Stress-Strain Relationship and Failure Criterion for Concrete after Freezing and Thawing Cycles
Luo Xin; Wei Jun
2006-01-01
The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out.Based on the damage mechanics theory, the damage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained.Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies the rationality of the damage-based one-dimensional stress-strain relationship proposed.
A Failure Criterion for Concrete
Ottosen, N. S.
1977-01-01
A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace in the devi......A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace...
A Failure Criterion for Concrete
Ottosen, N. S.
1977-01-01
A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace in the devi......A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace...
MENG Xiang-rui; GAO Zhao-ning; WANG Xiang-qian
2012-01-01
By turning to the theory of elastic thin plates,a mechanical model of the main roof breaking for severely inclined seam under long wall working was esbalished,in which formulaes were deduced for the calculation of the stress distribution.When the main roof stress distribution was characterized,the failure form of the roof in the long wall coal seam under work was given with the failure criterion deduced.The deduced failure criterion was then applied to the No.3232(3) face of the Lizuizi Coal Mine; the first pressure for the working face was accurately predicted.Results of the field application show that the main roof of the severely inclined coal seam under long wall working breaks in the O-X pattern,which is basically in accordance with the reality.
Li Xing; Guan Zhidong; Li Zengshan; Liu Lu
2014-01-01
A new stress-based multi-scale failure criterion is proposed based on a series of off-axis tension tests, and their corresponding fiber failure modes and matrix failure modes are determined at the microscopic level. It is a physical mechanism based, three-dimensional damage analysis cri-terion which takes into consideration the constituent properties on the macroscopic failure behavior of the composite laminates. A complete set of stress transformation, damage determination and evolution methods are established to realize the application of the multi-scale method in failure analysis. Open-hole tension (OHT) specimens of three material systems (CCF300/5228, CCF300/5428 and T700/5428) are tested according to ASTM standard D5766, and good agreements are found between the experimental results and the numerical predictions. It is found that fiber strength is a key factor influencing the ultimate strength of the laminates, while matrix failure alleviates the stress concentration around the hole. Different matchings of fiber and matrix result in different fail-ure modes as well as ultimate strengths.
Hackston, Abigail; Rutter, Ernest
2016-04-01
Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr-Coulomb failure criterion under axisymmetric shortening conditions, provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compressive stress direction in the two loading configurations. The normals to the Mohr-Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined saw cuts and failure surfaces produced in intact rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both rock types. Friction data for these and other porous sandstones accord well with the Byerlee (1978) generalization about rock friction being largely independent of rock type. For engineering and geodynamic modelling purposes, the stress-state-dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other rock types.
Formulation of cross-anisotropic failure criterion for soils
Yi-fei SUN
2013-10-01
Full Text Available Inherently anisotropic soil fabric has a considerable influence on soil strength. To model this kind of inherent anisotropy, a three-dimensional anisotropic failure criterion was proposed, employing a scalar-valued anisotropic variable and a modified general three- dimensional isotropic failure criterion. The scalar-valued anisotropic variable in all sectors of the deviatoric plane was defined by correlating a normalized stress tensor with a normalized fabric tensor. Detailed comparison between the available experimental data and the corresponding model predictions in the deviatoric plane was conducted. The proposed failure criterion was shown to well predict the failure behavior in all sectors, especially in sector II with the Lode angle ranging between 60º and 120º, where the prediction was almost in accordance with test data. However, it was also observed that the proposed criterion overestimated the strength of dense Santa Monica Beach sand in sector III where the intermediate principal stress ratio b varied from approximately 0.2 to 0.8, and slightly underestimated the strength when b was between approximately 0.8 and 1. The difference between the model predictions and experimental data was due to the occurrence of shear bending, which might reduce the measured strength. Therefore, the proposed anisotropic failure criterion has a strong ability to characterize the failure behavior of various soils and potentially allows a better description of the influence of the loading direction with respect to the soil fabric.
Failure Criterion for Brick Masonry: A Micro-Mechanics Approach
Kawa Marek
2015-02-01
Full Text Available The paper deals with the formulation of failure criterion for an in-plane loaded masonry. Using micro-mechanics approach the strength estimation for masonry microstructure with constituents obeying the Drucker-Prager criterion is determined numerically. The procedure invokes lower bound analysis: for assumed stress fields constructed within masonry periodic cell critical load is obtained as a solution of constrained optimization problem. The analysis is carried out for many different loading conditions at different orientations of bed joints. The performance of the approach is verified against solutions obtained for corresponding layered and block microstructures, which provides the upper and lower strength bounds for masonry microstructure, respectively. Subsequently, a phenomenological anisotropic strength criterion for masonry microstructure is proposed. The criterion has a form of conjunction of Jaeger critical plane condition and Tsai-Wu criterion. The model proposed is identified based on the fitting of numerical results obtained from the microstructural analysis. Identified criterion is then verified against results obtained for different loading orientations. It appears that strength of masonry microstructure can be satisfactorily described by the criterion proposed.
Nonlinear viscoelasticity and generalized failure criterion for biopolymer gels
Divoux, Thibaut; Keshavarz, Bavand; Manneville, Sébastien; McKinley, Gareth
2016-11-01
Biopolymer gels display a multiscale microstructure that is responsible for their solid-like properties. Upon external deformation, these soft viscoelastic solids exhibit a generic nonlinear mechanical response characterized by pronounced stress- or strain-stiffening prior to irreversible damage and failure, most often through macroscopic fractures. Here we show on a model acid-induced protein gel that the nonlinear viscoelastic properties of the gel can be described in terms of a 'damping function' which predicts the gel mechanical response quantitatively up to the onset of macroscopic failure. Using a nonlinear integral constitutive equation built upon the experimentally-measured damping function in conjunction with power-law linear viscoelastic response, we derive the form of the stress growth in the gel following the start up of steady shear. We also couple the shear stress response with Bailey's durability criteria for brittle solids in order to predict the critical values of the stress σc and strain γc for failure of the gel, and how they scale with the applied shear rate. This provides a generalized failure criterion for biopolymer gels in a range of different deformation histories. This work was funded by the MIT-France seed fund and by the CNRS PICS-USA scheme (#36939). BK acknowledges financial support from Axalta Coating Systems.
Study on triaxial test method and failure criterion of asphalt mixture
Jianlong Zheng
2015-04-01
Full Text Available Asphalt mixture is the most widely used pavement material all over the world. In China, more than 90% of service expressways are asphalt pavement. However, current asphalt pavement design method still has irrationality. Even though maximum tensile stress theory is used as failure criterion, pavement structure under the effects of wheel load is in three-dimensional complex stress state. Obviously, one-dimensional strength theory cannot reflect the failure characteristics and the resistance of pavement structure. So it is necessary to study the failure criterion of asphalt mixture under three-dimensional complex stress state. Due to limitations of test equipment, there are almost no studies in related area. Under this background, this paper develops a new triaxial test method, according to the investigation of strength characteristics of asphalt mixture under complex stress state through plane isobaric/axial tensile test, plane isobaric/axial compression test, plane tensile and compression/axial tensile test, to reveal the general rules of asphalt mixture's strength failure. The failure mode is divided into three types: tensile failure, shear failure and rheological failure. The tensile meridian and compression meridian in the stress space and strength envelope in the π plane where hydrostatic pressure is greater than zero are obtained, and the failure criterion of asphalt mixture under complex stress state is established, providing theoretical method and scientific basis for structure design as well as strength check of asphalt pavement under three-dimensional stress state.
Optimization of laminates subjected to failure criterion
E. Kormaníková
2011-01-01
Full Text Available The paper is aimed on laminate optimization subjected to maximum strain criterion. The optimization problem is based on the use of continuous design variables. The thicknesses of layers with the known orientation are used as design variables. The optimization problem with strain constraints are formulated to minimize the laminate weight. The design of the final thickness is rounded off to integer multiples of the commercially available layer thickness.
A modified failure criterion for transversely isotropic rocks
Omid Saeidi; Vamegh Rasouli; Rashid Geranmayeh Vaneghi; Raoof Gholami; Seyed Rahman Torabi
2014-01-01
A modified failure criterion is proposed to determine the strength of transversely isotropic rocks. Me-chanical properties of some metamorphic and sedimentary rocks including gneiss, slate, marble, schist, shale, sandstone and limestone, which show transversely isotropic behavior, were taken into consider-ation. Afterward, introduced triaxial rock strength criterion was modified for transversely isotropic rocks. Through modification process an index was obtained that can be considered as a strength reduction parameter due to rock strength anisotropy. Comparison of the parameter with previous anisotropy in-dexes in literature showed reasonable results for the studied rock samples. The modified criterion was compared to modified Hoek-Brown and Ramamurthy criteria for different transversely isotropic rocks. It can be concluded that the modified failure criterion proposed in this study can be used for predicting the strength of transversely isotropic rocks.
Failure criterion for graphene in biaxial loading—a molecular dynamics study
Yazdani, Hessam; Hatami, Kianoosh
2015-09-01
Molecular dynamics simulations are carried out in order to develop a failure criterion for infinite/bulk graphene in biaxial tension. Stresses along the principal edge configurations of graphene (i.e. armchair and zigzag directions) are normalized to the corresponding uniaxial ultimate strength values. The combinations of normalized stresses resulting in the failure of graphene are used to define failure envelopes (limiting stress ratio surfaces). Results indicate that a bilinear failure envelope can be used to represent the tensile strength of graphene in biaxial loading at different temperatures with reasonable accuracy. A circular failure envelope is also introduced for practical applications. Both failure envelopes define temperature-independent upper limits for the feasible combinations of normalized stresses for a graphene sheet in biaxial loading. Predicted failure modes of graphene under biaxial loading are also shown and discussed.
A theoretical derivation of the HoekeBrown failure criterion for rock materials
Jianping Zuo; Huihai Liu; Hongtao Li
2015-01-01
This study uses a three-dimensional crack model to theoretically derive the HoekeBrown rock failure criterion based on the linear elastic fracture theory. Specifically, we argue that a failure characteristic factor needs to exceed a critical value when macro-failure occurs. This factor is a product of the micro-failure orientation angle (characterizing the density and orientation of damaged micro-cracks) and the changing rate of the angle with respect to the major principal stress (characterizing the microscopic stability of damaged cracks). We further demonstrate that the factor mathematically leads to the empirical HoekeBrown rock failure criterion. Thus, the proposed factor is able to successfully relate the evolution of microscopic damaged crack characteristics to macro-failure. Based on this theoretical development, we also propose a quantitative relationship between the brittleeductile transition point and confining pressure, which is consistent with experimental observations.
Seismic bearing capacity of strip footings on rock masses using the Hoek–Brown failure criterion
Amin Keshavarz
2016-04-01
Full Text Available In this paper, the bearing capacity of strip footings on rock masses has been studied in the seismic case. The stress characteristics or slip line method was used for analysis. The problem was analyzed in the plane strain condition using the Hoek–Brown failure criterion. First, the equilibrium equations along the stress characteristics were obtained and the rock failure criterion was applied. Then, the equations were solved using the finite difference method. A computer code has been provided for analysis. Given the footing and rock parameters, the code can calculate the stress characteristics network and obtain the stress distribution under the footing. The seismic effects have been applied as the horizontal and vertical pseudo-static coefficients. The results of this paper are very close to those of the other studies. The seismic bearing capacity of weightless rock masses can be obtained using the proposed equations and graphs without calculating the whole stress characteristics network.
Bergström, J S; Rimnac, C M; Kurtz, S M
2005-03-01
The development of accurate theoretical failure, fatigue, and wear models for ultra-high molecular weight polyethylene (UHMWPE) is an important step towards better understanding the micromechanisms of the surface damage that occur in load bearing orthopaedic components and improving the lifetime of joint arthoplasties. Previous attempts to analytically predict the clinically observed damage, wear, and fatigue failure modes have met with limited success due to the complicated interaction between microstructural deformations and continuum level stresses. In this work, we examined monotonic uniaxial and multiaxial loading to failure of UHMWPE using eight failure criteria (maximum principal stress, Mises stress, Tresca stress, hydrostatic stress, Coulomb stress, maximum principal strain, Mises strain, and chain stretch). The quality of the predictions of the different models was assessed by comparing uniaxial tension and small punch test data at different rates with the failure model predictions. The experimental data were obtained for two conventional (unirradiated and gamma radiation sterilized in nitrogen) and two highly crosslinked (150kGy, remelted and annealed) UHMWPE materials. Of the different failures models examined, the chain stretch failure model was found to capture uniaxial and multiaxial failure data most accurately for all of the UHMWPE materials. In addition, the chain stretch failure criterion can readily be calculated for contemporary UHMWPE materials based on available uniaxial tension data. These results lay the foundation for future developments of damage and wear models capable of predicting multiaxial failure under cyclic loading conditions.
Zhu, Qi-Zhi
2017-02-01
A proper criterion describing when material fails is essential for deep understanding and constitutive modeling of rock damage and failure by microcracking. Physically, such a criterion should be the global effect of local mechanical response and microstructure evolution inside the material. This paper aims at deriving a new mechanisms-based failure criterion for brittle rocks, based on micromechanical unilateral damage-friction coupling analyses rather than on the basic results from the classical linear elastic fracture mechanics. The failure functions respectively describing three failure modes (purely tensile mode, tensile-shear mode as well as compressive-shear mode) are achieved in a unified upscaling framework and illustrated in the Mohr plane and also in the plane of principal stresses. The strength envelope is proved to be continuous and smooth with a compressive to tensile strength ratio dependent on material properties. Comparisons with experimental data are finally carried out. By this work, we also provide a theoretical evidence on the hybrid failure and the smooth transition from tensile failure to compressive-shear failure.
STRENGTH CRITERION FOR PLAIN CONCRETE UNDER MULTIAXIAL STRESS BASED ON DAMAGE POISSON'S RATIO
Ding Faxing; Yu Zhiwu
2006-01-01
A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete (NC) and high strength concrete (HSC) in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 Mpa. The conception of damage Poisson's ratio is defined and the expression for damage Poisson's ratio is determined basically.The failure mechanism of concrete is illustrated, which points out that damage Poisson's ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.
Key Christopher T.
2015-01-01
Full Text Available This study details and demonstrates a strain-based criterion for the prediction of polymer matrix composite material damage and failure under shock loading conditions. Shock loading conditions are characterized by high-speed impacts or explosive events that result in very high pressures in the materials involved. These material pressures can reach hundreds of kbar and often exceed the material strengths by several orders of magnitude. Researchers have shown that under these high pressures, composites exhibit significant increases in stiffness and strength. In this work we summarize modifications to a previous stress based interactive failure criterion based on the model initially proposed by Hashin, to include strain dependence. The failure criterion is combined with the multi-constituent composite constitutive model (MCM within a shock physics hydrocode. The constitutive model allows for decomposition of the composite stress and strain fields into the individual phase averaged constituent level stress and strain fields, which are then applied to the failure criterion. Numerical simulations of a metallic sphere impacting carbon/epoxy composite plates at velocities up to 1000 m/s are performed using both the stress and strain based criterion. These simulation results are compared to experimental tests to illustrate the advantages of a strain-based criterion in the shock environment.
Key, Christopher T.; Schumacher, Shane C.; Alexander, C. Scott
2015-09-01
This study details and demonstrates a strain-based criterion for the prediction of polymer matrix composite material damage and failure under shock loading conditions. Shock loading conditions are characterized by high-speed impacts or explosive events that result in very high pressures in the materials involved. These material pressures can reach hundreds of kbar and often exceed the material strengths by several orders of magnitude. Researchers have shown that under these high pressures, composites exhibit significant increases in stiffness and strength. In this work we summarize modifications to a previous stress based interactive failure criterion based on the model initially proposed by Hashin, to include strain dependence. The failure criterion is combined with the multi-constituent composite constitutive model (MCM) within a shock physics hydrocode. The constitutive model allows for decomposition of the composite stress and strain fields into the individual phase averaged constituent level stress and strain fields, which are then applied to the failure criterion. Numerical simulations of a metallic sphere impacting carbon/epoxy composite plates at velocities up to 1000 m/s are performed using both the stress and strain based criterion. These simulation results are compared to experimental tests to illustrate the advantages of a strain-based criterion in the shock environment.
Haimson, Bezalel; Chang, Chandong; Ma, Xiaodong
2016-04-01
The UW true triaxial testing system enables the application of independent compressive loads to cuboidal specimens (19×19×38 mm) along three principal directions. We used the apparatus to conduct extensive series of experiments in three crystalline rocks (Westerly granite, KTB amphibolite, and SAFOD granodiorite) and three clastic rocks of different porosities [TCDP siltstone (7%), Coconino sandstone (17%), and Bentheim sandstone (24%)]. For each rock, several magnitudes of σ3 were employed, between 0 MPa and 100-160 MPa, and for every σ3, σ2 was varied from test to test between σ2 = σ3 and σ2=(0.4 to 1.0) σ1.Testing consisted of keeping σ2and σ3constant, and raising σ1to failure (σ1,peak). The results, plotted as σ1,peakvs. σ2for each σ3 used, highlight the undeniable effect of σ2on the compressive failure of rocks. For each level of σ3, the lowest σ2 tested (σ2 = σ3) yielded the data point used for conventional-triaxial failure criterion. However, for the same σ3 and depending on σ2 magnitude, the maximum stress bringing about failure (σ1,peak) may be considerably higher, by as much as 50% in crystalline rocks, or 15% in clastic rocks, over that in a conventional triaxial test. An important consequence is that use of a Mohr-type criterion leads to overly conservative predictions of failure. The true triaxial test results demonstrate that a criterion in terms of all (three principal stresses is necessary to characterize failure. Thus, we propose a 'Generalized Nadai Criterion' (GNC) based on Nadai (1950), i.e. expressed in terms of the two stress invariants at failure (f), τoct,f = βσoct,f, where τoct,f = 1/3[(σ1,peak -σ2)2+(σ2 -σ3)2+(σ3 -σ1,peak)2]0.5 and σoct,f = (σ1,peak + σ2 + σ3)/3, and β is a function that varies from rock to rock. Moreover, the criterion depends also on the relative magnitude of σ2, represented by a parameter b [= (σ2 - σ3)/(σ1,peak - σ3)]. For each octahedral shear stress at failure (
Jin-feng Zou
2016-01-01
Full Text Available In order to investigate the influence of the intermediate principal stress on the stress and displacement of surrounding rock, a novel approach based on 3D Hoek-Brown (H-B failure criterion was proposed. Taking the strain-softening characteristic of rock mass into account, the potential plastic zone is subdivided into a finite number of concentric annulus and a numerical procedure for calculating the stress and displacement of each annulus was presented. Strains were obtained based on the nonassociated and associated flow rule and 3D plastic potential function. Stresses were achieved by the stress equilibrium equation and generalized Hoek-Brown failure criterion. Using the proposed approach, we can get the solutions of the stress and displacement of the surrounding rock considering the intermediate principal stress. Moreover, the proposed approach was validated with the published results. Compared with the results based on generalized Hoek-Brown failure criterion, it is shown that the plastic radius calculated by 3D Hoek-Brown failure criterion is smaller than those solved by generalized H-B failure criterion, and the influences of dilatancy effect on the results based on the generalized H-B failure criterion are greater than those based on 3D H-B failure criterion. The displacements considering the nonassociated flow rule are smaller than those considering associated flow rules.
Energy Criterion of Oil Film Failure during Friction
S.V. Fedorov
2014-12-01
Full Text Available The concepts developed by the thermodynamic theory of solid body strength and fracture are used to examine the conditions of lubricant film failure. We obtain a quantitative criterion that defines the lubricant film "defectness" - the critical value (constant for a given mineral oil of the internal (thermal energy density in the volume of the lubricant film. We propose analytic relations for evaluating scuffing in friction with lubrication and verify them experimentally on a full-scale stand for testing actual sliding bearings. We show the constancy of the critical value of the internal (thermal energy density in the volume of the oil film at the moment of scuffing for an inactive mineral oil.
A critical analysis of the Mises stress criterion used in frequency domain fatigue life prediction
Adam Niesłony
2016-10-01
Full Text Available Multiaxial fatigue failure criteria are formulated in time and frequency domain. The number of frequency domain criteria is rather small and the most popular one is the equivalent von Mises stress criterion. This criterion was elaborated by Preumont and Piefort on the basis of well-known von Mises stress concept, first proposed by Huber in 1907, and well accepted by the scientific community and engineers. It is important to know, that the criterion was developed to determine the yield stress and material effort under static load. Therefore the direct use of equivalent von Mises stress criterion for fatigue life prediction can lead to some incorrectness of theoretical and practical nature. In the present study four aspects were discussed: influence of the value of fatigue strength of tension and torsion, lack of parallelism of the SN curves, abnormal behaviour of the criterion under biaxial tensioncompression and influence of phase shift between particular stress state components. Information contained in this article will help to prevent improper use of this criterion and contributes to its better understanding
Validation of Hoek-Brown failure criterion charts for rock slopes
A.M. Nekouei; K. Ahangari
2013-01-01
Although stability charts suggested by Hoek and Bray on the basis of Mohr-Coulomb criterion are used for rock slopes, but complete and precise recognition is required for distinguishing cohesive strength and Mohr-Coulomb equivalent internal friction angle for rock mass. The paper by Lia et al. [6] is the only one that introduced rock slope charts according to Hoek-Brown failure criterion. In this paper, at first, this type of charts is introduced. Then, Mohr-Coulomb failure criterion charts [2] are compared and validated with Hoek-Brown failure criterion ones [6]. Next, Bishop method utilizing Slide software is compared with Hoek-Brown failure criterion stability charts. Average standard deviation (ASD), root mean square error (RMSE) and variance account for (VAF) were used for the comparison. According to the results, because of high distribution and very low correlation among the comparisons, Hoek-Brown failure crite-rion charts are not efficient.
The failure criterion based on hydrogen distribution ahead of the fatigue crack tip
Yu. G. Matvienko
2013-04-01
Full Text Available The hydrogen effect on the fracture toughness and fatigue crack growth behaviour in the martensitic high strength steel is investigated. The secondary ion mass spectrometry method has been employed to analyse the distribution of hydrogen concentration in the zone of the crack tip and at its edges. Changes in hydrogen concentration are observed in the vicinity of the propagating crack tip and at a remote site. The hydrogen peak is reduced and moves away from the fatigue crack tip with the increase of the maximum stress intensity factor . The concept of damage evolution is used to explain fatigue crack propagation in connection with the hydrogen redistribution ahead of the crack tip. The physical failure criterion based on the hydrogen peak in the vicinity of the fatigue crack tip and the maximum stress intensity factor has been proposed. The criterion reflects changes in the hydrogen peak which resulted from the hydrogen redistribution due to the increase of the maximum stress intensity factor as the crack length increases under fatigue loading.
A Reconsideration of the Extension Strain Criterion for Fracture and Failure of Rock
Wesseloo, J.; Stacey, T. R.
2016-12-01
The complex behaviours of rocks and rock masses have presented paradoxes to the rock engineer, including the fracturing of seemingly strong rock under low stress conditions, which often occurs near excavation boundaries. The extension strain criterion was presented as a fracture initiation criterion under these conditions (Stacey in Int J Rock Mech Min Sci 18:469-474, 1981). This criterion has been used successfully by some and criticised by others. In this paper, we review the literature on the extension strain criterion and present a case for the correct interpretation of the criterion and the conditions suitable for its use. We argue that the extension strain criterion can also be used to provide an indication of damage level under conditions of relatively low confining stress. We also present an augmentation of the criterion, the ultimate extension strain, which is applicable under extensional loading conditions when σ 2 is similar in magnitude to σ 1.
王学滨
2004-01-01
A mechanical model for strain softening pillar is proposed considering the characteristics of progressive shear failure and strain localization. The pillar undergoes elastic, strain softening and slabbing stages. In the elastic stage, vertical compressive stress and deformation at upper end of pillar are uniform, while in the strain softening stage there appears nonuniform due to occurrence of shear bands, leading to the decrease of load-carrying capacity.In addition, the size of failure zone increases in the strain softening stage and reaches its maximum value when slabbing begins. In the latter two stages, the size of elastic core always decreases. In the slabbing stage, the size of failure zone remains a constant and the pillar becomes thinner. Total deformation of the pillar is derived by linearly elastic Hooke's law and gradient-dependent plasticity where thickness of localization band is determined according to the characteristic length. Post-peak stiffness is proposed according to analytical solution of averaged compressive stressaverage deformation curve. Instability criterion of the pillar and roof strata system is proposed analytically using instability condition given by Salamon. It is found that the constitutive parameters of material of pillar, the geometrical size of pillar and the number of shear bands influence the stability of the system; stress gradient controls the starting time of slabbing, however it has no influence on the post-peak stiffness of the pillar.
Considerations on elliptical failure envelope associated to Mohr-Coulomb criterion
Comanici, A. M.; Barsanescu, P. D.
2016-08-01
Mohr-Coulomb theory is mostly used in civil engineering as it is suitable for soils, rock, concretes, etc., meaning that the theory is generally used for brittle facture of the materials, but there are cases when it matches ductile behaviour also. The failure envelope described by the Mohr-Coulomb criterion is not completely accurate to the real yield envelope. The ductile or brittle behaviour of materials could not be incorporated in a linear envelope suggested by classic stress state theories and so, there have been a number of authors who have refined the notion of yield envelope so that it would fit better to the actual behaviour of materials. The need of a realistic yield envelope comes from the demand that the failure state should be able to be predicted in a fair manner and with as little errors as possible. Of course, certain criteria will be closer to the actual situation, but there is a constant need to unify and refine the limit stress theories in order to avoid problems as defining boundaries of application areas on numerical programs. Mohr-Coulomb's yield envelope is the most used one on programs, can be reduced to Tresca theory when the materials are conducting a ductile behaviour and has a linear simplified form. The paper presents some considerations with respect to the elliptical failure envelope correlated to the Mohr-Coulomb theory. The equations have been rewritten for triaxial situation to describe a more accurate state of stress that is encountered under real conditions in materials. Using the Mohr's circles to define the yield envelope, the calculus has been made in in order to determine the yield stress at tensile tests
A new mixed-mode failure criterion for weak snowpack layers
Reiweger, I.; Gaume, J.; Schweizer, J.
2015-03-01
The failure of a weak snow layer is the first in a series of processes involved in dry-snow slab avalanche release. The nature of the initial failure within the weak layer is not yet fully understood but widely debated. The knowledge of the failure criterion is essential for developing avalanche release models and hence for avalanche hazard assessment. Yet different release models assume contradictory criteria as input parameters. We analyzed loading experiments on snow failure performed in a cold laboratory with samples containing a persistent weak snow layer of either faceted crystal, depth hoar, or buried surface hoar. The failure behavior of these layers can be described well with a modified Mohr-Coulomb model accounting for the possible compressive failure of snow. We consequently propose a new mixed-mode shear-compression failure criterion that can be used in avalanche release models.
Lauri Kalle Tapio Uotinen
2017-01-01
Full Text Available An in situ concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin concrete liner on prestressed rock surface, when the stress states in both rock and concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin concrete liner from level −3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the liner is 3.2 MPa and the tangential stress of rock is reduced by −33%. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week 9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin concrete liner significantly reduces the amount of damage.
Systemic risk in dynamical networks with stochastic failure criterion
Podobnik, B.; Horvatic, D.; Bertella, M. A.; Feng, L.; Huang, X.; Li, B.
2014-06-01
Complex non-linear interactions between banks and assets we model by two time-dependent Erdős-Renyi network models where each node, representing a bank, can invest either to a single asset (model I) or multiple assets (model II). We use a dynamical network approach to evaluate the collective financial failure —systemic risk— quantified by the fraction of active nodes. The systemic risk can be calculated over any future time period, divided into sub-periods, where within each sub-period banks may contiguously fail due to links to either i) assets or ii) other banks, controlled by two parameters, probability of internal failure p and threshold Th (“solvency” parameter). The systemic risk decreases with the average network degree faster when all assets are equally distributed across banks than if assets are randomly distributed. The more inactive banks each bank can sustain (smaller Th), the smaller the systemic risk —for some Th values in I we report a discontinuity in systemic risk. When contiguous spreading becomes stochastic ii) controlled by probability p2 —a condition for the bank to be solvent (active) is stochastic— the systemic risk decreases with decreasing p2. We analyse the asset allocation for the U.S. banks.
Failure Study of Composite Materials by the Yeh-Stratton Criterion
Yeh, Hsien-Yang; Richards, W. Lance
1997-01-01
The newly developed Yeh-Stratton (Y-S) Strength Criterion was used to study the failure of composite materials with central holes and normal cracks. To evaluate the interaction parameters for the Y-S failure theory, it is necessary to perform several biaxial loading tests. However, it is indisputable that the inhomogeneous and anisotropic nature of composite materials have made their own contribution to the complication of the biaxial testing problem. To avoid the difficulties of performing many biaxial tests and still consider the effects of the interaction term in the Y-S Criterion, a simple modification of the Y-S Criterion was developed. The preliminary predictions by the modified Y-S Criterion were relatively conservative compared to the testing data. Thus, the modified Y-S Criterion could be used as a design tool. To further understand the composite failure problem, an investigation of the damage zone in front of the crack tip coupled with the Y-S Criterion is imperative.
A simplified approach to directly consider intact rock anisotropy in HoekeBrown failure criterion
Mohamed AIsmael; Hassan FImam; Yasser El-Shayeb
2014-01-01
Many rock types have naturally occurring inherent anisotropic planes, such as bedding planes, foliation, or flow structures. Such characteristic induces directional features and anisotropy in rocks’ strength and deformational properties. The HoekeBrown (HeB) failure criterion is an empirical strength criterion widely applied to rock mechanics and engineering. A direct modification to HeB failure criterion to account for rock anisotropy is considered as the base of the research. Such modification introduced a new definition of the anisotropy as direct parameter named the anisotropic parameter (Kb). However, the computation of this parameter takes much experimental work and cannot be calculated in a simple way. The aim of this paper is to study the trend of the relation between the degree of anisotropy (Rc) and the minimum value of anisotropic parameter (Kmin), and to predict the Kmin directly from the uniaxial compression tests instead of triaxial tests, and also to decrease the amount of experimental work.
Han, Seok-Jung; Yang, Joon-Eon; Lee, Won-Jea [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2008-05-15
A safety issue of a Very High Temperature Reactor (VHTR) is to estimate the Reliability of a Passive safety System (RoPS). The Stress-Strength Interference (SSI) approach is widely adopted to estimate the RoPS. Major efforts for the RoPS addressed a quantification of the operational uncertainty of a passive safety system given a postulated accident scenario. However, another important problem is to determine the failure criteria of a passive safety system, because there is an ambiguity in the failure criteria for a VHTR due to the inherent safety characteristics. This paper focuses on an investigation of the reliability characteristics due to a change of the probability distribution in a failure criterion for the quantification of the RoPS.
Energy analysis of stability of twin shallow tunnels based on nonlinear failure criterion
张佳华; 许敬叔; 张标
2014-01-01
Based on nonlinear Mohr−Coulomb failure criterion, the analytical solutions of stability number and supporting force on twin shallow tunnels were derived using upper bound theorem of limit analysis. The optimized solutions were obtained by the technique of sequential quadratic programming. When nonlinear coefficient equals 1 and internal friction angle equals 0, the nonlinear Mohr−Coulomb failure criterion degenerates into linear failure criterion. The calculated results of stability number in this work were compared with previous results, and the agreement verifies the effectiveness of the present method. Under the condition of nonlinear Mohr−Coulomb failure criterion, the results show that the supporting force on twin shallow tunnels obviously increases when the nonlinear coefficient, burial depth, ground load or pore water pressure coefficients increase. When the clear distance is 0.5 to 1.0 times the diameter of tunnel, the supporting force of twin shallow tunnels reaches its maximum value, which means that the tunnels are the easiest to collapse. While the clear distance increases to 3.5 times the diameter of tunnel, the calculation for twin shallow tunnels can be carried out by the method for independent single shallow tunnel. Therefore, 3.5 times the diameter of tunnel serves as a critical value to determine whether twin shallow tunnels influence each other. In designing twin shallow tunnels, appropriate clear distance value must be selected according to its change rules and actual topographic conditions, meanwhile, the influences of nonlinear failure criterion of soil materials and pore water must be completely considered. During the excavation process, supporting system should be intensified at the positions of larger burial depth or ground load to avoid collapses.
Experiments and modeling of ballistic penetration using an energy failure criterion
Dolinski M.
2015-01-01
Full Text Available One of the most intricate problems in terminal ballistics is the physics underlying penetration and perforation. Several penetration modes are well identified, such as petalling, plugging, spall failure and fragmentation (Sedgwick, 1968. In most cases, the final target failure will combine those modes. Some of the failure modes can be due to brittle material behavior, but penetration of ductile targets by blunt projectiles, involving plugging in particular, is caused by excessive localized plasticity, with emphasis on adiabatic shear banding (ASB. Among the theories regarding the onset of ASB, new evidence was recently brought by Rittel et al. (2006, according to whom shear bands initiate as a result of dynamic recrystallization (DRX, a local softening mechanism driven by the stored energy of cold work. As such, ASB formation results from microstructural transformations, rather than from thermal softening. In our previous work (Dolinski et al., 2010, a failure criterion based on plastic strain energy density was presented and applied to model four different classical examples of dynamic failure involving ASB formation. According to this criterion, a material point starts to fail when the total plastic strain energy density reaches a critical value. Thereafter, the strength of the element decreases gradually to zero to mimic the actual material mechanical behavior. The goal of this paper is to present a new combined experimental-numerical study of ballistic penetration and perforation, using the above-mentioned failure criterion. Careful experiments are carried out using a single combination of AISI 4340 FSP projectiles and 25[mm] thick RHA steel plates, while the impact velocity, and hence the imparted damage, are systematically varied. We show that our failure model, which includes only one adjustable parameter in this present work, can faithfully reproduce each of the experiments without any further adjustment. Moreover, it is shown that the
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.
YANG Xiao-li; YAO Cong; ZHANG Jia-hua
2016-01-01
Based on the active failure mechanism and passive failure mechanism for a pressurized tunnel face, the analytical solutions of the minimum collapse pressure and maximum blowout pressure that could maintain the stability of pressurized tunnel faces were deduced using limit analysis in conjunction with nonlinear failure criterion under the condition of pore water pressure. Due to the objective existence of the parameter randomness of soil, the statistical properties of random variables were determined by the maximum entropy principle, and the Monte Carlo method was employed to calculate the failure probability of a pressurized tunnel. The results show that the randomness of soil parameters exerts great influence on the stability of a pressurized tunnel, which indicates that the research should be done on the topic of determination of statistical distribution for geotechnical parameters and the level of variability. For the failure probability of a pressurized tunnel under multiple failure modes, the corresponding safe retaining pressures and optimal range of safe retaining pressures are calculated by introducing allowable failure probability and minimum allowable failure probability. The results can provide practical use in the pressurized tunnel engineering.
Energy analysis of face stability of deep rock tunnels using nonlinear Hoek-Brown failure criterion
张佳华; 李永鑫; 许敬叔
2015-01-01
The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.
Mixed-mode shear-compression failure criterion for weak snowpack layers
Reiweger, Ingrid; Gaume, Johan; Schweizer, Jürg
2015-04-01
The failure of a weak snow layer below a cohesive slab is a prerequisite for the release of a dry-snow snow slab avalanche. Once an initial failure in the weak layer reaches its critical size to become self-propagating, the slab will release as an avalanche - provided the slope is steep enough. However, the nature of the initial failure within the weak layer is still unknown - but strongly debated among avalanche researchers. Moreover, different avalanche release models assume contradictory failure criteria as input parameters. We analysed a unique data set stemming from laboratory experiments on snow failure with samples containing a weak snow layer of either depth hoar or buried surface hoar. Depth and surface hoar layers are the most relevant weak layers for avalanche release. The failure behaviour of these types of weak layers can well be described with a modified Mohr-Coulomb model. We therefore propose a mixed-mode failure criterion to be used in avalanche release models.
Toshiyuki Meshii
2016-01-01
Full Text Available This paper examined whether the modified Ritchie-Knott-Rice (RKR failure criterion can be applied to examine the feasibility of miniaturized Charpy type SE(B specimens of thickness-to-width ratio B/W=1. The modified RKR failure criterion considered in this paper is the (4δt,σ22c criterion which predicts the onset of cleavage fracture when the midplane crack-opening stress measured at a distance equal to four times the crack-tip opening displacement, denoted as σ22d, exceeds a critical stress σ22c. Specimens with B values of 25, 10, 3, and 2 mm (denoted as 25t, 10t, 3t, and 2t specimens, resp. manufactured with 0.55% carbon steel were tested at 20°C. The results showed that the modified RKR criterion could appropriately predict the occurrence of cleavage fracture accompanied by negligibly small stable crack extension (denoted as KJc fracture naturally for the 25t and 10t specimens. The modified RKR criterion could also predict that KJc fracture does not occur for the 2t specimen. The σ22c obtained from specimens for the 25t and 10t specimens exhibited only a small difference, indicating that the Jc obtained from the 10t specimens can be used to predict the Jc that will be obtained with the 25t specimens.
张佳华; 王成洋
2015-01-01
On the basis of upper bound theorem, non-associated flow rule and non-linear failure criterion were considered together. The modified shear strength parameters of materials were obtained with the help of the tangent method. Employing the virtual power principle and strength reduction technique, the effects of dilatancy of materials, non-linear failure criterion, pore water pressure, surface loads and buried depth, on the stability of shallow tunnel were studied. In order to validate the effectiveness of the proposed approach, the solutions in the present work agree well with the existing results when the non-associated flow rule is reduced to the associated flow rule and the non-linear failure criterion is degenerated to the linear failure criterion. Compared with dilatancy of materials, the non-linear failure criterion exerts greater impact on the stability of shallow tunnels. The safety factor of shallow tunnels decreases and the failure surface expands outward when the dilatancy coefficient decreases. While the increase of nonlinear coefficient, the pore water pressure coefficient, the surface load and the buried depth results in the small safety factor. Therefore, the dilatancy as well as non-linear failure criterion should be taken into account in the design of shallow tunnel supporting structure. The supporting structure must be reinforced promptly to prevent potential mud from gushing or collapse accident in the areas with abundant pore water, large surface load or buried depth.
A yield criterion based on mean shear stress
Emmens, W.C.; Boogaard, van den A.H.
2014-01-01
This work investigates the relation between shear stress and plastic yield considering that a crystal can only deform in a limited set of directions. The shear stress in arbitrary directions is mapped for some cases showing relevant differences. Yield loci based on mean shear stress are con- structe
HE Zhen-jun; SONG Yu-pu
2008-01-01
Multiaxial compression tests were performed on 100 mm × 100 mm × 100 nun high-strength high-performance concrete (HSHPC) cubes and normal strength concrete (NSC) cubes. The failure modes of specimens were presented, the static compressive strengths in principal directions were measured, the influence of the stress ratios was analyzed. The experimental results show that the ultimate strengths for HSHPC and NSC under multiaxial compression are greater than the uniaxial compressive strengths at all stress ratios, and the multiaxial strength is dependent on the brittleness and stiffness of concrete, the stress state and the stress ratios. In addition, the Kupfer-Gerstle and Ottosen's failure criteria for plain HSHPC and NSC under multiaxial compressive loading were modified.
Research on failure criterion of composite based on unified macro-and micro-mechanical model
Sun Zhigang; Zhao Long; Chen Lei; Song Yingdong
2013-01-01
A new unified macro-and micro-mechanics failure analysis method for composite structures was developed in order to take the effects of composite micro structure into consideration.In this method,the macro stress distribution of composite structure was calculated by commercial finite element analysis software.According to the macro stress distribution,the damage point was searched and the micro-stress distribution was calculated by reformulated finite-volume direct averaging micromechanics (FVDAM),which was a multi-scale finite element method for composite.The micro structure failure modes were estimated with the failure strength of constituents.A unidirectional composite plate with a circular hole in the center under two kinds of loads was analyzed with the traditional macro-mechanical failure analysis method and the unified macro-and micro-mechanics failure analysis method.The results obtained by the two methods are consistent,which show this new method's accuracy and efficiency.
A MIXED MODE FRACTURE CRITERION BASED ON THE MAXIMUM TANGENTIAL STRESS IN BRITTLE INCLUSION
Ji Changjiang; Li Zhonghua; Sun Jun
2005-01-01
A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture criterion, including the fracture direction and the critical load, was established based on the maximum tangential stress in the inclusion for brittle inclusioninduced fracture materials. The proposed fracture criterion is a function of the inclusion fracture stress, its size and volume fraction, as well as the elastic constants of the inclusion and the matrix material. The present criterion will reduce to the conventional one as the inclusion having the same elastic behavior as the matrix material. The proposed solutions are in good agreement with detailed finite element analysis and measurement.
Evaluation of fatigue life via stress and strain damage criterions
Savkin, A. N.; Sedov, A. A.; Badikov, K. A.
2016-11-01
Attempts to describe the effect of the variable amplitude loading character on fatigue damage accumulation are made for a structural steel element. We show the possibility of durability prediction of steel taking into account stress and strain parameters of stationary cyclic loading and parameters that describe the range of random loading. It is proposed to quantify the influence of the loading character on durability by a damage model with the nonstationarity factor and spectrum fullness factor. The accuracy of the model is analyzed on the basis of steel 40Cr tests. The experimental evidence and analytical results of the proposed model are correlated.
Fu HUANG; Xiao-li YANG; Lian-heng ZHAO
2012-01-01
To analyze the stability of a shallow square tunnel,a new curved failure mechanism,representing the mechanical characteristics and collapsing form of this type of tunnel,is constructed.Based on the upper bound theorem of limit analysis and the Hoek-Brown nonlinear failure criterion,the supporting pressure derived from the virtual work rate equation is regarded as an objective function to achieve optimal calculation.By employing variational calculation to optimize the objective function,an upper bound solution for the supporting pressure and the collapsing block shape of a shallow square tunnel are obtained.To evaluate the validity of the failure mechanism proposed in this paper,the solutions computed by the curved failure mechanism are compared with the results calculated by the linear multiple blocks failure mechanism when the Hoek-Brown nonlinear failure criterion is converted into the Mohr-Coulomb linear criterion.The influences of rock mass parameters on the supporting pressure and collapsing block shape are discussed.
Exploring DSM-5 criterion A in Acute Stress Disorder symptoms following natural disaster.
Lavenda, Osnat; Grossman, Ephraim S; Ben-Ezra, Menachem; Hoffman, Yaakov
2017-10-01
The present study examines the DSM-5 Acute Stress Disorder (ASD) diagnostic criteria of exposure, in the context of a natural disaster. The study is based on the reports of 1001 Filipinos following the aftermath of super typhoon Haiyan in 2013. Participants reported exposure to injury, psychological distress and ASD symptoms. Findings indicated the association of criterion A with the prevalence of meeting all other ASD diagnostic criteria and high psychological distress. The diagnostic properties of Criterion A are discussed. Copyright © 2017 Elsevier B.V. All rights reserved.
Levitas, Valery I.; Chen, Hao; Xiong, Liming
2017-08-01
A continuum/atomistic approach for predicting lattice instability during crystal-crystal phase transformations (PTs) is developed for the general loading with an arbitrary stress tensor and large strains. It is based on a synergistic combination of the generalized Landau-type theory for PTs and molecular dynamics (MD) simulations. The continuum approach describes the entire dissipative transformation process in terms of an order parameter, and the general form of the instability criterion is derived utilizing the second law of thermodynamics. The feedback from MD allowed us to present the instability criterion for both direct and reverse PTs in terms of the critical value of the modified transformation work, which is linear in components of the true stress tensor. It was calibrated by MD simulations for direct and reverse PTs between semiconducting silicon Si i and metallic Si ii phases under just two different stress states. Then, it describes hundreds of MD simulations under various combinations of three normal and three shear stresses. In particular, the atomistic simulations show that the effects of all three shear stresses along cubic axes on lattice instability of Si i are negligible, which is in agreement with our criterion.
Three-Dimensional Analysis of Rolling by Twin Shear Stress Yield Criterion
ZHAO De-wen; XIE Ying-jie; LIU Xiang-hua; WANG Guo-dong
2006-01-01
Using the twin shear stress yield criterion, the surface integral of the co-line vectors, and the integration depending on upper limit, Kobayashi's three-dimensional velocity field of rolling was analyzed and an analytical expression of rolling torque and single force was obtained. Through redoing the same experiment of rolling pure lead as Sims, the calculated results by the above expression were compared with those of Kobayashi and Sims formulae. The results show that the twin shear stress yield criterion is available for rolling analysis and the calculated results by the new formula are a little higher than those by Kobayashi and Sims ones if the reduction ratio is less than 30%.
Strength criterion for rocks under compressive-tensile stresses and its application
Mingqing You
2015-08-01
Full Text Available Estimating in-situ stress with hydraulic borehole fracturing involves tensile strength of rock. Several strength criteria with three parameters result in tensile strengths with great differences, although they may describe the relation between strength of rock and confining pressure with low misfits. The exponential criterion provides acceptable magnitudes of tensile strengths for granites and over-estimates that for other rocks, but the criterion with tension cut-off is applicable to all rocks. The breakdown pressure will be lower than the shut-in pressure during hydraulic borehole fracturing, when the maximum horizontal principal stress is 2 times larger than the minor one; and it is not the peak value in the first cycle, but the point where the slope of pressure-time curve begins to decline.
An estimation method on failure stress of micro thickness Cu film-substrate structure
无
2009-01-01
The failure of thin film-substrate structure occurs mainly at the thin film or the interface. However, the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size, interface and stress state on the failure behavior of thin film-substrate structure. Based on the scanning electron microscope (SEM) in-situ in- vestigation on the failure models of the Cu thin film-substrate structure and the nano scratched testing results, the failure stresses in different thicknesses of the Cu film-substrate were characterized, which were compared and confirmed by other methods, such as Stoney formula and other empiric equations. These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods. The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film. Therefore, the novel estimating method of failure stress assists people to understand the critical interfacial strength and to set up the failure criterion of thin film-substrate structure.
An estimation method on failure stress of micro thickness Cu film-substrate structure
WANG XiShu; LI Ying; MENG XiangKang
2009-01-01
The failure of thin film-substrate structure occurs mainly at the thin film or the interface.However,the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size,interface and stress state on the failure behavior of thin film-substrate structure.Based on the scanning electron microscope(SEM)in-situ investigation on the failure models of the Cu thin film-substrata structure and the nano scratched testing results,the failure stresses in different thicknesses of the Cu film-substrate were characterized,which were compared and confirmed by other methods,such as Stoney formula and other empiric equations.These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods.The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film.Therefore,the novel estimating method of failure stress assists people to understand the critical interracial strength and to set up the failure criterion of thin film-substrate structure.
On thermal stress failure of the SNAP-19A RTG heat shield
Pitts, W. C.; Anderson, L. A.
1974-01-01
Results of a study on thermal stress problems in an amorphous graphite heat shield that is part of the launch-abort protect system for the SNAP-19A radio-isotope thermoelectric generators (RTG) that will be used on the Viking Mars Lander are presended. The first result is from a thermal stress analysis of a full-scale RTG heat source that failed to survive a suborbital entry flight test, possibly due to thermal stress failure. It was calculated that the maximum stress in the heat shield was only 50 percent of the ultimate strength of the material. To provide information on the stress failure criterion used for this calculation, some heat shield specimens were fractured under abort entry conditions in a plasma arc facility. It was found that in regions free of stress concentrations the POCO graphite heat shield material did fracture when the local stress reached the ultimate uniaxial stress of the material.
Failure Probability Model considering the Effect of Intermediate Principal Stress on Rock Strength
Yonglai Zheng
2015-01-01
Full Text Available A failure probability model is developed to describe the effect of the intermediate principal stress on rock strength. Each shear plane in rock samples is considered as a micro-unit. The strengths of these micro-units are assumed to match Weibull distribution. The macro strength of rock sample is a synthetic consideration of all directions’ probabilities. New model reproduces the typical phenomenon of intermediate principal stress effect that occurs in some true triaxial experiments. Based on the new model, a strength criterion is proposed and it can be regarded as a modified Mohr-Coulomb criterion with a uniformity coefficient. New strength criterion can quantitatively reflect the intermediate principal stress effect on rock strength and matches previously published experimental results better than common strength criteria.
Chen, Yuhang; Schellekens, Michiel; Zhou, Shiwei; Cadman, Joseph; Li, Wei; Appleyard, Richard; Li, Qing
2011-08-01
Tissue scaffolds aim to provide a cell-friendly biomechanical environment for facilitating cell growth. Existing studies have shown significant demands for generating a certain level of wall shear stress (WSS) on scaffold microstructural surfaces for promoting cellular response and attachment efficacy. Recently, its role in shear-induced erosion of polymer scaffold has also drawn increasing attention. This paper proposes a bi-directional evolutionary structural optimization (BESO) approach for design of scaffold microstructure in terms of the WSS uniformity criterion, by downgrading highly-stressed solid elements into fluidic elements and/or upgrading lowly-stressed fluidic elements into solid elements. In addition to this, a computational model is presented to simulate shear-induced erosion process. The effective stiffness and permeability of initial and optimized scaffold microstructures are characterized by the finite element based homogenization technique to quantify the variations of mechanical properties of scaffold during erosion. The illustrative examples show that a uniform WSS is achieved within the optimized scaffold microstructures, and their architectural and biomechanical features are maintained for a longer lifetime during shear-induced erosion process. This study provides a mathematical means to the design optimization of cellular biomaterials in terms of the WSS criterion towards controllable shear-induced erosion.
饶平平; 张常光; 宋忠强
2013-01-01
Based on Lade-Duncan failure criterion and considering the comprehensive effect of intermediate principal stress,dilatancy property and the real elastic strains in the plastic zone,a formula of rock resistant coefficient was derived.The results show that compared with Mohr-Coulomb failure criterion,Lade-Duncan criterion can increase the rock resistant coefficient and develop the strength potentials of surrounding rock by considering the effect of intermediate principal stress.The effect of dilatancy property on rock resistance coefficient can not be ignored,and if the dilatancy property is not considered,it would overestimate the resistant coefficient of surrounding rock,in that way,the design will be very dangerous.The assumption that elastic strain in plastic zone is constant will also overestimate resistance coefficient of surrounding rock,the error will become more apparent with increasing the dilatancy property.In the practical engineering,the real elastic strains in the plastic zone of surrounding rock should be considered.%基于Lade-Duncan屈服准则,合理考虑中主应力、剪胀特性以及塑性区真实弹性应变的综合影响,推导出巷道围岩抗力系数表达式.结果表明:与Mohr-Coulomb强度准则下的围岩抗力系数计算值对比,考虑中主应力影响的Lade-Duncan准则能充分发挥围岩的强度潜能,提高围岩抗力系数；剪胀特性对围岩抗力系数影响不可忽视,不考虑围岩剪胀特性,将高估巷道围岩抗力系数,设计偏危险；另外,假定塑性区的弹性应变为常数将高估围岩抗力系数,在围岩剪胀性较强时误差更明显,实际工程中应考虑围岩塑性区真实弹性应变.
Transferability of Charpy Absorbed Energy to Fracture Toughness Based on Weibull Stress Criterion
Hongyang JING; Lianyong XU; Lixing HUO; Fumiyoshi Minami
2005-01-01
The relationship between Charpy absorbed energy and the fracture toughness by means of the (crack tip opening displacement (CTOD)) method was analyzed based on the Weibull stress criterion. The Charpy absorbed energy and the fracture toughness were measured for the SN490B steel under the ductile-brittle transition temperature region. For the instrumented Charpy impact test, the curves between the loading point displacement and the load against time were recorded. The critical Weibull stress was taken as a fracture controlled parameter, and it could not be affected by the specimen configuration and the loading pattern based on the local approach. The parameters controlled brittle fracture are obtained from the Charpy absorbed energy results, then the fracture toughness for the compact tension (CT) specimen is predicted. It is found that the results predicted are in good agreement with the experimental. The fracture toughness could be evaluated by the Charpy absorbed energy, because the local approach gives a good description for the brittle fracture even though the Charpy impact specimen or the CT specimen is used for the given material.
Failure criterion for adhesively bonded joints using Arcan´s experimental method
Demetrio Jackson dos Santos
2014-08-01
Full Text Available Characterization of polymeric materials mechanical behavior requires some previous knowledge about their structure, which allows the choice of more appropriated models and methods. Polymeric materials, below their glass transition temperature (Tg, may be handled as perfect elastic solids, allowing the use of classic mechanics to characterize their behavior. Polymers above their Tg present a viscous contribution to mechanical behavior, which has to be taken into consideration by modeling it. Adhesively bonded joint, joining of different materials using a polymer as adhesive, adds to the mentioned requirements more parameters, such as surface roughness, adhesive thickness and different types of contributions to adhesively bonded joint strength. This work has the purpose of presenting a mechanical behavior characterization of adhesive bonded joints, concerning their average stress at rupture. A modified Arcan´s device was used to obtain the average stress at rupture under different angles or loading conditions, such as pure shear 0°, pure tensile strength 90° and combined conditions. The experimental results were applied to a theoretical model, which takes into consideration the hydrostatic contribution to the mechanical behavior, called Drucker-Prager Model, which was initially developed to characterize soils.
X60管线钢的本构关系及失效判据%Constitutive relation and failure criterion for X60 pipeline steel
马廷霞; 杨永和; 许震; 李安军; 唐愚
2014-01-01
X60管线钢是石油、天然气输送用的主要钢种，在外界载荷作用下，易发生局部变形或应力集中，而导致屈曲甚至拉裂失效。对其进行力学研究，评价其力学安全性已成为管道风险管理的重要内容之一。其中，本构关系方程是力学研究的基础内容，失效判据则决定了管道生命的周期。通过对比X60管线钢的静力拉伸实验应力应变关系和 Ramberg-Osgood本构关系，发现ε≤εP02．时，Ramberg-Osgood本构方程能够比较准确地反映X60管线钢的拉伸应力应变关系；但当ε＞εP02．时，基于Ramberg-Osgood模型所得理论本构曲线与实验结果有较大的误差。基于此，笔者根据 X60管线钢静力拉伸弹性阶段和塑性阶段的不同力学特征，采用插值法对 Ram berg-Osgood本构模型做出了修正，提出了X60管线钢在单向拉伸状态下的全局二段式应力应变关系式，该关系式更加准确地表达了X60管线钢的拉伸应力应变关系。考虑到焊缝及热影响区对管道强度和刚度的影响，结合塑性材料基于应力的失效判据和基于应变的失效判据，笔者提出了焊缝影响因子及X60管线钢的应变控制失效准则，建立了基于第四强度理论的管道失效时的临界应力计算方程。%The X60 pipeline steel is the steel which is most commonly applied to the transportation of oil and natural gas ,but under the external load ,deformation or stress concentration is more likely to occur on the X60 pipeline steel ,and thus it results to buckling even cracking failure .For studying the mechanical behavior of the X60 pipeline steel ,evaluating its mechanical safety has become one of the most important works for the pipeline risk management .Among all the works of risk management ,the constitutive relation equation is the basis of the w hole mechanics research ,and the failure criterion determines the pipeline’s life cycle .By comparing the
朱鹏辉; 王伟; 朱其志; 曹亚军
2015-01-01
基于黏性材料Lade-Duncan破坏准则，分析煤柱应力规律，将小主应力σ3看成是开采前的静水原岩应力推导出煤柱强度计算式，并与M-C准则，A. H. Wilson计算式结果相比较.经分析比对发现，没有考虑中主应力的M-C屈服准则，A. H. Wilson公式结果都偏小，且A. H. Wilson结果过分偏低，而考虑中主应力的Lade-Duncan破坏准则却在煤柱强度计算结果上明显存在优势，更合理.从内摩擦角和黏聚力这两个角度出发，讨论其对煤柱强度特性的影响规律及影响程度，结果表明煤柱极限强度受二者影响显著，且前者影响程度大于后者.%Based on the Lade-Duncan failure criterion of coherent material,the formula of limit strength of the coal pillar is derived by analyzing the stress discipline of the coal pillar and considering the minor principal stress σ3 as hydrostatic stress pre-mining. Compared with the limit strengths of the coal pillar using the Mohr-Coulomb failure criterion and the simplified A. H. Wilson formula,it shows that the results of the Mohr-Coulomb failure criterion and the simplified A. H. Wilson formula are small,which do not consider the intermediate principal stress,but the the results of Lade-Duncan failure criterion which considers the principal stress have evident advantages and are more reasonable. From the two respects of the internal friction and cohesion,the discipline and degree of the internal friction and cohesion influencing on the pillar strength characteristics are discussed. The results indicate that the limit strength of the coal pillar is significantly affected by them,and the former is greater than the latter.
Park, Namsu; Huh, Hoon
2013-12-01
This paper is concerned with the anisotropy effect on the stress-based fracture forming limit diagram using a modified Lou-Huh ductile fracture criterion. In sheet metal forming process, a usage of advanced high-strength steels (AHSSs) has been remarkably increasing for the lightweight car body and good formability. It is, however, unable to evaluate the formability of AHSS with the conventional forming limit diagram during complex forming processes since it is obtained by assuming the proportional loading path and AHSS shows sudden fracture involving little amount of necking. The stress-based fracture forming limit diagram was constructed using a modified Lou-Huh ductile fracture criterion in order to evaluate the formability of AHSS accurately. The anisotropy effect on the fracture strain is also evaluated to reflect the material behavior of sheet metals in constructing the criterion for the prediction of onset of the fracture. The constructed stress-based fracture forming limit diagrams deal with the stress state ranging from pure shear to equi-biaxial tension with the variation of orientation of sheet metals. It is clearly observed that the stress-based fracture forming limit diagrams are varied with the change of orientation of sheet metals.
先进高强度钢的断裂失效准则研究%STUDY OF FAILURE CRITERION OF ADVANCED HIGH STRENGTH STEEL
桂良进; 高付海; 范子杰
2012-01-01
The advanced high strength steel (AHSS) realizes the outstanding advantage of strength by transforming its internal different phases. It has become one of the hottest materials for current automotive lightweight researches. However, compared with traditional deep-drawing steels, the widespread use of AHSS in auto-industry is hampered due to its poor ductility,which leads to frequent occurrences of failure in the mode of fracture during the process of stamping. Therefore,the fracture prediction of AHSS becomes one of the focuses of current researchers. The dual phase (DP) steel can be seen as the representative of AHSS. In this paper,the fracture criteria of DP steel under different stress states are investigated by combining experimental and numerical analysis and an appropriate failure criterion is attempted to be established for predicting its fracture behavior.%先进高强度钢(AHSS)是通过相变获得高强度的应用前景最好的汽车轻量化材料.与传统深拉钢相比,AHSS韧性相对较低,在冲压成形过程中容易发生断裂,阻碍了它在汽车上的广泛应用,因而AHSS的断裂失效研究成为当前国内外研究的热点.论文以AHSS的代表钢种双相钢(DP)为研究对象,通过试验与数值计算相结合的方法研究其在不同三轴应力状态下的失效特性,尝试寻找一个适用于它的失效准则,用于其断裂失效的预测.
A study of the energy yield criterion of geomaterials
Gao Hong; Zheng Yingren; Feng Xiating; Zeng Jing
2010-01-01
The study results of the internal friction character of geomaterials conclude that the internal friction exists in mechanical elements all the time having a direction opposite to the shear stress,and the deformation failure mechanism of geomaterials greatly differs from that of metals.For metals,the failure results from shear stresses make the crystal structure slip;whereas for geomaterials,owing to its attribute of granular structures,their deformation follows the friction law,it is the co-action of shear stresses and perpendicular stresses that makes grains overcome the frictions between them,thus leading to the final failure of relative sliding.Therefore,on the basis of the cognition above,a triple shear energy criterion is proposed.Its corresponding Drucker-Prager criterion for geomaterials is also given.The new criterion can be rewritten to the Mohr-Coulomb criterion by neglecting the effect of the intermediate principal stress,and to the Mises criterion by not taking the internal friction angle into consideration.Then the studies of yield criteria commonly used are conducted systematical]y from the points of stress,strain and energy of geomaterials.The results show that no matter which expression form of stress,strain or energy is used for the yield criterion,the essence is the same and the triple shear energy yield criterion is the unified criterion of materials.Finally,the experimental verification is conducted in connection with the practical application of the triple shear energy yield criterion in an engineering project,and the calculation result shows that the Mohr-Coulomb criterion which only takes the single shear surface into account is more conservative than the energy criterion that does consider the effect of triple shear surfaces.
Li, Xibing; Du, Kun; Li, Diyuan
2015-11-01
True triaxial tests have been carried out on granite, sandstone and cement mortar using cubic specimens with the process of unloading the minor principal stress. The strengths and failure modes of the three rock materials are studied in the processes of unloading σ 3 and loading σ 1 by the newly developed true triaxial test system under different σ 2, aiming to study the mechanical responses of the rock in underground excavation at depth. It shows that the rock strength increases with the raising of the intermediate principal stress σ 2 when σ 3 is unloaded to zero. The true triaxial strength criterion by the power-law relationship can be used to fit the testing data. The "best-fitting" material parameters A and n ( A > 1.4 and n < 1.0) are almost located in the same range as expected by Al-Ajmi and Zimmerman (Int J Rock Mech Min Sci 563 42(3):431-439, 2005). It indicates that the end effect caused by the height-to-width ratio of the cubic specimens will not significantly affect the testing results under true triaxial tests. Both the strength and failure modes of cubic rock specimens under true triaxial unloading condition are affected by the intermediate principal stress. When σ 2 increases to a critical value for the strong and hard rocks (R4, R5 and R6), the rock failure mode may change from shear to slabbing. However, for medium strong and weak rocks (R3 and R2), even with a relatively high intermediate principal stress, they tend to fail in shear after a large amount of plastic deformation. The maximum extension strain criterion Stacey (Int J Rock Mech Min Sci Geomech Abstr 651 18(6):469-474, 1981) can be used to explain the change of failure mode from shear to slabbing for strong and hard rocks under true triaxial unloading test condition.
Shijian YUAN; Dazhi XIAO; Zhubin HE
2004-01-01
A generalized yield criterion is proposed based on the metal plastic deformation mechanics and the fundamental formula in theory of plasticity. Using the generalized yield criterion, the reason is explained that Mises yield criterion and Tresca yield criterion do not completely match with experimental data. It has been shown that the yield criteria of ductile metals depend not only on the quadratic invariant of the deviatoric stress tensor J2, but also on the cubic invariant of the deviatoric stress tensor J3 and the ratio of the yield stress in pure shear to the yield stress in uniaxial tension k/σs. The reason that Mises yield criterion and Tresca yield criterion are not in good agreement with the experimental data is that the effect of J3 and k/σs is neglected.
Rastellini, F.; Socorro, G.; Forgas, A.; Onate, E.
2016-08-01
Accurate prediction of failure and forming limits is essential when modelling sheet metal forming processes. Since traditional Forming Limit Curves (FLCs) are not valid for materials subjected to triaxial loading, a new failure criterion is proposed in this paper based on the stress triaxility and the effective plastic strain accumulated during the history of material loading. Formability zones are identified inside the proposed Triaxial Failure Diagram (TFD). FLCs may be mapped into the TFD defining a new Triaxial Failure Curve, or it can be defined by triaxial failure experiments. Several TFD examples are validated and constrasted showing acceptable accuracy in the numerical prediction of forming failure/limit of 3D thick sheet parts.
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
SONG Wei-hua; WANG Yu-feng; WANG Xin-hua
2008-01-01
For the study on the relationship between the dynamic phenomena in the mining such as mine earthquakes,outburst and faults slide,firstly,double shear friction experiments of sandstone were made,and its slide criterion was suggested considering the viewing of engineering.Secondly,in order to study the stability of underground rock and zone of tectonic stress field,based on the analysis on distribution characteristic of initial rock stress measurements,the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method.The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements.The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene.From then it is certain that tectonic stress is the major origin and necessary condition of mine earthquakes.The instability slide of the faults is the main manifest and the mining activity is the leading factor.Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines.
SONG Wei-hua; WANG Yu-feng; WANG Xin-hua
2008-01-01
For the study on the relationshfp between the dynamic phenomena in the min-ing such as mine earthquakes, outburst and faults slide, firstly, double shear friction ex-periments of sandstone were made, and its slide criterion was suggested considering the viewing of engineering. Secondly, in order to study the stability of underground rock and zone of tectonic stress field, based on the analysis on distribution characteristic of initial rock stress measurements, the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method. The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements. The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene. From then it is cer-tain that tectonic stress is the major origin and necessary condition of mine earthquakes. The instability slide of the faults is the main manifest and the mining activity is the leading factor. Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines.
Hall, M.M. Jr.; Symons, D.M.
1996-05-01
A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.
Can NT-proBNP be used as a criterion for heart failure hospitalization in emergency room?
Tuba Cimilli Ozturk
2011-01-01
Conclusions: NT-proBNP can be used as an easy diagnostic method for congestive heart failure. A certain cut-off value may be determined in further multi-centre controlled trials with larger patient groups.
Stress Transmission and Failure in Disordered Porous Media
Laubie, Hadrien; Radjai, Farhang; Pellenq, Roland; Ulm, Franz-Josef
2017-08-01
By means of extensive lattice-element simulations, we investigate stress transmission and its relation with failure properties in increasingly disordered porous systems. We observe a non-Gaussian broadening of stress probability density functions under tensile loading with increasing porosity and disorder, revealing a gradual transition from a state governed by single-pore stress concentration to a state controlled by multipore interactions and metric disorder. This effect is captured by the excess kurtosis of stress distributions and shown to be nicely correlated with the second moment of local porosity fluctuations, which appears thus as a (dis)order parameter for the system. By generating statistical ensembles of porous textures with varying porosity and disorder, we derive a general expression for the fracture stress as a decreasing function of porosity and disorder. Focusing on critical sites where the local stress is above the global fracture threshold, we also analyze the transition to failure in terms of a coarse-graining length. These findings provide a general framework which can also be more generally applied to multiphase and structural heterogeneous materials.
李丽民; 张国祥; 王恭兴
2011-01-01
传统的挡土墙土压力计算基于Mohr-Coulomb线性破坏准则,但大量试验数据表明,土体破坏时最大主应力和最小主应力的关系是非线性的.为此,基于Mohr-Coulomb非线性破坏准则,将挡土墙后填土划分为多个刚性滑块组成的破坏机构,根据极限分析中的上限理论建立容许的速度场.根据岩土实际应力情况,不同边界采用不同的切线强度计算参数,提出一种“多切线法”,推导得出挡土墙被动土压力的解析表达式,通过大型数学规划理论优化得到最优上限解.计算结果表明:当非线性破坏准则变为线性破坏准则时,结果与前人成果一致；非线性参数m、超载q、初始黏结力C0对被动土压力有重要影响；与单切线法相比,采用多切线法理论上更加严密,计算结果更接近真实值,具有较高的实用价值.%Conventional calculations of earth pressure for retaining walls are made in terms of the linear Mohr-Coulomb (MC) failure criterion. However, a substantial amount of experimental data shows that the relationship between the first principal stress and the third principal stress is nonlinear when soil is broken. Therefore, based on the Mohr-Coulomb nonlinear failure criterion and the multi-wedge translation failure mechanism, considering the effect of normal stress distribution on the cohesion and the internal friction angle, giving different boundary surfaces to different cohesion and internal friction angle, by the optimization theory, the multi-tangential technique is used to deduce the passive earth pressures of retaining walls. The minimum solution is obtained by optimization. From the calculation results, it can be seen that if the nonlinear Mohr-Coulomb yield criterion turns into the linear Mohr-Coulomb yield criterion, then the solutions presented in this paper agree well with the chen and soubra research conclusions, and the nonlinear parameter, overloading and initial cohesion have significant
Wu, Jian-Ying; Cervera, Miguel
2015-09-01
This work investigates systematically traction- and stress-based approaches for the modeling of strong and regularized discontinuities induced by localized failure in solids. Two complementary methodologies, i.e., discontinuities localized in an elastic solid and strain localization of an inelastic softening solid, are addressed. In the former it is assumed a priori that the discontinuity forms with a continuous stress field and along the known orientation. A traction-based failure criterion is introduced to characterize the discontinuity and the orientation is determined from Mohr's maximization postulate. If the displacement jumps are retained as independent variables, the strong/regularized discontinuity approaches follow, requiring constitutive models for both the bulk and discontinuity. Elimination of the displacement jumps at the material point level results in the embedded/smeared discontinuity approaches in which an overall inelastic constitutive model fulfilling the static constraint suffices. The second methodology is then adopted to check whether the assumed strain localization can occur and identify its consequences on the resulting approaches. The kinematic constraint guaranteeing stress boundedness and continuity upon strain localization is established for general inelastic softening solids. Application to a unified stress-based elastoplastic damage model naturally yields all the ingredients of a localized model for the discontinuity (band), justifying the first methodology. Two dual but not necessarily equivalent approaches, i.e., the traction-based elastoplastic damage model and the stress-based projected discontinuity model, are identified. The former is equivalent to the embedded and smeared discontinuity approaches, whereas in the later the discontinuity orientation and associated failure criterion are determined consistently from the kinematic constraint rather than given a priori. The bi-directional connections and equivalence conditions
Statins and oxidative stress in chronic heart failure.
Costa, Sónia; Reina-Couto, Marta; Albino-Teixeira, António; Sousa, Teresa
2016-01-01
Statins are the most commonly prescribed drugs for the treatment of dyslipidemia. They are also recommended in primary and secondary prevention of cardiovascular disease. In addition to decreasing cholesterol synthesis, statins interfere with the synthesis of isoprenoid intermediates, which may explain many of their pleiotropic properties, including their antioxidant effects. Oxidative stress is defined as an imbalance between the synthesis of reactive oxygen species and their elimination by antioxidant defense systems, with a prevailing pro-oxidant status that results in macromolecular damage and disruption of cellular redox signaling. Reactive oxygen species interfere with various processes that affect cardiac structure and function, contributing to the contractile dysfunction, myocardial hypertrophy and fibrosis observed in the pathophysiology of heart failure. By regulating several molecular pathways that control nicotinamide adenine dinucleotide phosphate oxidase and endothelial nitric oxide synthase activity, statins help restore redox homeostasis. These drugs also contribute to the control of inflammation and appear to have a protective role in various diseases. The results of observational studies and clinical trials with statins in heart failure have not been consensual. This review aims to analyze the role of oxidative stress in heart failure and the molecular mechanisms underlying statins' antioxidant properties. It also examines current scientific evidence on the use of these drugs as a specific treatment for heart failure. Copyright © 2015 Sociedade Portuguesa de Cardiologia. Published by Elsevier España. All rights reserved.
基于非线性破坏准则的边坡稳定性极限分析%Limit analysis of slope stability based on nonlinear failure criterion
张迎宾; 李亮; 赵炼恒; 姚辉; 任东亚
2011-01-01
Upper bound limit analysis method is an effective tool in solving geotechnical engineering problems. Conventional calculations in stability of slopes are formulated assuming the soils obeying a linear Mohr-Coulomb yield criterion. However, experimental evidences show that the failure criteria of almost all geomaterials are nonlinear over a wide range of normal stresses. In this paper, the soil masses of slopes are assumed to follow a nonlinear Mohr-Coulomb failure criterion. Based on the nonlinear failure criterion, the paper studies the problem of slope stability by combining the slice method and limit analysis upper bound method. The nonlinear strength parameters cohesionc, and internal friction angle ψ, are introduced through the tangent method. Joined influence of nonlinearity is established. The equations of equivalent in rates of external work and internal energy dissipation are established based on the joined influence. The equations of factors of safety for slope with different slide surface (straight line, broken-line, and circle) are deduced and the plastic analysis upper limit solutions are calculated well by these equations. A classical slope calculation case shows that the method is of correctness and high precision which consists with previous achievements. The new method can be used to guide the slope stability analysis based on the nonlinear failure criterion on the plastic upper limit theorem.%上限定理是求解岩土工程问题的有效工具.以上限定理为理论基础,分析边坡的稳定性问题,并考虑了岩土材料破坏准则的非线性特性.在非线性Mohr-Coulomb破坏准则下,采用条分法与极限分析上限法相结合的方法,对边坡稳定性进行分析.通过切线法引入非线性强度参数ct、(4)t,推导了岩土材料在非线性破坏准则下的相关联流动法则,建立功能方程,推导了边坡直线滑裂面、折线滑裂面和光滑曲线滑裂面安全系数F的计算方程.采用数学规
Cui, Xiao-Lei; Yang, Zhai-Ping; Wang, Xiao-Song
2017-01-01
To further explore the characterization of the multiaxial stress-strain responses of anisotropic tube metal from double-sided hydro-bulging tests, an analytical model for the equivalent stress and equivalent strain calculation was derived based on Hosford's 1979 yield criterion. Furthermore, thin-walled 5052-O aluminum alloy tubes were used to conduct the bulging experiment with an external pressure of 85 MPa. After the experimental data were substituted into the above analytical model, the Voce equation was used to fit the equivalent stress-strain relationship. It is concluded that the stress versus strain curves of the 5052-O tubes are strongly dependent on the loaded stress states, the adopted yield criteria, and the anisotropy coefficients. The external pressure of 85 MPa had little or no effect on the stress versus strain curves of the tubes, but the locations of the multiaxial stress versus strain curves were lower than that of the uniaxial stress versus strain curve. Moreover, the curve from Hosford's 1979 yield criterion not only had a higher saturation stress and material constant value than the curve from Mises and Hill's 1948 yield criteria but also had a dependence on the anisotropy coefficient.
Rapid behavioral maturation accelerates failure of stressed honey bee colonies.
Perry, Clint J; Søvik, Eirik; Myerscough, Mary R; Barron, Andrew B
2015-03-17
Many complex factors have been linked to the recent marked increase in honey bee colony failure, including pests and pathogens, agrochemicals, and nutritional stressors. It remains unclear, however, why colonies frequently react to stressors by losing almost their entire adult bee population in a short time, resulting in a colony population collapse. Here we examine the social dynamics underlying such dramatic colony failure. Bees respond to many stressors by foraging earlier in life. We manipulated the demography of experimental colonies to induce precocious foraging in bees and used radio tag tracking to examine the consequences of precocious foraging for their performance. Precocious foragers completed far fewer foraging trips in their life, and had a higher risk of death in their first flights. We constructed a demographic model to explore how this individual reaction of bees to stress might impact colony performance. In the model, when forager death rates were chronically elevated, an increasingly younger forager force caused a positive feedback that dramatically accelerated terminal population decline in the colony. This resulted in a breakdown in division of labor and loss of the adult population, leaving only brood, food, and few adults in the hive. This study explains the social processes that drive rapid depopulation of a colony, and we explore possible strategies to prevent colony failure. Understanding the process of colony failure helps identify the most effective strategies to improve colony resilience.
Slope Safety Factor Calculations With Non-Linear Yield Criterion Using Finite Elements
Clausen, Johan; Damkilde, Lars
2006-01-01
The factor of safety for a slope is calculated with the finite element method using a non-linear yield criterion of the Hoek-Brown type. The parameters of the Hoek-Brown criterion are found from triaxial test data. Parameters of the linear Mohr-Coulomb criterion are calibrated to the same triaxial...... are carried out at much higher stress levels than present in a slope failure, this leads to the conclusion that the use of the non-linear criterion leads to a safer slope design...
Slope Safety Factor Calculations With Non-Linear Yield Criterion Using Finite Elements
Clausen, Johan Christian; Damkilde, Lars
2006-01-01
The factor of safety for a slope is calculated with the finite element method using a non-linear yield criterion of the Hoek-Brown type. The parameters of the Hoek-Brown criterion are found from triaxial test data. Parameters of the linear Mohr-Coulomb criterion are calibrated to the same triaxial...... are carried out at much higher stress levels than present in a slope failure, this leads to the conclusion that the use of the non-linear criterion leads to a safer slope design....
Slope Safety Factor Calculations With Non-Linear Yield Criterion Using Finite Elements
Clausen, Johan Christian; Damkilde, Lars
2006-01-01
The factor of safety for a slope is calculated with the finite element method using a non-linear yield criterion of the Hoek-Brown type. The parameters of the Hoek-Brown criterion are found from triaxial test data. Parameters of the linear Mohr-Coulomb criterion are calibrated to the same triaxial...... are carried out at much higher stress levels than present in a slope failure, this leads to the conclusion that the use of the non-linear criterion leads to a safer slope design....
Slope Safety Factor Calculations With Non-Linear Yield Criterion Using Finite Elements
Clausen, Johan; Damkilde, Lars
2006-01-01
The factor of safety for a slope is calculated with the finite element method using a non-linear yield criterion of the Hoek-Brown type. The parameters of the Hoek-Brown criterion are found from triaxial test data. Parameters of the linear Mohr-Coulomb criterion are calibrated to the same triaxial...... are carried out at much higher stress levels than present in a slope failure, this leads to the conclusion that the use of the non-linear criterion leads to a safer slope design...
High lung volume increases stress failure in pulmonary capillaries
Fu, Z.; Costello, M. L.; Tsukimoto, K.; Prediletto, R.; Elliott, A. R.; Mathieu-Costello, O.; West, J. B.
1992-01-01
We previously showed that when pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to test whether stress failure occurred more frequently at high than at low lung volumes for the same Ptm. Lungs of anesthetized rabbits were inflated to a transpulmonary pressure of 20 cmH2O, perfused with autologous blood at 32.5 or 2.5 cmH2O Ptm, and fixed by intravascular perfusion. Samples were examined by both transmission and scanning electron microscopy. The results were compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O. There was a large increase in the frequency of stress failure of the capillary walls at the higher lung volume. For example, at 32.5 cmH2O Ptm, the number of endothelial breaks per millimeter cell lining was 7.1 +/- 2.2 at the high lung volume compared with 0.7 +/- 0.4 at the low lung volume. The corresponding values for epithelium were 8.5 +/- 1.6 and 0.9 +/- 0.6. Both differences were significant (P less than 0.05). At 52.5 cmH2O Ptm, the results for endothelium were 20.7 +/- 7.6 (high volume) and 7.1 +/- 2.1 (low volume), and the corresponding results for epithelium were 32.8 +/- 11.9 and 11.4 +/- 3.7. At 32.5 cmH2O Ptm, the thickness of the blood-gas barrier was greater at the higher lung volume, consistent with the development of more interstitial edema. Ballooning of the epithelium caused by accumulation of edema fluid between the epithelial cell and its basement membrane was seen at 32.5 and 52.5 cmH2O Ptm. At high lung volume, the breaks tended to be narrower and fewer were oriented perpendicular to the axis of the pulmonary capillaries than at low lung volumes. Transmission and scanning electron microscopy measurements agreed well. Our findings provide a physiological
Study on Splitting Failure Criterion of Surrounding Rock under Point Yield%裂纹尖端屈服条件下的围岩劈裂破坏判据研究
刘宁; 张春生
2011-01-01
The new fracture criterion is set up because the elastic fracture mechanics is not applicable for the plastic zone. Considering the interaction among cracks, the sliding multi-cracks model is adopted to simulate the splitting failure of rock in axial pressure. The plastic radius is calculated by Mises yield criterion and the dissipation energy for plastic deformation in total volume is also computed. The splitting failure criterion is established with principle of energy balance. The criterion is applied to the excavation of Langyashan pumped storage power station. The distribution charts of splitting failure zone are obtained, which coincides with results obtained by Lajtai empirical formula. It shows that the method is effective and feasible, which provides prediction criterion for splitting failure of underground engineering excavation in high geostress.%针对裂纹尖端附近出现塑性区时线弹性断裂力学理论不适用的问题,采用滑移裂纹组模型模拟岩石在轴向压力下的劈裂破坏,根据Mises屈服准则求出塑性区半径和整个体积中塑性变形引起的耗散能,基于能量平衡原理得到小范围屈服条件下的劈裂判据,将该判据应用于琅琊山抽水蓄能水电站机组的开挖分析中,计算获得了劈裂破坏区范围分布图,并与Lajtai经验公式进行比较,结果较为一致,表明该方法可行、有效,为地下工程开挖引起的劈裂破坏提供了预测判据.
Influence of residual stresses on failure pressure of cylindrical pressure vessels
M. Jeyakumar; T. Christopher
2013-01-01
The utilization of pressure vessels in aerospace applications is manifold. In this work, finite element analysis (FEA) has been carried out using ANSYS software package with 2D axisym-metric model to access the failure pressure of cylindrical pressure vessel made of ASTM A36 carbon steel having weld-induced residual stresses. To find out the effect of residual stresses on failure pressure, first an elasto-plastic analysis is performed to find out the failure pressure of pressure vessel not having residual stresses. Then a thermo-mechanical finite element analysis is performed to assess the residual stresses developed in the pressure vessel during welding. Finally one more elasto-plastic analysis is performed to assess the effect of residual stresses on failure pressure of the pressure vessel having residual stresses. This analysis indicates reduction in the failure pressure due to unfavorable residual stresses.
Failure of Ceramic Composites in Non-Uniform Stress Fields
Rajan, Varun P.
Continuous-fiber ceramic matrix composites (CMCs) are of interest as hot-section components in gas turbine engines due to their refractoriness and low density relative to metallic alloys. In service, CMCs will be subjected to spatially inhomogeneous temperature and stress fields. Robust tools that enable prediction of deformation and fracture under these conditions are therefore required for component design and analysis. Such tools are presently lacking. The present work helps to address this deficiency by developing models for CMC mechanical behavior at two length scales: that of the constituents and that of the components. Problems of interest are further divided into two categories: '1-D loadings,' in which the stresses are aligned with the fiber axes, and '2-D loadings,' in which the stress state is more general. For the former class of problems, the major outstanding issue is material fracture, not deformation. A fracture criterion based on the attainment of a global load maximum is developed, which yields results for pure bending of CMCs in reasonable agreement with available experimental data. For the latter class of problems, the understanding of both the micro-scale and macro-scale behavior is relatively immature. An approach based upon analysis of a unit cell (a single fiber surrounded by a matrix jacket) is pursued. Stress fields in the constituents of the composite are estimated using analytical models, the accuracy of which is confirmed using finite element analysis. As part of a fracture mechanics analysis, these fields enable estimation of the steady-state matrix cracking stress for arbitrary in-plane loading of a unidirectional ply. While insightful at the micro-scale, unit cell models are difficult to extend to coarser scales. Instead, material deformation is typically predicted using phenomenological constitutive models. One such model for CMC laminates is investigated and found to predict material instability where none should exist. Remedies to
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
ZUO Yu-jun; TANG Chun-an; ZHU Wan-cheng; LI Di-yuan; LI Shu-cai
2008-01-01
Based on mesoscopic damage mechanics, numerical code RFPA2D (dynamic edition) was developed to analyze the influence of tunnel reinforcing on failure process of surrounding rock under explosive stress waves. The results show that the propagation phenomenon of stress wave in the surrounding rock of tunnel and the failure process of surrounding rock under explosive stress waves are reproduced realistically by using numerical code RFPAED; from the failure process of surrounding rock,the place at which surrounding rock fractures is transferred because of tunnel reinforcing, and the rockfall and collapse caused by failure of surrounding rock are restrained by tunnel reinforcing; furthermore, the absolute values of peak values of major principal stress, and the minimal principal stress and shear stress at center point of tunnel roof are reduced because of tunnel reinforcing, and the displacement at center point of tunnel roof is reduced as well, consequently the stability of tunnel increases.
A new elliptic-parabolic yield surface model revised by an adaptive criterion for granular soils
无
2010-01-01
An adaptive criterion for shear yielding as well as shear failure of soils is proposed in this paper to address the fact that most criteria,including the Mohr-Coulomb criterion,the Lade criterion and the Matsuoka-Nakai criterion,cannot agree well with the experimental results when the value of the intermediate principal stress parameter is too big.The new criterion can adjust an adaptive parameter based on the experimental results in order to make the theoretical calculations fit the test results more accurately.The original elliptic-parabolic yield surface model can capture both soil contraction and dilation behaviors.However,it normally over-predicts the soil strength due to its application of the Extended Mises criterion.A new elliptic-parabolic yield surface mode is presented in this paper,which introduces the adaptive criterion in three-dimensional principal stress space.The new model can well model the stress-strain behavior of soils under general stress conditions.Compared to the original model which can only simulate soil behavior under triaxial compression conditions,the new model can simulate soil behaviors under both triaxial compression conditions and general stress conditions.
无
2001-01-01
By temperature normalization of the concept of equivalent damage stress proposed by Lemaitre,a new concept of relative damage stress has been put forward as the dominant mechanical factor for the failure of soldered joints under temperature cycling. Finite element numerical simulation results showed that the highest value of relative damage stress occurred at the high temperaturehold time during temperature cycling history.
苗胜军; 杨志军; 龙超; 谭文辉
2013-01-01
为探究适应脆性硬岩加载破坏的强度准则,以杏山铁矿混合花岗岩为对象,根据室内试验获得岩石物理力学参数及岩样切片扫描图,基于颗粒流理论和PFC程序建立混合花岗岩颗粒细观几何模型,采用Fish语言编制加载命令流并调整相应函数,对岩石单轴和三轴(s3=40 MPa)刚性加载试验进行模拟.通过岩石全应力–应变试验与模拟曲线、AE声发射与裂纹监测成果等综合比较研究,获得荷载作用下混合花岗岩细观力学特性及微宏观破裂演化规律.在此基础上,结合岩石单轴刚性加载试验曲线,裂纹数、摩擦力能量与轴向应变关系曲线,以及FLAC模拟,对脆性硬岩黏聚力弱化–摩擦力强化(CWFS)强度准则模型参数进行优化研究与验证.获得杏山铁矿混合花岗岩CWFS强度准则模型参数：初始黏聚力为23 MPa,残余黏聚力为4.3 MPa,初始摩擦角为0°,残余摩擦角为46.3°,临界塑性应变 pce, pfe分别为0.0015,0.0037.该研究成果对杏山铁矿露天转地下开采围岩体破坏机制和力学本构关系研究和工程稳定性分析等具有重要的意义.%It takes migmatitic granite of Xingshan iron mine as the object to study the failure criterion of brittle hard rock. According to the physical and mechanical parameters from laboratory experiments and grains section scanning,micro-geometric model of migmatitic granite grains were built based on particle flow theory and PFC programs,loading codes were developed and some functions were adjusted by Fish language to simulate uniaxial and triaxial( 3s = 40 MPa) compression experiments. Based on comprehensive comparison and analysis of the complete stress-strain curves,acoustic emission and“crack”monitoring results from laboratory and simulation, the micro-mechanical characteristics and the cracks revolution laws from microcosm to macrocosm of migmatitic granite were obtained. On this condition,cohesion weakening and
Social Support, Perceived Stress, and Markers of Heart Failure Severity
2012-08-01
be a significant predictor of heart failure hospitalizations and mortality, independent of other known risk factors (Chung, 25 Lennie, Dekker ...neighbors, friends, workmates, school mates, fellow volunteers , member of groups without religious affiliations, and members of religious groups...historical or physical findings or laboratory values in identifying congestive heart failure" as determined in their study of 1,586 patients, representing
Influence of effective stress coefficient on mechanical failure of chalk
Alam, Mohammad Monzurul; Fabricius, Ida Lykke; Hjuler, M.L.
2012-01-01
and vice versa. However, as the effective stress working on the rock decreases with increased effective stress coefficient, the reduction of elastic region will have less effect on pore collapse strength if we consider the change in the effective stress coefficient. This finding will help estimate a more...
Effect of Thermal Stresses on the Failure Criteria of Fiber Composites
Leong, Martin Klitgaard; Sankar, Bhavani V.
2010-01-01
When composite laminates are operated at cryogenic temperatures, thermal stresses arise. This is due to the difference in coefficients of thermal expansion of different plies and also between the fiber and matrix. While the former is taken into account in the composite structural analysis......, the latter, called micro-thermal stresses, has not been given much attention. In this paper the Direct Micromechanics Method is used to investigate the effects of micro-thermal stresses on the failure envelope of composites. Using FEA the unit-cell of the composite is analyzed. Assuming the failure criteria...... for the fiber and matrix are known, the exact failure envelope is developed. Using the micromechanics results, the Tsai-Wu failure envelope is modified to account for the micro-thermal stresses. The approach is demonstrated using two example structures at cryogenic temperature....
Impacts of Job Stress and Cognitive Failure on Patient Safety Incidents among Hospital Nurses
Young-Mi Park
2013-12-01
Conclusion: Patient safety incidents were affected by shift work, cognitive failure, and job stress. Many countermeasures to reduce the incidents caused by shift work, and plans to reduce job stress to reduce the workers' cognitive failure are required. In addition, there is a necessity to reduce job instability and clearly define the scope and authority for duties that are directly related to the patient's safety.
Franco, D; Durandy, Y; Deporte, A; Bismuth, H
1977-01-29
Emergency fibroscopy revealed bleeding lesions in 84 cirrhotic patients. In patients with moderate or no hepatic failure, the commonest actively bleeding sources were oesophagogastric varices and acute mucosal ulcers associated with the ingestion of anti-inflammatory drugs. In patients with severe hepatic failure, acute mucosal ulcers unrelated to drugs predominated and there was evidence that these were stress-induced erosions.
Revealing catastrophic failure of leaf networks under stress.
Brodribb, Timothy J; Bienaimé, Diane; Marmottant, Philippe
2016-04-26
The intricate patterns of veins that adorn the leaves of land plants are among the most important networks in biology. Water flows in these leaf irrigation networks under tension and is vulnerable to embolism-forming cavitations, which cut off water supply, ultimately causing leaf death. Understanding the ways in which plants structure their vein supply network to protect against embolism-induced failure has enormous ecological and evolutionary implications, but until now there has been no way of observing dynamic failure in natural leaf networks. Here we use a new optical method that allows the initiation and spread of embolism bubbles in the leaf network to be visualized. Examining embolism-induced failure of architecturally diverse leaf networks, we found that conservative rules described the progression of hydraulic failure within veins. The most fundamental rule was that within an individual venation network, susceptibility to embolism always increased proportionally with the size of veins, and initial nucleation always occurred in the largest vein. Beyond this general framework, considerable diversity in the pattern of network failure was found between species, related to differences in vein network topology. The highest-risk network was found in a fern species, where single events caused massive disruption to leaf water supply, whereas safer networks in angiosperm leaves contained veins with composite properties, allowing a staged failure of water supply. These results reveal how the size structure of leaf venation is a critical determinant of the spread of embolism damage to leaves during drought.
Influence of effective stress coefficient on mechanical failure of chalk
Alam, Mohammad Monzurul; Fabricius, Ida Lykke; Hjuler, M.L.
2012-01-01
The Effective stress coefficient is a measure of how chalk grains are connected with each other. The stiffness of chalk may decrease if the amount of contact cements between the grains decreases, which may lead to an increase of the effective stress coefficient. We performed CO2 injection in chal...
WANG Ronghua; FEI Heliang
2004-01-01
In this note, the tampered failure rate model is generalized from the step-stress accelerated life testing setting to the progressive stress accelerated life testing for the first time. For the parametric setting where the scale parameter satisfying the equation of the inverse power law is Weibull, maximum likelihood estimation is investigated.
Stress failure of pulmonary capillaries: role in lung and heart disease
West, J. B.; Mathieu-Costello, O.
1992-01-01
Pulmonary capillaries have extremely thin walls to allow rapid exchange of respiratory gases across them. Recently it has been shown that the wall stresses become very large when the capillary pressure is raised, and in anaesthetised rabbits, ultrastructural damage to the walls is seen at pressures of 40 mm Hg and above. The changes include breaks in the capillary endothelial layer, alveolar epithelial layer, and sometimes all layers of the wall. The strength of the thin part of the capillary wall can be attributed to the type IV collagen in the extracellular matrix. Stress failure of pulmonary capillaries results in a high-permeability form of oedema, or even frank haemorrhage, and is apparently the mechanism of neurogenic pulmonary oedema and high-altitude pulmonary oedema. It also explains the exercise-induced pulmonary haemorrhage that occurs in all racehorses. Several features of mitral stenosis are consistent with stress failure. Overinflation of the lung also leads to stress failure, a common cause of increased capillary permeability in the intensive care environment. Stress failure also occurs if the type IV collagen of the capillary wall is weakened by autoantibodies as in Goodpasture's syndrome. Neutrophil elastase degrades type IV collagen and this may be the starting point of the breakdown of alveolar walls that is characteristic of emphysema. Stress failure of pulmonary capillaries is a hitherto overlooked and potentially important factor in lung and heart disease.
Stress failure of pulmonary capillaries: role in lung and heart disease
West, J. B.; Mathieu-Costello, O.
1992-01-01
Pulmonary capillaries have extremely thin walls to allow rapid exchange of respiratory gases across them. Recently it has been shown that the wall stresses become very large when the capillary pressure is raised, and in anaesthetised rabbits, ultrastructural damage to the walls is seen at pressures of 40 mm Hg and above. The changes include breaks in the capillary endothelial layer, alveolar epithelial layer, and sometimes all layers of the wall. The strength of the thin part of the capillary wall can be attributed to the type IV collagen in the extracellular matrix. Stress failure of pulmonary capillaries results in a high-permeability form of oedema, or even frank haemorrhage, and is apparently the mechanism of neurogenic pulmonary oedema and high-altitude pulmonary oedema. It also explains the exercise-induced pulmonary haemorrhage that occurs in all racehorses. Several features of mitral stenosis are consistent with stress failure. Overinflation of the lung also leads to stress failure, a common cause of increased capillary permeability in the intensive care environment. Stress failure also occurs if the type IV collagen of the capillary wall is weakened by autoantibodies as in Goodpasture's syndrome. Neutrophil elastase degrades type IV collagen and this may be the starting point of the breakdown of alveolar walls that is characteristic of emphysema. Stress failure of pulmonary capillaries is a hitherto overlooked and potentially important factor in lung and heart disease.
Brewin, C R; Andrews, B; Rose, S
2000-07-01
A DSM-IV diagnosis of posttraumatic stress disorder (PTSD) required for the first time that individuals must report experiencing intense fear, helplessness, or horror at the time of the trauma. In a longitudinal study of 138 victims of violent crime, we investigated whether reports of intense trauma-related emotions characterized individuals who, after 6 months, met criteria for PTSD according to the DSM-III-R. We found that intense levels of all 3 emotions strongly predicted later PTSD. However, a small number of those who later met DSM-III-R or ICD criteria for PTSD did not report intense emotions at the time of the trauma. They did, however, report high levels of either anger with others or shame.
BILAM: a composite laminate failure-analysis code using bilinear stress-strain approximations
McLaughlin, P.V. Jr.; Dasgupta, A.; Chun, Y.W.
1980-10-01
The BILAM code which uses constant strain laminate analysis to generate in-plane load/deformation or stress/strain history of composite laminates to the point of laminate failure is described. The program uses bilinear stress-strain curves to model layer stress-strain behavior. Composite laminates are used for flywheels. The use of this computer code will help to develop data on the behavior of fiber composite materials which can be used by flywheel designers. In this program the stress-strain curves are modelled by assuming linear response in axial tension while using bilinear approximations (2 linear segments) for stress-strain response to axial compressive, transverse tensile, transverse compressive and axial shear loadings. It should be noted that the program attempts to empirically simulate the effects of the phenomena which cause nonlinear stress-strain behavior, instead of mathematically modelling the micromechanics involved. This code, therefore, performs a bilinear laminate analysis, and, in conjunction with several user-defined failure interaction criteria, is designed to provide sequential information on all layer failures up to and including the first fiber failure. The modus operandi is described. Code BILAM can be used to: predict the load-deformation/stress-strain behavior of a composite laminate subjected to a given combination of in-plane loads, and make analytical predictions of laminate strength.
Duffy, Stephen [Cleveland State Univ., Cleveland, OH (United States)
2013-09-09
This project will implement inelastic constitutive models that will yield the requisite stress-strain information necessary for graphite component design. Accurate knowledge of stress states (both elastic and inelastic) is required to assess how close a nuclear core component is to failure. Strain states are needed to assess deformations in order to ascertain serviceability issues relating to failure, e.g., whether too much shrinkage has taken place for the core to function properly. Failure probabilities, as opposed to safety factors, are required in order to capture the bariability in failure strength in tensile regimes. The current stress state is used to predict the probability of failure. Stochastic failure models will be developed that can accommodate possible material anisotropy. This work will also model material damage (i.e., degradation of mechanical properties) due to radiation exposure. The team will design tools for components fabricated from nuclear graphite. These tools must readily interact with finite element software--in particular, COMSOL, the software algorithm currently being utilized by the Idaho National Laboratory. For the eleastic response of graphite, the team will adopt anisotropic stress-strain relationships available in COMSO. Data from the literature will be utilized to characterize the appropriate elastic material constants.
Review on Stress Corrosion and Corrosion Fatigue Failure of Centrifugal Compressor Impeller
SUN Jiao; CHEN Songying; QU Yanpeng; LI Jianfeng
2015-01-01
Corrosion failure, especially stress corrosion cracking and corrosion fatigue, is the main cause of centrifugal compressor impeller failure. And it is concealed and destructive. This paper summarizes the main theories of stress corrosion cracking and corrosion fatigue and its latest developments, and it also points out that existing stress corrosion cracking theories can be reduced to the anodic dissolution (AD), the hydrogen-induced cracking (HIC), and the combined AD and HIC mechanisms. The corrosion behavior and the mechanism of corrosion fatigue in the crack propagation stage are similar to stress corrosion cracking. The effects of stress ratio, loading frequency, and corrosive medium on the corrosion fatigue crack propagation rate are analyzed and summarized. The corrosion behavior and the mechanism of stress corrosion cracking and corrosion fatigue in corrosive environments, which contain sulfide, chlorides, and carbonate, are analyzed. The working environments of the centrifugal compressor impeller show the behavior and the mechanism of stress corrosion cracking and corrosion fatigue in different corrosive environments. The current research methods for centrifugal compressor impeller corrosion failure are analyzed. Physical analysis, numerical simulation, and the fluid-structure interaction method play an increasingly important role in the research on impeller deformation and stress distribution caused by the joint action of aerodynamic load and centrifugal load.
Ma, Xiaodong; Rudnicki, John W.; Haimson, Bezalel C.
2017-04-01
We performed an extensive suite of true triaxial experiments in two porous sandstones, Bentheim (porosity ≈ 24%) and Coconino (17%). The experiments were conducted using a novel loading path, which maintains constant Lode angle (Θ) throughout the test. This path enabled the examination of the effects of Lode angle and mean stress on failure (σoct,f). Our tests covered σ3 magnitudes between 0 and 150 MPa and of Θ at -30° (axisymmetric extension), -16°, 0°, +11°, +21°, and +30° (axisymmetric compression). Test results revealed the respective contribution of each of the two stress invariants to failure stress, failure plane angle, and failure mode. In both sandstones, the shear stress required for failure increases with mean stress but decreases with Θ when shear failure mode dominates. However, the dependence of failure stress on mean stress and Θ is reversed when the compactive failure mode is in control. The compactive failure mode was evident in Bentheim sandstone when compaction bands were observed under high mean stress. The Coconino sandstone did not reach the compactive failure regime within the maximum confinement applied. The failure plane angle monotonically decreases with increasing mean stress and Θ. For Coconino sandstone, failure plane angle varies between 80° and 50° for σoct,f between 50 and 450 MPa whereas it drops to 0° as σoct,f, approaches 250 MPa in Bentheim sandstone. We employed the bifurcation theory to relate the stress conditions at failure to the development of failure planes. The theory is in qualitative agreement with the experimental data.
Voltage stress effects on microcircuit accelerated life test failure rates
Johnson, G. M.
1976-01-01
The applicability of Arrhenius and Eyring reaction rate models for describing microcircuit aging characteristics as a function of junction temperature and applied voltage was evaluated. The results of a matrix of accelerated life tests with a single metal oxide semiconductor microcircuit operated at six different combinations of temperature and voltage were used to evaluate the models. A total of 450 devices from two different lots were tested at ambient temperatures between 200 C and 250 C and applied voltages between 5 Vdc and 15 Vdc. A statistical analysis of the surface related failure data resulted in bimodal failure distributions comprising two lognormal distributions; a 'freak' distribution observed early in time, and a 'main' distribution observed later in time. The Arrhenius model was shown to provide a good description of device aging as a function of temperature at a fixed voltage. The Eyring model also appeared to provide a reasonable description of main distribution device aging as a function of temperature and voltage. Circuit diagrams are shown.
Failure of a fiber composite lamina under three-dimensional stresses
DeTeresa, S J
1999-08-31
The efficient use of thick-section fiber composites requires a proven three-dimensional failure model. Numerous failure criteria have been proposed, but the lack of critical experimental results makes it difficult to assess the accuracy of these models. It is shown that the various predictions for failure of a lamina due to the simple state of uniaxial stress plus superposed hydrostatic pressure are disparate. These differences are sufficient to allow evaluation of failure criteria using data that has the normal scatter found for composite materials. A high-pressure test system for fiber composites is described and results for the effects of pressure on the transverse and longitudinal compression strengths of a carbon fiber/epoxy lamina are discussed. Results are compared with a few representative failure models.
林晓玲
2013-01-01
Operation criterions are used to decide if the reactor can continue to work when the fuel clad failure. The method for establish the limits is presented. The tolerated maximum of failure fuel rods for the reactor safety should be calculated by risk analysis. The parameters are determined which can not only reflect the quantity but also be measured directly. The relationship is set up between the amounts with the parameters. The data calculated corresponding to maximum of failure fuel element which the reactor safety can stand are technical limits used to decide if the reactor can work continually.%运行判据是用于判断反应堆燃料元件发生破损时能否继续运行的指标条件,本文提出建立反应堆燃料元件破损运行判据的思路和方法,通过风险分析,确定监督运行最大容许破损数量；研究提出既能反映燃料元件破损数量又可直接监测的指标参量,并建立破损数量与可监测指标参量之间的对应关系；将最大容许破损数量对应的可监测指标参量值作为运行技术判据.
Xiao-Yang Liu, Xiao-Fei Chen, Yan-Hong Ren, Qing-Yuan Zhan, Chen Wang, Chun Yang
2011-01-01
Full Text Available Mechanical ventilation-induced excessive stretch of alveoli is reported to induce cellular stress failure and subsequent lung injury, and is therefore an injurious factor to the lung. Avoiding cellular stress failure is crucial to ventilator-induced lung injury (VILI treatment. In the present study, primary rat alveolar type II (ATII cells were isolated to evaluate their viability and the mechanism of their survival under tonic stretch. By the annexin V/ PI staining and flow cytometry assay, we demonstrated that tonic stretch-induced cell death is an immediate injury of mechanical stress. In addition, immunofluorescence and immunoblots assay showed that the cells experienced an expansion-contraction-reexpansion process, accompanied by partial focal adhesion (FA disassembly during contraction. Manipulation of integrin adherent affinity by altering bivalent cation levels in the culture medium and applying an integrin neutralizing antibody showed that facilitated adhesion affinity promoted cell death under tonic stretch, while lower level of adhesion protected the cells from stretch-induced stress failure. Finally, a simplified numerical model was established to reveal that adequate disassembly of FAs reduced the forces transmitting throughout the cell. Taken together, these results indicate that ATII cells escape stress failure caused by tonic stretch via active cell morphological remodeling, during which cells transiently disassemble FAs to unload mechanical forces.
Cellular Stress Failure in Ventilator-injured Lungs
Vlahakis, Nicholas E.; Hubmayr, Rolf D.
2005-01-01
The clinical and experimental literature has unequivocally established that mechanical ventilation with large tidal volumes is injurious to the lung. However, uncertainty about the micromechanics of injured lungs and the numerous degrees of freedom in ventilator settings leave many unanswered questions about the biophysical determinants of lung injury. In this review we focus on experimental evidence for lung cells as injury targets and the relevance of these studies for human ventilator-associated lung injury. In vitro, the stress-induced mechanical interactions between matrix and adherent cells are important for cellular remodeling as a means for preventing compromise of cell structure and ultimately cell injury or death. In vivo, these same principles apply. Large tidal volume mechanical ventilation results in physical breaks in alveolar epithelial and endothelial plasma membrane integrity and subsequent triggering of proinflammatory signaling cascades resulting in the cytokine milieu and pathologic and physiologic findings of ventilator-associated lung injury. Importantly, though, alveolar cells possess cellular repair and remodeling mechanisms that in addition to protecting the stressed cell provide potential molecular targets for the prevention and treatment of ventilator-associated lung injury in the future. PMID:15695492
Oxidative Stress and Heart Failure in Altered Thyroid States
Pallavi Mishra
2012-01-01
Full Text Available Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism. The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.
Increased Dicarbonyl Stress as a Novel Mechanism of Multi-Organ Failure in Critical Illness
van Bussel, Bas C. T.; van de Poll, Marcel C. G.; Schalkwijk, Casper G.; Bergmans, Dennis C. J. J.
2017-01-01
Molecular pathological pathways leading to multi-organ failure in critical illness are progressively being unravelled. However, attempts to modulate these pathways have not yet improved the clinical outcome. Therefore, new targetable mechanisms should be investigated. We hypothesize that increased dicarbonyl stress is such a mechanism. Dicarbonyl stress is the accumulation of dicarbonyl metabolites (i.e., methylglyoxal, glyoxal, and 3-deoxyglucosone) that damages intracellular proteins, modifies extracellular matrix proteins, and alters plasma proteins. Increased dicarbonyl stress has been shown to impair the renal, cardiovascular, and central nervous system function, and possibly also the hepatic and respiratory function. In addition to hyperglycaemia, hypoxia and inflammation can cause increased dicarbonyl stress, and these conditions are prevalent in critical illness. Hypoxia and inflammation have been shown to drive the rapid intracellular accumulation of reactive dicarbonyls, i.e., through reduced glyoxalase-1 activity, which is the key enzyme in the dicarbonyl detoxification enzyme system. In critical illness, hypoxia and inflammation, with or without hyperglycaemia, could thus increase dicarbonyl stress in a way that might contribute to multi-organ failure. Thus, we hypothesize that increased dicarbonyl stress in critical illness, such as sepsis and major trauma, contributes to the development of multi-organ failure. This mechanism has the potential for new therapeutic intervention in critical care. PMID:28178202
Increased Dicarbonyl Stress as a Novel Mechanism of Multi-Organ Failure in Critical Illness.
van Bussel, Bas C T; van de Poll, Marcel C G; Schalkwijk, Casper G; Bergmans, Dennis C J J
2017-02-07
Molecular pathological pathways leading to multi-organ failure in critical illness are progressively being unravelled. However, attempts to modulate these pathways have not yet improved the clinical outcome. Therefore, new targetable mechanisms should be investigated. We hypothesize that increased dicarbonyl stress is such a mechanism. Dicarbonyl stress is the accumulation of dicarbonyl metabolites (i.e., methylglyoxal, glyoxal, and 3-deoxyglucosone) that damages intracellular proteins, modifies extracellular matrix proteins, and alters plasma proteins. Increased dicarbonyl stress has been shown to impair the renal, cardiovascular, and central nervous system function, and possibly also the hepatic and respiratory function. In addition to hyperglycaemia, hypoxia and inflammation can cause increased dicarbonyl stress, and these conditions are prevalent in critical illness. Hypoxia and inflammation have been shown to drive the rapid intracellular accumulation of reactive dicarbonyls, i.e., through reduced glyoxalase-1 activity, which is the key enzyme in the dicarbonyl detoxification enzyme system. In critical illness, hypoxia and inflammation, with or without hyperglycaemia, could thus increase dicarbonyl stress in a way that might contribute to multi-organ failure. Thus, we hypothesize that increased dicarbonyl stress in critical illness, such as sepsis and major trauma, contributes to the development of multi-organ failure. This mechanism has the potential for new therapeutic intervention in critical care.
Stress and Failure Analysis of Rapidly Rotating Asteroid (29075) 1950 DA
Hirabayashi, Masatoshi
2014-01-01
Rozitis et al. recently reported that near-Earth asteroid (29075) 1950 DA, whose bulk density ranges from 1.0 g/cm3 to 2.4 g/cm3, is a rubble pile and requires a cohesive strength of at least 44 Pa to 74 Pa to keep from failing due to its fast spin period. Since their technique for giving failure conditions required the averaged stress over the whole volume, it discarded information about the asteroid's failure mode and internal stress condition. This paper develops a finite element model and revisits the stress and failure analysis of 1950 DA. For the modeling, we do not consider material-hardening and softening. Under the assumption of an associated flow rule and uniform material distribution, we identify the deformation process of 1950 DA when its constant cohesion reaches the lowest value that keeps its current shape. The results show that to avoid structural failure the internal core requires a cohesive strength of at least 75 Pa - 85 Pa. It suggests that for the failure mode of this body, the internal c...
Structures, stresses, and fluctuations in the delayed failure of colloidal gel
Lindstrom, S.B.; Kodger, T.E.; Sprakel, J.H.B.; Weitz, D.A.
2012-01-01
Sample-spanning networks of aggregated colloidal particles have a finite stiffness and deform elastically when subjected to a small shear stress. After some period of creep, these gels ultimately suffer catastrophic failure. This delayed yielding is governed by the association and dissociation dynam
Residual stress measurements with barkhausen noise in power plant creep failure analysis
Karvonen, I. [CoMoTest Oy, Maentsaelae (Finland)] Suominen, L. [Stresstech Oy, Jyvaeskylae (Finland)
1997-12-31
Continuously developing power and process industry needs predictive maintenance inspection methods in order to prevent failures with correctly timed and properly specified measures. Materials` monitoring has traditionally been non-destructive inspection to detect growing cracks or other deficiencies. Recently, after the development of portable stress measurement systems, some advances has been reached. Based on stress anomalies due to creep, fatigue or corrosion, new applications have been found in the use of Barkhausen noise inspection. When the Barkhausen noise findings have been simultaneously confirmed with other stress measuring methods, a wider acceptance of the application of the method can be proposed. (orig.) 7 refs.
The role of stress in heart failure – ground for sex specific pathophysiology
Viljetic B.
2011-04-01
Full Text Available In the last hundred years modern society went through numerous changes in life style, dietary habits, work load, physical activity and other environmental factors. As a species we are not well adapted to new de- mands. Higher levels of stress hormones provoke various effects, especially gradual change in the sensitivity of adrenergic, glucocorticoid and insulin receptors. All these changes are mutually associated and they gradually lead to metabolic syndrome, obesity, diabetes, heart failure and other types of pathology depending on genetic makeup and environmental factors. The aim of this paper is to summarize current knowledge concerning the impact of stress on cardiac function. Whereas stress response is sex specific we would emphasize a potential difference in pathophysiology of ischemic heart failure in men and women. Modern medicine has misinterpreted autonomous nervous system functions for years and this was reflected in heart failure (HF and arterial hypertension therapy. Stress before the onset of menopause has a lesser effect on cardiac function compared to stress after menopause. Postmenopausal women have a significantly higher risk of heart disease, which is related to the diminished protection of the female hormonal cycle, but low doses of estrogen have not proven protective in postmenopausal women. Potential new targets of sex- specific cardiac therapy would come from better understanding of the molecular mechanisms exerted by nuclear receptors for steroid hormones, transcription factors involved in heart remodeling, cross-talk in adrenergic signaling pathways and their down-stream molecules.
Constitutive modeling of void-growth-based tensile ductile failures with stress triaxiality effects
Mora Cordova, Angel
2014-07-01
In most metals and alloys, the evolution of voids has been generally recognized as the basic failure mechanism. Furthermore, stress triaxiality has been found to influence void growth dramatically. Besides strain intensity, it is understood to be the most important factor that controls the initiation of ductile fracture. We include sensitivity of stress triaxiality in a variational porous plasticity model, which was originally derived from hydrostatic expansion. Under loading conditions rather than hydrostatic deformation, we allow the critical pressure for voids to be exceeded so that the growth due to plasticity becomes dependent on the stress triaxiality. The limitations of the spherical void growth assumption are investigated. Our improved constitutive model is validated through good agreements with experimental data. Its capacity for reproducing realistic failure patterns is also indicated by a numerical simulation of a compact tensile (CT) test. © 2013 Elsevier Inc.
Numerical Simulation of Squeezing Failure in a Coal Mine Roadway due to Mining-Induced Stresses
Gao, Fuqiang; Stead, Doug; Kang, Hongpu
2015-07-01
Squeezing failure is a common failure mechanism experienced in underground coal mine roadways due mainly to mining-induced stresses, which are much higher than the strength of rock mass surrounding an entry. In this study, numerical simulation was carried out to investigate the mechanisms of roadway squeezing using a novel UDEC Trigon approach. A numerical roadway model was created based on a case study at the Zhangcun coal mine in China. Coal extraction using the longwall mining method was simulated in the model with calculation of the mining-induced stresses. The process of roadway squeezing under severe mining-induced stresses was realistically captured in the model. Deformation phenomena observed in field, including roof sag, wall convexity and failed rock bolts are realistically produced in the UDEC Trigon model.
Stellite failure on a P91 HP valve - failure investigation and modelling of residual stresses
Thorborg, Jesper; Hald, John; Hattel, Jesper Henri
2006-01-01
The sequence of the primary welding process and the following secondary processes of machining, and heat treatment has been modelled to predict the residual conditions in a Stellite 6 overlay weld on a P91 steam turbine valve. The different process steps are coupled in order to transfer the resid......The sequence of the primary welding process and the following secondary processes of machining, and heat treatment has been modelled to predict the residual conditions in a Stellite 6 overlay weld on a P91 steam turbine valve. The different process steps are coupled in order to transfer...... temperature dependent. The welding process is modelled by adding material to the calculation domain, while the machining process is modelled by removing material from the calculation domain to redistribute the stress fields. An in-house iso-parametric FEM-code is used for the implementation of the material...... models and the discretization of the appropriate addition and removal of material. The return mapping algorithm is used for the time discretization of the time independent plasticity model, and a Norton’s power law model is used for the time dependent model. Results from the numerical calculations...
R. Gholami; A. Moradzadeh; V. Rasouli; J. Hanachi
2014-01-01
Wellbore instability is reported frequently as one of the most significant incidents during drilling oper-ations. Analysis of wellbore instability includes estimation of formation mechanical properties and the state of in situ stresses. In this analysis, the only controllable parameter during drilling operation is the mud weight. If the mud weight is larger than anticipated, the mud will invade into the formation, causing tensile failure of the formation. On the other hand, a lower mud weight can result in shear failures of rock, which is known as borehole breakouts. To predict the potential for failures around the wellbore during drilling, one should use a failure criterion to compare the rock strength against induced tangen-tial stresses around the wellbore at a given mud pressure. The Mohr-Coulomb failure criterion is one of the commonly accepted criteria for estimation of rock strength at a given state of stress. However, the use of other criteria has been debated in the literature. In this paper, Mohr-Coulomb, Hoek-Brown and Mogi-Coulomb failure criteria were used to estimate the potential rock failure around a wellbore located in an onshore field of Iran. The log based analysis was used to estimate rock mechanical proper-ties of formations and state of stresses. The results indicated that amongst different failure criteria, the Mohr-Coulomb criterion underestimates the highest mud pressure required to avoid breakouts around the wellbore. It also predicts a lower fracture gradient pressure. In addition, it was found that the results obtained from Mogi-Coulomb criterion yield a better comparison with breakouts observed from the caliper logs than that of Hoek-Brown criterion. It was concluded that the Mogi-Coulomb criterion is a better failure criterion as it considers the effect of the intermediate principal stress component in the failure analysis.
R. Gholami
2014-02-01
Full Text Available Wellbore instability is reported frequently as one of the most significant incidents during drilling operations. Analysis of wellbore instability includes estimation of formation mechanical properties and the state of in situ stresses. In this analysis, the only controllable parameter during drilling operation is the mud weight. If the mud weight is larger than anticipated, the mud will invade into the formation, causing tensile failure of the formation. On the other hand, a lower mud weight can result in shear failures of rock, which is known as borehole breakouts. To predict the potential for failures around the wellbore during drilling, one should use a failure criterion to compare the rock strength against induced tangential stresses around the wellbore at a given mud pressure. The Mohr–Coulomb failure criterion is one of the commonly accepted criteria for estimation of rock strength at a given state of stress. However, the use of other criteria has been debated in the literature. In this paper, Mohr–Coulomb, Hoek–Brown and Mogi–Coulomb failure criteria were used to estimate the potential rock failure around a wellbore located in an onshore field of Iran. The log based analysis was used to estimate rock mechanical properties of formations and state of stresses. The results indicated that amongst different failure criteria, the Mohr–Coulomb criterion underestimates the highest mud pressure required to avoid breakouts around the wellbore. It also predicts a lower fracture gradient pressure. In addition, it was found that the results obtained from Mogi–Coulomb criterion yield a better comparison with breakouts observed from the caliper logs than that of Hoek–Brown criterion. It was concluded that the Mogi–Coulomb criterion is a better failure criterion as it considers the effect of the intermediate principal stress component in the failure analysis.
Stress Voiding in IC Interconnects - Rules of Evidence for Failure Analysts
FILTER, WILLIAM F.
1999-09-17
Mention the words ''stress voiding'', and everyone from technology engineer to manager to customer is likely to cringe. This IC failure mechanism elicits fear because it is insidious, capricious, and difficult to identify and arrest. There are reasons to believe that a damascene-copper future might be void-free. Nevertheless, engineers who continue to produce ICs with Al-alloy interconnects, or who assess the reliability of legacy ICs with long service life, need up-to-date insights and techniques to deal with stress voiding problems. Stress voiding need not be fearful. Not always predictable, neither is it inevitable. On the contrary, stress voids are caused by specific, avoidable processing errors. Analytical work, though often painful, can identify these errors when stress voiding occurs, and vigilance in monitoring the improved process can keep it from recurring. In this article, they show that a methodical, forensics approach to failure analysis can solve suspected cases of stress voiding. This approach uses new techniques, and patiently applies familiar ones, to develop evidence meeting strict standards of proof.
Elliott M. Groves
2013-01-01
Full Text Available Importance. Constrictive pericarditis is a rare clinical entity that frequently necessitates surgical intervention. Here we present a case of biventricular failure due to stress cardiomyopathy after pericardiectomy. This is an extremely rare complication that is not well described and does not have a definitive mechanism. Observations. A 40-year-old Ecuadorian woman who was found to have constrictive pericarditis due to Mycobacterium tuberculosis infection was referred to our institution. The presence of constrictive pericarditis was confirmed by echocardiography, computed tomography, magnetic resonance imaging, and cardiac catheterization. Following pericardiectomy, the patient developed biventricular failure consistent with stress cardiomyopathy (Takotsubo cardiomyopathy, based on the echocardiographic assessment of the ventricles, which demonstrated an akinetic apex and hyperactive base in both ventricles, the absence of significant epicardial coronary atherosclerosis, and prompt normalization of the cardiac function after intensive medical therapy. Conclusions and Relevance. Biventricular failure in the form of stress cardiomyopathy after pericardiectomy in the manner presented here has not been previously described in the literature. While postulations as to the cause of single ventricle dysfunction have been described, the exact mechanism is unclear and current theories do not explain the clinical features in this case of stress cardiomyopathy after pericardiectomy.
Displacement, stress and seismicity in roadway roofs during mining-induced failure
Shen, B.; King, A.; Guo, H. [CSIRO Exploration & Mining, Kenmore, Qld. (Australia)
2008-07-15
Roof stability in gateroads is a long-standing issue in many of the underground mines in Australia that use longwall extraction methods, due primarily to a significant increase of vertical stresses ahead of the longwall face. Although numerous studies have been done in the past, the process of roof rock deformation and breakage prior to and during a roof failure in an actual mining environment is still being debated. This paper describes a new integrated roof monitoring system and the results from applying this system in an Australian underground coal mine. The system integrates displacement, stress and seismic monitoring. It has been applied to two roadways in an Australian underground coal mine during two field experiments. The key roof behaviour identified by the integrated monitoring package during the two field monitoring experiments is reported and discussed in this paper. The experiments were conducted in the 'tailgate' roadways that are adjacent to the caved zone, or 'goaf', of the previously mined panels. It was found in the experiments that, prior to roof falls, roof displacement accelerates whereas the horizontal stresses reduce. Seismic activity intensifies before major roof displacement or stress changes are evident, and subsides in the later stage of roof failure when large roof displacement is visible. The seismic resonance frequencies decrease during roof failure development. The field monitoring studies have also identified a number of quantitative and site-specific roof fall precursors potentially useful for roof fall prediction and prevention.
A damage mechanics approach for quantifying stress changes due to brittle failure of porous rocks
Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena
2016-04-01
Natural fault zones or man-made injection or production of fluid impact the regional stress distribution in Earth's crust and can be responsible for localized stress discontinuities. Understanding the processes controlling fracturing of the porous rocks and mechanical behaviour of fault zones is therefore of interest for several applications including geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes controlling the deformation of porous rocks during and after brittle failure. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To illustrate the model, simulation of a compaction experiment of a sandstone leading to shear failure will be presented which allows to quantify the stress drop accompanying the failure. Finally, we will demonstrate that this approach can also be used at the field scale to simulate hydraulic fracturing and assess the resulting changes in the stress field.
STRESS AND FAILURE ANALYSIS OF RAPIDLY ROTATING ASTEROID (29075) 1950 DA
Hirabayashi, Masatoshi; Scheeres, Daniel J., E-mail: masatoshi.hirabayashi@colorado.edu [Research Associate, Colorado Center for Astrodynamics Research, Aerospace Engineering Sciences, University of Colorado Boulder. (United States)
2015-01-01
Rozitis et al. recently reported that near-Earth asteroid (29075) 1950 DA, whose bulk density ranges from 1.0 g cm{sup –3} to 2.4 g cm{sup –3}, is a rubble pile and requires a cohesive strength of at least 44-76 Pa to keep from failing due to its fast spin period. Since their technique for giving failure conditions required the averaged stress over the whole volume, it discarded information about the asteroid's failure mode and internal stress condition. This paper develops a finite element model and revisits the stress and failure analysis of 1950 DA. For the modeling, we do not consider material hardening and softening. Under the assumption of an associated flow rule and uniform material distribution, we identify the deformation process of 1950 DA when its constant cohesion reaches the lowest value that keeps its current shape. The results show that to avoid structural failure the internal core requires a cohesive strength of at least 75-85 Pa. It suggests that for the failure mode of this body, the internal core first fails structurally, followed by the surface region. This implies that if cohesion is constant over the whole volume, the equatorial ridge of 1950 DA results from a material flow going outward along the equatorial plane in the internal core, but not from a landslide as has been hypothesized. This has additional implications for the likely density of the interior of the body.
Oxidative Stress in Dog with Heart Failure: The Role of Dietary Fatty Acids and Antioxidants
Emmanuelle Sagols
2011-01-01
Full Text Available In dogs with heart failure, cell oxygenation and cellular metabolism do not work properly, leading to the production of a large amount of free radicals. In the organism, these free radicals are responsible of major cellular damages: this is oxidative stress. However, a suitable food intake plays an important role in limiting this phenomenon: on the one hand, the presence of essential fatty acids in the composition of membranes decreases sensitivity of cells to free radicals and constitutes a first protection against the oxidative stress; on the other hand, coenzyme Q10, vitamin E, and polyphenols are antioxidant molecules which can help cells to neutralize these free radicals.
Qiangling Yao
2016-01-01
Full Text Available The 6163 haulage roadway in the Qidong coal mine passes through a fault zone, which causes severe deformation in the surrounding rock, requiring repeated roadway repairs. Based on geological features in the fault area, we analyze the factors affecting roadway deformation and failure and propose the concept of roadway sensitive to stress disturbance (RSSD. We investigate the deformation and failure mechanism of the surrounding rocks of RSSD using field monitoring, theoretical analysis, and numerical simulation. The deformation of the surrounding rocks involves dilatation of shallow rocks and separation of deep rocks. Horizontal and longitudinal fissures evolve to bed separation and fracture zones; alternatively, fissures can evolve into fracture zones with new fissures extending to deeper rock. The fault affects the stress field of the surrounding rock to ~27 m radius. Its maximum impact is on the vertical stress of the rib rock mass and its minimum impact is on the vertical stress of the floor rock mass. Based on our results, we propose a zonal support system for a roadway passing through a fault. Engineering practice shows that the deformation of the surrounding rocks of the roadway can be effectively controlled to ensure normal and safe production in the mine.
张社荣; 孙博; 王超; 严磊
2014-01-01
Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic (brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence:when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis (such as σ2=σ3=0 MPa);conversely, the failure surface is parallel to the z axis (such asσ2=20 MPa,σ3=0 MPa).
Inflammation, Iron, Energy Failure, and Oxidative Stress in the Pathogenesis of Multiple Sclerosis
Lukas Haider
2015-01-01
Full Text Available Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system. Different trigger pathologies have been suggested by the primary cytodegenerative “inside-out” and primary inflammation-driven “outside-in” hypotheses. Recent data indicate that mitochondrial injury and subsequent energy failure are key factors in the induction of demyelination and neurodegeneration. The brain weighs only a few percent of the body mass but accounts for approximately 20% of the total basal oxygen consumption of mitochondria. Oxidative stress induces mitochondrial injury in patients with multiple sclerosis and energy failure in the central nervous system of susceptible individuals. The interconnected mechanisms responsible for free radical production in patients with multiple sclerosis are as follows: (i inflammation-induced production of free radicals by activated immune cells, (ii liberation of iron from the myelin sheets during demyelination, and (iii mitochondrial injury and thus energy failure-related free radical production. In the present review, the different sources of oxidative stress and their relationships to patients with multiple sclerosis considering tissue injury mechanisms and clinical aspects have been discussed.
Carbon monoxide pollution aggravates ischemic heart failure through oxidative stress pathway.
Reboul, Cyril; Boissière, Julien; André, Lucas; Meyer, Gregory; Bideaux, Patrice; Fouret, Gilles; Feillet-Coudray, Christine; Obert, Philippe; Lacampagne, Alain; Thireau, Jérôme; Cazorla, Olivier; Richard, Sylvain
2017-01-03
Risk of hospital readmission and cardiac mortality increases with atmospheric pollution for patients with heart failure. The underlying mechanisms are unclear. Carbon monoxide (CO) a ubiquitous environmental pollutant could be involved. We explored the effect of daily exposure of CO relevant to urban pollution on post-myocardial infarcted animals. Rats with ischemic heart failure were exposed 4 weeks to daily peaks of CO mimicking urban exposure or to standard filtered air. CO exposure worsened cardiac contractile dysfunction evaluated by echocardiography and at the cardiomyocyte level. In line with clinical reports, the animals exposed to CO also exhibited a severe arrhythmogenic phenotype with numerous sustained ventricular tachycardias as monitored by surface telemetric electrocardiograms. CO did not affect cardiac β-adrenergic responsiveness. Instead, mitochondrial dysfunction was exacerbated leading to additional oxidative stress and Ca(2+) cycling alterations. This was reversed following acute antioxidant treatment of cardiomyocytes with N-acetylcysteine confirming involvement of CO-induced oxidative stress. Exposure to daily peaks of CO pollution aggravated cardiac dysfunction in rats with ischemic heart failure by specifically targeting mitochondria and generating ROS-dependent alterations. This pathway may contribute to the high sensibility and vulnerability of individuals with cardiac disease to environmental outdoor air quality.
Xue-ying Chang
2017-01-01
Full Text Available Background. This study investigated whether quercetin could alleviate vascular calcification in experimental chronic renal failure rats induced by adenine. Methods. 32 adult male Wistar rats were randomly divided into 4 groups fed normal diet, normal diet with quercetin supplementation (25 mg/kg·BW/d, 0.75% adenine diet, or adenine diet with quercetin supplementation. All rats were sacrificed after 6 weeks of intervention. Serum renal functions biomarkers and oxidative stress biomarkers were measured and status of vascular calcification in aorta was assessed. Furthermore, the induced nitric oxide synthase (iNOS/p38 mitogen activated protein kinase (p38MAPK pathway was determined to explore the potential mechanism. Results. Adenine successfully induced renal failure and vascular calcification in rat model. Quercetin supplementation reversed unfavorable changes of phosphorous, uric acid (UA and creatinine levels, malonaldehyde (MDA content, and superoxide dismutase (SOD activity in serum and the increases of calcium and alkaline phosphatase (ALP activity in the aorta (P<0.05 and attenuated calcification and calcium accumulation in the medial layer of vasculature in histopathology. Western blot analysis showed that iNOS/p38MAPK pathway was normalized by the quercetin supplementation. Conclusions. Quercetin exerted a protective effect on vascular calcification in adenine-induced chronic renal failure rats, possibly through the modulation of oxidative stress and iNOs/p38MAPK pathway.
Carbon monoxide pollution aggravates ischemic heart failure through oxidative stress pathway
Reboul, Cyril; Boissière, Julien; André, Lucas; Meyer, Gregory; Bideaux, Patrice; Fouret, Gilles; Feillet-Coudray, Christine; Obert, Philippe; Lacampagne, Alain; Thireau, Jérôme; Cazorla, Olivier; Richard, Sylvain
2017-01-01
Risk of hospital readmission and cardiac mortality increases with atmospheric pollution for patients with heart failure. The underlying mechanisms are unclear. Carbon monoxide (CO) a ubiquitous environmental pollutant could be involved. We explored the effect of daily exposure of CO relevant to urban pollution on post-myocardial infarcted animals. Rats with ischemic heart failure were exposed 4 weeks to daily peaks of CO mimicking urban exposure or to standard filtered air. CO exposure worsened cardiac contractile dysfunction evaluated by echocardiography and at the cardiomyocyte level. In line with clinical reports, the animals exposed to CO also exhibited a severe arrhythmogenic phenotype with numerous sustained ventricular tachycardias as monitored by surface telemetric electrocardiograms. CO did not affect cardiac β–adrenergic responsiveness. Instead, mitochondrial dysfunction was exacerbated leading to additional oxidative stress and Ca2+ cycling alterations. This was reversed following acute antioxidant treatment of cardiomyocytes with N-acetylcysteine confirming involvement of CO-induced oxidative stress. Exposure to daily peaks of CO pollution aggravated cardiac dysfunction in rats with ischemic heart failure by specifically targeting mitochondria and generating ROS-dependent alterations. This pathway may contribute to the high sensibility and vulnerability of individuals with cardiac disease to environmental outdoor air quality. PMID:28045070
Breakfast and Snacks: Associations with Cognitive Failures, Minor Injuries, Accidents and Stress
Katherine Chaplin
2011-05-01
Full Text Available One strategy for examining effects of nutrients on cognitive function is to initially investigate foods that contain many different nutrients. If effects are demonstrated with these foods then further studies can address the role of specific nutrients. Breakfast foods (e.g., cereals, dairy products and fruit provide many important nutrients and consumption of breakfast has been shown to be associated with beneficial effects on cognitive function. Isolating effects of specific constituents of breakfast has proved more difficult and it is still unclear what impact breakfast has on real-life performance. The present study provided initial information on associations between breakfast consumption and cognitive failures and accidents. A second aim was to examine associations between consumption of snacks which are often perceived as being unhealthy (chocolate, crisps and biscuits. A sample of over 800 nurses took part in the study. The results showed that frequency of breakfast consumption (varied breakfasts: 62% cereal was associated with lower stress, fewer cognitive failures, injuries and accidents at work. In contrast, snacking on crisps, chocolate and biscuits was associated with higher stress, more cognitive failures and more injuries outside of work. Further research requires intervention studies to provide a clearer profile of causality and underlying mechanisms.
Selvaraj, Nambiar; Bobby, Zachariah; Sridhar, Magadi Gopalakrishna
2008-04-01
Among the various mechanisms proposed, the process of non-enzymatic glycation of proteins is believed to play an important role in the pathogenesis of chronic complications associated with renal failure. The two traditional factors found to modulate the early glycation of proteins are the prevailing concentration of glucose and half life of the protein. Among the various proteins that are known to undergo nonenzymatic glycation in vivo, hemoglobin has been the most thoroughly investigated. Determination of glycated hemoglobin in diabetic patients is currently acknowledged as the most reliable indicator for assessment of retrospective glycemic control and the planning of clinical management. The clinical utility of glycated hemoglobin measurements, however, in renal failure is controversial, given the numerous earlier studies showing no correlation between glycated hemoglobin and other indicators of blood glucose control in uremic subjects. With few exceptions, previous studies have suggested that the concentration of glycated hemoglobin was increased in uremic patients. There is documented evidence that increased glycated hemoglobin levels are found in certain non-diabetic states. So it stands to reason that hyperglycemia, although clearly being the culprit in diabetes, does not provide the complete answer to the etiology of increased early glycated products in non-diabetic conditions including chronic renal failure. This article reviews available evidence supporting increased glycation of hemoglobin in patients with chronic renal failure. Potential mechanisms for this increase are examined with special emphasis on the potential role of oxidative stress.
Oxidative stress and neutrophil function in cats with chronic renal failure.
Keegan, R F; Webb, C B
2010-01-01
Oxidative stress is an important component in the progression of chronic renal failure (CRF) and neutrophil function may be impaired by oxidative stress. Cats with CRF have increased oxidative stress and decreased neutrophil function compared with control cats. Twenty cats with previously diagnosed renal failure were compared with 10 age-matched control cats. A biochemical profile, CBC, urinalysis, antioxidant capacity, superoxide dismutase (SOD) enzyme activity, reduced to oxidized glutathione ratio (GSH : GSSG), and neutrophil phagocytosis and oxidative burst were measured. Statistical comparisons (2-tailed t-test) were reported as mean +/- standard deviation. The CRF cats had significantly higher serum blood urea nitrogen, creatinine, and phosphorus concentrations than control cats, and significantly lower PCV and urine specific gravity than control cats. The GSH : GSSG ratio was significantly higher in the CRF group (177.6 +/- 197, 61.7 +/- 33; P cats. Neutrophil oxidative burst after Escherichia coli phagocytosis, measured as an increase in mean fluorescence intensity, was significantly higher in CRF cats than controls (732 +/- 253, 524 +/- 54; P cats is consistent with activation of antioxidant defense mechanisms. It remains to be determined if supplementation with antioxidants such as SOD beyond the level of control cats would be of benefit in cats with CRF.
Fatigue Failure Results for Multi-Axial versus Uniaxial Stress Screen Vibration Testing
Wayne E. Whiteman
2002-01-01
Full Text Available To date, the failure potential and prediction between simultaneous multi-axial versus sequentially applied uniaxial vibration stress screen testing has been the subject of great debate. In most applications, current vibration tests are done by sequentially applying uniaxial excitation to the test specimen along three orthogonal axes. The most common standards for testing military equipment are published in MIL-STD-810F and NAVMAT P-9492. Previous research had shown that uniaxial testing may be unrealistic and inadequate. This current research effort is a continuing effort to systematically investigate the differences between fatigue damage mechanisms and the effects of uniaxial versus tri-axial testing. This includes assessing the ability of the tri-axial method in predicting the formation of damage mechanisms, specifically looking at the effects of stress or fatigue failure. Multi-axial testing achieves the synergistic effect of exciting all modes simultaneously and induces a more realistic vibration stress loading condition. As such, it better approximates real-world operating conditions. This paper provides the latest results on the differences between multi-axial and uniaxial testing of a simple notched cantilever beam.
Stress corrosion failure of large diameter pressure pipelines of prestressed concrete
Valiente, A. [Universidad Politecnico de Madrid (Spain). Dpto. de Ciencia de Materiales
2001-07-01
The failure of a 1.5 m diameter prestressed concrete line for water supply was examined. The water pressure opened a hole of 0.5 m{sup 2} in the pipe wall by breaking the concrete into fragments and by tensile severing of a number of coils of the wire winding. Flexural and tensile testing of samples of the broken materials showed no damage to the concrete, but showed significant losses of strength and ductility in the prestressing steel wire. The SEM analysis of the external and fracture surfaces of the circumferential wires revealed shallow cracking and corroded areas as expected from a stress corrosion cracking process. The failure analysis presented in this paper shows that such a process was able to exhaust the damage tolerance of the affected tube until the pipeline burst under the work pressures. (author)
On the failure analysis of bondlines: Stress or energy based fracture criteria?
Anyfantis, Konstantinos
2014-01-01
that characterizes a given bondline, both its cohesive strength and fracture toughness material parameters must be experimentally defined. Based on these properties, failure analysis of the bondline can be done either through stress- or energy-based criteria. The aim of this work is to investigate the effectiveness...... of each criteria type to effectively predict debonding initiation/propagation of different bondlines (brittle, quasi-brittle, ductile), which are eventually utilized for the evaluation of the joint's failure load. By representing a bondline according to its cohesive length scale, an effort is made...... experimentation programme. Fracture initiation and propagation of the bondlines was numerically simulated by cohesive zone models. (C) 2014 Elsevier Ltd. All rights reserved....
Noninvasive assessment of left ventricular wall stress in chronic congestive heart failure patients.
Gould, L; Gopalaswamy, C; Chandy, F; Abdou, O
1983-02-01
Therapy with prazosin can improve the condition of patients with congestive heart failure due to its vasodilating action. Therefore nine patients with volume overloaded left ventricles due to aortic insufficiency and mitral insufficiency received 1 mg. of prazosin four times a day for two weeks. Peak and end-systolic wall stress were estimated using a noninvasive echocardiographic technique. The peak systolic wall stress in this group was 155 x 10(3) dynes/cm2 which is similar to the reported normal value. However, the end systolic wall stress was 101 x 10(3) dynes/cm2 which is much higher than the reported normal values. Following the administration of oral prazosin, the end systolic stress was normalized while the peak systolic stress was reduced below normal. As a result of therapy with prazosin, the ejection fraction, the percentage of change in the minor axis, and the velocity of circumferential fiber shortening significantly increased. Thus, the oral administration of prazosin can improve left ventricular function in patients with mitral insufficiency and aortic insufficiency.
Faith C H Li
Full Text Available BACKGROUND: Whereas sudden death, most often associated with cardiovascular collapse, occurs in abusers of the psychostimulant methamphetamine (METH, the underlying mechanism is much less understood. The demonstration that successful resuscitation of an arrested heart depends on maintained functionality of the rostral ventrolateral medulla (RVLM, which is responsible for the maintenance of stable blood pressure, suggests that failure of brain stem cardiovascular regulation, rather than the heart, holds the key to cardiovascular collapse. We tested the hypothesis that cessation of brain stem cardiovascular regulation because of a loss of functionality in RVLM mediated by bioenergetics failure and oxidative stress underlies the cardiovascular collapse elicited by lethal doses of METH. METHODOLOGY/PRINCIPAL FINDINGS: Survival rate, cardiovascular responses and biochemical or morphological changes in RVLM induced by intravenous administration of METH in Sprague-Dawley rats were investigated. High doses of METH induced significant mortality within 20 min that paralleled concomitant the collapse of arterial pressure or heart rate and loss of functionality in RVLM. There were concurrent increases in the concentration of METH in serum and ventrolateral medulla, along with tissue anoxia, cessation of microvascular perfusion and necrotic cell death in RVLM. Furthermore, mitochondrial respiratory chain enzyme activity or electron transport capacity and ATP production in RVLM were reduced, and mitochondria-derived superoxide anion level was augmented. All those detrimental physiological and biochemical events were reversed on microinjection into RVLM of a mobile electron carrier in the mitochondrial respiratory chain, coenzyme Q10; a mitochondria-targeted antioxidant and superoxide anion scavenger, Mito-TEMPO; or an oxidative stress-induced necrotic cell death inhibitor, IM-54. CONCLUSION: We conclude that sustained anoxia and cessation of local blood flow
Evgeny Belyavskiy
2015-12-01
Full Text Available The diagnosis of heart failure with preserved ejection fraction (HFPEF remains on the basis of echocardiographic analyses at rest. However, some patients with HFPEF have symptoms such as dyspnea only during exercise. Accordingly, echocardiographic analyses at rest could be insufficiently sensitive to identify these patients. In line, recent studies demonstrated that in some patients with HFPEF left ventricular diastolic abnormalities occur only during exercise. This review discusses and analyzes the clinical relevance and evidence of using diastolic stress test echocardiography in patients with HFPEF.
Planning failure-censored constant-stress par tially accelerated life test
Ali A Ismail; Abdulhakim A Al-Babtain
2015-01-01
This article deals with the case of the failure-censored constant-stress partial y accelerated life test (CSPALT) for highly reliable materials or products assuming the Pareto distribution of the second kind. The maximum likelihood (ML) method is used to estimate the parameters of the CSPALT model. The performance of ML estimators is investigated via their mean square error. Also, the average confidence interval length (IL) and the associated co-verage probability (CP) are obtained. Moreover, optimum CSPALT plans that determine the optimal proportion of the test units al-located to each stress are developed. Such optimum test plans minimize the generalized asymptotic variance (GAV) of the ML estimators of the model parameters. For il ustration, Monte Carlo simulation studies are given and a real life example is provided.
An Empirical Kaiser Criterion.
Braeken, Johan; van Assen, Marcel A L M
2016-03-31
In exploratory factor analysis (EFA), most popular methods for dimensionality assessment such as the screeplot, the Kaiser criterion, or-the current gold standard-parallel analysis, are based on eigenvalues of the correlation matrix. To further understanding and development of factor retention methods, results on population and sample eigenvalue distributions are introduced based on random matrix theory and Monte Carlo simulations. These results are used to develop a new factor retention method, the Empirical Kaiser Criterion. The performance of the Empirical Kaiser Criterion and parallel analysis is examined in typical research settings, with multiple scales that are desired to be relatively short, but still reliable. Theoretical and simulation results illustrate that the new Empirical Kaiser Criterion performs as well as parallel analysis in typical research settings with uncorrelated scales, but much better when scales are both correlated and short. We conclude that the Empirical Kaiser Criterion is a powerful and promising factor retention method, because it is based on distribution theory of eigenvalues, shows good performance, is easily visualized and computed, and is useful for power analysis and sample size planning for EFA. (PsycINFO Database Record
EVALUATION OF OXIDATIVE STRESS MARKERS IN CHRONIC KIDNEY FAILURES OF SOUTH INDIAN POPULATION
Kemidi Ilaiah
2013-01-01
Full Text Available Oxidative stress defines an imbalance between the formation of reactive oxygen species and antioxidants. The existence of oxidative stress and higher incidence of cardiovascular diseases (CVD in association with uraemia is proven from studies on Chronic Kidney Disease (CKD patients. Non traditional risk factors like oxidative stress are being given special emphasis to explain high incidence and identification of new therapeutic interventions. Excess Reactive oxygen Species levels have been implicated to damage DNA, lipids, proteins etc., It may also affect the cells of host, particularly at the inflammation site contributing to proteinuria observed in Chronic Kidney Disease patients. The uremic status, oxidant and antioxidant levels were assessed in the present study. This prospective observational study was conducted for nine months. Patients meeting the study criteria were included. Malonyldialdehyde (MDA, glutathione-S-transferase (GST, Protein thiols, Total proteins, Serum urea, creatinine, albumin and Haemoglobin levels were estimated using suitable methods. Study recruited 108 Chronic Kidney Disease patients, divided into three groups namely, patients without haemodialysis (54, patients with haemodialysis (54 and control population (50. Serum urea, creatinine, MDA and GST levels were found to be significantly increased (P<0.0001, and total proteins, albumin, proteinthiols, and Haemoglobin levels were found to be significantly decreased in Chronic Renal Failure patients compared to normal controls (P<0.0001. Our study confirms the presence of oxidative stress in Chronic Kidney Disease patient population. Our study also emphasises the need for anti-oxidant therapy in CKD patients.
无
2010-01-01
The pore characteristics,mineral compositions,physical and mechanical properties of the subarkose sandstones were acquired by means of CT scan,X-ray diffraction and physical tests.A few physical models possessing the same pore characteristics and matrix properties but different porosities compared to the natural sandstones were developed.The 3D finite element models of the rock media with varied porosities were established based on the CT image processing of the physical models and the MIMICS software platform.The failure processes of the porous rock media loaded by the split Hopkinson pressure bar(SHPB) were simulated by satisfying the elastic wave propagation theory.The dynamic responses,stress transition,deformation and failure mechanisms of the porous rock media subjected to the wave stresses were analyzed.It is shown that an explicit and quantitative analysis of the stress,strain and deformation and failure mechanisms of porous rocks under the wave stresses can be achieved by using the developed 3D finite element models.With applied wave stresses of certain amplitude and velocity,no evident pore deformation was observed for the rock media with a porosity less than 15%.The deformation is dominantly the combination of microplasticity(shear strain),cracking(tensile strain) of matrix and coalescence of the cracked regions around pores.Shear stresses lead to microplasticity,while tensile stresses result in cracking of the matrix.Cracking and coalescence of the matrix elements in the neighborhood of pores resulted from the high transverse tensile stress or tensile strain which exceeded the threshold values.The simulation results of stress wave propagation,deformation and failure mechanisms and energy dissipation in porous rock media were in good agreement with the physical tests.The present study provides a reference for analyzing the intrinsic mechanisms of the complex dynamic response,stress transit mode,deformation and failure mechanisms and the disaster
Anssari-Benam, Afshin; Barber, Asa H; Bucchi, Andrea
2016-02-01
A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c = 25.36 µm and l c = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo.
Acute renal failure potentiates methylmalonate-induced oxidative stress in brain and kidney of rats.
Schuck, P F; Alves, L; Pettenuzzo, L F; Felisberto, F; Rodrigues, L B; Freitas, B W; Petronilho, F; Dal-Pizzol, F; Streck, E L; Ferreira, G C
2013-03-01
Tissue methylmalonic acid (MMA) accumulation is the biochemical hallmark of methylmalonic acidemia. The disease is clinically characterized by progressive neurological deterioration and kidney failure, whose pathophysiology is still unclear. In the present work we investigated the effects of acute MMA administration on various parameters of oxidative stress in cerebral cortex and kidney of young rats, as well as the influence of acute renal failure on MMA-elicited effects on these parameters. Acute renal failure was induced by gentamicin, an aminoglycoside antibiotic whose utilization over prolonged periods causes nephrotoxicity. The administration of gentamicin alone increased carbonyl content and inhibited superoxide dismutase (SOD) activity in cerebral cortex, as well as increased thiobarbituric acid-reactive substances (TBA-RS) and sulfhydryl levels and diminished glutathione peroxidase activity in kidney. On the other hand, MMA administration increased TBA-RS levels in cerebral cortex and decreased SOD activity in kidney. Furthermore, the simultaneous administration of MMA and gentamicin to the rats provoked an augment in TBA-RS levels and superoxide generation in cerebral cortex and in TBA-RS, carbonyl and sulfhydryl levels in kidney, while diminished SOD activity in both studied tissues. Finally, nitrate/nitrite content, reduced glutathione levels, 2',7'-dihydrodichlorofluorescein oxidation and catalase activity were not affected by this animal treatment in either tissue. In conclusion, our present data are in line with the hypothesis that MMA acts as a toxin in brain and kidney of rats and suggest that renal injury potentiates the toxicity of MMA on oxidative stress parameters in brain and peripheral tissues.
A General Criterion for Liquefaction in Granular Layers with Heterogeneous Pore Pressure
Goren, Liran; Aharonov, Einat; Sparks, David; Flekkøy, Eirik Grude
2013-01-01
Fluid-saturated granular and porous layers can undergo liquefaction and lose their shear resistance when subjected to shear forcing. In geosystems, such a process can lead to severe natural hazards of soil liquefaction, accelerating slope failure, and large earthquakes. Terzaghi's principle of effective stress predicts that liquefaction occurs when the pore pressure within the layer becomes equal to the applied normal stress on the layer. However, under dynamic loading and when the internal permeability is relatively small the pore pressure is spatially heterogeneous and it is not clear what measurement of pore pressure should be used in Terzaghi's principle. Here, we show theoretically and demonstrate using numerical simulations a general criterion for liquefaction that applies also for the cases in which the pore pressure is spatially heterogeneous. The general criterion demands that the average pore pressure along a continuous surface within the fluid-saturated granular or porous layer is equal to the appl...
Ch. Venkata Rama Krishna
2012-01-01
Full Text Available In this prospective study, we aimed to assess the clinical characteristics of acute renal failure (ARF, determine oxidative stress, as well as to predict the outcome in patients with severe falciparum malaria (FM. The study included a total of 75 subjects; there were 25 adult patients with acute severe FM and ARF, 25 adult patients with uncomplicated FM without ARF, and 25 age- and sex-matched healthy subjects who served as controls. In patients with severe FM and ARF (n = 25, renal failure was non-oliguric in 28% and oliguric in 72%. The average duration of renal failure was 10.53 ± 4.0 days. Sixty percent recovered and 40% died. All patients with non-oliguric presentation recovered. The mean serum malondialdehyde (MDA levels were 0.82 ± 0.43 μmol/L, 2.97 ± 1.11 μmol/L, and 6.86 ± 2.62 μmol/L, respectively, in healthy con-trols, in patients with uncomplicated FM, and in those with severe FM with ARF. The Acute Physiology Age and Chronic Health Evaluation II (APACHE II score, Sequential Organ Failure Assessment (SOFA score, and the Acute Tubular Necrosis-Individual Severity Index (ATN-ISI score were all significantly higher in the expired group (19 ± 5.49 when compared to the survivor group (14.4 ± 3.15 (P = 0.014. Kaplan-Meier survival analysis showed that survival was low in patients with delayed hospitalization and longer duration of symptoms. Also, we observed a high occurrence of acute respiratory distress syndrome and central nervous system involvement among the patients who expired.
Failure Assessment Diagram for Titanium Brazed Joints
Flom, Yury; Jones, Justin S.; Powell, Mollie M.; Puckett, David F.
2011-01-01
The interaction equation was used to predict failure in Ti-4V-6Al joints brazed with Al 1100 filler metal. The joints used in this study were geometrically similar to the joints in the brazed beryllium metering structure considered for the ATLAS telescope. This study confirmed that the interaction equation R(sub sigma) + R(sub Tau) = 1, where R(sub sigma) and R(sub Tau)are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in ATLAS brazed joints as well as for construction of the Failure Assessment Diagram (FAD).
Abdullah S Alhurani
2014-09-01
Full Text Available Objectives: The high mortality and morbidity rates associated with heart failure are still not well explained. A few psychosocial factors have been studied and explain some of this risk, but other factors, like stress, remain largely unexplored in heart failure. This study aimed to (1 examine the association of stress with 6-month cardiac event-free survival, (2 examine the relationship of stress with salivary cortisol, and (3 examine the association of salivary cortisol level with 6-month cardiac event-free survival. Method: A total of 81 heart failure patients participated. Stress was measured using the brief Perceived Stress Scale. Cortisol was measured from unstimulated whole expectorated saliva. Cox regression analyses were used to determine whether stress predicted event-free survival, and if salivary cortisol predicted event-free survival. Linear and multiple regressions were used to determine the association of stress with salivary cortisol. Results: Stress was not a significant predictor of event-free survival in heart failure (heart rate = 1.06; 95% confidence interval = 0.95–1.81; p = 0.32. Salivary cortisol was a significant predictor of event-free survival in the unadjusted model (heart rate = 2.30; 95% confidence interval = 0.99–5.927; p = 0.05, but not in the adjusted model. Stress (β 1.06; 95% confidence interval = 0.95–1.18; p = 0.32 was not a significant predictor of salivary cortisol level. Conclusion: Stress is a complex phenomenon, and our measure of stress may not have captured it well. Alternatively, the physical stressors acting in heart failure produce levels of neurohormonal activation that mask the effects of psychosocial stressors or an indirect association of stress with outcomes that is mediated through another construct. Future studies are needed to investigate stress in patients with heart failure to provide definitive answers.
Allan, Julia L; Farquharson, Barbara; Johnston, Derek W; Jones, Martyn C; Choudhary, Carolyn J; Johnston, Marie
2014-05-01
Nurses working for telephone-based medical helplines must maintain attentional focus while quickly and accurately processing information given by callers to make safe and appropriate treatment decisions. In this study, both higher levels of general occupational stress and elevated stress levels on particular shifts were associated with more frequent failures of attention, memory, and concentration in telephone nurses. Exposure to a stressful shift was also associated with a measurable increase in objectively assessed information-processing errors. Nurses who experienced more frequent cognitive failures at work made more conservative decisions, tending to refer patients on to other health professionals more often than other nurses. As stress is associated with cognitive performance decrements in telephone nursing, stress-reduction interventions could improve the quality and safety of care that callers to medical helplines receive. © 2013 The British Psychological Society.
Derivation of Plastic Work Rate Done per Unit Volume for Mean Yield Criterion and Its Application
Dewen ZHAO; Yingjie XIE; Xiaowen WANG; Xianghua LIU
2005-01-01
In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield (MY) criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.
Oxidative Stress, Bone Marrow Failure, and Genome Instability in Hematopoietic Stem Cells
Christine Richardson
2015-01-01
Full Text Available Reactive oxygen species (ROS can be generated by defective endogenous reduction of oxygen by cellular enzymes or in the mitochondrial respiratory pathway, as well as by exogenous exposure to UV or environmental damaging agents. Regulation of intracellular ROS levels is critical since increases above normal concentrations lead to oxidative stress and DNA damage. A growing body of evidence indicates that the inability to regulate high levels of ROS leading to alteration of cellular homeostasis or defective repair of ROS-induced damage lies at the root of diseases characterized by both neurodegeneration and bone marrow failure as well as cancer. That these diseases may be reflective of the dynamic ability of cells to respond to ROS through developmental stages and aging lies in the similarities between phenotypes at the cellular level. This review summarizes work linking the ability to regulate intracellular ROS to the hematopoietic stem cell phenotype, aging, and disease.
Smita I. Negi
2015-01-01
Full Text Available Animal models have suggested a role of renin-angiotensin system (RAS activation and subsequent cardiac oxidation in heart failure with preserved ejection fraction (HFpEF. Nevertheless, RAS blockade has failed to show efficacy in treatment of HFpEF. We evaluated the role of RAS activation and subsequent systemic oxidation in HFpEF. Oxidative stress markers were compared in 50 subjects with and without early HFpEF. Derivatives of reactive oxidative metabolites (DROMs, F2-isoprostanes (IsoPs, and ratios of oxidized to reduced glutathione (Eh GSH and cysteine (Eh CyS were measured. Angiotensin converting enzyme (ACE levels and activity were measured. On univariate analysis, HFpEF was associated with male sex (p=0.04, higher body mass index (BMI (p=0.003, less oxidized Eh CyS (p=0.001, lower DROMs (p=0.02, and lower IsoP (p=0.03. Higher BMI (OR: 1.3; 95% CI: 1.1–1.6 and less oxidized Eh CyS (OR: 1.2; 95% CI: 1.1–1.4 maintained associations with HFpEF on multivariate analysis. Though ACE levels were higher in early HFpEF (OR: 1.09; 95% CI: 1.01–1.05, ACE activity was similar to that in controls. HFpEF is not associated with significant systemic RAS activation or oxidative stress. This may explain the failure of RAS inhibitors to alter outcomes in HFpEF.
Failure mechanism of coated biomaterials under high impact-sliding contact stresses
Chen, Ying
This study uses a newly developed testing method--- inclined cyclic impact-sliding test to investigate the failure behaviors of different types of biomaterials, (SS316L, Ti6Al4V and CoCr) coated by different coatings (TiN, DLC and PEO), under extremely high dynamic contact stress conditions. This test method can simulate the combined impact and sliding/rolling loading conditions, which is very practical in many aspects of commercial usages. During the tests, fatigue cracking, chipping, peeling and material transferring were observed in damaged area. This research is mainly focused on the failure behaviors of load-bearing materials which cyclic impacting and sliding are always involved. This purpose was accomplished in the three stages: First, impact-sliding test was carried out on TiN coated unhardened M2. It was found that soft substrate can cause early failure of coating due to the considerable plastic deformation in the substrate. In this case, stronger substrate is required to support coating better when tested under high contact stresses. Second, PEO coated Ti-6Al-4V was tested under pure sliding and impact-sliding wear conditions. PEO coating was found not strong enough to afford the high contact pressure under cyclic impact-sliding wear test due to its porous surface structure. However, the wear performance of PEO coating was enhanced due to the sub-stoichiometric oxide. To sum up, for load-bearing biomedical implants involved in high impacting movement, PEO coating may not be a promising surface protection. Third, the dense, smooth PVD/CVD bio-inert coatings were reconsidered. DLC and TiN coatings, combined by different substrates together with different interface materials were tested under the cyclic impact-sliding test using a set of proper loading. The results show that to choose a proper combination of coating, interface and substrate based on their mechanical properties is of great importance under the test condition. Hard substrates provide support
Fracture Criterion for Fracture Mechanics of Magnets
潘灏; 杨文涛
2003-01-01
The applicability and limitation of some fracture criteria in the fracture mechanics of magnets are studied.It is shown that the magnetic field intensity factor can be used as a fracture criterion when the crack in a magnet is only affected by a magnetic field. For some magnetostrictive materials in which the components of magnetostriction strain do not satisfy the compatibility equation of deformation, the stress intensity factor can no longer be effectively applicable as a fracture criterion when the crack in a magnet is affected by a magnetic field and mechanical loads simultaneously.
C.T.J. Holweg (Cécile)
2003-01-01
textabstractInflammation is a characteristic feature of heart failure and of complications after heart transplantation. These inflammatory responses are regulated by cytokines and stress proteins. The production and function of cytokines and stress proteins can be controlled by genetic
The Assessing of the Failure Behavior of Glass/Polyester Composites Subject to Quasi Static Stresses
Stanciu, M. D.; Savin, A.; Teodorescu-Drăghicescu, H.
2017-06-01
Using glass fabric reinforced composites for structure of wind turbine blades requires high mechanical strengths especially to cyclic stresses. Studies have shown that approximately 50% of composite material failure occurs because of fatigue. Composites behavior to cyclic stresses involves three stages regarding to stiffness variation: the first stage is characterized by the accelerated decline of stiffness with micro-cracks, the second stage - a slight decrease of stiffness characterized by the occurrence of delamination and third stage characterized by higher decreases of resistance and occurrence of fracture thereof. The aim of the paper is to analyzed the behavior of composites reinforced with glass fibers fabric type RT500 and polyester resin subjected to tensile cyclic loading with pulsating quasi-static regime with asymmetry coefficient R = 0. The samples were tested with the universal tensile machine LS100 Lloyd Instruments Plus, with a load capacity of 100 kN. The load was applied with different speeds of 1 mm/min, 10 mm/min and 20 mm/min. After tests, it was observed that the greatest permanent strains were recorded in the first load cycles when the total energy storage by material was lost due to internal friction. With increasing number of cycles, the glass/polyester composites ability to store energy of deformation decreases, the flow phenomenon characterized by large displacements to smaller loading forces appearing.
朱建明; 程海峰; 姚仰平
2013-01-01
岩石材料是一种非均质材料，而破裂岩是指岩体内部含有大量的裂隙、空洞、界面等缺陷，在荷载作用下其微元体破坏更具有随机性。在损伤理论的基础上，从微元体的强度随机分布的角度出发，在微元体强度度量方法上考虑损伤阈值的影响，假设破裂岩的微元体强度服从Weibull分布，结合考虑中主应力的SMP准则，建立破裂岩统计损伤软化本构模型，运用多种计算方法对模型参数m和F0进行确定。通过对小官庄铁矿2种破裂岩闪长玢岩以及矽卡岩的验证表明：在不同围压下，全应力-应变试验曲线与预测曲线吻合良好，能够反映损伤阈值的影响，且在较低围压下更为理想。同时，此模型能够反映随着围压的增加岩石的峰值强度增加而延性增大的性质，进一步验证模型的适用性及较强的应用价值。%The rock material is a kind of non-homogeneous material and there are a large number of defects such as fissures,voids,interfaces in the broken rock. Its micro units damage more randomness under the loads. Starting from micro units strength are random distribution on the basis of damage theory,a method for measuring microcosmic element strength of rock is presented with consideration of damage threshold. Assuming the micro units strength of broken rock obey Weibull distribution,combined with the SMP criterion,which considers the intermediate principal stress,the statistical damage softening constitutive model is built. And the model parameters m and F0 are computed using some methods. Through the calculation results of two kinds of broken rock in Xiaoguanzhuang indicate that:the predicted stress-strain curves under different confining pressures agree well with the test data,and it can reflect not only the influence of damage threshold but also more desirable in the lower confining pressures. At the same time,this model can reflect the characteristic that the
Krystek J.
2010-12-01
Full Text Available Strength of unidirectional composite materials for some combinations of state of stress cannot be successsfully predicted even with modern failure criteria. In case of the combination of compression in the transverse direction and tension in the fiber direction, the criterion LaRC04 was adjusted in previous work. The predicted strengths in this case reach significantly larger values compared to the ultimate strengths of the material in the respective directions. The adjusted criterion is able to predict the failure of unidirectional composite in case of the mentioned combination of loading. The validation of the adjusted criterion is carried out by means of the comparison of experimental results and numerical analysis performed in finite element system MSC.Marc.
无
2010-01-01
In this paper,algebraic criteria are established to determine whether or not a real coefficient polynomial has one or two pairs of conjugate complex roots whose moduli are equal to 1 and the other roots have moduli less than 1 directly from its coefficients.The form and the function of the criteria are similar to those of the Jury criterion which can be used to determine whether or not all the moduli of the roots of a real coefficient polynomial are less than 1.
Karst Collapse Mechanism and Criterion for Its Stability
贺可强; 刘长礼; 王思敬
2001-01-01
Karst collapse, caused by natural or artificial abstraction of groundwater, has been a focus of environmental geological problems for its ever-increasing hazardousness. The potential erosion theory and vacuum suction erosion theory,which reveal the origin of karst collapse macroscopically, are popularly accepted. However, a mathematic prediction criterion for karst collapse cannot be established only by these two theories. From a new perspective, this paper attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. When the shear stress surpasses the shear strength of soil, a certain point or a certain plane in the unconsolidated soil covering karst caves will fail under the mechanical effects of water and air as well as its load-pressure, and with the increase of damaged points, a breaking plane appears and the soil on karst caves is completely damaged; as a result, the karst ground collapses. On the basis of the MohrCoulomb failure theory and previous studies, the paper presents a prediction criterion of karst collapse. Finally, by taking,for example, nine typical cases of collapse caused by pumping tests in Guizhou, the paper gives the calculation process of the model and proves its reliability.``
A Comprehensive Theory of Yielding and Failure for Isotropic Materials
Christensen, R M
2006-08-10
A theory of yielding and failure for homogeneous and isotropic materials is given. The theory is calibrated by two independent, measurable properties and from those it predicts possible failure for any given state of stress. It also differentiates between ductile yielding and brittle failure. The explicit ductile-brittle criterion depends not only upon the material specification through the two properties, but also and equally importantly depends upon the type of imposed stress state. The Mises criterion is a special (limiting) case of the present theory. A close examination of this case shows that the Mises material idealization does not necessarily imply ductile behavior under all conditions, only under most conditions. When the first invariant of the yield/failure stress state is sufficiently large relative to the distortional part, brittle failure will be expected to occur. For general material types, it is shown that it is possible to have a state of spreading plastic flow, but as the elastic-plastic boundary advances, the conditions for yielding on it can change over to conditions for brittle failure because of the evolving stress state. The general theory is of a three dimensional form and it applies to full density materials for which the yield/failure strength in uniaxial tension is less than or at most equal to the magnitude of that in uniaxial compression.
Sophal Pou, Laurent; Garcia, Raphael F.; Mimoun, David; Murdoch, Naomi; Karatekin, Ozgur
2017-04-01
Rocky remnants left over from the early formation of the Solar System, asteroids are a target of choice for planetary science since much about the history of planetary formation and small body evolution processes can be learnt by studying them. Here we consider the case of the binary asteroid (65803) Didymos, the target of several mission proposals e.g., AIM [1] and DART [2]. A mission to Didymos would be a great opportunity for in-situ geophysical investigation, providing information on the surface and interior of asteroids. Such studies would improve our knowledge of binary asteroid formation and subsequent evolution of asteroids, thus of the history of the Solar System. As Didymos is a binary asteroid [3] with the main 800-meter diameter asteroid named Didymain and a 150-meter sized moon named Didymoon, both are subject to tidal stress. Recent investigations suggest that Didymoon is tidally locked and moves in a retrograde motion around Didymain along an elliptic orbit with a 0.03 eccentricity at most. In the case of an eccentric orbit, the tidal stress varies periodically and may be strong enough to cause tidal quakes on Didymoon at some points of the orbit. For this study, we modelled Didymoon as a spherical, layered body with different internal structures: a homogeneous model, and two models with a 1-meter and 10-meter regolith layer on top of a stronger internal core. Simulations show that, for a cohesionless body with an internal friction angle of 30°, tidal stress is strong enough to cause failure at the surface of Didymoon. A maximal stress is reached around the poles and for a mean anomaly of 90°. These results would mean that if tidal quakes occur on Didymoon, then they are likely to happen at these locations. An extension of these results to an ellipsoidal model of Didymoon is also presented for comparison with the spherical case and for application to other bodies. [1]: P. Michel et al., Science case for the asteroid impact mission (aim): A
Ranjbar-Far, M.; Absi, J.; Mariaux, G.; Shahidi, S.
2010-09-01
This work is focused on the effect of the residual stresses resulting from the coating process and thermal cycling on the failure mechanisms within the thermal barrier coating (TBC) system. To reach this objective, we studied the effect of the substrate preheating and cooling rate on the coating process conditions. A new thermomechanical finite element model (FEM) considering a nonhomogeneous temperature distribution has been developed. In the results, we observed a critical stress corresponding to a low substrate temperature and high cooling rate during spraying of the top-coat material. Moreover, the analysis of the stress distribution after service shows that more critical stresses are obtained in the case where residual stresses are taken into account.
刘晶磊; 王建华
2013-01-01
In order to determine the failure criterion of suction anchors with taut mooring systems in soft clay, load-controlled and displacement-controlled model tests are conducted to study the bearing capacities of suction anchors with taut mooring systems under static load at the optimal loading point using an electric servo loading apparatus developed by the authors. The results show that the displacement along the mooring direction is about 0.6 times the diameter of anchor when the failure mode of anchor is vertical pullout;and the displacement along the mooring direction is about 0.3 times the diameter of anchor when the failure mode of anchor is lateral failure. At the same time, the bearing capacities of suction anchors are determined in terms of the failure criterion by model tests. The predicting results of limit analysis are basically in agreement with the results of model tests. Furthermore, it verifies the rationality of displacement failure criterion by the comparison of calculated results between finite element analysis and limit analysis on the full-scale anchors.%为了确定软土中张紧式吸力锚的破坏标准，采用自主研发的电动伺服加载装置，在荷载和位移控制方式下进行了张紧式吸力锚在最佳系泊点受静荷载作用的承载力模型试验。结果表明：不同的破坏模式，锚破坏时对应的位移也不同。当锚为竖向破坏时，对应锚沿系泊方向的位移约为0.6倍的锚径；当锚为水平破坏时，对应锚沿系泊方向的位移约为0.3倍的锚径。同时，按照模型试验所得的破坏标准确定的吸力锚的极限承载力与极限分析法的预测结果吻合较好。对足尺锚进行了有限元分析，将分析结果与极限分析法的预测结果进行比较，验证了模型试验所得位移破坏标准的合理性。
The quartic piecewise-linear criterion for the multiaxial yield behavior of human trabecular bone.
Sanyal, Arnav; Scheffelin, Joanna; Keaveny, Tony M
2015-01-01
Prior multiaxial strength studies on trabecular bone have either not addressed large variations in bone volume fraction and microarchitecture, or have not addressed the full range of multiaxial stress states. Addressing these limitations, we utilized micro-computed tomography (lCT) based nonlinear finite element analysis to investigate the complete 3D multiaxial failure behavior of ten specimens (5mm cube) of human trabecular bone, taken from three anatomic sites and spanning a wide range of bone volume fraction (0.09–0.36),mechanical anisotropy (range of E3/E1¼3.0–12.0), and microarchitecture. We found that most of the observed variation in multiaxial strength behavior could be accounted for by normalizing the multiaxial strength by specimen-specific values of uniaxial strength (tension,compression in the longitudinal and transverse directions). Scatter between specimens was reduced further when the normalized multiaxial strength was described in strain space.The resulting multiaxial failure envelope in this normalized-strain space had a rectangular boxlike shape for normal–normal loading and either a rhomboidal box like shape or a triangular shape for normal-shear loading, depending on the loading direction. The finite element data were well described by a single quartic yield criterion in the 6D normalized strain space combined with a piecewise linear yield criterion in two planes for normalshear loading (mean error SD: 4.660.8% for the finite element data versus the criterion).This multiaxial yield criterion in normalized-strain space can be used to describe the complete 3D multiaxial failure behavior of human trabecular bone across a wide range of bone volume fraction, mechanical anisotropy, and microarchitecture.
Jiří Witzany
2016-04-01
Full Text Available The strengthening and stabilization of damaged compressed masonry columns with composites based on fabrics of high-strength fibers and epoxy resin, or polymer-modified cement mixtures, belongs to novel, partially non-invasive and reversible progressive methods. The stabilizing and reinforcing effect of these fabrics significantly applies to masonry structures under concentric compressive loading whose failure mechanism is characterized by the appearance and development of vertical tensile cracks accompanied by an increase in horizontal masonry strain. During the appearance of micro and hairline cracks (10−3 to 10−1 mm, the effect of non-pre-stressed wrapping composite is very small. The favorable effect of passive wrapping is only intensively manifested after the appearance of cracks (10−1 mm and bigger at higher loading levels. In the case of “optimum” reinforcement of a masonry column, the experimental research showed an increase in vertical displacements δy (up to 247%, horizontal displacements δx (up to 742% and ultimate load-bearing capacity (up to 136% compared to the values reached in unreinforced masonry columns. In the case of masonry structures in which no intensive “bed joint filler–masonry unit” interaction occurs, e.g., in regular coursed masonry with little differences in the mechanical characteristics of masonry units and the binder, the reinforcing effect of the fabric applies only partially.
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.
Influence of Loading System Stiffness on Post-peak Stress-Strain Curve of Stable Rock Failures
Xu, Y. H.; Cai, M.
2017-09-01
It is well known from laboratory testing that the rock failure process becomes unstable in a soft test machine due to excessive energy released from the machine. Great efforts had been devoted to increasing the loading system stiffness (LSS) of laboratory test machines to ensure that the post-peak stress-strain curve of rock can be obtained for underground rock engineering design. A comprehensive literature review on the development of stiff test machines reveals that because of the differences in the manufacturing arrangement of the test machines, LSS values of the test machines used for rock property testing are always finite and vary in a large range, and the influence of LSS on stable rock failure is less understood. A FEM-based numerical experiment is carried out to study the influence of LSS on the stress-strain curves of stable rock failure in uniaxial compression, with a focus on the post-peak deformation stage. Three test machine loadings including idealized rigid loading, platen loading, and frame-platen loading with finite LSS are considered, and the simulation results are analyzed and compared. The modeling results obtained from the simulations indicate that even if the LSS value is large enough to inhibit unstable rock failure, as long as LSS is finite, it has an influence on the post-peak stress-strain curve of rock. It is revealed that because the input energy supplied by the external energy source to drive the stable rock failure process is affected by the finite LSS of a test machine, the post-peak descending slopes of the stress-strain curves are all steeper than the post-peak descending slope obtained under an ideal loading condition of infinite LSS. An insight from this numerical experiment is that it might be more feasible to develop laboratory test machines with variable LSS that can match the local mine stiffness in the field for rock property testing.
Achiaga, B.; Barea, R.; Candela, N.
2016-08-01
This paper is concerned with the mechanical behaviour of compacted ceramic green components of two α-SiC with different particle size-shape and purity with the purpose of evaluate the Drucker-Prager criterion in both material. Compaction pressures were between 60 and 100 MPa. The green compact were evaluated by two tests such as diametrical compression and uniaxial compression for different relative densities. These models are used both for die design as for parts design. The results show the different compression behaviour caused by the particles shape of each material. (Author)
Review of constitutive models and failure criteria for concrete
Seo, Jeong Moon; Choun, Young Sun [Korea Atomic Energy Research Institute, Taejeon (Korea)
2000-03-01
The general behavior, constitutive models, and failure criteria of concrete are reviewed. The current constitutive models for concrete cannot satisfy all of mechanical behavior of concrete. Among several constitutive models, damage models are recommended to describe properly the structural behavior of concrete containment buildings, because failure modes and post-failure behavior are important in containment buildings. A constitutive model which can describe the concrete behavior in tension is required because the containment buildings will reach failure state due to ultimate internal pressure. Therefore, a thorough study on the behavior and models under tension stress state in concrete and reinforced concrete has to be performed. There are two types of failure criteria in containment buildings: structural failure criteria and leakage failure criteria. For reinforced or prestressed concrete containment buildings, concrete cracking does not mean the structural failure of containment building because the reinforcement or post-tensioning system is able to resist tensile stress up to yield stress. Therefore leakage failure criteria will be prior to structural failure criteria, and a strain failure criterion for concrete has to be established. 120 refs., 59 figs., 1 tabs. (Author)
Abdel-Malek, S.; Halle, Th.; Meyer, L. W.
2003-09-01
Ductile fracture investigations are an important part in current research. The simulation of fracture by means of numerical codes needs precise material data that may be reached from accurate mechanical testing. In order to predict failure processes, the stress state history as a function of strain development has to be known. In this work tensile tests on HY80 steel were performed under quasistatic and high strain rate loading conditions at room temperature using smooth and notched specimens. The force-time and displacement-time behaviour was measured during testing. Additionally, scanning electron microscopy was used to investigate the fractured surfaces. Furthermore, different models were applied to describe the failure process. FE-calculations were used to receive the stress state in the material in the region of the notch as a function of strain development.
Houston, B K; Kelly, K E
1987-01-01
Ninety-five housewives were administered the Framingham Type A Scale and the Jenkins Activity Survey. Information concerning various aspects of their daily lives as well as various psychological and psychosocial variables were obtained via questionnaire and interview. Type As were found to differ from Type Bs in having more stressful work-related experiences. Further, Type As reported poorer marital adjustment and tended to report more marital disharmony than did Type Bs. Type A behavior was also related to more self-reported stress, tension, and physical health problems. Finally, Type As reported lower covert self-esteem and tended to report more fear-of-failure than Type Bs.
Development of a wrinkled pipeline fatigue ultimate limit state criterion
Semiga, V.; Tiku, S.; Dinovitzer, A. [BMT Fleet Technology Ltd., Kanata (Canada); Zhou, J.; Sen, M. [TransCanada PipeLines Ltd., Calgary, AB (Canada)
2009-07-01
This paper described research currently being conducted to develop a mechanics-based wrinkle ultimate limit state for evaluating the long-term integrity of wrinkled pipeline segments. Efforts included testing and non-linear finite element analysis (FEA) of small-scale and full-scale wrinkled pipeline segments. The aim of the program was to develop a set of monotonic and cyclic material properties for use in designing a failure assessment procedure. A failure criterion has also been developed to predict the fatigue life of experimental pipeline specimens. An experimental material properties database was developed for several pipeline materials ranging from API grade X60 to X100 steel pipelines. Multiple monotonic tensile tests were conducted for all materials used in the program. Experimental stress-strain curves were used to develop finite element material models during the modelling phase of the project. Complete strain life curves were also obtained. A small scale strip test was developed to predict the fatigue life of strip test specimens. Nonlinear kinematic material models were also developed. Results of the program to date indicate that the finite element method (FEM) model is capable of accurately estimating the cyclic fatigue life of pipelines with wrinkles. It was concluded that the FEM model will also be used to examine the interactions between soil and buried pipelines. 6 refs., 14 figs.
The PTSD supremacy: Criterion F in three Voyager cases.
Gaughwin, Peter
2009-04-01
The aim is to consider whether the courts and experts in their application of Criterion F for posttraumatic stress disorder (PTSD) have applied it consistently in civil claims brought years after the event. Three cases for compensation relating to the Voyager disaster are considered. It appears, from the cases considered in this paper, that while courts consider that Criterion F is crucial in making a diagnosis of PTSD, there are some inconsistencies in terms of understanding and applying this criterion, both by the courts and experts. This may be because of a lack of guidance in psychiatric texts as to how to apply Criterion F. Criterion F is, after the satisfaction of Criterion A(1), arguably the most important of the criteria for PTSD for, while the symptoms referred to in Criteria B-D have been shown to be fairly easy to simulate, it is arguably harder to do this with Criterion F, particularly in cases that arise a long time after the event. It is important therefore that psychiatrists assessing persons so long after an event adhere rigorously to Criterion F, because it is based on facts open to objective corroboration, while criteria B, C and D tend to rely on subjective experiences which are the most sensitive to distortion. Thus, it is to be hoped that if DSM-V is to maintain a criterion of clinically significant distress or impairment in the majority of the disorders described therein, it will provide some assistance as to how this criteria should be applied.
Failure Criteria for Evaluating Accidental Drops of Fuel Containers at INTEC
Miller, G. K.
1998-10-01
This report presents a failure criterion that has been developed for use in evaluating fuel containers at the Idaho Nuclear Technology and Engineering Center (INTEC) for accidental drop events. The criterion would typically be used in dynamic finite element analyses using the ABA-QUS/Explicit program. The failure criterion used in the past is generally considered to substantially underestimate the strength and ductility of the materials involved. The new criterion is intended to be more realistic, allowing for more accurate impact analyses. The criterion is based on the distortion energy theory, which is considered to be appropriate for the ductile materials typically used in fuel containers. Also addressed in development of the criterion were the effects of strain rate and hydrostatic stress. The importance of these factors, however, is highly dependent on the material used. Three materials specifically addressed in this study were stainless steel, aluminum, and lead. The criterion is presented in the form of guidelines and recommendations that are based on material data obtained from the literature. The most significant difference between these and the previous criterion is that ductile materials are allowed to strain to much higher levels before they are considered to fail.
A Less Conservative Circle Criterion
2008-01-01
A weak form of the Circle Criterion for Lur'e systems is stated. The result allows prove global boundedness of all system solutions. Moreover such a result can be employed to enlarge the set of nonlinearities for which the standard Circle Criterion can guarantee absolute stability.
The role of shear and tensile failure in dynamically triggered landslides
Gipprich, T.L.; Snieder, R.K.; Jibson, R.W.; Kimman, W.
2008-01-01
Dynamic stresses generated by earthquakes can trigger landslides. Current methods of landslide analysis such as pseudo-static analysis and Newmark's method focus on the effects of earthquake accelerations on the landslide mass to characterize dynamic landslide behaviour. One limitation of these methods is their use Mohr-Coulomb failure criteria, which only accounts for shear failure, but the role of tensile failure is not accounted for. We develop a limit-equilibrium model to investigate the dynamic stresses generated by a given ground motion due to a plane wave and use this model to assess the role of shear and tensile failure in the initiation of slope instability. We do so by incorporating a modified Griffith failure envelope, which combines shear and tensile failure into a single criterion. Tests of dynamic stresses in both homogeneous and layered slopes demonstrate that two modes of failure exist, tensile failure in the uppermost meters of a slope and shear failure at greater depth. Further, we derive equations that express the dynamic stress in the near-surface in the acceleration measured at the surface. These equations are used to approximately define the depth range for each mechanism of failure. The depths at which these failure mechanisms occur suggest that shear and tensile failure might collaborate in generating slope failure. ?? 2007 The Authors Journal compilation ?? 2007 RAS.
Chun Pan; Lu Chen; Yun-Hang Zhang; Wei Liu; Rosario Urbino; V Marco Ranieri; Hai-Bo Qiu
2016-01-01
Background:Stress index at post-recruitment maneuvers could be a method of positive end-expiratory pressure (PEEP) titration in acute respiratory distress syndrome (ARDS) patients.However,airway pressure (Paw) stress index may not reflect lung mechanics in the patients with high chest wall elastance.This study was to evaluate the Paw stress index on lung mechanics and the correlation between Paw stress index and transpulmonary pressure (PL) stress index in acute respiratory failure (ARF) patients.Methods:Twenty-four ARF patients with mechanical ventilation (MV) were consecutively recruited from July 2011 to April 2013 in Zhongda Hospital,Nanjing,China and Ospedale S.Giovanni Battista-Molinette Hospital,Turin,Italy.All patients underwent MV with volume control (tidal volume 6 ml/kg) for 20 min.PEEP was set according to the ARDSnet study protocol.The patients were divided into two groups according to the chest wall elastance/respiratory system elastance ratio.The high elastance group (H group,n =14) had a ratio ≥30％,and the low elastance group (L group,n =10) had a ratio ＜30％.Respiratory elastance,gas-exchange,Paw stress index,and PL stress index were measured.Student's t-test,regression analysis,and Bland-Altman analysis were used for statistical analysis.Results:Pneumonia was the major cause of respiratory failure (71.0％).Compared with the L group,PEEP was lower in the H group (5.7 ± 1.7 cmH2O vs.9.0 ± 2.3 cm2O,P ＜ 0.01).Compared with the H group,lung elastance was higher (20.0 ± 7.8 cmH2O/L vs.11.6 ± 3.6 cmH2O/L,P ＜ 0.01),and stress was higher in the L group (7.0 ± 1.9 vs.4.9 ± 1.9,P =0.02).A linear relationship was observed between the Paw stress index and the PL stress index in H group (R2 =0.56,P ＜ 0.01) and L group (R2 =0.85,P ＜ 0.01).Conclusion:In the ARF patients with MV,Paw stress index can substitute for PL to guide ventilator settings.
Guadalajara Boo, José Fernando; González Zárate, Jaime; Bucio Reta, Eduardo; Pérez, Patricia; Cué Carpio, Ramón José
2007-01-01
The purpose of this study is to calculate non invasivelly left ventricular systolic wall stress by echocardiography in patients with primary heart failure, and compare the results with those obtained in parients with overloaded heart failure, diastolic dysfunction by Inapropiatte hypertrophy, with normal ejection fraction and people with normal heart, there stablish the value of the results in clinical settings. We studied 33 patients with heart failure by dilated cardiomyopathy. There was no significant association between the systolic wall stress and the ejection fraction, fractional shortening, dp/dt or left ventricular mass in this group of study. There was a significant association between systolic h/r ratio and the systolic wall stress. This study shows that in primary heart failure the afterload increases and has inverse relationship with ejection fraction (r = 0.86); but, when heart failure obey to an excessive overload exists an exquisite inverse relationship between systolic wall stress and ejection fraction (r = 0.93). The excessive hypertrophy (Inappropriate) reduces the systolic wall stress but causes diastolic dysfunction. The increase of systolic wall stress in Aortic regurgitation with normal ventricular performance is responsible of adequate left ventricular hypertrophy, by other means, in mitral insufficiency the presence of low or normal systolic wall The purpose of this study is to calculate non invasivelly left ventricular systolic wall stress by echocardiography in patients with primary heart failure, and compare the results with those obtained in parients with overloaded heart failure, diastolic dysfunction by Inapropiatte hypertrophy, with normal ejection fraction and people with normal heart, there stablish the value of the results in clinical settings. We studied 33 patients with heart failure by dilated cardiomyopathy. There was no significant association between the systolic wall stress and the ejection fraction, fractional shortening
甄真
2013-01-01
Objective To study the role of inositol requiring enzyme 1(IRE1)-mediated endoplasmic reticulum stress on hepatocyte apoptosis of experimental fulminant hepatic failure(FHF). Methods Thirty male depuratory Wistar
Marczak Halina
2015-06-01
Full Text Available Determination of the global uniaxial compressive strength of rock mass on the basis of the Hoek-Brown failure criterion requires knowledge of the strength parameters: cohesion and the angle of internal friction. In the conventional method for the determination of these parameters given by Balmer, they are expressed by the minimum principal stress. Thus, this method does not allow for the assessment of an impact of hydrostatic pressure and stress path on the value of cohesion, friction angle and global uniaxial compression of rock mass. This problem can be eliminated by using the Hoek-Brown criterion expressed by the invariants of the stress state. The influence of hydrostatic pressure and the Lode angle on the strength parameters of the rock mass was analysed.
Stability Criterion for Humanoid Running
LIZhao-Hui; HUANGQiang; LIKe-Jie
2005-01-01
A humanoid robot has high mobility but possibly risks of tipping over. Until now, one main topic on humanoid robots is to study the walking stability; the issue of the running stability has rarely been investigated. The running is different from the walking, and is more difficult to maintain its dynamic stability. The objective of this paper is to study the stability criterion for humanoid running based on the whole dynamics. First, the cycle and the dynamics of running are analyzed. Then, the stability criterion of humanoid running is presented. Finally, the effectiveness of the proposed stability criterion is illustrated by a dynamic simulation example using a dynamic analysis and design system (DADS).
A Fracture-Based Criterion for Debonding Strength of Adhesive-Bonded Double-Strap Steel Joints
Prawit Santisukpotha
2012-01-01
Full Text Available This paper addresses the debonding strength of adhesive-bonded double-strap steel joints. A fracture-based criterion was formulated in terms of a stress singularity parameter, i.e., the stress intensity factor, which governs the magnitude of a singular stress field near the joint ends. No existing crack was assumed. A total of 24 steel joint specimens were tested under constant amplitude fatigue loadings at stress ratio of 0.2 and frequency of 2 Hz. The joint stiffness ratio was slightly less than one to control the maximum adhesive stresses at the joint ends. To detect the debonding, a simple and practical technique was developed. The test results showed that the interfacial failure near the steel/adhesive corner was a dominant failure mode. The failure was brittle and the debonding life was governed by the crack initiation stage. The finite element analysis was employed to calculate the stress intensity factors and investigate the effects of the adhesive layer thickness, lap length and joint stiffness ratio on the debonding strength.
Entropic criterion for model selection
Tseng, Chih-Yuan
2006-10-01
Model or variable selection is usually achieved through ranking models according to the increasing order of preference. One of methods is applying Kullback-Leibler distance or relative entropy as a selection criterion. Yet that will raise two questions, why use this criterion and are there any other criteria. Besides, conventional approaches require a reference prior, which is usually difficult to get. Following the logic of inductive inference proposed by Caticha [Relative entropy and inductive inference, in: G. Erickson, Y. Zhai (Eds.), Bayesian Inference and Maximum Entropy Methods in Science and Engineering, AIP Conference Proceedings, vol. 707, 2004 (available from arXiv.org/abs/physics/0311093)], we show relative entropy to be a unique criterion, which requires no prior information and can be applied to different fields. We examine this criterion by considering a physical problem, simple fluids, and results are promising.
Nakajo, A.; Van herle, J.; Favrat, D. [Laboratoire d' Energetique Industrielle (LENI), Institut de Genie Mecanique, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)
2011-08-15
A model based on the Euler-Bernoulli theory is used to assess the sensitivity of residual stresses in solid oxide fuel cells to the mechanical properties and geometry of the constituents. It considers different cell configurations, characterised by the presence or not of a compensating layer, and a cathode based on either lanthanum strontium manganite (LSM) or lanthanum strontium cobaltite ferrite (LSCF). The implementation of creep in the model provides insights into the parameters that affect the zero-stress temperature and behaviour during ageing. The amount of irreversible deformation generated in the cell layers after the sintering step depends on the mechanical properties of the layers, type of cell and to some extent, cooling rate. X-ray diffraction measurements from literature are used to verify the prediction. Depending on the mechanical properties, the stress state in the LSM cathode changes from tensile to compressive with respect to temperature. During combined ageing and thermal cycling, tensile stress might arise in the compatibility layer of LSCF-based cells, due to the relief of the initial compressive stress at operating temperature. The Weibull analysis provides the assessment of mechanical failure. A simplified approach is used for buckling-driven delamination, but the propagation of cracks is predicted for unlikely large pre-existing defects. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Glycation and oxidative stress in the failure of dental implants: a case series
Pietropaoli, Davide; Ortu, Eleonora; Severino, Marco; Ciarrocchi, Irma; Gatto, Roberto; Monaco, Annalisa
2013-01-01
...) and oxidative stress in periimplantitis. The Western Blotting analysis on periimplantitis and periodontal disease tissues showed marked increase of AGEs when compared to healthy control tissues...
A study of fuel failure behavior in high burnup HTGR fuel. Analysis by STRESS3 and STAPLE codes
Martin, David G.; Sawa, Kazuhiro; Ueta, Shouhei; Sumita, Junya [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment
2001-05-01
In current high temperature gas-cooled reactors (HTGRs), Tri-isotropic coated fuel particles are employed as fuel. In safety design of the HTGR fuels, it is important to retain fission products within particles so that their release to primary coolant does not exceed an acceptable level. From this point of view, the basic design criteria for the fuel are to minimize the failure fraction of as-fabricated fuel coating layers and to prevent significant additional fuel failures during operation. This report attempts to model fuel behavior in irradiation tests using the U.K. codes STRESS3 and STAPLE. Test results in 91F-1A and HRB-22 capsules irradiation tests, which were carried out at the Japan Materials Testing Reactor of JAERI and at the High Flux Isotope Reactor of Oak Ridge National Laboratory, respectively, were employed in the calculation. The maximum burnup and fast neutron fluence were about 10%FIMA and 3 x 10{sup 25} m{sup -2}, respectively. The fuel for the irradiation tests was called high burnup fuel, whose target burnup and fast neutron fluence were higher than those of the first-loading fuel of the High Temperature Engineering Test Reactor. The calculation results demonstrated that if only mean fracture stress values of PyC and SiC are used in the calculation it is not possible to predict any particle failures, by which is meant when all three load bearing layers have failed. By contrast, when statistical variations in the fracture stresses and particle specifications are taken into account, as is done in the STAPLE code, failures can be predicted. In the HRB-22 irradiation test, it was concluded that the first two particles which had failed were defective in some way, but that the third and fourth failures can be accounted for by the pressure vessel model. In the 91F-1A irradiation test, the result showed that 1 or 2 particles had failed towards the end of irradiation in the upper capsule and no particles failed in the lower capsule. (author)
郝平; 傅征祥; 田勤俭; 刘杰; 刘桂萍
2004-01-01
The great Kunlun earthquake occurred on Nov. 14, 2001 in Qinghai Province, China. Five large aftershocks with magnitude larger than 5.0 occurred near the Kunlun fault after main shock. Calculations of the change in Coulomb failure stress reveal that 4 of 5 large aftershocks occurred in areas with △σf>0 ～10(2～10-1 MPa) and one aftershock occurred in an area with △σf =-0.56 MPa. It is concluded that the permanent fault displacement due to the main shock is the main cause of activity of large aftershocks, but not the whole cause.
Stress Analysis and Failure Mechanisms of Plasma-Sprayed Thermal Barrier Coatings
Yang, Jiasheng; Wang, Liang; Li, Dachuan; Zhong, Xinghua; Zhao, Huayu; Tao, Shunyan
2017-06-01
Yttria-stabilized zirconia coatings were deposited by plasma spraying and heat-treated at 1100 °C for 50, 100, 150, and 200 h in air, respectively. Mechanical properties including microhardness and Young's modulus were evaluated using the nanoindentation test. Residual stresses in the ceramic topcoat and the thermally grown oxide (TGO) layer were measured using Raman spectroscopy and photoluminescence piezo-spectroscopy (PLPS) techniques, respectively. The results showed that both the modulus and hardness increased with the thermal exposure time up to 100 h and then gradually decreased. The accumulated tensile stress in the as-sprayed topcoat changed to compressive stress after thermal exposure, and the compressive stress in the topcoat increased with an increase of thermal exposure time up to 150 h. The average compressive stresses in the TGO layer were higher than that of the cross-sectional topcoat, and the measured in-plane compressive stress increased firstly and then gradually decreased with increasing exposure time. The local interface geometry strongly affect the nature and evolution of hydrostatic stresses in the TGO. Finally, the crack initiation and propagation at the topcoat/TGO/bondcoat interface has been discussed with respect to the residual stresses in the plasma-sprayed TBC system.
Progressive failure analysis of composite structure based on micro- and macro-mechanics models
孙志刚; 阮绍明; 陈磊; 宋迎东
2015-01-01
Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics (FVDAM). Compared with the results calculated by failure criterion based on macro-stress field (the maximum stress criteria and Hashin criteria) and micro-stress field (Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.
Hema Agnihotri
2010-01-01
Full Text Available Long-term clinical failures of cemented prosthesis depend, to a large extent, on the integrity of the luting agent. The causative factors that lead to microfracture and, hence, failure of the luting agents are the stresses acting inside the oral cavity. Therefore, the present study was designed to develop an understanding of the relationship between stresses in the tooth and the failure potential of the luting agent. Two-dimensional finite element stress analysis was performed on the mandibular second premolar. The behavior of zinc-phosphate and glass-ionomer were studied under different crowns (metal-ceramic and metal crown and loading conditions (mechanical force of 450 N acting vertically over the occlusal surface, thermal loads of 60° and 0°C. It was observed from the study that failure threshold of the luting agent was influenced both by the elastic modulus of the luting agent and by the type of the crown.
Cerullo, Michele
2014-01-01
A 2D plane strain finite element program has been developed to investigate very high cycle fatigue in wind turbine roller bearings due to rolling contact. Focus is on fatigue in the inner ring, where the effect of residual stresses and hardness variation along the depth is accounted for. Both...... classic Hertzian and elastohydrodynamic lubrication theories have been used to model the pressure distribution acting on the inner raceway and results are compared according to the Dang Van multiaxial fatigue criterion. The contact on the bearing raceway is simulated by substituting the roller...... its values to the fatigue limit parameters for the material. It is found that both for Hertzian and elastohydrodynamic lubrication contacts, the Dang Van criterion predicts that fatigue failure will first occur in the subsurface region and that, regardless of the specific pressure distribution used...
Failure Assessment of Stainless Steel and Titanium Brazed Joints
Flom, Yury A.
2012-01-01
Following successful application of Coulomb-Mohr and interaction equations for evaluation of safety margins in Albemet 162 brazed joints, two additional base metal/filler metal systems were investigated. Specimens consisting of stainless steel brazed with silver-base filler metal and titanium brazed with 1100 Al alloy were tested to failure under combined action of tensile, shear, bending and torsion loads. Finite Element Analysis (FEA), hand calculations and digital image comparison (DIC) techniques were used to estimate failure stresses and construct Failure Assessment Diagrams (FAD). This study confirms that interaction equation R(sub sigma) + R(sub tau) = 1, where R(sub sigma) and R(sub t u) are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in stainless steel and titanium brazed joints.
Ceme Ferreira Jordy
1995-09-01
Full Text Available Eletromiograma de superfície foi realizado no crânio e pescoço, durante stress provocado por frio, em 100 pacientes sofrendo cefaléia crônica isolada. Os resultados de diagnóstico obtidos com a eletromiografia revelaram erro de 24% a 32% na avaliação clínica da cefaléia tensional segundo os critérios anamnésicos referendados pelo Comitê de Classificação das Cefaléias, da Sociedade Internacional de Cefaléia (1988. A eletromiografia durante stress é proposta como novo critério de diagnóstico da Cefaléia tensional.We report the use of surface scalp and neck electromyography during experimental stress state in a series of 100 out-patients suffering from chronic tension headache. Results revealed a 24% to 32% of diagnostic errors in the diagnostic obtained by routine anamnestic procedures and following the criteria recommended by the Headache Classification Commitee of the International Headache Society (1988. The electromyography with stress is proposed as a new diagnostic criterion for tension headache.
Dalgaard, Ligaya; Eskildsen, Anita; Carstensen, Ole; Willert, Morten Vejs; Andersen, Johan Hviid; Glasscock, David J
2014-11-01
This study evaluated the effectiveness of a stress management intervention combining individual cognitive behavioral therapy (CBT) with a brief workplace intervention on self-reported measures of sleep and cognitive functioning among patients on sick leave due to work-related stress complaints. Participants were patients referred to the regional Department of Occupational Medicine. Inclusion criteria were (i) sick leave due to work-related stress complaints and (ii) a diagnosis of adjustment disorder/reactions to stress or mild depression. Participants (N=137) were randomized to either an intervention (N=57) or control (N=80) group. The intervention comprised six sessions with a psychologist and the offer of a small workplace intervention. Questionnaires were answered at baseline and after 4, and 10 months. Symptoms were significantly reduced over time in both groups but there was no significant treatment effect on sleep or cognitive outcomes at any time point. From 0-4 months, there was a tendency for larger improvements in the intervention group with regards to sleep and cognitive failures in distraction. Although neither was significant, the results came close to significance depicting a small effect size (Cohen's d) on sleep complaints and distractions (but not memory). The specific intervention was not superior to the control condition in reducing symptoms of sleep problems and cognitive difficulties at any time point during the 10-month follow-up period. Substantial improvements in symptoms over time were seen in both groups.
A new mixed-mode fracture criterion for large scale lattice models
T. Sachau
2013-08-01
Full Text Available Reasonable fracture criteria are crucial for the modeling of dynamic failure in computational spring lattice models. For experiments on the micro and on the meso scale exist successful criteria, which are based on the stress that a spring experiences. In this paper we test the applicability of these failure criteria to large scale models, where gravity plays an important role in addition to the externally applied deformation. The resulting brittle structures do not resemble the outcome predicted by fracture mechanics and geological observations. For this reason we derive an elliptical fracture criterion, which is based on the strain energy stored in a spring. Simulations using the new criterion result in realistic structures. It is another great advantage of this fracture model, that it can be combined with classic geological material parameters: the tensile strength σ0 and the shear cohesion τ0. While we tested the fracture model only for large scale structures, there is strong reason to believe that the model is equally applicable to lattice simulations on the micro and the meso scale.
李曰兵; 金伟娅; 高增梁; 雷月葆
2015-01-01
The accepted defective components using a deterministic approach in structural integrity assessment may still fail under the operation conditions used in the assessment. A probability analysis method is proposed in this paper to estimate the failure probability of the defective components corresponding to the critical conditions of the deterministic assessment method. The method not only can be used to validate the probabilistic requirement under the deterministic assessment criteria, but also guide to draft the safety factors in the deterministic assessment criteria based on the probabilistic requirement. Considering elastic fracture mechanics based flaw acceptance criteria given in ASME BPVC Section XI, a typical cooling down transient (normal operation) and a typical pressurized thermal shock transient(a fault condition) are analyzed using both the deterministic and probabilistic methods for a reactor pressure vessel(RPV) with defects. The critical crack sizes are calculated using the deterministic method with assigned safety factors and the corresponding failure probabilities are estimated. Then, the effect of the safety factor on the failure probabilities is discussed. The results of the case study show that the safety factors recommended by ASME Code may not be sufficient for the normal cooling down transient to satisfy the probabilistic requirement of nuclear safety.%在含缺陷结构完整性评定中，即使满足确定性分析要求，结构也会存在发生失效的可能。提出确定性缺陷验收准则所对应失效概率的分析方法，以计算在满足确定性分析要求的临界条件下结构的失效概率。采用该方法可以验证确定性缺陷验收准则是否能够满足结构的概率要求，也可依据概率要求指导确定性缺陷验收准则中安全系数的制定。针对ASME BPVC第XI卷中基于应力强度因子的缺陷验收准则，以正常降温工况和承压热冲击事故工况为例，对一典型含
A Planarity Criterion for Graphs
Dosen, Kosta
2012-01-01
It is proven that a connected graph is planar if and only if all its cocycles with at least four edges are "grounded" in the graph. The notion of grounding of this planarity criterion, which is purely combinatorial, stems from the intuitive idea that with planarity there should be a linear ordering of the edges of a cocycle such that in the two subgraphs remaining after the removal of these edges there can be no crossing of disjoint paths that join the vertices of these edges. The proof given in the paper of the right-to-left direction of the equivalence is based on Kuratowski's Theorem for planarity involving $K_{3,3}$ and $K_5$, but the criterion itself does not mention $K_{3,3}$ and $K_5$. Some other variants of the criterion are also shown necessary and sufficient for planarity.
Deformation and failure of bulk metallic glasses under different initial temperatures
Li J.C.
2015-01-01
Full Text Available Based on the coupled thermo-mechanical model, a constitutive model for bulk metallic glasses (BMGs, which is generalized to the multi-axial stress state and considers the effects of free volume, heat and hydrostatic stress, has been modified in the present paper. Besides, a failure criterion of critical free volume concentration is introduced based on the coalescence mechanism of free volume. The constitutive model as well as the failure criterion is implemented into the LS-DYNA commercial software by user material subroutine (UMAT. Then FEM simulations for different initial material temperatures are conducted and the evolutions of material parameter as well as corresponding macroscopic mechanical behaviour of material are analyzed. Relative analysis shows that the initial material temperature significantly affects the deformation and failure of material.
Zhi Wang; Zhong-Dao Zhang; Si-Hong Zhao; Zhi-Juan Chen
2017-01-01
Objective:To explore the effect of digoxin and Tongxin capsule combined therapy on oxidative stress, cytokines and vascular endothelial function in patients with chronic heart failure, and provide help for clinical treatment of patients with chronic heart failure.Methods:95 cases of chronic heart failure in our hospital were randomly divided into observation group (47 cases) and control group (48 cases). Control group patients were given basic treatment, and observation group received combination therapy of digoxin and Tongxinluo capsule, to detect and to investigate the changes of oxidative stress, cytokines and vascular endothelial function in two groups of patients before and after treatment.Results:There was no significant difference in oxidative stress, cytokines and vascular endothelial function between the two groups of chronic heart failure patients before treatment (P>0.05). Compared with before treatment, the malondialdehyde (MDA) and cytokines [tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), interleukin-6 (IL-6) and brain natriuretic peptide (BNP)] in two groups of patients with chronic heart failure after treatment decreased significantly (P<0.05), while indexes related to endothelial function [hyperemic brachial artery diameter after reactive hyperemia, brachial artery diameter change rate, brachial artery endothelial dependent diastolic function (FMD), and brachial artery endothelium dependent diastolic function (NMD)] and related indexes of oxidative stress [glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT)] were significantly increased (P<0.05). The related indexes and oxidative stress indexes (GSH-Px, CAT and SOD) of observation group after the combined treatment in patients with endothelial function were significantly higher than the control group after treatment (P<0.05). After treatment, cytokines and MDA levels were significantly lower than the control group (P<0.05).Conclusions:Tongxinluo capsule
A modified Burzynski criterion for anisotropic pressure-dependent materials
FARZAD MOAYYEDIAN; MEHRAN KADKHODAYAN
2017-01-01
In this paper the Burzynski criterion, which was introduced for isotropic pressure-dependent materials, is modified for anisotropic pressure-dependent materials in plane-stress condition. The modified criterion can be calibrated with 10 experimental data points such as tensile stress at 0°, 45° and 90°, compressive stress at 0° and 90° and R-values in tensile stress at 0°, 45° and 90° from rolling direction and also biaxial tensilestress and tensile R-value. To identify the anisotropic parameters an error function is set up through comparison of the predicted yield stresses and R-values with those from experiments. Then the Downhill simplex method is applied to solve 10 high-nonlinearity equations. Finally, considering Al 2008-T4 (BCC), Al 2090-T3 (FCC),AZ31 (HCP) and also Mg–0.5% Th alloy, Mg–4% Li alloy, pure textured magnesium, textured magnesium andTi–4Al–1/4O2, which are HCP materials with ep¼ 1%; 5%; 10% as case studies and comparing the results for the modified Burzynski criterion with experiments, it is shown that the Burzynski criterion is appropriate for pressure-dependent anisotropic materials with proper accuracy.
Blas-Valdivia, Vanessa; Cano-Europa, Edgar; Martinez-Perez, Yoalli; Lezama-Palacios, Ruth; Franco-Colin, Margarita; Ortiz-Butron, Rocio
2015-10-01
The aim of this study was to investigate if a protective effect from hypothyroidism in acute liver failure resulted from reduced endoplasmic reticulum stress and changes to the redox environment. Twenty male Sprague-Dawley rats were divided in four groups: (1) euthyroid (sham surgery), (2) hypothyroid, (3) euthyroid (sham surgery)+thioacetamide and (4) hypothyroid+thioacetamide. Hypothyroidism was confirmed two weeks after thyroidectomy, and thioacetamide (TAA) (400mg/kg, ip) was administrated to the appropriate groups for three days with supportive therapy. Grades of encephalopathy in all animals were determined using behavioral tests. Animals were decapitated and their blood was obtained to assess liver function. The liver was dissected: the left lobe was used for histology and the right lobe was frozen for biochemical assays. Body weight, rectal temperature and T4 concentration were lower in hypothyroid groups. When measurements of oxidative stress markers, redox environment, γ-glutamylcysteine synthetase and glutathione-S-transferase were determined, we observed that hypothyroid animals with TAA compensated better with oxidative damage than euthyroid animals treated with TAA. Furthermore, we measured reduced expressions of GADD34, caspase-12 and GRP78 and subsequently less hypothyroidism-induced cellular damage in hypothyroid animals. We conclude that hypothyroidism protects against hepatic damage caused by TAA because it reduces endoplasmic reticulum stress and changes to the redox environment.
Kupper, Nina; Denollet, Johan; Widdershoven, Jos; Kop, Willem J
2013-10-01
The distressed (Type D) personality is associated with adverse coronary heart disease outcomes, but the mechanisms accounting for this association remain to be elucidated. We examined whether myocardial and hemodynamic responses to mental stress are disrupted in Type D patients with chronic heart failure (HF). Ninety-nine HF patients (mean age 65±12years; 75% men) underwent a public speech task, during which heart rate (HR) and blood pressure (BP) were recorded. Type D personality and its components negative affectivity (NA) and social inhibition (SI) were assessed with the DS14. General linear models with repeated measures and logistic regression were used to assess differences in stress response and recovery. Type D personality was associated with a reduced HR response (F1,93=4.31, ppersonality with respect to the BP response. Examining continuous NA and SI scores and their interaction (NA∗SI), revealed a significant association of NA∗SI with the SBP response (F1,93=4.11, ppersonality may show an inadequate response to acute social stress, characterized by a blunted HR response. Copyright © 2013 Elsevier B.V. All rights reserved.
Perceived Parental Bonding, Fear of Failure and Stress during Class Presentations
Sideridis, Georgios D.; Kafetsios, Konstantinos
2008-01-01
The purpose of the present studies was to test the hypothesis that students' perceptions of parental bonding may be predictive of how individuals approach achievement situations. It was hypothesized that reports of parental overprotection would be predictive of elevated fears and subsequent stress and low achievement compared to perceived parental…
Regel, Jeppe Bendix; Orozova-Bekkevold, Ivanka; Andreassen, Katrine Alling
2017-01-01
, is significantly different from 1. The log-derived Biot's coefficient is above 0.8 in the Shetland Chalk Group and in the Tyne Group, and 0.6-0.8 in the Heno Sandstone Formation. We show that the effective vertical and horizontal stresses obtained using the log-derived Biot's coefficient result in a drilling...
Nagode, Marko; Šeruga, Domen
An approach is presented that enables the calculation of elastic strain energy in linear and nonlinear elastic solids during arbitrary thermomechanical load cycles. The approach uses the simple fact that the variation of both strain and complementary energies always forms a rectangular shape in stress-strain space, hence integration is no longer required to calculate the energy. Furthermore, the approach considers the mean stress effect so that predictions of fatigue damage are more realistically representative of real-life experimental observations. By doing so, a parameter has been proposed to adjust the mean stress effect. This parameter α is based on the well-known Smith-Watson-Topper energy criterion, but allows consideration of other arbitrary mean stress effects, e.g. the Bergmann type criterion. The approach has then been incorporated into a numerical method which can be applied to uniaxial and multiaxial, proportional and non-proportional loadings to predict fatigue damage. The end result of the method is the cyclic evolution of accumulated damage. Numerical examples show how the method presented in this paper could be applied to a nonlinear elastic material.
Criterion Reading Instructional Project (CRIP).
Linden Board of Education, NJ.
This booklet describes the Linden Title I Program between the years 1971-1974, with a focus on the Criterion Reading Instructional Project (CRIP). The program (in Linden, New Jersey) evolved from a supplemental reading and mathematics program to a structured developmental program of language arts designed to meet the needs of primary grade…
Weathers, Frank W; Keane, Terence M
2007-04-01
The Criterion A problem in the field of traumatic stress refers to the stressor criterion for posttraumatic stress disorder (PTSD) and involves a number of fundamental issues regarding the definition and measurement of psychological trauma. These issues first emerged with the introduction of PTSD as a diagnostic category in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III; American Psychiatric Association, 1980) and continue to generate considerable controversy. In this article, the authors provide an update on the Criterion A problem, with particular emphasis on the evolution of the DSM definition of the stressor criterion and the ongoing debate regarding broad versus narrow conceptualizations of traumatic events.
Influences of stress dilation on shape of failure surface for shallow tunnels
杨小礼; 王金明
2008-01-01
For shallow tunnels of single-lane railway and four-lane road,numerical simulation using finite differential code was conducted.The mechanical behavior of loose rock masses was studied considering the influences of shear dilation on the shape of the failure surface for the shallow tunnels,and the break angles using numerical simulation was compared with those using the Rankine’s analytical solutions and design code.From the comparisons,it is found that the difference between the break angle by numerical simulation and the design code is small when the shear dilation angle is equal to 0,with the maximum relative difference being less than 0.2% in road tunnels.With the dilation angle’s increase,the loose plasticity zone area of surrounding rock reduces obviously,and the break angle increases gradually.When the dilation angle is equal to the internal friction angle,the materials follow associated flow rule,and the numerical solution of the break angle is larger than the analytical solution,with the maximum relative difference being greater than 16.7% in road tunnels.Therefore,associated flow rule leads to overestimating break angle,and the dilation angle has an important influence on the failure surface shape for shallow tunnels in the loose surrounding rocks.
Koyanagi, Jun; Yoshimura, Akinori; Kawada, Hiroyuki; Aoki, Yuichiro
2010-02-01
We performed a numerical simulation of a time-dependent interfacial failure accompanied by a fiber failure, and examined their evolution under shear and compressive loads in single-fiber composites. The compressive load on the interface consists of Poisson’s contraction for matrix resin subjected to longitudinal tensile load. As time progresses, compressive stress at the interface in the fiber radial direction relaxes under the constant longitudinal tensile strain condition for the specimen, directly causing the relaxation of the interface frictional stress. This relaxation facilitates the failure of the interface. In this analysis, a specific criterion for interface failure is applied; apparent interfacial shear strength is enhanced by compressive stress, which is referred as quasi-parabolic criterion in the present study. The results of the stress recovery profile around the fiber failure and the interfacial debonding length as a function of time simulated by the finite element analysis employing the criterion are very similar to experimental results obtained using micro-Raman spectroscopy.
Marker selection by Akaike information criterion and Bayesian information criterion.
Li, W; Nyholt, D R
2001-01-01
We carried out a discriminant analysis with identity by descent (IBD) at each marker as inputs, and the sib pair type (affected-affected versus affected-unaffected) as the output. Using simple logistic regression for this discriminant analysis, we illustrate the importance of comparing models with different number of parameters. Such model comparisons are best carried out using either the Akaike information criterion (AIC) or the Bayesian information criterion (BIC). When AIC (or BIC) stepwise variable selection was applied to the German Asthma data set, a group of markers were selected which provide the best fit to the data (assuming an additive effect). Interestingly, these 25-26 markers were not identical to those with the highest (in magnitude) single-locus lod scores.
The role of curing stresses in subsequent response, damage and failure of textile polymer composites
Heinrich, Christian; Aldridge, Michael; Wineman, Alan S.; Kieffer, John; Waas, Anthony M.; Shahwan, Khaled W.
2013-05-01
An integrated computational framework for textile polymer composites is introduced. A novel polymer curing model is used in connection with modeling the polymer curing process during manufacturing of textile composites. The model is based on the notion of polymer networks that are continuously formed in a body of changing shape due to changes in temperature, chemistry and external loads. Nonlinear material behavior is incorporated through nonlocal continuum damage mechanics that preserves mesh objectivity in calculations that go beyond maximum loads. The integrated model is applied to the curing of plain weave textile composites made from carbon fiber tows and Epon™862 resin. The mechanical and chemical properties are measured during curing using concurrent Brillouin and Raman light scattering. It is shown that significant stresses can develop during cure. The effect of these stresses on the manufactured part performance, when subsequent service loads are applied, is evaluated and a reduction in ultimate load, in agreement with experimental observations, is observed.
Yu Yang; Bai Jianbiao; Chen Ke; Wang Xiangyu; Xiao Tongqiang; Chen Yong
2011-01-01
To solve the problem of supporting three downhill coal structures in the Yongan Coal Mine of Shanxi Jincheng,we studied the regular development of stress and plastic zones and characteristics of deformation of rock surrounding roadway groups after a period of roadway driving,mining one side as well as mining both sides,we used FLAC3D for our numerical and theoretical analyses.Field test were carried out,where we revealed the deformation mechanism of roadways and its coal pillars in complex stress conditions.We proposed a roadway stability control technology using backwall grouting with high-water rapid hardening material and combined support with bolt and cable anchoring after mining both sides.Our field practices showed that deformation of rock surrounding roadways can be controlled with this technology.
Barrionuevo Francisco
2010-12-01
Full Text Available Abstract Background Sox9 (Sry box containing gene 9 is a DNA-binding transcription factor involved in chondrocyte development and sex determination. The protein's absence in testicular Sertoli nurse cells has been shown to disrupt testicular function in adults but little is known at the genome-wide level about molecular events concomitant with testicular break-down. Methods To determine the genome-wide effect on mRNA concentrations triggered by the absence of Sox9 in Sertoli cells we analysed adult testicular tissue from wild-type versus mutant mice with high-density oligonucleotide microarrays and integrated the output of this experiment with regulatory motif predictions and protein-protein network data. Results We report the genome-wide mRNA signature of adult testes lacking Sox9 in Sertoli cells before and after the onset of late spermatogenic failure as compared to fertile controls. The GeneChip data integrated with evolutionarily conserved Sox9 DNA binding motifs and regulatory network data identified genes involved in feminization, stress response and inflammation. Conclusions Our results extend previous observations that genes required for female gonadogenesis are up-regulated in the absence of Sox9 in fetal Sertoli cells to the adult stage. Importantly, we identify gene networks involved in immunological processes and stress response which is reminiscent of a phenomenon occurring in a sub-group of infertile men. This suggests mice lacking Sox9 in their Sertoli cells to be a potentially useful model for adult human testicular failure.
A Focused Bayesian Information Criterion
Georges Nguefack-Tsague
2014-01-01
Full Text Available Myriads of model selection criteria (Bayesian and frequentist have been proposed in the literature aiming at selecting a single model regardless of its intended use. An honorable exception in the frequentist perspective is the “focused information criterion” (FIC aiming at selecting a model based on the parameter of interest (focus. This paper takes the same view in the Bayesian context; that is, a model may be good for one estimand but bad for another. The proposed method exploits the Bayesian model averaging (BMA machinery to obtain a new criterion, the focused Bayesian model averaging (FoBMA, for which the best model is the one whose estimate is closest to the BMA estimate. In particular, for two models, this criterion reduces to the classical Bayesian model selection scheme of choosing the model with the highest posterior probability. The new method is applied in linear regression, logistic regression, and survival analysis. This criterion is specially important in epidemiological studies in which the objective is often to determine a risk factor (focus for a disease, adjusting for potential confounding factors.
Ikram, Sohail; Saleem, Nashwa; Latif, Rana K
2016-10-01
Reverse takotsubo cardiomyopathy (TCM) is a less common variant of classic TCM that presents within a different patient profile and with its own hemodynamic considerations. A 46-year-old woman was admitted to our hospital for laryngoscopy and possible balloon dilatation for tracheal stenosis under general anesthesia. One year prior to this admission, the patient was admitted after a motor vehicle accident with subdural hematoma, subarachnoid hemorrhage, and fracture of the eighth thoracic vertebra. She underwent uneventful anesthesia for thoracic spine surgery and tracheostomy to help her wean from the ventilator during that admission. Since her previous admission, she developed posttraumatic anxiety and depression (a neuropsychiatric disorder triggered by subdural hematoma and subarachnoid hemorrhage) and was treated with antianxiety and antidepressant medication. At this admission, the patient developed acute left ventricle failure on induction of anesthesia secondary to reverse TCM. We report a case of reverse TCM, where posttraumatic emotional stress of a neuropsychiatric disorder combined with physical stress from anesthesia and laryngoscopy triggered TCM in a patient with previous uneventful anesthesia 1 year earlier.
Roirand, Q.; Missoum-Benziane, D.; Thionnet, A.; Laiarinandrasana, L.
2017-09-01
Textile composites are composed of 3D complex architecture. To assess the durability of such engineering structures, the failure mechanisms must be highlighted. Examinations of the degradation have been carried out thanks to tomography. The present work addresses a numerical damage model dedicated to the simulation of the crack initiation and propagation at the scale of the warp yarns. For the 3D woven composites under study, loadings in tension and combined tension and bending were considered. Based on an erosion procedure of broken elements, the failure mechanisms have been modelled on 3D periodic cells by finite element calculations. The breakage of one element was determined using a failure criterion at the mesoscopic scale based on the yarn stress at failure. The results were found to be in good agreement with the experimental data for the two kinds of macroscopic loadings. The deterministic approach assumed a homogeneously distributed stress at failure all over the integration points in the meshes of woven composites. A stochastic approach was applied to a simple representative elementary periodic cell. The distribution of the Weibull stress at failure was assigned to the integration points using a Monte Carlo simulation. It was shown that this stochastic approach allowed more realistic failure simulations avoiding the idealised symmetry due to the deterministic modelling. In particular, the stochastic simulations performed have shown several variations of the stress as well as strain at failure and the failure modes of the yarn.
Leite, Sara; Oliveira-Pinto, José; Tavares-Silva, Marta; Abdellatif, Mahmoud; Fontoura, Dulce; Falcão-Pires, Inês; Leite-Moreira, Adelino F; Lourenço, André P
2015-06-15
Inclusion of exercise testing in diagnostic guidelines for heart failure with preserved ejection fraction (HFpEF) has been advocated, but the target population, technical challenges, and underlying pathophysiological complexity raise difficulties to implementation. Hemodynamic stress tests may be feasible alternatives. Our aim was to test Trendelenburg positioning, phenylephrine, and dobutamine in the ZSF1 obese rat model to find echocardiographic surrogates for end-diastolic pressure (EDP) elevation and HFpEF. Seventeen-week-old Wistar-Kyoto, ZSF1 lean, and obese rats (n = 7 each) randomly and sequentially underwent (crossover) Trendelenburg (30°), 5 μg·Kg(-1)·min(-1) dobutamine, and 7.5 μg·Kg(-1)·min(-1) phenylephrine with simultaneous left ventricular (LV) pressure-volume loop and echocardiography evaluation under halogenate anesthesia. Effort testing with maximum O2 consumption (V̇o 2 max) determination was performed 1 wk later. Obese ZSF1 showed lower effort tolerance and V̇o 2 max along with higher resting EDP. Both Trendelenburg and phenylephrine increased EDP, whereas dobutamine decreased it. Significant correlations were found between EDP and 1) peak early filling Doppler velocity of transmitral flow (E) to corresponding myocardial tissue Doppler velocity (E') ratio, 2) E to E-wave deceleration time (E/DT) ratio, and 3) left atrial area (LAA). Diagnostic efficiency of E/DT*LAA by receiver-operating characteristic curve analysis for elevation of EDP above a cut-off of 13 mmHg during hemodynamic stress was high (area under curve, AUC = 0.95) but not higher than that of E/E' (AUC = 0.77, P = 0.15). Results in ZSF1 obese rats suggest that noninvasive echocardiography after hemodynamic stress induced by phenylephrine or Trendelenburg can enhance diagnosis of stable HFpEF and constitute an alternative to effort testing.
Tajra, Vitor; Vieira, Denis C L; Tibana, Ramires A; Teixeira, Tatiane G; Silva, Alessandro O; Farias, Darlan L; Nascimento, Dahan da C; de Sousa, Nuno M F; Willardson, Jeffrey; Prestes, Jonato
2015-03-01
The purpose of the present study was to compare the effects of resistance exercise (RE) leading to failure versus not to failure on 24-h blood pressure (BP) and rate-pressure product (RPP) responses in normotensive and hypertensive trained elderly women. Seven normotensive women and seven women with medically documented hypertension randomly performed three experimental sessions: (i) a non-exercise control session that involved 30 min of seated rest, (ii) whole body RE leading to failure that involved three sets with an eight repetitions maximum (8RM) load and (iii) whole body RE not to failure that involved three sets with 70% of an 8RM load. Systolic BP (SBP), diastolic BP (DBP) and mean BP (MBP) responses during each hour of sleep and awake states were measured. Results of all subjects revealed that the RPP was higher (P ≤ 0.05) during afternoon and night hours after the RE session leading to failure versus not to failure and the non-exercise control session. For the hypertensive group during the night hours, SBP remained higher after the RE session not to failure (P = 0.047) versus non-exercise control session. For the normotensive group, DBP remained higher after the RE session leading to failure over the 24-h period (approximately 8 mmHg h(-1), P = 0.044) and the period upon awaking (approximately 5 mmHg h(-1), P = 0.044) versus the hypertensive group. The normotensive elderly women of this pilot study presented a greater cardiovascular response to RE leading to failure, as a consequence of the higher training intensity. © 2014 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.
Implementation of a Stress-dependent Strength Material Model in PLAXIS 3D
Knudsen, Bjørn S.; Østergaard, Martin Underlin; Clausen, Johan
be performed in a pressure tank, where a pressure can be applied in order to simulate deep water situations. Since the test set-up is downscaled 15 to 30 times compared to real-life structures, stresses and strains will be downscaled too. For soils, normally a Mohr-Coulomb failure criterion is used...
Enforsing a system approach to composite failure criteria for reliability analysis
Dimitrov, Nikolay Krasimirov; Friis-Hansen, Peter; Berggreen, Christian
2011-01-01
parameters are random, multiple failure modes may be identified which will jeopardize the FORM analysis and a system approach should be applied to assure a correct analysis. Although crude Monte Carlo simulation automatically may account for such effects, time constraints limit its useability in problems...... challenges with the use of failure criteria, since composite materials are a discontinuous medium, which invoke multiple failure modes. Under deterministic conditions the material properties and the stress vector are constant and will result in a single dominating failure mode. When any of these input...... involving advanced FEM models. When applying more computationally efficient methods based on FORM/SORM it is important to carefully account for the multiple failure modes described by the failure criterion. The present paper discusses how to handle this problem and presents examples where reliability...
Celina Wojciechowska
2014-01-01
Full Text Available Background. The aim of study was to determine relationships between functional capacity (NYHA class, left ventricle ejection fraction (LVEF, hemodynamic parameters, and biomarkers of redox state and inflammation in patients with dilated cardiomyopathy (DCM. Methods. DCM patients (n=109, aged 45.97±10.82 years, NYHA class IIV, and LVEF 2.94±7.1% were studied. Controls comprised age-matched healthy volunteers (n=28. Echocardiography and right heart catheterization were performed. Serum activities of superoxide dismutase isoenzymes (MnSOD and CuZnSOD, concentrations of uric acid (UA, malondialdehyde (MDA, and C-reactive protein (hs-CRP were measured. Results. MnSOD, UA, hs-CRP, and MDA were significantly higher in DCM patients compared to controls. Except MDA concentration, above parameters were higher in patients in III-IV NYHA class or with lower LVEF. hsCRP correlated with of MnSOD (P<0.05 and CuZnSOD activity (P<0.01. Both isoenzymes positively correlated with mPAP and pulmonary capillary wedge pressure (MnSOD, resp., P<0.01 and P<0.05 and CuZnSOD P<0.05; P<0.05. UA positively correlated with MnSOD (P<0.05, mPAP (P<0.05, and PVRI (P<0.05. The negative correlation between LVEF and UA (P<0.01 was detected. Conclusion. There are relationships among the severity of symptoms of heart failure, echocardiographic hemodynamic parameters, oxidative stress, and inflammatory activation. Increased MnSOD activity indicates the mitochondrial source of ROS in patients with advanced heart failure.
A Criterion for Regular Sequences
D P Patil; U Storch; J Stückrad
2004-05-01
Let be a commutative noetherian ring and $f_1,\\ldots,f_r \\in R$. In this article we give (cf. the Theorem in $\\mathcal{x}$2) a criterion for $f_1,\\ldots,f_r$ to be regular sequence for a finitely generated module over which strengthens and generalises a result in [2]. As an immediate consequence we deduce that if $V(g_1,\\ldots,g_r) \\subseteq V(f_1,\\ldots,f_r)$ in Spec and if $f_1,\\ldots,f_r$ is a regular sequence in , then $g_1,\\ldots,g_r$ is also a regular sequence in .
Formation Criterion for Synthetic Jets
2005-10-01
formation data for the axisymmetric case were published over 50 years ago by Ingard and Labate.10 More recent studies33,34 suggest that L0/d > 1 for...with the axisymmetric data from Ingard and Labate10 and Smith et al.33 are compared in Fig. 7. It is found that the available data are consis- tent with...the jet formation criterion with an empirically determined constant K equal to approximately 0.16. The deviation of Ingard and Labate’s data at their
Uncertainty Relation and Inseparability Criterion
Goswami, Ashutosh K.; Panigrahi, Prasanta K.
2016-11-01
We investigate the Peres-Horodecki positive partial transpose criterion in the context of conserved quantities and derive a condition of inseparability for a composite bipartite system depending only on the dimensions of its subsystems, which leads to a bi-linear entanglement witness for the two qubit system. A separability inequality using generalized Schrodinger-Robertson uncertainty relation taking suitable operators, has been derived, which proves to be stronger than the bi-linear entanglement witness operator. In the case of mixed density matrices, it identically distinguishes the separable and non separable Werner states.
On the Modified Barkhausen Criterion
Lindberg, Erik; Murali, K.
2016-01-01
Oscillators are normally designed according to the Modified Barkhausen Criterion i.e. the complex pole pair is moved out in RHP so that the linear circuit becomes unstable. By means of the Mancini Phaseshift Oscillator it is demonstrated that the distortion of the oscillator may be minimized by i...... by introducing a nonlinear ”Hewlett Resistor” so that the complex pole-pair is in the RHP for small signals and in the LHP for large signals i.e. the complex pole pair of the instant linearized small signal model is moving around the imaginary axis in the complex frequency plane....
CRITERIA FOR ROCK ENGINEERING FAILURE
ZHUDeren; ZHANGYuzhuo
1995-01-01
A great number of underground rock projects are maintained in the rock mass which is subject to rock damage and failure development. In many cases, the rock. engineering is still under normal working conditions even though rock is already fails to some extent. This paper introduces two different concepts: rock failure and rock engineering failure. Rock failure is defined as a mechanical state under which an applicable characteristic is changed or lost.However, the rock engineering failure is an engineering state under which an applicable function is changed or lost. The failure of surrounding rocks is the major reason of rock engineering failure. The criterion of rock engineering failure depends on the limit of applicable functions. The rock engineering failure state possesses a corresponding point in rock failure state. In this paper, a description of rock engineering failure criterion is given by simply using a mechanical equation or expression. It is expected that the study of rock engineering failure criterion will be an optimal approach that combines research of rock mechanics with rock engineering problems.
Veeraveedu, Punniyakoti T; Sanada, Shoji; Okuda, Keiji; Fu, Hai Ying; Matsuzaki, Takashi; Araki, Ryo; Yamato, Masaki; Yasuda, Koubun; Sakata, Yasushi; Yoshimoto, Tomohiro; Minamino, Tetsuo
2017-08-15
ST2 is one of the interleukin (IL)-1 receptor family members comprising of membrane-bound (ST2L) and soluble (sST2) isoforms. Clinical trials have revealed that serum sST2 levels predict outcome in patient with myocardial infarction or chronic heart failure (HF). Meanwhile, we and others have reported that ablation of ST2 caused exaggerated cardiac remodeling in both ischemic and non-ischemic HF. Here, we tested whether IL-33, the ligand for ST2, protects myocardium against HF induced by mechanical overload using ligand specific knockout (IL-33(-/-)) mice. Transverse aortic constriction (TAC)/sham surgery were carried out in both IL-33 and WT-littermates. Echocardiographic measurements were performed at frequent interval during the study period. Heart was harvested for RNA and histological measurements. Following mechanical overload by TAC, myocardial mRNA expressions of Th1 cytokines, such as TNF-α were enhanced in IL-33(-/-) mice than in WT mice. After 8-weeks, IL-33(-/-) mice exhibited exacerbated left ventricular hypertrophy, increased chamber dilation, reduced fractional shortening, aggravated fibrosis, inflammation, and impaired survival compared with WT littermates. Accordingly, myocardial mRNA expressions of hypertrophic (c-Myc/BNP) molecular markers were also significantly enhanced in IL-33(-/-) mice than those in WT mice. We report for the first time that ablation of IL-33 directly and significantly leads to exacerbate cardiac remodeling with impaired cardiac function and survival upon mechanical stress. These data highlight the cardioprotective role of IL-33/ST2 system in the stressed myocardium and reveal a potential therapeutic role for IL-33 in non-ischemic HF. Copyright © 2017 Elsevier Inc. All rights reserved.
QINGWEI WANG; RICHARD K BROW; HONG LI; ERICA ANN RONCHETTO
2017-08-01
Hydrolysis resistance of boron-free E-glass fibre with different total iron oxide (Fe$_2$O$_3$) concentrations, iron redox index and durations of fibre ageing up to 180 days at 50$^{\\circ}$C with 50% relative humidity (RH) was studied. The effect ofageing on the fibre failure measured in two different test environments was examined by using two-point bending method.Based on the differences in failure strains of the fibres obtained from the two conditions as a function of ageing time, theGriffith theory of solid fracture was applied to estimate glass surface energy difference in ageing conditions. The resultsshowed that stress-assisted hydrolysis, when the fibres were under stress, could lead to about 5.18 times reduction in surfaceenergy to account for 2.30 times reduction in fibre failure strain when tested in 50% RH at room temperature.Our study showedthat the boron-free E-glass aged up to 180 days only deteriorated within 13%, independent of total Fe$_2$O$_3$ concentration andFeO/Fe$_2$O$_3$ total ratio, and stress-assisted hydrolysis played a key role during sample testing. Dynamic fatigue of the aged E-glass fibres was also investigated, showing little influence of total Fe$_2$O$_3$ concentration and FeO/Fe$_2$O$_3$ total ratio on fibre stress; corrosion susceptibility was observed.
Genet, Martin; Lee, Lik Chuan; Nguyen, Rebecca; Haraldsson, Henrik; Acevedo-Bolton, Gabriel; Zhang, Zhihong; Ge, Liang; Ordovas, Karen; Kozerke, Sebastian; Guccione, Julius M
2014-07-15
Ventricular wall stress is believed to be responsible for many physical mechanisms taking place in the human heart, including ventricular remodeling, which is frequently associated with heart failure. Therefore, normalization of ventricular wall stress is the cornerstone of many existing and new treatments for heart failure. In this paper, we sought to construct reference maps of normal ventricular wall stress in humans that could be used as a target for in silico optimization studies of existing and potential new treatments for heart failure. To do so, we constructed personalized computational models of the left ventricles of five normal human subjects using magnetic resonance images and the finite-element method. These models were calibrated using left ventricular volume data extracted from magnetic resonance imaging (MRI) and validated through comparison with strain measurements from tagged MRI (950 ± 170 strain comparisons/subject). The calibrated passive material parameter values were C0 = 0.115 ± 0.008 kPa and B0 = 14.4 ± 3.18; the active material parameter value was Tmax = 143 ± 11.1 kPa. These values could serve as a reference for future construction of normal human left ventricular computational models. The differences between the predicted and the measured circumferential and longitudinal strains in each subject were 3.4 ± 6.3 and 0.5 ± 5.9%, respectively. The predicted end-diastolic and end-systolic myofiber stress fields for the five subjects were 2.21 ± 0.58 and 16.54 ± 4.73 kPa, respectively. Thus these stresses could serve as targets for in silico design of heart failure treatments.
Liu, P. F.; Li, X. K.
2017-09-01
The purpose of this paper is to study micromechanical progressive failure properties of carbon fiber/epoxy composites with thermal residual stress by finite element analysis (FEA). Composite microstructures with hexagonal fiber distribution are used for the representative volume element (RVE), where an initial fiber breakage is assumed. Fiber breakage with random fiber strength is predicted using Monte Carlo simulation, progressive matrix damage is predicted by proposing a continuum damage mechanics model and interface failure is simulated using Xu and Needleman's cohesive model. Temperature dependent thermal expansion coefficients for epoxy matrix are used. FEA by developing numerical codes using ANSYS finite element software is divided into two steps: 1. Thermal residual stresses due to mismatch between fiber and matrix are calculated; 2. Longitudinal tensile load is further exerted on the RVE to perform progressive failure analysis of carbon fiber/epoxy composites. Numerical convergence is solved by introducing the viscous damping effect properly. The extended Mori-Tanaka method that considers interface debonding is used to get homogenized mechanical responses of composites. Three main results by FEA are obtained: 1. the real-time matrix cracking, fiber breakage and interface debonding with increasing tensile strain is simulated. 2. the stress concentration coefficients on neighbouring fibers near the initial broken fiber and the axial fiber stress distribution along the broken fiber are predicted, compared with the results using the global and local load-sharing models based on the shear-lag theory. 3. the tensile strength of composite by FEA is compared with those by the shear-lag theory and experiments. Finally, the tensile stress-strain curve of composites by FEA is applied to the progressive failure analysis of composite pressure vessel.
Hindley, Michael P.; Mitchell, Mark N.; Erasmus, Christiaan; McMurtry, Ross; Becker, Thorsten H.; Blaine, Deborah C.; Groenwold, Albert A.
2013-05-01
This paper presents a methodology that can be used for calculating the probability of failure of graphite core components in a nuclear core design, such as that of the Pebble Bed Modular Reactor. The proposed methodology is shown to calculate the failure of multiple geometries using the parameters obtained from tensile specimen test data. Experimental testing of various geometries is undertaken to verify the results. The analysis of the experimental results and a discussion on the accuracy of the failure prediction methodology are presented. The analysis is done at 50% probability of failure as well as lower probabilities of failure.
Xu, Y.; Song, H. W.; Zhang, S. H.; Cheng, M.
2011-08-01
The demand for weight reduction in modern vehicle construction has resulted in an increase in the application of hydroforming processes for the manufacture of automotive lightweight components. This trend led to the research of evaluation on formability of the sheet or tube hydroforming to be noted, particularly the prediction of fracture. In this study, a new proposed approach based on damage theory for fracture prediction considering the deformation history was introduced. And the modified ductile fracture criterion was applied to predict the failure for hydraulic bulging of AISI 304 austenitic steel sheets. The material parameters in terms of the function of strain rate in the failure criterion were determined from the equivalent fracture strains corresponding tensile tests under different stress conditions. Then, in the finite element simulation the effect of strain rates and their distribution as well during practical sheet metal forming process was considered. The hydraulic bulging tests were carried out to identify the fracture behavior predicted from FE analysis. A comparison between the prediction and experimental results showed that the proposed approach with a modified ductile fracture criteria can give better fracture predictions than traditional ways.
Lambert, Michael D.
2011-12-01
The stress and strength behavior of cylindrical tubular adhesive joints composed of dissimilar materials was explored. This was accomplished with the finite element method (FEM) and stress-based failure theories. Also, it was shown how a design of experiments (DOE) based method can be used to objectively organize the process of optimizing joint strength by using stress-based failure criteria. The finite element program used in this work was written in-house from scratch to implement the FEM for the purpose of solving both axisymmetric and three-dimensional linear elastic governing equations of static equilibrium. The formulation of the three-dimensional model is presented, and the required operations to arrive to the axisymmetric model are also presented. The axisymmetric model is two dimensional, capable of using four and eight node quadrilateral elements. However, only four node elements are used because a mesh of eight node elements requires more memory and increased mesh refinement. The three-dimensional model is capable of using eight and twenty node brick elements, but only eight node brick elements are used for the same reason. Both of the axisymmetric and three-dimensional models calculate the nodal displacements, strains, stress values for each material, and strength values for each material. The external static loads can be individually applied, or coupled together. The outputs seem to be most useful for interpretation when plotted through-the-thickness (TTT) and along-the-length (ATL) of the joint or tube. Outputs are valid only for materials that behave linearly elastic up to (or near) failure, and the stress-based failure criteria are used to define that limit. A small laboratory-sized joint was modeled to look at the theoretical stress and strength distributions plotted along-the-length of the joint at different radial locations. These stress and strength distributions can be correlated to the type of load being applied because of unique or prominent
Baranowski, Z.; Lugovoi, P. Z.
2008-04-01
The ray-path method is used to analyze the stress-strain state near mine workings acted upon by discontinuous waves. A dynamic failure criterion is proposed for analyzing the stability of mine workings. The efficiency of the approach is demonstrated with a specific example
McKinnon, William B.; Kirchoff, M.; Bland, M.
2013-10-01
The majority of mountains observed on Io are tectonic, upthrusted blocks. Their formation is generally thought to be related to Io’s heat-pipe volcanism, crustal subsidence, and accompanying lateral confinement. In previous work, we demonstrated that compressional thermal stresses from sustained local or regional shut down of Io’s heat-pipe volcanism could also play a vital role in mountain formation, and help explain the anticorrelation between Io’s mountains and volcanic centers [Kirchoff and McKinnon 2009, Formation of mountains on Io: Variable volcanism and thermal stresses, Icarus 201, 598-614; Kirchoff et al. 2011, Global distribution of volcanoes and mountains on Io: Control by asthenospheric heating and implications for mountain formation, Earth Planet. Sci. Lett. 301, 22-30]. Here we refine our previous model by using an “unconfined” horizontal boundary condition (zero average lateral stress), including brittle failure (crustal plasticity), and adding sulfur to our rheological model. The unconfined horizontal boundary condition accounts for stresses released on preexisting, more distant faults; including crustal plasticity allows us to more realistically represent stresses that would exceed the brittle failure limit otherwise, and addition of sulfur to the model composition of Io’s crust further improves the rheological model of the crust. Heated and melted at depth, liquid sulfur creates pore pressure in the lower crust and profoundly reduces the brittle failure limit. Including these modifications when the volcanic eruption rate decreases introduces a region of tensional failure in the upper crust and increases the size of the region in compressional failure in the lower crust. Finite element models show that increasing compression at depth imparts substantial bending stresses, which can drive surface faulting and block rotation. Such conditions further facilitate mountain formation at the surface, and highlight the difference between Io
Discussion on Several Failure Modes of Environmental Stress Testing%几种环境应力试验的失效模式探讨
庄少红
2013-01-01
环境应力试验是检验产品质量的重要手段之一，对评价产品质量意义重大。产品使用环境复杂多样，环境温度是影响产品性能不可避免的关键因素。建议采用高温应力、温度循环应力、温度冲击应力三种环境应力进行筛选试验，试验中向产品施加合理的环境应力和电应力。本文对环境应力筛选试验的失效模式进行了讨论。% Environmental stress testing is one of the important means for testing product quality, which is very significant for product quality evaluation. Products will be used in various environments, so the environment temperature is an inevitable influence on most products. We suggest that high temperature stress, temperature cyclic stress,and temperature shock stress be used for environmental stress screening tests, with proper environment stress and electrical stress applying to the product. This paper discuses the failure modes of environmental stress screening tests.
van Heugten-van der Kloet, Dalena; Huntjens, Rafaele; Giesbrecht, Timo; Merckelbach, Harald
2014-01-01
Sleep disturbances, fantasy proneness, cognitive failures, and dissociative symptoms are related to each other. However, the co-occurrence of these phenomena has been primarily studied in non-clinical samples. We investigated the correlations between these phenomena in dissociative identity disorder (DID) patients, post-traumatic stress disorder (PTSD) patients, and healthy controls. Both patient groups reported more sleep problems and lower sleep quality and displayed higher levels of fantasy proneness and cognitive failures than controls. However, the two patient groups did not differ with regard to these variables. Moreover, a higher level of unusual sleep experiences tended to predict participants belonging to the DID group, while specifically a lower sleep quality and more cognitive failures tended to predict participants belonging to the PTSD group.
Sun, Huarui, E-mail: huarui.sun@bristol.ac.uk; Bajo, Miguel Montes; Uren, Michael J.; Kuball, Martin [Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)
2015-01-26
Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage “hot spots” at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7–0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.
Zhi-Qing Fu; Xiao-Ying Li; Xiao-Chun Lu; Ya-Fei Mi; Tao Liu; Wei-Hua Ye
2012-01-01
Background Previous studies showed that overexpression of sarco-endoplasmic reticulum calcium ATPase (SERCA2a) in a variety of heart failure (HF) models was associated with greatly enhanced cardiac performance. However, it still undefined the effect of SERCA2a overexpression on the systemic inflammatory response and neuro-hormonal factors. Methods A rapid right ventricular pacing model of experimental HF was used in beagles. Then the animals underwent recombinant adeno-associated virus 1 (rAAV1) mediated gene transfection by direct intra-myocardium injection. HF animals were randomized to receive the SERCA2a gene, enhanced green fluorescent protein (control) gene, or equivalent phosphate buffered saline. Thirty days after gene delivery, the cardiac function was evaluated by echocardiographic testing. The protein level of SERCA2a was measured by western blotting. The proteomic analysis of left ventricular (LV) sample was determined using two-dimensional (2-D) gel electrophoresis and MALDI-TOF-MS. The serum levels of the systemic inflammatory and neuro-hormonal factors were assayed using radioimmunoassay kits. Results The cardiac function improved after SERCA- 2a gene transfer due to the significantly increased SERCA2a protein level. Beagles treated with SERCA2a had significantly decreased serum levels of the inflammatory markers (interleukin-6 and tumor necrosis factor-α) and neuro-hormonal factors (brain natriuretic peptide, endothelin-1 and angiotensin Ⅱ) compared with HF animals. The myocardial proteomic analysis showed that haptoglobin heavy chain, heat shock protein (alpha-crystallin-related, B6) were down-regulated, and galectin-1 was up-regulated in SERCA2a group compared with HF group, companied by up-regulated contractile proteins and NADH dehydrogenase. Conclusions These findings demonstrate that regional intramyocardial injections of rAAV1-SERCA2a vectors may improve global LV function, correlating with reverse activation of the systemic inflammatory
Ramirez-Sanchez, Israel; Taub, Pam R; Ciaraldi, Theodore P; Nogueira, Leonardo; Coe, Taylor; Perkins, Guy; Hogan, Michael; Maisel, Alan S; Henry, Robert R; Ceballos, Guillermo; Villarreal, Francisco
2013-10-09
Type 2 diabetes (T2D) and heart failure (HF) are associated with high levels of skeletal muscle (SkM) oxidative stress (OS). Health benefits attributed to flavonoids have been ascribed to antioxidation. However, for flavonoids with similar antioxidant potential, end-biological effects vary widely suggesting other mechanistic venues for reducing OS. Decreases in OS may follow the modulation of key regulatory pathways including antioxidant levels (e.g. glutathione) and enzymes such as mitochondrial superoxide dismutase (SOD2) and catalase. We examined OS-related alterations in SkM in T2D/HF patients (as compared vs. healthy controls) and evaluated the effects of three-month treatment with (-)-epicatechin (Epi) rich cocoa (ERC). To evidence Epi as the mediator of the improved OS profile we examined the effects of pure Epi (vs. water) on SkM OS regulatory systems in a mouse model of insulin resistance and contrasted results vs. normal mice. There were severe alterations in OS regulatory systems in T2D/HF SkM as compared with healthy controls. Treatment with ERC induced recovery in glutathione levels and decreases in the nitrotyrosilation and carbonylation of proteins. With treatment, key transcriptional factors translocate into the nucleus leading to increases in SOD2 and catalase protein expression and activity levels. In insulin resistant mice, there were alterations in muscle OS and pure Epi replicated the beneficial effects of ERC found in humans. Major perturbations in SkM OS can be reversed with ERC in T2D/HF patients. Epi likely mediates such effects and may provide an effective means to treat conditions associated with tissue OS. © 2013.
Gibbel, Mark; Larson, Timothy
2000-01-01
An Engineering-of-Failure approach to designing and executing an accelerated product qualification test was performed to support a risk assessment of a "work-around" necessitated by an on-orbit failure of another piece of hardware on the Mars Global Surveyor spacecraft. The proposed work-around involved exceeding the previous qualification experience both in terms of extreme cold exposure level and in terms of demonstrated low cycle fatigue life for the power shunt assemblies. An analysis was performed to identify potential failure sites, modes and associated failure mechanisms consistent with the new use conditions. A test was then designed and executed which accelerated the failure mechanisms identified by analysis. Verification of the resulting failure mechanism concluded the effort.
Toda, Shinji; Lin, Jian; Stein, Ross S.
2011-01-01
The 11 March 2011 Tohoku Earthquake provides an unprecedented test of the extent to which Coulomb stress transfer governs the triggering of aftershocks. During 11-31 March, there were 177 aftershocks with focal mechanisms, and so the Coulomb stress change imparted by the rupture can be resolved on the aftershock nodal planes to learn whether they were brought closer to failure. Numerous source models for the mainshock have been inverted from seismic, geodetic, and tsunami observations. Here, we show that, among six tested source models, there is a mean 47% gain in positively-stressed aftershock mechanisms over that for the background (1997-10 March 2011) earthquakes, which serve as the control group. An aftershock fault friction of 0.4 is found to fit the data better than 0.0 or 0.8, and among all the tested models, Wei and Sladen (2011) produced the largest gain, 63%. We also calculate that at least 5 of the seven large, exotic, or remote aftershocks were brought ≥0.3 bars closer to failure. With these tests as confirmation, we calculate that large sections of the Japan trench megathrust, the outer trench slope normal faults, the Kanto fragment beneath Tokyo, and the Itoigawa-Shizuoka Tectonic Line, were also brought ≥0.3 bars closer to failure.
Criterion Referenced Measures for Clinical Evaluations.
Pikulski, John J.
This paper discusses criterion referenced tests' characteristics and their use in clinical evaluation. The distinction between diagnostic tests and criterion referenced measures is largely a matter of emphasis. Some authorities believe that in diagnostic testing the emphasis is upon an evaluation of an individual's strengths and weaknesses in…
ON A GENERALIZED GAUSS CONVERGENCE CRITERION
ILEANA BUCUR
2015-07-01
Full Text Available In this paper we combine the well known Raabe-Duhamel, Kummer, Bertrand . . . criterions of convergence for series with positive terms and we obtain a new one which is more powerful than those cited before. Even the famous Gauss criterion,which was in fact our starting point, is a consequence of this new convergence test.
Wingate, Robert J.
2012-01-01
After the launch scrub of Space Shuttle mission STS-133 on November 5, 2010, large cracks were discovered in two of the External Tank intertank stringers. The NASA Marshall Space Flight Center, as managing center for the External Tank Project, coordinated the ensuing failure investigation and repair activities with several organizations, including the manufacturer, Lockheed Martin. To support the investigation, the Marshall Space Flight Center formed an ad-hoc stress analysis team to complement the efforts of Lockheed Martin. The team undertook six major efforts to analyze or test the structural behavior of the stringers. Extensive finite element modeling was performed to characterize the local stresses in the stringers near the region of failure. Data from a full-scale tanking test and from several subcomponent static load tests were used to confirm the analytical conclusions. The analysis and test activities of the team are summarized. The root cause of the stringer failures and the flight readiness rationale for the repairs that were implemented are discussed.
刘宇; 张肖宁; 薛忠军
2007-01-01
Fracture resistance of three kinds of stress absorbing layers were evaluated based on the J-integral theory of elasticity-plasticity fracture mechanics by semi-circular bending test, and the critical fracture resistance were compared with relative study. It is shown that gap gradation stress absorbing layer has the better fracture resistance. The results indicate that the critical fracture resistance-jCis appropriate to appraise the fracture resistance of stress absorbing layer, and the gap gradation asphalt mixtures with skeleton structure and full asphalt binders can increase its fracture resistance.%应用弹塑性断裂力学J积分理论,采用半圆弯曲试验评价了3种级配应力吸收层的抗裂性能,发现采用断级配设计的应力吸收层具有良好的抗裂性能,结果表明断裂韧度JC可以用来评价应力吸收层的抗裂性能,由丰富沥青胶浆填充断级配骨架结构的级配设计,可以提高沥青混合料的抗裂能力.
Simulation of failure process of jointed rock
无
2008-01-01
A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock.In the proposed algorithm,by using the Monte-Carlo technique,random joint network was generated in the domain of interest.Based on the joint network,the triangular DDA block system was automatically generated by adopting the advanced front method.In the process of generating blocks,numerous artificial joints came into being,and once the stress states at some artificial joints satisfy the failure criterion given beforehand,artificial joints will turn into real joints.In this way,the whole fragmentation process of rock mass can be replicated.The algorithm logic was described in detail,and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints.From the numerical results,it can be found that the crack initiates from the crack tip,the growth direction of the crack depends upon the loading and constraint conditions,and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.
SIF-based fracture criterion for interface cracks
Ji, Xing
2016-06-01
The complex stress intensity factor K governing the stress field of an interface crack tip may be split into two parts, i.e., hat{K} and s^{-iɛ}, so that K=hat{K}s^{-iɛ}, s is a characteristic length and ɛ is the oscillatory index. hat{K} has the same dimension as the classical stress intensity factor and characterizes the interface crack tip field. That means a criterion for interface cracks may be formulated directly with hat{K}, as Irwin (ASME J. Appl. Mech. 24:361-364, 1957) did in 1957 for the classical fracture mechanics. Then, for an interface crack, it is demonstrated that the quasi Mode I and Mode II tip fields can be defined and distinguished from the coupled mode tip fields. Built upon SIF-based fracture criteria for quasi Mode I and Mode II, the stress intensity factor (SIF)-based fracture criterion for mixed mode interface cracks is proposed and validated against existing experimental results.
Li Zhang
2016-07-01
Full Text Available Peroxisome proliferator-activated receptor α (PPARα is a key regulator to ameliorate liver injury in cases of acute liver failure (ALF. However, its regulatory mechanisms remain largely undetermined. Endoplasmic reticulum stress (ER stress plays an important role in a number of liver diseases. This study aimed to investigate whether PPARα activation inhibits ER stress-induced hepatocyte apoptosis, thereby protecting against ALF. In a murine model of D-galactosamine (D-GalN- and lipopolysaccharide (LPS-induced ALF, Wy-14643 was administered to activate PPARα, and 4-phenylbutyric acid (4-PBA was administered to attenuate ER stress. PPARα activation ameliorated liver injury, because pre-administration of its specific inducer, Wy-14643, reduced the serum aminotransferase levels and preserved liver architecture compared with that of controls. The protective effect of PPARα activation resulted from the suppression of ER stress-induced hepatocyte apoptosis. Indeed, (1 PPARα activation decreased the expression of glucose-regulated protein 78 (Grp78, Grp94 and C/EBP-homologous protein (CHOP in vivo; (2 the liver protection by 4-PBA resulted from the induction of PPARα expression, as 4-PBA pre-treatment promoted upregulation of PPARα, and inhibition of PPARα by small interfering RNA (siRNA treatment reversed liver protection and increased hepatocyte apoptosis; (3 in vitro PPARα activation by Wy-14643 decreased hepatocyte apoptosis induced by severe ER stress, and PPARα inhibition by siRNA treatment decreased the hepatocyte survival induced by mild ER stress. Here, we demonstrate that PPARα activation contributes to liver protection and decreases hepatocyte apoptosis in ALF, particularly through regulating ER stress. Therefore, targeting PPARα could be a potential therapeutic strategy to ameliorate ALF.
Liu, Dong'an; Peng, Linfa; Lai, Xinmin
In practice, the assembly error of the bipolar plate (BPP) in a PEM fuel cell stack is unavoidable based on the current assembly process. However its effect on the performance of the PEM fuel cell stack is not reported yet. In this study, a methodology based on FEA model, "least squares-support vector machine (LS-SVM)" simulation and statistical analysis is developed to investigate the effect of the assembly error of the BPP on the pressure distribution and stress failure of membrane electrode assembly (MEA). At first, a parameterized FEA model of a metallic BPP/MEA assembly is established. Then, the LS-SVM simulation process is conducted based on the FEA model, and datasets for the pressure distribution and Von Mises stress of MEA are obtained, respectively for each assembly error. At last, the effect of the assembly error is obtained by applying the statistical analysis to the LS-SVM results. A regression equation between the stress failure and the assembly error is also built, and the allowed maximum assembly error is calculated based on the equation. The methodology in this study is beneficial to understand the mechanism of the assembly error and can be applied to guide the assembly process for the PEM fuel cell stack.
Ground stress and its impact on the stability of the surrounding rock in the Lüliang mining area
Wang Lianguo; Lu Yinlong
2011-01-01
Ground stress is the fundamental cause of deformation and failure during underground structural engineering.Field stress measurements in the main coal bed in the Lüliang mining area were made by the bore hole,stress relief method.From these data the ground stress distribution of the mining area was obtained.The relationship between the horizontal principal stress and the deformation and failure of a roadway is discussed with an engineering example.The results indicate that horizontal stress dominates in the shallow crust in the Lüliang mining area.Roadways at different angles to the maximum principal stress have different levels of stress concentration.This leads to a significant difference in stability of the corresponding roadways.These research results provide an important criterion for determining roadway position and direction,stope layout,and roadway support design.
章顺虎; 赵德文; 陈晓东
2015-01-01
In order to overcome the nonlinearity of Mises criterion, a new linear yield criterion with a dodecagon shape of the same perimeter as Mises criterion was derived by means of geometrical analysis. Its specific plastic work rate expressed as a linear function of the yield stress, the maximum and minimum strains was also deduced and compared with that of Mises criterion. The physical meaning of the proposed yield criterion is that yielding of materials begins when the shear yield stress τs reaches the magnitude of 0.594σs. By introducing the Lode parameter, validation of evolution expressions of the proposed yield criterion with those based on Tresca, Mises and TSS criteria as well as available classical yield experimental results of various metals shows that the present results intersect with Mises results and coincide well with experimental data. Moreover, further application to the limit analysis of circle plate as an example is performed to demonstrate the effectiveness of the proposed yield criterion, and the subsequent comparison of limit loads with the Tresca analytical solutions and Mises numerical results shows that the present results are higher than the Tresca analytical results, and are in good agreement with the Mises numerical results.
Kucerova, A; Ibrahimbegovic, A; Zeman, J; Bittnar, Z
2009-01-01
In Part I of this paper we have presented a simple model capable of describing the localized failure of a massive structure. In this part, we discuss the identification of the model parameters from two kinds of experiments: a uniaxial tensile test and a three-point bending test. The former is used only for illustration of material parameter response dependence, and we focus mostly upon the latter, discussing the inverse optimization problem for which the specimen is subjected to a heterogeneous stress field.
Generalized non-linear strength theory and transformed stress space
YAO Yangping; LU Dechun; ZHOU Annan; ZOU Bo
2004-01-01
Based on the test data of frictional materials and previous research achievements in this field, a generalized non-linear strength theory (GNST) is proposed. It describes non-linear strength properties on the π-plane and the meridian plane using a unified formula, and it includes almost all the present non-linear strength theories, which can be used in just one material. The shape of failure function of the GNST is a smooth curve between the SMP criterion and the Mises criterion on the π-plane, and an exponential curve on the meridian plane. Through the transformed stress space based on the GNST, the combination of the GNST and various constitutive models using p and q as stress parameters can be realized simply and rationally in three-dimensional stress state.
Concrete Failure Modeling Based on Micromechanical Approach Subjected to Static Loading
Endah Wahyuni
2010-02-01
Full Text Available In this paper, a micromechanical model based on the Mori-Tanaka method and the spring-layer model is developed to study the stress-strain behavior of concrete. The concrete is modeled as a two-phase composite. And the failure of concrete is categorized as mortar failure and interface failure. The research presents a method for estimating the modulus of concrete under its whole loading process. The proposed micromechanical model owns the good capabilities for predicting the entire response of concrete under uniaxial compression. It is suitable that tensile strain is as the criterion of concrete failure and the prediction of crack direction also fits with experimental phenomenon.
Stephenson, R. A.; Ershov, A.
2001-12-01
One way in which theoretical rheological models of the lithosphere can be constrained by geological data is through estimations of the lithosphere's integrated strength. When an applied force exceeds this, then the lithosphere should lose its integrity and undergo irreversible deformation (WLF - "whole lithosphere failure"). The geological expression of this kind of deformational regime is the development of rifts (in extension) and inverted structures (in compression). By considering intracratonic structures rather than marginal ones it is possible to exclude additional extraneous influences and infer the net effect of intraplate stresses. Here, actual intraplate structures are considered in terms of a rheological model in which the non-brittle part of the lithosphere deforms viscously (by creep) in response to applied forces. This is in contrast to conventional estimations of total lithosphere strength based on "yield stress envelopes" in which "ductile" deformation is taken to be time-invariant (plastic). Taking into account the implications of adopting a viscous rheology in place of a plastic one in evaluating the "strength" of the lithosphere, it is necessary to incorporate the time-dependence of stresses, strains and strain rates and also the dependence of the bulk strain rate on the total applied force. This means that the duration of loading of tectonic forces prior to eventual rifting or inversion is also an important model variable. The mechanism that controls strain rate and stress distribution in the lithosphere prior to WLF in the model is one of stress redistribution from ductile deformation zones into elastic ones, as determined by stress relaxation in the former and stress amplification in the latter given an assumed constant applied boundary force. A stable equilibrium regime of deformation occurs when, at each point within the lithosphere, the stress reduction effected by viscous relaxation equals the stress increase effected by the applied force
Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei
2015-02-01
An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.
Dennis Lau; Y. S. Chan; S. W. Ricky Lee; Lifeng Fu; Yuming Ye; Sang Liu
2007-01-01
Reliability test is a very important step for any electronic products before they can be sold to the market. In the previous decades, various types of test have been developed. One of the widely used testing methods is the board bending test. A major issue of performing a reliability test is that numbers of testing samples are required since the test has to be repeated until consistent and satisfactory results can be obtained. A long time will be spent on the specimen design, the assembly processes and the testing procedures. In case the reliability test is not satisfied, the specimen will need to be redesigned,reproduced and retested. This is costly and not efficient from the commercial point of view. To simplify the reliability testing process, computational simulation is proposed to predict the reliability of printed circuit board assemblies (PCBA) at the early design stage. In the present study, 3-point bending test is the reliability test adopted. Finite element model validation and two case studies regarding the application of the model are the objectives of this work.Comparison between experimental results and computational results is carried out for model validation. The physical properties (stiffness and strain) of the model show a good agreement with the experiments at both the elastic deformation stage and the plastic deformation stage under the 3-point bending condition. The maximum von Mises stress at the solder joints of the model at which the samples are found to be failed is also very close to the strength of the solder. This further validates the model. For application, this stress data is used as a failure criterion to indicate whether a PCBA is reliable under different bending conditions.In the first study case, the stress analysis methodology is used to investigate the reliability of a PCBA with increased printed circuit board (PCB) thickness. The corresponding models are built and through the stress analysis on solder joints, the maximum
Optimization of the Structures at Shakedown and Rosen's Optimality Criterion
Alawdin, Piotr; Atkociunas, Juozas; Liepa, Liudas
2016-09-01
Paper focuses on the problems of application of extreme energy principles and nonlinear mathematical programing in the theory of structural shakedown. By means of energy principles, which describes the true stress-strain state conditions of the structure, the dual mathematical models of analysis problems are formed (static and kinematic formulations). It is shown how common mathematical model of the structures optimization at shakedown with safety and serviceability constraints (according to the ultimate limit state (ULS) and serviceability limit state (SLS) requirements) on the basis of previously mentioned mathematical models is formed. The possibilities of optimization problem solution in the context of physical interpretation of optimality criterion of Rosen's algorithm are analyzed.
Wittmann, K.; Mueller, H.; Macherauch, E. (Karlsruhe Univ. (T.H.) (Germany, F.R.). Inst. fuer Werkstoffkunde 1)
1989-01-01
For quantitative acquisition of the influence of surface decarburizing phenomena on the failure of construction parts under cyclic stress different surface decarburization stages were generated in the steels 42CrMo4 and 100Cr6. After construction part-specific thermal treatment the generated states of residual stress were then determined and life span-oriented fatigue tests were conducted. The studies showed that already a small decarburization in martensitic material conditions of the steels 42CrMo4 and 100Cr6 led to a reduction of the alternating bending strength. The decrease of alternate strength can be associated with the micro-notch effects caused by the internal oxides formed by surface oxidation and/or the residual tension stress developed during the hardening in sub-surface sample areas. Decarburization degrees of more than 50% cause a noticeable decrease of surface stability, an increase of residual tension stresses close to the surface and as a result a pronounced decrease in the alternating bending strength. Fracture surface investigations with scanning electron microscope showed that partially decarburized and surface-oxidized alternating bending samples create many incipient cracks which will initiate the break. (orig./MM).
Damien Vitiello
2014-01-01
Full Text Available Background. Changes in cardiopulmonary reserve and biomarkers related to wall stress, inflammation, and oxidative stress concomitantly with the evaluation of peripheral arterial blood flow have not been investigated in patients with heart failure with preserved ejection fraction (HFpEF compared with healthy subjects (CTL. Methods and Results. Eighteen HFpEF patients and 14 CTL were recruited. Plasma levels of inflammatory and oxidative stress biomarkers were measured at rest. Brain natriuretic peptide (BNP was measured at rest and peak exercise. Cardiopulmonary reserve was assessed using an exercise protocol with gas exchange analyses. Peripheral arterial blood flow was determined by strain gauge plethysmography. Peak VO2 (12.0±0.4 versus 19.1±1.1 mL/min/kg, P<0.001 and oxygen uptake efficiency slope (1.55±0.12 versus 2.06±0.14, P<0.05 were significantly decreased in HFpEF patients compared with CTL. BNP at rest and following stress, C-reactive-protein, interleukin-6, and TBARS were significantly elevated in HFpEF. Both basal and posthyperemic arterial blood flow were not significantly different between the HFpEF patients and CTL. Conclusions. HFpEF exhibits a severe reduction in cardiopulmonary reserve and oxygen uptake efficiency concomitantly with an elevation in a broad spectrum of biomarkers confirming an inflammatory and prooxidative status in patients with HFpEF.
无
2010-01-01
The unified solutions are presented for stresses and displacements around a circular tunnel subjected to a hydrostatic stress field.The rock mass is assumed to be elastic-brittle-plastic and governed by the Unified Strength Theory.The displacements are obtained accounting for three different definitions for elastic strains and different Young’s modulus in the plastic zone.The unified solutions obtained in this paper are especially versatile in reflecting the intermediate principal stress effect to different extents for different materials.The conventional solutions,based on the Mohr-Coulomb failure criterion and the Generalized Twin Shear Stress yield criterion,are special cases of the present unified solutions.The new unified solutions can compare with those computed by the latest generalized Hoek-Brown failure criterion.The results obtained demonstrate the importance of the intermediate principal stress influence for the stresses and displacements analysis.The effects of different definitions for elastic strains and different Young’s modulus in the plastic zone on the displacements are significant.
Camilla Ronchei
2015-10-01
Full Text Available The modified Carpinteri-Spagnoli (C-S criterion is a multiaxial high-cycle fatigue criterion based on the critical plane approach. According to such a criterion, the orientation of the critical plane is linked to both the averaged directions of the principal stress axes and the fatigue properties of the material. The latter dependence is taken into account through a rotational angle, . Then, the multiaxial fatigue strength estimation is performed by computing an equivalent stress amplitude on the critical plane. In the present paper, some modifications of the original expression are implemented in the modified C-S criterion. More precisely, such modified expressions of depend on the ratio between the fatigue limit under fully reversed shear stress and that under fully reversed normal stress (in accordance with the original expression, and can be employed for metals ranging from mild to very hard fatigue behaviour. Some experimental data available in the literature are compared with the theoretical results in order to verify if the modified expressions are able to improve the fatigue strength estimation capability of the modified C-S criterion
ZHANG Jianyu; SHAN Meijuan; ZHAO Libin; FEI Binjun
2015-01-01
An average failure index method based on accurate FEA was proposed for the tensile strength prediction of composite out-of-plane adhesive-bondedπjoints. Based on the simple and independent maximum stress failure criterion, the failure index was introduced to characterize the degree of stress components close to their corresponding material strength. With a brief load transfer analysis, the weak fillers were prominent and further detailed discussion was performed. The maximum value among the average failure indices which were related with different stress components was filtrated to represent the failure strength of the critical surface, which is either the two curved upside surfaces or the bottom plane of the fillers for compositeπjoints. The tensile strength of three kinds ofπjoints with different material systems, configurations and lay-ups was predicted by the proposed method and corresponding experiments were conducted. Good agreements between the numerical and experimental results give evidence of the effectiveness of the proposed method. In contrast to the existed time-consuming strength prediction methods, the proposed method provides a capability of quickly assessing the failure of complex out-of-plane joints and is easy and convenient to be widely utilized in engineering.
Constitutive behavior and progressive mechanical failure of electrodes in lithium-ion batteries
Zhang, Chao; Xu, Jun; Cao, Lei; Wu, Zenan; Santhanagopalan, Shriram
2017-07-01
The electrodes of lithium-ion batteries (LIB) are known to be brittle and to fail earlier than the separators during an external crush event. Thus, the understanding of mechanical failure mechanism for LIB electrodes (anode and cathode) is critical for the safety design of LIB cells. In this paper, we present experimental and numerical studies on the constitutive behavior and progression of failure in LIB electrodes. Mechanical tests were designed and conducted to evaluate the constitutive properties of porous electrodes. Constitutive models were developed to describe the stress-strain response of electrodes under uniaxial tensile and compressive loads. The failure criterion and a damage model were introduced to model their unique tensile and compressive failure behavior. The failure mechanism of LIB electrodes was studied using the blunt rod test on dry electrodes, and numerical models were built to simulate progressive failure. The different failure processes were examined and analyzed in detail numerically, and correlated with experimentally observed failure phenomena. The test results and models improve our understanding of failure behavior in LIB electrodes, and provide constructive insights on future development of physics-based safety design tools for battery structures under mechanical abuse.
MOUNIR eCHENNAOUI
2016-03-01
Full Text Available The aim of this study was to evaluate stress markers, mood states and sleep indicators in high-level swimmers during a major 7-days competition according to the outcomes. Nine swimmers (6 men and 3 women (age: 22 ± 2 years and 22 ± 4 years, respectively were examined. Before (PRE and after (POST each race (series, semi-finals and finals, salivary concentrations of cortisol, α-amylase (sAA and chromogranin-A (CgA were determined. Mood states were assessed by the profile of mood state (POMS questionnaire completed before and after the 7-days, and self-reported sleep diaries were completed daily. In the failure group, cortisol and sAA significantly increased between PRE-POST measurements (p<0.05, while sCgA was not changed. Significant overall decrease of cortisol (-52.6% and increase of sAA (+68.7% was shown in the failure group. In this group, fatigue, confusion and depression scores and sleep duration before the finals increased. The results in the success group show tendencies for increased cortisol and sCgA concentrations in response to competition, while sAA was not changed. Cortisol levels before the semi-finals and finals and sCgA levels before the finals were positively correlated to the fatigue score in the failure group only (r=0.89. sAA levels before and after the semi-finals were negatively correlated to sleep duration measured in the subsequent night (r=-0.90. In conclusion, the stress of the competition could trigger a negative mood profile and sleep disturbance which correspond to different responses of biomarkers related to the hypothalamo-pituitary-adrenal axis and the sympathetic nervous system activity, cortisol, sAA and CgA.
Amaral, Rui; Teixeira, Pedro; Azinpour, Erfan; Santos, Abel D.; César de Sá, J.
2016-08-01
In this work, experimental tests were carried out, under different loading conditions, in order to assess different ductile failure criteria, namely based on GTN, Johnson-Cook or Lemaitre models and to establish new proposals for improvement. Corresponding characterization for damage parameters is performed by an inverse analysis procedure, using reference experimental tests. Numerical simulations of a cross-shaped component are considered for the damage models, and results show a similar trend related with the experimental fracture evidence.
Cen, Duofeng; Huang, Da
2017-06-01
Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.
Sukumaran, Vijayakumar; Watanabe, Kenichi; Veeraveedu, Punniyakoti T.; Gurusamy, Narasimman; Ma, Meilei; Thandavarayan, Rajarajan A.; Lakshmanan, Arun Prasath; Yamaguchi, Ken'ichi; Suzuki, Kenji; Kodama, Makoto
2011-01-01
Studies have demonstrated that angiotensin II has been involved in immune and inflammatory responses which might contribute to the pathogenesis of immune-mediated diseases. Recent evidence suggests that oxidative stress may play a role in myocarditis. Here, we investigated whether olmesartan, an AT1R antagonist protects against experimental autoimmune myocarditis (EAM) by suppression of oxidative stress, endoplasmic reticulum (ER) stress and inflammatory cytokines. EAM was induced in Lewis rats by immunization with porcine cardiac myosin, were divided into two groups and treated with either olmesartan (10 mg/kg/day) or vehicle for a period of 21 days. Myocardial functional parameters measured by hemodynamic and echocardiographic analyses were significantly improved by the treatment with olmesartan compared with those of vehicle-treated rats. Treatment with olmesartan attenuated the myocardial mRNA expressions of proinflammatory cytokines, [Interleukin (IL)-1β, monocyte chemoattractant protein-1, tumor necrosis factor-α and interferon-γ)] and the protein expression of tumor necrosis factor-α compared with that of vehicle-treated rats. Myocardial protein expressions of AT1R, NADPH oxidase subunits (p47phox, p67phox, gp91phox) and the expression of markers of oxidative stress (3-nitrotyrosine and 4-hydroxy-2-nonenal), and the cardiac apoptosis were also significantly decreased by the treatment with olmesartan compared with those of vehicle-treated rats. Furthermore, olmesartan treatment down-regulated the myocardial expressions of glucose regulated protein-78, growth arrest and DNA damage-inducible gene, caspase-12, phospho-p38 mitogen-activated protein kinase (MAPK) and phospho-JNK. These findings suggest that olmesartan protects against EAM in rats, at least in part via suppression of oxidative stress, ER stress and inflammatory cytokines. PMID:21383952
Experimental and ﬁnite element analysis of fracture criterion in general yielding fracture mechanics
D M Kulkarni; Ravi Prakash; A N Kumar
2002-12-01
Efforts made over the last three decades to understand the fracture behaviour of structural materials in elastic and elasto-plastic fracture mechanics are numerous, whereas investigations related to fracture behaviour of materials in thin sheets or general yielding fracture regimes are limited in number. Engineering simulative tests are being used to characterize formability and drawability of sheet metals. However, these tests do not assure consistency in quality of sheet metal products. The prevention of failure in stressed structural components currently requires fracture mechanics based design parameters like critical load, critical crack-tip opening displacement or fracture toughness. The present attempt would aim to fulﬁll this gap and generate more information thereby increased understanding on fracture behaviour of sheet metals. In the present investigation, using a recently developed technique for determining fracture criteria in sheet metals, results are generated on critical CTOD and fracture toughness. Finite element analysis was performed to support the results on various fracture parameters. The differences are within 1 to 4%. At the end it is concluded that magnitude of critical CTOD and/or critical load can be used as a fracture criterion for thin sheets.
Multiaxial fatigue criterion based on parameters from torsion and axial S-N curve
M. Margetin
2016-07-01
Full Text Available Multiaxial high cycle fatigue is a topic that concerns nearly all industrial domains. In recent years, a great deal of recommendations how to address problems with multiaxial fatigue life time estimation have been made and a huge progress in the field has been achieved. Until now, however, no universal criterion for multiaxial fatigue has been proposed. Addressing this situation, this paper offers a design of a new multiaxial criterion for high cycle fatigue. This criterion is based on critical plane search. Damage parameter consists of a combination of normal and shear stresses on a critical plane (which is a plane with maximal shear stress amplitude. Material parameters used in proposed criterion are obtained from torsion and axial S-N curves. Proposed criterion correctly calculates life time for boundary loading condition (pure torsion and pure axial loading. Application of proposed model is demonstrated on biaxial loading and the results are verified with testing program using specimens made from S355 steel. Fatigue material parameters for proposed criterion and multiple sets of data for different combination of axial and torsional loading have been obtained during the experiment.
Bowles, David E.; Griffin, O. H., Jr.
1991-01-01
A micromechanics analysis is used to study the effects of constituent properties on thermally induced stresses in continuous fiber reinforced composites. A finite element formulation is described, and results are presented for unidirectional carbon/epoxy laminates. It is shown that significant stresses develop in composites exposed to thermal excursions typical of spacecraft operating environments and that the fiber thermoelastic properties have a minimal effect on the magnitude of these stresses. The finite element micromechanics analysis is then extended to the study of multidirectional laminates using a simple global/local formulation. Damage initiation predictions are compared with experimental data, and factors controlling the initiation of damage are identified. Ways of improving the durability of composites are discussed.
Wei, Shun-Guang; Yu, Yang; Weiss, Robert M; Felder, Robert B
2016-10-01
We previously reported that endoplasmic reticulum (ER) stress is induced in the subfornical organ (SFO) and the hypothalamic paraventricular nucleus (PVN) of heart failure (HF) rats and is reduced by inhibition of mitogen-activated protein kinase (MAPK) signaling. The present study further examined the relationship between brain MAPK signaling, ER stress, and sympathetic excitation in HF. Sham-operated (Sham) and HF rats received a 4-wk intracerebroventricular (ICV) infusion of vehicle (Veh) or the ER stress inhibitor tauroursodeoxycholic acid (TUDCA, 10 μg/day). Lower mRNA levels of the ER stress biomarkers GRP78, ATF6, ATF4, and XBP-1s in the SFO and PVN of TUDCA-treated HF rats validated the efficacy of the TUDCA dose. The elevated levels of phosphorylated p44/42 and p38 MAPK in SFO and PVN of Veh-treated HF rats, compared with Sham rats, were significantly reduced in TUDCA-treated HF rats as shown by Western blot and immunofluorescent staining. Plasma norepinephrine levels were higher in Veh-treated HF rats, compared with Veh-treated Sham rats, and were significantly lower in the TUDCA-treated HF rats. TUDCA-treated HF rats also had lower mRNA levels for angiotensin converting enzyme, angiotensin II type 1 receptor, tumor necrosis factor-α, interleukin-1β, cyclooxygenase-2, and NF-κB p65, and a higher mRNA level of IκB-α, in the SFO and PVN than Veh-treated HF rats. These data suggest that ER stress contributes to the augmented sympathetic activity in HF by inducing MAPK signaling, thereby promoting inflammation and renin-angiotensin system activity in key cardiovascular regulatory regions of the brain.
A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions
ukasz Pejkowski; Dariusz Skibicki
2016-01-01
This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The cri-terion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S–N curves: tension–compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promis-ing. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the non-proportionality of loading.
Filamentary and hierarchical pictures - Kinetic energy criterion
Klypin, Anatoly A.; Melott, Adrian L.
1992-01-01
We present a new criterion for formation of second-generation filaments. The criterion called the kinetic energy ratio, KR, is based on comparison of peculiar velocities at different scales. We suggest that the clumpiness of the distribution in some cases might be less important than the 'coldness' or 'hotness' of the flow for formation of coherent structures. The kinetic energy ratio is analogous to the Mach number except for one essential difference. If at some scale KR is greater than 1, as estimated at the linear stage, then when fluctuations of this scale reach nonlinearity, the objects they produce must be anisotropic ('filamentary'). In the case of power-law initial spectra the kinetic ratio criterion suggests that the border line is the power-spectrum with the slope n = -1.
Aesthetical criterion in art and science
Milovanović, Miloš
2016-01-01
In the paper, the authors elaborate some recently published research concerning the originality of artworks in terms of self-organization in the complex systems physics. It has been demonstrated that the originality issue such conceived leads to the criterion of a substantial aesthetics whose applicability is not restricted to the fine arts domain only covering also physics, biology, cosmology and other fields construed in the complex systems terms. Moreover, it is about a truth criterion related to the traditional personality conception revealing the ontological context transcendent to the gnoseological dualism of subjective and objective reality that is characteristic of modern science and humanities. Thus, it is considered to be an aesthetical criterion substantiating art and science as well as the other developments of the postmodern era. Its impact to psychology, education, ecology, culture and other humanities is briefly indicated.
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... sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health
Kyoung-Im Cho
2014-08-01
Full Text Available Increased atrial oxidative stress has an important role in inducing and maintaining atrial fibrillation (AF, and the activation of the small GTPase Rac1 contributes to the oxidative stress. We investigated the relationship of Rac1, atrial endothelial thromboprotective markers and AF inducibility and if simvastatin has a potential beneficial effect on a myocardial infarction (MI-induced heart failure (HF rat model. Rats were randomized into three groups (shams, MI group and simvastatin treatment group and underwent echocardiography, AF induction studies and left atrial (LA fibrosis analysis. Atrial Rac 1, sodium calcium exchanger (INCX, sarcoplasmic reticulum calcium ATPase (SERCA, endothelial nitric oxide synthase (eNOS and induced nitric oxide synthase (iNOS were measured. AF inducibility, AF duration and LA fibrosis were significantly higher in the MI group (p < 0.001 vs. sham, which were significantly reduced by simvastatin (p < 0.05 vs. MI. The reduced expressions of atrial eNOS, SERCA, thrombomodulin, tissue factor pathway inhibitor and tissue plasminogen activator in the MI group were significantly improved by simvastatin. Furthermore, the increased expression of atrial iNOS, INCX and Rac1 activity were significantly decreased by the simvastatin. Oxidative stress, endothelial dysfunction and thrombogenicity are associated with the promotion of AF in a rat model of ischemic HF. These were associated with increased Rac1 activity, and simvastatin treatment prevents these changes.
Force criterion of different electrolytes in microchannel
Ren Yu-Kun; Yan Hui; Jiang Hong-Yuan; Gu Jian-Zhong; Antonio Ramos
2009-01-01
The control and handling of fluids is central to many applications of the lab-on-chip. This paper analyzes the basic theory of manipulating different electrolytes and finds the two-dimensional model. Coulomb force and dielectric force belonging to the body force of different electrolytes in the microchannel were analyzed. The force criterion at the interface was concluded, and testified by the specific example. Three basic equations were analyzed and applied to simulate the phenomenon. The force criterion was proved to be correct based on the simulation results.
Position Mooring Control Based on a Structural Reliability Criterion
Fang, Shaoji; Leira, Bernt J.; Blanke, Mogens
2013-01-01
is achieved using structural reliability indices in a cost function, where both the mean mooring-line tension and dynamic effects are considered. An optimal set-point is automatically produced without need for manual interaction. The parameters of the extreme value distribution are calculated on-line thereby...... adapting the set-point calculations to the prevailing environment. In contrast to earlier approaches, several mooring line are simultaneously accounted for by the algorithm, not only the most critical one. Detailed simulations illustrate the features of the new method and it is shown that the structural...... reliability criterion based algorithm ensures the safety of mooring lines in a variety of external environmental conditions and also in situations of failure of a single line....
An aerodynamic load criterion for airships
Woodward, D. E.
1975-01-01
A simple aerodynamic bending moment envelope is derived for conventionally shaped airships. This criterion is intended to be used, much like the Naval Architect's standard wave, for preliminary estimates of longitudinal strength requirements. It should be useful in tradeoff studies between speed, fineness ratio, block coefficient, structure weight, and other such general parameters of airship design.
Stability Criterion for Discrete-Time Systems
K. Ratchagit
2010-01-01
Full Text Available This paper is concerned with the problem of delay-dependent stability analysis for discrete-time systems with interval-like time-varying delays. The problem is solved by applying a novel Lyapunov functional, and an improved delay-dependent stability criterion is obtained in terms of a linear matrix inequality.
A Criterion-Referenced Test for Archery.
Shifflett, Bethany; Schuman, Barbara J.
1982-01-01
A criterion-referenced test for a beginning archery class was developed and evaluated. Techniques for estimating test validity and reliability were applied to data. A method developed by R. A. Burk (1976) was used to establish a cutoff score that would distinguish between those mastering the class and nonmasters. (Authors/PP)
Luoyang Dual Spatial Criterion Ecological City Construction
Wang Fazeng; Wang Shengnan
2007-01-01
The construction of an ecological city has two foundational platforms:the small platform,namely urban district or simply called as"city ecosystem";and the big platform,namely around city district in certain region scope or also referred to as"city-region ecosystem".The construction of an ecological city must be launched in the dual spatial criteria:in city(urban district)criterion-optimizing the city ecosystem;in city-region(city territory)criterion-optimizing the city-region ecosystem.Luoyang has the bright characteristic and the typical image within cities of China,and even in the world.The construction of anecological city in dual spatial criteria-the city and the city-region-has the vital significance to urbanization advancement and sustainable development in Luoyang.In city-region criterion,the primary mission of Luoyang's ecological city construction is to create a fine ecological environment platform in its city territory.In city criterion,the basic duty of Luoyang's ecologic city construction is to enhance the ecological capacity and benefit of the central city.
A focused information criterion for graphical models
Pircalabelu, E.; Claeskens, G.; Waldorp, L.
2015-01-01
A new method for model selection for Gaussian Bayesian networks and Markov networks, with extensions towards ancestral graphs, is constructed to have good mean squared error properties. The method is based on the focused information criterion, and offers the possibility of fitting individual-tailore
A Criterion for the Generalized Riemann Hypothesis
Jin Hong LI
2009-01-01
In this paper, we study the automorphic L-functions attached to the classical automorphic forms on GL(2), i.e. holomorphic cusp form. And we also give a criterion for the Generalized Riemann Hypothesis (GRH) for the above L-functions.
Identical Synchronous Criterion for a Coupling System
HUANGXiangao; ANOWei; LUOXinmin; ZHUFuchen
2004-01-01
A new identical synchronous criterion of a coupling system, which is the time average of the derivative of the Lyapunov function, is proposed to determine the synchronous occurrence of any coupling system. Three examples with linear or nonlinear feedback synchronous systems are introduced to test some synchronous parameters that are the conditional Lyapunov exponents, the time average of the derivative of the Lyapunov function,the mean square error of the synchronization. Having obtained the synchronous parameters with the change of the feedback gains, we discover that Pecora and Carroll's criterion and He and Vaidya's reduced criterion are only fit to determine the synchronization of the identical selfsynchronization system which is a special example in the coupling systems, and are not taken as the general identical synchronous criterion of any coupling system. However,no matter whether the largest conditional Lyapunov exponent or the derivative of the Lyapunov function is positive or negative, synchronization of the coupling systems will occur,as long as the average change ratio of the derivative of the Lyapunov function tends to zero.
A scale invariance criterion for LES parametrizations
Urs Schaefer-Rolffs
2015-01-01
Full Text Available Turbulent kinetic energy cascades in fluid dynamical systems are usually characterized by scale invariance. However, representations of subgrid scales in large eddy simulations do not necessarily fulfill this constraint. So far, scale invariance has been considered in the context of isotropic, incompressible, and three-dimensional turbulence. In the present paper, the theory is extended to compressible flows that obey the hydrostatic approximation, as well as to corresponding subgrid-scale parametrizations. A criterion is presented to check if the symmetries of the governing equations are correctly translated into the equations used in numerical models. By applying scaling transformations to the model equations, relations between the scaling factors are obtained by demanding that the mathematical structure of the equations does not change.The criterion is validated by recovering the breakdown of scale invariance in the classical Smagorinsky model and confirming scale invariance for the Dynamic Smagorinsky Model. The criterion also shows that the compressible continuity equation is intrinsically scale-invariant. The criterion also proves that a scale-invariant turbulent kinetic energy equation or a scale-invariant equation of motion for a passive tracer is obtained only with a dynamic mixing length. For large-scale atmospheric flows governed by the hydrostatic balance the energy cascade is due to horizontal advection and the vertical length scale exhibits a scaling behaviour that is different from that derived for horizontal length scales.
Valentin Bragin
2010-01-01
Full Text Available Mitochondrial dysfunction may be a principal underlying event in aging, including age-associated brain degeneration. Mitochondria provide energy for basic metabolic processes. Their decay with age impairs cellular metabolism and leads to a decline of cellular function. Alzheimer disease (AD and cerebrovascular accidents (CVAs are two leading causes of age-related dementia. Increasing evidence strongly supports the theory that oxidative stress, largely due to reactive oxygen species (ROS, induces mitochondrial damage, which arises from chronic hypoperfusion and is primarily responsible for the pathogenesis that underlies both disease processes. Mitochondrial membrane potential, respiratory control ratios and cellular oxygen consumption decline with age and correlate with increased oxidant production. The sustained hypoperfusion and oxidative stress in brain tissues can stimulate the expression of nitric oxide synthases (NOSs and brain endothelium probably increase the accumulation of oxidative stress products, which therefore contributes to blood brain barrier (BBB breakdown and brain parenchymal cell damage. Determining the mechanisms behind these imbalances may provide crucial information in the development of new, more effective therapies for stroke and AD patients in the near future.
Bhatt, R. T.; Kiser, J. D.
2017-01-01
SiC/SiC composites fabricated by melt infiltration are being considered as potential candidate materials for next generation turbine components. However these materials are limited to 2400 F application because of the presence of residual silicon in the SiC matrix. Currently there is an increasing interest in developing and using silicon free SiC/SiC composites for structural aerospace applications above 2400 F. Full PIP or full CVI or CVI + PIP hybrid SiC/SiC composites can be fabricated without excess silicon, but the upper temperature stress capabilities of these materials are not fully known. In this study, the on-axis creep and rupture properties of the state-of-the-art full CVI and full PIP SiC/SiC composites with Sylramic-iBN fibers were measured at temperatures to 2700 F in air and their failure modes examined. In this presentation creep rupture properties, failure mechanisms and upper temperature capabilities of these two systems will be discussed and compared with the literature data.
Mohr-Coulomb yield criterion in rock plastic mechanics%岩石塑性变形条件下的Mohr-Coulomb屈服准则
王红才; 赵卫华; 孙东生; 郭彬彬
2012-01-01
Conventional Mohr-Coulomb strength criterion only describing the relationship between normal stress and shear stress on the failure surface at the peak strength is used as a criterion to determine whether the rock has failed. This study expands the concept of the Mohr-Coulomb strength criterion by suggesting that the Mohr-Coulomb yield criterion can express the stress relationship of strain and stress of failure surface under various stress states after plastic deformation occurs. Based on the experimental study, an experiment approach which employs triaxial compression testing data to determine plastic parameters c and cp which vary with the internal variable k was established, and parameter expression used to assess the accuracy of isotropic modeling and some testing results were given. The Mohr-Coulomb yield criterion of isotropic hardening or softening, in which stress-strain curves of whole process is simplified into a four-line model using initial, peak and remnant parameters of rock, is more applicable than the trilinear model by Toshikazu. The result in this study provides theoretical and experimental basis for engineering and geological numerical simulation, thus being of instructive importance.%传统的Mohr-Coulomb强度准则仅描述了峰值强度状态下正应力和剪应力之间的关系,作为岩石破坏的判据.本文拓展概念,提出Mohr-Coulomb屈服准则表述岩石发生塑性变形后不同应力状态下屈服面的应力应变关系.在总结实验研究的基础上建立了使用三轴压缩试验数据确定塑性参数c和Φ随内变量κ变化的实验技术方法,给出了评价各向同性模型精度的参量表达以及某些测试结果.采用具有各向同性强(软)化规律的Mohr-Coulomb屈服准则,利用岩石的初始屈服、峰值屈服和残余屈服三组参数可以将全过程应力应变曲线简化表征为四直线模型,它比三线性模型有更广泛的适用性.本文的结果为工程地质数值模
Bridging AIC and BIC: a new criterion for autoregression
Jie Ding; Vahid Tarokh; Yuhong Yang
2015-01-01
We introduce a new criterion to determine the order of an autoregressive model fitted to time series data. It has the benefits of the two well-known model selection techniques, the Akaike information criterion and the Bayesian information criterion. When the data is generated from a finite order autoregression, the Bayesian information criterion is known to be consistent, and so is the new criterion. When the true order is infinity or suitably high with respect to the sample size, the Akaike ...
Failure Pressure Analysis of Corroded Moderate-to-High Strength Pipelines
苏晨亮; 李昕; 周晶
2016-01-01
Based on the elastic-plastic, large-deformation finite element method, burst capacity of steel pipeline with longitudinal corrosion defect subjected to internal pressure is studied. The appropriate stress-based criterion is used to predict the failure pressure of finite element model of corroded pipeline under internal pressure. By considering the pipe steel grades and geometries of corrosion defects, a series of finite element analyses is conducted. The effects of corrosion depth, length and width on burst capacity are also discussed. A specific failure pressure solution for the assessment of corrosion defects in moderate-to-high strength pipeline is proposed on the base of numerical results. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods.
Abderrahim Nemmar
2016-05-01
Full Text Available Background/Aims: Epidemiological evidence indicates that patients with chronic kidney diseases have increased susceptibility to adverse outcomes related to long-term exposure to particulate air pollution. However, mechanisms underlying these effects are not fully understood. Methods: Presently, we assessed the effect of prolonged exposure to diesel exhaust particles (DEP on chronic renal failure induced by adenine (0.25% w/w in feed for 4 weeks, which is known to involve inflammation and oxidative stress. DEP (0.5m/kg was intratracheally (i.t. instilled every 4th day for 4 weeks (7 i.t. instillation. Four days following the last exposure to either DEP or saline (control, various renal endpoints were measured. Results: While body weight was decreased, kidney weight increased in DEP+adenine versus saline+adenine or DEP. Water intake, urine volume, relative kidney weight were significantly increased in adenine+DEP versus DEP and adenine+saline versus saline. Plasma creatinine and urea increased and creatinine clearance decreased in adenine+DEP versus DEP and adenine+saline versus saline. Tumor necrosis factor α, lipid peroxidation and reactive oxygen species were significantly increased in adenine+DEP compared with either DEP or adenine+saline. The antioxidant calase was significantly decreased in adenine+DEP compared with either adenine+saline or DEP. Notably, renal DNA damage was significantly potentiated in adenine+DEP compared with either adenine+saline or DEP. Similarly, systolic blood pressure was increased in adenine+DEP versus adenine+saline or DEP, and in DEP versus saline. Histological evaluation revealed more collagen deposition, higher number of necrotic cell counts and dilated tubules, cast formation and collapsing glomeruli in adenine+DEP versus adenine+saline or DEP. Conclusion: Prolonged pulmonary exposure to diesel exhaust particles worsen renal oxidative stress, inflammation and DNA damage in mice with adenine-induced chronic
Mariana Janini Gomes
2016-01-01
Full Text Available Objective. We evaluated the influence of exercise on functional capacity, cardiac remodeling, and skeletal muscle oxidative stress, MAPK, and NF-κB pathway in rats with aortic stenosis- (AS- induced heart failure (HF. Methods and Results. Eighteen weeks after AS induction, rats were assigned into sedentary control (C-Sed, exercised control (C-Ex, sedentary AS (AS-Sed, and exercised AS (AS-Ex groups. Exercise was performed on treadmill for eight weeks. Statistical analyses were performed with Goodman and ANOVA or Mann-Whitney. HF features frequency and mortality did not differ between AS groups. Exercise improved functional capacity, assessed by maximal exercise test on treadmill, without changing echocardiographic parameters. Soleus cross-sectional areas did not differ between groups. Lipid hydroperoxide concentration was higher in AS-Sed than C-Sed and AS-Ex. Activity of antioxidant enzymes superoxide dismutase and glutathione peroxidase was changed in AS-Sed and restored in AS-Ex. NADPH oxidase activity and gene expression of its subunits did not differ between AS groups. Total ROS generation was lower in AS-Ex than C-Ex. Exercise modulated MAPK in AS-Ex and did not change NF-κB pathway proteins. Conclusion. Exercise improves functional capacity in rats with AS-induced HF regardless of echocardiographic parameter changes. In soleus, exercise reduces oxidative stress, preserves antioxidant enzyme activity, and modulates MAPK expression.
Fitrolaki, Michaela-Diana; Dimitriou, Helen; Venihaki, Maria; Katrinaki, Marianna; Ilia, Stavroula; Briassoulis, George
2016-08-01
Mammalian heat-shock-protein (HSP) 90α rapidly responses to environmental insults. We examined the hypothesis that not only serum HSP72 but also HSP90α is increased in the systemic inflammatory response syndrome (SIRS), severe-sepsis (SS), and/or sepsis (S) compared to healthy children (H); we assessed HSP90α relation to (a) multiple organ system failure (MOSF) and (b) inflammatory-metabolic response and severity of illness.A total of 65 children with S, SS, or SIRS and 25 H were included. ELISA was used to evaluate extracellular HSP90α and HSP72, chemiluminescence interleukins (ILs), flow-cytometry neutrophil-CD64 (nCD64)-expression.HSP90α, along with HSP72, were dramatically increased among MOSF patients. Patients in septic groups and SIRS had elevated HSP90α compared to H (P SIRS, and MOSF, HSP90α is related to the inflammatory stress, fever, outcome endpoints, and predicted mortality and inversely related to the low-LDL/low-HDL stress metabolic pattern.
Formability Prediction of Advanced High Strength Steel with a New Ductile Fracture Criterion
Lou, Yanshan; Lim, Sungjun; Huh, Jeehyang; Huh, Hoon
2011-08-01
A ductile fracture criterion is newly proposed to accurately predict forming limit diagrams (FLD) of sheet metals. The new ductile fracture criterion is based on the effect of the non-dimensional stress triaxiality, the stress concentration factor and the effective plastic strain on the nucleation, growth and coalescence of voids. The new ductile fracture criterion has been applied to estimate the formability of four kind advanced high strength steels (AHSS): DP780, DP980, TRIP590, and TWIP980. FLDs predicted are compared with experimental results and those predicted by other ductile fracture criteria. The comparison demonstrates that FLDs predicted by the new ductile fracture criterion are in better agreement with experimental FLDs than those predicted by other ductile fracture criteria. The better agreement of FLDs predicted by the new ductile fracture criterion is because conventional ductile fracture criteria were proposed for fracture prediction in bulk metal forming while the new one is proposed to predict the onset of fracture in sheet metal forming processes.
Fatigue criterion to system design, life and reliability: A primer
Zaretsky, Erwin V.
1992-01-01
A method for estimating a component's design survivability by incorporating finite element analysis and probabilistic material properties was developed. The method evaluates design parameters through direct comparisons of component survivability expressed in terms of Weibull parameters. The analysis was applied to a rotating disk with mounting bolt holes. The highest probability of failure occurred at, or near, the maximum shear stress region of the bolt holes. Distribution of material failure as a function of Weibull slope affects the probability of survival. Where Weibull parameters are unknown for a rotating disk, it may be permissible to assume Weibull parameters, as well as the stress-life exponent, in order to determine the qualitative effect of disk speed on the probability of survival.
Hummel, Scott L; Seymour, E Mitchell; Brook, Robert D; Kolias, Theodore J; Sheth, Samar S; Rosenblum, Hannah R; Wells, Joanna M; Weder, Alan B
2012-11-01
Recent studies suggest that oxidative stress and vascular dysfunction contribute to heart failure with preserved ejection fraction (HFPEF). In salt-sensitive HFPEF animal models, diets low in sodium and high in potassium, calcium, magnesium, and antioxidants attenuate oxidative stress and cardiovascular damage. We hypothesized that the sodium-restricted Dietary Approaches to Stop Hypertension diet (DASH/SRD) would have similar effects in human hypertensive HFPEF. Thirteen patients with treated hypertension and compensated HFPEF consumed the DASH/SRD for 21 days (all food/most beverages provided). The DASH/SRD reduced clinic systolic (155-138 mm Hg; P=0.02) and diastolic blood pressure (79-72 mm Hg; P=0.04), 24-hour ambulatory systolic (130-123 mm Hg; P=0.02) and diastolic blood pressure (67-62 mm Hg; P=0.02), and carotid-femoral pulse wave velocity (12.4-11.0 m/s; P=0.03). Urinary F2-isoprostanes decreased by 31% (209-144 pmol/mmol Cr; P=0.02) despite increased urinary aldosterone excretion. The reduction in urinary F2-isoprostanes closely correlated with the reduction in urinary sodium excretion on the DASH/SRD. In this cohort of HFPEF patients with treated hypertension, the DASH/SRD reduced systemic blood pressure, arterial stiffness, and oxidative stress. These findings are characteristic of salt-sensitive hypertension, a phenotype present in many HFPEF animal models and suggest shared pathophysiological mechanisms linking these 2 conditions. Further dietary modification studies could provide insights into the development and progression of hypertensive HFPEF.
Hamilton, Dale J; Zhang, Aijun; Li, Shumin; Cao, Tram N; Smith, Jessie A; Vedula, Indira; Cordero-Reyes, Andrea M; Youker, Keith A; Torre-Amione, Guillermo; Gupte, Anisha A
2016-03-15
Mitochondrial dysfunction has been implicated as a cause of energy deprivation in heart failure (HF). Herein, we tested individual and combined effects of two pathogenic factors of nonischemic HF, inhibition of nitric oxide synthesis [with l-N(G)-nitroarginine methyl ester (l-NAME)] and hypertension [with angiotensin II (AngII)], on myocardial mitochondrial function, oxidative stress, and metabolic gene expression. l-NAME and AngII were administered individually and in combination to mice for 5 wk. Although all treatments increased blood pressure and reduced cardiac contractile function, the l-NAME + AngII group was associated with the most severe HF, as characterized by edema, hypertrophy, oxidative stress, increased expression of Nppa and Nppb, and decreased expression of Atp2a2 and Camk2b. l-NAME + AngII-treated mice exhibited robust deterioration of cardiac mitochondrial function, as observed by reduced respiratory control ratios in subsarcolemmal mitochondria and reduced state 3 levels in interfibrillar mitochondria for complex I but not for complex II substrates. Cardiac myofibrils showed reduced ADP-supported and oligomycin-inhibited oxygen consumption. Mitochondrial functional impairment was accompanied by reduced mitochondrial DNA content and activities of pyruvate dehydrogenase and complex I but increased H2O2 production and tissue protein carbonyls in hearts from AngII and l-NAME + AngII groups. Microarray analyses revealed the majority of the gene changes attributed to the l-NAME + AngII group. Pathway analyses indicated significant changes in metabolic pathways, such as oxidative phosphorylation, mitochondrial function, cardiac hypertrophy, and fatty acid metabolism in l-NAME + AngII hearts. We conclude that l-NAME + AngII is associated with impaired mitochondrial respiratory function and increased oxidative stress compared with either l-NAME or AngII alone, resulting in nonischemic HF.
Santosh Singh
Full Text Available BACKGROUND AND PURPOSE: Liver dysfunction led hyperammonemia (HA causes a nervous system disorder; hepatic encephalopathy (HE. In the brain, ammonia induced glutamate-excitotoxicity and oxidative stress are considered to play important roles in the pathogenesis of HE. The brain ammonia metabolism and antioxidant enzymes constitute the main components of this mechanism; however, need to be defined in a suitable animal model. This study was aimed to examine this aspect in the rats with acute liver failure (ALF. METHODS: ALF in the rats was induced by intraperitoneal administration of 300 mg thioacetamide/Kg. b.w up to 2 days. Glutamine synthetase (GS and glutaminase (GA, the two brain ammonia metabolizing enzymes vis a vis ammonia and glutamate levels and profiles of all the antioxidant enzymes vis a vis oxidative stress markers were measured in the cerebral cortex and cerebellum of the control and the ALF rats. RESULTS: The ALF rats showed significantly increased levels of ammonia in the blood (HA but little changes in the cortex and cerebellum. This was consistent with the activation of the GS-GA cycle and static levels of glutamate in these brain regions. However, significantly increased levels of lipid peroxidation and protein carbonyl contents were consistent with the reduced levels of all the antioxidant enzymes in both the brain regions of these ALF rats. CONCLUSION: ALF activates the GS-GA cycle to metabolize excess ammonia and thereby, maintains static levels of ammonia and glutamate in the cerebral cortex and cerebellum. Moreover, ALF induces oxidative stress by reducing the levels of all the antioxidant enzymes which is likely to play important role, independent of glutamate levels, in the pathogenesis of acute HE.
Failure Assessment Diagram for Brazed 304 Stainless Steel Joints
Flom, Yory
2011-01-01
Interaction equations were proposed earlier to predict failure in Albemet 162 brazed joints. Present study demonstrates that the same interaction equations can be used for lower bound estimate of the failure criterion in 304 stainless steel joints brazed with silver-based filler metals as well as for construction of the Failure Assessment Diagrams (FAD).
Information criterion based fast PCA adaptive algorithm
Li Jiawen; Li Congxin
2007-01-01
The novel information criterion (NIC) algorithm can find the principal subspace quickly, but it is not an actual principal component analysis (PCA) algorithm and hence it cannot find the orthonormal eigen-space which corresponds to the principal component of input vector.This defect limits its application in practice.By weighting the neural network's output of NIC, a modified novel information criterion (MNIC) algorithm is presented.MNIC extractes the principal components and corresponding eigenvectors in a parallel online learning program, and overcomes the NIC's defect.It is proved to have a single global optimum and nonquadratic convergence rate, which is superior to the conventional PCA online algorithms such as Oja and LMSER.The relationship among Oja, LMSER and MNIC is exhibited.Simulations show that MNIC could converge to the optimum fast.The validity of MNIC is proved.
Sampling Criterion for EMC Near Field Measurements
Franek, Ondrej; Sørensen, Morten; Ebert, Hans;
2012-01-01
An alternative, quasi-empirical sampling criterion for EMC near field measurements intended for close coupling investigations is proposed. The criterion is based on maximum error caused by sub-optimal sampling of near fields in the vicinity of an elementary dipole, which is suggested as a worst......-case representative of a signal trace on a typical printed circuit board. It has been found that the sampling density derived in this way is in fact very similar to that given by the antenna near field sampling theorem, if an error less than 1 dB is required. The principal advantage of the proposed formulation is its...... parametrization with respect to the desired maximum error in measurements. This allows the engineer performing the near field scan to choose a suitable compromise between accuracy and measurement time....
Age Effects in Adaptive Criterion Learning.
Cassidy, Brittany S; Gutchess, Angela H
2016-11-01
Although prior work has examined age-related changes to criterion placement and flexibility, no study tested these constructs through a paradigm that employs adaptive feedback to encourage specific criterion changes. The goal of this study was to assess age differences in how young and older adults adapt and shift criteria in recognition memory decisions based on trial-by-trial feedback. Young and older adults completed an adaptive criterion learning paradigm. Over 3 study/test cycles, a biased feedback technique at test encouraged more liberal or strict responding by false-positive feedback toward false alarms or misses. Older adults were more conservative than young, even when feedback first encouraged a liberal response bias, and older adults adaptively placed criteria in response to biased feedback, much like young adults. After first being encouraged to respond conservatively, older adults shifted criteria less than young when feedback encouraged more lenient responding. These findings evidence labile adaptive criteria placement and criteria shifting with age. However, age-related tendencies toward conservative response biases may limit the extent to which criteria can be shifted in a lenient direction. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
An information criterion for marginal structural models.
Platt, Robert W; Brookhart, M Alan; Cole, Stephen R; Westreich, Daniel; Schisterman, Enrique F
2013-04-15
Marginal structural models were developed as a semiparametric alternative to the G-computation formula to estimate causal effects of exposures. In practice, these models are often specified using parametric regression models. As such, the usual conventions regarding regression model specification apply. This paper outlines strategies for marginal structural model specification and considerations for the functional form of the exposure metric in the final structural model. We propose a quasi-likelihood information criterion adapted from use in generalized estimating equations. We evaluate the properties of our proposed information criterion using a limited simulation study. We illustrate our approach using two empirical examples. In the first example, we use data from a randomized breastfeeding promotion trial to estimate the effect of breastfeeding duration on infant weight at 1 year. In the second example, we use data from two prospective cohorts studies to estimate the effect of highly active antiretroviral therapy on CD4 count in an observational cohort of HIV-infected men and women. The marginal structural model specified should reflect the scientific question being addressed but can also assist in exploration of other plausible and closely related questions. In marginal structural models, as in any regression setting, correct inference depends on correct model specification. Our proposed information criterion provides a formal method for comparing model fit for different specifications.
The Bohm criterion and sheath formation
Riemann, K.U. (Bochum Univ. (Germany). Inst. fuer Theoretische Physik 1)
1990-11-01
In the limit of a small Debye length ({lambda}{sub D}{yields}0) the analysis of the plasma boundary layer leads to a two scale problem of a collision free sheath and of a quasineutral presheath. Bohm's criterion expresses a necessary condition for the formation of a stationary sheath in front of a negative absorbing wall. The basic features of the plasma-sheath transition and their relation to the Bohm criterion are discussed and illustrated from a simple cold-ion fluid model. A rigorous kinetic analysis of the vicinity of the sheath edge allows to generalize Bohm's criterion acounting not only for arbitrary ion- and electron distributions, but also for general boundary conditions at the wall. It is shown that the generalized sheath condition is (apart from special exceptions) fulfilled marginally and related to a sheath edge field singularity. Due to this singularity a smooth matching of the presheath and sheath solutions requires an additional transition layer. Previous investigations concerning special problems of the plasma-sheath transition are reviewed in the light of the general relations. (orig.).
Regularization Parameter Selections via Generalized Information Criterion.
Zhang, Yiyun; Li, Runze; Tsai, Chih-Ling
2010-03-01
We apply the nonconcave penalized likelihood approach to obtain variable selections as well as shrinkage estimators. This approach relies heavily on the choice of regularization parameter, which controls the model complexity. In this paper, we propose employing the generalized information criterion (GIC), encompassing the commonly used Akaike information criterion (AIC) and Bayesian information criterion (BIC), for selecting the regularization parameter. Our proposal makes a connection between the classical variable selection criteria and the regularization parameter selections for the nonconcave penalized likelihood approaches. We show that the BIC-type selector enables identification of the true model consistently, and the resulting estimator possesses the oracle property in the terminology of Fan and Li (2001). In contrast, however, the AIC-type selector tends to overfit with positive probability. We further show that the AIC-type selector is asymptotically loss efficient, while the BIC-type selector is not. Our simulation results confirm these theoretical findings, and an empirical example is presented. Some technical proofs are given in the online supplementary material.
Social influences on adaptive criterion learning.
Cassidy, Brittany S; Dubé, Chad; Gutchess, Angela H
2015-07-01
People adaptively shift decision criteria when given biased feedback encouraging specific types of errors. Given that work on this topic has been conducted in nonsocial contexts, we extended the literature by examining adaptive criterion learning in both social and nonsocial contexts. Specifically, we compared potential differences in criterion shifting given performance feedback from social sources varying in reliability and from a nonsocial source. Participants became lax when given false positive feedback for false alarms, and became conservative when given false positive feedback for misses, replicating prior work. In terms of a social influence on adaptive criterion learning, people became more lax in response style over time if feedback was provided by a nonsocial source or by a social source meant to be perceived as unreliable and low-achieving. In contrast, people adopted a more conservative response style over time if performance feedback came from a high-achieving and reliable source. Awareness that a reliable and high-achieving person had not provided their feedback reduced the tendency to become more conservative, relative to those unaware of the source manipulation. Because teaching and learning often occur in a social context, these findings may have important implications for many scenarios in which people fine-tune their behaviors, given cues from others.
On the hodological criterion for homology.
Faunes, Macarena; Francisco Botelho, João; Ahumada Galleguillos, Patricio; Mpodozis, Jorge
2015-01-01
Owen's pre-evolutionary definition of a homolog as "the same organ in different animals under every variety of form and function" and its redefinition after Darwin as "the same trait in different lineages due to common ancestry" entail the same heuristic problem: how to establish "sameness."Although different criteria for homology often conflict, there is currently a generalized acceptance of gene expression as the best criterion. This gene-centered view of homology results from a reductionist and preformationist concept of living beings. Here, we adopt an alternative organismic-epigenetic viewpoint, and conceive living beings as systems whose identity is given by the dynamic interactions between their components at their multiple levels of composition. We posit that there cannot be an absolute homology criterion, and instead, homology should be inferred from comparisons at the levels and developmental stages where the delimitation of the compared trait lies. In this line, we argue that neural connectivity, i.e., the hodological criterion, should prevail in the determination of homologies between brain supra-cellular structures, such as the vertebrate pallium.
On the hodological criterion for homology
Macarena eFaunes
2015-06-01
Full Text Available Owen’s pre-evolutionary definition of a homologue as the same organ in different animals under every variety of form and function and its redefinition after Darwin as the same trait in different lineages due to common ancestry entail the same heuristic problem: how to establish sameness. Although different criteria for homology often conflict, there is currently a generalized acceptance of gene expression as the best criterion. This gene-centered view of homology results from a reductionist and preformationist concept of living beings. Here, we adopt an alternative organismic-epigenetic viewpoint, and conceive living beings as systems whose identity is given by the dynamic interactions between their components at their multiple levels of composition. We posit that there cannot be an absolute homology criterion, and instead, homology should be inferred from comparisons at the levels and developmental stages where the delimitation of the compared trait lies. In this line, we argue that neural connectivity, i.e., the hodological criterion, should prevail in the determination of homologies between brain supra-cellular structures, such as the vertebrate pallium.
On the hodological criterion for homology
Faunes, Macarena; Francisco Botelho, João; Ahumada Galleguillos, Patricio; Mpodozis, Jorge
2015-01-01
Owen's pre-evolutionary definition of a homolog as “the same organ in different animals under every variety of form and function” and its redefinition after Darwin as “the same trait in different lineages due to common ancestry” entail the same heuristic problem: how to establish “sameness.”Although different criteria for homology often conflict, there is currently a generalized acceptance of gene expression as the best criterion. This gene-centered view of homology results from a reductionist and preformationist concept of living beings. Here, we adopt an alternative organismic-epigenetic viewpoint, and conceive living beings as systems whose identity is given by the dynamic interactions between their components at their multiple levels of composition. We posit that there cannot be an absolute homology criterion, and instead, homology should be inferred from comparisons at the levels and developmental stages where the delimitation of the compared trait lies. In this line, we argue that neural connectivity, i.e., the hodological criterion, should prevail in the determination of homologies between brain supra-cellular structures, such as the vertebrate pallium. PMID:26157357
Kolman, D.G.; Butt, D.P.
1998-03-01
The degradation of 316 stainless steel (SS) storage container materials is a potential problem for radioactive waste disposition. Container materials will be exposed to significant ionizing radiation, elevated temperatures, embrittling and/or alloying agents (e.g., gallium), chloride-containing compounds (as much as 20 wt% Cl or Cl{sup {minus}}), oxidizing compounds, and a limited quantity of moisture. Additionally, containers will contain welds that have heterogeneous composition due to solute segregation and that may retain significant residual stress. All of the above-listed environmental and material conditions have been shown to be deleterious to material integrity under certain conditions. Unfortunately, the precise conditions within each container and environment is unknown and may vary widely from container to container. Thus, no single test or set of tests will be able mimic the broad range of storage container conditions. Additionally, material behavior cannot be predicted because the synergistic effects of temperature, time, chloride, moisture, sensitization, weldments, salt formation, etc., have not been fully studied. The complexity and uncertainty of storage conditions precludes any detailed recommendations. This document attempts to detail selected previous studies and to suggest some general guidelines for storage of radioactive waste. Because of the voluminous research in this area, this review cannot be considered to be comprehensive. Readers are directed to references that contain detailed reviews of particular processes for more information. Note that the effect of gallium on the degradation of SS storage containers has been discussed elsewhere and will not be discussed here.
Guillaume, Joseph H. A.; El Sawah, Sondoss
2014-06-01
Sustainable groundwater resource management can only be achieved if planning processes address the basic dynamics of the groundwater system. Conceptual and distributed groundwater models do not necessarily translate into an understanding of how a plan might operate in reality. Prompted by Australian experiences, `iterative closed-question modelling' has been used to develop a process of iterative dialogue about management options, objectives and knowledge. Simple hypothetical models of basic system dynamics that satisfy agreed assumptions are used to stress-test the ability of a proposed management plan to achieve desired future conditions. Participants learn from models in which a plan succeeds and fails, updating their assumptions, expectations or plan. Their new understanding is tested against further hypothetical models. The models act as intellectual devices that confront users with new scenarios to discuss. This theoretical approach is illustrated using simple one and two-cell groundwater models that convey basic notions of capture and spatial impacts of pumping. Simple extensions can address uncertain climate, managed-aquifer recharge and alternate water sources. Having learnt to address the dynamics captured by these models, participants may be better placed to address local conditions and develop more effective arrangements to achieve management outcomes.
New criterion of material resistance for brittle fracture
M. Maj
2010-01-01
Full Text Available Wide variety of cast material applications and efforts to find optimum fields for casting operation are the reasons why it is so important to collect as many data on the properties of materials as possible. The problem of primary importance is to know how these materials will behave under the normally and rapidly changing loads, in other words – to know their fatigue strength. This study gives a short characteristic of fatigue tests and compares various data collected during measurements of the low-cycle fatigue strength coefficient K with the values of constant KIc, representing fracture toughness. The results of the investigations described here have revealed some important correlations that exist between the total elongation A5 and the proposed brittleness criterion B, conventional stress K, and fracture toughness KIc. The development of measurements seems to be of great importance and opens the field for further studies on practical implementation of this method.
An Improved Ductile Fracture Criterion for Fine-blanking Process
ZHAO Zhen; ZHUANG Xin-cun; XIE Xiao-long
2008-01-01
In order to accurately simnulate the fine-blanking process,a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile,compression,torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria,which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore,an improved fracture criterion based on Rice and Tracey model,taking the influence of both volume change and shape change of voids into account,is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
无
2011-01-01
This paper studies the effects of fiber orientaion and holes position on stress concentration and the determination of weakened areas in the composite of glass fiber reinforced epoxy resin around the hole for joints by using the finite element method.In this study,for the observation of areas affected by stress concentration Tsai-Wu failure criterion is used to determine the failed elements and ANSYS Software is implemented for modeling.In order to compare the effect of geometric parameters on stress concen...
Fatemeh Moradi
2016-12-01
Full Text Available The aim of present study was to investigate whether food restriction combined with exercise training could attenuate the oxidative stress and promote angiogenesis in a rat model of heart failure. 50 male wistar rats weighing 250-300 g were randomly divided into 5 groups including: 1 sham; they were fed ad libitum food, n=10. 2 Heart failure group; 3 Exercise group; they run on a treadmill 5 days per week for 4 weeks, n=10. 4 Food restricted group; they were fed with 60% of their daily average food intake, n=10. 5 Food restricted plus exercise group; as well as feeding with 60% of their daily average food intake for 8 weeks and run on a treadmill 5 days for the 4 next weeks, n=10. Subcutaneous injection of isoproterenol (130 mg/kg was used to induce experimental heart failure. Echocardiographic parameters were monitored. Plasma levels of malondialdehyde (MDA and prooxidant/ antioxidant balance (PAB, as oxidative parameters were measured. In continue gene expression of angiogenic factors such as hypoxia inducible factor-1a (HIF-1a, vascular endothelial growth factor A (VEGFA and endothelial nitric oxide synthase (eNOS as well as histopathological examination were investigated. Isoproterenol-treated hearts showed lower functional indexes including LVEDd; Left Ventricular End Diastolic dimension (p<0.05, FS; Fractional Shortening (p<0.001, EF; Ejection Fraction, (p<0.001. In addition, significant increase in plasma levels of MDA (p<0.001 and PAB (p<0.001 were observed. Food restriction and exercise significantly improved all measured parameters. The protective role of food restriction and exercise training on myocardial damage was further confirmed by promoting the gene expression of angiogenic factors (p<0.001 in left ventricle and reducing the myocardial fibrosis (p<0.05. Our results suggest that combined food restriction with exercise training is superior to either therapy alone for improving functional indexes, strengthen balance of
Krzych, Łukasz J; Wybraniec, Maciej T; Siennicka, Agnieszka; Lees, Belinda; Gościńska-Bis, Kinga; Wójcik, Maciej; Błaszczyk, Robert; Szymański, Filip M; Orszulak, Michał; Michalski, Błażej; Kamiński, Karol; Kopeć, Grzegorz; Hrynkiewicz-Szymańska, Anna; Jankowska, Ewa A
2016-01-01
We aimed to evaluate the prevalence and determinants of different stress coping strategies in Polish patients suffering from heart failure with reduced ejection fraction (HFREF). This manuscript is a sub-study of the CAPS-LOCK-HF multicentre psychological status assessment of patients with HFREF. Patients with > six-month history of HFREF and clinical stability for ≥ three months and left ventricular ejection fraction (LVEF) study. Demographic and clinical variables were obtained from medical records, while a standardised Coping Inventory for Stressful Situations (CISS) was applied to all subjects. The study comprised 758 patients (599 men; 79%) with a median age of 64 years (IQR 58-71). Median LVEF was 33% (25-40). Subjects most commonly used task-oriented coping strategies (median CISS score 55 points; IQR 49-61), followed by avoidance (45 points; 39-50) and emotion-oriented coping strategies (41 points; 34-48). Distraction-based avoidance coping strategies (20 points; 16-23) were more pronounced than social diversion strategies (16 points; 14-19). Multiple regression analysis showed that higher New York Heart Association (NYHA) class and lower systolic blood pressure were independent predictors of task-oriented style. Emotion-oriented coping was more common among females and higher NYHA classes, and in patients who did not take angiotensin-converting enzyme inhibitors. Patients who used avoidance-oriented strategies were more frequently those in sinus rhythm on assessment and those who had less history of neoplastic disease. Patients with HFREF most commonly use favourable task-oriented coping strategies. However, female patients and those with higher NYHA classes tend to use potentially detrimental emotion-oriented coping strategies.
Beating the Stoner criterion using molecular interfaces
Ma'Mari, Fatma Al; Moorsom, Timothy; Teobaldi, Gilberto; Deacon, William; Prokscha, Thomas; Luetkens, Hubertus; Lee, Steve; Sterbinsky, George E.; Arena, Dario A.; MacLaren, Donald A.; Flokstra, Machiel; Ali, Mannan; Wheeler, May C.; Burnell, Gavin; Hickey, Bryan J.; Cespedes, Oscar
2015-08-01
Only three elements are ferromagnetic at room temperature: the transition metals iron, cobalt and nickel. The Stoner criterion explains why iron is ferromagnetic but manganese, for example, is not, even though both elements have an unfilled 3d shell and are adjacent in the periodic table: according to this criterion, the product of the density of states and the exchange integral must be greater than unity for spontaneous spin ordering to emerge. Here we demonstrate that it is possible to alter the electronic states of non-ferromagnetic materials, such as diamagnetic copper and paramagnetic manganese, to overcome the Stoner criterion and make them ferromagnetic at room temperature. This effect is achieved via interfaces between metallic thin films and C60 molecular layers. The emergent ferromagnetic state exists over several layers of the metal before being quenched at large sample thicknesses by the material's bulk properties. Although the induced magnetization is easily measurable by magnetometry, low-energy muon spin spectroscopy provides insight into its distribution by studying the depolarization process of low-energy muons implanted in the sample. This technique indicates localized spin-ordered states at, and close to, the metal-molecule interface. Density functional theory simulations suggest a mechanism based on magnetic hardening of the metal atoms, owing to electron transfer. This mechanism might allow for the exploitation of molecular coupling to design magnetic metamaterials using abundant, non-toxic components such as organic semiconductors. Charge transfer at molecular interfaces may thus be used to control spin polarization or magnetization, with consequences for the design of devices for electronic, power or computing applications (see, for example, refs 6 and 7).
Convex functions and the rolling circle criterion
1995-01-01
Given 0≤R1≤R2≤∞, CVG(R1,R2) denotes the class of normalized convex functions f in the unit disc U, for which ∂f(U) satisfies a Blaschke Rolling Circles Criterion with radii R1 and R2. Necessary and sufficient conditions for R1=R2, growth and distortion theorems for CVG(R1,R2) and rotation theorem for the class of convex functions of bounded type, are found.
Early Stop Criterion from the Bootstrap Ensemble
Hansen, Lars Kai; Larsen, Jan; Fog, Torben L.
1997-01-01
This paper addresses the problem of generalization error estimation in neural networks. A new early stop criterion based on a Bootstrap estimate of the generalization error is suggested. The estimate does not require the network to be trained to the minimum of the cost function, as required...... by other methods based on asymptotic theory. Moreover, in contrast to methods based on cross-validation which require data left out for testing, and thus biasing the estimate, the Bootstrap technique does not have this disadvantage. The potential of the suggested technique is demonstrated on various time...
Application of geometric midline yield criterion to analysis of three-dimensional forging
ZHAO De-wen; WANG Gen-ji; LIU Xiang-hua; WANG Guo-dong
2008-01-01
A kinematically admissible continuous velocity field was proposed for the analysis of three-dimensional forging. The linear yield criterion expressed by geometric midline of error triangle between Tresca and Twin shear stress yield loci on the π-plane, called GM yield criterion for short, was firstly applied to analysis of the velocity field for the forging. The analytical solution of the forging force with the effects of external zone and bulging parameter is obtained by strain rate inner product. Compression tests of pure lead are performed to compare the calculated results with the measured ones. The results show that the calculated total pressures are higher than the measured ones whilst the relative error is no more than 9.5%. It is implied that the velocity field is reasonable and the geometric midline yield criterion is available. The solution is still an upper-bound one.
Deduction of plastic work rate per unit volume for unified yield criterion and its application
ZHAO De-wen; LI Jing; LIU Xiang-hua; WANG Guo-dong
2009-01-01
A unified linear expression of plastic work rate per unit volume is deduced from the unified linear yield criterion and the associated flow rule. The expression is suitable for various linear yield loci in the error triangle between Tresca's and twin shear stress yield loci on the π-plane. It exhibits generalization in which the different value of criterion parameter b corresponds to a specific linear formula of plastic work rate per unit volume. Finally, with the unified linear expression of plastic work rate and upper-bound parallel velocity field the strip forging without bulge is successfully analyzed and an analytical result is also obtained. The comparison with traditional solutions shows that when b=1/(1+(√3)) the result is the same as the upper bound result by Mises' yield criterion, and it also is identical to that by slab method with m=1, σ0=0.
Deformation and Failure Characteristics of the Rock Masses around Deep Underground Caverns
Chong Zhang
2015-01-01
Full Text Available The deformation and failure characteristics of deep rock masses are the focus of this study on deep rock mass engineering. The study identifies the deformation and failure characteristics of a deep cavern under different ground stress conditions using model test and theoretical analysis methods. First, the similarity theory for model tests is introduced, and then the scale factors used in the present study are calculated according to the Froude criterion. Based on the study objectives, the details of the study methods (the similarity coefficient, the loading conditions, the test steps, etc. are introduced. Finally, the failure characteristics of the deep cavern and the strain distribution characteristics surrounding the caverns under different ground stress conditions are identified using the model test. It was found that compared with shallow rock masses the rock masses of the deep cavern have a much greater tensile range, which reaches 1.5 times the diameter of the cavern under the conditions established in the present study. Under different ground stress conditions, there are differences in failure characteristics and the reasons of the differences were analyzed. The implication of the test results on the design of support system for deep caverns was presented.
Jensen, Line Skov; Lova, Lotte; Hansen, Zandra Kulikovsky; Schønemann, Emilie; Larsen, Line Lyngby; Colberg Olsen, Maria Sophia; Juhl, Nadja; Magnussen, Bogi Roin
2012-01-01
Stress er en tilstand som er meget omdiskuteret i samfundet, og dette besværliggør i en vis grad konkretiseringen af mulige løsningsforslag i bestræbelsen på at forebygge den såkaldte folkesygdom. Hovedkonklusionen er, at selv om der bliver gjort meget for at forebygge, er der ikke meget der aktivt kan sættes i værk for at reducere antallet af stressramte, før en fælles forståelse af stressårsager og effektiv stresshåndtering er fremlagt. Problemformuleringen er besvaret gennem en undersø...
Fatigue acceptance test limit criterion for larger diameter rolled thread fasteners
Kephart, A.R.
1997-05-01
This document describes a fatigue lifetime acceptance test criterion by which studs having rolled threads, larger than 1.0 inches in diameter, can be assured to meet minimum quality attributes associated with a controlled rolling process. This criterion is derived from a stress dependent, room temperature air fatigue database for test studs having a 0.625 inch diameter threads of Alloys X-750 HTH and direct aged 625. Anticipated fatigue lives of larger threads are based on thread root elastic stress concentration factors which increase with increasing thread diameters. Over the thread size range of interest, a 30% increase in notch stress is equivalent to a factor of five (5X) reduction in fatigue life. The resulting diameter dependent fatigue acceptance criterion is normalized to the aerospace rolled thread acceptance standards for a 1.0 inch diameter, 0.125 inch pitch, Unified National thread with a controlled Root radius (UNR). Testing was conducted at a stress of 50% of the minimum specified material ultimate strength, 80 Ksi, and at a stress ratio (R) of 0.10. Limited test data for fastener diameters of 1.00 to 2.25 inches are compared to the acceptance criterion. Sensitivity of fatigue life of threads to test nut geometry variables was also shown to be dependent on notch stress conditions. Bearing surface concavity of the compression nuts and thread flank contact mismatch conditions can significantly affect the fastener fatigue life. Without improved controls these conditions could potentially provide misleading acceptance data. Alternate test nut geometry features are described and implemented in the rolled thread stud specification, MIL-DTL-24789(SH), to mitigate the potential effects on fatigue acceptance data.
A CRITERION FOR TESTING WHETHER A DIFFERENCE IDEAL IS PRIME
Chunming YUAN; Xiao-Shan GAO
2009-01-01
This paper presents a criterion for testing the irreducibility of a polynomial over an algebraic extension field. Using this criterion and the characteristic set method, the authors give a criterion for testing whether certain difference ascending chains are strong irreducible, and as a consequence, whether the saturation ideals of these ascending chains are prime ideals.
Condensation of saturated vapours on isentropic compression: a simple criterion
Patwardhan, V.S.
1987-01-01
A criterion is derived and tested for determining whether the isentropic compression of saturated vapours leads to superheat or condensation. This criterion needs only values of the critical temperature, the acentric factor and the liquid specific heat. The application of the criterion for selection of a working fluid both for heat pumps and heat engines is discussed.
Liu, Miao; Mao, Cuiying; Li, Jiayu; Han, Fanglei; Yang, Ping
2017-01-01
Background: A previous study suggested that activin A inhibited myocardial cell apoptosis. This study thus aimed to explore the effects of the activin A–follistatin system on myocardial cell apoptosis in heart failure (HF) rats in order to determine whether or not the mechanism operates through the endoplasmic reticulum stress (ERS) pathway. Methods: Myocardial infarction (MI) by vascular deprivation was used to induce HF. The enzyme-linked immunosorbent assay was used to detect activin A, follistatin and brain natriuretic peptide (BNP) contents in serum. Immunohistochemical staining for activin A, follistatin, CCAAT-enhancer-binding protein (C/EBP) homologous protein (CHOP) and caspase-3 was performed on the myocardial tissue. The activin A-stimulated apoptosis of H9c2 cells was tested by flow cytometry. Western blot was used to detect the expression levels of activin A, follistatin and ERS-related proteins. Results: It was found that the high expression of activin A could cause activin A–follistatin system imbalance, inducing myocardial cell apoptosis via ERS in vivo. When HF developed to a certain stage, the expression of follistatin was upregulated to antagonize the expression of activin A. Activin A inhibited cardiomyocyte apoptosis with a low concentration and promoted apoptosis with a high concentration in vitro, also via ERS. Conclusion: Activin A–follistatin system participated in ERS-mediated myocardial cell apoptosis in HF. PMID:28208629
Lihui Sun; Haoyuan Wu; Bensheng Yang; Qiangqiang Li
2015-01-01
There are many soft-rock roadway coal mines in China. The surrounding rocks of the high-stress soft-rock roadways in deep mine are especially difficult to be supported using the traditional supporting way. In this study, the south wing rail roadway on the second level of Yunjialing coal mine in China was used as an example to analyze the deformation and failure characteristics and influencing factors of roadway. On this basis, this study proposed the equalized yielding support idea which employs the yielding rings to realize the pressure equalization on the bolts and cables in the section. To achieve this purpose, the first bolt-mesh-cable equalizing pressure yielding support was integrated with the second grouting reinforcement. The results proved that the yield rings of the bolts and cables on the spandrel of the arched roadway firstly developed yielding deformation;then the deformation extended to the vault of the roadway;the bolts and cables achieved a yielding extreme value of 15 and 18 tonnes, respectively. The roadway surrounding rock tended to be stable at the 26th day after the maintenance. The equalizing pressure yielding supporting technology plays a moderate pressure-releasing and actively controlling role on the surrounding rocks in the soft-rock roadway with large deformation.
Guang-jun Song; Da-ming Wu; Wei-yue Song; Ming-shi Song; Gui-xian Hu
2012-01-01
The prediction of long term failure behaviors and lifetime of aged glass polymers from the short term tests of reduced rupture creep compliance (or strain) is one of difficult problems in polymer science and engineering.A new "universal reduced rupture creep approach" with exact theoretical analysis and computations is proposed in this work.Failure by creep for polymeric material is an important problem to be addressed in the engineering.A universal equation on reduced extensional failure creep compliance for PMMA has been derived.It is successful in relating the reduced extensional failure creep compliance with aging time,temperature,levels of stress,the average growth dimensional number and the parameter in K-W-W function.Based on the universal equation,a method for the prediction of failure behavior,failure strain criterion,failure time of PMMA has been developed which is named as a universal "reduced rupture creep approach".The results show that the predicted failure strain and failure time of PMMA at different aging times for different levels of stress are all in agreement with those obtained directly from experiments,and the proposed method is reliable and practical.The dependences of reduced extensional failure creep compliance on the conditions of aging time,failure creep stress,the structure of fluidized-domain constituent chains are discussed.The shifting factor,exponent for time-stress superposition at different levels of stress and the shifting factor,exponent for time-time aging superposition at different aging time are theoretically defined respectively.
Kinematic criterion for breaking of shoaling waves
Liberzon, Dan; Itay, Uri
2016-11-01
Validity of a kinematic criterion for breaking of shoaling waves was examined experimentally. Results obtained by simultaneous measurements of water surface velocity by PTV and of the propagation velocity of a steep crest up to the point of breaking inception during shoaling will be reported. The experiments performed in a large wave tank examining breaking behavior of gentle spillers during shoaling on three different slopes suggest a validity of the recently proposed kinematic criterion. The breaking inception was found to occur when the horizontal velocity of the water surface on the steep (local steepness of 0.41-0.6) crest reaches a threshold value of 0.85-0.95 of that of the crest propagation. The exact moment and position of breaking inception detected using a Phase Time Method (PTM), characterizing a unique shape of the local frequency fluctuations at the inception. Future implementation of the PTM method for detection of breaking events in irregular wave fields will be discussed. Supported by German-Israeli Foundation for Scientific Research and Development (GIF) Grant #2019392.
Extensions and Applications of the Bohm Criterion
Baalrud, Scott D; Yee, Benjamin; Hopkins, Matthew; Barnat, Edward
2014-01-01
The generalized Bohm criterion is revisited in the context of incorporating kinetic effects of the electron and ion distribution functions into the theory. The underlying assumptions and results of two different approaches are compared: The conventional `kinetic Bohm criterion' and a fluid-moment hierarchy approach. The former is based on the asymptotic limit of an infinitely thin sheath ($\\lambda_D/l =0$), whereas the latter is based on a perturbative expansion of a sheath that is thin compared to the plasma ($\\lambda_D/l \\ll 1$). Here $\\lambda_D$ is the Debye length, which characterizes the sheath length scale, and $l$ is a measure of the plasma or presheath length scale. The consequences of these assumptions are discussed in terms of how they restrict the class of distribution functions to which the resulting criteria can be applied. Two examples are considered to provide concrete comparisons between the two approaches. The first is a Tonks-Langmuir model including a warm ion source [Robertson 2009 \\textit...
Contribution of criterion A2 to PTSD screening in the presence of traumatic events.
Pereda, Noemí; Forero, Carlos G
2012-10-01
Criterion A2 according to the Diagnostic and Statistical Manual of Mental Disorders (4(th) ed.; DSM-IV; American Psychiatric Association [APA], 1994) for posttraumatic stress disorder (PTSD) aims to assess the individual's subjective appraisal of an event, but it has been claimed that it might not be sufficiently specific for diagnostic purposes. We analyse the contribution of Criterion A2 and DSM-IV criteria to detect PTSD for the most distressing life events experienced by our subjects. Young adults (N = 1,033) reported their most distressing life events, together with PTSD criteria (Criteria A2, B, C, D, E, and F). PTSD prevalence and criterion specificity and agreement with probable diagnoses were estimated. Our results indicate 80.30% of the individuals experienced traumatic events and met one or more PTSD criteria; 13.22% cases received a positive diagnosis of PTSD. Criterion A2 showed poor agreement with the final probable PTSD diagnosis (correlation with PTSD .13, specificity = .10); excluding it from PTSD diagnosis did not the change the estimated disorder prevalence significantly. Based on these findings it appears that Criterion A2 is scarcely specific and provides little information to confirm a probable PTSD case.
PTSD's risky behavior criterion: Relation with DSM-5 PTSD symptom clusters and psychopathology.
Contractor, Ateka A; Weiss, Nicole H; Dranger, Paula; Ruggero, Camilo; Armour, Cherie
2017-06-01
A new symptom criterion of reckless and self-destructive behaviors (E2) was recently added to posttraumatic stress disorder's (PTSD) diagnostic criteria in DSM-5, which is unsurprising given the well-established relation between PTSD and risky behaviors. Researchers have questioned the significance and incremental validity of this symptom criterion within PTSD's symptomatology. Unprecedented to our knowledge, we aim to compare trauma-exposed groups differing on their endorsement status of the risky behavior symptom on several psychopathology constructs (PTSD, depression, distress tolerance, rumination, anger). The sample included 123 trauma-exposed participants seeking mental health treatment (M age=35.70; 68.30% female) who completed self-report questionnaires assessing PTSD symptoms, depression, rumination, distress tolerance, and anger. Results of independent samples t-tests indicated that participants who endorsed the E2 criterion at a clinically significant level reported significantly greater PTSD subscale severity; depression severity; rumination facets of repetitive thoughts, counterfactual thinking, and problem-focused thinking; and anger reactions; and significantly less absorption and regulation (distress tolerance facets) compared to participants who did not endorse the E2 criterion at a clinically significant level. Results indicate the utility of the E2 criterion in identifying trauma-exposed individual with greater posttraumatic distress, and emphasize the importance of targeting such behaviors in treatment. Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.
STRESS AND STRAIN ANALYSIS AROUND UNDERGROUND ROOM
Krešimir Tor
2000-12-01
Full Text Available By excavation of opening in the rock, a stress concentration around the opening occurs. The state of stresses and strains around an opening is analysed by theory of elasticity and by Finite Element Method (FEM.The aim of the paper is to determine the dimension of the FEM model for the stress and strain analysis around an elliptical opening in rock massif. The numerical calculation have been performed for two different boundary conditions: with forces or with displacements. Boundary conditions given by displacements give better approximation in the state of stress and strains. An example of the excavation of a road tunnel is used to represent stress concentration at the opening and the places where the plastic zones occur. The computation has been done after FEM comprising the Hock-Brown criterion of failure. The results of stability analysis point to the zones where failure of the rock material may be anticipa¬ted. This is important when planning and designing the primary supp¬orts. The comparison of the results of numerical modelling and field recording during excavation is of particular significance (the paper is published in Croatian.
张立松; 闫相祯; 杨秀娟; 田中兰; 杨恒林
2014-01-01
The uncertainties of some key influence factors on coal crushing, such as rock strength, pore pressure and magnitude and orientation of three principal stresses, can lead to the uncertainty of coal crushing and make it very difficult to predict coal crushing under the condition of in-situ reservoir. To account for the uncertainty involved in coal crushing, a deterministic prediction model of coal crushing under the condition of in-situ reservoir was established based on Hoek-Brown criterion. Through this model, key influence factors on coal crushing were selected as random variables and the corresponding probability density functions were determined by combining experiment data and Latin Hypercube method. Then, to analyze the uncertainty of coal crushing, the first- order second-moment method and the presented model were combined to address the failure probability involved in coal crushing analysis. Using the presented method, the failure probabilities of coal crushing were analyzed for WS5-5 well in Ningwu basin, China, and the relations between failure probability and the influence factors were furthermore discussed. The results show that the failure probabilities of WS5-5 CBM well vary from 0.6 to 1.0; moreover, for the coal seam section at depth of 784.3-785 m, the failure probabilities are equal to 1, which fit well with experiment results; the failure probability of coal crushing presents nonlinear growth relationships with the increase of principal stress difference and the decrease of uniaxial compressive strength.
BOUROUIS FAIROUZ
2012-04-01
Full Text Available Sandwich beams loaded in three points bending may fail in several ways including tension or compression failure of facings. In this paper , The effect of the transverse shear on the face yielding and face wrinkling failure modes of sandwich beams loaded in three points bending have been studied, the beams were made of various composites materials carbon/epoxy, kevlar/epoxy, glass/epoxy at sequence [+θ/-θ]3s, [0°/90°]3s. . The stresses in the face were calculated using maximum stress criterion and the simple beam theory. The obtained different results show that the sandwich beams with carbon/epoxy, and glass/epoxy face sheets are the best materials, inreturn the kevlar /epoxy facing characterised by low resistance of transverse shear in compression and tensile.
Discriminant Validity Assessment: Use of Fornell & Larcker criterion versus HTMT Criterion
Hamid, M. R. Ab; Sami, W.; Mohmad Sidek, M. H.
2017-09-01
Assessment of discriminant validity is a must in any research that involves latent variables for the prevention of multicollinearity issues. Fornell and Larcker criterion is the most widely used method for this purpose. However, a new method has emerged for establishing the discriminant validity assessment through heterotrait-monotrait (HTMT) ratio of correlations method. Therefore, this article presents the results of discriminant validity assessment using these methods. Data from previous study was used that involved 429 respondents for empirical validation of value-based excellence model in higher education institutions (HEI) in Malaysia. From the analysis, the convergent, divergent and discriminant validity were established and admissible using Fornell and Larcker criterion. However, the discriminant validity is an issue when employing the HTMT criterion. This shows that the latent variables under study faced the issue of multicollinearity and should be looked into for further details. This also implied that the HTMT criterion is a stringent measure that could detect the possible indiscriminant among the latent variables. In conclusion, the instrument which consisted of six latent variables was still lacking in terms of discriminant validity and should be explored further.
A probabilisitic based failure model for components fabricated from anisotropic graphite
Xiao, Chengfeng
The nuclear moderator for high temperature nuclear reactors are fabricated from graphite. During reactor operations graphite components are subjected to complex stress states arising from structural loads, thermal gradients, neutron irradiation damage, and seismic events. Graphite is a quasi-brittle material. Two aspects of nuclear grade graphite, i.e., material anisotropy and different behavior in tension and compression, are explicitly accounted for in this effort. Fracture mechanic methods are useful for metal alloys, but they are problematic for anisotropic materials with a microstructure that makes it difficult to identify a "critical" flaw. In fact cracking in a graphite core component does not necessarily result in the loss of integrity of a nuclear graphite core assembly. A phenomenological failure criterion that does not rely on flaw detection has been derived that accounts for the material behaviors mentioned. The probability of failure of components fabricated from graphite is governed by the scatter in strength. The design protocols being proposed by international code agencies recognize that design and analysis of reactor core components must be based upon probabilistic principles. The reliability models proposed herein for isotropic graphite and graphite that can be characterized as being transversely isotropic are another set of design tools for the next generation very high temperature reactors (VHTR) as well as molten salt reactors. The work begins with a review of phenomenologically based deterministic failure criteria. A number of this genre of failure models are compared with recent multiaxial nuclear grade failure data. Aspects in each are shown to be lacking. The basic behavior of different failure strengths in tension and compression is exhibited by failure models derived for concrete, but attempts to extend these concrete models to anisotropy were unsuccessful. The phenomenological models are directly dependent on stress invariants. A set of
Henninger, C
2007-11-15
Many material assemblies subjected to thermo-mechanical loadings develop thermal residual stresses which modify crack onset conditions. Besides if one of the components has a plastic behaviour, plastic residual deformations may also have a contribution. One of the issues in brittle fracture mechanics is to predict crack onset without any pre-existing defect. Leguillon proposed an onset criterion based on both a Griffth-like energetic condition and a maximum stress criterion. The analysis uses matched asymptotics and the theory of singularity. The good fit between the model and experimental measurements led on homogeneous isotropic materials under pure mechanical loading incited us to take into account residual stresses in the criterion. The comparison between the modified criterion and the experimental measurements carried out on an aluminum/epoxy assembly proves to be satisfying concerning the prediction of failure of the interface between the two components. Besides, it allows, through inversion, identifying the fracture properties of this interface. The modified criterion is also applied to the delamination of the tile/structure interface in the plasma facing components of the Tore Supra tokamak. Indeed thermal and plastic residual stresses appear in the metallic part of these coating tiles. (author)
Influence of Damage Evolution on the Failure Surface of Concrete
LUO Xin; WEI Jun
2006-01-01
The damage which represents the alternation of internal state of material was introduced to concrete strength theory according to the theory of mechanics of continuous medium and the failure criterion of deteriorated concrete was discussions. In the tests, ultrasonic velocity is used to establish the damage variable and to establish the damage-coupled failure criterion of concrete under freeze-thaw. The results show that the failure surface is gradually shrinking with the increase of freeze-thaw times. Furthermore, by the comparison between the theoretical data and the testing data from the literature, the rationality of strength theory proposed in the paper acquire confirmation. The damagecoupled failure criterion presented here can indicate the influence of damage evolution on the failure surface of concrete.
A criterion for separating process calculi
Banti, Federico; Tiezzi, Francesco; 10.4204/EPTCS.41.2
2010-01-01
We introduce a new criterion, replacement freeness, to discern the relative expressiveness of process calculi. Intuitively, a calculus is strongly replacement free if replacing, within an enclosing context, a process that cannot perform any visible action by an arbitrary process never inhibits the capability of the resulting process to perform a visible action. We prove that there exists no compositional and interaction sensitive encoding of a not strongly replacement free calculus into any strongly replacement free one. We then define a weaker version of replacement freeness, by only considering replacement of closed processes, and prove that, if we additionally require the encoding to preserve name independence, it is not even possible to encode a non replacement free calculus into a weakly replacement free one. As a consequence of our encodability results, we get that many calculi equipped with priority are not replacement free and hence are not encodable into mainstream calculi like CCS and pi-calculus, t...
Extended equal areas criterion: foundations and applications
Yusheng, Xue [Nanjim Automation Research Institute, Nanjim (China)
1994-12-31
The extended equal area criterion (EEAC) provides analytical expressions for ultra fast transient stability assessment, flexible sensitivity analysis, and means to preventive and emergency controls. Its outstanding performances have been demonstrated by thousands upon thousands simulations on more than 50 real power systems and by on-line operation records in an EMS environment of Northeast China Power System since September 1992. However, the researchers have mainly based on heuristics and simulations. This paper lays a theoretical foundation of EEAC and brings to light the mechanism of transient stability. It proves true that the dynamic EEAC furnishes a necessary and sufficient condition for stability of multi machine systems with any detailed models, in the sense of the integration accuracy. This establishes a new platform for further advancing EEAC and better understanding of problems. An overview of EEAC applications in China is also given in this paper. (author) 30 refs.
Focusing criterion in DHM image reconstruction
Mihailescu, M.; Mihale, N.; Popescu, R. C.; Acasandrei, A.; Paun, I. A.; Dinescu, M.; Scarlat, E.
2015-02-01
This study is presenting the theoretical approach and the practical results of a precise activity involved in the hologram reconstruction in order to find the optimally focused image of MG63 osteoblast-like cells cultivated on polymeric flat substrates. The morphology and dynamic of the cell is investigated by digital holographic microscopy (DHM) technique. The reconstruction is digitally performed using an algorithm based on the scalar theory of diffraction in the Fresnel approximation. The quality of the 3D images of the cells is crucially depending on the focusing capability of the reconstruction chain to fit the parameters of the optical recorder, particularly the focusing value. Our proposal to find the focused image is based on the images decomposition on gray levels and their histogram analysis. More precisely the focusing criterion is based on the evaluation of the form of this distribution.
Nash equilibrium and multi criterion aerodynamic optimization
Tang, Zhili; Zhang, Lianhe
2016-06-01
Game theory and its particular Nash Equilibrium (NE) are gaining importance in solving Multi Criterion Optimization (MCO) in engineering problems over the past decade. The solution of a MCO problem can be viewed as a NE under the concept of competitive games. This paper surveyed/proposed four efficient algorithms for calculating a NE of a MCO problem. Existence and equivalence of the solution are analyzed and proved in the paper based on fixed point theorem. Specific virtual symmetric Nash game is also presented to set up an optimization strategy for single objective optimization problems. Two numerical examples are presented to verify proposed algorithms. One is mathematical functions' optimization to illustrate detailed numerical procedures of algorithms, the other is aerodynamic drag reduction of civil transport wing fuselage configuration by using virtual game. The successful application validates efficiency of algorithms in solving complex aerodynamic optimization problem.
Fuzzy Clustering with Novel Separable Criterion
无
2006-01-01
Fuzzy clustering has been used widely in pattern recognition, image processing, and data analysis. An improved fuzzy clustering algorithm was developed based on the conventional fuzzy c-means (FCM) to obtain better quality clustering results. The update equations for the membership and the cluster center are derived from the alternating optimization algorithm. Two fuzzy scattering matrices in the objective function assure the compactness between data points and cluster centers, and also strengthen the separation between cluster centers in terms of a novel separable criterion. The clustering algorithm properties are shown to be an improvement over the FCM method's properties. Numerical simulations show that the clustering algorithm gives more accurate clustering results than the FCM method.
Influence of residual stresses on the tensile strength of composite-metal sandwich laminates
Herakovich, C. T.; Wong, D. M.
1977-01-01
The tensile strength of boron-epoxy/aluminum sandwich laminates is discussed relative to the residual thermal stresses generated by curing and bonding at elevated temperatures. It is shown that the sandwich laminates investigated exhibit three dinstinct modes of failure, depending upon the fiber orientation of the composite. Sandwich laminates with moderate to high percentage of 0-deg fibers exhibit early failures initiated by edge effect; laminates with moderate to high percentage of 90-deg fibers fail according to a first-ply failure criterion; laminates with moderate to high percentages of plus or minus 45 deg plies fail at strains equal to or greater than the failure strain of the corresponding all-composite laminate.
Cazacu, Oana; Stewart, Joel B.
2013-05-01
A new analytic plastic potential is developed using a rigorous limit analysis approach. Conditions of homogeneous boundary strain rate are imposed on every cylinder concentric with the cavity. It is shown that, due to the tension-compression asymmetry of the incompressible matrix, the third invariant of the stress deviator has a strong influence on the yielding of the porous solid. New and intriguing results are obtained; namely, for axisymmetric loadings and plane strain conditions, the stress state at yielding is not hydrostatic. In the case when the matrix has the same yield in tension as in compression, the new criterion reduces to Gurson's criterion for cylindrical voids.
... heart failure due to systolic dysfunction. http://www.uptodate.com/home. Accessed Sept. 26, 2014. Colucci WS. ... patient with heart failure or cardiomyopathy. http://www.uptodate.com/home. Accessed Sept. 26, 2014. Colucci WS. ...
Fukushima, Arata; Kinugawa, Shintaro; Takada, Shingo; Matsumoto, Junichi; Furihata, Takaaki; Mizushima, Wataru; Tsuda, Masaya; Yokota, Takashi; Matsushima, Shouji; Okita, Koichi; Tsutsui, Hiroyuki
2016-05-15
Insulin resistance can occur as a consequence of heart failure (HF). Activation of the renin-angiotensin system (RAS) may play a crucial role in this phenomenon. We thus investigated the effect of a direct renin inhibitor, aliskiren, on insulin resistance in HF after myocardial infarction (MI). MI and sham operation were performed in male C57BL/6J mice. The mice were divided into 4 groups and treated with sham-operation (Sham, n=10), sham-operation and aliskiren (Sham+Aliskiren; 10mg/kg/day, n=10), MI (n=11), or MI and aliskiren (MI+Aliskiren, n=11). After 4 weeks, MI mice showed left ventricular dilation and dysfunction, which were not affected by aliskiren. The percent decrease of blood glucose after insulin load was significantly smaller in MI than in Sham (14±5% vs. 36±2%), and was ameliorated in MI+Aliskiren (34±5%) mice. Insulin-stimulated serine-phosphorylation of Akt and glucose transporter 4 translocation were decreased in the skeletal muscle of MI compared to Sham by 57% and 69%, and both changes were ameliorated in the MI+Aliskiren group (91% and 94%). Aliskiren administration in MI mice significantly inhibited plasma renin activity and angiotensin II (Ang II) levels. Moreover, (pro)renin receptor expression and local Ang II production were upregulated in skeletal muscle from MI and were attenuated in MI+Aliskiren mice, in tandem with a decrease in superoxide production and NAD(P)H oxidase activities. In conclusion, aliskiren ameliorated insulin resistance in HF by improving insulin signaling in the skeletal muscle, at least partly by inhibiting systemic and (pro)renin receptor-mediated local RAS activation, and subsequent NAD(P)H oxidase-induced oxidative stress.
艾池; 刘国勇; 刘顺利; 隋杨; 赵万春
2011-01-01
考虑井壁周围岩体中流体的渗流作用,建立了套管错断口井壁岩体的平衡微分方程.然后按照损伤程度的不同将错断口井壁岩体划分为不同的区域(失稳破坏区、损伤区、弹性区),考虑不同区域内岩石材料参数的不同,分析了错断口周围岩体各个区域内的应力分布规律,确定了失稳破坏区和损伤区的半径,并在此基础上得到了岩体发生失稳破坏和损伤时的临界应力条件,从而为套管错断后井壁稳定性的研究和错断口吐岩块现象的预防提供了理论依据.%The balanced differential equation of wellbore wall is built around failure casing considering fluid seepage. The area around failure casing is divided into different areas (unstable failure zone, damaged zone, elastic zone) according to the degree of damage, their stress distribution were obtained with consideration of variations of rock properties in different areas. The radius of unstable failure zone and damaged zone are determined. Critical stresses of rock failure and damage are obtained which provides a theoretical basis for the wellbore stability investigation and casing failure prevention.
A Statistics-Based Cracking Criterion of Resin-Bonded Silica Sand for Casting Process Simulation
Wang, Huimin; Lu, Yan; Ripplinger, Keith; Detwiler, Duane; Luo, Alan A.
2017-02-01
Cracking of sand molds/cores can result in many casting defects such as veining. A robust cracking criterion is needed in casting process simulation for predicting/controlling such defects. A cracking probability map, relating to fracture stress and effective volume, was proposed for resin-bonded silica sand based on Weibull statistics. Three-point bending test results of sand samples were used to generate the cracking map and set up a safety line for cracking criterion. Tensile test results confirmed the accuracy of the safety line for cracking prediction. A laboratory casting experiment was designed and carried out to predict cracking of a cup mold during aluminum casting. The stress-strain behavior and the effective volume of the cup molds were calculated using a finite element analysis code ProCAST®. Furthermore, an energy dispersive spectroscopy fractographic examination of the sand samples confirmed the binder cracking in resin-bonded silica sand.
A comparative calculation of the wind turbines capacities on the basis of the L-{sigma} criterion
Menet, Jean-Luc; Valdes, Laurent-Charles; Menart, Bruno [Universite de Valenciennes et du Hainaut-Cambresis, Groupe de Recherche Energies et Environnement, Valenciennes, 59 (France)
2001-04-01
Usually, wind sites are equipped with fast-running Horizontal Axis Wind Turbines of the airscrew type, which has a high efficiency. In this article, the argument is put forward that the choice of a wind turbine must not be based only on high efficiency. We propose a comparative criterion adapted to the comparison of a horizontal axis wind turbine with a vertical axis wind turbine: the L-{sigma} criterion. This criterion consists in comparing wind turbines which intercept the same front width of wind, by allocating them a same reference value of the maximal mechanical stress on the blades or the paddles. On the basis of this criterion, a quantitative comparison points to a clear advantage of the Savonius rotors, because of their lower angular velocity, and provides some elements for the improvement of their rotor. (Author)
Study on interface failure of shape memory alloy (SMA) reinforced smart structure with damages
Zili Hu; Ke Xiong; Xinwei Wang
2005-01-01
Shape memory alloy (SMA) reinforced smart structure can be used to make structural shape and strength selfadapted and structural damage self-restrained. Although SMA smart structures without damages were extensively studied,researches on SMA smart structures with damages have rarely been reported thus far. In this paper, thermo-mechanical behaviors of SMA fiber reinforced smart structures with damages are analyzed through a shear lag model and the variational principle. Mathematical expressions of the meso-displacement field and the stress-strain field of a typical element with damages are obtained, and a failure criterion for interface failure between SMA fibers and matrix is established,which is applied to an example. Results presented herein may provide a theoretical foundation for further studies on integrity of SMA smart structures.
Bronkhorst, Curt A [Los Alamos National Laboratory; Dennis - Koller, Darcie [Los Alamos National Laboratory; Cerreta, Ellen K [Los Alamos National Laboratory; Gray Ill, George T [Los Alamos National Laboratory; Bourne, Neil [AWE-ALDERMASTON
2010-12-16
A number of plate impact experiments have been conducted on high purity polycrystalline tantalum and copper samples using graded flyer plate configurations to alter the loading profile. These experiments are designed in a way so that a broad range of damage regimes are probed. The results show that the nucleation of damage primarily occurs at the grain boundaries of the materials. This affords us the opportunity to propose a porosity damage nucleation criterion which begins to account for the length scales of the microstructure (grain size distribution) and the mechanical response of the grain boundary regions (failure stress distribution). This is done in the context of a G-T-N type model for the ductile damage and failure response of both the materials examined. The role of micro-inertial effects on the porosity growth process is also considered.
Bronkhorst, Curt A [Los Alamos National Laboratory; Dennis - Koller, Darcie [Los Alamos National Laboratory; Cerreta, Ellen K [Los Alamos National Laboratory; Gray Ill, George T [Los Alamos National Laboratory; Bourne, Neil [AWE-ALDERMASTON
2010-12-16
A number of plate impact experiments have been conducted on high purity polycrystalline tantalum and copper samples using graded flyer plate configurations to alter the loading profile. These experiments are designed in a way so that a broad range of damage regimes are probed. The results show that the nucleation of damage primarily occurs at the grain boundaries of the materials. This affords us the opportunity to propose a porosity damage nucleation criterion which begins to account for the length scales of the microstructure (grain size distribution) and the mechanical response of the grain boundary regions (failure stress distribution). This is done in the context of a G-T-N type model for the ductile damage and failure response of both the materials examined. The role of micro-inertial effects on the porosity growth process is also considered.
Failure of wooden sandwich beam reinforced with glass/epoxy faces
Papakaliatakis, G. E.; Zacharopoulos, D. A. [Department of Civil Engineering, Democritus University of Thrace, Xanthi, 67100, Greece gpapakal@civil.duth.gr, dzachar@civil.duth.gr (Greece)
2015-12-31
The mechanical properties and the failure of wooden beam strengthened with two faces from glass/epoxy composite and a wooden beam without strengthening was studied. Stresses and deflections on both beams, which are imposed in three point bending loading. On the idealized geometry of the specimens with detailed nonlinear orthotropic analysis was performed with a finite elements program. The failure study of the wooden beams was performed, applying the criterion of Tsai-Hill. The shear strength of the adhesive was taken into account. All the specimens were tested with three point bending loading and the experimental results were compared to those of the theoretical approach with the finite elements analysis. Comparing the results, the advantage of strengthened wooden beam against the simple wooden beam becomes obvious. Theoretical predictions were in good agreement with experimental results.
A Study on Electrical Reliability Criterion on Through Silicon Via Packaging.
Lwo, Ben-Je; Tseng, Kuo-Hao; Tseng, Kun-Fu
2016-06-01
Three-dimensional (3D) structure with through silicon via (TSV) technology is emerging as a key issue in microelectronic packaging industry, and electrical reliability has become one of the main technical subjects for the TSV designs. However, criteria used for TSV reliability tests have not been consistent in the literature, so that the criterion itself becomes a technical argument. To this end, this paper first performed several different reliability tests on the testing packaging with TSV chains, then statistically analyzed the experimental data with different failure criteria on resistance increasing, and finally constructed the Weibull failure curves with parameter extractions. After comparing the results, it is suggested that using different criteria may lead to the same failure mode on Weibull analyses, and 65% of failed devices are recommended as a suitable termination for reliability tests.
Undrained response of reconstituted clay to cyclic pure principal stress rotation
严佳佳; 周建; 龚晓南; 曹洋
2015-01-01
A series of monotonic and rotational shearing tests are carried out on reconstituted clay using a hollow cylinder apparatus under undrained condition. In the rotational shearing tests, the principal stress axes rotate cyclically with the magnitudes of the principal stresses keeping constant. The anisotropy of the reconstituted clay is analyzed from the monotonic shearing tests. Obvious pore pressure is induced by the principal stress rotation alone even with shear stress q0=5 kPa. Strain components also accumulate with increasing the number of cycles and increases suddenly at the onset of failure. The deviatoric shear strain of 7.5%can be taken as the failure criterion for clay subjected to the pure cyclic principal stress rotation. The intermediate principal stress parameter b plays a significant role in the development of pore pressure and strain. Specimens are weakened by cyclic rotational shearing as the shear modulus decreases with increasing the number of cycles, and the shear modulus reduces more quickly with larger b. Clear deviation between the directions of the principal plastic strain increment and the principal stress is observed during pure principal stress rotation. Both the coaxial and non-coaxial plastic mechanisms should be taken into consideration to simulate the deformation behavior of clay under pure principal stress rotation. The mechanism of the soil response to the pure principal stress rotation is discussed based on the experimental observations.
Childhood trauma and personality disorder criterion counts: a co-twin control analysis.
Berenz, Erin C; Amstadter, Ananda B; Aggen, Steven H; Knudsen, Gun Peggy; Reichborn-Kjennerud, Ted; Gardner, Charles O; Kendler, Kenneth S
2013-11-01
Correlational studies consistently report relationships between childhood trauma (CT) and most personality disorder (PD) criteria and diagnoses. However, it is not clear whether CT is directly related to PDs or whether common familial factors (i.e., shared environment and/or genetic factors) better account for that relationship. The current study used a cotwin control design to examine support for a direct effect of CT on PD criterion counts. Participants were from the Norwegian Twin Registry (N = 2,780), including a subset (n = 898) of twin pairs (449 pairs, 45% monozygotic [MZ]) discordant for CT meeting DSM-IV Posttraumatic Stress Disorder Criterion A. All participants completed the Norwegian version of the Structured Interview for DSM-IV Personality. Significant associations between CT and all PD criterion counts were detected in the general sample; however, the magnitude of observed effects was small, with CT accounting for no more than approximately 1% of variance in PD criterion counts. A significant, yet modest, interactive effect was detected for sex and CT on Schizoid and Schizotypal PD criterion counts, with CT being related to these disorders among women but not men. After common familial factors were accounted for in the discordant twin sample, CT was significantly related to Borderline and Antisocial PD criterion counts, but no other disorders; however, the magnitude of observed effects was quite modest (r2 = .006 for both outcomes), indicating that the small effect observed in the full sample is likely better accounted for by common genetic and/or environmental factors. CT does not appear to be a key factor in PD etiology.
Enhanced Schapery Theory Software Development for Modeling Failure of Fiber-Reinforced Laminates
Pineda, Evan J.; Waas, Anthony M.
2013-01-01
Progressive damage and failure analysis (PDFA) tools are needed to predict the nonlinear response of advanced fiber-reinforced composite structures. Predictive tools should incorporate the underlying physics of the damage and failure mechanisms observed in the composite, and should utilize as few input parameters as possible. The purpose of the Enhanced Schapery Theory (EST) was to create a PDFA tool that operates in conjunction with a commercially available finite element (FE) code (Abaqus). The tool captures the physics of the damage and failure mechanisms that result in the nonlinear behavior of the material, and the failure methodology employed yields numerical results that are relatively insensitive to changes in the FE mesh. The EST code is written in Fortran and compiled into a static library that is linked to Abaqus. A Fortran Abaqus UMAT material subroutine is used to facilitate the communication between Abaqus and EST. A clear distinction between damage and failure is imposed. Damage mechanisms result in pre-peak nonlinearity in the stress strain curve. Four internal state variables (ISVs) are utilized to control the damage and failure degradation. All damage is said to result from matrix microdamage, and a single ISV marks the micro-damage evolution as it is used to degrade the transverse and shear moduli of the lamina using a set of experimentally obtainable matrix microdamage functions. Three separate failure ISVs are used to incorporate failure due to fiber breakage, mode I matrix cracking, and mode II matrix cracking. Failure initiation is determined using a failure criterion, and the evolution of these ISVs is controlled by a set of traction-separation laws. The traction separation laws are postulated such that the area under the curves is equal to the fracture toughness of the material associated with the corresponding failure mechanism. A characteristic finite element length is used to transform the traction-separation laws into stress-strain laws
Prediction of Brittle Failure for TBM Tunnels in Anisotropic Rock: A Case Study from Northern Norway
Dammyr, Øyvind
2016-06-01
Prediction of spalling and rock burst is especially important for hard rock TBM tunneling, because failure can have larger impact than in a drill and blast tunnel and ultimately threaten excavation feasibility. The majority of research on brittle failure has focused on rock types with isotropic behavior. This paper gives a review of existing theory and its application before a 3.5-m-diameter TBM tunnel in foliated granitic gneiss is used as a case to study brittle failure characteristics of anisotropic rock. Important aspects that should be considered in order to predict brittle failure in anisotropic rock are highlighted. Foliation is responsible for considerable strength anisotropy and is believed to influence the preferred side of v-shaped notch development in the investigated tunnel. Prediction methods such as the semi- empirical criterion, the Hoek- Brown brittle parameters, and the non-linear damage initiation and spalling limit method give reliable results; but only as long as the angle between compression axis and foliation in uniaxial compressive tests is relevant, dependent on the relation between tunnel trend/plunge, strike/dip of foliation, and tunnel boundary stresses. It is further demonstrated that local in situ stress variations, for example, due to the presence of discontinuities, can have profound impact on failure predictions. Other carefully documented case studies into the brittle failure nature of rock, in particular anisotropic rock, are encouraged in order to expand the existing and relatively small database. This will be valuable for future TBM planning and construction stages in highly stressed brittle anisotropic rock.
Failure mechanism and coupled static-dynamic loading theory in deep hard rock mining: A review
Xibing Li
2017-08-01
Full Text Available Rock failure phenomena, such as rockburst, slabbing (or spalling and zonal disintegration, related to deep underground excavation of hard rocks are frequently reported and pose a great threat to deep mining. Currently, the explanation for these failure phenomena using existing dynamic or static rock mechanics theory is not straightforward. In this study, new theory and testing method for deep underground rock mass under coupled static-dynamic loading are introduced. Two types of coupled loading modes, i.e. “critical static stress + slight disturbance” and “elastic static stress + impact disturbance”, are proposed, and associated test devices are developed. Rockburst phenomena of hard rocks under coupled static-dynamic loading are successfully reproduced in the laboratory, and the rockburst mechanism and related criteria are demonstrated. The results of true triaxial unloading compression tests on granite and red sandstone indicate that the unloading can induce slabbing when the confining pressure exceeds a certain threshold, and the slabbing failure strength is lower than the shear failure strength according to the conventional Mohr-Column criterion. Numerical results indicate that the rock unloading failure response under different in situ stresses and unloading rates can be characterized by an equivalent strain energy density. In addition, we present a new microseismic source location method without premeasuring the sound wave velocity in rock mass, which can efficiently and accurately locate the rock failure in hard rock mines. Also, a new idea for deep hard rock mining using a non-explosive continuous mining method is briefly introduced.
Low-angle normal faults-low differential stress at mid crustal levels
Power, W. L.
1985-01-01
A simple model for frictional slip on pre-existing faults that considers the local stress state near the fault and the effect of non-hydrostatic fluid pressures predicts that low-angle normal faulting is restricted to areas of the crust characterized by low differential stress and nearly lithostatic fluid pressures. The model considers frictional slip on a cohesionless low-angle normal fault governed by the failure criterion tau = mu sub f (sigma (*) sub n) =mu sub f (sigma sub n - P sub f) where tau and sigma sub n are the shear and normal stresses across the fault plane, mu sub f is the static coefficient of friction, and P sub f is the pore fluid pressure. As a first approximation, the model considers a vertical greatest principal compressive stress, sigma sub 1. It is apparent that if slip on low-angle normal faults is governed by the avove frictional failure criterion, slip on the low-angle normal fault occurs only if the least effective principal stress, sigma (*) sub 3 = sigma sub 3 - P sub f, is tensile, whenever tan superscrip -1(mu sub f d, where d is the dip of the fault. If detachment faulting occurs at any significant depth in the crust, P sub f sigma sub 3 is required. In light of this conclusion I allow P sub f to vary as necessary to allow slip on the low-angle normal fault.
Corrosion Failures in Marine Environment
R. Krishnan
1985-04-01
Full Text Available This paper gives a brief description of typical marine environments and the most common form of corrosion of materials used in this environment. Some typical case histories of failures pertaining to pitting, bimetallic corrosion, dealloying, cavitation and stress corrosion cracking are illustrated as typical examples of corrosion failures.
Bayesian information criterion for censored survival models.
Volinsky, C T; Raftery, A E
2000-03-01
We investigate the Bayesian Information Criterion (BIC) for variable selection in models for censored survival data. Kass and Wasserman (1995, Journal of the American Statistical Association 90, 928-934) showed that BIC provides a close approximation to the Bayes factor when a unit-information prior on the parameter space is used. We propose a revision of the penalty term in BIC so that it is defined in terms of the number of uncensored events instead of the number of observations. For a simple censored data model, this revision results in a better approximation to the exact Bayes factor based on a conjugate unit-information prior. In the Cox proportional hazards regression model, we propose defining BIC in terms of the maximized partial likelihood. Using the number of deaths rather than the number of individuals in the BIC penalty term corresponds to a more realistic prior on the parameter space and is shown to improve predictive performance for assessing stroke risk in the Cardiovascular Health Study.
Biasibetti, Micheli; Rojas, Denise B; Hentschke, Vítor S; Moura, Dinara Jaqueline; Karsten, Marlus; Wannmacher, Clóvis M D; Saffi, Jenifer; Dal Lago, Pedro
2014-11-01
In heart failure (HF), there is an imbalance between the production of reactive oxygen species and the synthesis of antioxidant enzymes, causing damage to the cardiovascular function and increased susceptibility to DNA damage. The aim of this study was to evaluate the influence of low-level laser therapy (LLLT) on parameters of oxidative stress and DNA damage in skeletal muscle and plasma of rats with HF. Wistar rats were allocated into six groups: "placebo" HF rats (P-HF, n = 9), "placebo" Sham rats (P-sham, n = 8), HF rats at a dose 3 J/cm(2) of LLLT (3 J/cm(2)-HF, n = 8), sham rats at a dose 3 J/cm(2) of LLLT (3 J/cm(2)-sham, n = 8), HF rats at a dose 21 J/cm(2) of LLLT (21 J/cm(2)-HF, n = 8) and sham rats at a dose 21 J/cm(2) of LLLT (21 J/cm(2)-sham, n = 8). Animals were submitted to a LLLT protocol for 10 days at the right gastrocnemius muscle. Comparison between groups showed a significant reduction in superoxide dismutase (SOD) activity in the 3 J/cm(2)-HF group (p = 0.03) and the 21 J/cm(2)-HF group (p = 0.01) compared to the P-HF group. 2',7'-Dihydrodichlorofluorescein (DCFH) oxidation levels showed a decrease when comparing 3 J/cm(2)-sham to P-sham (p = 0.02). The DNA damage index had a significant increase either in 21 J/cm(2)-HF or 21 J/cm(2)-sham in comparison to P-HF (p = 0.004) and P-sham (p = 0.001) and to 3 J/cm(2)-HF (p = 0.007) and 3 J/cm(2)-sham (p = 0.037), respectively. Based on this, laser therapy appears to reduce SOD activity and DCFH oxidation levels, changing the oxidative balance in the skeletal muscle of HF rats. Otherwise, high doses of LLLT seem to increase DNA damage.
Suboptimal Criterion Learning in Static and Dynamic Environments.
Norton, Elyse H; Fleming, Stephen M; Daw, Nathaniel D; Landy, Michael S
2017-01-01
Humans often make decisions based on uncertain sensory information. Signal detection theory (SDT) describes detection and discrimination decisions as a comparison of stimulus "strength" to a fixed decision criterion. However, recent research suggests that current responses depend on the recent history of stimuli and previous responses, suggesting that the decision criterion is updated trial-by-trial. The mechanisms underpinning criterion setting remain unknown. Here, we examine how observers learn to set a decision criterion in an orientation-discrimination task under both static and dynamic conditions. To investigate mechanisms underlying trial-by-trial criterion placement, we introduce a novel task in which participants explicitly set the criterion, and compare it to a more traditional discrimination task, allowing us to model this explicit indication of criterion dynamics. In each task, stimuli were ellipses with principal orientations drawn from two categories: Gaussian distributions with different means and equal variance. In the covert-criterion task, observers categorized a displayed ellipse. In the overt-criterion task, observers adjusted the orientation of a line that served as the discrimination criterion for a subsequently presented ellipse. We compared performance to the ideal Bayesian learner and several suboptimal models that varied in both computational and memory demands. Under static and dynamic conditions, we found that, in both tasks, observers used suboptimal learning rules. In most conditions, a model in which the recent history of past samples determines a belief about category means fit the data best for most observers and on average. Our results reveal dynamic adjustment of discrimination criterion, even after prolonged training, and indicate how decision criteria are updated over time.
Hou, Yanqing; Verhagen, Sandra; Wu, Jie
2016-12-01
Ambiguity Resolution (AR) is a key technique in GNSS precise positioning. In case of weak models (i.e., low precision of data), however, the success rate of AR may be low, which may consequently introduce large errors to the baseline solution in cases of wrong fixing. Partial Ambiguity Resolution (PAR) is therefore proposed such that the baseline precision can be improved by fixing only a subset of ambiguities with high success rate. This contribution proposes a new PAR strategy, allowing to select the subset such that the expected precision gain is maximized among a set of pre-selected subsets, while at the same time the failure rate is controlled. These pre-selected subsets are supposed to obtain the highest success rate among those with the same subset size. The strategy is called Two-step Success Rate Criterion (TSRC) as it will first try to fix a relatively large subset with the fixed failure rate ratio test (FFRT) to decide on acceptance or rejection. In case of rejection, a smaller subset will be fixed and validated by the ratio test so as to fulfill the overall failure rate criterion. It is shown how the method can be practically used, without introducing a large additional computation effort. And more importantly, how it can improve (or at least not deteriorate) the availability in terms of baseline precision comparing to classical Success Rate Criterion (SRC) PAR strategy, based on a simulation validation. In the simulation validation, significant improvements are obtained for single-GNSS on short baselines with dual-frequency observations. For dual-constellation GNSS, the improvement for single-frequency observations on short baselines is very significant, on average 68%. For the medium- to long baselines, with dual-constellation GNSS the average improvement is around 20-30%.
Macleod, Anna
1998-01-01
Systems Failure A solo exhibition of new work by Anna Macleod developed in conversation with curator Liz Burns. The Dock, Carrick on Shannon, Co Leitrim. Ireland. 12th February – 17th April 2010. The works for the exhibition Systems Failure include drawings, prints and small constructions that examine the delicate balance that exists between need and aspects of failure rooted in the relationship between humanity and land use. The work seeks to question the relationship between scient...
A Difference Criterion for Dimensionality Reduction
Aved, A. J.; Blasch, E.; Peng, J.
2015-12-01
A dynamic data-driven geoscience application includes hyperspectral scene classification which has shown promising potential in many remote-sensing applications. A hyperspectral image of a scene spectral radiance is typically measured by hundreds of contiguous spectral bands or features, ranging from visible/near-infrared (VNIR) to shortwave infrared (SWIR). Spectral-reflectance measurements provide rich information for object detection and classification. On the other hand, they generate a large number of features, resulting in a high dimensional measurement space. However, a large number of features often poses challenges and can result in poor classification performance. This is due to the curse of dimensionality which requires model reduction, uncertainty quantification and optimization for real-world applications. In such situations, feature extraction or selection methods play an important role by significantly reducing the number of features for building classifiers. In this work, we focus on efficient feature extraction using the dynamic data-driven applications systems (DDDAS) paradigm. Many dimension reduction techniques have been proposed in the literature. A well-known technique is Fisher's linear discriminant analysis (LDA). LDA finds the projection matrix that simultaneously maximizes a within class scatter matrix and minimizes a between class scatter matrix. However, LDA requires matrix inverse which can be a major issue when the within matrix is singular. We propose a difference criterion for dimension reduction that does not require a matrix inverse for software implementation. We show how to solve the optimization problem with semi-definite programming. In addition, we establish an error bound for the proposed algorithm. We demonstrate the connection between relief feature selection and a two class formulation of multi-class problems, thereby providing a sound basis for observed benefits associated with this formulation. Finally, we provide
Chunhui ZHANG
Full Text Available How to quantitatively evaluate the permeability change of coalbed subjected to liquid nitrogen cooling is a key issue of enhanced-permeability technology of coalbed. To analyze the evolution process of permeability of coupled coal deformation, failure and liquid introgen cooling, the coal is supposed as elastic, brittle and plastic material. Its deformation process includes elastic deformation stage, brittle strength degradation stage and residual plastic flow stage. Combined with strength degradation index, dilatancy index of the element and Mohr-Column strength criterion, the element scale constitutive model with the effects of confining pressure on peak-post mechanical behaviors is built. Based on the deformation process of coal rock, there exist two stages of permeability evolution of the element including decrease of permeability due to elastic contraction and increase due to coal rock element's failure. The relationships between the permeability and elastic deformation, shear failure and tension failure for coal are studied. The permeability will be influenced by the change of pore space due to elastic contraction or tension of element. Conjugate shear zones appear during the shear failure of the element, in which the flow follows so-called cubic law between smooth parallel plates. The calculation formulas of the permeability and the aperture of the fractures are given out based on the volumetric strain. When tension failure criterion is satisfied with the rock element fails and two orthogonal fractures appear. The calculation formulas of the permeability and the width of the fractures are given out based on the volumetric strain. Further, combined with the thermal conduction theory the permeability evolution model of coupled coal deformation, failure and liquid nitrogen cooling is presented. Then Fish function method in FLAC is employed to perform the model. The permeability's evolution process for coal bed cryogenically stimulated
Singh, Gyanender, E-mail: sing0550@umn.edu [Department of Mechanical Engineering, University of Minnesota, 111, Church St. SE, Minneapolis, MN 55455 (United States); Fok, Alex [Minnesota Dental Research in Biomaterials and Biomechanics, School of Dentistry, University of Minnesota, 515, Delaware St. SE, Minneapolis, MN 55455 (United States); Department of Mechanical Engineering, University of Minnesota, 111, Church St. SE, Minneapolis, MN 55455 (United States); Mantell, Susan [Department of Mechanical Engineering, University of Minnesota, 111, Church St. SE, Minneapolis, MN 55455 (United States)
2017-06-15
Highlights: • Failure probability of VHTR reflector bricks predicted though crack modeling. • Criterion chosen for defining failure strongly affects the predictions. • Breaching of the CRC could be significantly delayed through crack arrest. • Capability to predict crack initiation and propagation demonstrated. - Abstract: Graphite is used in nuclear reactor cores as a neutron moderator, reflector and structural material. The dimensions and physical properties of graphite change when it is exposed to neutron irradiation. The non-uniform changes in the dimensions and physical properties lead to the build-up of stresses over the course of time in the core components. When the stresses reach the critical limit, i.e. the strength of the material, cracking occurs and ultimately the components fail. In this paper, an explicit crack modeling approach to predict the probability of failure of a VHTR prismatic reactor core reflector brick is presented. Firstly, a constitutive model for graphite is constructed and used to predict the stress distribution in the reflector brick under in-reactor conditions of high temperature and irradiation. Fracture simulations are performed as part of a Monte Carlo analysis to predict the probability of failure. Failure probability is determined based on two different criteria for defining failure time: A) crack initiation and B) crack extension to near control rod channel. A significant difference is found between the failure probabilities based on the two criteria. It is predicted that the reflector bricks will start cracking during the time range of 5–9 years, while breaching of the control rod channels will occur during the period of 11–16 years. The results show that, due to crack arrest, there is a significantly delay between crack initiation and breaching of the control rod channel.
Modified Schur-Cohn Criterion for Stability of Delayed Systems
Juan Ignacio Mulero-Martínez
2015-01-01
Full Text Available A modified Schur-Cohn criterion for time-delay linear time-invariant systems is derived. The classical Schur-Cohn criterion has two main drawbacks; namely, (i the dimension of the Schur-Cohn matrix generates some round-off errors eventually resulting in a polynomial of s with erroneous coefficients and (ii imaginary roots are very hard to detect when numerical errors creep in. In contrast to the classical Schur-Cohn criterion an alternative approach is proposed in this paper which is based on the application of triangular matrices over a polynomial ring in a similar way as in the Jury test of stability for discrete systems. The advantages of the proposed approach are that it halves the dimension of the polynomial and it only requires seeking real roots, making this modified criterion comparable to the Rekasius substitution criterion.
Mondal, Nandan K; Chen, Zengsheng; Trivedi, Jaimin R; Sorensen, Erik N; Pham, Si M; Slaughter, Mark S; Griffith, Bartley P; Wu, Zhongjun J
2017-09-26
Nonsurgical bleeding (NSB) in heart failure (HF) patients with continuous-flow left ventricular assist device (CF-LVAD) support is the most common clinical complication. The aim of this study was to investigate the association between oxidative stress and platelet glycoproteins GPIbα and GPVI shedding on the incidence of NSB in CF-LVAD patients. Fifty-one HF patients undergoing CF-LVAD implantation and 11 healthy volunteers were recruited. Fourteen patients developed NSB (bleeder group) during 1 month follow-up duration, while others were considered nonbleeder group (n = 37). Several biomarkers of oxidative stress were quantified at baseline and weekly intervals in all patients. Surface expression and plasma elements of platelet receptor glycoproteins GPIbα and GPVI were measured. Oxidative stress biomarkers and platelet GPIbα and GPVI receptor-shedding (decreased surface expression and higher plasma levels) were found to be preexisting conditions in baseline samples of both groups of HF patients when compared with healthy volunteers. Significantly elevated oxidative stress biomarkers and platelet glycoprotein receptor shedding were observed in postimplant bleeder group temporarily when compared with nonbleeder group. Strong significant associations between biomarkers of oxidative stress and platelet glycoprotein receptor shedding were observed, suggesting a possible role of oxidative stress in platelet integrin shedding leading to NSB in CF-LVAD patients. Receiver operating characteristic analyses of GPIbα and GPVI indicated that the likelihood of NSB had a predictive power of bleeding complication in CF-LVAD patients. In conclusion, elevated oxidative stress may play a role in GPIbα and GPVI shedding in the event of NSB. Thus, oxidative stress and GPIbα and GPVI shedding may be used as potential biomarkers for bleeding risk stratification in those patients.
Failure in imperfect anisotropic materials
Legarth, Brian Nyvang
2005-01-01
The fundamental cause of crack growth, namely nucleation and growth of voids, is investigated numerically for a two phase imperfect anisotropic material. A unit cell approach is adopted from which the overall stress strain is evaluated. Failure is observed as a sudden stress drop and depending...
New Quality Assessment Criterion of AlSi5Cu1 Alloy
M. Wierzbińska
2007-07-01
Full Text Available The paper presents the discussion of the results of mechanical testing for aluminium foundry alloy AlSi5Cu1Mg for high-loaded machine elements. Values of yield strength (Rp0.2, tensile strength (Rm, elongation(A5 and hardness (HB are usually considered as the primary quality assessment criterion for a manufacturing process. It was concluded, that this criterion, A5 index particularly, is unsatisfactory to estimate the plasticity of the alloy and its crack resistance in the presence of sharp-pointed stress concentrators or microcracks. More adequate parameter is plane strain fracture toughness KIc. However, size of the samples appeared to be twice as large as would be needed to fulfill requirements of test conditions, and the test itself is laborious and time-consuming that it becomes impractical as a acceptance test. Therefore, substitute test for quality assessment – determination of tensile strength in the presence of a sharp notch kmR was applied. The comparative analysis of kmR/Rp0.2 ratio, as a more enhanced fatigue resistance criterion than kmR and plane strain fracture toughness KIc of the alloy was performed. It was assumed that kmR/Rp0.2 parameter has good correlation with the critical stress intensity factor KIc Thus, under manufacturing process conditions, being unable to carry out KIc test, it may be successfully replaced by kmR test.
Activity criterion of pre-existing fabrics in non-homogeneous deformation domain
无
2010-01-01
The Anderson’s model can be applied only to elastic homogeneous deformation and cannot explain complicated phenomena of natural faults, which to a large degree limits the model to practical application. By combing the Coulomb-Mohr Criterion with the sandbox modeling and considering non-homogeneous deformation, mechanisms of how basement pre-existing fabrics control fault formation and evolution are analyzed and a mechanical factor, activation-coefficient (faS) of pre-existing fabrics, is proposed. It is determined by the attitude and mechanical properties of pre-existing fabric, and the stress state (the magnitudes and directions of the three principal stresses). The coefficient has taken the heterogeneity of rocks into account and may serve as a criterion for evaluating the activity of a pre-existing fabric. The Mohr-Coulomb Criterion is expanded to non-homogeneous deformation domain in terms of activation-coefficient (faS) of pre-existing fabrics, the general law of the activity of a pre-existing fabric is predicted, the fault complexity real of rift basin is revealed in theory, and the controlling law of basement pre-existing faults to fault formation and evolution is determined, and checked with sandbox modeling. A new way is provided for in-depth study of faulting.
Modeling of stress-triggered faulting and displacement magnitude along Agenor Linea, Europa
Nahm, A.; Cameron, M. E.; Smith-Konter, B. R.; Pappalardo, R. T.
2012-12-01
We investigate the relationship between shear and normal stresses at Agenor Linea (AL) to better understand the role of tidal stress sources and implications for faulting on Europa. AL is a ~1500 km long, E-W trending, 20-30 km wide zone of geologically young deformation located in the southern hemisphere, and it forks into two branches at its eastern end. Based on photogeological evidence and stress orientation predictions, AL is primarily a right-lateral strike slip fault and may have accommodated up to 20 km of right-lateral slip. We compute tidal shear and normal stresses along present-day AL using SatStress, a numerical code that calculates tidal stresses at any point on the surface of a satellite for both diurnal and non-synchronous rotation (NSR) stresses. We adopt model parameters appropriate for Europa with a spherically symmetric, 20 km thick ice shell underlain by a global subsurface ocean and assume a coefficient of friction μ = 0.6. Along AL, shear stresses are primarily right-lateral (~1.8 MPa), while normal stresses are predominantly compressive along the west side of the structure (~0.7 MPa) and tensile along the east side (~2.9 MPa). Failure along AL is assessed using the Coulomb failure criterion, which states that shear failure occurs when the shear stress exceeds the frictional resistance of the fault. Where fault segments meet these conditions for shear failure, coseismic displacements are determined (assuming complete stress drop). We calculate shallow displacements as large as ~50 m at 1 km depth and ~10 m at 3 km depth. Triggered stresses from coseismic fault slip may also contribute to the total slip. We investigate the role of stress triggering by computing the change in Coulomb failure stress (ΔCFS) along AL. Where slip has occurred, negative ΔCFS is calculated; positive ΔCFS values indicate segments where failure is promoted. Positive ΔCFS is calculated at the western tip and the intersection of the branches with the main fault at a
Schepis, Ty S; Tapscott, Brian E; Krishnan-Sarin, Suchitra
2016-04-01
Substantial evidence links greater impulsivity and stress exposure to poorer smoking cessation outcomes. Results from adolescents also indicate that stress-related change in risk taking can impede cessation attempts. We investigated the effects of stress-related change in impulsivity, risk taking, attention and nicotine withdrawal, and craving in young adult smokers on time to smoking relapse in a relapse analogue paradigm. Twenty-six young adult smokers (50% women; mean age: 20.9 ± 1.8) were exposed to a stress imagery session followed by a contingency management-based relapse analogue paradigm. Participants smoked at least 5 cigarettes daily, with a mean baseline carbon monoxide (CO) level of 13.7 (± 5.1) ppm. Repeated measures analysis of variance (ANOVA) and paired t tests examined stress induction validity and Cox regressions of proportional hazards examined the effects of stress-related changes in nicotine withdrawal, nicotine craving, attention, impulsivity, and risk taking on time to relapse. While stress-related change in impulsivity, nicotine craving and withdrawal did not predict time to relapse (all ps > .10), greater stress-related increases in reaction time (RT) variability (p = .02) were predictive of shorter time to relapse, with trend-level findings for inattention and risk taking. Furthermore, changes in stress-related risk taking affected outcome in women more than in men, with a significant relationship between stress-related change in risk taking only in women (p = .026). Smoking cessation attempts in young adults may be adversely impacted by stress-related increases in risk taking and attentional disruption. Clinicians working with young adults attempting cessation may need to target these stress-related impairments by fostering more adaptive coping and resilience.
The criterion for time symmetry of probabilistic theories and the reversibility of quantum mechanics
Holster, A. T.
2003-10-01
Physicists routinely claim that the fundamental laws of physics are 'time symmetric' or 'time reversal invariant' or 'reversible'. In particular, it is claimed that the theory of quantum mechanics is time symmetric. But it is shown in this paper that the orthodox analysis suffers from a fatal conceptual error, because the logical criterion for judging the time symmetry of probabilistic theories has been incorrectly formulated. The correct criterion requires symmetry between future-directed laws and past-directed laws. This criterion is formulated and proved in detail. The orthodox claim that quantum mechanics is reversible is re-evaluated. The property demonstrated in the orthodox analysis is shown to be quite distinct from time reversal invariance. The view of Satosi Watanabe that quantum mechanics is time asymmetric is verified, as well as his view that this feature does not merely show a de facto or 'contingent' asymmetry, as commonly supposed, but implies a genuine failure of time reversal invariance of the laws of quantum mechanics. The laws of quantum mechanics would be incompatible with a time-reversed version of our universe.
Battaglia, Eleonora; Bonollo, Franco; Ferro, Paolo
2017-05-01
Defects, particularly porosity and oxides, in high-pressure die casting can seriously compromise the in-service behavior and durability of products subjected to static or cyclic loadings. In this study, the influence of dimension, orientation, and position of casting defects on the mechanical properties of an AlSi12(b) (EN-AC 44100) aluminum alloy commercial component has been studied. A finite element model has been carried out in order to calculate the stress distribution induced by service loads and identify the crack initiation zones. Castings were qualitatively classified on the basis of porosities distribution detected by X-ray technique and oxides observed on fracture surfaces of specimens coming from fatigue and tensile tests. A damage criterion has been formulated which considers the influence of defects position and orientation on the mechanical strength of the components. Using the proposed damage criterion, it was possible to describe the mechanical behavior of the castings with good accuracy.
A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow
Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)] [and others
1995-09-01
This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.
A New Ductile Fracture Criterion for Various Deformation Conditions Based on Microvoid Model
HUANG Jian-ke; DONG Xiang-huai
2009-01-01
To accurately predict the occurrence of ductile fracture in metal forming processes, the Gurson-Tvergaard (GT) porous material model with optimized adjustment parameters is adopted to analyze the macroscopic stress-strain response, and a practical void nucleation law is proposed with a few material constants for engineering applications. Mechanical and metallographie analyses of uniaxial tension, torsion and upsetting experiments are performed. According to the character of the metal forming processes, the basic mechanisms of ductile fracture are divided into two modes: tension-type mode and shear-type mode. A unified fracture criterion is proposed for wide applicable range, and the comparison of experimental results with numerical analysis results confirms the validity of the newly proposed ductile fracture criterion based on the GT porous material model.
Wavelength selection in injection-driven Hele-Shaw flows: A maximum amplitude criterion
Dias, Eduardo; Miranda, Jose
2013-11-01
As in most interfacial flow problems, the standard theoretical procedure to establish wavelength selection in the viscous fingering instability is to maximize the linear growth rate. However, there are important discrepancies between previous theoretical predictions and existing experimental data. In this work we perform a linear stability analysis of the radial Hele-Shaw flow system that takes into account the combined action of viscous normal stresses and wetting effects. Most importantly, we introduce an alternative selection criterion for which the selected wavelength is determined by the maximum of the interfacial perturbation amplitude. The effectiveness of such a criterion is substantiated by the significantly improved agreement between theory and experiments. We thank CNPq (Brazilian Sponsor) for financial support.
Flow and failure of an aluminium alloy from low to high temperature and strain rate
Sancho Rafael
2015-01-01
Full Text Available The mechanical behaviour of an aluminium alloy is presented in this paper. The study has been carried out to analyse the flow and failure of the aluminium alloy 7075-T73. An experimental study has been planned performing tests of un-notched and notched tensile specimens at low strain rates using a servo-hydraulic machine. High strain rate tests have been carried out using the same geometry in a Hopkinson Split Tensile Bar. The dynamic experiments at low temperature were performed using a cryogenic chamber, and the high temperature ones with a furnace, both incorporated to the Hopkinson bar. Testing temperatures ranged from − 50 ∘C to 100 ∘C and the strain rates from 10−4 s−1 to 600 s−1. The material behaviour was modelled using the Modified Johnson-Cook model and simulated using LS-DYNA. The results show that the Voce type of strain hardening is the most accurate for this material, while the traditional Johnson-Cook is not enough accurate to reproduce the necking of un-notched specimens. The failure criterion was obtained by means of the numerical simulations using the analysis of the stress triaxiality versus the strain to failure. The diameters at the failure time were measured using the images taken with an image camera, and the strain to failure was computed for un-notched and notched specimens. The numerical simulations show that the analysis of the evolution of the stress triaxiality is crucial to achieve accurate results. A material model using the Modified Johnson-Cook for flow and failure is proposed.
刘超; 孙秦; 刘彦杰
2014-01-01
通过将改进的X-W延性金属断裂模型结合修正的von-Mises准则嵌入ABAQUS/explicit用户材料子程序VUMAT的方式，对一系列铝合金2A12-T4试件的渐进断裂过程进行数值模拟，该模型以连续损伤力学为基础，并考虑静水压力和 Lode 角对损伤变量的作用。为了预测该模型的有效性并预测金属的延性断裂，对铝合金2A12-T4光滑圆棒、带缺口的棒材和紧凑拉伸试件(CT试件)进行单向拉伸试验及数值模拟。同时对比分析几何非线性和屈服准则的影响在数值仿真计算中的差异。结果表明，该断裂模型结合修正的von-Mises屈服准则可很好地预测2A12-T4试件渐进破坏试验的载荷-位移曲线及各试件的宏观断裂形貌。其中，“隧道”效应能够很好地解释CT试件处于平面应变状态的中心层和平面应力状态的表面层的抗断裂能力的差异。%A modified X-W ductile fracture model with modified von-Mises yield criterion based on the continuum damage mechanics which combined the effect of pressure and Lode angle on damage variable was implemented into ABAQUS/explicit through the user subroutine VUMAT to simulate the progressive failure of specimens of aluminum alloy 2A12-T4. In order to verify the modified fracture model and predict the progressive failure behavior of the ductile metals, a series of experiments of aluminum alloy 2A12-T4 specimens including smooth and notched round bars and compact tension (CT) specimen as well as corresponding numerical performances were conducted. Meanwhile, different numerical simulations with or without geometric non-linearity and different yield criteria were studied by comparing the difference. The numerical results show that the fracture model with modified von-Mises yield criterion can accurately and effectively predict the experimental results of 2A12-T4 specimens including load-displacement curves and macroscopic fracture morphology. Among them, the
A review of macroscopic ductile failure criteria.
Corona, Edmundo; Reedlunn, Benjamin
2013-09-01
The objective of this work was to describe several of the ductile failure criteria com- monly used to solve practical problems. The following failure models were considered: equivalent plastic strain, equivalent plastic strain in tension, maximum shear, Mohr- Coulomb, Wellman's tearing parameter, Johnson-Cook and BCJ MEM. The document presents the main characteristics of each failure model as well as sample failure predic- tions for simple proportional loading stress histories in three dimensions and in plane stress. Plasticity calculations prior to failure were conducted with a simple, linear hardening, J2 plasticity model. The resulting failure envelopes were plotted in prin- cipal stress space and plastic strain space, where the dependence on stress triaxiality and Lode angle are clearly visible. This information may help analysts select a ductile fracture model for a practical problem and help interpret analysis results.
Pathophysiology of heart failure.
Chiariello, M; Perrone-Filardi, P
1999-01-01
Heart failure is a leading cause of mortality and morbidity in Western countries. Common etiology is mostly represented by ischemic and hypertensive heart disease. Clinically, heart failure can be defined as an impaired cardiac performance, unable to meet the energy requirements of the periphery. Pathophysiologically, the clinical onset of heart failure symptoms already represents an advanced stage of disease when compensatory mechanisms triggered by the underlying decrease in contractility are no longer capable of maintaining adequate cardiac performance during exercise and, subsequently, under resting conditions. Independent of its underlying etiology, cardiac failure is always characterized by an impairment in the intrinsic contractility of myocytes. As a consequence of reduced contractility, a number of central and peripheral compensatory mechanisms take place that are capable of effectively counteracting reduced intravascular intrinsic performance for a long period of time. Among them, recruitment of preload reserve, enhanced neurohormonal stimulation and cardiac hypertrophy are the most important. All of them, however, also carry unfavorable effects that contribute to further deterioration of cardiac function. In fact, increased end-diastolic volume determines increased wall stress that further reduces systolic performance; sympathetic and angiotensin stimulation increases peripheral resistance and contributes to increase volume expansion; hypertrophic myocytes demonstrate impaired intrinsic contractility and relaxation, and hypertrophy causes a clinically relevant deterioration of ventricular relaxation and compliance that substantially participates in increased end-diastolic pressure, and, therefore, to limited exercise performance. Diastolic dysfunction usually accompanies systolic dysfunction, although in some cases it may represent the prevalent mechanism of congestive heart failure in patients in whom systolic performance is preserved. Biological causes
Sven Krabbenhoft
2012-01-01
Full Text Available This paper presents the results of a series of triaxial tests with dry sand at confining pressures varying from 1.5 kPa to 100 kPa at relative densities of 0.20, 0.59, and 0.84. The results, which are in reasonable accordance with an equation given by Bolton, show that the friction angle is strongly dependent on the stress level and on the basis of the test results, a nonlinear Mohr failure criterion has been proposed. This yield criterion has been implemented in a finite element program and an analysis of the bearing capacity of a circular shaped model foundation, diameter 100 mm, has been conducted. Comparisons have been made with results from 1g model scale tests with a foundation of similar size and a good agreement between numerical results and test results has been found.
Information on stress conditions in the oceanic crust from oval fractures in a deep borehole
Morin, R.H.
1990-01-01
Oval images etched into the wall of a deep borehole were detected in DSDP Hole 504B, eastern equatorial Pacific Ocean, from analysis of an acoustic televiewer log. A systematic inspection of these ovals has identified intriguing consistencies in appearance that cannot be explained satisfactorily by a random, coincidental distribution of pillow lavas. As an alternative hypothesis, Mohr-Coulomb failure criterion is used to account for the generation and orientation of similarly curved, stress-induced fractures. Consequently, these oval features can be interpreted as fractures and related directly to stress conditions in the oceanic crust at this site. The azimuth of the oval center corresponds to the orientation of maximum horizontal principal stress (SH), and the oval width, which spans approximately 180?? of the borehole, is aligned with the azimuth of minimum horizontal principal stress (Sh). The oval height is controlled by the fracture angle and thus is a function of the coefficient of internal friction of the rock. -from Author
Benzerga, Ahmed Amine; Leblond, Jean Baptiste; Needleman, Alan
2016-01-01
anisotropy, or the influence of nonlocal effects that bring a material size scale into the models. Often the voids are not present in the material from the beginning, and realistic nucleation models are important. The final failure process by coalescence of neighboring voids is an issue that has been given......Ductile fracture of structural metals occurs mainly by the nucleation, growth and coalescence of voids. Here an overview of continuum models for this type of failure is given. The most widely used current framework is described and its limitations discussed. Much work has focused on extending void...... growth models to account for non-spherical initial void shapes and for shape changes during growth. This includes cases of very low stress triaxiality, where the voids can close up to micro-cracks during the failure process. The void growth models have also been extended to consider the effect of plastic...
Robust Hammerstein Adaptive Filtering under Maximum Correntropy Criterion
Zongze Wu
2015-10-01
Full Text Available The maximum correntropy criterion (MCC has recently been successfully applied to adaptive filtering. Adaptive algorithms under MCC show strong robustness against large outliers. In this work, we apply the MCC criterion to develop a robust Hammerstein adaptive filter. Compared with the traditional Hammerstein adaptive filters, which are usually derived based on the well-known mean square error (MSE criterion, the proposed algorithm can achieve better convergence performance especially in the presence of impulsive non-Gaussian (e.g., α-stable noises. Additionally, some theoretical results concerning the convergence behavior are also obtained. Simulation examples are presented to confirm the superior performance of the new algorithm.
Industry Software Trustworthiness Criterion Research Based on Business Trustworthiness
Zhang, Jin; Liu, Jun-fei; Jiao, Hai-xing; Shen, Yi; Liu, Shu-yuan
To industry software Trustworthiness problem, an idea aiming to business to construct industry software trustworthiness criterion is proposed. Based on the triangle model of "trustworthy grade definition-trustworthy evidence model-trustworthy evaluating", the idea of business trustworthiness is incarnated from different aspects of trustworthy triangle model for special industry software, power producing management system (PPMS). Business trustworthiness is the center in the constructed industry trustworthy software criterion. Fusing the international standard and industry rules, the constructed trustworthy criterion strengthens the maneuverability and reliability. Quantitive evaluating method makes the evaluating results be intuitionistic and comparable.
The Bohm criterion for a dusty plasma sheath
B P Pandey; Anjan Dutta
2005-07-01
The formation of the sheath in a dusty plasma is investigated. The Bohm criterion is derived for two different cases: (a) when electrons are in thermodynamic equilibrium and dust grains provide the immobile, stationary background and (b) when both electrons and ions are in thermodynamic equilibrium and dust grains are moving. In the first case, Bohm criterion gets modified due to the fluctuation of the charge on the grain surface. In the second case, the collisional and Coulombic drag play important role in determining the Bohm criterion.
Energy Criterion for the Spectral Stability of Discrete Breathers
Kevrekidis, Panayotis G.; Cuevas-Maraver, Jesús; Pelinovsky, Dmitry E.
2016-08-01
Discrete breathers are ubiquitous structures in nonlinear anharmonic models ranging from the prototypical example of the Fermi-Pasta-Ulam model to Klein-Gordon nonlinear lattices, among many others. We propose a general criterion for the emergence of instabilities of discrete breathers analogous to the well-established Vakhitov-Kolokolov criterion for solitary waves. The criterion involves the change of monotonicity of the discrete breather's energy as a function of the breather frequency. Our analysis suggests and numerical results corroborate that breathers with increasing (decreasing) energy-frequency dependence are generically unstable in soft (hard) nonlinear potentials.
A definitive criterion for cathodic protection
Alexander, Roger [Cathodic Protection Network International Ltd., Reading (United Kingdom)
2009-07-01
The corrosion reaction is defined using the Pourbaix Diagram and includes consideration of the pH, temperature, pressure, nobility of the metal and conductivity of the electrolyte. The passive zone can be established in a laboratory by creating a closed circuit condition in which the voltages can be measured. Natural corrosion cells occurring in simple conditions can be evaluated for the purpose of monitoring the performance of cathodic protection. Metal pipelines are complex networks of conductors submerged in electrolyte of infinitely variable qualities. The present method used to ascertain the effectiveness of cathodic protection has many inherent errors and results in costly and unpredictable corrosion failures. An electrode has been devised to define the exact electrical status of the corrosion reaction at its location. The design allows a closed circuit measurement of the corrosion current that can determine whether or not corrosion has been stopped by cathodic protection. This has allowed the development of software that can calculate the condition and corrosion status throughout a network of pipelines, using electrical circuit analysis common in the electronics industry. (author)
Is the 80% leak criterion always appropriate?
Haines, Harvey [Kiefner and Associates, Inc., Vienna, VA (United States); McNealy, Rick [Applus-RTD, Houston, TX (United States); Rosenfeld, M.J. [Kiefner and Associates, Inc., Worthington, OH (United States)
2010-07-01
For evaluating metal loss depth by corrosion, ASME B31G recommends 80% of the wall thickness as an upper limit. A pipeline can still be safe with deeper corrosion, but the main question is whether conservative criteria are necessary because of errors in corrosion depth measurement. Corrosion depths over 80% might be acceptable if the measurement error was well understood and if errors could be treated in a routine and practical manner. Measurement errors are well understood when published values exist for commercial ILI tools and errors can be reassessed during remediation using in-the-ditch measurements. In the case of low-pressure pipelines, the 80% recommendation seems to be overly conservative and restricts re-inspection intervals unnecessarily. Otherwise, 80% seems appropriate in view of the current ILI and manual pit gauge depth measurement technology, but if the accuracy of ILI inspections was improved, fewer immediate digs could be possible. Corrosion deeper than 80% seems to cause leaks by perforation rather than mechanical failure.
2008-01-01
2008275 Relationship of calcineure in mRNA level in peripheral blood and cardiac muscle of patients with heart failure.WANG Mengmeng(王萌萌),et al.Dept Cardiol,Shandong Prov Hosp,Shandong Univ,Jinan 250021.Chin Cir J 2008;23(2):113-116.Objective To study the relationship of calcineurin mRNA level between peripheral lymphocytes and cardiac muscles of patients with chronic heart failure.Methods
2008-01-01
2008037 Factors associated with efficacy of cardiac resynchronization therapy for patients with congestive heart failure. SHI Haoying(史浩颖), et al. Dept Cardiol, Zhongshan Hosp Fudan Univ, Shanghai 200032. Chin J Cardiol 2007;35(12):1099-1163. Objective The efficacy of cardiac resynchronization therapy (CRT) in patients with congestive heart failure and the potential factors associated with responder or nonresponder were investigated. Methods Fifty
Bakker, SJL; IJzerman, RG; Teerlink, T; Westerhoff, HV; Gans, ROB; Heine, RJ
2000-01-01
Central obesity is increasingly recognized as a risk factor for atherosclerosis and type 2 diabetes mellitus. Here we present a hypothesis that may explain the excess atherosclerosis, endothelial dysfunction and progressive beta-cell failure. Central obesity is associated with increased cytosolic tr
van Heugten-van der Kloet, Dalena; Huntjens, Rafaele; Giesbrecht, Timo; Merckelbach, Harald
2014-01-01
Sleep disturbances, fantasy proneness, cognitive failures, and dissociative symptoms are related to each other. However, the co-occurrence of these phenomena has been primarily studied in non-clinical samples. We investigated the correlations between these phenomena in dissociative identity disorder
Bakker, SJL; IJzerman, RG; Teerlink, T; Westerhoff, HV; Gans, ROB; Heine, RJ
2000-01-01
Central obesity is increasingly recognized as a risk factor for atherosclerosis and type 2 diabetes mellitus. Here we present a hypothesis that may explain the excess atherosclerosis, endothelial dysfunction and progressive beta-cell failure. Central obesity is associated with increased cytosolic tr
van Heugten-van der Kloet, Dalena; Huntjens, Rafaele; Giesbrecht, Timo; Merckelbach, Harald
2014-01-01
Sleep disturbances, fantasy proneness, cognitive failures, and dissociative symptoms are related to each other. However, the co-occurrence of these phenomena has been primarily studied in non-clinical samples. We investigated the correlations between these phenomena in dissociative identity disorder
Phenomenological Studies of Macroscale Failure in Metals
Kashiwa, Bryan Andrew [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hull, Lawrence Mark [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-12-06
Highlights of recent phenomenological studies of metal failure are given. Failure leading to spallation and fragmentation are typically of interest. The current ‘best model’ includes the following; a full history stress in tension; nucleation initiating dynamic relaxation; toward a tensile yield function; failure dependent on strain, strain rate, and temperature; a mean-preserving ‘macrodefect’ is introduced when failure occurs in tension; and multifield theoretical refinements
Bayesian Information Criterion as an Alternative way of Statistical Inference
Nadejda Yu. Gubanova
2012-05-01
Full Text Available The article treats Bayesian information criterion as an alternative to traditional methods of statistical inference, based on NHST. The comparison of ANOVA and BIC results for psychological experiment is discussed.
Norm Referenced and Criterion Based Measures with Preschoolers
MacTurk, Robert H.; Neisworth, John T.
1978-01-01
Seventeen handicapped and nonhandicapped preschool children were given both the norm referenced Gesell Developmental Schedules and the criterion based HICOMP progress measure on a quarterly (10 week) basis. (Author/SBH)
On the Matrix Formulation of Kaiser's Varimax Criterion.
Neudecker, H.
1981-01-01
A full-fledged matrix derivation of Sherin's matrix formulation of Kaiser's varimax criterion is provided. Matrix differential calculus is used in conjunction with the Hadamard (or Schur) matrix product. Two results on Hadamard products are presented. (Author/JKS)
Bayesian Information Criterion as an Alternative way of Statistical Inference
Nadejda Yu. Gubanova; Simon Zh. Simavoryan
2012-01-01
The article treats Bayesian information criterion as an alternative to traditional methods of statistical inference, based on NHST. The comparison of ANOVA and BIC results for psychological experiment is discussed.
Angular criterion for distinguishing between Fraunhofer and Fresnel diffraction
Medina, F F; García-Sucerquia, J; Matteucci, G
2003-01-01
The distinction between Fresnel and Fraunhofer diffraction is a crucial condition for the accurate analysis of diffracting structures. In this paper we propose a criterion based on the angle subtended by the first zero of the diffraction pattern from the center of the diffracting aperture. The determination of the zero of the diffraction pattern is the crucial point for assuring the precision of the criterion. It mainly depends on the dynamical range of the detector. Therefore, the applicability of adequate thresholds for different detector types is discussed. The criterion is also generalized by expressing it in terms of the number of Fresnel zones delimited by the aperture. Simulations are reported for illustrating the feasibility of the criterion.
Failure modes of composite sandwich beams
Gdoutos E.
2008-01-01
Full Text Available A thorough investigation of failure behavior of composite sandwich beams under three-and four-point bending was undertaken. The beams were made of unidirectional carbon/epoxy facings and a PVC closed-cell foam core. The constituent materials were fully characterized and in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. The initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions.
Self-Adjointness Criterion for Operators in Fock Spaces
Falconi, Marco, E-mail: marco.falconi@univ-rennes1.fr [Université de Rennes I, IRMAR and Centre Henri Lebesgue (France)
2015-12-15
In this paper we provide a criterion of essential self-adjointness for operators in the tensor product of a separable Hilbert space and a Fock space. The class of operators we consider may contain a self-adjoint part, a part that preserves the number of Fock space particles and a non-diagonal part that is at most quadratic with respect to the creation and annihilation operators. The hypotheses of the criterion are satisfied in several interesting applications.
Trace Ratio Criterion for Feature Extraction in Classification
Guoqi Li
2014-01-01
Full Text Available A generalized linear discriminant analysis based on trace ratio criterion algorithm (GLDA-TRA is derived to extract features for classification. With the proposed GLDA-TRA, a set of orthogonal features can be extracted in succession. Each newly extracted feature is the optimal feature that maximizes the trace ratio criterion function in the subspace orthogonal to the space spanned by the previous extracted features.
Plastic flow rule for sands with friction, dilation, density and stress state coupling
Wojciechowski Marek
2015-06-01
Full Text Available In this paper we propose a flow rule and failure criterion for sands in plane strain conditions based on Drucker-Prager formulation and enhanced with empirical Houlsby formula, which couples friction, dilation, density and stress state in the material. The resulting elasto-plastic, non-associated, shear hardening material model is implemented as a numerical procedure in the frame of finite element method and a simple compression example is presented. Because of the empirical nature of Houlsby formula, it is believed that results of numerical simulations will be more realistic both in deformation and shear strength estimation of sands.
Welten, Carlijn C M; Koeter, Maarten W J; Wohlfarth, Tamar D; Storosum, Jitschak G; van den Brink, Wim; Gispen-de Wied, Christine C; Leufkens, Hubert G M; Denys, D.
2016-01-01
OBJECTIVE: To investigate whether early nonresponse to antipsychotic treatment of acute mania predicts treatment failure and, if so, to establish the best definition or criterion of an early nonresponse. DATA SOURCES: Short-term efficacy studies assessing antipsychotics that were submitted to the Du
Feldt, Leonard S.
This paper considers, from a theoretical point of view, two measurement approaches used in measuring success and failure in skills tests in physical education. The first, "fixed length" (FL) testing, entails counting the number of successful performances in a fixed number of trials. The second, "trials-to-criterion" (TTC)…
On the Smoothed Minimum Error Entropy Criterion
Badong Chen
2012-11-01
Full Text Available Recent studies suggest that the minimum error entropy (MEE criterion can outperform the traditional mean square error criterion in supervised machine learning, especially in nonlinear and non-Gaussian situations. In practice, however, one has to estimate the error entropy from the samples since in general the analytical evaluation of error entropy is not possible. By the Parzen windowing approach, the estimated error entropy converges asymptotically to the entropy of the error plus an independent random variable whose probability density function (PDF corresponds to the kernel function in the Parzen method. This quantity of entropy is called the smoothed error entropy, and the corresponding optimality criterion is named the smoothed MEE (SMEE criterion. In this paper, we study theoretically the SMEE criterion in supervised machine learning where the learning machine is assumed to be nonparametric and universal. Some basic properties are presented. In particular, we show that when the smoothing factor is very small, the smoothed error entropy equals approximately the true error entropy plus a scaled version of the Fisher information of error. We also investigate how the smoothing factor affects the optimal solution. In some special situations, the optimal solution under the SMEE criterion does not change with increasing smoothing factor. In general cases, when the smoothing factor tends to infinity, minimizing the smoothed error entropy will be approximately equivalent to minimizing error variance, regardless of the conditional PDF and the kernel.
Use of forming limit curve as a failure criterion in maritime crash analysis
Alti-Veltin, B.; Vredeveldt, A.W.
2015-01-01
Calculation of the energy absorption of marine structures at certain impact scenarios by means of finite element analysis is regularly being performed by researchers. Recent studies at TNO, focusing on the vulnerability of a liquefied natural gas tank, showed that in collisions the deformation of th
Modified Expression for the Failure Criterion of Bucket Foundations Subjected to Combined Loading
Larsen, Kim André; Ibsen, Lars Bo; Barari, Amin
2013-01-01
Recently, various loading tests with small- and large-scale bucket foundations were performed on buckets of varying sizes, embedment ratios, and load paths with saturated dense Aalborg University Sand No. 1 at the geotechnical laboratory of Aalborg University. In the present study, the capacity...... and behavior of bucket foundations subjected to combined loads were investigated on the basis of the results of these experimental studies. Although previous authors had proposed a linear relationship between the moment capacity and the vertical load, this relationship did not fit the observed capacities...
Prediction of Underground Cavity Roof Collapse using the Hoek–Brown Failure Criterion
Suchowerska, A. M.; Merifield, R. S.; Carter, J. P.
2012-01-01
Preventing roof collapse in underground cavities is a challenge to geotechnical engineering. In this study, three independent methods have been used to evaluate the roof collapse of underground rectangular cavities for a range of geometries and rock properties. The rock mass strength has been...
L. A. F. de Souza
Full Text Available The experimental results of testing structures or structural parts are limited and, sometimes, difficult to interpret. Thus, the development of mathematical-numerical models is needed to complement the experimental analysis and allow the generalization of results for different structures and types of loading. This article makes two computational studies of reinforced concrete structures problems found in the literature, using the Finite Element Method. In these analyses, the concrete is simulated with the damage classical model proposed by Mazars and the steel by a bilinear elastoplastic constitutive model. Numerical results show the validity of the application of constitutive models which consider the coupling of theories with the technique of finite element discretization in the simulation of linear and two-dimensional reinforced concrete structures.
Dworkin, P H
1989-04-01
Numerous factors may contribute to a child's failure to learn. Certain causes of school failure, such as specific learning disabilities, mental retardation, sensory impairment, and chronic illness may be regarded as intrinsic characteristics of the child. Other causes, such as family dysfunction, social problems, and ineffective schooling, are characteristics of the child's environment. Still other influences on school performance, such as temperamental dysfunction, attention deficits, and emotional illness, may be viewed as the consequence of the interaction between the child and his or her environment. The reasons for a child's school failure must not be considered in isolation but rather within the context of social and environmental circumstances. Evaluation must consider the myriad of reasons for a child's school failure and attempt to identify "clusters" of adverse influences on school performance. Detailed information must be sought from the student, parents, and school system through the history and physical examination. Questionnaires are useful in data gathering. Ancillary methods of assessment that may be of value include neurodevelopmental screening and laboratory studies. Further investigations and referrals, particularly psychoeducational evaluation, are of major importance. Traditional roles of the pediatrician in school failure include the treatment of underlying medical conditions, counseling, the coordination of further investigations and referrals, and the facilitation of communication with community services and resources. Participation with other disciplines in the development of a child's educational plan is feasible and useful.
Stress envelope of silicon carbide composites at elevated temperatures
Nozawa, Takashi, E-mail: nozawa.takashi67@jaea.go.jp [Japan Atomic Energy Agency, 2-166 Omotedate, Obuchi, Rokkasho, Aomori 039-3212 (Japan); Kim, Sunghun [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Ozawa, Kazumi; Tanigawa, Hiroyasu [Japan Atomic Energy Agency, 2-166 Omotedate, Obuchi, Rokkasho, Aomori 039-3212 (Japan)
2014-10-15
To identify a comprehensive stress envelope, i.e., strength anisotropy map, of silicon carbide fiber-reinforced silicon carbide matrix composite (SiC/SiC composite) for practical component design, tensile and compressive tests were conducted using the small specimen test technique specifically tailored for high-temperature use. In-plane shear properties were, however, estimated using the off-axial tensile method and assuming that the mixed mode failure criterion, i.e., Tsai–Wu criterion, is valid for the composites. The preliminary test results indicate no significant degradation to either proportional limit stress (PLS) or fracture strength by tensile loading at temperatures below 1000 °C. A similarly good tolerance of compressive properties was identified at elevated temperatures, except for a slight degradation in PLS. With the high-temperature test data of tensile, compressive and in-plane shear properties, the stress envelopes at elevated temperatures were finally obtained. A slight reduction in the design limit was obvious at elevated temperatures when the compressive mode is dominant, whereas a negligibly small impact on the design is expected by considering the tensile loading case.
Wang Chu
2015-01-01
Full Text Available Formability of pure molybdenum in thermal forming process has been greatly improved, but it is still hard to avoid the generation of rupture and other quality defects. In this paper, a ductile fracture criterion of pure molybdenum sheet in thermal forming was established by considering the plastic deformation capacity of material and stress states, which can be used to describe fracture behaviour and critical rupture prediction of pure molybdenum sheet during hot forming process. Based on the isothermal uniaxial tensile tests which performed at 993 to 1143 K with strain rate range from 0.0005 to 0.2 s−1, the material parameters are calculated by the combination method of experiment with FEsimulation. Based on the observation, new fracture criteria can be expressed as a function of Zener-Hollomon parameter. The critical fracture value that calculated by Oyane-Sato criterion increases with increasing temperature and decreasing strain rate. The ductile fracture criterion with Zener-Hollomon parameter of pure molybdenum in thermal forming is proposed.
Chandrashekhar, Y; Anand, I S
1993-01-01
Maximal oxygen consumption (VO2 max) is one of the most important predictors of prognosis in chronic heart failure and is now used to define degree of heart failure. While most centres can routinely do treadmill exercise testing (TMT), VO2 max measurements are not widely available. We, therefore, analysed the ability to predict VO2 max from common TMT variables: Peak exercise heart rate, exercise time, and METS achieved in 26 patients with chronic congestive heart failure (NYHA II-III, ejection fraction 43 +/- 2%) in whom exercise VO2 studies were simultaneously done by breath to breath expiratory gas analysis using a metabolic cart. METS achieved during exercise and exercise time correlated reasonably well although not perfectly (r = 0.78 & 0.73 respectively, tail critical value +/-0.41). Resting ejection fraction did not correlate at all (r = 0.0004). The regression equation (2.7) (METS) + 5.8 defined VO2 max with SE of 0.47. Although in unvariate analysis, exercise time, METS achieved & peak heart rate predicted VO2 max, only METS achieved was predictive in step wise regression. None of the parameters predicted the anaerobic threshold accurately although there was a modest relation between AT and peak exercise VO2. We conclude that most exercise variables do not accurately predict VO2 max in patients with chronic congestive heart failure. METS achieved is the best predictor and the VO2 max can be predicted using a regression equation. Anaerobic threshold cannot be predicted without tests involving expiratory gas analysis.
王洪亮; 范鹏贤; 王明洋; 李文培; 钱岳红
2011-01-01
In order to investigate the progressive failure process of brittle rock, the mechanical properties of red sandstone from south area of Shandong province are studied by the RMT-150C rock mechanical experimental system.The stress-strain curves of samples under different strain rates are recorded The deformation and progressive failure process of rock samples is divided into several stages.including crack closure stage, linear elastic deformation stage, crack initiation and stable crack growth stage and unstable crack growth stage.Then the crack initial stresses and crack damage stresses are determined by the moving point technique according to the data of stress-strain curves and other deduced data.The influence of strain rate on the ultimate critical strength the crack initial stress and the crack damage stress are also investigatect The results show that the ultimate critical strength first decreases and then increases as the strain rate increases; and the rate of crack initial stress and crack damage with the ultimate critical strength decreases.The mechanism of the experimcntal results are analyzed and explained by the stress concentration model of rock with mmuniformities.And the influence of strain rate on the progressive failure process is studied%为了深入研究脆性岩石的渐进破坏过程,利用RMT-150C型岩石力学试验系统对产自鲁南地区的一种红砂岩进行了系统的力学性质试验研究,得出该类型砂岩试样在不同应变率条件下的力学表现.将试件的渐进破坏过程通过特征应力分为裂纹闭合阶段、线弹性变形阶段、裂纹起裂和稳定扩展阶段以及裂纹不稳定扩展阶段,通过对应力-应变曲线、轴向变形刚度、体积应变曲线和裂纹体积应变等数据的分析,以及采用动点回归技术确定了试样的起裂应力和致损应力,并进一步研究了该类红砂岩的渐进破坏过程及红砂岩峰值强度、起裂应力等参数和应变率之间的
韩山明; 林丽娟; 喻钊; 蒋苓利; 张波
2012-01-01
分析了发生软失效的两种原因:电场诱导和热诱导.针对一种采用0.35 μm BCD工艺的LDMOS器件,讨论了改变器件漂移区长度对软泄漏电流的影响.最终通过对漂移区长度以及源端和衬底接触间距的优化,消除了器件原先存在的软泄漏电流现象,并且没有过分增大器件的触发电压.%Two types of soft failures, field induced soft failure and thermally induced soft failure, were analyzedBased on an LDMOS device using 0. 35 μm BCD process, effect of drift region length on soft leakage current wasdiscussed. The phenomenon of soft leakage current existed in the device was eliminated by optimizing drift regionlength and space between source and substrate contacts, which did not increase triggering voltage of the deviceexcessively.
Edge effects and delamination failures
Herakovich, C. T.
1989-01-01
The fundamental relationship between the morphology of a composite laminate and the resulting free edge effects is explored and related to delamination failures. Cross-ply, angle-ply, and quasi-isotropic laminates are discussed in detail. It is shown that the local mismatch in elastic properties of adjacent layers and the global stacking sequence of a laminate both have a significant influence on the interlaminar stresses and delamination failures.
Earing Prediction in Cup Drawing using the BBC2008 Yield Criterion
Vrh, Marko; Halilovič, Miroslav; Starman, Bojan; Štok, Boris; Comsa, Dan-Sorin; Banabic, Dorel
2011-08-01
The paper deals with constitutive modelling of highly anisotropic sheet metals. It presents FEM based earing predictions in cup drawing simulation of highly anisotropic aluminium alloys where more than four ears occur. For that purpose the BBC2008 yield criterion, which is a plane-stress yield criterion formulated in the form of a finite series, is used. Thus defined criterion can be expanded to retain more or less terms, depending on the amount of given experimental data. In order to use the model in sheet metal forming simulations we have implemented it in a general purpose finite element code ABAQUS/Explicit via VUMAT subroutine, considering alternatively eight or sixteen parameters (8p and 16p version). For the integration of the constitutive model the explicit NICE (Next Increment Corrects Error) integration scheme has been used. Due to the scheme effectiveness the CPU time consumption for a simulation is comparable to the time consumption of built-in constitutive models. Two aluminium alloys, namely AA5042-H2 and AA2090-T3, have been used for a validation of the model. For both alloys the parameters of the BBC2008 model have been identified with a developed numerical procedure, based on a minimization of the developed cost function. For both materials, the predictions of the BBC2008 model prove to be in very good agreement with the experimental results. The flexibility and the accuracy of the model together with the identification and integration procedure guarantee the applicability of the BBC2008 yield criterion in industrial applications.
Chen, Ran; Tonon, Fulvio
2011-03-01
The paper presents a closed-form solution for the convergence curve of a circular tunnel in an elasto-brittle-plastic rock mass with both the Hoek-Brown and generalized Hoek-Brown failure criteria, and a linear flow rule, i.e., the ratio between the minor and major plastic strain increments is constant. The improvement over the original solution of Brown et al. (J Geotech Eng ASCE 109(1):15-39, 1983) consists of taking into account the elastic strain variation in the plastic annulus, which was assumed to be fixed in the original solution by Brown et al. The improvement over Carranza-Torres' solution (Int J Rock Mech Min Sci 41(Suppl 1):629-639, 2004) consists of providing a closed-form solution, rather than resorting to numerical integration of an ordinary differential equation. The presented solution, by rigorously following the theory of plasticity, takes into account that the elastic strain components change with radial and circumferential stress changes within the plastic annulus. For the original Hoek-Brown failure criterion, disregarding the elastic strain change leads to underestimate the convergence by up to 55%. For a rock mass failing according to the generalized Hoek-Brown failure criterion, using the original failure criterion leads to a high probability (97%) of underestimating the convergence by up to 100%. As a consequence, the onset or degree of squeezing may be underestimated, and the loading on the support/reinforcement calculated with the convergence/confinement method may be largely underestimated.
Failure Criteria for Reinforced Materials
Rathkjen, Arne
Failure of materials is often characterized as ductile yielding, brittle fracture, creep rupture, etc., and different criteria given in terms of different parameters have been used to describe different types of failure. Only criteria expressing failure in terms of stress are considered in what...... place until the matrix, the continuous component of the composite, fails. When an isotropic matrix is reinforced as described above, the result is an anisotropic composite material. Even if the material is anisotropic, it usually exhibits a rather high degree of symmetry and such symmetries place...... certain restrictions on the form of the failure criteria for anisotropic materials. In section 2, some failure criteria for homogenous materials are reviewed. Both isotropic and anisotropic materials are described, and in particular the constraints imposed on the criteria from the symmetries orthotropy...
[Baroreflex failure after chemodectoma resection].
Gómez Esteban, J C; Boyero, S; Fernández, C; Sagasta, A; Pérez, T; Velasco, F; Allue, I; Lezcano, E; Zarranz, J J
2004-10-01
Baroreflex failure after chemodectoma resection We present a case of baroreflex failure secondary to a unilateral injury of the glossopharyngeal nerve. The patient was operated for a left-sided chemodectoma in the carotid body. Some months after surgery she started to report presyncopal episodes exacerbated by mental stress and when standing up. During these episodes, the patient presented hypertensive crises and tachycardia. However, blood pressure was below normal ranges at rest. The diagnosis was baroreflex failure secondary to unilateral injury of the glossopharyngeal nerve. The case reported herein illustrates the fact that the presence of a bilateral injury is not essential for the occurrence of this disorder.
Slope Safety Calculation With A Non-Linear Mohr Criterion Using Finite Element Method
Clausen, Johan; Damkilde, Lars
2005-01-01
Safety factors for soil slopes are calculated using a non-linear Mohr envelope. The often used linear Mohr-Coulomb envelope tends to overestimate the safety as the material parameters are usually determined at much higher stress levels, than those present at slope failure. Experimental data...
Slope Safety Calculation With A Non-Linear Mohr Criterion Using Finite Element Method
Clausen, Johan; Damkilde, Lars
2005-01-01
Safety factors for soil slopes are calculated using a non-linear Mohr envelope. The often used linear Mohr-Coulomb envelope tends to overestimate the safety as the material parameters are usually determined at much higher stress levels, than those present at slope failure. Experimental data...
1997-01-01
970318 A study on evoked potentials in cor pul-monale patients with chronic respiratory failure.QIAO Hui(乔慧), et al. Beijing Neurosurg Instit,Beijing, 100050. Chin J Geriatr 1997; 16(1): 43-45. Objective: Evoked protential was used to detect thechange of brain function in cor pulmonale patients with
2009-01-01
2009170 Curcumin attenuates left ventricular dysfunction and remodeling in rabbits with chronic heart failure. TANG Yanhong(唐艳红),et al.Dept Cardiol,Renmin Hosp,Wuhan Univ,Wuhan 430060.Chin J Cardiol,2009;37(3):262-267.
2008-01-01
2008411 Expression of S100B during heart failure in rats. JIANG Zhenni(蒋珍妮), et al. Dept Cardiol, 2nd Affili Hosp, Zhejiang Univ, Coll Med Hangzhou 310009. Chin J Emerg Med 2008;17(5):475-478. Objective To evaluate the value of S100B gene on cardiovascular remodeling in rats with abdominal aorta coarctation.
1997-01-01
970284 Effects of enalapril on heart rate variabilityin patients with congestive heart failure. ZHANGYouhua(章友华), et a1. Dept Cardiol, Cardiovasc Instit& Fuwai Hosp, CAMS & PUMC, Beijing, 100037. ChinCir J 1996; 11(2): 729-732.
Jakobsen, K. P.; Burcharth, H. F.; Ibsen, Lars Bo;
1999-01-01
The present appendix contains the derivation of ten different limit state equations divided on three different failure modes. Five of the limit state equations can be used independently of the characteristics of the subsoil, whereas the remaining five can be used for either drained or undrained...
Creep Analysis of a Variable Thickness Rotating FGM Disc using Tresca Criterion
Kishore Khanna
2015-04-01
Full Text Available The study investigates steady-state creep in a rotating Al-SiCp disc having different thickness profiles and reinforcement (SiCp gradients. The disc material is assumed to creep according to threshold-stress based law and yield following Tresca criterion. The stresses and strain rates in the disc are estimated by solving the disc equilibrium equation along with creep constitutive equations. It was observed that on increasing the disc thickness gradient, the radial stress decreases towards the inner radius but increases towards the outer radius, whereas the tangential stress decreases over the entire radius. With the increase in SiCp gradient in the FGM disc, the radial stress increases significantly throughout, however, the tangential stress increases towards the inner radius but decreases towards the outer radius. The strain rates in the disc reduce significantly over the entire disc radius and become relatively uniform with the increase in either disc thickness gradient or reinforcement gradient. Thus, the composite disc having higher thickness and higher reinforcement gradients exhibits lesser distortion.Defence Science Journal, Vol. 65, No. 2, March 2015, pp.163-170, DOI:http://dx.doi.org/10.14429/dsj.65.8045
Predicting Failure Progression and Failure Loads in Composite Open-Hole Tension Coupons
Arunkumar, Satyanarayana; Przekop, Adam
2010-01-01
Failure types and failure loads in carbon-epoxy [45n/90n/-45n/0n]ms laminate coupons with central circular holes subjected to tensile load are simulated using progressive failure analysis (PFA) methodology. The progressive failure methodology is implemented using VUMAT subroutine within the ABAQUS(TradeMark)/Explicit nonlinear finite element code. The degradation model adopted in the present PFA methodology uses an instantaneous complete stress reduction (COSTR) approach to simulate damage at a material point when failure occurs. In-plane modeling parameters such as element size and shape are held constant in the finite element models, irrespective of laminate thickness and hole size, to predict failure loads and failure progression. Comparison to published test data indicates that this methodology accurately simulates brittle, pull-out and delamination failure types. The sensitivity of the failure progression and the failure load to analytical loading rates and solvers precision is demonstrated.
Lin CL
2015-07-01
reduced under oral B307 treatment (P<0.05. Oral B307 treatment may briefly alleviate cardiac failure in aging HD R6/2 mice via suppressing cardiac oxidative stress, inflammation, and apoptosis. We suggested that the herbal formula B307 may be further developed as a potential health supplement for ameliorating cardiac failure associated with aging. Keywords: Chinese herbal medicines, cardiomyocytes, echocardiography, aging, transgenic mouse model
Bipartite quantum systems: on the realignment criterion and beyond
Lupo, Cosmo; Aniello, Paolo [Dipartimento di Scienze Fisiche dell' Universita di Napoli ' Federico II' , via Cintia, I-80126 Napoli (Italy); Scardicchio, Antonello [Princeton Center for Theoretical Physics and Department of Physics, Princeton University, Princeton, NJ 08544 (United States)], E-mail: lupo@na.infn.it, E-mail: aniello@na.infn.it, E-mail: ascardic@princeton.edu
2008-10-17
Inspired by the 'computable cross norm' or 'realignment' criterion, we propose a new point of view about the characterization of the states of bipartite quantum systems. We consider a Schmidt decomposition of a bipartite density operator. The corresponding Schmidt coefficients, or the associated symmetric polynomials, are regarded as quantities that can be used to characterize bipartite quantum states. In particular, starting from the realignment criterion, a family of necessary conditions for the separability of bipartite quantum states are derived. We conjecture that these conditions, which are weaker than the parent criterion, can be strengthened in such a way to obtain a new family of criteria that are independent of the original one. This conjecture is supported by numerical examples for the low dimensional cases. These ideas can be applied to the study of quantum channels, leading to a relation between the rate of contraction of a map and its ability to preserve entanglement.
A Joint Optimization Criterion for Blind DS-CDMA Detection
Sergio A. Cruces-Alvarez
2007-01-01
Full Text Available This paper addresses the problem of the blind detection of a desired user in an asynchronous DS-CDMA communications system with multipath propagation channels. Starting from the inverse filter criterion introduced by Tugnait and Li in 2001, we propose to tackle the problem in the context of the blind signal extraction methods for ICA. In order to improve the performance of the detector, we present a criterion based on the joint optimization of several higher-order statistics of the outputs. An algorithm that optimizes the proposed criterion is described, and its improved performance and robustness with respect to the near-far problem are corroborated through simulations. Additionally, a simulation using measurements on a real software-radio platform at 5 GHz has also been performed.
Heart Failure Protein May Signal Early Brain Damage
... page: https://medlineplus.gov/news/fullstory_162447.html Heart Failure Protein May Signal Early Brain Damage Higher levels ... stress. Blood levels of NT-proBNP rise when heart failure worsens and fall when it gets better. Previous ...
Dynamic analysis of fault rockburst based on gradient-dependent plasticity and energy criterion
Xuebin Wang; Xiaobin Yang; Zhihui Zhang; Yishan Pan
2004-01-01
Fault rockburst is treated as a strain localization problem under dynamic loading condition considering strain gradient and strain rate. As a kind of dynamic fracture phenomena, rockburst has characteristics of strain localization, which is considered as a one-dimensional shear problem subjected to normal compressive stress and tangential shear stress. The constitutive relation of rock material is bilinear (elastic and strain softening) and sensitive to shear strain rate. The solutions proposed based on gradientdependent plasticity show that intense plastic strain is concentrated in fault band and the thickness of the band depends on the characteristic length of rock material. The post-peak stiffness of the fault band was determined according to the constitutive parameters of rock material and shear strain rate. Fault band undergoing strain softening and elastic rock mass outside the band constitute a system and the instability criterion of the system was proposed based on energy theory. The criterion depends on the constitutive relation of rock material, the structural size and the strain rate. The static result regardless of the strain rate is the special case of the present analytical solution. High strain rate can lead to instability of the system.
Li's criterion for the Riemann hypothesis - numerical approach
Krzysztof Maślanka
2004-01-01
Full Text Available There has been some interest in a criterion for the Riemann hypothesis proved recently by Xian-Jin Li [Li X.-J.: The Positivity of a Sequence of Numbers and the Riemann Hypothesis. J. Number Theory 65 (1997, 325-333]. The present paper reports on a numerical computation of the first 3300 of Li's coefficients which appear in this criterion. The main empirical observation is that these coefficients can be separated in two parts. One of these grows smoothly while the other is very small and oscillatory. This apparent smallness is quite unexpected. If it persisted till infinity then the Riemann hypothesis would be true.
Paleomagnetism as a structural polarity criterion: application to Tunisian diapirs
Henry, Bernard; Rouvier, Henri; Le Goff, Maxime; Smati, Amor; Hatira, Nouri; Laatar, Essaied; Mansouri, Abdelbaki; Perthuisot, Vincent
2000-03-01
In the Upper Aptian-Albian units, close to Triassic displaced bodies of northwestern Tunisia, the primary magnetization acquired during the Cretaceous period of normal magnetic polarity yields an unquestionable structural polarity criterion. The use of this criterion confirms the diapiric origin of these Triassic bodies and aids understanding of the evolution of the diapirs. It also appears to be a useful tool for the analysis of the geometry of overturning. An Eocene halokinesis on the platform south of the Tunisian Channel is also indicated by analysis of magnetic overprint in the Jebel Slata.
A New Criterion for Disruption Prediction on HL-2A
YANG Qing-Wei; JI Xiao-Quan; DING Xuan-Tong; HL-2A team; ZHOU Hang-Yu; FENG Bei-Bin; LIU Yi; PAN Yu-Dong; LI Wei; DUAN Xu-Ru; CHEN Wei; CUI Zheng-Ying
2006-01-01
@@ A new criterion has been proposed to predict the major disruptions caused by tearing mode instabilities. According to the HL-2A experimental results, the statistical analyses are employed to investigate the relationships between MHD activities and the plasma disruptions. Two kinds of the tearing mode activities can finally cause the disruption on HL-2A operations. By introducing a new parameter, i.e. an integral of poloidal magnetic field over time, as the criterion of disruption precursor, almost all of the disruptions can be predicted.
Automatic control systems satisfying certain general criterions on transient behavior
Boksenbom, Aaron S; Hood, Richard
1952-01-01
An analytic method for the design of automatic controls is developed that starts from certain arbitrary criterions on the behavior of the controlled system and gives those physically realizable equations that the control system can follow in order to realize this behavior. The criterions used are developed in the form of certain time integrals. General results are shown for systems of second order and of any number of degrees of freedom. Detailed examples for several cases in the control of a turbojet engine are presented.
Non-Equilibrium Gibbs' Criterion for Completely Wetting Volatile Liquids
Tsoumpas, Yannis; Galvagno, Mariano; Rednikov, Alexey; Ottevaere, Heidi; Thiele, Uwe; Colinet, Pierre
2014-01-01
During the spreading of a liquid over a solid substrate, the contact line can stay pinned at sharp edges until the contact angle exceeds a critical value. At (or sufficiently near) equilibrium, this is known as Gibbs' criterion. Here, we show both experimentally and theoretically that for completely wetting volatile liquids there also exists a dynamically-produced critical angle for depinning, which increases with the evaporation rate. This suggests that one may introduce a simple modification of the Gibbs' criterion for (de)pinning, that accounts for the non-equilibrium effect of evaporation.
A derivability criterion based on the existence of adjunctions
Rodriguez-Gonzalez, Beatriz
2012-01-01
In this paper we introduce a derivability criterion of functors based on the existence of adjunctions rather than on the existence of resolutions. It constitutes a converse of Quillen-Maltsiniotis derived adjunction theorem. We present two applications of our derivability criterion. On the one hand, we prove that the two notions for homotopy colimits corresponding to Grothendieck derivators and Quillen model categories are equivalent. On the other hand, we deduce that the internal hom for derived Morita theory constructed by B. To\\"en is indeed the right derived functor of the internal hom of dg-categories.
Many-particle entanglement criterion for superradiant-like states
Tasgin, Mehmet Emre
2016-01-01
We derive a many-particle inseparability criterion for mixed states using the relation between single-mode and many-particle nonclassicalities. It works very well not only in the vicinity of the Dicke states, but also for the superposition of them: superradiant ground state of finite/infinite number of particles and time evolution of single-photon superradiance. We also obtain a criterion for ensemble-field entanglement which works fine for such kind of states. Even though the collective excitations of the many-particle system is sub-Poissonian --which results in entanglement-- the wave function displays bunching.
OIL MONITORING DIAGNOSTIC CRITERIONS BASED ON MAXIMUM ENTROPY PRINCIPLE
Huo Hua; Li Zhuguo; Xia Yanchun
2005-01-01
A method of applying maximum entropy probability density estimation approach to constituting diagnostic criterions of oil monitoring data is presented. The method promotes the precision of diagnostic criterions for evaluating the wear state of mechanical facilities, and judging abnormal data. According to the critical boundary points defined, a new measure on monitoring wear state and identifying probable wear faults can be got. The method can be applied to spectrometric analysis and direct reading ferrographic analysis. On the basis of the analysis and discussion of two examples of 8NVD48A-2U diesel engines, the practicality is proved to be an effective method in oil monitoring.
Szmytka F.; Limodin N.; Wang L; Osmond P.; Adrien J.; Charkaluk E.; Buffiere J.Y.
2014-01-01
A thermal-mechanical fatigue criterion is proposed to assess the lifetime of aluminium alloys produced by a lost foam casting process. It is based on the observed size distribution of pores sizes which are considered as critical zones for cracks initiation and gives reliable results when both pores sizes are identified from X-ray tomography and mean stresses are taken into account. Lifetime probabilities are finally successfully compared with experimental results.
Szmytka F.
2014-06-01
Full Text Available A thermal-mechanical fatigue criterion is proposed to assess the lifetime of aluminium alloys produced by a lost foam casting process. It is based on the observed size distribution of pores sizes which are considered as critical zones for cracks initiation and gives reliable results when both pores sizes are identified from X-ray tomography and mean stresses are taken into account. Lifetime probabilities are finally successfully compared with experimental results.
1993-01-01
930150 Epidermal growth factor and its recep-tor in the renal tissue of patients with acute re-nal failure and normal persons.LIU Zhihong(刘志红),et al.Jinling Hosp,Nanjing,210002.Natl Med J China 1992;72(10):593-595.Epidermal growth factor(EGF)and its receptor(EGF-R)were identified by immunohis-tochemical method(4 layer PAP)in the renaltissue specimens obtained from 11 normal kid-neys and 17 cases of acute renal failure(ARF).The quantitative EGF and EGF-R in the tissuewere expressed as positive tubules per mm~2.The amount of EGF and EGF-R in renal tissue
Baumgartner, S. [Axpo AG, Parkstrasse 23, CH-5401 Baden (Switzerland); Bieli, R. [Kernkraftwerk Leibstadt AG, CH-5325 Leibstadt (Switzerland); Bergmann, U. C. [Westinghouse Electric Sweden AB, SE-721 63 Vaesteraas (Sweden)
2012-07-01
An overview is given of existing CPR design criteria and the methods used in BWR reload analysis to evaluate the impact of channel bow on CPR margins. Potential weaknesses in today's methodologies are discussed. Westinghouse in collaboration with KKL and Axpo - operator and owner of the Leibstadt NPP - has developed an optimized CPR methodology based on a new criterion to protect against dryout during normal operation and with a more rigorous treatment of channel bow. The new steady-state criterion is expressed in terms of an upper limit of 0.01 for the dryout failure probability per year. This is considered a meaningful and appropriate criterion that can be directly related to the probabilistic criteria set-up for the analyses of Anticipated Operation Occurrences (AOOs) and accidents. In the Monte Carlo approach a statistical modeling of channel bow and an accurate evaluation of CPR response functions allow the associated CPR penalties to be included directly in the plant SLMCPR and OLMCPR in a best-estimate manner. In this way, the treatment of channel bow is equivalent to all other uncertainties affecting CPR. Emphasis is put on quantifying the statistical distribution of channel bow throughout the core using measurement data. The optimized CPR methodology has been implemented in the Westinghouse Monte Carlo code, McSLAP. The methodology improves the quality of dryout safety assessments by supplying more valuable information and better control of conservatisms in establishing operational limits for CPR. The methodology is demonstrated with application examples from the introduction at KKL. (authors)
1992-01-01
920647 Comparative effects of commonvasodilators on experimental cardiac fai-lure. LI Zhijian (李志坚), et al. Dept Cardiol,2nd Hosp, Tianjin Med Coll. Tianjin Med J1992; 20(8): 456-458. A 9×9 latin square design was employed forcomparing the effects of (1) placebo, (2) nitr-oprusside, (3) phentolamine, (4) isosorbide dini-trate. (5) captopril, (6) captopril-isosorbide
2005-01-01
2005186 The diagnostic application of bedside measurement of plasma brain natriuretic in patients with heart failure. SHAO Le-wen (邵乐文) , Advanced Ward Dept, 1st Hosp, Med Sch, Zhejiang Univ, Hangzhou 310003. Chin J Intern Med, 2005;44(2): 99-101. Objective: To investigate differential diagnosis value of ultra-rapid bedside measurement of brain na-triuretic peptide (BNP) in patients with dyspnea.
2010-01-01
2010316 Tissue doppler imaging observation on effect of long-term use of gingko biloba tabtet on left ventricular function in patients with chronic heart failure. ZHANG Hui(张辉),et al. Dept Cardiovasc Med, 2nd Hosp, Hebei Med Univ,Shijiazhuang 050000. Chin J Integr Tradit & West Med 2010;30(5):478-481. Objective To quantitatively observe the effect of long-term
2008-01-01
2008463 Protective effect of recombination rat augmenter of liver regeneration on kidney in acute renal failure rats. TANG Xiaopeng(唐晓鹏), et al. Dept Nephrol, 2nd Affili Hosp Chongqing Med Univ, Chongqing 400010.Chin J Nephrol 2008;24(6):417-421. Objective To investigate the protective effects of recombination rat augmenter of liver regeneration (rrALR) on tubular cell injury and renal dysfunction
Demakis, George J; Gervais, Roger O; Rohling, Martin L
2008-09-01
This study examined the influence of performance on cognitive and psychological symptom validity tests on neuropsychological and psychological test performance in claimants evaluated in a medico-legal context (N = 301) with symptoms of PTSD. A second purpose of this study was to examine the influence of the severity of PTSD symptoms on cognitive test performance after excluding patients who failed to put forth adequate best effort and who exaggerated psychiatric symptoms. Patients were administered a battery of neuropsychological measures that were aggregated into a composite measure, the Cognitive-Test Battery Mean (C-TBM). Patients were also administered a battery of psychological tests that were aggregated into another composite measure, the Psychological-Test Battery Mean (P-TBM). We found that failure on cognitive symptom validity tests was associated with significantly poorer neuropsychological functioning, but there was not a significant effect on psychological symptoms. Conversely, failure on psychological symptom validity tests was associated with higher levels of psychopathology, but there was not a significant effect on cognitive ability. Finally, once patients were screened for adequate effort and genuine symptom reporting, the severity of PTSD symptoms did not appear to influence cognitive ability. This is the first study that assessed both types of symptom validity testing in PTSD claimants, which is important given that previous literature has demonstrated cognitive impairment in PTSD and that individuals with PTSD tend to claim cognitive impairment. Implications of these findings are discussed with regard to the existing literature and the relationship between these two types of symptom validity tests.
Xia, Xiaomin; Su, Chuanyang; Fu, Juanli; Zhang, Pu; Jiang, Xiaoji; Xu, Demei; Hu, Lihua; Song, Erqun; Song, Yang
2014-10-01
This study investigated the protective effect of α-lipoic acid (LA) on lipopolysaccharide (LPS)/d-galactosamine (d-GalN)-induced fulminant hepatic failure in mice. First, we found that LA markedly reduced LPS/d-GalN-induced increases in serum ALT and AST activities, which were supplemented with histopathological examination, suggested that LA has a protective effect on this model of hepatic damage. Livers challenged with LPS/d-GalN exhibited extensive areas of vacuolization with the disappearance of nuclei and the loss of hepatic architecture. On the contrary, these pathological alterations were ameliorated by LA treatment. Next, we found that ROS and TBARS levels were increased in LPS/d-GalN treated liver homogenates, which were attenuated by LA administration. Consistently, decreases in hepatic CAT and GPx activities were observed in LPS/d-GalN group and were significantly restored by LA administration. Moreover, pretreatment with LA markedly reduced LPS/d-GalN-induced iNOS, COX-2, TNF-α, NF-κB, IL-1β and IL-6 expressions. Furthermore, our data showed that TUNEL-positive cells increased in LPS/d-GalN-treated mice liver which was counteracted by LA administration. LPS/d-GalN induced apoptosis of hepatocytes, as estimated by caspase 3, caspase 8 and caspase 9 activations. Also, the increasing of Bax and the decreasing of Bcl-2 expressions also supported LPS/d-GalN induced apoptosis. Interestingly, LA marked relieved these apoptotic features. Taking together, our results indicated that LA plays an important role on LPS/d-GalN-induced fulminant hepatic failure through its antioxidant, anti-inflammatory and anti-apoptotic activities.
LaMont, Colin H
2015-01-01
The failure of the information-based Akaike Information Criterion (AIC) in the context of singular models can be rectified by the definition of a Frequentist Information Criterion (FIC). FIC applies a frequentist approximation to the computation of the model complexity, which can be estimated analytically in many contexts. Like AIC, FIC can be understood as an unbiased estimator of the model predictive performance and is therefore identical to AIC for regular models in the large-observation-number limit ($N\\rightarrow \\infty$) . In the presence of unidentifiable parameters, the complexity exhibits a more general, non-AIC-like scaling ($\\gg N^0$). For instance, both BIC-like ($\\propto\\log N$) and Hannan-Quinn-like ($\\propto \\log \\log N$) scaling with observation number $N$ are observed. Unlike the Bayesian model selection approach, FIC is free from {\\it ad hoc} prior probability distributions and appears to be widely applicable to model selection problems. Finally we demonstrate that FIC (information-based inf...
Reliability based design optimization using akaike information criterion for discrete information
Lim, Woochul; Lee, Tae Hee [Hanyang Univ., Seoul (Korea, Republic of)
2012-08-15
Reliability based design optimization (RBDO) can be used to determine the reliability of a system by means of probabilistic design criteria, i.e., the possibility of failure considering stochastic features of design variables and input parameters. To assure these criteria, various reliability analysis methods have been developed. Most of these methods assume that distribution functions are continuous. However, in real problems, because real data is often discrete in form, it is important to estimate the distributions for discrete information during reliability analysis. In this study, we employ the Akaike information criterion (AIC) method for reliability analysis to determine the best estimated distribution for discrete information and we suggest an RBDO method using AIC. Mathematical and engineering examples are illustrated to verify the proposed method.
Huffman, Katelyn A.
Understanding the orientation and magnitude of tectonic stress in active tectonic margins like subduction zones is important for understanding fault mechanics. In the Nankai Trough subduction zone, faults in the accretionary prism are thought to have historically slipped during or immediately following deep plate boundary earthquakes, often generating devastating tsunamis. I focus on quantifying stress at two locations of interest in the Nankai Trough accretionary prism, offshore Southwest Japan. I employ a method to constrain stress magnitude that combines observations of compressional borehole failure from logging-while-drilling resistivity-at-the-bit generated images (RAB) with estimates of rock strength and the relationship between tectonic stress and stress at the wall of a borehole. I use the method to constrain stress at Ocean Drilling Program (ODP) Site 808 and Integrated Ocean Drilling Program (IODP) Site C0002. At Site 808, I consider a range of parameters (assumed rock strength, friction coefficient, breakout width, and fluid pressure) in the method to constrain stress to explore uncertainty in stress magnitudes and discuss stress results in terms of the seismic cycle. I find a combination of increased fluid pressure and decreased friction along the frontal thrust or other weak faults could produce thrust-style failure, without the entire prism being at critical state failure, as other kinematic models of accretionary prism behavior during earthquakes imply. Rock strength is typically inferred using a failure criterion and unconfined compressive strength from empirical relations with P-wave velocity. I minimize uncertainty in rock strength by measuring rock strength in triaxial tests on Nankai core. I find strength of Nankai core is significantly less than empirical relations predict. I create a new empirical fit to our experiments and explore implications of this on stress magnitude estimates. I find using the new empirical fit can decrease stress
Morelle, X. P.; Chevalier, J.; Bailly, C.; Pardoen, T.; Lani, F.
2017-01-01
The nonlinear deformation and fracture of RTM6 epoxy resin is characterized as a function of strain rate and temperature under various loading conditions involving uniaxial tension, notched tension, uniaxial compression, torsion, and shear. The parameters of the hardening law depend on the strain-rate and temperature. The pressure-dependency and hardening law, as well as four different phenomenological failure criteria, are identified using a subset of the experimental results. Detailed fractography analysis provides insight into the competition between shear yielding and maximum principal stress driven brittle failure. The constitutive model and a stress-triaxiality dependent effective plastic strain based failure criterion are readily introduced in the standard version of Abaqus, without the need for coding user subroutines, and can thus be directly used as an input in multi-scale modeling of fibre-reinforced composite material. The model is successfully validated against data not used for the identification and through the full simulation of the crack propagation process in the V-notched beam shear test.
Morelle, X. P.; Chevalier, J.; Bailly, C.; Pardoen, T.; Lani, F.
2017-08-01
The nonlinear deformation and fracture of RTM6 epoxy resin is characterized as a function of strain rate and temperature under various loading conditions involving uniaxial tension, notched tension, uniaxial compression, torsion, and shear. The parameters of the hardening law depend on the strain-rate and temperature. The pressure-dependency and hardening law, as well as four different phenomenological failure criteria, are identified using a subset of the experimental results. Detailed fractography analysis provides insight into the competition between shear yielding and maximum principal stress driven brittle failure. The constitutive model and a stress-triaxiality dependent effective plastic strain based failure criterion are readily introduced in the standard version of Abaqus, without the need for coding user subroutines, and can thus be directly used as an input in multi-scale modeling of fibre-reinforced composite material. The model is successfully validated against data not used for the identification and through the full simulation of the crack propagation process in the V-notched beam shear test.
CHF - tests; Congestive heart failure - tests; Cardiomyopathy - tests; HF - tests ... the best test to: Identify which type of heart failure (systolic versus diastolic, valvular) Monitor your heart failure ...
Heart failure - home monitoring
... failure - discharge Heart failure - fluids and diuretics Heart failure - what to ask ... Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David Zieve, MD, ...
A conjugacy criterion for Hall subgroups in finite groups
Revin, D O
2010-01-01
A finite group $G$ is said to satisfy $C_\\pi$ for a set of primes $\\pi$, if $G$ possesses exactly one class of conjugate $\\pi$-Hall subgroups. In the paper we obtain a criterion for a finite group $G$ to satisfy $C_\\pi$ in terms of a normal series of the group.
The criterion of pulse reconstruction quality based on Wigner representation
Yeremenko, S.; Baltuska, A.; Pshenichnikov, M.S; Wiersma, D. A.
2000-01-01
We propose a new criterion for the assessment of ultrashort pulse reconstruction quality. Our idea is based on the use of a two-dimensional Wigner representation of the electric field. This allows introducing a single measure to represent the quality of both phase and amplitude retrieval. The new cr
An Elementary Proof of a Criterion for Linear Disjointness
Dobbs, David E.
2013-01-01
An elementary proof using matrix theory is given for the following criterion: if "F"/"K" and "L"/"K" are field extensions, with "F" and "L" both contained in a common extension field, then "F" and "L" are linearly disjoint over "K" if (and only if) some…
Decision models for use with criterion-referenced tests
van der Linden, Willem J.
1980-01-01
The problem of mastery decisions and optimizing cutoff scores on criterion-referenced tests is considered. This problem can be formalized as an (empirical) Bayes problem with decisions rules of a monotone shape. Next, the derivation of optimal cutoff scores for threshold, linear, and normal ogive lo
Slope stability analysis using limit equilibrium method in nonlinear criterion.
Lin, Hang; Zhong, Wenwen; Xiong, Wei; Tang, Wenyu
2014-01-01
In slope stability analysis, the limit equilibrium method is usually used to calculate the safety factor of slope based on Mohr-Coulomb criterion. However, Mohr-Coulomb criterion is restricted to the description of rock mass. To overcome its shortcomings, this paper combined Hoek-Brown criterion and limit equilibrium method and proposed an equation for calculating the safety factor of slope with limit equilibrium method in Hoek-Brown criterion through equivalent cohesive strength and the friction angle. Moreover, this paper investigates the impact of Hoek-Brown parameters on the safety factor of slope, which reveals that there is linear relation between equivalent cohesive strength and weakening factor D. However, there are nonlinear relations between equivalent cohesive strength and Geological Strength Index (GSI), the uniaxial compressive strength of intact rock σ ci , and the parameter of intact rock m i . There is nonlinear relation between the friction angle and all Hoek-Brown parameters. With the increase of D, the safety factor of slope F decreases linearly; with the increase of GSI, F increases nonlinearly; when σ ci is relatively small, the relation between F and σ ci is nonlinear, but when σ ci is relatively large, the relation is linear; with the increase of m i , F decreases first and then increases.
Lost-sales inventory systems with a service level criterion
Bijvank, Marco; Vis, Iris F. A.
2012-01-01
Competitive retail environments are characterized by service levels and lost sales in case of excess demand. We contribute to research on lost-sales models with a service level criterion in multiple ways. First, we study the optimal replenishment policy for this type of inventory system as well as
Satisfying the Einstein-Podolsky-Rosen criterion with massive particles
Peise, Jan; Kruse, I.; Lange, K.;
2016-01-01
In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of quantum mechanics by devising a quantum state of two massive particles with maximally correlated space and momentum coordinates. The EPR criterion qualifies such continuous-variable entangled states, as shown successfully...
Criterion-based laparoscopic training reduces total training time
Brinkman, W.M.; Buzink, S.N.; Alevizos, L.; De Hingh, I.H.J.T.; Jakimowicz, J.J.
2011-01-01
The benefits of criterion-based laparoscopic training over time-oriented training are unclear. The purpose of this study is to compare these types of training based on training outcome and time efficiency. Methods During four training sessions within 1 week (one session per day) 34 medical interns (
Criterion-based laparoscopic training reduces total training time
Brinkman, W.M.; Buzink, S.N.; Alevizos, L.; De Hingh, I.H.J.T.; Jakimowicz, J.J.
2012-01-01
The benefits of criterion-based laparoscopic training over time-oriented training are unclear. The purpose of this study is to compare these types of training based on training outcome and time efficiency. Methods During four training sessions within 1 week (one session per day) 34 medical interns (
Alignment of Lyapunov Vectors: A Quantitative Criterion to Predict Catastrophes?
Beims, Marcus W; Gallas, Jason A C
2016-11-15
We argue that the alignment of Lyapunov vectors provides a quantitative criterion to predict catastrophes, i.e. the imminence of large-amplitude events in chaotic time-series of observables generated by sets of ordinary differential equations. Explicit predictions are reported for a Rössler oscillator and for a semiconductor laser with optoelectronic feedback.
Alignment of Lyapunov Vectors: A Quantitative Criterion to Predict Catastrophes?
Beims, Marcus W.; Gallas, Jason A. C.
2016-11-01
We argue that the alignment of Lyapunov vectors provides a quantitative criterion to predict catastrophes, i.e. the imminence of large-amplitude events in chaotic time-series of observables generated by sets of ordinary differential equations. Explicit predictions are reported for a Rössler oscillator and for a semiconductor laser with optoelectronic feedback.
A convenient accuracy criterion for time domain FE-calculations
Jensen, Morten Skaarup
1997-01-01
An accuracy criterion that is well suited to tome domain finite element (FE) calculations is presented. It is then used to develop a method for selecting time steps and element meshes that produce accurate results without significantly overburderning the computer. Use of this method is illustrate...
Creativity.4in1: Four-Criterion Construct of Creativity
Kharkhurin, Anatoliy V.
2014-01-01
The purpose of this theoretical article is to provide an extended definition of creativity that embraces potential cross-cultural variations in this construct. Creativity is defined as a 4-criterion construct, which includes attributes of novelty, utility, aesthetics, and authenticity. Novelty attribute stipulates that a creative work brings…
Criterion-based laparoscopic training reduces total training time
Brinkman, W.M.; Buzink, S.N.; Alevizos, L.; De Hingh, I.H.J.T.; Jakimowicz, J.J.
2012-01-01
The benefits of criterion-based laparoscopic training over time-oriented training are unclear. The purpose of this study is to compare these types of training based on training outcome and time efficiency. Methods During four training sessions within 1 week (one session per day) 34 medical interns