. The effect of normal strain is also included. The governing, equilibrium equations and boundary conditions are derived by employing the virtual work principle. Numerical results for stresses and displacements are compared well with those obtained using 3-D elasticity solution.
Contact changes of sheared systems: Scaling, correlations, and mechanisms
van Deen, Merlijn S.; Tighe, Brian P.; van Hecke, Martin
2016-12-01
We probe the onset and effect of contact changes in two-dimensional soft harmonic particle packings which are sheared quasistatically under controlled strain. First, we show that, in the majority of cases, the first contact changes correspond to the creation or breaking of contacts on a single particle, with contact breaking overwhelmingly likely for low pressures and/or small systems, and contact making and breaking equally likely for large pressures and in the thermodynamic limit. The statistics of the corresponding strains are near-Poissonian, in particular for large-enough systems. The mean characteristic strains exhibit scaling with the number of particles N and pressure P and reveal the existence of finite-size effects akin to those seen for linear response quantities [C. P. Goodrich et al., Phys. Rev. Lett. 109, 095704 (2012), 10.1103/PhysRevLett.109.095704; C. P. Goodrich et al., Phys. Rev. E 90, 022138 (2014)]., 10.1103/PhysRevE.90.022138 Second, we show that linear response accurately predicts the strains of the first contact changes, which allows us to accurately study the scaling of the characteristic strains of making and breaking contacts separately. Both of these show finite-size scaling, and we formulate scaling arguments that are consistent with the observed behavior. Third, we probe the effect of the first contact change on the shear modulus G and show in detail how the variation of G remains smooth and bounded in the large-system-size limit: Even though contact changes occur then at vanishingly small strains, their cumulative effect, even at a fixed value of the strain, are limited, so, effectively, linear response remains well defined. Fourth, we explore multiple contact changes under shear and find strong and surprising correlations between alternating making and breaking events. Fifth, we show that by making a link with extremal statistics, our data are consistent with a very slow crossover to self-averaging with system size, so the