WorldWideScience

Sample records for block cracking

  1. Evaluation of Bi-Material Crack Using The Finite Block Method

    Science.gov (United States)

    Hinneh, P.; Wen, P. H.

    2016-08-01

    The Finite Block Method has been employed in this paper to evaluate the stress intensity factor of a bi-material plate. The complex stress intensity factor components K1 and K2 determined by the Finite Block Method is compared with an equivalent Finite Element Method (ABAQUS) analysis. The paper demonstrates the accuracy of the Meshfree approach by the Finite Block Method without the arduous demand of meshing around the crack surface as seen on standard FEM crack analysis. This paper also describes the application of the polygonal singular core and the collocations points around the interface crack. A computational example for various E1/E2 material combinations is presented.

  2. Tumbler blocking of the closure and holder of a crack detector gamma source

    International Nuclear Information System (INIS)

    The tumbler blocking mechanism uses a slot in the source holder as a key for releasing the closure of the gamma crack detector. At least one recess is made in the source holder. In the shielding container body and its closure, at least three holes serve to fit the two-part tumblers and springs. In the shielded position the tip of the second tumbler fits into the source holder recess, preventing the holder from moving out of the shielded position. The first and third tumblers check whether the source holder is retracted to the end position. The device features simple design and reliable function. (J.B.). 3 figs

  3. Use of ultrasonic back-reflection intensity for predicting the onset of crack growth due to low-cycle fatigue in stainless steel under block loading.

    Science.gov (United States)

    Islam, Md Nurul; Arai, Yoshio; Araki, Wakako

    2015-02-01

    The present study proposes the use of ultrasonic back-reflected waves for evaluating low cycle fatigue crack growth from persistent slip bands (PSBs) of stainless steel under block loading. Fatigue under high-low block loading changes the back-reflected intensity of the ultrasonic wave that emanates from the surface. Measuring the change in ultrasonic intensity can predict the start of crack growth with reasonable accuracy. The present study also proposes a modified constant cumulative plastic strain method and a PSB damage evolution model to predict the onset of crack growth under block loads.

  4. Numerical Investigation of the Effect of the Location of Critical Rock Block Fracture on Crack Evolution in a Gob-side Filling Wall

    Science.gov (United States)

    Li, Xuehua; Ju, Minghe; Yao, Qiangling; Zhou, Jian; Chong, Zhaohui

    2016-03-01

    Generation, propagation, and coalescence of the shear and tensile cracks in the gob-side filling wall are significantly affected by the location of the fracture of the critical rock block. The Universal Discrete Element Code software was used to investigate crack evolution characteristics in a gob-side filling wall and the parameter calibration process for various strata and the filling wall was clearly illustrated. The cracks in both the filling wall and the coal wall propagate inward in a V-shape pattern with dominant shear cracks generated initially. As the distance between the fracture and the filling wall decreases, the number of cracks in the filling wall decreases, and the stability of the filling wall gradually improves; thus, by splitting the roof rock at the optimal location, the filling wall can be maintained in a stable state. Additionally, we conducted a sensitivity analysis that demonstrated that the higher the coal seam strength, the fewer cracks occur in both the filling wall and the coal wall, and the less failure they experience. With the main roof fracturing into a cantilever structure, the higher the immediate roof strength, the fewer cracks are in the filling wall. With the critical rock block fracturing above the roadway, an optimal strength of the immediate roof can be found that will stabilize the filling wall. This study presents a theoretical investigation into stabilization of the filling wall, demonstrating the significance of pre-splitting the roof rock at a desirable location.

  5. Study of matrix micro-cracking in nano clay and acrylic tri-block-copolymer modified epoxy/basalt fiber-reinforced pressure-retaining structures

    Directory of Open Access Journals (Sweden)

    2011-10-01

    Full Text Available In fiber-reinforced polymer pressure-retaining structures, such as pipes and vessels, micro-level failure commonly causes fluid permeation due to matrix cracking. This study explores the effect of nano-reinforcements on matrix cracking in filament-wound basalt fiber/epoxy composite structures. The microstructure and mechanical properties of bulk epoxy nanocomposites and hybrid fiber-reinforced composite pipes modified with acrylic tri-block-copolymer and organophilic layered silicate clay were investigated. In cured epoxy, the tri-block-copolymer phase separated into disordered spherical micelle inclusions; an exfoliated and intercalated structure was observed for the nano-clay. Block-copolymer addition significantly enhanced epoxy fracture toughness by a mechanism of particle cavitation and matrix shear yielding, whereas toughness remained unchanged in nano-clay filled nanocomposites due to the occurrence of lower energy resistance phenomena such as crack deflection and branching.Tensile stiffness increased with nano-clay content, while it decreased slightly for block-copolymer modified epoxy. Composite pipes modified with either the organic and inorganic nanoparticles exhibited moderate improvements in leakage failure strain (i.e. matrix cracking strain; however, reductions in functional and structural failure strength were observed.

  6. On autoclaved aerated concrete block wall and plaster layer anti-crack%浅谈蒸压加气混凝土砌块墙体及粉刷层防裂

    Institute of Scientific and Technical Information of China (English)

    林恩凯

    2009-01-01

    According to the comparison on characteristics of the autoclaved aerated concrete block and traditional red brick, the author analyzes causes of wall crack quality common diseases, and provides corresponding control measures, so as to solve the crack problem of the autoclaved aerated concrete block wall and the plaster layer, thus promoting application of the autoclaved aerated concrete block.%通过比较蒸压加气混凝土砌块与传统红砖的特性,分析其墙体裂缝质量通病的原因,并提出相应的控制措施,以解决蒸压加气混凝土砌块墙体及粉刷层的开裂问题,从而推广蒸压加气混凝土砌块的应用.

  7. Crack-controlling and Leak-prevention Technology of Small Hollow Cinder Concrete Building Block Filler Wall%炉渣混凝土空心小型砌块填充墙控裂防渗技术

    Institute of Scientific and Technical Information of China (English)

    贾华远; 孙建军; 孙春霞

    2001-01-01

    Some technical problems such as hollowness, crack, leak of small building block filler wall containing light aggregates such as cinder will be solved with some technical improvements in such aspects as wall structure, masonry method, plastering method and so on.%炉渣等轻集料空心小型砌块填充墙须通过墙体构造、砌筑工艺、抹灰工艺诸方面的技术进步,方可解决墙体空、裂、渗的技术难题。

  8. Seismic stability analysis of concrete gravity dams with penetrated cracks

    Directory of Open Access Journals (Sweden)

    Shou-yan JIANG

    2012-03-01

    Full Text Available The seismic stability of a cracked dam was examined in this study. Geometric nonlinearity and large deformations, as well as the contact condition at the crack site, were taken into consideration. The location of penetrated cracks was first identified using the concrete plastic-damage model based on the nonlinear finite element method (FEM. Then, the hard contact algorithm was used to simulate the crack interaction in the normal direction, and the Coloumb friction model was used to simulate the crack interaction in the tangential direction. After verification of numerical models through a case study, the seismic stability of the Koyna Dam with two types of penetrated cracks is discussed in detail with different seismic peak accelerations, and the collapse processes of the cracked dam are also presented. The results show that the stability of the dam with two types of penetrated cracks can be ensured in an earthquake with a magnitude of the original Koyna earthquake, and the cracked dam has a large earthquake-resistant margin. The failure processes of the cracked dam in strong earthquakes can be divided into two stages: the sliding stage and the overturning stage. The sliding stage ends near the peak acceleration, and the top block slides a long distance along the crack before the collapse occurs. The maximum sliding displacement of the top block will decrease with an increasing friction coefficient at the crack site.

  9. Modified Dugdale cracks and Fictitious cracks

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1998-01-01

    A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... areas, so-called fictitious cracks, in front of the crack.The Modified Dugdale theory presented in this paper is also based on the concept of Dugdale cracks. Any cohesive stress distribution, however, can be considered in front of the crack. Formally the strength of a material weakened by a modified.......For brittle materials (considered by the Griffith theory )G_CR = 2 Gamma where Gamma is surface energy of material considered. For more tough materials (considered by the modified Dugdale theory) G_CR is a function f(sigma_L delta_CR) where sigma_L and delta_CR are theoretical strength and flow limit...

  10. Behavior of cracked materials

    CERN Document Server

    François, Marc Louis Maurice

    2009-01-01

    Due to their microstructure, quasi brittle materials present rough cracks. Under sliding of the crack lips, this roughness involves in one hand induced opening and in the other hand some apparent plasticity which is due to the interlocking of the crack lips combined with Coulomb's friction. The proposed model is written under the irreversible thermodynamics framework. Micromechanics uses the Del Piero and Owen's structured deformation theory. Opening of the crack depends upon the crack shape and the relative sliding of the crack lips. The thermodynamic force associated to the sliding has the mechanical meaning of the force acting in order to make the crack slide. Yield surface is defined as a limitation of this force with respect to the Coulomb's friction and the Barenblatt cohesion. The crack orientation is defined as the one for which the criterion is reached for the lowest stress level. A decreasing cohesion, respect to sliding is supposed. Tension and compression reference cases are envisaged.

  11. Tubing weld cracking test

    International Nuclear Information System (INIS)

    A tubing weld cracking (TWC) test was developed for applications involving advanced austenitic alloys (such as modified 800H and 310HCbN). Compared to the Finger hot cracking test, the TWC test shows an enhanced ability to evaluate the crack sensitivity of tubing materials. The TWC test can evaluate the cracking tendency of base as well as filter materials. Thus, it is a useful tool for tubing suppliers, filler metal producers and fabricators

  12. Eliminating cracking during drying

    CERN Document Server

    Jin, Qiu; Schofield, Andrew B; Xu, Lei; 10.1140/epje/i2013-13028-9

    2013-01-01

    When colloidal suspensions dry, stresses build up and cracks often occur - a phenomenon undesirable for important industries such as paint and ceramics. We demonstrate an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. Since the emulsion droplets eventually also evaporate, our technique achieves an effective function while making little changes to the component of final product, and may therefore serve as a promising approach for cracking elimination. Furthermore, adding droplets also varies the speed of air invasion and provides a powerful method to adjust drying rate. With the effective control over cracking and drying rate, our study may find important applications in many drying and cracking related industrial processes.

  13. Elevated temperature crack growth

    Science.gov (United States)

    Kim, K. S.; Vanstone, R. H.

    1992-01-01

    The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.

  14. Heart Block

    Science.gov (United States)

    ... the signal causes the heart to contract and pump blood. Heart block occurs if the electrical signal is ... degree heart block limits the heart's ability to pump blood to the rest of the body. This type ...

  15. Population Blocks.

    Science.gov (United States)

    Smith, Martin H.

    1992-01-01

    Describes an educational game called "Population Blocks" that is designed to illustrate the concept of exponential growth of the human population and some potential effects of overpopulation. The game material consists of wooden blocks; 18 blocks are painted green (representing land), 7 are painted blue (representing water); and the remaining…

  16. Effect of crack propagation on crack tip fields

    Directory of Open Access Journals (Sweden)

    F.V. Antunes

    2013-07-01

    Full Text Available Crack closure influences fatigue crack growth rate and must be included in the design of components. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, which becomes residual as the crack propagates. The objective here is to study numerically the effect of crack propagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked to the hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident, which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of square elements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantified and compared with literature models. Finally, the removal of material at the first node behind crack tip with load cycling was observed for plane strain state and some hardening models in plane stress state.

  17. Fatigue crack propagation in self-assembling nanocomposites

    Science.gov (United States)

    Klingler, Andreas; Wetzel, Bernd

    2016-05-01

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  18. Quantity effect of radial cracks on the cracking propagation behavior and the crack morphology.

    Directory of Open Access Journals (Sweden)

    Jingjing Chen

    Full Text Available In this letter, the quantity effect of radial cracks on the cracking propagation behavior as well as the circular crack generation on the impacted glass plate within the sandwiched glass sheets are experimentally investigated via high-speed photography system. Results show that the radial crack velocity on the backing glass layer decreases with the crack number under the same impact conditions during large quantities of repeated experiments. Thus, the "energy conversion factor" is suggested to elucidate the physical relation between the cracking number and the crack propagation speed. Besides, the number of radial crack also takes the determinative effect in the crack morphology of the impacted glass plate. This study may shed lights on understanding the cracking and propagation mechanism in laminated glass structures and provide useful tool to explore the impact information on the cracking debris.

  19. Modelling of Corrosion Cracks

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed.......Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed....

  20. Zitongxi Block

    Institute of Scientific and Technical Information of China (English)

    1996-01-01

    @@ Zitongxi Block (Western Zitong Block), is located in Zitong County, northwest of Sichuan Province (as shown on Fig. 8 ). Geologically. it is situated in the Zitong Depression, southwest of the middle Longmenshan faulted and folded belt, covering an area of 1 830 km2. Transportation is very convenient. A crisscross network of highways run through the block and the Baocheng railway is nearby. The climate is moderate. Most area belongs to hilly land with the elevation of 500-600 m.The Tongjiang River runs across the area.

  1. SURFACING ELECTRODE WITH CRACKING RESISTANCE AND WEARABILITY

    Institute of Scientific and Technical Information of China (English)

    Yang Shanglei; Lu Xueqin; Lou Songnian; Zou Zengda

    2005-01-01

    A new surfacing electrode is developed with cracking resistance and wearability based on high microhardness of TiC and VC, carbides of Ti and V are formed in deposited metal by means of high temperature arc metallurgic reaction. The results show the hardness of surfacing metal increases with the increase of ferrotitanium (Fe-Ti), ferrovanadium (Fe-V) and graphite in the coat. However,when graphite reaches the volume fraction of 11%, the hardness reaches its peak value, and when beyond 11%, the hardness falls off. As Fe-Ti, Fe-V and graphite increase, the cracking resistance of deposited metal and usability of electrode declines. Carbides are dispersedly distributed in the matrix structure. The matrix microstructure of deposited metal is lath martensite. Carbides present irregular block. When using the researched surfacing electrode to continue weld with non-preheated, no seeable crack or only a few micro-cracks can be observed in the surface of deposited metal. The hardness is above 60 HRC. The wear resistance is better than that of EDZCr-C-15.

  2. Statistical crack mechanics

    International Nuclear Information System (INIS)

    Although it is possible to simulate the ground blast from a single explosive shot with a simple computer algorithm and appropriate constants, the most commonly used modelling methods do not account for major changes in geology or shot energy because mechanical features such as tectonic stresses, fault structure, microcracking, brittle-ductile transition, and water content are not represented in significant detail. An alternative approach for modelling called Statistical Crack Mechanics is presented in this paper. This method, developed in the seventies as a part of the oil shale program, accounts for crack opening, shear, growth, and coalescence. Numerous photographs and micrographs show that shocked materials tend to involve arrays of planar cracks. The approach described here provides a way to account for microstructure and give a representation of the physical behavior of a material at the microscopic level that can account for phenomena such as permeability, fragmentation, shear banding, and hot-spot formation in explosives

  3. Ghost Block

    OpenAIRE

    Webb, Neil

    2011-01-01

    Filmed on the English south coast 'Ghost Block' depicts the uncanny and eerie atmosphere at the site of a WW2 coastal defence line. The concrete cubes were used as an anti-invasion blockade against potential landing forces. This protection line now slowly decaying and becoming enmeshed into the environment still acts as a defence to repel unwanted visitors. The area is a natural reserve to nesting birds that often lay eggs directly onto the beach surface. The blocks act as a final barrier ...

  4. Epidural block

    Science.gov (United States)

    ... Drugs & Supplements Videos & Tools Español You Are Here: Home ... It numbs or causes a loss of feeling in the lower half your body. This lessens the pain of contractions during childbirth. An epidural block may also be used to ...

  5. Crack detection '86

    International Nuclear Information System (INIS)

    The participants of the conference heard 36 papers of which 13 were incorporated in INIS. The incorporated papers deal with the quality control of the equipment of nuclear power plants, with technical specifications and possibilities of diverse crack detection devices, as well as with personnel training for nondestructive materials testing. (E.S.)

  6. Cracking the Credit Hour

    Science.gov (United States)

    Laitinen, Amy

    2012-01-01

    The basic currency of higher education--the credit hour--represents the root of many problems plaguing America's higher education system: the practice of measuring time rather than learning. "Cracking the Credit Hour" traces the history of this time-based unit, from the days of Andrew Carnegie to recent federal efforts to define a credit hour. If…

  7. 不同水基磁悬液对不同厚度涂覆层试块近表面裂纹的磁粉检测%Magnetic Particle Testing of Near Surface Cracks for Different Thickness Coatings Block by Different Water-based Magnetic Fluids

    Institute of Scientific and Technical Information of China (English)

    洪勇; 史红兵; 沈沆; 舒霞; 吴玉程

    2016-01-01

    Fe3O4 water-based magnetic fluid of averaged particle diameter 18nm was prepared by chemical co-precipitation and characterized by TEM,VSM and XRD.Test block with a coating artificial crack for different thickness coatings was constructed by machining,welding and grinding processing and so on.We used nano-Fe3O4 magnetic fluids and water-based magnetic HR-1 red magnetic paste that can be bought in the market to the magnetic particle testing of crack defects block,the result shows:with the coating thickness increasing,the magnetic image of both using nano-Fe3O4 magnetic particle and HR-1 magnetic paste was changed as from being dense to being thinning.At the relatively thin coating location,nano-Fe3O4 magnetic image resolution was a bit better than the conventional HR-1 red magnetic paste,but at the thicker location,nano-Fe3O4 magnetic image was slightly superior to the conventional HR-1 red magnetic paste while applying an extra magnetic field,but when the magnetic field was moved away,nano-Fe3O4 magnetic image became loose,discontinuous,so the display effect was no better than conventional HR-1 red magnetic paste.%用化学共沉淀法制备平均粒径约为18 nm的Fe3O4水基磁悬液,并用XRD(X射线衍射)、TEM(透射电镜)、VSM(磁滞回线)测试手段进行了表征.利用锯床加工、焊接、打磨等工序制作不同厚度带裂纹缺陷涂覆层的人工试块;并分别用纳米Fe3O4水基磁悬液和HR-1型红磁膏配置的水基磁悬液,对制作的含裂纹缺陷试块进行磁粉检测.结果表明:随着涂覆层厚度的增大,使用纳米Fe3O4磁悬液和常规HR-1型红磁膏进行检测所得的磁痕均由密实变得稀疏;涂覆层厚度较小时,纳米Fe3O4磁悬液的磁痕清晰度稍优于常规HR-1型红磁膏的磁痕清晰度;涂覆层厚度较大时,外加磁场施加过程中,纳米Fe3O4磁悬液的磁痕清晰度稍优于常规HR-1型红磁膏的磁痕清晰度;但外加磁场撤离后,纳米Fe3O4磁悬液的磁痕显示

  8. Neural crack identification

    International Nuclear Information System (INIS)

    The inverse, crack identification problem in elasticity can be formulated as an output error minimization problem which, nevertheless, can not be solved without difficulties by classical numerical optimization. A review of all these previous results, where we used neural networks, filter-driven optimization and genetic algorithms is presented and in a companion lecture during this conference. The use of neural networks for the solution of the inverse problem makes possible the on-line solution of the problem. In fact, one usually approximates the inverse mapping (measurements versus crack quantities). Most of the effort is spent for the learning of this relation, while a sufficiently trained neural network provides predictions with, practically, zero computational cost. Potential applications include on-line, in-flight health monitoring systems with applications in civil and mechanical engineering and production control. In this paper we present new developments in the design of specialized neural networks for the solution of the crack identification problem. Emphasis is posed on the effective use of the learning data, which are produced by the boundary element method. Several technical data will be discussed. They include thoughts about the effective choice of the neural network architecture, the number of training examples and of the learning algorithms will be provided, together with the results of our recent numerical investigation. A detailed application for one or more elliptical cracks using static analysis results with the use of back-propagation trained neural networks will be provided. The general methodology follows our previously published results. By using more refined algorithms for the numerical solution of the neural network learning problem, which are based on the MERLIN optimization system developed in the department of the second author, we are able to solve complicated tasks. First results based on dynamic investigations (wave propagation driven

  9. Crack patterns over uneven substrates.

    Science.gov (United States)

    Nandakishore, Pawan; Goehring, Lucas

    2016-02-28

    Cracks in thin layers are influenced by what lies beneath them. From buried craters to crocodile skin, crack patterns are found over an enormous range of length scales. Regardless of absolute size, their substrates can dramatically influence how cracks form, guiding them in some cases, or shielding regions from them in others. Here we investigate how a substrate's shape affects the appearance of cracks above it, by preparing mud cracks over sinusoidally varying surfaces. We find that as the thickness of the cracking layer increases, the observed crack patterns change from wavy to ladder-like to isotropic. Two order parameters are introduced to measure the relative alignment of these crack networks, and, along with Fourier methods, are used to characterise the transitions between crack pattern types. Finally, we explain these results with a model, based on the Griffith criteria of fracture, that identifies the conditions for which straight or wavy cracks will be seen, and predicts how well-ordered the cracks will be. Our metrics and results can be applied to any situation where connected networks of cracks are expected, or found. PMID:26762761

  10. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

    ) by a constant flow stress (sigma_L). A number of materials, however, do not at all exhibit this kind of flow. Such materials are considered in this paper by Modified Dugdale crack models which apply for any cohesive stress distribution in crack front areas. Formally modified Dugdale crack models exhibit......The Dugdale crack model is widely used in materials science to predict strength of defective (cracked) materials. A stable Dugdale crack in an elasto-plastic material is prevented from spreading by uniformly distributed cohesive stresses acting in narrow areas at the crack tips. These stresses......_Ldelta_CR where sigma_L is strength, and at the same time constant flow stress, of the uncracked material while delta_CR is flow limit (displacement).Obviously predictions by the Dugdale model are most reliable for materials with stress-strain relations where flow can actually be described (or well approximated...

  11. Huhe Block

    Institute of Scientific and Technical Information of China (English)

    1996-01-01

    @@ Huhe Block is located in the mid-west part of Inner Mogolia Autonomous Region, covering an area of 15 079km2, in the range of 109°40'-112°00'E and 39°23()-40°40'N. Topographically. the Fengzhen hill is to the east, the Yinshan Mounts is to the north, the Hetao Plain and Ordos Plateau are respectively in its west and south.The Yellow River flows across this block. The elevation is 1 000 m in the flat area and in the range of 1 000-1 300m. in the plateau area, good for the development of agriculture and industry as well as husbandry. It belongs to inland plateau climate with annually averaged temperature of 8℃, the minimum being -12℃ in winter and the maximum 22℃ in summer.

  12. Reduced-order modeling for mistuned centrifugal impellers with crack damages

    Science.gov (United States)

    Wang, Shuai; Zi, Yanyang; Li, Bing; Zhang, Chunlin; He, Zhengjia

    2014-12-01

    An efficient method for nonlinear vibration analysis of mistuned centrifugal impellers with crack damages is presented. The main objective is to investigate the effects of mistuning and cracks on the vibration features of centrifugal impellers and to explore effective techniques for crack detection. Firstly, in order to reduce the input information needed for component mode synthesis (CMS), the whole model of an impeller is obtained by rotation transformation based on the finite element model of a sector model. Then, a hybrid-interface method of CMS is employed to generate a reduced-order model (ROM) for the cracked impeller. The degrees of freedom on the crack surfaces are retained in the ROM to simulate the crack breathing effects. A novel approach for computing the inversion of large sparse matrix is proposed to save memory space during model order reduction by partitioning the matrix into many smaller blocks. Moreover, to investigate the effects of mistuning and cracks on the resonant frequencies, the bilinear frequency approximation is used to estimate the resonant frequencies of the mistuned impeller with a crack. Additionally, statistical analysis is performed using the Monte Carlo simulation to study the statistical characteristics of the resonant frequencies versus crack length at different mistuning levels. The results show that the most significant effect of mistuning and cracks on the vibration response is the shift and split of the two resonant frequencies with the same nodal diameters. Finally, potential quantitative indicators for detection of crack of centrifugal impellers are discussed.

  13. A catalytic cracking process

    Energy Technology Data Exchange (ETDEWEB)

    Degnan, T.F.; Helton, T.E.

    1995-07-20

    Heavy oils are subjected to catalytic cracking in the absence of added hydrogen using a catalyst containing a zeolite having the structure of ZSM-12 and a large-pore crystalline zeolite having a Constraint Index less than about 1. The process is able to effect a bulk conversion of the oil at the same time yielding a higher octane gasoline and increased light olefin content. (author)

  14. Subcritical crack growth in marble

    Science.gov (United States)

    Nara, Yoshitaka; Nishida, Yuki; Toshinori, Ii; Harui, Tomoki; Tanaka, Mayu; Kashiwaya, Koki

    2016-04-01

    It is essential to study time-dependent deformation and fracturing in various rock materials to prevent natural hazards related to the failure of a rock mass. In addition, information of time-dependent fracturing is essential to ensure the long-term stability of a rock mass surrounding various structures. Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. It is known that subcritical crack growth is influenced by not only stress but also surrounding environment. Studies of subcritical crack growth have been widely conducted for silicate rocks such as igneous rocks and sandstones. By contrast, information of subcritical crack growth in carbonate rocks is not enough. Specifically, influence of surrounding environment on subcritical crack growth in carbonate rock should be clarified to ensure the long-term stability of a rock mass. In this study, subcritical crack growth in marble was investigated. Especially, the influence of the temperature, relative humidity and water on subcritical crack growth in marble is investigated. As rock samples, marbles obtained in Skopje-City in Macedonia and Carrara-City in Italy were used. To measure subcritical crack growth, we used the load relaxation method of the double-torsion (DT) test. All measurements by DT test were conducted under controlled temperature and relative humidity. For both marbles, it was shown that the crack velocity in marble in air increased with increasing relative humidity at a constant temperature. Additionally, the crack velocity in water was much higher than that in air. It was also found that the crack velocity increased with increasing temperature. It is considered that temperature and water have significant influences on subcritical crack growth in marble. For Carrara marble in air, it was recognized that the value of subcritical crack growth index became low when the crack velocity was higher than 10-4 m/s. This is similar to Region II of subcritical crack growth

  15. Cryptography cracking codes

    CERN Document Server

    2014-01-01

    While cracking a code might seem like something few of us would encounter in our daily lives, it is actually far more prevalent than we may realize. Anyone who has had personal information taken because of a hacked email account can understand the need for cryptography and the importance of encryption-essentially the need to code information to keep it safe. This detailed volume examines the logic and science behind various ciphers, their real world uses, how codes can be broken, and the use of technology in this oft-overlooked field.

  16. Catalytic cracking of lignites

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, M.; Nowak, S.; Naegler, T.; Zimmermann, J. [Hochschule Merseburg (Germany); Welscher, J.; Schwieger, W. [Erlangen-Nuernberg Univ. (Germany); Hahn, T. [Halle-Wittenberg Univ., Halle (Germany)

    2013-11-01

    A most important factor for the chemical industry is the availability of cheap raw materials. As the oil price of crude oil is rising alternative feedstocks like coal are coming into focus. This work, the catalytic cracking of lignite is part of the alliance ibi (innovative Braunkohlenintegration) to use lignite as a raw material to produce chemicals. With this new one step process without an input of external hydrogen, mostly propylene, butenes and aromatics and char are formed. The product yield depends on manifold process parameters. The use of acid catalysts (zeolites like MFI) shows the highest amount of the desired products. Hydrogen rich lignites with a molar H/C ratio of > 1 are to be favoured. Due to primary cracking and secondary reactions the ratio between catalyst and lignite, temperature and residence time are the most important parameter to control the product distribution. Experiments at 500 C in a discontinuous rotary kiln reactor show yields up to 32 wt-% of hydrocarbons per lignite (maf - moisture and ash free) and 43 wt-% char, which can be gasified. Particularly, the yields of propylene and butenes as main products can be enhanced four times to about 8 wt-% by the use of catalysts while the tar yield decreases. In order to develop this innovative process catalyst systems fixed on beads were developed for an easy separation and regeneration of the used catalyst from the formed char. (orig.)

  17. Biogenic Cracks in Porous Rock

    Science.gov (United States)

    Hemmerle, A.; Hartung, J.; Hallatschek, O.; Goehring, L.; Herminghaus, S.

    2014-12-01

    Microorganisms growing on and inside porous rock may fracture it by various processes. Some of the mechanisms of biofouling and bioweathering are today identified and partially understood but most emphasis is on chemical weathering, while mechanical contributions have been neglected. However, as demonstrated by the perseverance of a seed germinating and cracking up a concrete block, the turgor pressure of living organisms can be very significant. Here, we present results of a systematic study of the effects of the mechanical forces of growing microbial populations on the weathering of porous media. We designed a model porous medium made of glass beads held together by polydimethylsiloxane (PDMS), a curable polymer. The rheological properties of the porous medium, whose shape and size are tunable, can be controlled by the ratio of crosslinker to base used in the PDMS (see Fig. 1). Glass and PDMS being inert to most chemicals, we are able to focus on the mechanical processes of biodeterioration, excluding any chemical weathering. Inspired by recent measurements of the high pressure (~0.5 Mpa) exerted by a growing population of yeasts trapped in a microfluidic device, we show that yeast cells can be cultured homogeneously within porous medium until saturation of the porous space. We investigate then the effects of such an inner pressure on the mechanical properties of the sample. Using the same model system, we study also the complex interplay between biofilms and porous media. We focus in particular on the effects of pore size on the penetration of the biofilm within the porous sample, and on the resulting deformations of the matrix, opening new perspectives into the understanding of life in complex geometry. Figure 1. Left : cell culture growing in a model porous medium. The white spheres represent the grains, bonds are displayed in grey, and microbes in green. Right: microscopy picture of glass beads linked by PDMS bridges, scale bar: 100 μm.

  18. HYDROGEN TRANSFER IN CATALYTIC CRACKING

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Hydrogen transfer is an important secondary reaction of catalytic cracking reactions, which affects product yield distribution and product quality. It is an exothermic reaction with low activation energy around 43.3 kJ/mol. Catalyst properties and operation parameters in catalytic cracking greatly influence the hydrogen transfer reaction. Satisfactory results are expected through careful selection of proper catalysts and operation conditions.

  19. Experiences on IGSCC crack manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Veron, P. [Equipos Nucleares, S.A., Maliano (Spain)

    1997-02-01

    The author presents his experience in manufacturing IGSCC realistic defects, mainly in INCONEL 600 MA Steam Generator Tubes. From that experience he extracts some knowledge about this cracking (influence of chemistry in the environment, stress state, crack growth rate, and occurrence in laboratory condition of break before leak).

  20. A consistent partly cracked XFEM element for cohesive crack growth

    DEFF Research Database (Denmark)

    Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node constant strain triangle (CST) and a standard algorithm...... was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained...

  1. On grouting using a suspension of ultrafine clay on artificially cracked rock samples

    International Nuclear Information System (INIS)

    Recently there has been increasing social interest in the effective disposal of low-level radioactive wastes. The use of underground rock caverns is considered as a possible repository space. This paper presents a new grouting method which uses a suspension of liquefied ultrafine clay in fractured rock masses. In order to demonstrate the effect to block open cracks, two experiments were carried out on large-sized granite samples with open cracks. The experiments proved the method to be highly effective

  2. Prediction of fatigue lives of MAR-M247 LC based on the crack closure concept

    Energy Technology Data Exchange (ETDEWEB)

    Gelmedin, Domnin; Lang, Karl-Heinz [Karlsruhe Institute of Technology, Institute for Applied Materials - Materials Science and Engineering (IAM-WK) Campus Sued, Engelbert-Arnold-Strasse 4, 76131 Karlsruhe (Germany); Newman, James C. Jr. [Department of Aerospace Engineering, Mississippi State University, 314C Walker Engineering Building P. O. Box A Mississippi State, MS 39762 (United States)

    2012-10-15

    Low cycle fatigue (LCF), high cycle fatigue (HCF), and combined LCF and HCF tests are carried out on MAR-M247 LC at 650 C in air environment. Under combined LCF and HCF loading, block striations form on the fracture surface which are used to complete an effective crack growth curve by using the linear summation model. Crack growth lives starting from equivalent initial flaw sizes are calculated by the crack closure code FASTRAN and compared with experimental fatigue lives. Under HCF loading, predicted and experimental fatigue lives agree well for lifetimes above 10{sup 5} cycles. Lower lifetimes are overestimated indicating that the linear summation model is not valid for MAR-M247 LC in this loading range. Interactions between the non-crystallographic HCF crack growth and striated crack growth that is caused by the LCF loading are probably responsible for this behavior. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Probabilistic Analysis of Crack Width

    Directory of Open Access Journals (Sweden)

    J. Marková

    2000-01-01

    Full Text Available Probabilistic analysis of crack width of a reinforced concrete element is based on the formulas accepted in Eurocode 2 and European Model Code 90. Obtained values of reliability index b seem to be satisfactory for the reinforced concrete slab that fulfils requirements for the crack width specified in Eurocode 2. However, the reliability of the slab seems to be insufficient when the European Model Code 90 is considered; reliability index is less than recommended value 1.5 for serviceability limit states indicated in Eurocode 1. Analysis of sensitivity factors of basic variables enables to find out variables significantly affecting the total crack width.

  4. A computational algorithm for crack determination: The multiple crack case

    Science.gov (United States)

    Bryan, Kurt; Vogelius, Michael

    1992-01-01

    An algorithm for recovering a collection of linear cracks in a homogeneous electrical conductor from boundary measurements of voltages induced by specified current fluxes is developed. The technique is a variation of Newton's method and is based on taking weighted averages of the boundary data. The method also adaptively changes the applied current flux at each iteration to maintain maximum sensitivity to the estimated locations of the cracks.

  5. Peridynamic model for fatigue cracking.

    Energy Technology Data Exchange (ETDEWEB)

    Silling, Stewart Andrew; Abe Askari (Boeing)

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the "remaining life" of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  6. Peridynamic model for fatigue cracking.

    Energy Technology Data Exchange (ETDEWEB)

    Silling, Stewart A.; Abe Askari (Boeing)

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the %22remaining life%22 of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  7. 21 CFR 137.190 - Cracked wheat.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  8. Effect of crack opening on UT response

    Energy Technology Data Exchange (ETDEWEB)

    Virkkunen, I.; Kemppainen, M. [Trueflaw OY, Espoo (Finland); Pitkaenen, J. [Posiva, Olkiluoto (Finland)

    2006-07-01

    Crack opening is one of the key parameters affecting the UT response of the crack. Tight cracks with small opening tend to be more difficult to detect and characterize than cracks that have wider opening. In particular, the opening of crack tip has marked effect on the crack tip diffraction signal often used for crack sizing. Service-induced cracks found exhibit wide variety of different openings. The opening is affected by the service loads and crack growth mechanism. In general, cracks grown by high loads tend to have wider opening than cracks produced by small loads. Furthermore, residual stresses may alter the opening. In order to simulate the wide variety of openings of the service-induced cracks, a novel method for producing artificial flaws with controlled opening is presented. A set of similar realistic flaws was produced by controlled thermal fatigue loading. The as-produced ''baseline'' UT response of these cracks was recorded with phased array technique using shear waves. Some of the flaws were then subjected to different loading sequences to manipulate their opening. The UT response of the modified cracks was then recorded and compared to that of the baseline response. The crack tip signals were measured also with longitudinal waves before cutting the specimen. Finally, the sample was carefully sectioned to reveal the opening of the produced flaws and the effect of crack opening to the UT response is analyzed. (orig.)

  9. Fiber Sensing of Micro -Crack

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Optical fiber sensors are used for sensing micro-cracking in composite and metal materials in aerospace applications. The sensing mechanism is based on the detection of acoustic emission signals, which are known to emanate from micro-cracks when they grow under further loading. The sensor head consists of a fiber Bragg grating that is capable of detecting acoustic emission signals generated by pencil lead breaking, of frequencies up to 200 kHz.

  10. Fiber Sensing of Micro -Crack

    Institute of Scientific and Technical Information of China (English)

    Hong-Liang Cui

    2003-01-01

    Optical fiber sensors are used for sensing micro -cracking in composite and metal materials in aerospace applications.The sensing mechanism is based on the detection of acoustic emission signals, which are known to emanate from micro-cracks when they grow under further loading. The sensor head consists of a fiber Bragg grating that is capable of detecting acoustic emission signals generated by pencil lead breaking, of frequencies up to 200 kHz.

  11. Copper containing hydrocarbon cracking catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Lussier, R.J.; Magee, J.S. Jr.

    1975-12-30

    A copper-exchanged zeolite cracking catalyst capable of producing high octane gasoline of increased aromatic and olefinic content is described. Mixtures of copper and hydrogen ions are exchanged into a Y-type zeolite using a combination of exchange and calcination steps. The exchanged zeolite is advantageously combined with a major portion of inorganic oxide matrix to produce a catalyst suitable for use in standard commercial fluid and moving bed cat-cracking units. (auth)

  12. Ultrasound guided supraclavicular block.

    LENUS (Irish Health Repository)

    Hanumanthaiah, Deepak

    2013-09-01

    Ultrasound guided regional anaesthesia is becoming increasingly popular. The supraclavicular block has been transformed by ultrasound guidance into a potentially safe superficial block. We reviewed the techniques of performing supraclavicular block with special focus on ultrasound guidance.

  13. Application of forecasting structural cracks technique of 3DMove in Chengdao buried hill

    Institute of Scientific and Technical Information of China (English)

    WU; Shiguo; WANG; Xiuling; JI; Yuxin; LIU; Yuzhen

    2005-01-01

    3DMove software, based on the three-dimension structural model of geologic interpretation, can forecast reservoir cracks from the point of view of formation of the structural geology, and analyze the characteristics of the cracks. 3DMove software dominates in forecasting cracks. We forecast the developments and directions of the cracks in Chengbei buried hill with the application of forecasting technique in 3DMove software, and obtain the chart about strain distributing on top in buried hill and the chart about relative density and orientation and the chart about the analysis of crack unsealing. In Chengbei 30 buried hill zone, north-west and north-east and approximately east-west cracks in Cenozoic are very rich and the main directions in every fault block are different. Forecasting results that are also verified by those of drilling approximately accord with the data from well logging, the case of which shows that the technique has the better ability in forecasting cracks, and takes more effects on exploration and exploitation of crack reservoir beds in ancient buried hill reservoirs.

  14. Fem Modelling and Analysis of Reinforced Concrete Section with Light Weight Blocks Infill

    Directory of Open Access Journals (Sweden)

    T. Subramani

    2014-06-01

    Full Text Available In an attempt to reduce the self weight of reinforced concrete structures, a new development of lightweight sandwich reinforced concrete (LSRC section has been proposed as an alternative option to solid section. LSRC section is a reinforced concrete section which contains lightweight blocks as infill material. An experimental investigation into the strength of LSRC beams has shown promising results under flexural tests. To ensure the serviceability of LSRC members under service load, it is necessary to accurately predict the cracking and deflection of this section. This paper will focus on analysing the behaviour of the tested beam specimens after cracking occurs. ANSYS 12.1 was employed to study the crack propagation of LSRC beams under bending. The numerical model shows the crack in the area of AAC blocks which associates with the brittle failure of LSRC beams. The crack propagation of the beams analysed by ANSYS agrees well with the results from the experimental investigation.

  15. CRACKING OF PALM OIL TO PRODUCE OLEOCHEMICALS

    OpenAIRE

    Nwokedi I.C.; ,Okoye, C.C.

    2015-01-01

    The FTIR and GC - MS tests are necessary for identification of oleochemicals produced via cracking. In this research, thermal cracking (without catalyst) and catalytic cracking of palm oil were carried out in a batch reactor. The thermal cracking was performed at temperatures of 700 o C to 900 o C at a time of 30 to 150 minutes while the catalytic cracking was done at temperatures of 100 o C to 400 o C, time of 30 ...

  16. Formation and interpretation of dilatant echelon cracks.

    Science.gov (United States)

    Pollard, D.D.; Segall, P.; Delaney, P.T.

    1982-01-01

    The relative displacements of the walls of many veins, joints, and dikes demonstrate that these structures are dilatant cracks. We infer that dilatant cracks propagate in a principal stress plane, normal to the maximum tensile or least compressive stress. Arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks. Breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction. Near the parent-crack tip, a rotation of the local principal stresses is induced in the same sense, but not necessarily through the same angle. Incipient echelon cracks form at the parent-crack tip normal to the local maximum tensile stress. Further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane. The walls of these twisted cracks may be idealized as helicoidal surfaces. An array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle. Thus, many echelon cracks grow from a single parent because the work done in creating the array, as measured by its surface area decreases as the number of cracks increases. -from Authors

  17. Fatigue reliability of cracked engineering structures

    Science.gov (United States)

    Lanning, David Bruce, Jr.

    1997-12-01

    This study investigates the reliability of engineering structures containing fatigue cracks. Stress concentrations and welded joints are probable locations for the initiation and propagation of fatigue cracks. Due to the many unknowns of loading, materials properties, crack sizes and crack shapes present at these locations, a statistics-based reliability analysis is valuable in the careful consideration of these many different random factors involved in a fatigue life analysis, several of which are expanded upon in this study. The basic problem of a crack near a stress concentration is first considered. A formulation for the aspect ratio (a/c) of a propagating semi-elliptical fatigue crack located at the toe of a welded T-joint is developed using Newman and Raju's stress intensity factor for a cracked flat plate with a weld magnification factor and compared to that of a cracked flat plate, and the reliability in terms of fatigue lifetime is calculated with the aid of Paris' crack propagation equation for membrane and bending loadings. Crack closure effects are then introduced in the consideration of short crack effects, where crack growth rates typically may exceed those found using traditional linear elastic fracture mechanics solutions for long cracks. The probability of a very small, microstructurally influenced crack growing to a size influenced by local plastic conditions is calculated utilizing the probability of a crack continuing to grow past an obstacle, such as a grain boundary. The result is then combined with the probability for failure defined using the crack closure-modified Paris equation to find an overall reliability for the structure. Last, the probability of fracture is determined when a crack front encounters regions of non-uniform toughness, such as typical in the heat affected zone of a welded joint. An expression for the effective crack lengths of the dissimilar regions is derived, and used in a weakest-link fracture model in the evaluation

  18. Creative Construction: Unit Blocks.

    Science.gov (United States)

    Texas Child Care, 1999

    1999-01-01

    Describes the use of unit blocks with young children in early childhood education (ECE) settings to expand all areas of the curriculum. Discusses the origin of blocks in ECE programs, presents developmental stages of block play, describes children's building styles, and makes recommendations for getting started in block play for children of…

  19. Simulation of Chloride Diffusion in Cracked Concrete with Different Crack Patterns

    OpenAIRE

    Xiao-Yong Wang; Li-Na Zhang

    2016-01-01

    Chloride-induced corrosion of steel rebar is one of the primary durability problems for reinforced concrete structures in marine environment. Furthermore, if the surfaces of concrete structures have cracks, additional chloride can penetrate into concrete through cracked zone. For chloride ingression into cracked concrete, former researches mainly focus on influence of crack width on chloride diffusion coefficients. Other crack characteristics, such as chloride depth, crack shape (equal-width ...

  20. A stress corrosion cracking experience

    Energy Technology Data Exchange (ETDEWEB)

    Dicic, Z.

    1999-07-01

    Severe cracking was found on two discs when a steam turbine was inspected during the outage to replace the last stage blades (LSB). The cracks were on the inlet side in the form of star burst around balance holes, and in the form of long circumferential cracks in the region of the fillet radius between the disc and the shaft. In order to return the turbine to service, the turbine was modified by removing the disc that was damaged more severely, and by machining of the other to remove the cracks. The basis for the modifications was established after having performed metallurgical and deposit examination, and reviews of stress calculations and design features. Additional modifications were performed in order to improve the internal environment at location where the cracking had occurred. The turbine is a non-reheat, 3,600 RPM, single shaft, monoblock unit used in a combined cycle plant. The steam cycle is a two pressure system; The high pressure (HP) steam parameters are: 1,450 psig, and 950 F, and the low pressure (LP) induction steam: 60 psig, saturated. The first eight stages are action type. The induction steam inlet is followed by five reaction stages. There are no extractions. The source of steam is a two pressure, unfired Heat Recovery Steam Generator (HRSG). The boiler feed water is treated with phosphates.

  1. Crack propagation in prestressed plates

    Energy Technology Data Exchange (ETDEWEB)

    Farshad, M.; Flueler, P. [EMPA, Duebendorf (Switzerland)

    1995-12-31

    A second-order theory of initially stressed plates in the plane stress mode was used to find the dynamic stress field in the vicinity of a crack tip. Rapid crack propagation (RCP) behaviour associated with stresses caused by internal pressure and temperature was examined. The flat plate was placed under thermal conditions and was prestressed in such a way as to simulate hoop stress that may be expected in a pipe made of the same material. The presence of the tensile prestress in the thin plate raised the levels of the principal stress values and affected the direction at which the maxima of principal stress occurred. Second-order effects played an important role in the vicinity of the crack tip. Increased crack speed caused increased stress levels. There existed a limiting value at which the stresses at the crack tip became unbounded. The limiting value was affected by prestressing. The concept of simulating RCP testing of polymer pipes by a test on a conditioned plate of the same material, prestressed to simulate hoop stress caused by internal pressure, was judged to be reasonable. 6 refs. 5 figs.

  2. SHORT FATIGUE CRACK PARAMETER BASED ON THE TOTAL CRACK AREA

    Institute of Scientific and Technical Information of China (English)

    Z.X.Wu; X.C.Wu

    2001-01-01

    The progressive fatigue damage of a material is closely related to the whole populationof cracks on the surface of an un-notched specimen.In order to understand whichparameter is a more useful indicator of fatigue damage,rotatory bending fatigue testswere carried out using smooth specimens of medium-carbon steel.The behavior ofshort crack propagation during fatigue was examined and a new parameter "totalcrack area" was suggested.The aim of this paper is to extend the research on fatiguedamage in the already studied steel and to study how these damage parameters arecorrelated with the process of fatigue damage in order to evaluate the effectiveness ofdamage detection methods.

  3. Simulation of Chloride Diffusion in Cracked Concrete with Different Crack Patterns

    Directory of Open Access Journals (Sweden)

    Xiao-Yong Wang

    2016-01-01

    Full Text Available Chloride-induced corrosion of steel rebar is one of the primary durability problems for reinforced concrete structures in marine environment. Furthermore, if the surfaces of concrete structures have cracks, additional chloride can penetrate into concrete through cracked zone. For chloride ingression into cracked concrete, former researches mainly focus on influence of crack width on chloride diffusion coefficients. Other crack characteristics, such as chloride depth, crack shape (equal-width crack or tapered crack, crack density, and spacing, are not studied in detail. To fill this gap, this paper presents a numerical procedure to simulate chloride ingression into cracked concrete with different crack geometry characteristics. Cracked concrete is divided into two parts, sound zone and cracked zone. For stress-free concrete, the diffusion coefficient of sound zone is approximately assumed to be the same as sound concrete, and the diffusion coefficient of cracked zone is expressed as a piecewise function of crack width. Two-dimensional finite element method is used to determine chloride concentration. It is found that, with the increasing of crack width, crack depth, and crack amount, chloride ingression will aggravate. The analysis results generally agree with experimental results.

  4. Preheating to around 100°C under endcap blocks before welding at KHI.

    CERN Multimedia

    Loveless, D

    2000-01-01

    The 600mm thick sector blocks of the CMS endcaps are made from three layers of 200mm plates welded together. During the manufacture at KHI, the blocks are preheated to around 100°C to prevent cracks in the welds.

  5. IDENTIFICATION OF CRACKED ROTOR BY WAVELET TRANSFORM

    Institute of Scientific and Technical Information of China (English)

    邹剑; 陈进; 蒲亚鹏

    2002-01-01

    The dynamic equation of cracked rotor in rotational frame was modelled, the numerical simulation solutions of the cracked rotor and the uncracked rotor were obtained. By the wavelet transform, the time-frequency properties of the cracked rotor and the uncracked rotor were discussed, the difference of the time-frequency properties between the cracked rotor and the uncracked rotor was compared. A new detection algorithm using wavelet transform to identify crack was proposed. The experiments verify the availability and validity of the wavelet transform in identification of crack.

  6. Life and death of a single catalytic cracking particle.

    Science.gov (United States)

    Meirer, Florian; Kalirai, Sam; Morris, Darius; Soparawalla, Santosh; Liu, Yijin; Mesu, Gerbrand; Andrews, Joy C; Weckhuysen, Bert M

    2015-04-01

    Fluid catalytic cracking (FCC) particles account for 40 to 45% of worldwide gasoline production. The hierarchical complex particle pore structure allows access of long-chain feedstock molecules into active catalyst domains where they are cracked into smaller, more valuable hydrocarbon products (for example, gasoline). In this process, metal deposition and intrusion is a major cause for irreversible catalyst deactivation and shifts in product distribution. We used x-ray nanotomography of industrial FCC particles at differing degrees of deactivation to quantify changes in single-particle macroporosity and pore connectivity, correlated to iron and nickel deposition. Our study reveals that these metals are incorporated almost exclusively in near-surface regions, severely limiting macropore accessibility as metal concentrations increase. Because macropore channels are "highways" of the pore network, blocking them prevents feedstock molecules from reaching the catalytically active domains. Consequently, metal deposition reduces conversion with time on stream because the internal pore volume, although itself unobstructed, becomes largely inaccessible. PMID:26601160

  7. 7-lump kinetic model for residual oil catalytic cracking

    Institute of Scientific and Technical Information of China (English)

    XU Ou-guan; SU Hong-ye; MU Sheng-jing; CHU Jian

    2006-01-01

    In this paper a novel 7-lump kinetic model is proposed to describe residual oil catalytic cracking, in which coke is lumped separately for accurate prediction. The reactor block is modeled as a combination of an ideal pipe flow reactor (PFR)and a continuously stirred tank reactor (CSTR). Unit factors are designed to correct the deviation between model predictions and practical plant data and tuned by modified Levenberg-Marquardt algorithm. The parameters estimated are reliable and good agreement between the model predictions and plant observations is observed. The model helps us get good insight into the performance of an industrial riser reactor that would be useful for optimization of residual oil catalytic cracking.

  8. Cracking and corrosion recovery boiler

    Energy Technology Data Exchange (ETDEWEB)

    Suik, H. [Tallinn Technical University, Horizon Pulp and Paper, Tallinn (Estonia)

    1998-12-31

    The corrosion of heat surfaces and the cracking the drums are the main problems of the recovery boiler. These phenomena have been appeared during long-term operation of boiler `Mitsubishi - 315` erected at 1964. Depth of the crack is depending on the number of shutdowns and on operation time. Corrosion intensity of different heat surfaces is varying depend on the metal temperature and the conditions at place of positioning of tube. The lowest intensity of corrosion is on the bank tubes and the greatest is on the tubes of the second stage superheater and on the tubes at the openings of air ports. (orig.) 5 refs.

  9. Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials

    DEFF Research Database (Denmark)

    Brincker, Rune

    In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation...

  10. Crack growth resistance in nuclear graphites

    Science.gov (United States)

    Ouagne, Pierre; Neighbour, Gareth B.; McEnaney, Brian

    2002-05-01

    Crack growth resistance curves for the non-linear fracture parameters KR, JR and R were measured for unirradiated PGA and IM1-24 graphites that are used as moderators in British Magnox and AGR nuclear reactors respectively. All the curves show an initial rising part, followed by a plateau region where the measured parameter is independent of crack length. JR and R decreased at large crack lengths. The initial rising curves were attributed to development of crack bridges in the wake of the crack front, while, in the plateau region, the crack bridging zone and the frontal process zone, ahead of the crack tip, reached steady state values. The decreases at large crack lengths were attributed to interaction of the frontal zone with the specimen end face. Microscopical evidence for graphite fragments acting as crack bridges showed that they were much smaller than filler particles, indicating that the graphite fragments are broken down during crack propagation. There was also evidence for friction points in the crack wake zone and shear cracking of some larger fragments. Inspection of KR curves showed that crack bridging contributed ~0.4 MPa m0.5 to the fracture toughness of the graphites. An analysis of JR and R curves showed that the development of the crack bridging zone in the rising part of the curves contributed ~20% to the total work of fracture. Energies absorbed during development of crack bridges and steady state crack propagation were greater for PGA than for IM1-24 graphite. These differences reflect the greater extent of irreversible processes occurring during cracking in the coarser microtexture of PGA graphite.

  11. FRACTAL KINEMATICS OF CRACK PROPAGATION IN GEOMATERIALS

    Institute of Scientific and Technical Information of China (English)

    谢和平

    1995-01-01

    Experimental results indicate that propagation paths of cracks in geomaterials are often irregular, producing rough fracture surfaces which are fractal. A formula is derived for the fractal kinematics of crack propagation in geomaterials. The formula correlates the dynamic and static fracture toughnesses with crack velocity, crack length and a microstructural parameter, and allows the fractal dimension to be obtained. From the equations for estimating crack velocity and fractal dimension it can be shown that the measured crack velocity, Vo , should be much smaller than the fractal crack velocity, V. It can also be shown that the fractal dimension of the crack propagation path can be calculated directly from Vo and from the fracture toughness.

  12. China Cracks Down Internet Piracy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ National Copyright Administration of China carried out a special operation to crack down on behaviors involving network infringement and piracy from September to December in 2005 ,according to the speech of Yan Xiaohong,Deputy Commissioner of National Copyright Administration on the Press Conference of the State Council.Now the relevant conditions are as follows:

  13. China Cracks Down Internet Piracy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

      National Copyright Administration of China carried out a special operation to crack down on behaviors involving network infringement and piracy from September to December in 2005 ,according to the speech of Yan Xiaohong,Deputy Commissioner of National Copyright Administration on the Press Conference of the State Council.Now the relevant conditions are as follows:……

  14. HYDROTHERMAL CRACKING OF RESIDUAL OILS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The hydrothermal cracking of heavy oils, such as Canadian oil sand bitumen and Arabian heavy vacuum residue, as well as their model compound were performed over sulfided Ni/Al2O3 and NiMo/Al2O3 catalysts under 663~703 K and 6.0~8.0 MPa of hydrogen pressure in a batch autoclave reactor. According to the reaction mechanism of hydrothermal cracking, a small amount of free redical initiators, such as di-tert-peroxide, sulfur, etc., was added into the feed to generate free redicals at lower temperature, and obviously showed promotional effect on the conversion of hydrocarbons. The reaction mechanisms of hydrothermal cracking as well as the enhancing effect of initiators were studied by a probe reaction with 1-phenyldodecane as a model compound. The hydrothermal cracking of hydrocarbon proceeded via free redical mechanism and hydrogenating quench. The initiators might easily generate free redicals under reaction temperature, these redicals might abstract H from hydrocarbon molecule and reasonably initiate the chain reactions, therefore, promote the conversion of hydrocarbon even at lower reaction temperature.

  15. Wear crack characterization by photothermal radiometry

    Energy Technology Data Exchange (ETDEWEB)

    Bodnar, J.L. [GRSM/LEO, Faculte des Sciences, 51 - Reims (France); Egee, M. [GRSM/LEO, Faculte des Sciences, 51 - Reims (France)

    1996-08-01

    After demonstrating recently the possibilities of scanning photothermal radiometry for wear crack detection (Bodnar et al., J. Phys. IV, 4 (1994) 591-594), we now study its possibilities for dimensional characterization of these kinds of flaws. In this respect, we present here the results obtained from our study of two types of emerging cracks, i.e. thin and shallow cracks in samples with a reflecting surface as well as wider and deeper cracks in samples with an absorbing surface. (orig.)

  16. Fatigue crack growth from a cracked elastic particle into a ductile matrix

    NARCIS (Netherlands)

    Groh, S.; Olarnrithinun, S.; Curtin, W. A.; Needleman, A.; Deshpande, V. S.; Van der Giessen, E.

    2008-01-01

    The monotonic and cyclic crack growth rate of cracks is strongly influenced by the microstructure. Here, the growth of cracks emanating from pre-cracked micron-scale elastic particles and growing into single crystals is investigated, with a focus on the effects of (i) plastic confinement due to the

  17. Propagation and band width of smeared cracks

    NARCIS (Netherlands)

    Slobbe, A.T.

    2015-01-01

    The crack band approach (in the smeared crack concept) is widely used for the modeling of concrete fracture and is an important analysis technique within advanced engineering. However, the simulations can be impeded by mesh-induced directional bias. Cracks prefer to propagate along continuous mesh l

  18. An analytical thermal fatigue crack growth approach

    International Nuclear Information System (INIS)

    The paper presents recent works on the thermal fatigue crack growth approach in structure integrity analysis proposed by nuclear standard codes such as A16 Appendix of RCC-MR. The proposed approach for crack growth is used to study the mechanisms leading to cracking of piping as a result of thermal loading in mixed flow zones

  19. Assessment of cracking in dissimilar metal welds

    International Nuclear Information System (INIS)

    During the refueling in 2000, indications were observed by non-destructive testing at four locations in the reactor pressure vessel (RPV) nozzle to safe end weld in Ringhals 4. All indications were confined to the outlet nozzle (hotleg) oriented at 25 deg, a nozzle with documented repair welding. Six boat samples were removed from the four locations, and the samples were subsequently subjected to a metallographic examination. The objectives were to establish the fracture morphology, and if possible the root cause for cracking. The examination revealed that cracks were present at all four boat sample locations and that they all were confined to the weld metal, alloy 182. Cracking extended in the axial direction of the safe-end. There was no evidence of any cracks extending into the RPV-steel, or the stainless steel safe-end. All cracking was interdendritic and significantly branched. Among others, these observations strongly suggested crack propagation mainly was caused by interdendritic stress corrosion cracking. In addition, crack type defects and isolated areas on the fracture surfaces suggested the presence of hot cracking, which would have been formed during fabrication. The reason for crack initiation could not be established based on the boat samples examined. However, increased stress levels due to repair welding, cold work from grinding, and defects produced during fabrication, e. g. hot cracks, may alone or in combination have contributed to crack initiation

  20. Cracked Teeth: A Review of the Literature

    OpenAIRE

    Lubisich, Erinne B.; Hilton, Thomas J.; Ferracane, Jack

    2010-01-01

    Although cracked teeth are a common problem for patients and dentists, there is a dearth of evidence-based guidelines on how to prevent, diagnose, and treat cracks in teeth. The purpose of this article is to review the literature to establish what evidence exists regarding the risk factors for cracked teeth and their prevention, diagnosis, and treatment.

  1. Fatigue crack growth simulations of 3-D linear elastic cracks under thermal load by XFEM

    Institute of Scientific and Technical Information of China (English)

    Himanshu PATHAK[1; Akhilendra SINGH[2; I.V. SINGH[3; S. K. YADAV[3

    2015-01-01

    This paper deals with the fatigue crack growth simulations of three-dimensional linear elastic cracks by XFEM under cyclic thermal load. Both temperature and displacement approximations are extrinsically enriched by Heaviside and crack front enrichment functions. Crack growth is modelled by successive linear extensions, and the end points of these linear extensions are joined by cubic spline segments to obtain a modified crack front. Different crack geometries such as planer, non-planer and arbitrary spline shape cracks are simulated under thermal shock, adiabatic and isothermal loads to reveal the sturdiness and versatility of the XFEM approach.

  2. Monte Carlo simulation of micro crack propagation behavior for stress corrosion cracking

    International Nuclear Information System (INIS)

    A calculation code of Monte Carlo simulation for micro crack propagation behavior of stress corrosion cracking has been developed. Improvements for micro crack growth rate treatments and stress distributions have been made. Calculated crack depth distributions were compared with the CBB test results for sensitized stainless steels and low carbon stainless steels with hardened layer. For sensitized stainless steels, the calculated crack depth distribution could well reproduce the CBB test results by taking into account crack growth rates obtained from experiments. For low carbon stainless steels, although considering stress distributions improved the overestimation of crack depths, the calculated crack depth distribution could not well reproduce the CBB test result. The results revealed that the effects of the crack growth rate and the stress distribution on micro crack propagation behaviors. (author)

  3. Blocking and associability change.

    Science.gov (United States)

    Jones, Peter M; Haselgrove, Mark

    2013-07-01

    Blocking of learning about a conditioned stimulus (the "blocked" cue) occurs when it is trained alongside an additional stimulus (the "blocking" cue) that has been previously presented with the outcome. A number of theories (e.g., N. J. Mackintosh. 1975a. A Theory of Attention: Variations in the Associability of Stimuli With Reinforcement. Psychological Review, 82, 276-298; J. M. Pearce & G. Hall. 1980. A Model for Pavlovian Learning: Variation in the Effectiveness of Conditioned But Not Unconditioned Stimuli. Psychological Review, 87, 532-552) account for this attenuation in learning by proposing that attention paid to the blocked cue is restricted. In three experiments, we examined the associability of both blocked and blocking cues. In Experiment 1, rats were trained with a blocking protocol before being given a test discrimination composed of two components; one of these components required the use of the previously blocked cue as a discriminative stimulus, and the other component was soluble by using the blocking cue. To our surprise, the component that depended on the blocked cue was more readily solved than the component dependent on the blocking cue. The results of Experiments 2 and 3 suggest that this is due to the quantity of exposure that each stimulus received during initial training. Implications for theories of blocking, and more widely associative learning, are discussed. PMID:23668185

  4. Blocking and associability change.

    Science.gov (United States)

    Jones, Peter M; Haselgrove, Mark

    2013-07-01

    Blocking of learning about a conditioned stimulus (the "blocked" cue) occurs when it is trained alongside an additional stimulus (the "blocking" cue) that has been previously presented with the outcome. A number of theories (e.g., N. J. Mackintosh. 1975a. A Theory of Attention: Variations in the Associability of Stimuli With Reinforcement. Psychological Review, 82, 276-298; J. M. Pearce & G. Hall. 1980. A Model for Pavlovian Learning: Variation in the Effectiveness of Conditioned But Not Unconditioned Stimuli. Psychological Review, 87, 532-552) account for this attenuation in learning by proposing that attention paid to the blocked cue is restricted. In three experiments, we examined the associability of both blocked and blocking cues. In Experiment 1, rats were trained with a blocking protocol before being given a test discrimination composed of two components; one of these components required the use of the previously blocked cue as a discriminative stimulus, and the other component was soluble by using the blocking cue. To our surprise, the component that depended on the blocked cue was more readily solved than the component dependent on the blocking cue. The results of Experiments 2 and 3 suggest that this is due to the quantity of exposure that each stimulus received during initial training. Implications for theories of blocking, and more widely associative learning, are discussed.

  5. Modelling of ultrasonic nondestructive testing in anisotropic materials - Rectangular crack

    International Nuclear Information System (INIS)

    Nondestructive testing with ultrasound is a standard procedure in the nuclear power industry when searching for defects, in particular cracks. To develop and qualify testing procedures extensive experimental work on test blocks is usually required. This can take a lot of time and therefore be quite costly. A good mathematical model of the testing situation is therefore of great value as it can reduce the experimental work to a great extent. A good model can be very useful for parametric studies and as a pedagogical tool. A further use of a model is as a tool in the qualification of personnel. In anisotropic materials, e.g. austenitic welds, the propagation of ultrasound becomes much more complicated as compared to isotropic materials. Therefore, modelling is even more useful for anisotropic materials, and it in particular has a greater pedagogical value. The present project has been concerned with a further development of the anisotropic capabilities of the computer program UTDefect, which has so far only contained a strip-like crack as the single defect type for anisotropic materials. To be more specific, the scattering by a rectangular crack in an anisotropic component has been studied and the result is adapted to include transmitting and receiving ultrasonic probes. The component under study is assumed to be anisotropic with arbitrary anisotropy. On the other hand, it is assumed to be homogeneous, and this in particular excludes most welds, where it is seldom an adequate approximation to assume homogeneity. The anisotropy may be arbitrarily oriented and the same is true of the rectangular crack. The crack may also be located near a backside of the component. To solve the scattering problem for the crack an integral equation method is used. The probe model has been developed in an earlier project and to compute the signal response in the receiving probe an electromechanical reciprocity argument is employed. As a rectangle is a truly 3D scatterer the sizes of the

  6. Delayed hydride cracking: theoretical model testing to predict cracking velocity

    International Nuclear Information System (INIS)

    Pressure tubes from Candu nuclear reactors as any other component manufactured with Zr alloys are prone to delayed hydride cracking. That is why it is important to be able to predict the cracking velocity during the component lifetime from parameters easy to be measured, such as: hydrogen concentration, mechanical and microstructural properties. Two of the theoretical models reported in literature to calculate the DHC velocity were chosen and combined, and using the appropriate variables allowed a comparison with experimental results of samples from Zr-2.5 Nb tubes with different mechanical and structural properties. In addition, velocities measured by other authors in irradiated materials could be reproduced using the model described above. (author)

  7. Mesh sensitivity effects on fatigue crack growth by crack-tip blunting and re-sharpening

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2007-01-01

    Crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading is one of the basic mechanisms for fatigue crack growth in ductile metals. Based on an elastic–perfectly plastic material model, crack growth computations have been continued up to 700 full cycles by using...... refinement is used to study the possibility of this type of behaviour within the present method. Even with much refined meshes no indication of crack surface folding is found here....

  8. Crack detection by stimulated infrared thermography

    Science.gov (United States)

    Bodnar, Jean-Luc

    2014-03-01

    In this paper, the potential of stimulated infrared thermography is studied for the detection of cracks located in metallic materials. To start with, the feasibility of the method is shown with the use of numerical simulations. Stimulated infrared thermography allows detecting emerging cracks in samples whether reflective or not as well as non-emerging cracks. In addition, crack detection is due to the radiative effects and/or the thermal effects induced by the defects. Then, the experimental device implemented for the study is detailed. Finally, experiments confirm that stimulated infrared thermography enables to detect microscopic cracks, whether emerging or non-emerging, in metal samples.

  9. Experimental simulation of frost wedging-induced crack propagation in alpine rockwall

    Science.gov (United States)

    Jia, Hailiang; Leith, Kerry; Krautblatter, Michael

    2016-04-01

    Frost wedging is widely presumed to be the principal mechanism responsible for shattering jointed low-porosity rocks in high alpine rockwalls. The interaction of ice and rock physics regulates the efficacy of frost wedging. In order to better understand temporal aspects of this interaction, we present results of a series of laboratory experiments monitoring crack widening as a result of ice formation in an artificial crack (4mm wide, 80mm deep) cut 20 mm from the end of a rectangular granite block. Our results indicate that i) freezing direction plays a key role in determining the magnitude of crack widening; in short-term (1 day) experiments, maximum crack widening during top-down freezing (associated with 'autumn' conditions) was around 0.11mm, while inside-out freezing (resulting from 'spring' conditions) produced only 0.02 mm of deformation; ii) neither ice, nor water pressure (direct tension and hydraulic fracturing respectively) caused measurable irreversible crack widening during short-term tests, as the calculated maximum stress intensity at the crack tip was less than the fracture toughness of our granite sample; iii) development of ice pressure is closely related to the mechanical properties of the fracture in which it forms, and as such, the interaction of ice and rock is intrinsically dynamic; iv) irreversible crack widening (about 0.03mm) was only observed following a long-term (53 day) experiment representing a simplified transition from autumn to winter conditions. We suggest this is the result of stress corrosion aided by strong opening during freezing, and to a lesser degree by ice segregation up to one week after the initial freezing period, and downward migration of liquid water during the remainder of the test. Our results suggest the fundamental assumption of frost wedging, that rapid freezing from open ends of cracks can seal water inside the crack and thus cause damage through excessive stresses induced by volumetric expansion seems

  10. Generalized Block Failure

    DEFF Research Database (Denmark)

    Jönsson, Jeppe

    2015-01-01

    Block tearing is considered in several codes as a pure block tension or a pure block shear failure mechanism. However in many situations the load acts eccentrically and involves the transfer of a substantial moment in combination with the shear force and perhaps a normal force. A literature study...... yield lines around the block leads to simple interaction formulas similar to other interaction formulas in the codes.......Block tearing is considered in several codes as a pure block tension or a pure block shear failure mechanism. However in many situations the load acts eccentrically and involves the transfer of a substantial moment in combination with the shear force and perhaps a normal force. A literature study...

  11. The underclad cracking in PWR reactor vessels

    International Nuclear Information System (INIS)

    The article describes the kind of cracking which can occur under the stainless steel cladding during the manufacturing process of PWR vessels: - cold cracking recently found in France on vessel nozzles-reheat cracking discovered some ten years ago in particular in Germany and in USA. Methods of examination for underclad cracking are put forward, together with results obtained on vessel nozzles of units currently being built in Belgium. Some nozzles are affected by the phenomenon of reheat cracking, whilst the hypothesis of cold cracking, which had been proposed because of the similar situation found in France should probably be abandoned. On the basis of the investigations and studies made, it is established that the cracking involved does not jeopardize the integrity of the vessels during their life time. (author)

  12. Blocked Randomization with Randomly Selected Block Sizes

    Directory of Open Access Journals (Sweden)

    Jimmy Efird

    2010-12-01

    Full Text Available When planning a randomized clinical trial, careful consideration must be given to how participants are selected for various arms of a study. Selection and accidental bias may occur when participants are not assigned to study groups with equal probability. A simple random allocation scheme is a process by which each participant has equal likelihood of being assigned to treatment versus referent groups. However, by chance an unequal number of individuals may be assigned to each arm of the study and thus decrease the power to detect statistically significant differences between groups. Block randomization is a commonly used technique in clinical trial design to reduce bias and achieve balance in the allocation of participants to treatment arms, especially when the sample size is small. This method increases the probability that each arm will contain an equal number of individuals by sequencing participant assignments by block. Yet still, the allocation process may be predictable, for example, when the investigator is not blind and the block size is fixed. This paper provides an overview of blocked randomization and illustrates how to avoid selection bias by using random block sizes.

  13. Blocked randomization with randomly selected block sizes.

    Science.gov (United States)

    Efird, Jimmy

    2011-01-01

    When planning a randomized clinical trial, careful consideration must be given to how participants are selected for various arms of a study. Selection and accidental bias may occur when participants are not assigned to study groups with equal probability. A simple random allocation scheme is a process by which each participant has equal likelihood of being assigned to treatment versus referent groups. However, by chance an unequal number of individuals may be assigned to each arm of the study and thus decrease the power to detect statistically significant differences between groups. Block randomization is a commonly used technique in clinical trial design to reduce bias and achieve balance in the allocation of participants to treatment arms, especially when the sample size is small. This method increases the probability that each arm will contain an equal number of individuals by sequencing participant assignments by block. Yet still, the allocation process may be predictable, for example, when the investigator is not blind and the block size is fixed. This paper provides an overview of blocked randomization and illustrates how to avoid selection bias by using random block sizes. PMID:21318011

  14. BLOCK H-MATRICES AND SPECTRUM OF BLOCK MATRICES

    Institute of Scientific and Technical Information of China (English)

    黄廷祝; 黎稳

    2002-01-01

    The block H-matrices are studied by the concept of G-functions, several concepts of block matrices are introduced. Equivalent characters of block H-matrices are obtained. Spectrum localizations claracterized by Gfunctions for block matrices are got.

  15. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Science.gov (United States)

    Kruml, T.; Hutař, P.; Náhlík, L.; Seitl, S.; Polák, J.

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 μm was followed in symmetrical cycling with constant strain amplitude ( R ɛ = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  16. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Kruml, T., E-mail: kruml@ipm.cz [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic); Hutar, P.; Nahlik, L.; Seitl, S.; Polak, J. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic)

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 {mu}m was followed in symmetrical cycling with constant strain amplitude (R{sub {epsilon}} = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  17. Lesson Thirteen Trifascicular Block

    Institute of Scientific and Technical Information of China (English)

    鲁端; 王劲

    2005-01-01

    @@ A complete trifascicular block would result in complete AV block. The idio ventricular rhythm has a slower rate and a wide QRS complex because the pacemaker is located at the peripheral part of the conduction system distal to the sites of the block1. Such a rhythm may be difficult to differentiate from bifascicular or bundle branch block combined with complete block at a higher level such as the AV node or His bundle2. Besides a slower ventricular rate, a change in the morphology of the QRS complex from a previous known bifascicular pattern would be strongly suggestive of a trifascicular origin of the complete AV block3. A His bundle recording is required for a definitive diagnosis, however.

  18. Crack propagation in fracture mechanical graded structures

    Directory of Open Access Journals (Sweden)

    B. Schramm

    2015-10-01

    Full Text Available The focus of manufacturing is more and more on innovative and application-oriented products considering lightweight construction. Hence, especially functional graded materials come to the fore. Due to the application-matched functional material gradation different local demands such as absorbability, abrasion and fatigue of structures are met. However, the material gradation can also have a remarkable influence on the crack propagation behavior. Therefore, this paper examines how the crack propagation behavior changes when a crack grows through regions which are characterized by different fracture mechanical material properties (e.g. different threshold values KI,th, different fracture toughness KIC. In particular, the emphasis of this paper is on the beginning of stable crack propagation, the crack velocity, the crack propagation direction as well as on the occurrence of unstable crack growth under static as well as cyclic loading. In this context, the developed TSSR-concept is presented which allows the prediction of crack propagation in fracture mechanical graded structures considering the loading situation (Mode I, Mode II and plane Mixed Mode and the material gradation. In addition, results of experimental investigations for a mode I loading situation and numerical simulations of crack growth in such graded structures confirm the theoretical findings and clarify the influence of the material gradation on the crack propagation behavior.

  19. Crack initiation in smooth fatigue specimens of austenitic stainless steel in light water reactor environments.

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O. K.; Smith, J. L.

    1999-04-08

    The fatigue design curves for structural materials specified in Section III of the ASME Boiler and Pressure Vessel Code are based on tests of smooth polished specimens at room temperature in air. The effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves; however, recent test data illustrate the detrimental effects of LWR coolant environments on the fatigue resistance of austenitic stainless steels (SSs). Certain loading and environmental conditions have led to test specimen fatigue lives that are significantly shorter than those obtained in air. Results of fatigue tests that examine the influence of reactor environments on crack initiation and crack growth of austenitic SSs are presented. Block loading was used to mark the fracture surface to determine crack length as a function of fatigue cycles in water environments, Crack lengths were measured by scanning electron microscopy. The mechanism for decreased fatigue life in LWR environments is discussed, and crack growth rates in the smooth fatigue specimens are compared with existing data from studies of crack growth rates.

  20. Investigating fracture-cracked systems with geophysical methods in Bayburt Kıratlı travertine

    Science.gov (United States)

    Öğretmen, Zeynep; Şeren, Aysel

    2014-12-01

    There are many outcropping masses on the Kıratlı travertine fields where a new or open quarry is planned to be exploited. In this study, ground penetrating radar (GPR) and vertical electrical sounding (VES) have been applied on these fields in order to identify massive or weathered blocks and fracture-cracked systems in a short time and at low cost. GPR data were acquired on two areas, named Ocakustu (Ocakustu 1, Ocakustu 2) and Alarduc (Alarduc 1, Alarduc 2), using a 100 MHz unshielded and 250 MHz shielded antennas on 35 profiles. Generally, radargrams obtained from GPR profiles revealed massive or weathered blocks and fracture-cracked systems of these fields. The quarry operation was stopped in Ocakustu 1 due to the intensely fracture-cracked and weathered structures of the travertine field imaged by GPR. Detailed information was not obtained under the topping layer of 4 m from GPR sections on Ocakustu 2 area. Therefore, VES was also performed along four profiles which made it possible to define the areal extension and thickness of the lithotype in this site. Electrical resistivity tomography (ERT) sections have been generated by the inversion of the VES data. The subsurface geometries with resistivity values in the area were determined from these sections. Massive blocks with high resistivity could be seen at depths of 2-10 m and 10-20 m below the surface on these results and it was suggested that the quarry should be extended these parts. In addition, according to the GPR data, fracture-cracked blocks were present in Alarduc where a travertine quarry is thought to be operated. The places that will be started and orientated to quarry can be determined with respect to radargrams on Alarduc 1. Ultimately, the exploitation of a quarry was not recommended due to the extremely fracture-cracked systems found in Alarduc 2.

  1. Block Advertisement Protocol

    OpenAIRE

    Nemirovsky, Danil

    2015-01-01

    Bitcoin, a decentralized cryptocurrency, has attracted a lot of attention from academia, financial service industry and enthusiasts. The trade-off between transaction confirmation throughput and centralization of hash power do not allow Bitcoin to perform at the same level as modern payment systems. Block Advertisement Protocol is proposed as a step to resolve this issue. The protocol allows block mining and block relaying to happen in parallel. The protocol dictates a miner to advertise the ...

  2. Block Cipher Analysis

    DEFF Research Database (Denmark)

    Miolane, Charlotte Vikkelsø

    ensurethat no attack violatesthe securitybounds specifiedbygeneric attack namely exhaustivekey search and table lookup attacks. This thesis contains a general introduction to cryptography with focus on block ciphers and important block cipher designs, in particular the Advanced Encryption Standard...... on small scale variants of AES. In the final part of the thesis we present a new block cipher proposal Present and examine its security against algebraic and differential cryptanalysis in particular....

  3. Controlling fatigue crack paths for crack surface marking and growth investigations

    Directory of Open Access Journals (Sweden)

    S. Barter

    2016-01-01

    Full Text Available While it is well known that fatigue crack growth in metals that display confined slip, such as high strength aluminium alloys, develop crack paths that are responsive to the loading direction and the local microstructural orientation, it is less well known that such paths are also responsive to the loading history. In these materials, certain loading sequences can produce highly directional slip bands ahead of the crack tip and by adjusting the sequence of loads, distinct fracture surface features or progression marks, even at very small crack depths can result. Investigating the path a crack selects in fatigue testing when particular combinations of constant and variable amplitude load sequences are applied is providing insight into crack growth. Further, it is possible to design load sequences that allow very small amounts of crack growth to be measured, at very small crack sizes, well below the conventional crack growth threshold in the aluminium alloy discussed here. This paper reports on observations of the crack path phenomenon and a novel test loading method for measuring crack growth rates for very small crack depths in aluminium alloy 7050-T7451 (an important aircraft primary structural material. The aim of this work was to firstly generate short- crack constant amplitude growth data and secondly, through the careful manipulation of the applied loading, to achieve a greater understanding of the mechanisms of fatigue crack growth in the material being investigated. A particular focus of this work is the identification of the possible sources of crack growth retardation and closure in these small cracks. Interpreting these results suggests a possible mechanism for why small fatigue crack growth through this material under variable amplitude loading is faster than predicted from models based on constant amplitude data alone.

  4. Online Bridge Crack Monitoring with Smart Film

    Directory of Open Access Journals (Sweden)

    Benniu Zhang

    2013-01-01

    Full Text Available Smart film crack monitoring method, which can be used for detecting initiation, length, width, shape, location, and propagation of cracks on real bridges, is proposed. Firstly, the fabrication of the smart film is developed. Then the feasibility of the method is analyzed and verified by the mechanical sensing character of the smart film under the two conditions of normal strain and crack initiation. Meanwhile, the coupling interference between parallel enameled wires of the smart film is discussed, and then low-frequency detecting signal and the custom communication protocol are used to decrease interference. On this basis, crack monitoring system with smart film is designed, where the collected crack data is sent to the remote monitoring center and the cracks are simulated and recurred. Finally, the monitoring system is applied to six bridges, and the effects are discussed.

  5. Numerical Study of Corrosion Crack Opening

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle; Frandsen, Henrik Lund; Svensson, Staffan

    2008-01-01

    for the corrosion crack opening. Experiments and theoretical analysis by a numerical method, FEM, support that the relation between the reduction of the reinforcement bar diameter due to corrosion and the corresponding increase in crack width for a given time interval, measured on the surface of a concrete specimen...... is proportional. More recently, the constant of proportionality, the so-called crack-corrosion index, has been studied further with respect to its dependence on the diameter of the reinforcement and the concrete cover. In the present paper the above-mentioned work is presented and extended with more realistic 3D......-models of the cracked concrete beam. The crack-corrosion index is evaluated for a variation of different parameters, i.e. bar diameter, concrete cover, crack length and type of corrosion product. This paper is an extended version of a paper by Thoft-Christensen et al. (2005) presented at the IFIP WG 7.5 Conference...

  6. Fluid structural response of axially cracked cylinders

    International Nuclear Information System (INIS)

    The fluid structural (FS) response of a cylindrical pressure vessel to a suddenly occurring longitudinal through-wall crack is predicted. The effects of vessel internals and depressurization of the compressed water on dynamic crack opening displacements are investigated. A three dimensional (3D) structural finite element model is used as a basis for the development of a two dimensional (2D) FS model. A slice of the vessel taken at the crack midspan and normal to the cylinder axis is modeled. Crack opening displacements are compared between the 2D and 3D models, between the different assumptions about fluid depressurization, and between the static and dynamic solutions. The results show that effects of dynamic amplification associated with the sudden opening of the crack in the cylinder are largely offset by the local depressurization of the fluid adjacent to the crack

  7. Crack formation and prevention in colloidal drops

    Science.gov (United States)

    Kim, Jin Young; Cho, Kun; Ryu, Seul-a; Kim, So Youn; Weon, Byung Mook

    2015-01-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles. PMID:26279317

  8. Pavement Crack Detection Using Spectral Clustering Method

    Directory of Open Access Journals (Sweden)

    Jin Huazhong

    2015-01-01

    Full Text Available Pavement crack detection plays an important role in pavement maintaining and management, nowadays, which could be performed through remote image analysis. Thus, edges of pavement crack should be extracted in advance; in general, traditional edge detection methods don’t consider phase information and the spatial relationship between the adjacent image areas to extract the edges. To overcome the deficiency of the traditional approaches, this paper proposes a pavement crack detection algorithm based on spectral clustering method. Firstly, a measure of similarity between pairs of pixels is taken into account through orientation energy. Then, spatial relationship is needed to find regions where similarity between pixels in a given region is high and similarity between pixels in different regions is low. After that, crack edge detection is completed with spectral clustering method. The presented method has been run on some real life images of pavement crack, experimental results display that the crack detection method of this paper could obtain ideal result.

  9. DBEM crack propagation for nonlinear fracture problems

    Directory of Open Access Journals (Sweden)

    R. Citarella

    2015-10-01

    Full Text Available A three-dimensional crack propagation simulation is performed by the Dual Boundary Element Method (DBEM. The Stress Intensity Factors (SIFs along the front of a semi elliptical crack, initiated from the external surface of a hollow axle, are calculated for bending and press fit loading separately and for a combination of them. In correspondence of the latter loading condition, a crack propagation is also simulated, with the crack growth rates calculated using the NASGRO3 formula, calibrated for the material under analysis (steel ASTM A469. The J-integral and COD approaches are selected for SIFs calculation in DBEM environment, where the crack path is assessed by the minimum strain energy density criterion (MSED. In correspondence of the initial crack scenario, SIFs along the crack front are also calculated by the Finite Element (FE code ZENCRACK, using COD, in order to provide, by a cross comparison with DBEM, an assessment on the level of accuracy obtained. Due to the symmetry of the bending problem a pure mode I crack propagation is realised with no kinking of the propagating crack whereas for press fit loading the crack propagation becomes mixed mode. The crack growth analysis is nonlinear because of normal gap elements used to model the press fit condition with added friction, and is developed in an iterative-incremental procedure. From the analysis of the SIFs results related to the initial cracked configuration, it is possible to assess the impact of the press fit condition when superimposed to the bending load case.

  10. Block Scheduling Revisited.

    Science.gov (United States)

    Queen, J. Allen

    2000-01-01

    Successful block scheduling depends on provision of initial and ongoing instructional training. Teaching strategies should vary and include cooperative learning, the case method, the socratic seminar, synectics, concept attainment, the inquiry method, and simulations. Recommendations for maximizing block scheduling are outlined. (Contains 52…

  11. Surviving Block Scheduling.

    Science.gov (United States)

    Haley, Marjorie

    A discussion of block scheduling for second language instruction looks at the advantages and disadvantages and offers some suggestions for classroom management and course organization. It is argued that block scheduling may offer a potential solution to large classes, insufficient time for labs, too little individualized instruction; few…

  12. Transition from Multiple Macro-Cracking to Multiple Micro-Cracking in Cementitious Composites

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; LENG Bing

    2008-01-01

    This paper presents an experimental study of the possibility of transition from multiple macro-cracking to multiple micro-cracking in cementitious composites.Conventional polyvinyl alcohol fiber reinforced cementitious composites normally exhibit macroscopic strain-hardening and multiple cracking after the first cracks appear.However,the individual crack width at the saturated stage is normally 60 to 80 μm.In the current study,the effect of fine aggregate size on the cracking performance,especially the individual crack width in the strain-hardening stage was studied by bending tests.The results show that the individual crack widths can be reduced from 60-80 μm to 10-30 μm by modifying the particle size of the fine aggregates used in the composites.

  13. Automatic crack length measurement, inductive and videoelectronic

    International Nuclear Information System (INIS)

    Tracking of crack propagation with a small fault of less than 2% is permitted by two recently developed methods. Because of the direct manner of crack inspection, the video-electronic method has the advantage over the inductive measurement, although with a scanning frequency given by television control, only relatively small crack velocities as compared with the inductive method can be detected with sufficient accuracy. Because of strong material contraction at the crack top with both methods, minor measurement adulterations may arise. The equipment causes relatively low costs during operation. Both methods enable fully automatic evaluation and control of the experiment. (orig.)

  14. Fatigue crack growth detect, assess, avoid

    CERN Document Server

    Richard, Hans Albert

    2016-01-01

    This book offers a concise introduction to fatigue crack growth, based on practical examples. It discusses the essential concepts of fracture mechanics, fatigue crack growth under constant and variable amplitude loading and the determination of the fracture-mechanical material parameters. The book also introduces the analytical and numerical simulation of fatigue crack growth as well as crack initiation. It concludes with a detailed description of several practical case studies and some exercises. The target group includes graduate students, researchers at universities and practicing engineers.

  15. Expansive Soil Crack Depth under Cumulative Damage

    Directory of Open Access Journals (Sweden)

    Bei-xiao Shi

    2014-01-01

    Full Text Available The crack developing depth is a key problem to slope stability of the expansive soil and its project governance and the crack appears under the roles of dry-wet cycle and gradually develops. It is believed from the analysis that, because of its own cohesion, the expansive soil will have a certain amount of deformation under pulling stress but without cracks. The soil body will crack only when the deformation exceeds the ultimate tensile strain that causes cracks. And it is also believed that, due to the combined effect of various environmental factors, particularly changes of the internal water content, the inherent basic physical properties of expansive soil are weakened, and irreversible cumulative damages are eventually formed, resulting in the development of expansive soil cracks in depth. Starting from the perspective of volumetric strain that is caused by water loss, considering the influences of water loss rate and dry-wet cycle on crack developing depth, the crack developing depth calculation model which considers the water loss rate and the cumulative damages is established. Both the proposal of water loss rate and the application of cumulative damage theory to the expansive soil crack development problems try to avoid difficulties in matrix suction measurement, which will surely play a good role in promoting and improving the research of unsaturated expansive soil.

  16. Slow crack growth in polycarbonate films

    CERN Document Server

    Cortet, Pierre-Philippe; Vanel, Loic; Ciliberto, Sergio

    2005-01-01

    We study experimentally the slow growth of a single crack in polycarbonate films submitted to uniaxial and constant imposed stress. The specificity of fracture in polycarbonate films is the appearance of flame shaped macroscopic process zones at the tips of the crack. Supported by an experimental study of the mechanical properties of polycarbonate films, an analysis of the stress dependence of the mean ratio between the process zone and crack lengths, during the crack growth, show a quantitative agreement with the Dugdale-Barenblatt model of the plastic process zone. We find that the fracture growth curves obey strong scaling properties that lead to a well defined growth master curve.

  17. Crack depth determination with inductive thermography

    Science.gov (United States)

    Oswald-Tranta, B.; Schmidt, R.

    2015-05-01

    Castings, forgings and other steel products are nowadays usually tested with magnetic particle inspection, in order to detect surface cracks. An alternative method is active thermography with inductive heating, which is quicker, it can be well automated and as in this paper presented, even the depth of a crack can be estimated. The induced eddy current, due to its very small penetration depth in ferro-magnetic materials, flows around a surface crack, heating this selectively. The surface temperature is recorded during and after the short inductive heating pulse with an infrared camera. Using Fourier transformation the whole IR image sequence is evaluated and the phase image is processed to detect surface cracks. The level and the local distribution of the phase around a crack correspond to its depth. Analytical calculations were used to model the signal distribution around cracks with different depth and a relationship has been derived between the depth of a crack and its phase value. Additionally, also the influence of the heating pulse duration has been investigated. Samples with artificial and with natural cracks have been tested. Results are presented comparing the calculated and measured phase values depending on the crack depth. Keywords: inductive heating, eddy current, infrared

  18. Wettability Induced Crack Dynamics and Morphology

    CERN Document Server

    Ghosh, Udita Uday; Bhandari, Aditya Bikram; Chakraborty, Suman; DasGupta, Sunando

    2014-01-01

    Substrate wettability alteration induced control over crack formation process in thin colloidal films has been addressed in the present study. Colloidal nanosuspension (53nm, mean particle diameter) droplets have been subjected to natural drying to outline the effects of substrate surface energies over the dry-out characteristics with emphasis on crack dynamics, crack morphology and underlying particle arrangements. Experimental findings indicate that number of cracks formed decreases with increase in substrate hydrophobicity. These physical phenomena have been explained based on the magnitude of stress dissipation incurred by the substrate. DLVO predictions are also found to be in tune with the reported experimental investigations.

  19. Dynamics of cracking in drying colloidal sheets.

    Science.gov (United States)

    Sengupta, Rajarshi; Tirumkudulu, Mahesh S

    2016-04-01

    Colloidal dispersions are known to display a fascinating network of cracks on drying. We probe the fracture mechanics of free-standing films of aqueous polymer-particle dispersions. Thin films of the dispersion are cast between a pair of plain steel wires and allowed to dry under ambient conditions. The strain induced on the particle network during drying is relieved by cracking. The stress which causes the films to crack has been calculated by measuring the deflection of the wires. The critical cracking stress varied inversely to the two-thirds' power of the film thickness. We also measure the velocity of the tip of a moving crack. The motion of a crack has been modeled as a competition between the release of the elastic energy stored in the particle network, the increase in surface energy as a result of the growth of a crack, the rate of viscous dissipation of the interstitial fluid and the kinetic energy associated with a moving crack. There is fair agreement between the measured crack velocities and predictions. PMID:26924546

  20. Investigations of Low Temperature Time Dependent Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J

    2002-09-30

    The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.

  1. Surface effects and assessment of crack propagation

    International Nuclear Information System (INIS)

    A realistic analysis of microcrack interaction at stress concentrations require a three dimensional analysis, and evaluation of fracture parameters along the crack front. Due to its complexity the problem can only be tackled through computational techniques. In this work, we describe the use of the Boundary Element Technique for analysis of surface effects at crack vertex. It is shown that the existence of a vertex singularity at this location poses limitations on actual crack geometries, and hence some common assumptions might not be adequate for a realistic description of surface crack growth. (author). 15 refs, 5 figs

  2. Fatigue Crack Closure Analysis Using Digital Image Correlation

    Science.gov (United States)

    Leser, William P.; Newman, John A.; Johnston, William M.

    2010-01-01

    Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

  3. Crack spacing of unsaturated soils in the critical state

    Institute of Scientific and Technical Information of China (English)

    SUN JiChao; WANG GuangQian; SUN QiCheng

    2009-01-01

    The cracking mechanism of unsaturated soils due to evaporation is poorly understood, and the magnitude of crack spacing is usually hard to estimate. In this work, cracks were postulated to occur suc-cedently rather than simultaneously, that is, secondary cracks appear after primary cracks as evaporation continues. Formulae of the secondary crack spacing and secondary trend crack spacing were then derived after stress analysis. The calculated spacing values were consistent with the published experimental data. Meanwhile, the effect of the Poisson ratio on the crack spacing was analyzed, which showed that the magnitude of crack spacing was proportional to the Poisson ratio in the range of [0.30,0.35].

  4. Effect of Crack Closure on Ultrasonic Detection of Fatigue Cracks at Fastener Holes

    Science.gov (United States)

    Bowles, S. J.; Harding, C. A.; Hugo, G. R.

    2009-03-01

    The ultrasonic response from closed fatigue cracks grown in aluminium alloy specimens using a representative aircraft spectrum loading has been characterised as a function of tensile applied load using pulse-echo 45° shear-wave ultrasonic C-scans with focused immersion transducers. Observed trends with crack size and applied load are described and compared to results for artificial machined defects. The results demonstrate that crack closure significantly reduces the ultrasonic response compared to open cracks or machined defects.

  5. Mode Ⅰ Plane Crack Interacting with an Interfacial Crack Along a Circular Inhomogeneity

    Institute of Scientific and Technical Information of China (English)

    WANG Rui; MA Jian-jun; LIU Zheng-guang

    2006-01-01

    The elastic interaction of the mode Ⅰ plane crack with an interfacial crack along a circular inhomogeneity is dealt with. The dislocation density and the stress intensity factors (SIFs) of the mode I plane crack are obtained numerically. A new kind of dislocation equilibrium equation about the plane crack is applied. The influence of some material parameters on the dislocation density and SIFs are analyzed.

  6. Extended propagation model for interfacial crack in composite material structure

    Institute of Scientific and Technical Information of China (English)

    闫相桥; 冯希金

    2002-01-01

    An interfacial crack is a common damage in a composite material structure . An extended propaga-tion model has been established for an interfacial crack to study the dependence of crack growth on the relativesizes of energy release rates at left and right crack tips and the properties of interfacial material characterize thegrowth of interfacial crack better.

  7. Chloride Penetration through Cracks in High-Performance Concrete and Surface Treatment System for Crack Healing

    Directory of Open Access Journals (Sweden)

    In-Seok Yoon

    2012-01-01

    Full Text Available For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.

  8. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    DEFF Research Database (Denmark)

    Martakos, G.; Andreasen, J. H.; Berggreen, Christian;

    2016-01-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect...

  9. What can cracked polymer do

    Science.gov (United States)

    Jiao, Kexin; Zhou, Chuanhong; Kohli, Punit; Poudel, Anish; Chu, Tsuchin

    2015-03-01

    Buckling, delamination, and cracking are very well known phenomenon observed in most thin films. They were theoretically explained by the existence of mechanical instability due to the residue stress generated when a thin film is deposited on substrates or undergoing environmental stimulus. Buckled structures at micro- or nano-scale have been of great interests and have been used extensively in many applications including particles self-assembling, surface wettability modification, and micro-electronic device fabrication. However, peeling of a layer from a substrate due to delamination or fractures on a thin film due to cracking is mostly taken as an undesirable result. Therefore, strategies are inspired for preventing or removing these often undesired structures. We found that after being heated above its decomposition temperature and then cooled to room temperature, a PDMS thin film showed micro-fibers of 100 μm width and up to 1.5 cm in length. By studying the formation mechanism, control of the dimensions and of the growth pattern on a substrate for PDMS micro-fibers were realized. Giving credit to their high flexibility and optical transparency, a PDMS micro-fiber were utilized in high resolution near field imaging achieved by attaching a micro-lens on the fiber. Interestingly, a surface covered by PDMS micro-fibers will turn from superhydrophobic into superhydrophilic by further heating providing potential applications in surface wettability modification. In future, we will investigate and simulate the growth of PDMS micro-fiber and look for more possible applications.

  10. Predictability of blocking

    International Nuclear Information System (INIS)

    Tibaldi and Molteni (1990, hereafter referred to as TM) had previously investigated operational blocking predictability by the ECMWF model and the possible relationships between model systematic error and blocking in the winter season of the Northern Hemisphere, using seven years of ECMWF operational archives of analyses and day 1 to 10 forecasts. They showed that fewer blocking episodes than in the real atmosphere were generally simulated by the model, and that this deficiency increased with increasing forecast time. As a consequence of this, a major contribution to the systematic error in the winter season was shown to derive from the inability of the model to properly forecast blocking. In this study, the analysis performed in TM for the first seven winter seasons of the ECMWF operational model is extended to the subsequent five winters, during which model development, reflecting both resolution increases and parametrisation modifications, continued unabated. In addition the objective blocking index developed by TM has been applied to the observed data to study the natural low frequency variability of blocking. The ability to simulate blocking of some climate models has also been tested

  11. Development of crack shape: LBB methodology for cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Moulin, D.; Chapuliot, S.; Drubay, B. [Commissariat a l Energie Atomique, Gif sur Yvette (France)

    1997-04-01

    For structures like vessels or pipes containing a fluid, the Leak-Before-Break (LBB) assessment requires to demonstrate that it is possible, during the lifetime of the component, to detect a rate of leakage due to a possible defect, the growth of which would result in a leak before-break of the component. This LBB assessment could be an important contribution to the overall structural integrity argument for many components. The aim of this paper is to review some practices used for LBB assessment and to describe how some new R & D results have been used to provide a simplified approach of fracture mechanics analysis and especially the evaluation of crack shape and size during the lifetime of the component.

  12. Corrosion and Cracking of Reinforced Concrete

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of the deterioration of reinforced concrete has in recent years changed from being a deterministic modelling based on experience to be stochastic modelling based on sound and consistent physical, chemical and mechanical principles. In this paper is presented a brief review of modern mod...... for time to initial corrosion, time to initial cracking, and time to a given crack width may be obtained....

  13. Sulfide stress cracking of pipeline steels

    International Nuclear Information System (INIS)

    The problem of the sulfide stress corrosion cracking of pipeline steels and their welded joints have been presented for pipeline steels. Results of hydrogen sulfide stress cracking inhibitors and corrosion inhibitors of three types protective actions on pipeline steels of two grades petroleum range of products are given. (author)

  14. Crack Formation in Grouted Annular Composite

    DEFF Research Database (Denmark)

    Sørensen, Eigil V.

    The objective of the present analysis is to identify the reason for extensive crack formation which occurred during an annulus grouting performance test, to evaluate possible consequences of the cracking, and to recommend measures to be taken in order to avoid similar problems in the future....

  15. Problems in fracture mechanics of indentation cracks

    International Nuclear Information System (INIS)

    Vickers indentation cracks are an appropriate tool to determine the crack-tip toughness K10 of ceramics from the total crack opening displacements. Two different procedures were applied to determine the crack opening displacement (COD) field under residual and externally applied stress fields. First, a semi-analytical procedure was used to compute the COD field from residual stresses introduced in the uncracked body by the indentation test. This approach allows a description by analytical relations. In order to check the accuracy of these calculations and to outline some problems in detail, also finite element (FE) computations were carried out. In an experimental example the stress intensity factor of glass is determined. Apart from the crack opening profile, also relations for the total stress intensity factor and the T-stress term are provided. As a second type of indentation crack, cone cracks were considered as developing under spherical contact load. Mixed-mode stress intensity factors were computed. The results obtained by application of the weight function method are used to calculate the cone angle under the condition of K11=0 during crack generation. A good agreement with measured data from literature is found. (orig.)

  16. Crack propagation directions in unfilled resins.

    Science.gov (United States)

    Baran, G; Sadeghipour, K; Jayaraman, S; Silage, D; Paul, D; Boberick, K

    1998-11-01

    Posterior composite restorative materials undergo accelerated wear in the occlusal contact area, primarily through a fatigue mechanism. To facilitate the timely development of new and improved materials, a predictive wear model is desirable. The objective of this study was to develop a finite element model enabling investigators to predict crack propagation directions in resins used as the matrix material in composites, and to verify these predictions by observing cracks formed during the pin-on-disc wear of a 60:40 BISGMA:TEGDMA resin and an EBPADMA resin. Laser confocal scanning microscopy was used to measure crack locations. Finite element studies were done by means of ABAQUS software, modeling a cylinder sliding on a material with pre-existing surface-breaking cracks. Variables included modulus, cylinder/material friction coefficient, crack face friction, and yield behavior. Experimental results were surprising, since most crack directions were opposite previously published observations. The majority of surface cracks, though initially orthogonal to the surface, changed direction to run 20 to 30 degrees from the horizontal in the direction of indenter movement. Finite element modeling established the importance of subsurface shear stresses, since calculations provided evidence that cracks propagate in the direction of maximum K(II)(theta), in the same direction as the motion of the indenter, and at an angle of approximately 20 degrees. These findings provide the foundation for a predictive model of sliding wear in unfilled glassy resins.

  17. Uncertainty Quantification in Fatigue Crack Growth Prognosis

    Directory of Open Access Journals (Sweden)

    Shankar Sankararaman

    2011-01-01

    Full Text Available This paper presents a methodology to quantify the uncertainty in fatigue crack growth prognosis, applied to structures with complicated geometry and subjected to variable amplitude multi-axial loading. Finite element analysis is used to address the complicated geometry and calculate the stress intensity factors. Multi-modal stress intensity factors due to multi-axial loading are combined to calculate an equivalent stress intensity factor using a characteristic plane approach. Crack growth under variable amplitude loading is modeled using a modified Paris law that includes retardation effects. During cycle-by-cycle integration of the crack growth law, a Gaussian process surrogate model is used to replace the expensive finite element analysis. The effect of different types of uncertainty – physical variability, data uncertainty and modeling errors – on crack growth prediction is investigated. The various sources of uncertainty include, but not limited to, variability in loading conditions, material parameters, experimental data, model uncertainty, etc. Three different types of modeling errors – crack growth model error, discretization error and surrogate model error – are included in analysis. The different types of uncertainty are incorporated into the crack growth prediction methodology to predict the probability distribution of crack size as a function of number of load cycles. The proposed method is illustrated using an application problem, surface cracking in a cylindrical structure.

  18. Strength of Cracked Reinforced Concrete Disks

    DEFF Research Database (Denmark)

    Hoang, Cao Linh; Nielsen, Mogens Peter

    1999-01-01

    The paper deals with models, based on the theory of plasticity, to be used in strength assessments of reinforced concrete disks suffering from different kinds of cracking. Based on the assumption that the sliding strength of concrete is reduced in sections where cracks are located, solutions...

  19. Numerical simulation of crack propagation in pressure equipments; Simulation numerique de la propagation de fissures dans les structures sous pression

    Energy Technology Data Exchange (ETDEWEB)

    Le Grognec, P.; Hariri, S. [Ecole des Mines de Douai, 59 (France); Afzali, M.; Jaffal, H. [Centre Technique des Industries Mecaniques, 60 - Senlis (France)

    2008-11-15

    The aim of this work is to determine the evolution of the degree of noxiousness of a defect in a pressure equipment during its propagation. The estimation of the degree of noxiousness involves the calculation of stress intensity factors at each advance of the crack front. The cracks considered are semi-elliptic. The geometries and loads can be complex in order to cover the main industrial cases. Numerical modelling by finite element method is based on the creation of a crack-block, representing the optimized mesh near the discontinuity. The Paris law allows to describe the fatigue behaviour under cyclic load. A specific program (Python), having the advantages of the calculation codes Castem and Abaqus, allows to compute the propagation approach and makes easier the estimation of the residual lifetime of a structure under cracked pressure. (O.M.)

  20. Block copolymer battery separator

    Energy Technology Data Exchange (ETDEWEB)

    Wong, David; Balsara, Nitash Pervez

    2016-04-26

    The invention herein described is the use of a block copolymer/homopolymer blend for creating nanoporous materials for transport applications. Specifically, this is demonstrated by using the block copolymer poly(styrene-block-ethylene-block-styrene) (SES) and blending it with homopolymer polystyrene (PS). After blending the polymers, a film is cast, and the film is submerged in tetrahydrofuran, which removes the PS. This creates a nanoporous polymer film, whereby the holes are lined with PS. Control of morphology of the system is achieved by manipulating the amount of PS added and the relative size of the PS added. The porous nature of these films was demonstrated by measuring the ionic conductivity in a traditional battery electrolyte, 1M LiPF.sub.6 in EC/DEC (1:1 v/v) using AC impedance spectroscopy and comparing these results to commercially available battery separators.

  1. The geometry of soil crack networks

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    The subject of this work is the modification and specification of an approach to detail the estimation of soil crack network characteristics. The modification aims at accounting for the corrected soil crack volume based on the corrected shrinkage geometry factor compared to known estimates of crack volume and shrinkage geometry factor. The mode of the correction relies on recent results of the soil reference shrinkage curve. The main exposition follows the preliminary brief review of available approaches to dealing with the geometry of soil crack networks and gives a preliminary brief summary of the approach to be modified and specified. To validate and illustrate the modified approach the latter is used in the analysis of available data on soil cracking in a lysimeter.

  2. XFEM for Thermal Crack of Massive Concrete

    Directory of Open Access Journals (Sweden)

    Guowei Liu

    2013-01-01

    Full Text Available Thermal cracking of massive concrete structures occurs as a result of stresses caused by hydration in real environment conditions. The extended finite element method that combines thermal fields and creep is used in this study to analyze the thermal cracking of massive concrete structures. The temperature field is accurately simulated through an equivalent equation of heat conduction that considers the effect of a cooling pipe system. The time-dependent creep behavior of massive concrete is determined by the viscoelastic constitutive model with Prony series. Based on the degree of hydration, we consider the main properties related to cracking evolving with time. Numerical simulations of a real massive concrete structure are conducted. Results show that the developed method is efficient for numerical calculations of thermal cracks on massive concrete. Further analyses indicate that a cooling system and appropriate heat preservation measures can efficiently prevent the occurrence of thermal cracks.

  3. Probabilistic analysis of linear elastic cracked structures

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper presents a probabilistic methodology for linear fracture mechanics analysis of cracked structures. The main focus is on probabilistic aspect related to the nature of crack in material. The methodology involves finite element analysis; statistical models for uncertainty in material properties, crack size, fracture toughness and loads; and standard reliability methods for evaluating probabilistic characteristics of linear elastic fracture parameter. The uncertainty in the crack size can have a significant effect on the probability of failure, particularly when the crack size has a large coefficient of variation. Numerical example is presented to show that probabilistic methodology based on Monte Carlo simulation provides accurate estimates of failure probability for use in linear elastic fracture mechanics.

  4. Crack spacing threshold of double cracks propagation for large-module rack

    Institute of Scientific and Technical Information of China (English)

    赵铁柱; 石端伟; 姚哲皓; 毛宏勇; 程术潇; 彭惠

    2015-01-01

    Large-module rack of the Three Gorges shiplift is manufactured by casting and machining, which is unable to avoid slag inclusions and surface cracks. To ensure its safety in the future service, studying on crack propagation rule and the residual life estimation method of large-module rack is of great significance. The possible crack distribution forms of the rack in the Three Gorges shiplift were studied. By applying moving load on the model in FRANC3D and ANSYS, quantitative analyses of interference effects on double cracks in both collinear and offset conditions were conducted. The variation rule of the stress intensity factor (SIF) influence factor,RK, of double collinear cracks changing with crack spacing ratio,RS, was researched. The horizontal and vertical crack spacing threshold of double cracks within the design life of the shiplift were obtained, which are 24 and 4 times as large as half of initial crack length,c0, respectively. The crack growth rates along the length and depth directions in the process of coalescence on double collinear cracks were also studied.

  5. Unsaturated Seepage Analysis of Cracked Soil including Development Process of Cracks

    Directory of Open Access Journals (Sweden)

    Ling Cao

    2016-01-01

    Full Text Available Cracks in soil provide preferential pathways for water flow and their morphological parameters significantly affect the hydraulic conductivity of the soil. To study the hydraulic properties of cracks, the dynamic development of cracks in the expansive soil during drying and wetting has been measured in the laboratory. The test results enable the development of the relationships between the cracks morphological parameters and the water content. In this study, the fractal model has been used to predict the soil-water characteristic curve (SWCC of the cracked soil, including the developmental process of the cracks. The cracked expansive soil has been considered as a crack-pore medium. A dual media flow model has been developed to simulate the seepage characteristics of the cracked expansive soil. The variations in pore water pressure at different part of the model are quite different due to the impact of the cracks. This study proves that seepage characteristics can be better predicted if the impact of cracks is taken into account.

  6. Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jeong Woo [KIMM, Daejeon (Korea, Republic of); Woo, Eun Taek; Han, Seung Ho [Dong-A University, Busan (Korea, Republic of)

    2015-07-15

    To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.

  7. Crack shape developments and leak rates for circumferential complex-cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Brickstad, B.; Bergman, M. [SAQ Inspection Ltd., Stockholm (Sweden)

    1997-04-01

    A computerized procedure has been developed that predicts the growth of an initial circumferential surface crack through a pipe and further on to failure. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes and for the through-wall cracks, crack opening areas and leak rates are also calculated. The procedure is based on a large number of three-dimensional finite element calculations of cracked pipes. The results from these calculations are stored in a database from which the PC-program, denoted LBBPIPE, reads all necessary information. In this paper, a sensitivity analysis is presented for cracked pipes subjected to both stress corrosion and vibration fatigue.

  8. Fully plastic crack opening analyses of complex-cracked pipes for Ramberg-Osgood materials

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Jae Uk; Choi, Jae Boong [Sungkyunkwan University, Suwon (Korea, Republic of); Huh, Nam Su [Seoul National University, Seoul (Korea, Republic of); Kim, Yun Jae [Korea University, Seoul (Korea, Republic of)

    2016-04-15

    The plastic influence functions for calculating fully plastic Crack opening displacement (COD) of complex-cracked pipes were newly proposed based on systematic 3-dimensional (3-D) elastic-plastic Finite element (FE) analyses using Ramberg-Osgood (R-O) relation, where global bending moment, axial tension and internal pressure are considered separately as a loading condition. Then, crack opening analyses were performed based on GE/EPRI concept by using the new plastic influence functions for complex-cracked pipes made of SA376 TP304 stainless steel, and the predicted CODs were compared with FE results based on deformation plasticity theory of tensile material behavior. From the comparison, the confidence of the proposed fully plastic crack opening solutions for complex-cracked pipes was gained. Therefore, the proposed engineering scheme for COD estimation using the new plastic influence functions can be utilized to estimate leak rate of a complex-cracked pipe for R-O material.

  9. On fatigue crack growth in ductile materials by crack-tip blunting

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    One of the basic mechanisms for fatigue crack growth in ductile metals is that depending on crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading. In a standard numerical analysis accounting for finite strains it is not possible to follow this process during...... many cycles, as severe mesh distortion at the crack-tip results from the huge geometry changes developing during the cyclic plastic straining. In the present numerical studies, based on an elastic-perfectly plastic material model, crack growth computations are continued up to 200 full cycles by using...... remeshing at several stages of the plastic deformation. Three different values of the load ratio R = K-min/K-max are considered. It is shown that the crack-up opening displacement, CTOD, typically undergoes a transient behaviour, with no crack closure during many cycles, before a steady-state cycling...

  10. Crack Growth in Concrete Gravity Dams Based on Discrete Crack Method

    Directory of Open Access Journals (Sweden)

    A. R. Lohrasbi

    2008-01-01

    Full Text Available Seepage is the most parameter in water management safety and in stable agricultural. This seepage is passed through the cracks that are present to some degree in hydraulic structures. They may exist as basic defects in the constituent materials or may be induced in construction or during service life. To avoid such failure in concrete dams, safety would be an important factor. Over-design carries heavy penalty in terms of excess weight. So the fracture mechanics theory is a principal necessity of evaluating the stability of such crack propagation. For the process of crack propagation analysis in concrete structures, there are two general models: discrete crack and smeared crack. This study surveys the crack propagation in concrete gravity dams based on discrete crack methods. Moreover, we use a program provided specifically for this purpose.

  11. General forms of elastic-plastic matching equations for mode-Ⅲ cracks near crack line

    Institute of Scientific and Technical Information of China (English)

    Zhi-jian YI; Chao-hua ZHAO; Qing-guo YANG; Kai PENG; Zong-ming HUANG

    2009-01-01

    Crack line analysis is an effective way to solve elastic-plastic crack problems.Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode-Ⅲ crack problems under the perfect elastic-plastic condition,matching procedures of the crack line analysis method are summarized and refined to give general forms and formulation steps of plastic field,elastic-plastic boundary,and elastic-plastic matching equations near the crack line. The research unifies mode-Ⅲ crack problems under different conditions into a problem of determining four integral constants with four matching equations.An example is given to verify correctness,conciseness,and generality of the procedure.

  12. Blocking in Category Learning

    OpenAIRE

    Bott, Lewis; Hoffman, Aaron B.; Murphy, Gregory L.

    2007-01-01

    Many theories of category learning assume that learning is driven by a need to minimize classification error. When there is no classification error, therefore, learning of individual features should be negligible. We tested this hypothesis by conducting three category learning experiments adapted from an associative learning blocking paradigm. Contrary to an error-driven account of learning, participants learned a wide range of information when they learned about categories, and blocking effe...

  13. Investigating Reaction-Driven Cracking

    Science.gov (United States)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required

  14. Cracks assessment using ultrasonic technology

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, Maria Pia; Tomasella, Marcelo [OLDELVAL S.A. Oleoductos del Valle, Rio Negro (Argentina). Pipeline Integrity Dept.

    2005-07-01

    The goal of Oldelval Integrity Program is to prevent ruptures and leaks, developing strategies for a better handling of the integrity of our pipelines. In order to achieve it we have studied and modeled each process that involved in the integrity pipeline. Those processes are mainly based on defects reported by an internal inspection tool and supplied with field inspection and monitoring data. Years of evaluation, study and the continuous effort overturned towards a phenomenon that worries to the industry, as it is the SCC. Since 1998 up to 2004 SCC was included in the integrity program with some preventive maintenance programs. The accomplishment of the inspection based on ultrasound tools, is the culmination of years of evaluation and investigations supported by field digs and materials susceptibility. This paper describes Oldelval's results with ultrasonic crack detection tool, and how it can be reliably to detect SCC. (author)

  15. Investigations of soil cracking and preferential flow in a weighing lysimeter filled with cracking clay soil

    Science.gov (United States)

    Greve, A.; Andersen, M. S.; Acworth, R. I.

    2010-10-01

    SummaryAn improved understanding of deep drainage processes in irrigated cracking soils is needed for sustainable irrigation management. To investigate the effect of crack dynamics and macropore flow on drainage in cracking soils, a series of irrigation experiments was carried out in a weighing lysimeter. Subsurface soil cracks of the initially very dry soil were investigated with a videoscope and changes in the surface expression of cracks in response to irrigation events were monitored by time-lapse photography. A bromide tracer was applied to one irrigation event. Variations in the combined soil and moisture mass and the volume of drainage out of the soil column was logged and the drainage EC and bromide content were determined. No drainage occurred out of the soil column during the first 3 out of 6 irrigation events, even though substantial surface runoff into the cracks occurred and, at least initially, soil cracks provided an uninterrupted flow path through the profile. The breakthrough of the bromide tracer, as well as an initially low EC of the drainage water indicate that preferential flow accounted for a substantial part of the first of the two drainage events, even though the soil cracks were sealed on the surface at the onset of the irrigation causing the drainage. The results show that lateral infiltration of macropore flow into the soil matrix can be substantial and should not be neglected while simulating macropore flow and deep drainage in cracking soils. The results also indicate that soil cracks can remain pathways for preferential flow even after they are closed at the soil surface. The type of water application appears to have an impact on the location of crack formation, with flood irrigation favouring reappearance of cracks at previous crack locations and simulated rainfall resulting in shifting crack locations.

  16. Growing Up with Their Blocks.

    Science.gov (United States)

    Winarski, Diana L.

    1995-01-01

    Describes one teacher's use of traditional wooden blocks in fifth-grade curriculum. Notes that use of blocks can teach communication, teamwork, precision, and arithmetic concepts. Also describes four easy classroom block projects. (TM)

  17. Subcritical crack growth in two titanium alloys.

    Science.gov (United States)

    Williams, D. N.

    1973-01-01

    Measurement of subcritical crack growth during static loading of precracked titanium alloys in salt water using samples too thin for plane strain loading to predominate was examined as a method for determining the critical stress intensity for crack propagation in salt water. Significant internal crack growth followed by arrest was found at quite low stress intensities, but crack growth rates were relatively low. Assuming these techniques provided a reliable measurement of the critical stress intensity, the value for annealed Ti-4Al-1.5Mo-0.5V alloy was apparently about 35 ksi-in. to the 1/2 power, while that for annealed Ti-4Al-3Mo-1V was below 45 ksi-in. to the 1/2 power. Crack growth was also observed in tests conducted in both alloys in an air environment. At 65 ksi-in. to the 1/2 power, the extent of crack growth was greater in air than in salt water. Ti-4Al-3Mo-1V showed arrested crack growth in air at a stress intensity of 45 ksi-in. to the 1/2 power.

  18. Crack detection in a beam with an arbitrary number of transverse cracks using genetic algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Khaji, N. [Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Mehrjoo, M. [Islamic Azad University, Tehran (Iran, Islamic Republic of)

    2014-03-15

    In this paper, a crack detection approach is presented for detecting depth and location of cracks in beam-like structures. For this purpose, a new beam element with an arbitrary number of embedded transverse edge cracks, in arbitrary positions of beam element with any depth, is derived. The components of the stiffness matrix for the cracked element are computed using the conjugate beam concept and Betti's theorem, and finally represented in closed-form expressions. The proposed beam element is efficiently employed for solving forward problem (i.e., to gain precise natural frequencies and mode shapes of the beam knowing the cracks' characteristics). To validate the proposed element, results obtained by new element are compared with two-dimensional (2D) finite element results and available experimental measurements. Moreover, by knowing the natural frequencies and mode shapes, an inverse problem is established in which the location and depth of cracks are determined. In the inverse approach, an optimization problem based on the new finite element and genetic algorithms (GAs) is solved to search the solution. It is shown that the present algorithm is able to identify various crack configurations in a cracked beam. The proposed approach is verified through a cracked beam containing various cracks with different depths.

  19. Crack growth monitoring at CFRP bond lines

    Science.gov (United States)

    Rahammer, M.; Adebahr, W.; Sachse, R.; Gröninger, S.; Kreutzbruck, M.

    2016-02-01

    With the growing need for lightweight technologies in aerospace and automotive industries, fibre-reinforced plastics, especially carbon-fibre (CFRP), are used with a continuously increasing annual growth rate. A promising joining technique for composites is adhesive bonding. While rivet holes destroy the fibres and cause stress concentration, adhesive bond lines distribute the load evenly. Today bonding is only used in secondary structures due to a lack of knowledge with regard to long-term predictability. In all industries, numerical simulation plays a critical part in the development process of new materials and structures, while it plays a vital role when it comes to CFRP adhesive bondings conducing the predictability of life time and damage tolerance. The critical issue with adhesive bondings is crack growth. In a dynamic tensile stress testing machine we dynamically load bonded CFRP coupon specimen and measure the growth rate of an artificially started crack in order to feed the models with the results. We also investigate the effect of mechanical crack stopping features. For observation of the bond line, we apply two non-contact NDT techniques: Air-coupled ultrasound in slanted transmission mode and active lockin-thermography evaluated at load frequencies. Both methods give promising results for detecting the current crack front location. While the ultrasonic technique provides a slightly higher accuracy, thermography has the advantage of true online monitoring, because the measurements are made while the cyclic load is being applied. The NDT methods are compared to visual inspection of the crack front at the specimen flanks and show high congruence. Furthermore, the effect of crack stopping features within the specimen on the crack growth is investigated. The results show, that not all crack fronts are perfectly horizontal, but all of them eventually come to a halt in the crack stopping feature vicinity.

  20. Interaction between short fatigue cracks and grain boundaries. Systematic experiments with focussed ion beam microscope and microstructural tomography; Ueber die Wechselwirkung kurzer Ermuedungsrisse mit Korngrenzen. Systematische Experimente mit Focussed Ion Beam Microscope und mikrostruktureller Tomographie

    Energy Technology Data Exchange (ETDEWEB)

    Schaef, Wolfgang

    2011-04-15

    Increasing the microstructural resistance of metallic materials to short fatigue crack growth is a major task of today's materials science. In this regard, grain boundaries and precipitates are well known to decelerate short cracks, but a quantitative understanding of the blocking effect is still missing. This is due to the fact that crack deceleration is influenced by many parameters: cyclic load, crack length, distance to obstacles, orientations of grains and obstacles. Even the examination of a huge number of short cracks would not be sufficient to identify the effect of these parameters independently, especially since fatigue crack growth is a 3D problem and investigations of the sub surface orientation of cracks and grain boundaries are scarce. The Focused Ion Beam Microscope (FIB) offers new methods for systematic experiments and 3D-investigation of short fatigue cracks that will help to quantify the microstructural impact on short fatigue crack growth. The ion beam is used to cut micro notches in selected grains on the surface of samples characterised by Electron Backscatter Diffraction (EBSD). Plane fatigue cracks initiate under cyclic loading in defined distances to the grain boundaries. By this technique it is possible for the first time to present quantitative data to describe the effect of grain boundaries on short fatigue cracks in nickel based superalloys (CMSX-4) as well as in mild steels.

  1. Chaos caused by fatigue crack growth

    International Nuclear Information System (INIS)

    The nonlinear dynamic responses including chaotic oscillations caused by a fatigue crack growth are presented. Fatigue tests have been conducted on a novel fatigue-testing rig, where the loading is generated from inertial forces. The nonlinearity is in the form of discontinuous stiffness caused by the opening and closing of a growing crack. Nonlinear dynamic tools such as Poincare maps and bifurcation diagrams are used to unveil the global dynamics of the system. The results obtained indicate that fatigue crack growth strongly influences the dynamic response of the system leading to chaos

  2. Chaos caused by fatigue crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Foong, C.-H.; Pavlovskaia, Ekaterina; Wiercigroch, Marian; Deans, William

    2003-06-01

    The nonlinear dynamic responses including chaotic oscillations caused by a fatigue crack growth are presented. Fatigue tests have been conducted on a novel fatigue-testing rig, where the loading is generated from inertial forces. The nonlinearity is in the form of discontinuous stiffness caused by the opening and closing of a growing crack. Nonlinear dynamic tools such as Poincare maps and bifurcation diagrams are used to unveil the global dynamics of the system. The results obtained indicate that fatigue crack growth strongly influences the dynamic response of the system leading to chaos.

  3. Cracks in high-manganese cast steel

    Directory of Open Access Journals (Sweden)

    A. Chojecki

    2009-10-01

    Full Text Available The reasons which account for the formation of in service cracks in castings made from Hadfield steel were discussed. To explain the source of existence of the nuclei of brittle fractures, the properties of cast steel were examined within the range of solidification temperatures, remembering that feeding of this material is specially difficult, causing microporosity in hot spots. This creates conditions promoting the formation of microcracks which tend to propagate during service conditions involving high dynamic stresses, and explains why the cracks are mainly characterized by a brittle nature. The reason for crack formation in service are micro-porosities formed during casting solidification.

  4. Slow crack growth in spinel in water

    Science.gov (United States)

    Schwantes, S.; Elber, W.

    1983-01-01

    Magnesium aluminate spinel was tested in a water environment at room temperature to establish its slow crack-growth behavior. Ring specimens with artificial flaws on the outside surface were loaded hydraulically on the inside surface. The time to failure was measured. Various precracking techniques were evaluated and multiple precracks were used to minimize the scatter in the static fatigue tests. Statistical analysis techniques were developed to determine the strength and crack velocities for a single flaw. Slow crack-growth rupture was observed at stress intensities as low as 70 percent of K sub c. A strengthening effect was observed in specimens that had survived long-time static fatigue tests.

  5. Block diagonal and schur complement preconditioners for block-toeplitz systems with small size blocks

    OpenAIRE

    Ching, WK; Ng, MK; Wen, YW

    2007-01-01

    In this paper we consider the solution of Hermitian positive definite block-Toeplitz systems with small size blocks. We propose and study block diagonal and Schur complement preconditioners for such block-Toeplitz matrices. We show that for some block-Toeplitz matrices, the spectra of the preconditioned matrices are uniformly bounded except for a fixed number of outliers where this fixed number depends only on the size of the block. Hence, conjugate gradient type methods, when applied to solv...

  6. Right bundle branch block

    DEFF Research Database (Denmark)

    Bussink, Barbara E; Holst, Anders Gaarsdal; Jespersen, Lasse;

    2013-01-01

    AimsTo determine the prevalence, predictors of newly acquired, and the prognostic value of right bundle branch block (RBBB) and incomplete RBBB (IRBBB) on a resting 12-lead electrocardiogram in men and women from the general population.Methods and resultsWe followed 18 441 participants included.......5%/2.3% in women, P Right bundle branch block was associated with significantly...... increased all-cause and cardiovascular mortality in both genders with age-adjusted hazard ratios (HR) of 1.31 [95% confidence interval (CI), 1.11-1.54] and 1.87 (95% CI, 1.48-2.36) in the gender pooled analysis with little attenuation after multiple adjustment. Right bundle branch block was associated...

  7. Bactericidal block copolymer micelles.

    Science.gov (United States)

    Vyhnalkova, Renata; Eisenberg, Adi; van de Ven, Theo

    2011-05-12

    Block copolymer micelles with bactericidal properties were designed to deactivate pathogens such as E. coli bacteria. The micelles of PS-b-PAA and PS-b-P4VP block copolymers were loaded with biocides TCMTB or TCN up to 20 or 30 wt.-%, depending on the type of antibacterial agent. Bacteria were exposed to loaded micelles and bacterial deactivation was evaluated. The micelles loaded with TCN are bactericidal; bacteria are killed in less than two minutes of exposure. The most likely interpretation of the data is that the biocide is transferred to the bacteria by repeated micelle/bacteria contacts, and not via the solution. PMID:21275041

  8. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    Science.gov (United States)

    Martakos, G.; Andreasen, J. H.; Berggreen, C.; Thomsen, O. T.

    2016-08-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect of the embedded crack arresters was evaluated in terms of the achieved enhancement of the damage tolerance of the tested sandwich panels. A finite element (FE) model of the experimental setup was used for predicting propagation rates and direction of the crack growth. The FE simulation was based on the adoption of linear fracture mechanics and a fatigue propagation law (i.e. Paris law) to predict the residual fatigue life-time and behaviour of the test specimens. Finally, a comparison between the experimental results and the numerical simulations was made to validate the numerical predictions as well as the overall performance of the crack arresters.

  9. E-Block: A Tangible Programming Tool with Graphical Blocks

    OpenAIRE

    Danli Wang; Yang Zhang; Shengyong Chen

    2013-01-01

    This paper designs a tangible programming tool, E-Block, for children aged 5 to 9 to experience the preliminary understanding of programming by building blocks. With embedded artificial intelligence, the tool defines the programming blocks with the sensors as the input and enables children to write programs to complete the tasks in the computer. The symbol on the programming block's surface is used to help children understanding the function of each block. The sequence information is transfer...

  10. Comments on the Yule Marble Haines block: potential replacement, Tomb of the Unknown Soldier, Arlington National Cemetery

    Science.gov (United States)

    Mossotti, Victor G.

    2014-01-01

    Marble for the Tomb of the Unknown Soldier at Arlington National Cemetery was cut from the Colorado Yule Marble Quarry in 1931. Although anecdotal reports suggest that cracks were noticed in the main section of the monument shortly after its installation at the Arlington National Cemetery in Arlington, Virginia, detailed documentation of the extent of cracking did not appear until 1963. Although debate continues as to whether the main section of the Tomb of the Unknowns monument should be repaired or replaced, Mr. John S. Haines of Glenwood Springs, Colorado, in anticipation of the permanent closing of the Yule Quarry, donated a 58-ton block of Yule Marble, the so-called Haines block, as a potential backup. The brief study reported here was conducted during mid-summer 2009 at the behest of the superintendent of Arlington National Cemetery. The field team entered the subterranean Yule Marble Quarry with the Chief Extraction Engineer in order to contrast the method used for extraction of the Haines block with the method that was probably used to extract the marble block that is now cracked. Based on surficial inspection and shallow coring of the Haines block, and on the nature of crack propagation in Yule Marble as judged by close inspection of a large collection of surrogate Yule Marble blocks, the team found the block to be structurally sound and cosmetically equivalent to the marble used for the current monument. If the Haines block were needed, it would be an appropriate replacement for the existing cracked section of the Tomb of the Unknown Soldier Monument.

  11. Finite Element Analysis of Fretting Behavior Between an Engine Cylinder Block and a Main Bearing Cap

    Institute of Scientific and Technical Information of China (English)

    LIAO Ri-dong; ZUO Zheng-xing

    2006-01-01

    The finite element analysis of the fretting behavior between a cylinder block and a main bearing cap is presented. The stresses, relative fretting slip, fretting friction work parameter W and crack initiation location parameter G on the fretting contact surface of the cylinder block are obtained and analyzed. It shows that the fretting fatigue problem of the cylinder block can be quantitatively explained by W or G. The effects of pretightening force, friction factor and material combination of the cylinder block and the main bearing cap are studied. The computational results indicate that the fretting fatigue of the cylinder block can be allayed by increasing the elastic modulus of the cylinder block, but not by changing the other two factors.

  12. Dynamic Strain and Crack Monitoring Sensor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Los Gatos Research proposes to develop a new automated vehicle health monitoring sensor system capable of measuring loads and detecting crack, corrosion, and...

  13. Inner Crack Detection Method for Cantilever Beams

    Science.gov (United States)

    Li, Zheng; Zhang, Wei; Li, Yixuan; Su, Xianyue

    2008-02-01

    In this paper, continuous wavelet transform has been performed to extract the inner crack information from the guided waves in cantilever beams, and the location and size of crack can be detected exactly. Considering its best time-frequency property, Gabor continuous wavelet transform is employed to analyze the complicated flexible wave signals in cantilever beam, which is inspirited by an impact on the free end. Otherwise, in order to enhance the sensitivity of detection for some small cracks, an improved method is discussed. Here, both computational and experimental methods are carried out for comparing the influence of different crack location in beam. Therefore, the method proposed can be expected to expand to a powerful damage detection method in a broad engineering application.

  14. The Effect of Water on Crack Interaction

    Science.gov (United States)

    Gaede, O.; Regenauer-Lieb, K.

    2009-04-01

    While the mechanical coupling between pore fluid and solid phase is relatively well understood, quantitative studies dealing with chemical-mechanical weakening in geological materials are rare. Many classical poroelastic problems can be addressed with the simple law of effective stress. Experimental studies show that the presence of a chemically active fluid can have effects that exceed the predictions of the law of effective stress. These chemical fluid-rock interactions alter the mechanical properties of the solid phase. Especially chemical-mechanical weakening has important ramifications for many areas of applied geosciences ranging from nuclear waste disposal over reservoir enhancement to fault stability. In this study, we model chemically induced changes of the size of the process zone around a crack tip. The knowledge of the process zone size is used to extend existing effective medium approximations of cracked solids. The stress distribution around a crack leads to a chemical potential gradient. This gradient will be a driver for mass diffusion through the solid phase. As an example, mass diffusion is towards the crack tip for a mode I crack. In this case a chemical reaction, that weakens the solid phase, will increase the size of the process zone around the crack tip. We apply our model to the prominent hydrolytic weakening effect observed in the quartz-water system (Griggs and Blacic, 1965). Hydrolytic weakening is generally attributed to water hydrolyzing the strong Si-O bonds of the quartz crystal. The hydrolysis replaces a Si-O-Si bridge with a relatively weak hydrogen bridge between two silanol groups. This enhances dislocation mobility and hence the yield stress is reduced. The plastic process zone around a crack tip is therefore larger in a wet crystal than in a dry crystal. We calculate the size of the process zone by solving this coupled mechanical-chemical problem with the Finite Element code ABAQUS. We consider single crack, collinear crack and

  15. Initiating, growing and cracking of hydrogen blisters

    Institute of Scientific and Technical Information of China (English)

    REN Xuechong; SHAN Guangbin; CHU Wuyang; SU Yanjing; GAO Kewei; QIAO Lijie; JIANG Bo; CHEN Gang; CUI Yinhui

    2005-01-01

    The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blisters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with entering of vacancies and hydrogen atoms. With increasing hydrogen pressure, plastic deformation occurs first, the hydrogen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propagating of cracks until it breaks.

  16. A Place for Block Play.

    Science.gov (United States)

    Moore, Gary T.

    1997-01-01

    Discusses the importance of block play--including its contributions to perceptual, fine motor, and cognitive development--and components of a good preschool block play area. Recommends unit blocks complemented by stacking blocks, toys, beads, cubes, and Brio wooden toys. Makes recommendations for space, size, locations and connections to other…

  17. Finite Element Analysis of the Effect of Crack Depth and Crack Opening On the Girder

    Directory of Open Access Journals (Sweden)

    Md. Kamrul Hassan

    2011-01-01

    Full Text Available In order to identify the effect of crack depth and opening on the girder, finite element method (FEM has been used in this paper. In FE analysis, six nodded two dimensional plane elements (PLANE-2 are considered. Each node has two degree of freedom such as UX and UY. For the plane elements, a plane stress width/thickness option is chosen. For analytical model of crack of the concrete bridge girder, crack opening was increased from 0.2 mm to 1mm at an interval 0.2 mm and crack depth also increased from 30 mm to 150 mm at an interval 30 mm. The models were discreatized by a triangular mesh and convergence test was executed to obtain satisfactory results from the Plane-2 element. From the numerical result, it is seen that the principal stress become a higher with increased the crack depth and also crack opening with respect to load increasing. But the crack depth at 90 mm and crack opening at 0.6 mm, it has more effect on the girder because the stress concentration is higher than other crack depth and opening.

  18. Thermal fatigue crack growth in stainless steel

    International Nuclear Information System (INIS)

    A judgment of residual service life of engineering parts exposed to thermal fatigue makes it possible to deal with economic and safety issues in power plants. The aim of this study is to analyze a fatigue crack initiation and propagation in A321 stainless steel bodies subjected to repeated thermal shocks. For this purpose, various methods of crack propagation monitoring were used. The first stage of experiments included mechanical cyclic loading of specimens with the central notch at fixed temperatures ranging from 20 °C to 410 °C. The crack growth rate was only minimally influenced by temperature in this case. Thermal loading of the same specimens with ΔT varying from 150 °C to 340 °C showed very rapid crack initiation in the notches and its asymmetric growth. Metallographic and fractographic analyses of failed specimens were carried out after 1000, 3000 and 6000 thermal cycles. The comparison of the fracture surface micromorphology confirmed the similarity in the mechanism of the thermal and mechanical fatigue crack growth. Stress analysis using the finite element method consisting of transient thermal and mechanical solutions was performed in order to simulate the experiments. Thermal fatigue crack growth assessment was carried out on the basis of the experiments and the computed thermally induced stress intensity factors. This model successfully confirms the discussed analogy of thermal and mechanical stress induced damage. Highlights: ► A fatigue crack initiation and propagation in A321 stainless steel was analyzed. ► Mechanical and thermal experiments were performed, simulated also by FEM. ► Similarity in the mechanism of thermal and mechanical fatigue crack growth found. ► Application of the Paris model for the thermal cycling confirmed.

  19. Composite Pressure Vessel Including Crack Arresting Barrier

    Science.gov (United States)

    DeLay, Thomas K. (Inventor)

    2013-01-01

    A pressure vessel includes a ported fitting having an annular flange formed on an end thereof and a tank that envelopes the annular flange. A crack arresting barrier is bonded to and forming a lining of the tank within the outer surface thereof. The crack arresting barrier includes a cured resin having a post-curing ductility rating of at least approximately 60% through the cured resin, and further includes randomly-oriented fibers positioned in and throughout the cured resin.

  20. Next Generation Steam Cracking Reactor Concept

    OpenAIRE

    Van Goethem, M.W.M.

    2010-01-01

    The steam cracking process is an important asset in the hydrocarbon processing industry. The main products are lower olefins and hydrogen, with ethylene being the world's largest volume organic chemical at a worldwide capacity of ~ 120 million tonnes per year. Feed stocks are hydrocarbons such as: ethane, LPG, naphtha's, gas condensates and gas oil. The research goal of this thesis is to search for the intrinsic optimal steam cracking reaction conditions, pushing the olefin yields to the maxi...

  1. Crack tip stress fields under complex loads

    International Nuclear Information System (INIS)

    The author and his assocates have worked towards the development of an experimental method for estimating SIF distributions in 3D cracked body problems where neither SIF distribution nor flaw shape were known a-priori. The method consists of a marriage between the 'frozen stress' photoelastic method and the near field equations of linear elastic fracture mechanics. Originally proposed for Mode I measurements only, the method has since been refined and extended to mixed mode problems. Comparisons of the method with results from fatigue crack growth studies on reactor steels suggest that flaw shapes generated in the photoelastic models under Mode I loading closely reproduce those in the steel models under certain conditions. The method has since been applied to a variety of complex 3D cracked body problems. The paper describes the results obtained from applying the method to two basic problem classes: i) Part circular 'artificial' (machined) surface flaws in uniaxially loaded flat plates inclined at an angle to the plate surface from the applied load direction. This produced all three local modes of deformation near the flaw border. ii) Natural nozzle corner cracks inclined at an angle to the axis of the reactor vessel. Initially these cracks were planar and exhibited Mode I loading near the nozzle wall and mixed mode loading near the vessel wall. Upon initiation of stable flaw growth under internal pressure above critical temperature, the portion of the crack near the nozzle wall remained in its plane and retained its Mode I character. However, that portion of the crack under mixed mode loading immediately reoriented itself to eliminate the shear modes, producing a non-planar flaw under pure Mode I loading. Results suggest that stable growing cracks in isotropic materials do not exhibit shear modes. (orig./HP)

  2. Effects of Block Scheduling

    Directory of Open Access Journals (Sweden)

    William R. Veal

    1999-09-01

    Full Text Available This study examined the effects of a tri-schedule on the academic achievement of students in a high school. The tri-schedule consists of traditional, 4x4 block, and hybrid schedules running at the same time in the same high school. Effectiveness of the schedules was determined from the state mandated test of basic skills in reading, language, and mathematics. Students who were in a particular schedule their freshman year were tested at the beginning of their sophomore year. A statistical ANCOVA test was performed using the schedule types as independent variables and cognitive skill index and GPA as covariates. For reading and language, there was no statistically significant difference in test results. There was a statistical difference mathematics-computation. Block mathematics is an ideal format for obtaining more credits in mathematics, but the block format does little for mathematics achievement and conceptual understanding. The results have content specific implications for schools, administrations, and school boards who are considering block scheduling adoption.

  3. Spice Blocks Melanoma Growth

    Science.gov (United States)

    Science Teacher, 2005

    2005-01-01

    Curcumin, the pungent yellow spice found in both turmeric and curry powders, blocks a key biological pathway needed for development of melanoma and other cancers, according to a study that appears in the journal Cancer. Researchers from The University of Texas M. D. Anderson Cancer Center demonstrate how curcumin stops laboratory strains of…

  4. Contaminated soil concrete blocks

    NARCIS (Netherlands)

    Korte, de A.C.J.; Brouwers, H.J.H.; Limbachiya, Mukesh C.; Kew, Hsein Y.

    2009-01-01

    According to Dutch law the contaminated soil needs to be remediated or immobilised. The main focus in this article is the design of concrete blocks, containing contaminated soil, that are suitable for large production, financial feasible and meets all technical and environmental requirements. In ord

  5. Low efficiency deasphalting and catalytic cracking

    International Nuclear Information System (INIS)

    This patent describes a process for converting an asphaltene and metals containing heavy hydrocarbon feed to lighter, more valuable products the metals comprising Ni and V. It comprises: demetallizing the feed by deasphalting the feed in a solvent deasphalting means operating at solvent deasphalting conditions including a solvent: feed volume ratio of about 1:1 to 4:1, using a solvent selected from the group of C4 to 400 degrees F. hydrocarbons and mixtures thereof; recovering from the solvent rich fraction a demetallized oil intermediate product, having a boiling range and containing at least 10 wt.% of the asphaltenes, and 5 to 30% of the Ni and V, and at least 10 wt.% of the solvent present in the solvent rich phase produced in the deasphalting means; catalytically cracking the demetallized oil intermediate product in a catalytic cracking means operating at catalytic cracking conditions to produce a catalytically cracked product vapor fraction having a lower boiling range than the boiling range of the demetallized oil intermediate product; and fractionating the catalytically cracked product in a fractionation means to produce catalytically cracked product fractions

  6. Protection of brittle film against cracking

    Science.gov (United States)

    Musil, J.; Sklenka, J.; Čerstvý, R.

    2016-05-01

    This article reports on the protection of the brittle Zrsbnd Sisbnd O film against cracking in bending by the highly elastic top film (over-layer). In experiments the Zrsbnd Sisbnd O films with different elemental composition and structure were used. Both the brittle and highly elastic films were prepared by magnetron sputtering using a dual magnetron. The brittle film easily cracks in bending. On the other hand, the highly elastic film exhibits enhanced resistance to cracking in bending. Main characteristic parameters of both the brittle and highly elastic films are given. Special attention is devoted to the effect of the structure (crystalline, amorphous) of both the brittle and highly elastic top film on the resistance of cracking of the brittle film. It was found that (1) both the X-ray amorphous and crystalline brittle films easily crack in bending, (2) the highly elastic film can have either X-ray amorphous or crystalline structure and (3) both the X-ray amorphous and crystalline, highly elastic top films perfectly protect the brittle films against cracking in bending. The structure, mechanical properties and optical transparency of the brittle and highly elastic sputtered Zrsbnd Sisbnd O films are described in detail. At the end of this article, the principle of the low-temperature formation of the highly elastic films is also explained.

  7. Axial crack propagation and arrest in pressurized fuselage

    Science.gov (United States)

    Kosai, M.; Shimamoto, A.; Yu, C.-T.; Walker, S. I.; Kobayashi, A. S.; Tan, P.

    1994-01-01

    The crack arrest capability of a tear strap in a pressurized precracked fuselage was studied through instrumented axial rupture tests of small scale models of an idealized fuselage. Upon pressurization, rapid crack propagation initiated at an axial through crack along the stringer and immediately kinked due to the mixed modes 1 and 2 state caused by the one-sided opening of the crack flap. The diagonally running crack further turned at the tear straps. Dynamic finite element analysis of the rupturing cylinder showed that the crack kinked and also ran straight in the presence of a mixed mode state according to a modified two-parameter crack kinking criterion.

  8. Extended FEM modeling of crack paths near inclusions

    DEFF Research Database (Denmark)

    Nielsen, Chris Valentin; Legarth, Brian Nyvang; Niordson, Christian Frithiof

    2012-01-01

    the effects on the crack path when changing the relative stiffness between inclusion and matrix material, the relative distance between initial crack and inclusion, and the size of the inclusion. Both edge cracks and internal cracks are studied. An example with an internal crack near an inclusion is presented......The extended FEM is applied to model crack growth near inclusions. A procedure to handle different propagation rates at different crack tips is presented. The examples considered investigate uniform tension as well as equibiaxial tension under plane strain conditions. A parameter study analyzes...

  9. Crack shape analysis of PWSCC in S/G tubings

    Energy Technology Data Exchange (ETDEWEB)

    Park, I. K. [Sunmon Univ., Chonan (Korea, Republic of)

    2000-10-01

    Crack shape of PWSCC was analyzed, based on the fractured pulled-out S/G tubings of Ulchin-1 steam generator. The shape of the cracks in kiss roll transitions was elliptical shape for short cracks, and car shape for long cracks with flat crack front. The bulging was observed under the inner wall after shot-peening. Crack shape change after shot-peening was resulted from the crack growth restraint in axial direction due to compressive residual stresses on the primary side surface.

  10. Physical and Numerical Simulation for Inner Crack Healing in Metals

    Institute of Scientific and Technical Information of China (English)

    Jingtao HAN; Dongbin WEI; Yongjun ZHANG

    2004-01-01

    The research purpose on the healing of inner crack in metallic materials is to provide an effective approach for improving their properties and prolonging their lifetime. The crack healing process of 20MnMo steel with inner pre-crack was analyzed. It was found that all inner cracks could be healed in different degree. There were very fine ferrite grains in healing region. The micro-crack healing process in single crystal of BBC-Fe was simulated by the molecule dynamics method, which showed that the critical temperature of crack healing in BBC-Fe is 673K. There were micro-voids, dislocations and twins left after crack healing.

  11. Thermally activated processes of fatigue crack growth in steels

    Science.gov (United States)

    Tanaka, Masaki; Fujii, Atsushi; Noguchi, Hiroshi; Higashida, Kenji

    2014-02-01

    Fatigue crack growth rates in steels at high and low temperatures have been investigated using Paris curves. The fatigue crack growth rates at high temperatures are quite different from those at low temperatures. Arrhenius plots between fatigue crack growth rate (da/dN) and test temperatures at constant stress intensity factor range (ΔKI) indicate a difference of the rate-controlling process for fatigue crack growth with temperature. Slip deformation at the crack tip governs fatigue crack growth at high temperatures, while hydrogen diffusion is associated with crack growth at low temperatures.

  12. Finite element microscopic stress analysis of cracked composite systems

    Science.gov (United States)

    Ko, W. L.

    1978-01-01

    This paper considers the stress concentration problems of two types of cracked composite systems: (1) a composite system with a broken fiber (a penny-shaped crack problem), and (2) a composite system with a cracked matrix (an annular crack problem). The cracked composite systems are modeled with triangular and trapezoidal ring finite elements. Using NASTRAN (NASA Structural Analysis) finite element computer program, the stress and deformation fields in the cracked composite systems are calculated. The effect of fiber-matrix material combination on the stress concentrations and on the crack opening displacements is studied.

  13. Edit Distance with Block Deletions

    OpenAIRE

    Dana Shapira; Storer, James A.

    2011-01-01

    Several variants of the edit distance problem with block deletions are considered. Polynomial time optimal algorithms are presented for the edit distance with block deletions allowing character insertions and character moves, but without block moves. We show that the edit distance with block moves and block deletions is NP-complete (Nondeterministic Polynomial time problems in which any given solution to such problem can be verified in polynomial time, and any NP problem can be converted into...

  14. Fermion-Scalar Conformal Blocks

    CERN Document Server

    Iliesiu, Luca; Poland, David; Pufu, Silviu S; Simmons-Duffin, David; Yacoby, Ran

    2015-01-01

    We compute the conformal blocks associated with scalar-scalar-fermion-fermion 4-point functions in 3D CFTs. Together with the known scalar conformal blocks, our result completes the task of determining the so-called `seed blocks' in three dimensions. Conformal blocks associated with 4-point functions of operators with arbitrary spins can now be determined from these seed blocks by using known differential operators.

  15. Hierarchical Formation of Intrasplat Cracks in Thermal Spray Ceramic Coatings

    Science.gov (United States)

    Chen, Lin; Yang, Guan-Jun; Li, Cheng-Xin; Li, Chang-Jiu

    2016-06-01

    Intrasplat cracks, an essential feature of thermally sprayed ceramic coatings, play important roles in determining coating properties. However, final intrasplat crack patterns are always considered to be disordered and irregular, resulting from random cracking during splat cooling, since the detailed formation process of intrasplat cracks has scarcely been considered. In the present study, the primary formation mechanism for intrasplat cracking was explored based on both experimental observations and mechanical analysis. The results show that the intrasplat crack pattern in thermally sprayed ceramic splats presents a hierarchical structure with four sides and six neighbors, indicating that intrasplat crack patterns arise from successive domain divisions due to sequential cracking during splat cooling. The driving forces for intrasplat cracking are discussed, and the experimental data quantitatively agree well with theoretical results. This will provide insight for further coating structure designs and tailoring by tuning of intrasplat cracks.

  16. Analysis of internal crack healing mechanism under rolling deformation.

    Science.gov (United States)

    Gao, Haitao; Ai, Zhengrong; Yu, Hailiang; Wu, Hongyan; Liu, Xianghua

    2014-01-01

    A new experimental method, called the 'hole filling method', is proposed to simulate the healing of internal cracks in rolled workpieces. Based on the experimental results, the evolution in the microstructure, in terms of diffusion, nucleation and recrystallisation were used to analyze the crack healing mechanism. We also validated the phenomenon of segmented healing. Internal crack healing involves plastic deformation, heat transfer and an increase in the free energy introduced by the cracks. It is proposed that internal cracks heal better under high plastic deformation followed by slow cooling after rolling. Crack healing is controlled by diffusion of atoms from the matrix to the crack surface, and also by the nucleation and growth of ferrite grain on the crack surface. The diffusion mechanism is used to explain the source of material needed for crack healing. The recrystallisation mechanism is used to explain grain nucleation and growth, accompanied by atomic migration to the crack surface. PMID:25003518

  17. Stress corrosion cracking of copper canisters

    Energy Technology Data Exchange (ETDEWEB)

    King, Fraser (Integrity Corrosion Consulting Limited (Canada)); Newman, Roger (Univ. of Toronto (Canada))

    2010-12-15

    A critical review is presented of the possibility of stress corrosion cracking (SCC) of copper canisters in a deep geological repository in the Fennoscandian Shield. Each of the four main mechanisms proposed for the SCC of pure copper are reviewed and the required conditions for cracking compared with the expected environmental and mechanical loading conditions within the repository. Other possible mechanisms are also considered, as are recent studies specifically directed towards the SCC of copper canisters. The aim of the review is to determine if and when during the evolution of the repository environment copper canisters might be susceptible to SCC. Mechanisms that require a degree of oxidation or dissolution are only possible whilst oxidant is present in the repository and then only if other environmental and mechanical loading conditions are satisfied. These constraints are found to limit the period during which the canisters could be susceptible to cracking via film rupture (slip dissolution) or tarnish rupture mechanisms to the first few years after deposition of the canisters, at which time there will be insufficient SCC agent (ammonia, acetate, or nitrite) to support cracking. During the anaerobic phase, the supply of sulphide ions to the free surface will be transport limited by diffusion through the highly compacted bentonite. Therefore, no HS. will enter the crack and cracking by either of these mechanisms during the long term anaerobic phase is not feasible. Cracking via the film-induced cleavage mechanism requires a surface film of specific properties, most often associated with a nano porous structure. Slow rates of dissolution characteristic of processes in the repository will tend to coarsen any nano porous layer. Under some circumstances, a cuprous oxide film could support film-induced cleavage, but there is no evidence that this mechanism would operate in the presence of sulphide during the long-term anaerobic period because copper sulphide

  18. Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds

    Energy Technology Data Exchange (ETDEWEB)

    Aaltonen, P.; Toivonen, A.; Ehrnsten, U. (VTT Technical Research Centre of Finland, Espoo (Finland)); Haenninen, H.; Brederholm, A. (Aalto Univ. School of Science and Engineering, Faculty of Engineering and Architecture, Espoo (Finland))

    2010-05-15

    Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 deg C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed. (orig.)

  19. Geochemical study on oil-cracked gases and kerogen-cracked gases (Ⅱ)——Discrimination methods between oil-cracked gases and kerogen-cracked gases

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In the processes of discrimination between oil-cracked gases and kerogen-cracked gases,Behar and Pinzgofer et al.’s results were adopted in the former researches,in which the ratio of C2/C3 is basically a constant while the ratio of C1/C2 gradually increases in the course of primary cracking of kerogen. Otherwise in the course of secondary cracking of oil,the ratio of C2/C3 increases rapidly while C1/C2 keeps relatively stable. Our study on analogue experiment shows that,whether it is oil or kerogen,in its process of gas generating by cracking,the ratios of C2/C3,C1/C2 or C1/C3 will all be increased with the growth of thermal conditions. In comparison,the ratio of C2/C3,which is affected by genetic type to some comparatively less extent,mainly responds to the maturity of gases,while the value of C2/C3 is about 2,and that of C2/iC4 is about 10,and the corresponding value of Ro is about 1.5%―1.6%. The influence of gas source on C2/C3 is less than that of gas maturity,otherwise C1/C2(or C1/C3) is obviously affected by cracking matrices. The ratios of C1/C2,C1/C3 of oil-cracked gases are less than that of kerogen-cracked gases,under the condition that the ratios of C2/C3 are similar in value,so are the value of dryness indexes. There exists wide diffidence between this view and the former discrimination method in theory. The analysis of the spot sample indicates that we can apply the above basic view to dealing efficiently with the problem of the discrimination between oil-cracked gas and kerogen-cracked gas.

  20. Environmentally assisted cracking in light water reactors.

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O. K.; Chung, H. M.; Clark, R. W.; Gruber, E. E.; Shack, W. J.; Soppet, W. K.; Strain, R. V.

    2007-11-06

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from January to December 2002. Topics that have been investigated include: (a) environmental effects on fatigue crack initiation in carbon and low-alloy steels and austenitic stainless steels (SSs), (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs in BWRs, (c) evaluation of causes and mechanisms of irradiation-assisted cracking of austenitic SS in PWRs, and (d) cracking in Ni-alloys and welds. A critical review of the ASME Code fatigue design margins and an assessment of the conservation in the current choice of design margins are presented. The existing fatigue {var_epsilon}-N data have been evaluated to define the effects of key material, loading, and environmental parameters on the fatigue lives of carbon and low-alloy steels and austenitic SSs. Experimental data are presented on the effects of surface roughness on fatigue crack initiation in these materials in air and LWR environments. Crack growth tests were performed in BWR environments on SSs irradiated to 0.9 and 2.0 x 10{sup 21} n x cm{sup -2}. The crack growth rates (CGRs) of the irradiated steels are a factor of {approx}5 higher than the disposition curve proposed in NUREG-0313 for thermally sensitized materials. The CGRs decreased by an order of magnitude in low-dissolved oxygen (DO) environments. Slow-strain-rate tensile (SSRT) tests were conducted in high-purity 289 C water on steels irradiated to {approx}3 dpa. The bulk S content correlated well with the susceptibility to intergranular SCC in 289 C water. The IASCC susceptibility of SSs that contain >0.003 wt. % S increased drastically. bend tests in inert environments at 23 C were conducted on broken pieces of SSRT specimens and on unirradiated specimens of the same materials after hydrogen charging. The results of the tests and a review of other data in the literature

  1. Stochastic modeling of crack initiation and short-crack growth under creep and creep-fatigue conditions

    Science.gov (United States)

    Kitamura, Takayuki; Ghosn, Louis J.; Ohtani, Ryuichi

    1992-01-01

    A simplified stochastic model is proposed for crack initiation and short-crack growth under creep and creep-fatigue conditions. Material inhomogeneity provides the random nature of crack initiation and early growth. In the model, the influence of microstructure is introduced by the variability of: (1) damage accumulation along grain boundaries, (2) critical damage required for crack initiation or growth, and (3) the grain-boundary length. The probabilities of crack initiation and growth are derived by using convolution integrals. The model is calibrated and used to predict the crack density and crack-growth rate of short cracks of 304 stainless steel under creep and creep-fatigue conditions. The mean-crack initiation lives are predicted to be within an average deviation of about 10 percent from the experimental results. The predicted comulative distributions of crack-growth rate follow the experimental data closely. The applicability of the simplified stochastic model is discussed and the future research direction is outlined.

  2. Evaluation method of cracking resistance of lightweight aggregate concrete

    Institute of Scientific and Technical Information of China (English)

    季韬; 张彬彬; 陈永波; 庄一舟

    2014-01-01

    The cracking behavior of lightweight aggregate concrete (LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete (NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.

  3. NCCN Evidence Blocks.

    Science.gov (United States)

    Carlson, Robert W; Jonasch, Eric

    2016-05-01

    NCCN has developed a series of Evidence Blocks: graphics that provide ratings for each recommended treatment regimen in terms of efficacy, toxicity, quality and consistency of the supporting data, and affordability. The NCCN Evidence Blocks are currently available in 10 tumor types within the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines). At a glance, patients and providers can understand how a given treatment was assessed by the NCCN Guidelines Panel and get a sense of how a given treatment may match individual needs and preferences. Robert W. Carlson, MD, CEO of NCCN, described the reasoning behind this new feature and how the tool is used, and Eric Jonasch, MD, Professor of Genitourinary Medical Oncology at The University of Texas MD Anderson Cancer Center, and Vice Chair of the NCCN Kidney Cancer Panel, described its applicability in the management of metastatic renal cell carcinoma. PMID:27226499

  4. ENDOFEM INTEGRATED METHODOLOGY FOR FATIGUE CRACK GROWTH

    Institute of Scientific and Technical Information of China (English)

    C.F.Lee; L.T.Hsiao

    2002-01-01

    In this paper, the FEM with the incremental endochronic cyclic plasticity (EndoFEM) and the rc controlled node-released strategy are employed to study the fatigue crack opened/closed load (Pop) of A1 2024-T3 CCT specimens provided by Mageed and Pandey under several crack lengths and the constant amplitude with various load ratio (R). After statisfactory results are achieved by comparisons of computed Pop values and cited experimental data, the simulations will be extended to the crack lengths with significant bending effect due to short ligaments or high peak (Pmax) or high positive or very low negative R cyclic loads. Through these simulations, the complete map of Pop/Pmax vs. Kmax and R can be constructed and thereafter its correspondant empirical formulae can be proposed. Using these formulae and selecting the traditional fatigue crack growth parameter ΔKeff, the A1 2024-T3 fatigue crack growth rate da/dN vs. ΔK and R data, provided by Hiroshi and Schijve, can be employed to proposed empirical formulae of da/dN vs. ΔKeff and R. After integration, fatigue-crack-growth length a vs. N curves computed by EndoFEM can be obtained. The results are agreed very well with the existing experimental curves. According to the above procedures of simulation and steps of comparions with experiment, this paper may provides an integrate methodology of numerical simulation in the studies of fatigue crack growth for academic and industrial researches and design analysis.

  5. TRANSPORT THROUGH CRACKED CONCRETE: LITERATURE REVIEW

    Energy Technology Data Exchange (ETDEWEB)

    Langton, C.

    2012-05-11

    Concrete containment structures and cement-based fills and waste forms are used at the Savannah River Site to enhance the performance of shallow land disposal systems designed for containment of low-level radioactive waste. Understanding and measuring transport through cracked concrete is important for describing the initial condition of radioactive waste containment structures at the Savannah River Site (SRS) and for predicting performance of these structures over time. This report transmits the results of a literature review on transport through cracked concrete which was performed by Professor Jason Weiss, Purdue University per SRR0000678 (RFP-RQ00001029-WY). This review complements the NRC-sponsored literature review and assessment of factors relevant to performance of grouted systems for radioactive waste disposal. This review was performed by The Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, and The University of Aberdeen, Aberdeen Scotland and was focused on tank closure. The objective of the literature review on transport through cracked concrete was to identify information in the open literature which can be applied to SRS transport models for cementitious containment structures, fills, and waste forms. In addition, the literature review was intended to: (1) Provide a framework for describing and classifying cracks in containment structures and cementitious materials used in radioactive waste disposal, (2) Document the state of knowledge and research related to transport through cracks in concrete for various exposure conditions, (3) Provide information or methodology for answering several specific questions related to cracking and transport in concrete, and (4) Provide information that can be used to design experiments on transport through cracked samples and actual structures.

  6. Crack propagation modeling using Peridynamic theory

    Science.gov (United States)

    Hafezi, M. H.; Alebrahim, R.; Kundu, T.

    2016-04-01

    Crack propagation and branching are modeled using nonlocal peridynamic theory. One major advantage of this nonlocal theory based analysis tool is the unifying approach towards material behavior modeling - irrespective of whether the crack is formed in the material or not. No separate damage law is needed for crack initiation and propagation. This theory overcomes the weaknesses of existing continuum mechanics based numerical tools (e.g. FEM, XFEM etc.) for identifying fracture modes and does not require any simplifying assumptions. Cracks grow autonomously and not necessarily along a prescribed path. However, in some special situations such as in case of ductile fracture, the damage evolution and failure depend on parameters characterizing the local stress state instead of peridynamic damage modeling technique developed for brittle fracture. For brittle fracture modeling the bond is simply broken when the failure criterion is satisfied. This simulation helps us to design more reliable modeling tool for crack propagation and branching in both brittle and ductile materials. Peridynamic analysis has been found to be very demanding computationally, particularly for real-world structures (e.g. vehicles, aircrafts, etc.). It also requires a very expensive visualization process. The goal of this paper is to bring awareness to researchers the impact of this cutting-edge simulation tool for a better understanding of the cracked material response. A computer code has been developed to implement the peridynamic theory based modeling tool for two-dimensional analysis. A good agreement between our predictions and previously published results is observed. Some interesting new results that have not been reported earlier by others are also obtained and presented in this paper. The final objective of this investigation is to increase the mechanics knowledge of self-similar and self-affine cracks.

  7. SUPERFICIAL CERVICAL PLEXUS BLOCK

    Directory of Open Access Journals (Sweden)

    Komang Mega Puspadisari

    2014-01-01

    Full Text Available Superficial cervical plexus block is one of the regional anesthesia in  neck were limited to thesuperficial fascia. Anesthesia is used to relieve pain caused either during or after the surgery iscompleted. This technique can be done by landmark or with ultrasound guiding. The midpointof posterior border of the Sternocleidomastoid was identified and the prosedure done on thatplace or on the level of cartilage cricoid.

  8. Recent evaluations of crack-opening-area in circumferentially cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, S.; Brust, F.; Ghadiali, N.; Wilkowski, G.; Miura, N.

    1997-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. The results from twenty-five full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program, and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. Standard statistical analyses were performed to assess used to verify the analytical models. Standard statistical analyses were performed to assess quantitatively the accuracy of the predictive models. The evaluation also involved finite element analyses for determining the crack-opening profile often needed to perform leak-rate calculations.

  9. Managing access block.

    Science.gov (United States)

    Cameron, Peter; Scown, Paul; Campbell, Donald

    2002-01-01

    There is pessimism regarding the ability of the Acute Health Sector to manage access block for emergency and elective patients. Melbourne Health suffered an acute bed crisis in 2001 resulting in record ambulance diversions and emergency department (ED) delays. We conducted an observational study to reduce access block for emergency patients whilst maintaining elective throughput at Melbourne Health. This involved a clinician-led taskforce using previously proven principles for organisational change to implement 51 actions to improve patient access over a three-month period. The primary outcome measures were ambulance diversion, emergency patients waiting more than 12 hours for an inpatient bed, elective throughput and theatre cancellations. Despite a reduction in multi-day bed numbers all primary objectives were met, ambulance diversion decreased to minimal levels, 12-hour waits decreased by 40% and elective throughput was maintained. Theatre cancellations were also minimised. We conclude that access block can be improved by clinician-led implementation of proven process improvements over a short time frame. The ability to sustain change over the longer term requires further study.

  10. E-Block: A Tangible Programming Tool with Graphical Blocks

    Directory of Open Access Journals (Sweden)

    Danli Wang

    2013-01-01

    Full Text Available This paper designs a tangible programming tool, E-Block, for children aged 5 to 9 to experience the preliminary understanding of programming by building blocks. With embedded artificial intelligence, the tool defines the programming blocks with the sensors as the input and enables children to write programs to complete the tasks in the computer. The symbol on the programming block's surface is used to help children understanding the function of each block. The sequence information is transferred to computer by microcomputers and then translated into semantic information. The system applies wireless and infrared technologies and provides user with feedbacks on both screen and programming blocks. Preliminary user studies using observation and user interview methods are shown for E-Block's prototype. The test results prove that E-Block is attractive to children and easy to learn and use. The project also highlights potential advantages of using single chip microcomputer (SCM technology to develop tangible programming tools for children.

  11. VALIDATION OF CRACK INTERACTION LIMIT MODEL FOR PARALLEL EDGE CRACKS USING TWO-DIMENSIONAL FINITE ELEMENT ANALYSIS

    Directory of Open Access Journals (Sweden)

    R. Daud

    2013-06-01

    Full Text Available Shielding interaction effects of two parallel edge cracks in finite thickness plates subjected to remote tension load is analyzed using a developed finite element analysis program. In the present study, the crack interaction limit is evaluated based on the fitness of service (FFS code, and focus is given to the weak crack interaction region as the crack interval exceeds the length of cracks (b > a. Crack interaction factors are evaluated based on stress intensity factors (SIFs for Mode I SIFs using a displacement extrapolation technique. Parametric studies involved a wide range of crack-to-width (0.05 ≤ a/W ≤ 0.5 and crack interval ratios (b/a > 1. For validation, crack interaction factors are compared with single edge crack SIFs as a state of zero interaction. Within the considered range of parameters, the proposed numerical evaluation used to predict the crack interaction factor reduces the error of existing analytical solution from 1.92% to 0.97% at higher a/W. In reference to FFS codes, the small discrepancy in the prediction of the crack interaction factor validates the reliability of the numerical model to predict crack interaction limits under shielding interaction effects. In conclusion, the numerical model gave a successful prediction in estimating the crack interaction limit, which can be used as a reference for the shielding orientation of other cracks.

  12. Failure analysis of corrosion cracking and simulated testing for a fluid catalytic cracking unit

    Institute of Scientific and Technical Information of China (English)

    Hua Chen; Xiaogang Li; Chaofang Dong; Ming Li; Jinwen Yang

    2005-01-01

    The failure of a fluid catalysis and cracking unit (FCCU) in a Chinese refinery was investigated by using nondestructive detection methods, fracture surface examination, hardness measurement, chemical composition and corrosion products analysis. The results showed that the failure was caused by the dew point nitrate stress corrosion cracking. For a long operation period, the wall temperature of the regenerator in the FCCU was below the fume dew point. As a result, an acid fume NOx-SOx-H2O medium presented on the surface, resulting in stress corrosion cracking of the component with high residual stress. In order to confirm the relative conclusion, simulated testing was conducted in laboratory, and the results showed similar cracking characteristics. Finally, some suggestions have been made to prevent the stress corrosion cracking of an FCCU from re-occurring in the future.

  13. Sizing cracks in thin-walled CANDU reactor pressure tubes using crack-tip diffraction

    International Nuclear Information System (INIS)

    The most practical nondestructive means of measuring the depth of cracks approximately 0.4 mm deep in CANDU reactor pressure tubes is the ultrasonic crack-tip diffraction method. Initially, optimum ultrasonic parameters for wave mode, transducer frequency, main-bang pulse characteristics, incident and diffracted angles were obtained on three fatigue cracks, based on the criteria of maximum signal amplitude and accuracy in determination of crack depth. In addition, three signal processing techniques, auto and cross-correlation, rectification and smoothing and the magnitude of the analytic signal, were used to obtain time measurements. The results of these measurements are presented. Except for the first fatigue crack, the depth calculations were accurate to within the specified range of ± 0.1 mm

  14. Evaluation of Stress Intensity Factors for Multiple Cracked Circular Disks Under Crack Surface Tractions with SBFEM

    Institute of Scientific and Technical Information of China (English)

    LIU Jun-yu; LIN Gao; LI Xiao-chuan; XU Feng-lin

    2013-01-01

    Stress intensity factors (SIFs) for the cracked circular disks under different distributing surface tractions are evaluated with the scaled boundary finite element method (SBFEM).In the SBFEM,the analytical advantage of the solution in the radial direction allows SIFs to be directly determined from its definition,therefore no special crack-tip treatment is necessary.Furthermore anisotropic material behavior can be treated easily.Different distributions of surface tractions are considered for the center and double-edge-cracked disks.The benchmark examples are modeled and an excellent agreement between the results in the present study and those in published literature is found.It shows that SBFEM is effective and possesses high accuracy.The SIFs of the cracked orthotropic material circular disks subjected to different surface tractions are also evaluated.The technique of substructure is applied to handle the multiple cracks problem.

  15. Crack injection in silver gold alloys

    Science.gov (United States)

    Chen, Xiying

    Stress corrosion cracking (SCC) is a materials degradation phenomena resulting from a combination of stress and a corrosive environment. Among the alphabet soup of proposed mechanism of SCC the most important are film-rupture, film-induced cleavage and hydrogen embrittlement. This work examines various aspects of film-induced cleavage in gold alloys for which the operation of hydrogen embrittlement processes can be strictly ruled out on thermodynamic grounds. This is so because in such alloys SCC occurs under electrochemical conditions within which water is stable to hydrogen gas evolution. The alloy system examined in this work is AgAu since the corrosion processes in this system occur by a dealloying mechanism that results in the formation of nanoporous gold. The physics behind the dealloying process as well as the resulting formation of nanoporous gold is today well understood. Two important aspects of the film-induced cleavage mechanism are examined in this work: dynamic fracture in monolithic nanoporous gold and crack injection. In crack injection there is a finite thickness dealloyed layer formed on a AgAu alloy sample and the question of whether or not a crack that nucleates within this layer can travel for some finite distance into the un-corroded parent phase alloy is addressed. Dynamic fracture tests were performed on single edge-notched monolithic nanoporous gold samples as well as "infinite strip" sample configurations for which the stress intensity remains constant over a significant portion of the crack length. High-speed photography was used to measure the crack velocity. In the dynamic fracture experiments cracks were observed to travel at speeds as large as 270 m/s corresponding to about 68% of the Raleigh wave velocity. Crack injection experiments were performed on single crystal Ag77Au23, polycrystalline Ag72Au28 and pure gold, all of which had thin nanoporous gold layers on the surface of samples. Through-thickness fracture was seen in both the

  16. Crack buckling in soft gels under compression

    Institute of Scientific and Technical Information of China (English)

    Rong Long; Chung-Yuen Hui

    2012-01-01

    Recent interest in designing soft gels with high fracture toughness has called for simple and robust methods to test fracture behavior.The conventional method of applying tension to a gel sample suffers from a difficulty of sample gripping.In this paper,we study a possible fracture mechanism of soft gels under uni-axial compression.We show that the surfaces of a pre-existing crack,oriented parallel to the loading axis,can buckle at a critical compressive stress.This buckling instability can open the crack surfaces and create highly concentrated stress fields near the crack tip,which can lead to crack growth.We show that the onset of crack buckling can be deduced by a dimensional argument combined with an analysis to determine the critical compression needed to induce surface instabilities of an elastic half space.The critical compression for buckling was verified for a neoHookean material model using finite element simulations.

  17. Crack detection tools for feeder inspection

    International Nuclear Information System (INIS)

    Since 1998, the Hydro Quebec Research Centre (IREQ), in collaboration with Gentilly-2 (G2), has been working on the development of inspection devices for the feeder tubes of CANDU power plants. After the 14-probe METAR, which is now the standard equipment for thickness measurement of CANDU feeder pipes, IREQ addressed the industry's growing problem of crack detection in feeder bends and in welded areas. This paper presents three tools developed for this purpose: the Cracking Crawler for crack detection in bends, the Orbital bracelet for crack detection in pipe-to-pipe welds and the Grayloc Scanner for crack detection in the grayloc welds. In addition to the robotic development, the ultrasonic (U-T) techniques developed for automated feeder weld inspection will be described. An earlier version of some of these tools was presented at the 6th International Conference on CANDU Maintenance in 2003, while detailed herein is the latest development and the results of their first field trials, up to the licensing and technical transfer. (author)

  18. Flaw Tolerance for Multiple Fatique Cracks

    Energy Technology Data Exchange (ETDEWEB)

    Gosselin, Stephen R.; Simonen, Fredric A.; Carter, R. G.

    2005-07-01

    This paper documents important details of the technical bases for changes to Appendix L. Calculations identified aspect ratios for equivalent single cracks (ESC) between the extremes of a 6:1 ratio and a full circumferential crack that can be used in Appendix L flaw tolerance assessments to account for the initiation, growth, and linking of multiple fatigue cracks. Probabilistic fracture mechanics (PFM) calculations determined ESC aspect ratios that result in the same through-wall crack probability as multiple small cracks (0.02 inch depth) that initiate and coalesce. The computations considered two materials (stainless and low alloy steels), three pipe diameters, five cyclic membrane-to-gradient stress ratios and a wide range of primary loads. Subsequent deterministic calculations identified the ESC aspect ratio for the hypothetical reference flaw depth assumptions in Appendix L. This paper also describes computations that compare the Appendix L flaw tolerance allowable operating period for the ESC models with results obtained when the a single default 6:1 aspect ratio reference flaw.

  19. Imaging Cracks by Laser Excited Thermography

    Science.gov (United States)

    Schlichting, J.; Kervalishvili, G. N.; Maierhofer, Ch.; Kreutzbruck, M.

    2010-02-01

    During the last years active thermography is increasingly used in a number of NDT problems in production and maintenance. In this work we focus on the detection of vertical cracks starting at the surface, which is an important indication of structural failure. By using local thermal excitation it is possible to image anisotropies in the lateral diffusivity by recording the temporal temperature data with an infrared camera. The regional transient behaviour of temperature distribution then can provide quantitative information of the crack parameter. In doing so, we present an advanced technique for the determination of the crack depth. The experimental set-up is based on an Nd:YAG laser. The beam is focused on the test sample by using an optical scanner to create the required lateral heat flow. The time resolved temperature distribution is recorded with an infrared camera (InSb FPA, 3 to 5 μm) providing a frame rate of up to 500 Hz. In addition we report on numerical simulation to investigate the concept of local heat excitation for a quantitative estimation of crack parameters. The modeling also includes the influence of surface to surface radiation inside the crack. We obtained a good consistency between experimental and theoretical data.

  20. Enhanced Strength via crack friction and Pressure

    Science.gov (United States)

    Wiegand, Donald; Ellis, Kevin; Leppard, Claire

    2011-03-01

    The effect of pressure on the mechanical response of particulate polymer composites is being studied. Between about 0.1 and 7 MPa for one composite the results indicate that slow crack growth is the dominant failure mode. With continuously creasing strain at low pressures the stress initially increases to a maximum, the compressive strength, then decreases indicating work softening and them becomes approximately constant at a plateau value. Both the compressive strength and the plateau stress increases linearly with pressure but the plateau stress increases with a steeper slope such that at higher pressures work softening is not observed. The results are analyzed in terms of shear cracks with friction between the crack surfaces. The model predicts a threshold stress for crack growth which increases linearly with pressure and further predicts that the compressive strength increases linearly with pressure as observed and with the same slope as the threshold stress. These results clearly indicate that the pressure dependence of the compressive strength is due to the pressure dependence of the threshold stress for crack growth. The changes in the plateau region can also be attributed to frictional effects. Supported by AWE Aldermaston.

  1. Block Transfer Handbook: Constructing and Negotiating Block Transfer Agreements.

    Science.gov (United States)

    Finlay, Finola

    The purpose of this handbook is to provide resources for institutions or articulation committees who are engaged in the task of investigating the feasibility of block transfer agreements. Block transfer is the process whereby a block of credits is granted to students who have successfully completed a certificate, diploma, or cluster of courses…

  2. Shaft Crack Identification Based on Vibration and AE Signals

    Directory of Open Access Journals (Sweden)

    Wenxiu Lu

    2011-01-01

    Full Text Available The shaft crack is one of the main serious malfunctions that often occur in rotating machinery. However, it is difficult to locate the crack and determine the depth of the crack. In this paper, the acoustic emission (AE signal and vibration response are used to diagnose the crack. The wavelet transform is applied to AE signal to decompose into a series of time-domain signals, each of which covers a specific octave frequency band. Then an improved union method based on threshold and cross-correlation method is applied to detect the location of the shaft crack. The finite element method is used to build the model of the cracked rotor, and the crack depth is identified by comparing the vibration response of experiment and simulation. The experimental results show that the AE signal is effective and convenient to locate the shaft crack, and the vibration signal is feasible to determine the depth of shaft crack.

  3. A physical model for measuring thermally-induced block displacements

    Science.gov (United States)

    Bakun-Mazor, Dagan; Feldhiem, Aviran; Keissar, Yuval; Hatzor, Yossef H.

    2016-04-01

    A new model for thermally-induced block displacement in discontinuous rock slopes has been recently suggested. The model consists of a discrete block that is separated from the rock mass by a tension crack and rests on an inclined plane. The tension crack is filled with a wedge block or rock fragments. Irreversible block sliding is assumed to develop in response to climatic thermal fluctuations and consequent contraction and expansion of the sliding block material. While a tentative analytical solution for this model is already available, we are exploring here the possibility of obtaining such a permanent, thermally-induced, rock block displacement, under fully controlled conditions at the laboratory, and the sensitivity of the mechanism to geometry, mechanical properties, and temperature fluctuations. A large scale concrete physical model (50x150x60 cm^3) is being examined in a Climate-Controlled Room (CCR). The CCR permits accurate control of ambient temperature from 5 to 45 Celsius degrees. The permanent plastic displacement is being measured using four displacement transducers and a high resolution (29M pixel) visual range camera. A series of thermocouples measure the heating front inside the sliding block, hence thermal diffusivity is evaluated from the measured thermal gradient and heat flow. In order to select the appropriate concrete mixture, the mechanical and thermo-physical properties of concrete samples are determined in the lab. Friction angle and shear stiffness of the sliding interface are determined utilizing a hydraulic, servo-controlled direct shear apparatus. Uniaxial compression tests are performed to determine the uniaxial compressive strength, Young's modulus and Poison's ratio of the intact block material using a stiff triaxial load frame. Thermal conductivity and linear thermal expansion coefficient are determined experimentally using a self-constructed measuring system. Due to the fact that this experiment is still in progress, preliminary

  4. Propagation of stress corrosion cracks in alpha-brasses

    Energy Technology Data Exchange (ETDEWEB)

    Beggs, Dennis Vinton

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, ..delta..t greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, ..delta..x, decreased linearly with ..delta..t. With ..delta..t less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, ..delta..x = ..delta..x* which approached a limiting value of 1 ..mu..m. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  5. Demographic Data - MDC_Block

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — A polygon feature class of Miami-Dade Census 2000 Blocks. Census blocks are areas bounded on all sides by visible and/or invisible features shown on a map prepared...

  6. Effect of dislocation blocking on fracture behavior of Al and {alpha}-Fe: a multiscale study

    Energy Technology Data Exchange (ETDEWEB)

    Noronha, S.J.; Farkas, D

    2004-01-25

    We use a multiscale approach in which results from atomistic simulations are combined with discrete dislocation (DD) dynamics simulations of crack-tip plasticity. The method is used to study the effects of dislocation blocking on the fracture behavior of {alpha}-iron and aluminum. We studied the effects of blocking for distances ranging from 5 nm to 1 mm and find that the fracture resistance is increased with increasing blocking distance. The atomistic and dislocation dynamics simulations show that the blocking of dislocations causes a net decrease in the shear stress projected on the slip plane, preventing further dislocation emission. Semi-brittle cleavage occurs after a certain number of dislocations are emitted, explicitly demonstrating the embrittling effects of dislocation blocking. This effect can contribute to the brittle behavior observed in some nanocrystalline metals.

  7. Sizing stress corrosion cracks using laser ultrasonics

    Energy Technology Data Exchange (ETDEWEB)

    Rehman, Hamood; McNealy, Rick; Fingerhut, Martin [Applus-RTD. Houston, TX (United States); Klein, Marvin; Ansari, Homayoon [Intelligent Optical Systems, Inc. Los Angeles, CA (United States); Kania Richard [TransCanada. Calgary, AB (Canada); Rapp, Steve [Spectra Energy, Houston, TX (United States)

    2010-07-01

    Despite various efforts, no reliable tools and techniques are available to enable an operator to quantify the impact of an SCC (Stress Corrosion Cracking) colony on the safety and integrity of a pipeline. Reliable non-destructive detection and measurement tools are not available either. There is therefore a large gap between current technology and the needs of the pipeline industry. Recent developments promise that with a concentrated effort, a comprehensive solution can be devised. This paper describes technical work performed to develop and validate both the inspection tool and the time of flight diffraction (TOFD) technique for sizing the depth of SCC. It also presents preliminary results of work on a closely related project that provides, on the basis of this technology, an integrated approach and tool for mapping, sizing, and evaluating SCC, through which significant cracks are filtered from more benign cracks within an SCC colony.

  8. Inverse Crack Problems in Piezoelectric Solids

    Science.gov (United States)

    Sladek, Jan; Sladek, Vladimir; Zhang, Chuanzeng

    2010-05-01

    In the present paper, the meshless local Petrov-Galerkin (MLPG) method is applied to cracked piezoelectric solids under a stationary or transient dynamic load and unspecified electrical conditions on the crack surfaces. On the outer surface of the cracked solid the electrical boundary conditions are over-specified. The coupled governing partial differential equations are satisfied in a weak-form on small fictitious sub-domains. Nodal points are introduced and spread on the analyzed domain and each node is surrounded by a small circle for simplicity, but without loss of generality. The spatial variations of the displacements and the electric potential are approximated by the Moving Least-Squares (MLS) scheme. After performing the spatial integrations, a system of linear algebraic equations for unknown nodal values is obtained. Singular value decomposition (SVD) is applied to solve the ill-conditioned linear system of algebraic equations obtained from the local integral equations (LIEs) after the MLS approximation.

  9. Environmentally assisted cracking in LWR materials

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Park, J.H.; Shack, W.J. [Argonne National Lab., IL (United States); Zhang, J.; Brust, F.W.; Dong, P. [Battelle Columbus Labs., Columbus, OH (United States)

    1998-03-01

    The effect of dissolved oxygen level on fatigue life of austenitic stainless steels is discussed and the results of a detailed study of the effect of the environment on the growth of cracks during fatigue initiation are presented. Initial test results are given for specimens irradiated in the Halden reactor. Impurities introduced by shielded metal arc welding that may affect susceptibility to stress corrosion cracking are described. Results of calculations of residual stresses in core shroud weldments are summarized. Crack growth rates of high-nickel alloys under cyclic loading with R ratios from 0.2--0.95 in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 C are summarized.

  10. In situ fatigue-crack-propagation experiment

    International Nuclear Information System (INIS)

    An in-reactor fatigue experiment was conducted in the Oak Ridge Research Reactor to determine the effects of dynamic irradiation on fatigue crack propagation. Eight 20% cold-worked 316 stainless steel specimens were precracked to various initial crack lengths, linked together to form a chain, and inserted into a specially designed in-reactor fatigue machine. Test conditions included a maximum temperature of 4600C, an environment of sodium, a frequency of 1 cycle/min, and a stress ratio of 0.10. Results indicated that (1) no effects of dynamic irradiation were observed for a fluence of 1.5 x 1021 n/cm2 (E > 0.1 MeV); and (2) crack growth rates in elevated temperature sodium were a factor of 3 to 4 lower than in room temperature air

  11. Computer Simulations of the Fatigue Crack Propagation

    Directory of Open Access Journals (Sweden)

    A. Materna

    2000-01-01

    Full Text Available The following hypothesis for design of structures based on the damage tolerance philosophy is laid down: the perpendicular fatigue crack growth rate v in a certain point of a curved crack front is given by the local value of stress intensity factor per unit of nominal stress K' and the local triaxiality T which describes the constraint. The relationship v = f (K', T is supposed to be typical for a given loading spectrum and material. Such relationship for a 2024 Al alloy and the flight-simulation spectrum was derived from the fatigue test of the rectangular panel with the central hole and used for three-dimensional simulation of the corner fatigue crack propagation in the model of the wing spar flangeplate. Finite element and boundary element methods were used for these computations. The results of the simulation are in good agreement with the experiment.

  12. Porous block nanofiber composite filters

    Energy Technology Data Exchange (ETDEWEB)

    Ginley, David S.; Curtis, Calvin J.; Miedaner, Alexander; Weiss, Alan J.; Paddock, Arnold

    2016-08-09

    Porous block nano-fiber composite (110), a filtration system (10) and methods of using the same are disclosed. An exemplary porous block nano-fiber composite (110) includes a porous block (100) having one or more pores (200). The porous block nano-fiber composite (110) also includes a plurality of inorganic nano-fibers (211) formed within at least one of the pores (200).

  13. Cracking control in mass concrete for three gorges dam; Sankyo damu ni okeru masu konkurito no hibiware yokusei

    Energy Technology Data Exchange (ETDEWEB)

    Chu, CHuanying

    1999-09-10

    The provisional cofferdam work of the mainstream of Three Gorges Dam project was successfully finished on November 8, 1997. Now, the work enters its second stage, and the placing of large-scale concrete was started. The total quantity of concrete used in this project reaches 15.00 million m{sup 3}. Inhibition of dam concrete cracking is an important subject. In order to manufacture concrete with good crack-resistance, cements, fly ashes, aggregates and blending agents are strictly selected; and hydration-generating heat is reduced by means of strict temperature control, precooling of aggregates, reduction of placing temperature and concrete temperature in mixers, and the like. As a consequence of maintaining the highest temperature value in concrete blocks to be lower than a predetermined value, harmful cracks can be prevented from occurring when the temperature in the dam lowers. (NEDO)

  14. Crack velocity jumps engendered by a transformational process zone

    Science.gov (United States)

    Boulbitch, A.; Korzhenevskii, A. L.

    2016-06-01

    We study a concerted propagation of a fast crack with the process zone where a rearrangement of the solid structure takes place. The latter is treated as a second-order local phase transformation. We demonstrate that the propagation of such a zone gives rise to a nonlinear frictionlike force exerted on the crack tip, resisting its propagation. Depending on the temperature, it produces three regimes of crack motion, which differ in the behavior of the crack tip process zone: (i) always existing, (ii) only emerging at a high crack speed, and (iii) flickering. We show that the latter regime exhibits crack velocity jumps.

  15. Velocity-Dependent Fatigue Crack Paths in Nanograined Pt Films

    Science.gov (United States)

    Meirom, R. A.; Clark, T.; Polcawich, R.; Pulskamp, J.; Dubey, M.; Muhlstein, C. L.

    2008-08-01

    Studies of crack growth in nanograined films assert that mechanical damage accumulates at grain boundaries irrespective of the crack velocity and loading conditions. This work shows that crack advance in nanograined Pt films involves a dislocation-slip mechanism that is a function of the crack growth rate and mode of loading. Crack paths in Pt were initially intergranular, but transitioned to a transgranular mode that persisted until catastrophic failure. This research demonstrates that crack growth mechanisms modeled for nanograined Ni cannot be generalized to other pure, metallic systems.

  16. A Pipeline Fracture Model of Hydrogen-induced Cracking

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The relationship between hydrogen concentration and crack tip stress, strain field, hydrogen diffusion and internal pressure respectively in the crack tip process zone was investigated, and the length of the crack tip process zone of hydrogen-induced cracking (HIC) was determined. Based on the mechanism of fracture of micro-crack nucleation, a dislocation model was presented for the fracture criteria of HIC. The influence factors of pipeline tube fracture ductile KISCC in the presence of hydrogen was analyzed, and the critical pressure bearing capability of a pipeline with hydrogen-induced cracking and the critical J-integrity (JISCC) were calculated, which is very important for pipeline safety.

  17. CORE SATURATION BLOCKING OSCILLATOR

    Science.gov (United States)

    Spinrad, R.J.

    1961-10-17

    A blocking oscillator which relies on core saturation regulation to control the output pulse width is described. In this arrangement an external magnetic loop is provided in which a saturable portion forms the core of a feedback transformer used with the thermionic or semi-conductor active element. A first stationary magnetic loop establishes a level of flux through the saturation portion of the loop. A second adjustable magnet moves the flux level to select a saturation point giving the desired output pulse width. (AEC)

  18. Realistic and efficient 2D crack simulation

    Science.gov (United States)

    Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek

    2010-04-01

    Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.

  19. The effect of root preparation technique and instrumentation length on the development of apical root cracks.

    Science.gov (United States)

    Adorno, Carlos G; Yoshioka, Takatomo; Suda, Hideaki

    2009-03-01

    The purpose of this study was to compare the effects of root canal preparation techniques and instrumentation length on the development of apical root cracks. Forty extracted mandibular premolars with straight roots were randomly selected and mounted on resin blocks with simulated periodontal ligaments, and the apex was exposed. The teeth were divided into four groups of 10 teeth each for different canal preparation techniques and instrumentation lengths: group A: step-back preparation (SB) with stainless steel files (SF) using root canal length (RCL) to guide instrumentation length; group B: SB using RCL - 1 mm; group C: crown-down preparation (CD) with Profile using RCL; and group D: CD with PF using RCL - 1 mm. Digital images of the instrumentation sequence were compared for each tooth. Statistical analysis revealed a significant effect of instrumentation length (p 0.05) on the development of apical cracks.

  20. Role of plasticity-induced crack closure in fatigue crack growth

    Directory of Open Access Journals (Sweden)

    Jesús Toribio

    2013-07-01

    Full Text Available The premature contact of crack surfaces attributable to the near-tip plastic deformations under cyclic loading, which is commonly referred to as plasticity induced crack closure (PICC, has long been focused as supposedly controlling factor of fatigue crack growth (FCG. Nevertheless, when the plane-strain near-tip constraint is approached, PICC lacks of straightforward evidence, so that its significance in FCG, and even the very existence, remain debatable. To add insights into this matter, large-deformation elastoplastic simulations of plane-strain crack under constant amplitude load cycling at different load ranges and ratios, as well as with an overload, have been performed. Modeling visualizes the Laird-Smith conceptual mechanism of FCG by plastic blunting and re-sharpening. Simulation reproduces the experimental trends of FCG concerning the roles of stress intensity factor range and overload, but PICC has never been detected. Near-tip deformation patterns discard the filling-in a crack with material stretched out of the crack plane in the wake behind the tip as supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises doubts about the trustworthiness of closure assessment from the compliance variation. This demonstrates ambiguities of PICC as a supposedly intrinsic factor of FCG and, by implication, favors the stresses and strains in front of the crack tip as genuine fatigue drivers.

  1. Evolution of residual stresses with fatigue crack growth in integral structures with crack retarders

    International Nuclear Information System (INIS)

    Bonded straps are investigated for their ability to retard a growing fatigue crack in metallic structures. The evolution of the residual stresses in the vicinity of the strap with fatigue crack growth has been studied. Cracks were grown in single edge-notched tension (SEN(T)) specimens reinforced with either a titanium or a carbon fibre reinforced plastics (CFRP) strap. The residual stress evolution has been measured in situ during crack growth using neutron diffraction, and modelled with a finite element approach. The peak residual stresses induced by the mismatch of the coefficient of thermal expansion between the strap and plate materials were seen to be fairly constant with crack growth. Good correlation between the experimental and the modelling results was found, except at very long crack lengths for a specimen that exhibited considerable fracture surface roughness at long crack lengths. The difference was attributed to wedging of the fracture surface changing the expected stress state, rather than any effect of the strap.

  2. Fatigue crack initiation life prediction of railroad

    International Nuclear Information System (INIS)

    Study of multiaxial high-cycle fatigue initiation life prediction for railroad is done in this paper. Using ANSYS 11.0 software three dimensional elasto-plastic finite element model of rail/wheel contact is constructed and fine mesh technique in contact region is used to achieve both computational efficiency and accuracy. Stress analysis is performed and fatigue damage in railroad is evaluated numerically using multiaxial fatigue crack initiation model. Using the stress history during one loading cycle and fatigue damage model, the effects of vertical loading, material hardness material fatigue properties and wheel/rail contact situation on fatigue crack initiation life are investigated.

  3. Multiple Gastrointestinal Complications of Crack Cocaine Abuse

    Directory of Open Access Journals (Sweden)

    Neal Carlin

    2014-01-01

    Full Text Available Cocaine and its alkaloid free base “crack-cocaine” have long since been substances of abuse. Drug abuse of cocaine via oral, inhalation, intravenous, and intranasal intake has famously been associated with a number of medical complications. Intestinal ischemia and perforation remain the most common manifestations of cocaine associated gastrointestinal disease and have historically been associated with oral intake of cocaine. Here we find a rare case of two relatively uncommon gastrointestinal complications of hemorrhage and pancreatitis presenting within a single admission in a chronic crack cocaine abuser.

  4. LABORATORY STUDY ON CRACKS IN SATURATED SANDS

    Institute of Scientific and Technical Information of China (English)

    Peng Fujiao; Tan Qingming; Che-Min Cheng

    2000-01-01

    It has been reported[1]that when a loosely packed column of saturated sand in a vertical cylindrical container is shock loaded axially by dropping to the floor,large horizontal cracks initiate,grow and eventually fade away in the sand as it settles under gravity.This paper shows that a similar phenomenon can also be observed when shock loading is replaced by forcing water to percolate upward through the sand column.It is believed that our result sheds further light on the physics of formation of these cracks.

  5. Detection of wear cracks by photothermal radiometry

    Energy Technology Data Exchange (ETDEWEB)

    Bodnar, J.L. (Groupe de Recherche Surfaces et Materiaux, Lab. d' Energetique et d' Optique, Faculte des Sciences, 51 - Reims (France)); Menu, C. (Groupe de Recherche Surfaces et Materiaux, Lab. d' Energetique et d' Optique, Faculte des Sciences, 51 - Reims (France)); Egee, M. (Groupe de Recherche Surfaces et Materiaux, Lab. d' Energetique et d' Optique, Faculte des Sciences, 51 - Reims (France)); Pigeon, P. (Commissariat a l' Energie Atomique, Centre d' Etudes et de Recherche sur les Materiaux, Centre d' Etudes Nucleaires Saclay, 91 - Gif-sur-Yvette (France)); Blanc, A. le (Commissariat a l' Energie Atomique, Centre d' Etudes et de Recherche sur les Materiaux, Centre d' Etudes Nucleaires Saclay, 91 - Gif-sur-Yvette (France))

    1993-04-13

    Among the non-destructive techniques, testing methods using thermal waves are starting to be developed in industry. Photothermal radiometry under cw excitation, which is one of these methods, has been used in this work for the detection of wear cracks, either emerging on the surface of the sample or covered with a thin layer. Before conducting the experimental study, we have developed a three-dimensional mathematical model. It is shown that the influence of the flaw on the photothermal signal is indeed the result of two phenomena: a thermal barrier effect and an optical effect owing to the higher emissivity of the crack when it is emerging. (orig.)

  6. CRACK2. Modelling calcium carbonate deposition from bicarbonate solutions in cracks in concrete

    DEFF Research Database (Denmark)

    Brodersen, Knud Erik

    2003-01-01

    by diffusion in pore systems in columns of cementitious materials. The hydroxyl is precipitating calcite from a flow of bicarbonate solution in a crack connecting the ends of a row of such columns. Thecementitious material is simulated as calcium hydroxide mixed with inert material but with sodium hydroxide...... and on the composition of the outflowing solution, which can be compared directly with experimental results.Leaching behavior of sodium can be used to tune the model to experimental observations. The calcite is mostly precipitated on top of the original crack surface and may under certain circumstances fill the crack...

  7. Experimental study of heat dissipation at the crack tip during fatigue crack propagation

    Directory of Open Access Journals (Sweden)

    A. Vshivkov

    2016-01-01

    Full Text Available This work is devoted to the development of an experimental method for studying the energy balance during cyclic deformation and fracture. The studies were conducted on 304 stainless steel AISE and titanium alloy OT4-0 samples. The investigation of the fatigue crack propagation was carried out on flat samples with different geometries and types of stress concentrators. The heat flux sensor was developed based on the Seebeck effect. This sensor was used for measuring the heat dissipation power in the examined samples during the fatigue tests. The measurements showed that the rate of fatigue crack growth depends on the heat flux at the crack tip.

  8. One-Block CYRCA: an automated procedure for identifying multiple-block alignments from single block queries

    OpenAIRE

    Frenkel-Morgenstern, Milana; Singer, Alice; Bronfeld, Hagit; Pietrokovski, Shmuel

    2005-01-01

    One-Block CYRCA is an automated procedure for identifying multiple-block alignments from single block queries (). It is based on the LAMA and CYRCA block-to-block alignment methods. The procedure identifies whether the query blocks can form new multiple-block alignments (block sets) with blocks from a database or join pre-existing database block sets. Using pre-computed LAMA block alignments and CYRCA sets from the Blocks database reduces the computation time. LAMA and CYRCA are highly sensit...

  9. The wild tapered block bootstrap

    DEFF Research Database (Denmark)

    Hounyo, Ulrich

    In this paper, a new resampling procedure, called the wild tapered block bootstrap, is introduced as a means of calculating standard errors of estimators and constructing confidence regions for parameters based on dependent heterogeneous data. The method consists in tapering each overlapping block...... of the series first, the applying the standard wild bootstrap for independent and heteroscedastic distrbuted observations to overlapping tapered blocks in an appropriate way. Its perserves the favorable bias and mean squared error properties of the tapered block bootstrap, which is the state-of-the-art block......-order asymptotic validity of the tapered block bootstrap as well as the wild tapered block bootstrap approximation to the actual distribution of the sample mean is also established when data are assumed to satisfy a near epoch dependent condition. The consistency of the bootstrap variance estimator for the sample...

  10. Effects of plastic anisotropy on crack-tip behaviour

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Tvergaard, Viggo; Kuroda, Mitsutoshi

    2002-01-01

    For a crack in a homogeneous material the effect of plastic anisotropy on crack-tip blunting and on the near-tip stress and strain fields is analyzed numerically. The full finite strain analyses are carried out for plane strain under small scale yielding conditions, with purely symmetric mode I...... loading remote from the crack-tip. In cases where the principal axes of the anisotropy are inclined to the plane of the crack it is found that the plastic zones as well as the stress and strain fields just around the blunted tip of the crack become non-symmetric. In these cases the peak strain...... on the blunted tip occurs off the center line of the crack, thus indicating that the crack may want to grow in a different direction. When the anisotropic axes are parallel to the crack symmetry is retained, but the plastic zones and the near-tip fields still differ from those predicted by standard isotropic...

  11. Crack Growth along Interfaces in Porous Ceramic Layers

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, Andy

    2001-01-01

    Crack growth along porous ceramic layers was studied experimentally. Double cantilever beam sandwich specimens were loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope enabling in situ observations of...

  12. Chloride Ingress in Concrete Cracks under Cyclic Loading

    DEFF Research Database (Denmark)

    Küter, André; Geiker, Mette Rica; Olesen, John Forbes;

    2005-01-01

    Traditional approaches towards service life design and redesign of reinforced concrete are based on the assumption of a homogenous uncracked concrete. This assumption is questionable, as concrete always contains cracks and cracks affect the ingress rate of aggressive substances. Thus...

  13. A MOVING CRACK IN A NONHOMOGENEOUS MATERIAL STRIP

    Institute of Scientific and Technical Information of China (English)

    Wang Baolin; Han Jiecai

    2006-01-01

    This paper considers an anti-plane moving crack in a nonhomogencous material strip of finite thickness. The shear modulus and the mass density of the strip are considered for a class of functional forms for which the equilibrium equation has analytical solutions. The problem is solved by means of the singular integral equation technique. The stress field near the crack tip is obtained. The results are plotted to show the effect of the material non-homogeneity and crack moving velocity on the crack tip field. Crack bifurcation behaviour is also discussed. The paper points out that use of an appropriate fracture criterion is essential for studying the stability of a moving crack in nonhomogeneous materials. The prediction whether the unstable crack growth will be enhanced or retarded is strongly dependent on the type of the fracture criterion used. is a suitable failure criterion for moving cracks in nonhomogeneous materials.

  14. Acoustic emission assessment of interface cracking in thermal barrier coatings

    Science.gov (United States)

    Yang, Li; Zhong, Zhi-Chun; Zhou, Yi-Chun; Zhu, Wang; Zhang, Zhi-Biao; Cai, Can-Ying; Lu, Chun-Sheng

    2016-04-01

    In this paper, acoustic emission (AE) and digital image correlation methods were applied to monitor interface cracking in thermal barrier coatings under compression. The interface failure process can be identified via its AE features, including buckling, delamination incubation and spallation. According to the Fourier transformation of AE signals, there are four different failure modes: surface vertical cracks, opening and sliding interface cracks, and substrate deformation. The characteristic frequency of AE signals from surface vertical cracks is 0.21 MHz, whilst that of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. The energy released of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. Based on the energy released from cracking and the AE signals, a relationship is established between the interface crack length and AE parameters, which is in good agreement with experimental results.

  15. Vibration Pattern Related to Transverse Cracks in Rotors

    OpenAIRE

    Nicolò Bachschmid; Ezio Tanzi

    2002-01-01

    A method for calculating the breathing behavior of transverse cracks of different types in rotating shafts is described. Thermal effects are included. Some results in terms of vibration excitation related to different shapes of cracks are presented.

  16. Partial discharge-induced crack growth in dielectric materials

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Partial discharge(PD) of an air-filled semi-permeable crack in a dielectric material is studied based on the streamer-type discharge mechanism to explore the effects of applied mechanical-electric fields on crack growth.Within the frame of two-dimensional deformation,the electric field inside the crack is first derived by taking the crack deformation into account.Then,the effects of electric field before PD are discussed through considering the contribution of the induced electric field inside the deformed crack space to the total energy release rate.Finally,PD and its effects on crack growth are investigated.It is found that:(1) before PD,the applied electric field always retards crack growth;(2) during PD,the applied electric field can induce crack growth in dielectric materials.

  17. Fatigue crack shape prediction based on vertex singularity

    Directory of Open Access Journals (Sweden)

    Hutař P.

    2008-11-01

    Full Text Available Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using analytic equations. Contrary to this, at the free surface or in the boundary layer close to free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and a crack shape for a three-dimensional structure is described in this paper. The results presented make it possible to estimate fatigue crack growth rate and crack shape using the concept of the generalized stress intensity factor. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.

  18. Failure investigation of type 410 stainless steel retaining block studs of swing check valves in pressurized water reactors

    International Nuclear Information System (INIS)

    Retaining block studs in swing check valves employed in Emergency Core Cooling System of pressurized water reactors have been the subject of cracking during the past few years. The studs are made from ASTM A-193 Gr. 6 type 410 stainless steel material. USNRC issued an information notice on the issue encouraging utilities to take appropriate actions to monitor/replace the studs so as to prevent a potential dislodging of the valve retaining blocks that can cause flow blockage in the valves. The current paper summarizes the results of a metallurgical investigation aimed at establishing the mechanism and cause(s) of the valve stud cracking. Potential candidate replacement materials to remedy the cracking issue are also considered

  19. Environmentally assisted cracking in light water reactors

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O.K.; Chung, H.M.; Gruber, E.E. [and others

    1996-07-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from April 1995 to December 1995. Topics that have been investigated include fatigue of carbon and low-alloy steel used in reactor piping and pressure vessels, EAC of Alloy 600 and 690, and irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests were conducted on ferritic steels in water that contained various concentrations of dissolved oxygen (DO) to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Crack-growth-rate tests were conducted on compact-tension specimens from several heats of Alloys 600 and 690 in simulated LWR environments. Effects of fluoride-ion contamination on susceptibility to intergranular cracking of high- and commercial- purity Type 304 SS specimens from control-tensile tests at 288 degrees Centigrade. Microchemical changes in the specimens were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements may contribute to IASCC of these materials.

  20. Stress Corrosion Cracking of Pipeline Steels

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    This paper provides a review of the differences between high pH and near-neutral pH stress corrosion cracking ofpipeline steels, influencing factors, and mechanisms. The characteristics and historical information on both forms ofSCC are discussed. The prospect for research in the future is also presented.

  1. Next Generation Steam Cracking Reactor Concept

    NARCIS (Netherlands)

    Van Goethem, M.W.M.

    2010-01-01

    The steam cracking process is an important asset in the hydrocarbon processing industry. The main products are lower olefins and hydrogen, with ethylene being the world's largest volume organic chemical at a worldwide capacity of ~ 120 million tonnes per year. Feed stocks are hydrocarbons such as: e

  2. Fatigue crack growth in Aluminium Alloys

    NARCIS (Netherlands)

    Van Kranenburg, C.

    2010-01-01

    Fatigue is a gradual process of local strength reduction. It is a phenomenon of damage accumulation at stress concentrations caused by fluctuating stresses and/or strains. In metals this results in microscopic cracks. These will start to grow under continued cyclic loading until final failure occurs

  3. Kinetic studies of stress-corrosion cracking

    Science.gov (United States)

    Noronha, P. J.

    1977-01-01

    Use of time-to-failure curves for stress-corrosion cracking processes may lead to incorrect estimates of structural life, if material is strongly dependent upon prestress levels. Technique characterizes kinetics of crackgrowth rates and intermediate arrest times by load-level changes.

  4. 3D characterisation of RCF crack networks

    Directory of Open Access Journals (Sweden)

    Ahlström Johan

    2014-06-01

    Full Text Available Rolling contact fatigue (RCF damage is becoming more frequent with increased traffic and loading conditions in the railway industry. Defects which are characterized by a two-lobe darkened surface and a V-shaped surface-breaking crack are often so-called squats. The origination and propagation of squats in railway rails is the topic of many recent studies; the associated crack networks develop with complicated geometry near the surface of rails that is difficult to characterise using most non-destructive methods. The cracks can be examined with repeated metallographic sectioning, but the process is time-consuming and destructive. In order to reduce time, as well as information and material loss, high-resolution and high-energy X-ray imaging of railway rails was done in the current study. Combining the exposures from a range of angles using image analysis, a 3D representation of the complex crack network is achieved. The latter was complemented with metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction.

  5. Pregnant crack addicts in a psychiatric unit

    Directory of Open Access Journals (Sweden)

    Gabriela de Moraes Costa

    2012-01-01

    Full Text Available OBJECTIVE: In this study we aim to characterize a sample of 85 pregnant crack addicts admitted for detoxification in a psychiatric inpatient unit. METHOD: Cross-sectional study. Sociodemographic, clinical, obstetric and lifestyle information were evaluated. RESULTS: Age of onset for crack use varied from 11 to 35 years (median = 21. Approximately 25% of the patients smoked more than 20 crack rocks in a typical day of use (median = 10; min-max = 1-100. Tobacco (89.4%, alcohol (63.5% and marijuana (51.8% were the drugs other than crack most currently used. Robbery was reported by 32 patients (41.2%, imprisonment experience by 21 (24.7%, trade of sex for money/drugs by 38 (44.7%, home desertion by 33 (38.8%; 15.3% were positive for HIV, 5.9% for HCV, 1.2% for HBV and 8.2% for syphilis. After discharge from the psychiatric unit, only 25% of the sample followed the proposed treatment in the chemical dependency outpatient service. CONCLUSION: Greater risky behaviors for STD, as well as high rates of maternal HIV and Syphilis were found. Moreover, the high rates of concurrent use of other drugs and involvement in illegal activities contribute to show their chaotic lifestyles. Prevention and intervention programs need to be developed to address the multifactorial nature of this problem.

  6. Effect of flow velocity on crack initiation

    International Nuclear Information System (INIS)

    Constant extension rate tensile (CERT) tests are traditionally used to understand the influence of material composition, heat treatment, temperature and environmental variables on stress corrosion crack (SCC) initiation. However, fluid flow rate has not been investigated as a parameter that could affect SCC initiation until recently. These studies have exhibited longer time to failure under high flow conditions indicating delayed crack initiation. Because these experiments have been performed in highly oxygenated water, no correlation has been established between the influence of flow velocity on the electrochemical corrosion potential (ECP) and the time to failure of tensile test specimens. The interrelationship between the fluid flow velocity, ECP and the time to failure is of great interest to the Boiling Water Reactor (BWR) applications primarily because of the previous observations that the ECP of Type 304 stainless steel increases with fluid flow velocity. This paper describes an attempt that has been made to understand the interrelationship between fluid flow velocity, ECP and the time for crack initiation in high temperature high purity water simulating both the BWR chemistry and the component flow velocity conditions. The range of flow velocities employed in the present study was 0.002 to 2 ft/s. The studies indicate that while high flow velocities can increase ECP there is a delayed effect on crack initiation

  7. Instantaneous crack detection using dual PZT transducers

    Science.gov (United States)

    Kim, Seung Bum; Sohn, Hoon

    2008-03-01

    A new guided wave based nondestructive testing (NDT) technique is developed to detect crack damage in metallic plates commonly used in aircraft without using prior baseline data or a predetermined decision boundary. In conventional guided wave based techniques, damage is often identified by comparing the "current" data obtained from a potentially damaged condition of a structure with the "past" baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. In order to tackle this issue, a reference-free damage detection technique is previously developed using two pairs of collocated lead zirconate titanate transducers (PZTs) placed on both sides of a plate. In this study, this reference-free technique is further advanced so that the PZT transducers can be placed only on one side of the specimen. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves. This study suggests a reference-free statistical approach that enables damage classification using only the current data set. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to instantaneous crack detection.

  8. Crack detection by mobile photothermal probe

    Energy Technology Data Exchange (ETDEWEB)

    Besnard, R.; Le Blanc, A. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. de Technologie des Materiaux; Bodnar, J.L.; Egee, M.; Menu, C. [Reims Univ., 51 (France); Sellier, J.Y. [Societe Intercontrole, 94 - Rungis (France)

    1993-12-31

    This paper deals with an industrial method for crack detection. The apparatus presented is based on a mobile photothermal probe. It can be used under different modes (sinusoidal, pulsed or scanned excitation). Moreover, the description of the device provided includes theoretical and experimental results. (TEC). 7 refs., 6 figs.

  9. 46 CFR 59.10-5 - Cracks.

    Science.gov (United States)

    2010-10-01

    ... does not exceed 12 inches in length and after completion the weld is stress-relieved. Cracks in... the root of the weld shall be chipped or ground out to insure a clean surface of the originally... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed....

  10. Block Voter Model

    CERN Document Server

    Sampaio, C I N

    2011-01-01

    We introduce and study the block voter model with noise on two-dimensional square lattices using Monte Carlo simulations and finite-size scaling techniques. The model is defined by an outflow dynamics where a central set of $N_{PCS}$ spins, here denoted by persuasive cluster spins (PCS), tries to influence the opinion of their neighbouring counterparts. We consider the collective behaviour of the entire system with varying PCS size. When $N_{PCS}>2$, the system exhibits an order-disorder phase transition at a critical noise parameter $q_{c}$ which is a monotonically increasing function of the size of the persuasive cluster. We conclude that how large the PCS is more power of persuasion it has. It also seems that the resulting critical behaviour is Ising-like independent of the range of the interactions.

  11. Spintronics: Conceptual Building Blocks

    Science.gov (United States)

    Ansermet, J.-Ph.

    The purpose of this introduction to spintronics is to provide some elementary description of its conceptual building blocks. Thus, it is intended for a newcomer to the field. After recalling rudimentary descriptions of spin precession and spin relaxation, spin-dependent transport is treated within the Boltzmann formalism. This suffices to introduce key notions such as the spin asymmetry of the conductivities in the two-current model, the spin diffusion length, and spin accumulation. Two basic mechanisms of spin relaxation are then presented, one arising from spin-orbit scattering and the other from electron-magnon collisions. Finally, the action of a spin-polarized current on magnetization is presented in a thermodynamics framework. This introduces the notion of spin torque and the characteristic length scale over which the transverse spin polarization of conduction electron decays as it is injected into a magnet.

  12. Photovoltaic building blocks

    DEFF Research Database (Denmark)

    Hanberg, Peter Jesper; Jørgensen, Anders Michael

    2014-01-01

    it directcompetitive with fossil energy sources a further reduction is needed. By increasing the efficiency of the solar cells one gain an advantage through the whole chain of cost. So that per produced Watt of power less material is spent, installation costs are lower, less area is used etc. With an average...... efficiency of about 15% for commercial Silicon solar cells there is still much to gain. DTU Danchip provides research facilities, equipment and expertise for the building blocks that comprises fabricating the efficient solar cell. In order to get more of the sun light into the device we provide thin film......Photovoltaics (PV), better known as solar cells, are now a common day sight on many rooftops in Denmark.The installed capacity of PV systems worldwide is growing exponentially1 and is the third most importantrenewable energy source today. The cost of PV is decreasing fast with ~10%/year but to make...

  13. Atomic Basic Blocks

    Science.gov (United States)

    Scheler, Fabian; Mitzlaff, Martin; Schröder-Preikschat, Wolfgang

    Die Entscheidung, einen zeit- bzw. ereignisgesteuerten Ansatz für ein Echtzeitsystem zu verwenden, ist schwierig und sehr weitreichend. Weitreichend vor allem deshalb, weil diese beiden Ansätze mit äußerst unterschiedlichen Kontrollflussabstraktionen verknüpft sind, die eine spätere Migration zum anderen Paradigma sehr schwer oder gar unmöglich machen. Wir schlagen daher die Verwendung einer Zwischendarstellung vor, die unabhängig von der jeweils verwendeten Kontrollflussabstraktion ist. Für diesen Zweck verwenden wir auf Basisblöcken basierende Atomic Basic Blocks (ABB) und bauen darauf ein Werkzeug, den Real-Time Systems Compiler (RTSC) auf, der die Migration zwischen zeit- und ereignisgesteuerten Systemen unterstützt.

  14. Analytical Crack Model for 2-D Reinforced Concrete Structures

    Institute of Scientific and Technical Information of China (English)

    车铁; 宋玉普

    2002-01-01

    A two-dimensional smeared crack model for reinforced concrete members is presented. Special emphasis is placedon the bond between concrete and reinforcement as the main factor influencing tension stiffening in cracked reinforcedconcrete. With the derived tangential stress-strain equations for concrete in the direction perpendicular to the cracks, theconstitutive relationship for cracked reinforced concrete is established. Experimental specimens have been analyzed withthe analytical model, and the analytical and experimental results are found to be in good agreement.

  15. Analysis of fatigue transverse cracks in turbine shafts

    International Nuclear Information System (INIS)

    During a safety control of the low pressure turbines CP0/CP1 shafts, some transverse cracks have been identified. In a first step, the crack propagation has been studied by the following three actions: improvement of the control methods, material characterization to calculate the crack propagation threshold taking into account the operating conditions, a 3-D numerical analysis of the shaft solicitations with the calculation of KI KII KIII for the crack propagation estimation. (A.L.B.)

  16. A dynamical law for slow crack growth in polycarbonate films

    CERN Document Server

    Cortet, Pierre-Philippe; Ciliberto, Sergio

    2007-01-01

    We study experimentally the slow growth of a single crack in polycarbonate films submitted to uniaxial and constant imposed stress. For this visco-plastic material, we uncover a dynamical law that describes the dependence of the instantaneous crack velocity with experimental parameters. The law involves a Dugdale-Barenblatt static description of crack tip plastic zones associated to an Eyring's law and an empirical dependence with the crack length that may come from a residual elastic field.

  17. Pressure Pulsation Signal Analysis for Centrifugal Compressor Blade Crack Determination

    OpenAIRE

    Hongkun Li; Xuefeng Zhang; Xiaowen Zhang; Shuhua Yang; Fujian Xu

    2014-01-01

    Blade is a key piece of component for centrifugal compressor. But blade crack could usually occur as blade suffers from the effect of centrifugal forces, gas pressure, friction force, and so on. It could lead to blade failure and centrifugal compressor closing down. Therefore, it is important for blade crack early warning. It is difficult to determine blade crack as the information is weak. In this research, a pressure pulsation (PP) sensor installed in vicinity to the crack area is used to d...

  18. A Brief Review on Dynamics of a Cracked Rotor

    OpenAIRE

    Chandan Kumar; Vikas Rastogi

    2009-01-01

    Fatigue crack is an important rotor fault, which can lead to catastrophic failure if undetected properly and in time. Study and Investigation of dynamics of cracked shafts are continuing since last four decades. Some review papers were also published during this period. The aim of this paper is to present a review on recent studies and investigations done on cracked rotor. It is not the intention of the authors to provide all literatures related with the cracked rotor. However, the main empha...

  19. Detection and sizing of underbead cracks using ultrasonic nondestructive examination

    Energy Technology Data Exchange (ETDEWEB)

    Scarbrough, J.D.; Wierzbicki, W.M.

    1982-02-11

    Ultrasonic nondestructive examination (NDE) will detect three mil deep underbead cracks in welds joining thin walled iridium hemishells. A correlation was developed to relate the amplitude of the signal reflected from the crack with crack wall area. The observed cracks occur in the weld underbead in the arc taper area during encapsulation of /sup 238/PuO/sub 2/ pellets for thermoelectric generators used in deep space exploration.

  20. Crack arrest saturation model under combined electrical and mechanical loadings

    OpenAIRE

    R.R. Bhargava; A. Setia

    2009-01-01

    Purpose: The investigation aims at proposing a model for cracked piezoelectric strip which is capable to arrest the crack.Design/methodology/approach: Under the combined effect of electrical and mechanical loadings applied at the edges of the strip, the developed saturation zone is produced at each tip of the crack. To arrest further opening of the crack, the rims of the developed saturation zones are subjected to in-plane cohesive, normal uniform constant saturation point electrical displace...

  1. Fatigue crack Behaviour in a High Strength Tool Steel

    DEFF Research Database (Denmark)

    Højerslev, Christian; Carstensen, Jesper V.; Brøndsted, Povl;

    2002-01-01

    The influence of microstructure on fatigue crack initiation and crack growth of a hardened and tempered high speed steel was investigated. The evolution of fatigue cracks was followed in four point bending at room temperature. It was found that a carbide damage zone exists above a threshold load ...... microns in front of the fatigue crack tip, which is comparable with the relevant mean free carbide spacing....

  2. Crack resistance of austenitic pipes with circumferential through-wall cracks

    International Nuclear Information System (INIS)

    For monotonously increasing load the correct evaluation of the crack resistance properties of a structure is essential for safety analyses. Considerable attention has been given to the through-wall case, since this is generally believed to be the controlling case with regard to complete pipe failure. The maximum load conditions for circumferential crack growth in pipes under displacement-controlled loadings has been determined. The need for crack resistance curves, measured on circumferentially through-wall cracked straight pipes of austenitic stainless steel 316L under bending, is emphasized by the limitation in the data range on small specimens and by the differences in the procedures. To answer open questions and to improve calculational methods a joint fracture mechanics program is being performed by Electricite de France, Novatome and Siemens-Interatom. The working program contains experimental and theoretical investigations on the applicability of small-specimen data to real structures. 10 refs., 10 figs., 4 tabs

  3. Crack Growth Monitoring by Embedded Optical Fibre Bragg Grating Sensors: Fibre Reinforced Plastic Crack Growing Detection

    DEFF Research Database (Denmark)

    Pereira, Gilmar Ferreira; Mikkelsen, Lars Pilgaard; McGugan, Malcolm

    2015-01-01

    caused by the crack, and to correlate with the FBG sensor. A Material-Sensor model was developed in order to predict the sensor output response under a crack/delamination situation, which can be used as an analysis tool for future application of this measurement technology in more complex structures.......This article presents a novel method to asses a crack growing/damage event in fibre reinforced plastic, or adhesive using Fibre Bragg Grating (FBG) sensors embedded in a host material. Different features of the crack mechanism that induce a change in the FBG response were identified. Double...... Cantilever Beams specimens made with glass fibre glued with structural adhesive, were instrumented with an array of FBG sensors embedded in the material and tested using an experimental fracture procedure. A digital image correlation technique was used to determine the presence of the specific phenomena...

  4. On the relative role of processes whose sequence results in crack growth in the cladding of LMFBR fuel pins

    Science.gov (United States)

    Mikhlin, E. Ya.

    1991-08-01

    Processes are discussed the joint effect of which results in crack development in austenitic steel-clad oxide fuel pins. Such processes include generation of Te which is considered as the main embrittling agent, its transport and accumulation at the cladding inner surface, where together with Cs it forms a liquid surface-acting medium, and finally, development of intergranular cracks in the cladding caused by the contact with this medium. As the process of crack growth in itself proceeds faster than accumulation of liquid surfactants at the cladding, the cracks will be able to reach the critical length only after the necessary amount of Te has been accumulated. Its accumulation is determined and therefore, controlled by the process of Te transport in the fuel grains. It is shown that the main contribution to the accumulation of Te at the cladding surface is provided by the hottest internal zones of the fuel pellet. On the basis of the analysis given, means are discussed, for inhibiting or blocking the crack growth.

  5. Influence of mechanical properties induced by hydrogen absorption on the stress corrosion cracking initiation of Zircaloy-4

    International Nuclear Information System (INIS)

    The mechanical properties of Zircaloy-4 alloy having different hydrogen contents comprised between 100 and 350 ppm, established by tensile tests, were correlated with the SCC susceptibility in iodine vapors at 320 deg. C. The maximum values of stress and strain from C-rings, induced by a Zircaloy-4 block of 18 mm length was estimated by means of ANSYS code. Using metallographic method and SEM it was emphasized the transgranular character of SCC cracks. The following conclusions are pointed out: 1. No major difference resulted between the values of yield stress and ultimate tensile stress in samples with hydrogen contents within the range (100-350) ppm; The presence of zirconium hydrides resulted in brittleness of zirconium alloy; 3. In the case of pre-cracked and non-hydrided samples, the applied stress threshold for propagation mechanism of SCC cracks is 300 MPa; in these testing conditions the deformation value is 2.7%; 4. By means of optic and scanning electron microscopy it was emphasized the transgranular character of SCC cracks obtained in the pre-cracked samples tested in these conditions. (authors)

  6. Detection and sizing of stress corrosion cracks in austenitic components using ultrasonic testing and synthetic aperture focusing technique

    Energy Technology Data Exchange (ETDEWEB)

    Dugan, Sandra; Wagner, Sabine [Stuttgart Univ. (Germany). Materialpruefungsanstalt; Dillhoefer, Alexander [NDT Global GmbH and Co.KG, Stutensee (Germany); Rieder, Hans; Spies, Martin [Fraunhofer-Institut fuer Zerstoerungsfreie Pruefverfahren (IZFP), Saarbruecken (Germany)

    2015-05-01

    Flaw detection and sizing using NDT techniques is an important factor for reliably assessing the integrity of components. In the case of dissimilar metal welds and austenitic stainless steel welds, the grain structure of the weld in combination with the elastic anisotropy of the material will present major challenges for UT. A study on austenitic base metal test blocks with artificially grown IGSCCs has shown that the Synthetic Aperture Focusing Technique (SAFT) can improve the signal-to-noise ratio, particularly for crack tip signals. In welded test blocks, the influence of the inhomogeneous, anisotropic weld has to be considered.

  7. Detection and sizing of stress corrosion cracks in austenitic components using ultrasonic testing and synthetic aperture focusing technique

    International Nuclear Information System (INIS)

    Flaw detection and sizing using NDT techniques is an important factor for reliably assessing the integrity of components. In the case of dissimilar metal welds and austenitic stainless steel welds, the grain structure of the weld in combination with the elastic anisotropy of the material will present major challenges for UT. A study on austenitic base metal test blocks with artificially grown IGSCCs has shown that the Synthetic Aperture Focusing Technique (SAFT) can improve the signal-to-noise ratio, particularly for crack tip signals. In welded test blocks, the influence of the inhomogeneous, anisotropic weld has to be considered.

  8. Application of the cracked pipe element to creep crack growth prediction

    Energy Technology Data Exchange (ETDEWEB)

    Brochard, J.; Charras, T.

    1997-04-01

    The modification of a computer code for leak before break analysis is very briefly described. The CASTEM2000 code was developed for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading. The modification extends the capabilities of the cracked pipe element to the determination of fracture parameters under creep conditions (C*, {phi}c and {Delta}c). The model has the advantage of evaluating significant secondary effects, such as those from thermal loading.

  9. On the interaction of ultrasound with cracks: Applications to fatigue crack growth

    Science.gov (United States)

    Buck, O.; Thompson, R. B.; Rehbein, D. K.

    1986-01-01

    Partial contact of two rough fatigue crack surfaces leads to transmission and diffraction of an acoustic signal at those contacts. Recent experimental and theoretical efforts to understand and quantify such contact in greater detail are discussed. The objective is to develop an understanding of the closure phenomenon and its application to the interpretation of fatigue data, in particular the R-ratio, spike overload/underload and threshold effects on crack propagation.

  10. Optimisation of the Crack Pattern in Continuously Reinforced Concrete Pavements

    NARCIS (Netherlands)

    Ren, D.

    2015-01-01

    Recent field investigations on several new Continuously Reinforced Concrete Pavements (CRCP) in Belgium indicate that its crack pattern is characterized by low mean crack spacing along with a high percentage of clusters of closely spaced cracks. Field surveys also indicate that it is difficult to si

  11. Evolving fracture patterns: columnar joints, mud cracks, and polygonal terrain

    CERN Document Server

    Goehring, Lucas

    2012-01-01

    When cracks form in a thin contracting layer, they sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of crack formation, as later cracks tend to intersect with earlier cracks at right angles. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120$^\\circ$. However, hexagonal crack patterns are typically only seen when a crack network opens and heals repeatedly, in a thin layer, or advances by many intermittent steps into a thick layer. Here it is shown how both types of pattern can arise from identical forces, and how a rectilinear crack pattern evolves towards a hexagonal one. Such an evolution is expected when cracks undergo many opening cycles, where the cracks in any cycle are guided by the positions of cracks in the previous cycle, but when they can slightly vary their position, and order of opening. The general features of this evolution are outlined, and compared to a review of the specific p...

  12. Micro-crack detection in high-performance cementitious materials

    DEFF Research Database (Denmark)

    Lura, Pietro; Guang, Ye; Tanaka, Kyoji;

    2005-01-01

    aggregate size. Gallium intrusion of the cracks and subsequent examination by electron probe micro analysis, EPMA, are used to identify the cracks. The gallium intrusion technique allows controllable impregnation of cracks in the cement paste. A distinct contrast between gallium and the surrounding material...

  13. Finite elements simulation of reflective cracking in asphaltic overlays

    NARCIS (Netherlands)

    Scarpas, A.; De Bondt, A.H.

    1996-01-01

    Overlaying is one of the most popular and cost effective techniques of rehabilitation of cracked pavements. The placing of reinforcement between the overlay and the top layer of the cracked pavement is currently being utilised as a possible technique for delaying the development of cracks into the o

  14. Crack path in aeronautical titanium alloy under ultrasonic torsion loading

    Directory of Open Access Journals (Sweden)

    A. Nikitin

    2016-01-01

    Full Text Available This paper discusses features of fatigue crack initiation and growth in aeronautical VT3-1 titanium alloy under pure torsion loading in gigacycle regime. Two materials: extruded and forged VT3-1 titanium alloys were studied. Torsion fatigue tests were performed up to fatigue life of 109 cycles. The results of the torsion tests were compared with previously obtained results under fully reversed axial loading on the same alloys. It has been shown that independently on production process as surface as well subsurface crack initiation may appear under ultrasonic torsion loading despite the maximum stress amplitude located at the specimen surface. In the case of surface crack initiation, a scenario of crack initiation and growth is similar to HCF regime except an additional possibility for internal crack branching. In the case of subsurface crack, the initiation site is located below the specimen surface (about 200 μm and is not clearly related to any material flaw. Internal crack initiation is produced by shear stress in maximum shear plane and early crack growth is in Mode II. Crack branching is limited in the case of internal crack initiation compared to surface one. A typical ‘fish-eye’ crack can be observed at the torsion fracture surface, but mechanism of crack initiation seems not to be the same than under axial fatigue loading.

  15. Fretting fatigue crack propagation rate under variable loading conditions

    Directory of Open Access Journals (Sweden)

    C. Gandiolle

    2016-01-01

    Full Text Available Fretting fatigue experiments aim to represent industrial problems and most of them endure variable loading. Being able to assess lifetime of assemblies, especially for low propagation rate conditions, is essential as experimental validation is often too expensive. Both experimental and numerical approaches are proposed to follow the crack propagation rate of steel on steel cylinder/plane fretting fatigue contact submitted to variable loading conditions. An original experimental monitoring has been implemented on the fretting-fatigue test device to observe crack propagation using a potential drop technique. A calibration curve relating crack length and electrical potential was established for the studied contact. It allows direct knowledge of the crack length and crack propagation rate. It was applied to mixed load test showing crack arrest for the last loading condition. To explain this behavior, a 2-dimensional FE modeling was implemented to simulate the complexes multi-axial contact stressing. The crack propagation rate was formalized using an effective stress intensity factor amplitude ΔKeff coupled with Paris law of the material. The crack arrest condition for a given loading was related to ΔKeff along the expected crack path crossing the material crack arrest threshold ΔK0. The failure was related to ΔKeff reaching the critical stress intensity factor KIC. A good correlation with experiments was observed allowing to predict the crack arrest condition although the model tends to overestimate the final crack length extension.

  16. Studies of Hot Crack Properties of Laser Welded Stainless Steel

    DEFF Research Database (Denmark)

    Juhl, Thomas Winther

    to the crack behaviour, but do not show an expected correlation between the crack resistance and the solidification rate. The employment of pulsed seams is therefore assessed not to be usable in the present selection methods. From evaluation of several crack tests, the Weeter spot weld test has been chosen...

  17. A new NDT-method for crack detection

    International Nuclear Information System (INIS)

    A new NDT-system has been developed to find cracks during the production steps, the test method indicates the cracks immediately, the method will be described also the surface condition and the crack sizes, examples from practice will be explained and illustrated by slides. (orig.)

  18. Catalytic oxidative cracking of hexane as a route to olefins

    NARCIS (Netherlands)

    Boyadjian, Cassia; Lefferts, Leon; Seshan, K.

    2010-01-01

    Catalytic oxidative cracking of naphtha is conceptually an alternative process to steam cracking. The performance of sol–gel synthesized Li/MgO in oxidative cracking of hexane as a model compound of naphtha, has been studied and compared to that of conventionally prepared catalyst. At a temperature

  19. Research on pavement crack recognition methods based on image processing

    Science.gov (United States)

    Cai, Yingchun; Zhang, Yamin

    2011-06-01

    In order to overview and analysis briefly pavement crack recognition methods , then find the current existing problems in pavement crack image processing, the popular methods of crack image processing such as neural network method, morphology method, fuzzy logic method and traditional image processing .etc. are discussed, and some effective solutions to those problems are presented.

  20. Special samples for investigation into kinetics of blind fatigue cracks

    International Nuclear Information System (INIS)

    Samples designed for investigation into kinetics of elliptic and semi-elliptic fatigue cracks in construction large-size elements and for evaluation of structural material resistance to fracture are developed. Data on form changing of blind fatigue cracks in vessel steel 15KH2MFA are obtained; it is shown, that material anisotropy and load kind affect essentially blind fatigue crack forms

  1. Interpreting load ratio dependence of near-threshold fatigue crack growth by a new crack closure model

    International Nuclear Information System (INIS)

    It was still short of generalized fatigue crack growth (FCG) models in the near-threshold regime due to its complex influencing factors. The near-threshold FCG behaviour of a rotor steel 25Cr2Ni2MoV at different load ratios was investigated experimentally, and the FCG driving mechanism was theoretically analysed based on equivalent driving force model. It was found that the crack growth process was determined by combined effects of equivalent driving force at constant amplitude loading and crack closure. A new crack closure model was proposed by considering the influences of load ratio and FCG rate, which could successfully interpret the effect of load ratio on FCG. The correlation of the crack closure model with the transition of driving forces in crack advance was beneficial to unify crack closure theory and crack growth driving parameters in the near-threshold regime

  2. The Block-block Bootstrap: Improved Asymptotic Refinements

    OpenAIRE

    Donald W.K. Andrews

    2002-01-01

    The asymptotic refinements attributable to the block bootstrap for time series are not as large as those of the nonparametric iid bootstrap or the parametric bootstrap. One reason is that the independence between the blocks in the block bootstrap sample does not mimic the dependence structure of the original sample. This is the join-point problem. In this paper, we propose a method of solving this problem. The idea is not to alter the block bootstrap. Instead, we alter the original sample sta...

  3. Convergence rates of empirical block length selectors for block bootstrap

    OpenAIRE

    Nordman, Daniel J.; Lahiri, Soumendra N.

    2014-01-01

    We investigate the accuracy of two general non-parametric methods for estimating optimal block lengths for block bootstraps with time series – the first proposed in the seminal paper of Hall, Horowitz and Jing (Biometrika 82 (1995) 561–574) and the second from Lahiri et al. (Stat. Methodol. 4 (2007) 292–321). The relative performances of these general methods have been unknown and, to provide a comparison, we focus on rates of convergence for these block length selectors for the moving block ...

  4. CRACK2 - Modelling calcium carbonate deposition from bicarbonate solution in cracks in concrete

    Energy Technology Data Exchange (ETDEWEB)

    Brodersen, K

    2003-03-01

    The numerical CRACK2 model simulates precipitation of calcite from calcium bicarbonate solution (e.g. groundwater) passing through cracks in concrete or other cementitious materials. A summary of experimental work is followed by a detailed description of the model. Hydroxyl ions are transported by diffusion in pore systems in columns of cementitious materials. The hydroxyl is precipitating calcite from a flow of bicarbonate solution in a crack connecting the ends of a row of such columns. The cementitious material is simulated as calcium hydroxide mixed with inert material but with sodium hydroxide dissolved in the pore solution. Diffusive migration of cesium as radioactive isotope is also considered. Electrical interaction of the migrating ions is taken into account. Example calculations demonstrate effects of parameter variations on distribution of precipitated calcite in the crack and on the composition of the outflowing solution, which can be compared directly with experimental results. Leaching behavior of sodium can be used to tune the model to experimental observations. The calcite is mostly precipitated on top of the original crack surface and may under certain circumstances fill the crack. The produced thin layers of low porosity calcite act as a diffusion barrier limiting contact between cement and solution. Pore closure mechanisms in such layers are discussed. Implications for safety assessment of radioactive waste disposal are shortly mentioned. The model is also relevant for conventional uses of concrete. (au)

  5. Delamination effects on cracked steel members reinforced by prestressed composite patch

    OpenAIRE

    Colombi, P.; Bassetti, A.; Nussbaumer, A

    2002-01-01

    Prestressed composite patch bonded on cracked steel section is a promising technique to reinforce cracked details or to prevent fatigue cracking on steel structural elements. It introduces compressive stresses that produce crack closure effect. Moreover, it modifies the crack geometry by bridging the crack lips and reduces the stress range at crack tip. Fatigue tests were performed on notched steel plate reinforced by CFRP strips as a step toward the validation of crack patching for fatigue l...

  6. Results of crack-arrest tests on irradiated a 508 class 3 steel

    Energy Technology Data Exchange (ETDEWEB)

    Iskander, S.K.; Milella, P.P.; Pini, M.A.

    1998-02-01

    Ten crack-arrest toughness values for irradiated specimens of A 508 class 3 forging steel have been obtained. The tests were performed according to the American Society for Testing and Materials (ASTM) Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, K{sub la} of Ferritic Steels, E 1221-88. None of these values are strictly valid in all five ASTM E 1221-88 validity criteria. However, they are useful when compared to unirradiated crack-arrest specimen toughness values since they show the small (averaging approximately 10{degrees}C) shifts in the mean and lower-bound crack-arrest toughness curves. This confirms that a low copper content in ASTM A 508 class 3 forging material can be expected to result in small shifts of the transition toughness curve. The shifts due to neutron irradiation of the lower bound and mean toughness curves are approximately the same as the Charpy V-notch (CVN) 41-J temperature shift. The nine crack-arrest specimens were irradiated at temperatures varying from 243 to 280{degrees}C, and to a fluence varying from 1.7 to 2.7 x 10{sup 19} neutrons/cm{sup 2} (> 1 MeV). The test results were normalized to reference values that correspond to those of CVN specimens irradiated at 284{degrees}C to a fluence of 3.2 x 10{sup 19} neutrons/cm{sup 2} (> 1 MeV) in the same capsule as the crack-arrest specimens. This adjustment resulted in a shift to lower temperatures of all the data, and in particular moved two data points that appeared to lie close to or lower than the American Society of Mechanical Engineers K{sub la} curve to positions that seemed more reasonable with respect to the remaining data. A special fixture was designed, fabricated, and successfully used in the testing. For reasons explained in the text, special blocks to receive the Oak Ridge National Laboratory clip gage were designed, and greater-than-standard crack-mouth opening displacements measured were accounted for. 24 refs., 13 figs., 12 tabs.

  7. Effect of three dimensional stress state on unstable fracture condition and crack opening level in a new crack growth model

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A new model for the analysis of fatigue crack growth in the metal structures was proposed.This model shows a promising capability of explaining various fatigue phenomena.The new crack growth model is further completed by a continuous empirical formula for estimating the value of variable fracture toughness during crack propagation and a modified continuous equation for the crack tip stress/strain constraint factor used to calculate the stress intensity factor at the opening level.The prediction results are ...

  8. Large Block Test Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Lin, W

    2001-12-01

    This report documents the Large-Block Test (LBT) conducted at Fran Ridge near Yucca Mountain, Nevada. The LBT was a thermal test conducted on an exposed block of middle non-lithophysal Topopah Spring tuff (Tptpmn) and was designed to assist in understanding the thermal-hydrological-mechanical-chemical (THMC) processes associated with heating and then cooling a partially saturated fractured rock mass. The LBT was unique in that it was a large (3 x 3 x 4.5 m) block with top and sides exposed. Because the block was exposed at the surface, boundary conditions on five of the six sides of the block were relatively well known and controlled, making this test both easier to model and easier to monitor. This report presents a detailed description of the test as well as analyses of the data and conclusions drawn from the test. The rock block that was tested during the LBT was exposed by excavation and removal of the surrounding rock. The block was characterized and instrumented, and the sides were sealed and insulated to inhibit moisture and heat loss. Temperature on the top of the block was also controlled. The block was heated for 13 months, during which time temperature, moisture distribution, and deformation were monitored. After the test was completed and the block cooled down, a series of boreholes were drilled, and one of the heater holes was over-cored to collect samples for post-test characterization of mineralogy and mechanical properties. Section 2 provides background on the test. Section 3 lists the test objectives and describes the block site, the site configuration, and measurements made during the test. Section 3 also presents a chronology of events associated with the LBT, characterization of the block, and the pre-heat analyses of the test. Section 4 describes the fracture network contained in the block. Section 5 describes the heating/cooling system used to control the temperature in the block and presents the thermal history of the block during the test

  9. Analysis of fatigue crack growth from countersunk fastener hole

    Science.gov (United States)

    Suh, Jungjun

    This research dealt with fatigue cracks that form at countersunk open holes and mainly focused on obtaining stress intensity factor solutions for countersunk holes employing both experimental and computational approaches. Cracks developing from countersunk holes are an extremely important issue for ensuring the structural integrity of many types of aircraft components, and are crucial to aircraft safety. Four different crack shapes (single knee crack, single corner crack, two non-symmetric knee cracks and two non-symmetric corner cracks) were studied in this research. The locations of the cracks were chosen to represent the previous numerical and experimental study by C. Y. Park. A stress ratio (R = sigmamin/sigmamax), 0.3 was used for all the specimens tested to minimize the crack closure effect. The use of transparent PMMA polymer specimens allowed for direct observation of changes in crack size and shape. The stress intensity factor ranges along the crack front were determined using the back calculation method proposed by James and Anderson. Then, the stress intensity factor ranges were normalized as geometric factors to obtain non-dimensional stress intensity factors. The geometric factors for a total of 36 crack fronts are determined for the single crack experiments, and the geometric factors for a total of 76 crack fronts are obtained for the two non-symmetric experiments. The geometric factors obtained in this research can apply to structural metals since the geometric factors only depend on crack geometry and not on material properties. One of the objectives of this research was to assess the validity of finite element predictions of stress intensity factors. Thus, computational approach was conducted with StressCheck. Generally, StressCheck results agree reasonably well with the experimental results. The average percent differences in geometric factor are within 9.1% compared to the experimental results.

  10. Covariant Approaches to Superconformal Blocks

    CERN Document Server

    Fitzpatrick, A Liam; Khandker, Zuhair U; Li, Daliang; Poland, David; Simmons-Duffin, David

    2014-01-01

    We develop techniques for computing superconformal blocks in 4d superconformal field theories. First we study the super-Casimir differential equation, deriving simple new expressions for superconformal blocks for 4-point functions containing chiral operators in theories with N-extended supersymmetry. We also reproduce these results by extending the "shadow formalism" of Ferrara, Gatto, Grillo, and Parisi to supersymmetric theories, where superconformal blocks can be represented as superspace integrals of three-point functions multiplied by shadow three-point functions.

  11. Dimensional Reduction for Conformal Blocks

    CERN Document Server

    Hogervorst, Matthijs

    2016-01-01

    We consider the dimensional reduction of a CFT, breaking multiplets of the d-dimensional conformal group SO(d+1,1) up into multiplets of SO(d,1). This leads to an expansion of d-dimensional conformal blocks in terms of blocks in d-1 dimensions. In particular, we obtain a formula for 3d conformal blocks as an infinite sum over 2F1 hypergeometric functions with closed-form coefficients.

  12. Repair welding of cracked steam turbine blades

    International Nuclear Information System (INIS)

    The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER316L austenitic stainless steel filler wire and ER410 martensitic stainless steel filler wire. The repair welding procedure with austenitic filler wire was developed to avoid preheating of the blade as also hydrogen induced cold cracking, and involved evaluation of three different austenitic filler wires, viz. ER309L, ER316L and ERNiCr-3. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microstructural examination. After various trials using different procedures, the procedure of local PWHT using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld, was found to give the most satisfactory results. A similar procedure was used for preheating while using ER410 filler metal. Mechanical testing of weldments before and after PWHT involved tensile tests at room temperature, face and root bend tests, and microhardness measurements across the fusion line and heat affected zone. During procedure qualification, mock-ups and actual repair welding, dye penetrant testing was used at different stages and where ever possible radiography was carried out. These procedures were developed for repair welding of cracked blades in the low-pressure (LP) steam turbines of Indian nuclear power plants. The procedure with ER316 L filler wire has so far been applied for repair welding of 2 cracked blades (made of AISI 410 SS) of LP steam turbines, while the procedure

  13. Repair welding of cracked steam turbine blades

    Energy Technology Data Exchange (ETDEWEB)

    Bhaduri, A.K.; Gill, T.P.S.; Albert, S.K.; Shanmugam, K.; Iyer, D.R. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India)]|[Nuclear Power Corp., Mumbai (India)

    1999-07-01

    The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER316L austenitic stainless steel filler wire and ER410 martensitic stainless steel filler wire. The repair welding procedure with austenitic filler wire was developed to avoid preheating of the blade as also hydrogen induced cold cracking, and involved evaluation of three different austenitic filler wires, viz. ER309L, ER316L and ERNiCr-3. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microstructural examination. After various trials using different procedures, the procedure of local PWHT using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld, was found to give the most satisfactory results. A similar procedure was used for preheating while using ER410 filler metal. Mechanical testing of weldments before and after PWHT involved tensile tests at room temperature, face and root bend tests, and microhardness measurements across the fusion line and heat affected zone. During procedure qualification, mock-ups and actual repair welding, dye penetrant testing was used at different stages and where ever possible radiography was carried out. These procedures were developed for repair welding of cracked blades in the low-pressure (LP) steam turbines of Indian nuclear power plants. The procedure with ER316 L filler wire has so far been applied for repair welding of 2 cracked blades (made of AISI 410 SS) of LP steam turbines, while the procedure

  14. Cracking phenomena in lithium-di-silicate glass ceramics

    Indian Academy of Sciences (India)

    Rajat Banerjee

    2001-04-01

    Lithium-di-silicate glass ceramic (Li2O, SiO2) with uniformly oriented crystals was placed on a Vickers indentation with extrusion axis horizontally parallel to the base axis. The material was rotated through 0°– 90° and at each angle a 20 N load was applied to ascertain the crack path. It was observed that the crack length decreases and the crack deviates from its original path with increasing angle. The deviation of the crack was correlated with the component of the crack driving force and the theoretical strength of the aligned crystals at different angles.

  15. Limit load of cylinder with twin surface cracks under tension

    International Nuclear Information System (INIS)

    The influence of interaction between two surface cracks on the limit load (LL) was examined by finite element analysis. The circumferential surface cracks were assumed to be on the straight pipe that was subjected to uniform tensile load. Changes in the LL due to relative spacing and shape of crack were evaluated. The LL was equivalent to coalesced crack when the cracks were on the same plane or their offset and horizontal distance were the same, although it decreased as offset distance increased in the other cases. Based on the analysis results, an outline of the assessment criterion for evaluating the influence of the interaction was discussed. (author)

  16. Simulation of Interfacial Corner Cracks in Bimaterial Systems

    DEFF Research Database (Denmark)

    Veluri, Badrinath; Jensen, Henrik Myhre

    2012-01-01

    . The crack propagation is investigated by estimating the fracture mechanics parameters that include the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the crack front. A numerical approach is then applied for coupling the far field solutions utilizing...... the capability of the Finite Element Method to the near field (crack tip) solutions based on the J-integral. The developed two-dimensional numerical approach for the calculation of fracture mechanical properties has been validated with three-dimensional models for varying crack front shapes. In this study...

  17. Fatigue crack growth retardation in spot heated mild steel sheet

    Indian Academy of Sciences (India)

    B B Verma; P K Ray

    2002-08-01

    A fatigue crack can be effectively retarded by heating a spot near the crack tip under nil remote stress condition. The subcritical spot heating at a proper position modifies the crack growth behaviour in a way, more or less, similar to specimen subjected to overload spike. It is observed that the extent of crack growth retardation increases with increasing level of overload as well as with increasing spot temperature. It is also observed that modification in crack growth behaviour is a function of location of heating spot and maximum retardation is observed at + 5 position.

  18. Adductor Canal Block versus Femoral Nerve Block and Quadriceps Strength

    DEFF Research Database (Denmark)

    Jæger, Pia Therese; Nielsen, Zbigniew Jerzy Koscielniak; Henningsen, Lene Marianne;

    2013-01-01

    : The authors hypothesized that the adductor canal block (ACB), a predominant sensory blockade, reduces quadriceps strength compared with placebo (primary endpoint, area under the curve, 0.5-6 h), but less than the femoral nerve block (FNB; secondary endpoint). Other secondary endpoints were...

  19. Fracture mechanics parameters for cracks on a slightly undulating interface

    Science.gov (United States)

    Yang, Lin; Qu, Jianmin

    1993-11-01

    Typical bimaterial interfaces are nonplanar due to surface facets or roughness. Crack-tip stress fields of an interface crack must be influenced by nonplanarity of the interface. Consequently, interface toughness is affected. The crack-tip fields of a finite crack on an elastic/rigid interface with periodic undulation are studied. Particular emphasis is given to the fracture mechanics parameters, such as the stress intensity factors, crack-tip energy release rate, and crack-tip mode mixity. When the amplitude of interface undulation is very small relative to the crack length (which is the case for rough interfaces), asymptotic analysis is used to convert the nonplanarity effects into distributed dislocations located on the planar interface. Then, the resulting stress fields near the crack tip are obtained by using the Fourier integral transform method. It is found that the stress fields at the crack tip are strongly influenced by nonplanarity of the interface. Generally speaking, nonplanarity of the interface tends to shield the crack tip by reducing the crack-tip stress concentration.

  20. Detection of subcritical crack propagation for concrete dams

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Subcritical propagation of cracks is a warning sign of fracture.If such propagation is detected at an early stage,timely maintenance measures can be taken to prevent the failure of structures.To detect the subcritical propagation of a crack,the crack needs to be monitored continuously in a long term, which is not realistic under certain conditions.However,cracks in concrete dams can be monitored continuously by dam monitoring to offer possible detection for subcritical propagation.In this paper, with measured crack openings from dam monitoring,a state equation for characterizing crack development is established based on the grey system theory.The relation between the stability of the equation and the subcritical crack propagation is investigated,then a criterion is proposed for detecting subcritical propagation.An example demonstrates the validity of the criterion and its potential for practical application.

  1. Failure study of a cracked speed boat steering wheel

    Directory of Open Access Journals (Sweden)

    Goran Vukelic

    2015-10-01

    Full Text Available Failure of a cracked steering wheel is studied in this paper. Steering wheel, mounted on a speed boat, had cracks emanating from one of the fastener holes until final fracture occurred. Failure analysis, combining experimental and numerical techniques, was performed. Experimentally, fasteners torque moments were measured, visual inspection performed and material type determined (aluminum alloy AA 6061. Additionally, scanning electron microscopy examination was employed to characterize the microstructure of the fractured surface. Using finite element analysis, stress analysis of a cracked steering wheel was conducted. Stress intensities of uncracked and cracked steering wheel were compared to find out about stress concentration points. Possible causes of crack occurrence include excessive fastener torque moment, fretting between fastener and hole combined with poor machining that left marks that serve as potential crack initiation points. Obtained results are valuable for predicting fracture behavior of the cracked steering wheel and can be taken as a reference for design and exploitation process of such component.

  2. Theoretical and numerical studies on morphological transitions in crack growth

    CERN Document Server

    Mühle, V

    1999-01-01

    This paper investigates the formation of crack patterns in stationary and transient temperature fields analytically with linear elastic fracture mechanics and numerically with the finite elements method (FEM). In particular, we consider the experimental situation of a narrow thin strip of hot glass slowly lowered into cold water, with temperature difference and velocity as variable parameters. The parameter regions of no crack, one straight crack and one oscillating crack are determined. The type of phase transition related to the borderline between straight and oscillating crack is characterized. The theoretical results are compared with those of other Similar investigations and comparisons are done for the propagation of multiple cracks. Quenching of a wide thin strip leads to a hierarchy of cracks whose scaling properties are analyzed. Without any fitting, theory and experiment agree surprisingly well.

  3. Development of a Distributed Crack Sensor Using Coaxial Cable

    Science.gov (United States)

    Zhou, Zhi; Jiao, Tong; Zhao, Peng; Liu, Jia; Xiao, Hai

    2016-01-01

    Cracks, the important factor of structure failure, reflect structural damage directly. Thus, it is significant to realize distributed, real-time crack monitoring. To overcome the shortages of traditional crack detectors, such as the inconvenience of installation, vulnerability, and low measurement range, etc., an improved topology-based cable sensor with a shallow helical groove on the outside surface of a coaxial cable is proposed in this paper. The sensing mechanism, fabrication method, and performances are investigated both numerically and experimentally. Crack monitoring experiments of the reinforced beams are also presented in this paper, illustrating the utility of this sensor in practical applications. These studies show that the sensor can identify a minimum crack width of 0.02 mm and can measure multiple cracks with a spatial resolution of 3 mm. In addition, it is also proved that the sensor performs well to detect the initiation and development of cracks until structure failure. PMID:27483280

  4. Near tip strain evolution of a growing fatigue crack

    Directory of Open Access Journals (Sweden)

    M.-L. Zhu

    2015-07-01

    Full Text Available Near tip full-field strains in a growing fatigue crack have been studied in situ using the Digital Image Correlation (DIC technique in a compact tension specimen of stainless steel 316L under tension-tension cyclic loading. An error analysis of displacements and strains has been carried out, and the results show that the precision of displacements and strains in the wake of the crack is worse than that in front of the crack. A method for the determination of crack tip location is proposed for the DIC analysis. Strain ratchetting is observed ahead of the growing fatigue crack tip and found to be dependent on the distance to the crack tip; whilst normal strains appear to stabilise behind the crack tip.

  5. Soil cracking modelling using the mesh-free SPH method

    CERN Document Server

    Bui, H H; Kodikara, J; Sanchez, M

    2015-01-01

    The presence of desiccation cracks in soils can significantly alter their mechanical and hydrological properties. In many circumstances, desiccation cracking in soils can cause significant damage to earthen or soil supported structures. For example, desiccation cracks can act as the preference path way for water flow, which can facilitate seepage flow causing internal erosion inside earth structures. Desiccation cracks can also trigger slope failures and landslides. Therefore, developing a computational procedure to predict desiccation cracking behaviour in soils is vital for dealing with key issues relevant to a range of applications in geotechnical and geo-environment engineering. In this paper, the smoothed particle hydrodynamics (SPH) method will be extended for the first time to simulate shrinkage-induced soil cracking. The main objective of this work is to examine the performance of the proposed numerical approach in simulating the strong discontinuity in material behaviour and to learn about the crack ...

  6. Experimental and theoretical strain distributions for stationary and growing cracks

    Science.gov (United States)

    Gerberich, W. W.; Davidson, D. L.; Kaczorowski, M.

    E XPERIMENTAL strain distributions are determined very near the crack tip in Fe-3wt.%Si single crystals. Both in situ stereoimaging and electron channeling techniques give reasonably reproducible distributions. By growing fatigue cracks on a {100} cleavage plane, the singularity strengths have been determined for both growing and stationary cracks under relatively plane stress and plane strain conditions. This has allowed a comparison to existing theoretical models. It is shown that the HRR singularity (Hutchinson, Rice and Rosengren, 1968) for stationary cracks is very good to within I μm of the crack tip and a hardening model for the growing crack (gao and hwang, Advances in Fracture Research, edited by D. Francois. 5th Int. Conf. on Fracture, Cannes, France, 2, 669, 1981) is surprisingly good. Other issues such as fracture criteria are discussed since strains greater than unity were measured at the crack tip in this relatively brittle material.

  7. ANALYSIS ON ACOUSTICAL SCATTERING BY A CRACKED ELASTIC STRUCTURE

    Institute of Scientific and Technical Information of China (English)

    ZhongWeffang; WuYongdong; WuGuorong; LiangYide

    2003-01-01

    The acoustical scattering by a cracked elastic structure is studied. The mixed method of boundary element and fractal finite element is adopted to solve the cracked structure-acoustic coupling problem. The fractal two-level finite element method is employed for the cracked structure, which can reduce the degree of freedoms (DOFs) greatly, and the boundary element method is used for the exterior acoustic field which can automatically satisfy Sommerfeld's radiation condition. Numerical examples show that the resonance frequency is lower with the crack's depth increase, and that the effect on the acoustical field by the crack is particularly pronounced in the vicinity of the crack tip. This mixed method of boundary element and finite element is effective in solving the scattering problem by a cracked structure.

  8. Development of a Distributed Crack Sensor Using Coaxial Cable.

    Science.gov (United States)

    Zhou, Zhi; Jiao, Tong; Zhao, Peng; Liu, Jia; Xiao, Hai

    2016-01-01

    Cracks, the important factor of structure failure, reflect structural damage directly. Thus, it is significant to realize distributed, real-time crack monitoring. To overcome the shortages of traditional crack detectors, such as the inconvenience of installation, vulnerability, and low measurement range, etc., an improved topology-based cable sensor with a shallow helical groove on the outside surface of a coaxial cable is proposed in this paper. The sensing mechanism, fabrication method, and performances are investigated both numerically and experimentally. Crack monitoring experiments of the reinforced beams are also presented in this paper, illustrating the utility of this sensor in practical applications. These studies show that the sensor can identify a minimum crack width of 0.02 mm and can measure multiple cracks with a spatial resolution of 3 mm. In addition, it is also proved that the sensor performs well to detect the initiation and development of cracks until structure failure.

  9. Detection of subcritical crack propagation for concrete dams

    Institute of Scientific and Technical Information of China (English)

    BAO TengFei; YU Hong

    2009-01-01

    Subcritical propagation of cracks is a warning sign of fracture.If such propagation is detected at an early stage,timely maintenance measures can be taken to prevent the failure of structures.To detect the subcritical propagation of a crack,the crack needs to be monitored continuously in a long term,which is not realistic under certain conditions.However,cracks in concrete dams can be monitored continuously by dam monitoring to offer possible detection for subcritical propagation.In this paper,with measured crack openings from dam monitoring,a state equation for characterizing crack development is established based on the grey system theory.The relation between the stability of the equation and the subcritical crack propagation is investigated,then a criterion is proposed for detecting subcritical propagation.An example demonstrates the validity of the criterion and its potential for practical application.

  10. Characterization of mixed mode crack opening in concrete

    DEFF Research Database (Denmark)

    Jacobsen, Jonas Sejersbøl; Poulsen, Peter Noe; Olesen, John Forbes

    2012-01-01

    In real concrete structures cracks often open in mixed mode after their initiation. To capture the direct material behavior of a mixed mode crack opening a stiff biaxial testing machine, capable of imposing both normal and shear loads on a given crack area, has been applied. The opening and sliding...... components of the mixed mode displacement are measured using a custom made orthogonal gauge, and the measurements are used directly as the closed loop control signals. A double notch, concrete specimen is used for the crack investigation. The tests are divided into two steps, a pure Mode I opening step...... by material aspects such as the aggregate size and concrete strength. Despite the occurrence of a few, local, secondary cracks during the mixed mode crack opening, the results can be treated as the mixed mode material point behavior of a crack in concrete. Results are reported for a range of mixed mode angles...

  11. Metallurgical evaluation of stress corrosion cracking in large diameter piping

    International Nuclear Information System (INIS)

    Ultrasonic testing (UT) of stainless-steel piping in the primary coolant water system of Savannah River Site (SRS) reactors indicates the presence of short, partly through-wall stress corrosion cracks in the heat-affected zone of approximately 7% of the circumferential pipe welds. These cracks are thought to develop by intergranular nucleation and mixed mode propagation. Metallographic evaluations have confirmed the UT indications of crack size and provided evidence that crack growth involved the accumulation of chloride ions inside the growing crack. It is postulated that the development of an oxygen depletion cell inside the crack results in the migration of chloride ions to the crack tip to balance the accumulation of positively charged metallic ions. The results of this metallurgical evaluation, combined with structural assessments of system integrity, support the existence of leak-before-break conditions in the SRS reactor piping system

  12. FEM Modeling of Crack Propagation in a Model Multiphase Alloy

    Institute of Scientific and Technical Information of China (English)

    Lihe QIAN; Seishi NISHIDO; Hiroyuki TODA; Tosliro KOBAYASHI

    2006-01-01

    In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region Jintegral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized dendritic two-phase Al-7%Si alloy was modeled using an elastic-plastic finite element method. The variation of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of α-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.

  13. Analysis of WWER 1000 collector cracking mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Matocha, K.; Wozniak, J. [Vitkovice J.S.C., Ostrava (Switzerland)

    1997-12-31

    The presentation reviews the large experimental program, started in 1993 in Vitkovice, where the main aim was: (1) a detailed study of strain and thermal ageing, dissolved oxygen content and temperature on subcritical crack growth in 10NiMo8.5 (10GN2MFA) steel, (2) a detailed study of the effect of high temperature water and tube expansion technology on fracture behaviour of ligaments between holes for heat exchange tubes, and (3) a detailed study of the effect of drilling, tube expansion technology and heat treatment on residual stresses on the surface of holes for heat exchange tubes. The aim of all these investigations was to find a dominant damage mechanism responsible for collector cracking to be able to judge the efficiency of implemented modifications and suggested countermeasures and to answer a very important question whether proper operation conditions (mainly water chemistry) make the operation of steam generators made in Vitcovice safe throughout the planned lifetime. 10 refs.

  14. Subcritical crack growth in fibrous materials

    CERN Document Server

    Santucci, Stéphane; Deschanel, Stéphanie; Vanel, Loic; Ciliberto, Sergio

    2006-01-01

    We present experiments on the slow growth of a single crack in a fax paper sheet submitted to a constant force $F$. We find that statistically averaged crack growth curves can be described by only two parameters : the mean rupture time $\\tau$ and a characteristic growth length $\\zeta$. We propose a model based on a thermally activated rupture process that takes into account the microstructure of cellulose fibers. The model is able to reproduce the shape of the growth curve, the dependence of $\\zeta$ on $F$ as well as the effect of temperature on the rupture time $\\tau$. We find that the length scale at which rupture occurs in this model is consistently close to the diameter of cellulose microfibrils.

  15. Mitigation strategies for autogenous shrinkage cracking

    DEFF Research Database (Denmark)

    Bentz, Dale P.; Jensen, Ole Mejlhede

    2004-01-01

    of the cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of "water-entrained" concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field......As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper......, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore...

  16. Circumferential cracking of steam generator tubes

    Energy Technology Data Exchange (ETDEWEB)

    Karwoski, K.J.

    1997-04-01

    On April 28, 1995, the U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 95-03, {open_quote}Circumferential Cracking of Steam Generator Tubes.{close_quote} GL 95-03 was issued to obtain information needed to verify licensee compliance with existing regulatory requirements regarding the integrity of steam generator tubes in domestic pressurized-water reactors (PWRs). This report briefly describes the design and function of domestic steam generators and summarizes the staff`s assessment of the responses to GL 95-03. The report concludes with several observations related to steam generator operating experience. This report is intended to be representative of significant operating experience pertaining to circumferential cracking of steam generator tubes from April 1995 through December 1996. Operating experience prior to April 1995 is discussed throughout the report, as necessary, for completeness.

  17. SCREENING TESTS FOR IMPROVED METHANE CRACKING MATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    Klein, J; Jeffrey Holder, J

    2007-07-16

    Bench scale (1 to 6 gram) methane cracking tests have been performed on a variety of pure elements, some alloys, and SAES{reg_sign} commercial getters St 101, St 198, St 707, St 737, and St 909 to determine methane cracking performance (MCP) of 5% methane in a helium carrier at 700 C, 101.3 kPa (760 torr) with a 10 sccm feed. The MCP was almost absent from some materials tested while others showed varying degrees of MCP. Re, Cr, V, Gd, and Mo powders had good MCP, but limited capacities. Nickel supported on kieselguhr (Ni/k), a Zr-Ni alloy, and the SAES{reg_sign} getters had good MCP in a helium carrier. The MCP of these same materials was suppressed in a hydrogen carrier stream and the MCP of the Zr-based materials was reduced by nitride formation when tested with a nitrogen carrier gas.

  18. International Conference on Dynamic Crack Propagation

    CERN Document Server

    1973-01-01

    The planning meeting for a conference on Dynamic Crack Propagation was held at M.LT. in February 1971 and attended by research workers from several industrial, governmental and academic organizations. It was felt that a more specialized meeting would provide a better opportunity for both U.S. and foreign researchers to exchange their ideas and views on dynamic fracture, a subject which is seldom emphasized in national or international fracture conferences. Dynamic crack propagation has been a concern to specialists in many fields: continuum mechanics, metallurgy, geology, polymer chemistry, orthopedics, applied mathematics, as well as structural design and testing. It impinges on a wide variety of problems such as rock breaking and earthquakes, pressure vessels and line pipes, comminution and the per­ formance of armament and ordnance, etc. Advances have been numerous, covering theories and experiments from both the microscopic and macro­ scopic points of view. Hence, the need for comparing the theoretical ...

  19. Stress-corrosion cracking of titanium alloys.

    Science.gov (United States)

    Blackburn, M. J.; Feeney, J. A.; Beck, T. R.

    1973-01-01

    In the light of research material published up to May 1970, the current understanding of the experimental variables involved in the stress-corrosion cracking (SCC) behavior of titanium and its alloys is reviewed. Following a brief summary of the metallurgy and electrochemistry of titanium alloys, the mechanical, electrochemical, and metallurgical parameters influencing SCC behavior are explored with emphasis on crack growth kinetics. Macro- and microfeatures of fractures are examined, and it is shown that many transgranular SCC failures exhibit morphological and crystallographic features similar to mechanical cleavage failures. Current SCC models are reviewed with respect to their ability to explain the observed SCC behavior of titanium and its alloys. Possible methods for eliminating or minimizing stress corrosion hazards in titanium or titanium alloy components are described.

  20. Durability of cracked fibre reinforced concrete structures

    DEFF Research Database (Denmark)

    Hansen, Ernst Jan De Place

    1998-01-01

    and the pore structure.Mechanical load is obtained by exposing beams to 4-point bending until a predefined crack width is reached. A test arrangement is developed. The surface crack pattern is characterized using video-scanning and digital image analysis. As environmental load, exposure to 1) a concentrated...... chloride solution or 2) water (capillary suction) is used. Penetration of chlorides will be characterized qualitatively (Color-test) as well as quantitatively (Rapid Chloride Test from Germann).Additional durability tests (freeze-thaw, water vapour diffusion, chloride permeability) and studies of pore...... structure are made on specimens drilled or sawed from beams after unloading (mechanical load). The pore structure of the concretes will be studied by microscopy, sorption and suction curves. The test programme involves three different concrete qualities (water-cement ratios). Both steel fibres (ZP...

  1. On non-singular GRADELA crack fields

    Directory of Open Access Journals (Sweden)

    Elias C. Aifantis

    2014-01-01

    Full Text Available A brief account is provided on crack-tip solutions that have recently been published in the literature by employing the so-called GRADELA model and its variants. The GRADELA model is a simple gradient elasticity theory involving one internal length in addition to the two Lame' constants, in an effort to eliminate elastic singularities and discontinuities and to interpret elastic size effects. The non-singular strains and non-singular (but sometimes singular or even hypersingular stresses derived this way under different boundary conditions differ from each other and their physical meaning in not clear. This is discussed which focus on the form and physical meaning of non-singular solutions for crack-tip stresses and strains that are possible to obtain within the GRADELA model and its extensions.

  2. Numerical Simulation on Temperature and Microstructure during Quenching Process of Large-sized AISI P20 Steel Die Blocks

    Institute of Scientific and Technical Information of China (English)

    SONGDong-li; GUJian-feng; ZHANGWei-min; LIUYang; PANJian-sheng

    2004-01-01

    In this paper, a model of coupled thermal and phase transformation is described. The temperature and microstructure during the quenching process for large-sized AISI P20 steel die blocks have been simulated using the finite element method (FEM). The optimum quenching technology of large-sized AISI P20 steel die blocks has been proposed based on the simulation results, which not only can effectively avoid quenching cracks and obtain deeper hardened depth, but also can improve the microstructure and properties of the large-sized die blocks.

  3. Numerical Simulation on Temperature and Microstructure during Quenching Process of Large-sized AISI P20 Steel Die Blocks

    Institute of Scientific and Technical Information of China (English)

    SONG Dong-li; GU Jian-feng; ZHANG Wei-min; LIU Yang; PAN Jian-sheng

    2004-01-01

    In this paper, a model of coupled thermal and phase transformation is described. The temperature and microstructure during the quenching process for large-sized AISI P20 steel die blocks have been simulated using the finite element method (FEM). The optimum quenching technology of large-sized AISI P20 steel die blocks has been proposed based on the simulation results, which not only can effectively avoid quenching cracks and obtain deeper hardened depth,but also can improve the microstructure and properties of the large-sized die blocks.

  4. Multi-block and path modelling procedures

    DEFF Research Database (Denmark)

    Høskuldsson, Agnar

    2008-01-01

    The author has developed a unified theory of path and multi-block modelling of data. The data blocks are arranged in a directional path. Each data block can lead to one or more data blocks. It is assumed that there is given a collection of input data blocks. Each of them is supposed to describe one...... or more intermediate data blocks. The output data blocks are those that are at the ends of the paths and have no succeeding data blocks. The optimisation procedure finds weights for the input data blocks so that the size of the total loadings for the output data blocks are maximised. When the optimal...... weight vectors have been determined, the score and loading vectors for the data blocks in the path are determined. Appropriate adjustment of the data blocks is carried out at each step. Regression coefficients are computed for each data block that show how the data block is estimated by data blocks...

  5. Fluid catalytic cracking of biomass pyrolysis vapors

    Energy Technology Data Exchange (ETDEWEB)

    Mante, Ofei Daku [Virginia Polytechnic Institute and State University, Biological Systems Engineering, Blacksburg, VA (United States); Agblevor, Foster A. [Utah State University, Biological Engineering, Logan, UT (United States); McClung, Ron [BASF Inc, Florham, NJ (United States)

    2011-12-15

    Catalytic cracking of pyrolysis oils/vapors offers the opportunity of producing bio-oils which can potentially be coprocessed with petroleum feedstocks in today's oil refinery to produce transportation fuel and chemicals. Catalyst properties and process conditions are critical in producing and maximizing desired product. In our studies, catalyst matrix (kaolin) and two commercial fluid catalytic cracking (FCC) catalysts, FCC-H and FCC-L, with different Y-zeolite contents were investigated. The catalytic cracking of hybrid poplar wood was conducted in a 50-mm bench-scale bubbling fluidized-bed pyrolysis reactor at 465 C with a weight hourly space velocity of 1.5 h{sup -1}. The results showed that the yields and quality of the bio-oils was a function of the Y-zeolite content of the catalyst. The char/coke yield was highest for the higher Y-zeolite catalyst. The organic liquid yields decreased inversely with increase in zeolite content of the catalyst whereas the water and gas yields increased. Analysis of the oils by both Fourier-transform infrared and {sup 13}C-nuclear magnetic resonance indicated that the catalyst with higher zeolite content (FCC-H) was efficient in the removal of compounds like levoglucosan, carboxylic acids and the conversion of methoxylated phenols to substituted phenols and benzenediols. The cracking of pyrolysis products by kaolin suggests that the activity of the FCC catalyst on biomass pyrolysis vapors can be attributed to both Y-zeolite and matrix. The FCC-H catalyst produced much more improved oil. The oil was low in oxygen (22.67 wt.%), high in energy (29.79 MJ/kg) and relatively stable over a 12-month storage period. (orig.)

  6. Experimental analysis of direct thermal methane cracking

    OpenAIRE

    Abánades Velasco, Alberto; Martínez-Val Peñalosa, Jose Maria; Ruíz, E.; Ferruelo, E. M.; Hernández, F.; Cabanillas, A.; Rubio, J.A.; López, C.; Gavela, R.; G. Barrera; Rubbia, C.; Salmieri, D.; Rodilla, E.; Gutiérrez, D

    2011-01-01

    The analysis of the viability of Hydrogen production without CO2 emissions is one of the most challenging activities that have been initiated for a sustainable energy supply. As one of the tracks to fulfil such objective, direct methane cracking has been analysed experimentally to assess the scientific viability and reaction characterization in a broad temperature range, from 875 to 1700 ?C. The effect of temperature, sweeping/carrier gas fraction proposed in some concepts, methane flow ...

  7. CDF Central Preshower and Crack Detector Upgrade

    OpenAIRE

    Artikov, A.

    2007-01-01

    The CDF Central Preshower and Crack Detector Upgrade consist of scintillator tiles with embedded wavelength-shifting fibers, clear-fiber optical cables, and multi-anode photomultiplier readout. A description of the detector design, test results from R&D studies, and construction phase are reported. The upgrade was installed late in 2004, and a large amount of proton-antiproton collider data has been collected since then. Detector studies using those data are also discussed.

  8. WALNUT: NOT A HARD NUT TO CRACK

    OpenAIRE

    Khanna Deepa; Parle Milind

    2011-01-01

    Walnuts grow on large trees, known for their beauty, timber and tasty edible nuts. There are many varieties of walnuts that vary in hardiness, nut size and thickness of the nut shell. When it comes to their health benefits, Walnuts definitely are not hard nuts to crack. They contain free radical scavenging compounds like ellagic acid, juglone and certain phytosterols that support the immune system and appear to have anti-cancer properties. Walnuts have higher contents of polyunsaturated fatty...

  9. Structures for dense, crack free thin films

    Science.gov (United States)

    Jacobson, Craig P.; Visco, Steven J.; De Jonghe, Lutgard C.

    2011-03-08

    The process described herein provides a simple and cost effective method for making crack free, high density thin ceramic film. The steps involve depositing a layer of a ceramic material on a porous or dense substrate. The deposited layer is compacted and then the resultant laminate is sintered to achieve a higher density than would have been possible without the pre-firing compaction step.

  10. Sharp contact corners, fretting and cracks

    Directory of Open Access Journals (Sweden)

    D. A. Hills

    2013-07-01

    Full Text Available Contacts with sharp edges subject to oscillatory loading are likely to nucleate cracks from the corners, if the loading is sufficiently severe. To a first approximation, the corners behave like notches, where the local elastic behaviour is relieved by plasticity, and which in turn causes irreversibilities that give rise to crack nucleation, but also by frictional slip. One question we aim to answer here is; when is the frictional slip enveloped by plastic slip, so that the corner is effectively a notch in a monolithic material? We do this by employing the classical Williams asymptotic solution to model the contact corner, and, in doing so, we render the solution completely general in the sense that it is independent of the overall geometry of the components. We then re-define the independent parameters describing the properties of the Williams solution by using the inherent length scale, a procedure that was described at the first IJFatigue and FFEMS joint workshop [1]. By proceeding in this way, we can provide a self-contained solution that can be ‘pasted in’ to any complete contact problem, and hence the likelihood of crack nucleation, and the circumstances under which it might occur, can be classified. Further, this reformulation of Williams' solution provides a clear means of obtaining the strength (defined by crack nucleation conditions of a material pair with a particular contact angle. This means that the results from a test carried out using a laboratory specimen may easily be carried over to any complicated contact problem found in engineering practice, and a mechanical test of the prototypical geometry, which may often be quite difficult, is avoided.

  11. Environmentally assisted cracking in Light Water Reactors

    International Nuclear Information System (INIS)

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) during the six months from October 1992 to March 1993. Fatigue and EAC of piping, pressure vessels, and core components in LWRs are important concerns as extended reactor lifetimes are envisaged. Topics that have been investigated include (1) fatigue of low-alloy steel used in piping, steam generators, and reactor pressure vessels. (2) EAC of cast stainless steels (SSs), (3) radiation-induced segregation and irradiation-assisted stress corrosion cracking of Type 304 SS after accumulation of relatively high fluence, and (4) EAC of low-alloy steels. Fatigue tests were conducted on medium-sulfur-content A106-Gr B piping and A533-Gr B pressure vessel steels in simulated PWR water and in air. Additional crack growth data were obtained on fracture-mechanics specimens of cast austenitic SSs in the as-received and thermally aged conditions and chromium-nickel-plated A533-Gr B steel in simulated boiling-water reactor (BWR) water at 289 degrees C. The data were compared with predictions based on crack growth correlations for ferritic steels in oxygenated water and correlations for wrought austenitic SS in oxygenated water developed at ANL and rates in air from Section XI of the ASME Code. Microchemical and microstructural changes in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath from operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy

  12. Growth of inclined fatigue cracks using the biaxial CJP model

    Directory of Open Access Journals (Sweden)

    G. Laboviciute

    2015-07-01

    Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model

  13. Aluminosilicate nanoparticles for catalytic hydrocarbon cracking.

    Science.gov (United States)

    Liu, Yu; Pinnavaia, Thomas J

    2003-03-01

    Aluminosilicate nanoparticles containing 9.0-20 nm mesopores were prepared through the use of protozeolitic nanoclusters as the inorganic precursor and starch as a porogen. The calcined, porogen-free composition containing 2 mol % aluminum exhibited the porosity, hydrothermal stability, and acidity needed for the cracking of very large hydrocarbons. In fact, the hydrothermal stability of the nanoparticles to pure steam at 800 degrees C, along with the cumene cracking activity, surpassed the analogous performance properties of ultrastable Y zeolite, the main catalyst component of commercial cracking catalysts. The remarkable hydrothermal stability and catalytic reactivity of the new nanoparticles are attributable to a unique combination of two factors, the presence of protozeolitic nanoclusters in the pore walls and the unprecedented pore wall thickness (7-15 nm). In addition, the excellent catalytic longevity of the nanoparticles is most likely facilitated by the small domain size of the nanoparticles that greatly improves access to the acid sites on the pore walls and minimizes the diffusion length of coke precursors out of the pores. PMID:12603109

  14. Hydrogen-induced cracking of drip shield

    Energy Technology Data Exchange (ETDEWEB)

    Lu, S C

    1999-08-01

    A simple and conservative model has been developed to evaluate the effects of hydrogen-induced cracking on the drip shield. The basic premise of the model is that failure will occur once the hydrogen content exceeds a certain limit or critical value, HC. This model is very conservative because it assumes that, once the environmental and material conditions can support that particular corrosion process, failure will be effectively instantaneous. In the description of the HIC model presented in Section 6.1, extensive evidence has been provided to support a qualitative assessment of Ti-7 as an excellent choice of material for the drip shield with regard to degradation caused by hydrogen-induced cracking. LTCTF test data observed at LLNL, although unqualified, provides additional indication beyond a qualitative level that hydrogen concentration appears to be low in titanium materials. Quantitative evaluation based on the HIC model described in Section 6.1 indicates that the hydrogen concentration does not exceed the critical value. It is concluded that drip shield material (Ti-7) is able to sustain the effects of hydrogen-induced cracking.

  15. Stress corrosion cracking of steam turbine rotors

    International Nuclear Information System (INIS)

    In the wake of the catastrophic failure of a low-pressure (LP) turbine disk at the Hinkley Point Nuclear Station in 1969, considerable research and development has been devoted to the problem of stress corrosion cracking (SCC) in steam turbine rotors. Principle factors affecting the susceptibility of rotors to SCC have been identified as disk yield strength, applied stress level, and surface film/crevice chemistry. Microstructure and cleanliness of the steel have been found to have relatively little effect. Advances in steel making and forging over the last 20 years have provided manufacturers with additional design and material options to mitigate the problem. Increases in forging size capabilities of steel companies and the welded construction of rotors now permit designing with integral and partial integral rotors that use materials with lower yield strength (more SCC resistant) as well as eliminating the SCC problem in bores and keyways. However, a recent survey of US utilities has shown that SCC in the blade attachment legion of LP rotors is an increasing concern. This problem has led to development of repair and refurbishment methods for rim attachments, especially weld buildup of rims with corrosion-resistant alloys. Life prediction of rotors under SCC conditions currently involves estimating crack growth time from assumed defects to critical size. Factors that govern the location and time of crack initiation are not understood adequately. 50 refs., 23 figs., 1 tab

  16. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    Energy Technology Data Exchange (ETDEWEB)

    Utz, S.; Soppa, E.; Silcher, H.; Kohler, C. [Stuttgart Univ. (Germany). Materials Testing Inst.

    2013-07-01

    The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

  17. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    International Nuclear Information System (INIS)

    The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

  18. OPAL Various Lead Glass Blocks

    CERN Multimedia

    These lead glass blocks were part of a CERN detector called OPAL (one of the four experiments at the LEP particle detector). OPAL uses some 12 000 blocks of glass like this to measure particle energies in the electromagnetic calorimeter. This detector measured the energy deposited when electrons and photons were slowed down and stopped.

  19. Block storage subsystem performance analysis

    CERN Document Server

    CERN. Geneva

    2016-01-01

    You feel that your service is slow because of the storage subsystem? But there are too many abstraction layers between your software and the raw block device for you to debug all this pile... Let's dive on the platters and check out how the block storage sees your I/Os! We can even figure out what those patterns are meaning.

  20. Classical Virasoro irregular conformal block

    CERN Document Server

    Rim, Chaiho

    2015-01-01

    Virasoro irregular conformal block with arbitrary rank is obtained for the classical limit or equivalently Nekrasov-Shatashvili limit using the beta-deformed irregular matrix model (Penner-type matrix model for the irregular conformal block). The same result is derived using the generalized Mathieu equation which is equivalent to the loop equation of the irregular matrix model.

  1. Numerical simulations of material mismatch and ductile crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Oestby, Erling

    2002-07-01

    Both the global geometry and inhomogeneities in material properties will influence the fracture behaviour of structures in presence of cracks. In this thesis numerical simulations have been used to investigate how some aspects of both these issues affect the conditions at the crack-tip. The thesis is organised in an introduction chapter, summarising the major findings and conclusions, a review chapter, presenting the main aspects of the developments in the field of fracture mechanics, and three research papers. Paper I considers the effect of mismatch in hardening exponent on the local near-tip stress field for stationary interface cracks in bi-materials under small scale yielding conditions. It is demonstrated that the stress level in the weaker material increases compared to what is found in the homogeneous material for the same globally applied load level, with the effect being of increasing importance as the crack-tip is approached. Although a coupling between the radial and angular dependence of the stress fields exists, the evolving stress field can still be normalised with the applied J. The effect on the increase in stress level can closely be characterised by the difference in hardening exponent, {delta}n, termed the hardening mismatch, and is more or less independent of the absolute level of hardening in the two materials. Paper II and Ill deal with the effects of geometry, specimen size, hardening level and yield stress mismatch in relation to ductile crack growth. The ductile crack growth is simulated through use of the Gurson model. In Paper H the effect of specimen size on the crack growth resistance is investigated for deep cracked bend and shallow cracked tensile specimens. At small amounts of crack growth the effect of specimen size on the crack growth resistance is small, but a more significant effect is found for larger amounts of crack growth. The crack growth resistance decreases in smaller specimens loaded in tension, whereas the opposite is

  2. Refinement and evaluation of crack-opening-area analyses for circumferential through-wall cracks in pipes

    International Nuclear Information System (INIS)

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet impingement shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. These leak rates depend on the crack-opening area of a through-wall crack in the pipe. In addition to LBB analyses, which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section 11. This study was requested by the NRC to review, evaluate, and refine current analytical models for crack-opening-area analyses of pipes with circumferential through-wall cracks. Twenty-five pipe experiments were analyzed to determine the accuracy of the predictive models. Several practical aspects of crack-opening such as; crack-face pressure, off-center cracks, restraint of pressure-induced bending, cracks in thickness transition regions, weld residual stresses, crack-morphology models, and thermal-hydraulic analysis, were also investigated. 140 refs., 105 figs., 41 tabs

  3. A viscoelastic Unitary Crack-Opening strain tensor for crack width assessment in fractured concrete structures

    Science.gov (United States)

    Sciumè, Giuseppe; Benboudjema, Farid

    2016-09-01

    A post-processing technique which allows computing crack width in concrete is proposed for a viscoelastic damage model. Concrete creep is modeled by means of a Kelvin-Voight cell while the damage model is that of Mazars in its local form. Due to the local damage approach, the constitutive model is regularized with respect to finite element mesh to avoid mesh dependency in the computed solution (regularization is based on fracture energy). The presented method is an extension to viscoelasticity of the approach proposed by Matallah et al. (Int. J. Numer. Anal. Methods Geomech. 34(15):1615-1633, 2010) for a purely elastic damage model. The viscoelastic Unitary Crack-Opening (UCO) strain tensor is computed accounting for evolution with time of surplus of stress related to damage; this stress is obtained from decomposition of the effective stress tensor. From UCO the normal crack width is then derived accounting for finite element characteristic length in the direction orthogonal to crack. This extension is quite natural and allows for accounting of creep impact on opening/closing of cracks in time dependent problems. A graphical interpretation of the viscoelastic UCO using Mohr's circles is proposed and application cases together with a theoretical validation are presented to show physical consistency of computed viscoelastic UCO.

  4. The Shamrock lumbar plexus block

    DEFF Research Database (Denmark)

    Sauter, Axel R; Ullensvang, Kyrre; Niemi, Geir;

    2015-01-01

    BACKGROUND: The Shamrock technique is a new method for ultrasound-guided lumbar plexus blockade. Data on the optimal local anaesthetic dose are not available. OBJECTIVE: The objective of this study is to estimate the effective dose of ropivacaine 0.5% for a Shamrock lumbar plexus block. DESIGN: A...... prospective dose-finding study using Dixon's up-and-down sequential method. SETTING: University Hospital Orthopaedic Anaesthesia Unit. INTERVENTION: Shamrock lumbar plexus block performance and block assessment were scheduled preoperatively. Ropivacaine 0.5% was titrated with the Dixon and Massey up......-and-down method using a stepwise change of 5 ml in each consecutive patient. Combined blocks of the femoral, the lateral femoral cutaneous and the obturator nerve were prerequisite for a successful lumbar plexus block. PATIENTS: Thirty patients scheduled for lower limb orthopaedic surgery completed the study...

  5. Fatigue crack initiation and crack growth studies for pipes made of carbon steel

    International Nuclear Information System (INIS)

    Leak-Before-Break (LBB), a fail-safe design philosophy, is based on fatigue/fracture mechanics concepts and requires rigorous integrity assessment of piping component with postulated part through thickness flaw. It is required to be demonstrated that the unstable tearing will never occur before the crack penetrates through thickness and gives easily detectable leakage. This requires investigation on fatigue crack initiation followed by fatigue crack growth (FCG) of piping components with different postulated part through flaws for the qualification of LBB design criterion. In view of it, six numbers of tests were carried out on 8-inches Sch.100 straight pipes having circumferential part through wall notch and made of SA333Gr6 carbon steel and subjected to pure alternating bending moment using four point bend setup. The material is similar to that used in primary heat transport (PHT) piping of Indian Pressurised Heavy Water Reactor (PHWR)

  6. Stress corrosion cracking experience in steam generators at Bruce NGS

    International Nuclear Information System (INIS)

    In late 1990 and through 1991, units 1 and 2 at the Bruce A Nuclear Generating Station (BNGS-A) experienced a number of steam generator tube leaks. Tube failures were identified by eddy current to be circumferential cracks at U-bend supports on the hot-leg side of the boilers. In late 1991, tubes were removed from these units for failure characterization. Two active failure modes were found: corrosion fatigue in both units 1 and 2 and stress corrosion cracking (SCC) in unit 2. In unit 2, lead was found in deposits, on tubes, and in cracks, and the cracking was mixed-mode: transgranular and intergranular. This convincingly indicated the involvement of lead in the stress corrosion cracking failures. A program of inspection and tube removals was carried out to investigate more fully the extent of the problem. This program found significant cracking only in lead-affected boilers in unit 2, and also revealed a limited extent of non-lead-related intergranular stress corrosion cracking in other boilers and units. Various aspects of the failures and tube examinations are presented in this paper. Included is discussion of the cracking morphology, measured crack size distributions, and chemical analysis of tube surfaces, crack faces, and deposits -- with particular emphasis on lead

  7. Mechanism of electric fatigue crack growth in lead zirconate titanate

    International Nuclear Information System (INIS)

    A series of experiments was performed with through-thickness cracks in ferroelectric double cantilever beam (DCB) specimens. Cyclic electric fields of different amplitudes were applied which resulted in cyclic crack propagation perpendicular to the electric field direction. Crack propagation was observed optically and three regimes were identified: a pop-in from a notch, steady-state crack growth and a decrease of the crack growth rate with increasing cycle number. Crack growth only occurred if the applied field exceeded the coercive field strength of the material. Furthermore, the crack extended during each field reversal and the crack growth rate increased with increasing field. Based on the experimental observations, a mechanistic understanding was developed and contrasted with a nonlinear finite element analysis which quantified the stress intensity in the DCB specimens. The driving forces for crack formation at the notch and subsequent fatigue crack growth were computed based on the distribution of residual stresses due to ferroelectric switching. The finite element results are in good agreement with the experimental observations and support the proposed mechanism

  8. Crack status analysis for concrete dams based on measured entropy

    Institute of Scientific and Technical Information of China (English)

    WU BangBin; WU ZhongRu; CHEN Bo; SU HuaiZhi; BAO TengFei; WANG ShaoWei

    2016-01-01

    The integrity and safety of concrete dams are seriously affected by the existing cracks in dam bodies,and some serious cracks may cause dam failure or disaster.The propagation of cracks in concrete dams is accompanied by changes in energy distribution,which can be represented by changes in the structure's system entropy.Therefore,the entropy theory can be used in analyzing the behavior of dam cracks.Due to the randomness and locality of crack propagation,it is difficult to predict the location of cracks by traditional monitoring methods.To solve this problem,the influence of spatial positions of monitoring points on inspection zones is represented by a weight index,and the weight index is determined by the distance measure method proposed in this paper.Through the weighted linear fusion method,the entropy of multiple monitoring points is obtained for analyzing the behavior of dam cracks in the selected zones.Meanwhile,the catastrophe theory is used as the variation criterion of an entropy sequence in order to predict the instability time of dam cracks.Case studies are put forward on a high arch dam,and the fusion entropy is calculated according to the monitoring data from strain gauges.Results show that the proposed method can effectively predict the occurrence time and location of dam cracks regardless of the layout of monitoring instruments,and it is a new way to analyze the occurrence and propagation of dam cracks.

  9. Fatigue crack growth in an aluminum alloy-fractographic study

    Science.gov (United States)

    Salam, I.; Muhammad, W.; Ejaz, N.

    2016-08-01

    A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

  10. Identifying fatigue crack geometric features from acoustic emission signals

    Science.gov (United States)

    Bao, Jingjing; Poddar, Banibrata; Giurgiutiu, Victor

    2016-04-01

    Acoustic emission (AE) caused by the growth of fatigue crack were well studied by researchers. Conventional approaches predominantly are based on statistical analysis. In this study we focus on identifying geometric features of the crack from the AE signals using physics based approach. One of the main challenges of this approach is to develop a physics of materials based understanding of the generation and propagation of acoustic emissions due to the growth of a fatigue crack. As the geometry changes due to the crack growth, so does the local vibration modes around the crack. Our aim is to understand these changing local vibration modes and find possible relation between the AE signal features and the geometric features of the crack. Finite element (FE) analysis was used to model AE events due to fatigue crack growth. This was done using dipole excitation at the crack tips. Harmonic analysis was also performed on these FE models to understand the local vibration modes. Experimental study was carried out to verify these results. Piezoelectric wafer active sensors (PWAS) were used to excite cracked specimen and the local vibration modes were captured using laser Doppler vibrometry. The preliminary results show that the AE signals do carry the information related to the crack geometry.

  11. Crack monitoring capability of plastic optical fibers for concrete structures

    Science.gov (United States)

    Zhao, Jinlei; Bao, Tengfei; Chen, Rui

    2015-08-01

    Optical fibers have been widely used in structural health monitoring. Traditional silica fibers are easy to break in field applications due to their brittleness. Thus, silica fibers are proposed to be replaced by plastic optical fibers (POFs) in crack monitoring in this study. Moreover, considering the uncertainty of crack propagation direction in composite materials, the influence of the angles between fibers and cracks on the monitoring capability of plastic optical fibers is studied. A POF sensing device was designed and the relationship between light intensity loss and crack width under different fiber/crack angles was first measured through the device. Then, three-point bend tests were conducted on concrete beams. POFs were glued to the bottom surfaces of the beams and light intensity loss with crack width was measured. Experimental results showed that light intensity loss in plastic optical fibers increased with crack width increase. Therefore, application of plastic optical fibers in crack monitoring is feasible. Moreover, the results also showed that the sensitivity of the POF crack sensor decreased with the increase of angles between fibers and cracks.

  12. Unloading Effect on Delayed Hydride Cracking in Zirconium Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Kim, Sung Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2010-05-15

    It is well-known that a tensile overload retards not only the crack growth rate (CGR) in zirconium alloys during the delayed hydride cracking (DHC) tests but also the fatigue crack growth rate in metals, the cause of which is unclear to date. A considerable decrease in the fatigue crack growth rate due to overload is suggested to occur due either to the crack closure or to compressive stresses or strains arising from unloading of the overload. However, the role of the crack closure or the compressive stress in the crack growth rate remains yet to be understood because of incomplete understanding of crack growth kinetics. The aim of this study is to resolve the effect of unloading on the CGR of zirconium alloys, which comes in last among the unresolved issues as listed above. To this end, the CGRs of the Zr-2.5Nb tubes were determined at a constant temperature under the cyclic load with the load ratio, R changing from 0.13 to 0.66 where the extent of unloading became higher at the lower R. More direct evidence for the effect of unloading after an overload is provided using Simpson's experiment investigating the effect on the CGR of a Zr-2.5Nb tube of the stress states of the prefatigue crack tip by unloading or annealing after the formation of a pre-fatigue crack

  13. Fatigue crack growth rate test using a frequency sweep method

    Institute of Scientific and Technical Information of China (English)

    Xun ZHOU; Xiao-li YU

    2008-01-01

    Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses (FEAs) are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor (SIF) of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris's crack partition. The cause of the fatigue crack growth is also dis-cussed.

  14. Block Curricula: A Guide to Teaching with Unit Blocks and Hollow Blocks in the Classroom.

    Science.gov (United States)

    Clark, Phyllis; Tiedemann, Nancy

    This curriculum guide for preschool teachers was designed for use with wooden unit and hollow blocks to foster a variety of math, science, language, and social skills. Following an introduction to the curriculum and a discussion of cooperative learning and stages of block building, the guide is divided into three parts. Part 1 of the guide, "Unit…

  15. Criminal Justice Systems. Block I: Law Enforcement. Block II: The Courts. Block III: Corrections. Block IV: Community Relations. Block V: Proficiency Skills. Block VI: Criminalistics. Student Guide.

    Science.gov (United States)

    Florida State Dept. of Education, Tallahassee. Div. of Vocational, Adult, and Community Education.

    This student guide together with an instructor guide comprise a set of curriculum materials on the criminal justice system. The student guide contains self-contained instructional material that students can study at their own pace most of the time. Six major subject areas or blocks, which are further broken down into several units, with some units…

  16. Criminal Justice Systems. Block I: Law Enforcement. Block II: The Courts. Block III: Corrections. Block IV: Community Relations. Block V: Proficiency Skills. Block VI: Criminalistics. Instructor Guide.

    Science.gov (United States)

    Florida State Dept. of Education, Tallahassee. Div. of Vocational, Adult, and Community Education.

    This instructor guide together with a student guide comprise a set of curriculum materials on the criminal justice system. The instructor guide is a resource for planning and managing individualized, competency-based instruction in six major subject areas or blocks, which are further broken down into several units with some units having several…

  17. A review of hot cracking in austenitic stainless steel weldments

    International Nuclear Information System (INIS)

    The occurrence of hot cracking in austenitic stainless steel weldments is discussed with respect to its origin and metallurgical contributory factors. Of the three types of hot cracking, namely solidification cracking, liquation and ductility dip cracking, solidification cracking occurs in the interdendritic regions in weld metal while liquation and ductility dip cracking occur intergranularly in the heat-affected zone (HAZ). Segregation of impurity and minor elements such as sulphur, phosphorous, silicon, niobium, boron etc to form low melting eutectic phases has been found to be the major cause of hot cracking. Control of HAZ cracking requires minimisation of impurity elements in the base metal. In stabilized stainless steels containing niobium, higher amounts of delta-ferrite have been found necessary to prevent cracking than in unstabilized compositions. Titanium compounds have been found to cause liquation cracking in maraging steels and titanium containing stainless steels and superalloys. In nitrogen added stainless steels, cracking resistance decreases when the solidification mode changes to primary austenitic due to nitrogen addition. A review of the test methods to evaluate hot cracking behaviour showed that several external restraint and semi-self-restraint tests are available. The finger Test, WRC Fissure Bend Test, the PVR test and the Varestraint Test are described along with typical test results. Hot ductility testing to reveal HAZ cracking tendency during welding is described, which is of particular importance to stabilized stainless steels. Based on the literature, recommendations are made for welding stabilized and nitrogen added steels, indicating areas of further work. (author). 81 refs., 30 figs., 1 tab

  18. An investigation of crack-tip stress field criteria of predicting cleavage-crack initiation

    Energy Technology Data Exchange (ETDEWEB)

    Keeney-Walker, J.; Bass, B.R.; Landes, J.D. (Oak Ridge National Lab., TN (United States))

    1991-09-01

    Cleavage-crack initiation in large-scale wide-plate (WP) specimens could not be accurately predicted from small, compact (CT) specimens by using a linear-elastic fracture-mechanics, K{sub Ic}, methodology. In the wide-plate tests conducted by the Heavy-Section Steel Technology Program at Oak Ridge National Laboratory, crack initiation has consistently occurred at stress-intensity (K{sub I}) values ranging from two to four times those predicted by the CT specimens. Studies were initiated to develop crack-tip stress field criteria incorporating effects of geometry, size, and constraint that will lead to improved predictions of cleavage initiation in WP specimens from CT specimens. The work centers around nonlinear two-and three-dimensional finite-element analyses of the crack-tip stress fields in these geometries. Analyses were conducted on CT and WP specimens for which cleavage initiation fracture had been measured in laboratory tests. The local crack-tip field generated for these specimens were then used in the evaluation of fracture correlation parameters to augment the K{sub I} parameter for predicting cleavage initiation. Parameters of hydrostatic constraint and of maximum principal stress, measured volumetrically, are included in these evaluations. The results suggest that the cleavage initiation process can be correlated with the local crack-tip fields via a maximum principal stress criterion based on achieving a critical area within a critical stress contour. This criterion has been successfully applied to correlate cleavage initiation in 2T-CT and WP specimen geometries. 23 refs., 16 figs., 5 tabs.

  19. Predicting the crack response for a pipe with a complex crack

    Science.gov (United States)

    Lukes, Robert G.

    Traditional flaw evaluation in the nuclear field uses conservative methods to predict maximum load carrying capacity for flaws in a given pipe. There is a need in the nuclear industry for more accurate estimates of the load carrying capacity of nuclear piping such that probabilistic tools can be used to predict the time to failure for various types of cracks. These more accurate estimates will allow the nuclear industry to repair flaws at a more appropriate time considering external factors such as costs and man-rem planning along with the flaw repair. Analysis of the maximum load carrying capacity of a pipe with a complex crack (CC) has gained increased importance due to the recent identification of long CC's that have appeared in dissimilar metal (DM) welds thought to be caused by primary water stress corrosion cracking (PWSCC). A coded solution for a single material with a weld was developed that gives an accurate maximum load and crack driving force prediction for a pipe with a through wall crack (TWC), called LBBEng. To support the analysis of a CC, traditionally, an assumption is used that the CC performs similar to that of a TWC of a reduced thickness (TWCr). This modification gives a conservative prediction of the maximum load carrying capacity for a CC in a single material but was never verified for a CC in a DM weld. From the evaluation of the DM weld test data, along with finite element analysis, it can be demonstrated that the crack response of a CC can be predicted by a TWC model when modifications are made to the reduced thickness method.

  20. Crack Characterisation for In-service Inspection Planning - An Update

    Energy Technology Data Exchange (ETDEWEB)

    Waale, Jan [lnspecta Technology AB, Stockholm (Sweden)

    2006-05-15

    One important factor to optimize the NDT equipment and NDT procedure is to know the characteristics of the specific defects being sought for in each case. Thus, access is necessary to reliable morphology data of defects from all possible degradation mechanisms in all existing materials of the components that are subject to the NDT. In 1994 the Swedish Nuclear Power Inspectorate (SKI) initiated a project for compiling crack morphology data based on systematic studies of cracks that have been observed in different plants (nuclear and non-nuclear) in order to determine typical as well as more extreme values of e.g. orientation, width and surface roughness. Although, a large number of identified cracking incidents was covered by the work it was recognised that further studies were needed to increase the data base, and thereby getting more confidence in the use of different crack characteristic data for NDT development and qualification purposes. That is the major reason why the present work was initiated. A thorough review of the SKI archives was performed aiming to find useful material from the time period between 1994 and today to compile complementary data and produce an update. Furthermore, older material was collected and evaluated. Thus, the data cover cracking found within the time period 1977-2003. In addition, useful material was supplied by the Swedish nuclear power plants. The evaluation and presentation of the results are similar to the 1994 study, with a few exceptions. The base for the evaluation is failure analysis reports, where the crack morphology parameters were measured from photos on cracked surfaces or cross sections through cracks. The resulting data were divided into seven groups depending on the cracking mechanism/material group combination. The data groups are: IGSCC in austenitic stainless steels; IGSCC in nickel base alloys; IDSCC in nickel base weld metal; TGSCC in austenitic stainless steels Thermal fatigue in austenitic stainless steels

  1. Application of the cracked pipe element to creep crack growth prediction

    Energy Technology Data Exchange (ETDEWEB)

    Brochard, J.; Charras, T. [C.E.A.-C.E.-Saclay DRN/DMT, Gif Sur Yvette (France); Ghoudi, M. [C.E.A.-C.E.-Saclay, Gif Sur Yvette (France)

    1997-04-01

    Modifications to a computer code for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading are very briefly described. The modifications extend the capabilities of the CASTEM2000 code to the determination of fracture parameters under creep conditions. The main advantage of the approach is that thermal loads can be evaluated as secondary stresses. The code is applicable to piping systems for which crack propagation predictions differ significantly depending on whether thermal stresses are considered as primary or secondary stresses.

  2. Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Migration

    Science.gov (United States)

    DeCarvalho, Nelson V.; Chen, B. Y.; Pinho, Silvestre T.; Baiz, P. M.; Ratcliffe, James G.; Tay, T. E.

    2013-01-01

    A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments.

  3. Block copolymer patterns and templates

    Directory of Open Access Journals (Sweden)

    Mingqi Li

    2006-09-01

    Full Text Available This review describes the chemical and physical aspects of patternable block copolymers and their use for nanostructure fabrication. The patternability of block copolymers results from their ability to self-assemble into microdomains and the manipulation of these patterns by a variety of physical and chemical means. Procedures for achieving long-range lateral order, as well as orientation order of microdomain patterns, are discussed. The level of control that these strategies afford has enabled block copolymers to be used as templates for fabricating a variety of nanostructures.

  4. Effects of gamma ray and sub-cracks on ethanol-assisted crack healing in poly(methyl methacrylate)

    Energy Technology Data Exchange (ETDEWEB)

    Lin, P.Y.; Lin, Y.T. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (China); Yang, Fuqian [Department of Chemical and Materials Engineering, University of Kentucky, Lexington KY 40506 (United States); Lee, Sanboh, E-mail: sblee@mx.nthu.edu.tw [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (China)

    2015-07-15

    The effects of gamma ray and sub-cracks on ethanol-assisted crack healing in poly(methyl methacrylate) (PMMA) were investigated. The transport of ethanol in the gamma-irradiated PMMA was analyzed, using the Harmon model. Both the cracked-gamma-irradiated PMMA and the cracked PMMA with sub-cracks were ethanol-treated at a temperature above the effective glass transition point of the corresponding bulk PMMA. The crack closure rate, which followed the modified Arrhenius equation, increased with increasing gamma ray dose at a given temperature. The fracture strength of the healed PMMA increased with increasing gamma ray dose for short healing time at a given healing temperature, while long healing time led to the decrease of the fracture strength of the healed PMMA with increasing gamma ray dose. The fracture strength of the healed PMMA increased with increasing number of sub-cracks. These results provide the potential to develop self-healing polymeric materials in which structural damage can activate an autonomous healing process without any external stimuli. - Highlights: • The process of sorption and desorption of ethanol in PMMA can heal crack. • Crack closure rate is controlled by Case I diffusion in gamma-irradiated PMMA. • Mechanical strength versus healing time follows the power law with exponent 1/4. • Gamma irradiation degrades solvent healing while sub-cracks enhance.

  5. ANALYSIS ON THE COHESIVE STRESS AT HALF INFINITE CRACK TIP

    Institute of Scientific and Technical Information of China (English)

    王利民; 徐世烺

    2003-01-01

    The nonlinear fracture behavior of quasi-brittle materials is closely related with the cohesive force distribution of fracture process zone at crack tip. Based on fracture character of quasi-brittle materials, a mechanical analysis model of half infinite crack with cohesive stress is presented. A pair of integral equations is established according to the superposition principle of crack opening displacement in solids, and the fictitious adhesive stress is unknown function. The properties of integral equations are analyzed, and the series function expression of cohesive stress is certified. By means of the data of actual crack opening displacement, two approaches to gain the cohesive stress distribution are proposed through resolving algebra equation. They are the integral transformation method for continuous displacement of actual crack opening, and the least square method for the discrete data of crack opening displacement. The calculation examples of two approaches and associated discussions are given.

  6. Matrix Crack Detection by an Embedded Polarimetric Sensor

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Polarimetric optical fibre sensors have been embedded within the 0° ply and close to the 0/90 interface of transparent cross-ply GFRP coupons. The laminate ply cracks may initiate and propagate across the coupon when the coupons were subjected to an increasing quasi-static load in a servo-hydraulic testing machine.Crack accumulation have been monitored using a long gauge-length extensometer. The response of the strain signal, the optical signal and the load signal to cracks at different positions in the coupon in relation to the extensometer and optical sensor positions have been acquired and compared by means of video images of the crack growth. The relationship between crack growth and sensor response was demonstrated. The displacement induced by a new transverse crack has been predicted and compared with experimental data.

  7. Cooling-dominated cracking in thermally stressed volcanic rocks

    Science.gov (United States)

    Browning, John; Meredith, Philip; Gudmundsson, Agust

    2016-08-01

    Most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion. Both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating. We present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite. Results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating. Seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic. These new data are important for assessing the contribution of cooling-induced damage within volcanic structures and layers such as dikes, sills, and lava flows.

  8. A Finite Element Method for Cracked Components of Structures

    Institute of Scientific and Technical Information of China (English)

    刘立名; 段梦兰; 秦太验; 刘玉标; 柳春图; 余建星

    2003-01-01

    In this paper, a method is developed for determining the effective stiffness of the cracked component. The stiffness matrix of the cracked component is integrated into the global stiffness matrix of the finite element model of the global platform for the FE calculation of the structure in any environmental conditions. The stiffness matrix equation of the cracked component is derived by use of the finite variation principle and fracture mechanics. The equivalent parameters defining the element that simulates the cracked component are mathematically presented, and can be easily used for the FE calculation of large scale cracked structures together with any finite element program. The theories developed are validated by both lab tests and numerical calculations, and applied to the evaluation of crack effect on the strength of a fixed platform and a self-elevating drilling rig.

  9. TRANSVERSE VIBRATION CHARACTERISTICS OF VISCOELASTIC RECTANGULAR PLATE WITH CRACK

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Based on the two-dimensional viscoelastic differential constitutive relation and the thin plate theory, the differential equations of motion of the viscoelastic plate with an all-over part-through crack are established and the expression of additional rotation induced by the crack is derived. The complex eigenvalue equations of the viscoelastic plate with crack are derived by the differential quadrature method, and the δ method is used at the crack continuity conditions. Dimensionless complex frequencies of a crack viscoelastic plate with four edges simply supported, two opposite edges simply supported and other two edges clamped are calculated. The effects of the crack parameter, the aspect ratio and dimensionless delay time of the material on the transverse vibration of the viscoelastic plate are analyzed.

  10. Structural and leakage integrity of tubes affected by circumferential cracking

    Energy Technology Data Exchange (ETDEWEB)

    Hernalsteen, P. [TRACTEBEL, Brussels (Belgium)

    1997-02-01

    In this paper the author deals with the notion that circumferential cracks are generally considered unacceptable. He argues for the need to differentiate two facets of such cracks: the issue of the size and growth rate of a crack; and the issue of the structural strength and leakage potential of the tube in the presence of the crack. In this paper the author tries to show that the second point is not a major concern for such cracks. The paper presents data on the structural strength or burst pressure characteristics of steam generator tubes derived from models and data bases of experimental work. He also presents a leak rate model, and compares the performance of circumferential and axial cracks as far as burst strength and leak rate. The final conclusion is that subject to improvement in NDE capabilities (sizing, detection, growth), that Steam Generator Defect Specific Management can be used to allow circumferentially degraded tubes to remain in service.

  11. Fatigue Reliability of Deck Structures Subjected to Correlated Crack Growth

    Institute of Scientific and Technical Information of China (English)

    G.Q. Feng; Y. Garbatov; C. Guedes Soares

    2013-01-01

    The objective of this work is to analyse fatigue reliability of deck structures subjected to correlated crack growth. The stress intensity factors of the correlated cracks are obtained by finite element analysis and based on which the geometry correction functions are derived. The Monte Carlo simulations are applied to predict the statistical descriptors of correlated cracks based on the Paris-Erdogan equation. A probabilistic model of crack growth as a function of time is used to analyse the fatigue reliability of deck structures accounting for the crack propagation correlation. A deck structure is modelled as a series system of stiffened panels, where a stiffened panel is regarded as a parallel system composed of plates and are longitudinal. It has been proven that the method developed here can be conveniently applied to perform the fatigue reliability assessment of structures subjected to correlated crack growth.

  12. Analysis on features for propagation of Zircaloy-4 crack growth

    International Nuclear Information System (INIS)

    In this paper, the fractal properties and entropy properties of the low-cycle fatigue fracture of Zircaloy-4 are primarily investigated. By analyzing the trend of fractal dimension and entropy in the growth direction, obvious segmented zone are discovered in crack growth period. Along the growth direction of crack, the complexity falls gradually in low frequency and vertical high frequency. However, level high frequency and diagonally high frequency are the most complicated in the metaphase of crack growth period. Moreover, in despite of discrepancy of physical meanings and solving methods, fractal dimension and entropy have the accordant rules in characteristic curves in crack growth direction. It means that the fractal dimension and entropy are correlative. Finally, the crack growth period could be plotted out into some stages based on variate curve of the low frequency direction. The subsections in the other directions are analyzed separately as singular point of crack growth . (authors)

  13. Severity estimation of cracked shaft vibrations within fluid film bearings

    Science.gov (United States)

    Prabhu, B. S.; Sekhar, A. S.

    1995-07-01

    The equations of motion, with four degrees of freedom, taking into consideration the flexibility, damping and cross coupling of the fluid film bearings are derived for a cracked Jeffcott rotor supported on fluid film bearings. Dimensionless equations are developed for dynamic radial load, dynamic pressure developed in the fluid film bearings and coefficient of dissipation considering the journal vibrations in two harmonics; bearing fluid film stiffness and damping coefficients. These are applied to a cracked Jeffcott rotor supported on different types of bearings, i.e., cylindrical journal bearings, offset cylindrical bearings, tilting pad journal bearings and three-lobe bearings. Based on the allowable dynamic pressure developed in the fluid bearings, the severity of cracked shaft and allowable crack depths are estimated in this study. Measurement of dynamic pressure and dissipation for monitoring the crack growth is suggested. However, 2x vibration is the best indicator of cracks in the shafts.

  14. Nondestructive testing for crack of tunnel lining using GPR

    Institute of Scientific and Technical Information of China (English)

    LIU Dun-wen; DENG Yu; YANG Fei; XU Guo-yuan

    2005-01-01

    Lining craze, as a common engineering damage, affects the bearing capacity and the safety of tunnels.To improve the capabilities of the surface crack detection in the tunnel lining, ground penetrating radar(GPR) was employed. The principle and method of GPR for cracks investigation of tunnel lining were expounded. As an application example, some field measurements in order to detect the depth of cracks for the tunnel lining were achieved in a new tunnel. All GPR investigations were made with the antennae of 1 GHz. The cracks of concrete structure were located, and the distributing and depth of cracks are inspected and estimated by GPR. The results of investigation show GPR is accurate and efficient to detect cracks of tunnel lining.

  15. Fatigue crack arrest in a self-healing polymer composite

    Energy Technology Data Exchange (ETDEWEB)

    Brown, E. N. (Eric N.); White, S. R. (Scott R.); Sottos, Nancy R.

    2004-01-01

    A comprehensive experimental program is performed to assess the in situ fatigue behavior of a self-healing polymer. A fatigue-life-extension protocol is established for characterizing healing efficiency of the self-healing epoxy under cyclic loading. At moderate {Delta}K{sub I} and at high {Delta}K{sub I}, when a rest period is employed, in situ healing extends fatigue life though temporary crack arrest and retardation. In situ self-healing permanently arrests crack growth at low {delta}K{sub I} and at moderate {Delta}K{sub I}, when a rest period is employed. Fatigue crack retardation and arrest result from two primary crack-tip shielding mechanisms: hydrodynamic pressure in the viscous healing agent and artificial crack closure. Application of self-healing functionality to fatigue slows the crack growth rate and increases the fatigue threshold.

  16. Engineering Solution for the Uniform Strength of Partially Cracked Concrete

    DEFF Research Database (Denmark)

    Hansen, Elin A.; Hansen, Will; Brincker, Rune

    2005-01-01

    Significant computational resources are required to predict the remaining strength from numerical fracture analysis of a jointed plain concrete pavement that contains a partial depth crack. It is, therefore, advantageous when the failure strength can be adequately predicted with an engineering...... solution. Current engineering or closed-form solutions are based on the elastic effective crack approach with the fracture parameters toughness and critical crack tip opening of concrete. The solutions do not directly consider the effect of the distance to the boundary conditions (restrained slab length......) and the cracking process caused by stress softening across the crack. A proposed engineering solution methodology includes these latter variables. The application of the solution is demonstrated on a slab containing a partial depth midslab crack and subjected to in-plane tension. The solution captures the effects...

  17. Dislocation structures around crack tips of fatigued polycrystalline copper

    Energy Technology Data Exchange (ETDEWEB)

    Kaneko, Yoshihisa [Department of Intelligent Materials Engineering, Faculty of Engineering, Osaka City University, Sugimota 3-3-138, Osaka 558-8585 (Japan)]. E-mail: kaneko@imat.eng.osaka-cu.ac.jp; Ishikawa, Masao [Department of Intelligent Materials Engineering, Faculty of Engineering, Osaka City University, Sugimota 3-3-138, Osaka 558-8585 (Japan); Hashimoto, Satoshi [Department of Intelligent Materials Engineering, Faculty of Engineering, Osaka City University, Sugimota 3-3-138, Osaka 558-8585 (Japan)

    2005-07-25

    Dislocation structures near fatigue cracks of polycrystalline copper specimens were analyzed using the electron channelling contrast imaging (ECCI) technique. Prior to the ECCI observations, optical microscopy was conducted to classify the fatigue crack morphologies into several kinds. It was found that the dislocation structures were correlated with the slip morphologies observed using the optical microscope. The cell structure almost corresponded to the severely deformed plastic zone where the individual slip bands could not be identified. The labyrinth dislocation structure was detected at the double-slip region. Ladder-like dislocation structure was detected ahead of the Stage I type fatigue crack. Hence, it can be said that the persistent slip band (PSB) was a favorable crack path. However, the microscopic route of the crack growth was not along the PSB but along the cell structure, which was developed locally in the vicinity of the crack tip.

  18. Environmentally assisted cracking in light water reactors

    International Nuclear Information System (INIS)

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking in high water reactors during the six months from April 1991 through September 1991. Topics that have been investigated during this period include (1) fatigue and stress corrosion cracking (SCC) of low-alloy steel used in piping and in steam generator and reactor pressure vessels; (2) role of chromate and sulfate in simulated boiling water reactor (BWR) water on SCC of sensitized Type 304 SS; and (3) radiation-induced segregation (RIS) and irradiation-assisted SCC of Type 304 SS after accumulation of relatively high fluence. Fatigue data were obtained on medium-S-content A533-Gr B and A106-Gr B steels in high-purity (HP) deoxygenated water, in simulated pressurized water reactor (PWR) water, and in air. Crack-growth-rates (CGRs) of composite specimens of A533-Gr B/Inconel-182/Inconel-600 (plated with nickel) and homogeneous specimens of A533-Gr B were determined under small- amplitude cyclic loading in HP water with ∼ 300 ppb dissolved oxygen. CGR tests on sensitized Type 304 SS indicate that low chromate concentrations in BWR water (25--35 ppb) may actually have a beneficial effect on SCC if the sulfate concentration is below a critical level. Microchemical and microstructural changes in HP and commercial-purity Type 304 SS specimens from control-blade absorber tubes used in two operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy, and slow-strain,rate- tensile tests were conducts on tubular specimens in air and in simulated BWR water at 289 degrees C

  19. Recursion Relations for Conformal Blocks

    CERN Document Server

    Penedones, João; Yamazaki, Masahito

    2015-01-01

    In the context of conformal field theories in general space-time dimension, we find all the possible singularities of the conformal blocks as functions of the scaling dimension $\\Delta$ of the exchanged operator. In particular, we argue, using representation theory of parabolic Verma modules, that in odd spacetime dimension the singularities are only simple poles. We discuss how to use this information to write recursion relations that determine the conformal blocks. We first recover the recursion relation introduced in 1307.6856 for conformal blocks of external scalar operators. We then generalize this recursion relation for the conformal blocks associated to the four point function of three scalar and one vector operator. Finally we specialize to the case in which the vector operator is a conserved current.

  20. MarineMineralsProgramBlocks

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains OCS block outlines and delineated polygons in ESRI ArcGIS shape file format for the BOEM Gulf of Mexico Region that contain sediment...

  1. Left bundle-branch block

    DEFF Research Database (Denmark)

    Risum, Niels; Strauss, David; Sogaard, Peter;

    2013-01-01

    The relationship between myocardial electrical activation by electrocardiogram (ECG) and mechanical contraction by echocardiography in left bundle-branch block (LBBB) has never been clearly demonstrated. New strict criteria for LBBB based on a fundamental understanding of physiology have recently...

  2. Micromechanical approach to nonlinear poroelasticity : Application to cracked rocks

    OpenAIRE

    DEUDE, V; DORMIEUX, L; Kondo, D; MAGHOUS, S

    2002-01-01

    This paper considers a saturated porous medium in which the matrix is a cracked solid. Progressive crack closure is responsible for an overall nonlinear poroelastic behavior. The state equations of nonlinear poroelasticity are derived in a differential form within a micromechanical framework. When a hydraulic connection exists between the cracks and the pores of the porous space, the tangent drained stiffness tensor as well as the tangent Biot tensor and modulus are shown to depend on Terzagh...

  3. Method and instrument for detecting crack in concrete

    International Nuclear Information System (INIS)

    Cracks are one of the major defects in concrete dams, and their occurrence in such dams weakens the integrity and carrying capacity of a dam, thus quickening the aging of the concrete structure. Crack detection in concrete to determine crack performance is important. Ultrasonic longitudinal wave diffraction is generally used to measure crack depth in concrete, but its maximum depth detection is less than one m. A study was conducted on the wave propagation characteristics of surface waves in concrete and changes in their wave properties such as wave speed, wave mode, etc., after interacting with various kinds of cracks. Based on this research, a high-power and low-frequency surface wave exciter and receiving and analyzing devices to detect cracks inside concrete were developed, and they were used to carry out field detection of cracks in 20 engineering projects. Using surface waves to detect cracks in concrete has a number of advantages compared with the traditional ultrasonic longitudinal wave diffraction technique. The detection is not affected by water or other inclusions in the crack, and it can be used to detect different kinds of cracks. It increases the detection accuracy considerably by use of single frequency pulse surface waves compared to the SASW method. The detection depth also may be considerably increased. The Surface Wave Nondestructive Instrument RL-2000 series is especially suitable for crack detection in various concrete structures, and it is applicable for detection not only of cracks inside concrete but also other defects such as honeycombs, voids and low strength areas. 7 refs., 7 figs., 1 tab

  4. Method and instrument for detecting crack in concrete

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z.; Wang, B.; Yao, C. [China Inst. of Water Resources and Hydropower Research. Beijing, (China)

    1999-07-01

    Cracks are one of the major defects in concrete dams, and their occurrence in such dams weakens the integrity and carrying capacity of a dam, thus quickening the aging of the concrete structure. Crack detection in concrete to determine crack performance is important. Ultrasonic longitudinal wave diffraction is generally used to measure crack depth in concrete, but its maximum depth detection is less than one m. A study was conducted on the wave propagation characteristics of surface waves in concrete and changes in their wave properties such as wave speed, wave mode, etc., after interacting with various kinds of cracks. Based on this research, a high-power and low-frequency surface wave exciter and receiving and analyzing devices to detect cracks inside concrete were developed, and they were used to carry out field detection of cracks in 20 engineering projects. Using surface waves to detect cracks in concrete has a number of advantages compared with the traditional ultrasonic longitudinal wave diffraction technique. The detection is not affected by water or other inclusions in the crack, and it can be used to detect different kinds of cracks. It increases the detection accuracy considerably by use of single frequency pulse surface waves compared to the SASW method. The detection depth also may be considerably increased. The Surface Wave Nondestructive Instrument RL-2000 series is especially suitable for crack detection in various concrete structures, and it is applicable for detection not only of cracks inside concrete but also other defects such as honeycombs, voids and low strength areas. 7 refs., 7 figs., 1 tab.

  5. ORMGEN3D, 3-D Crack Geometry FEM Mesh Generator

    International Nuclear Information System (INIS)

    1 - Description of program or function: ORMGEN3D is a finite element mesh generator for computational fracture mechanics analysis. The program automatically generates a three-dimensional finite element model for six different crack geometries. These geometries include flat plates with straight or curved surface cracks and cylinders with part-through cracks on the outer or inner surface. Mathematical or user-defined crack shapes may be considered. The curved cracks may be semicircular, semi-elliptical, or user-defined. A cladding option is available that allows for either an embedded or penetrating crack in the clad material. 2 - Method of solution: In general, one eighth or one-quarter of the structure is modelled depending on the configuration or option selected. The program generates a core of special wedge or collapsed prism elements at the crack front to introduce the appropriate stress singularity at the crack tip. The remainder of the structure is modelled with conventional 20-node iso-parametric brick elements. Element group I of the finite element model consists of an inner core of special crack tip elements surrounding the crack front enclosed by a single layer of conventional brick elements. Eight element divisions are used in a plane orthogonal to the crack front, while the number of element divisions along the arc length of the crack front is user-specified. The remaining conventional brick elements of the model constitute element group II. 3 - Restrictions on the complexity of the problem: Maxima of 5,500 nodes, 4 layers of clad elements

  6. Coke formation during thermal cracking of a heavy crude oil

    OpenAIRE

    Urán Castaño, Laura Cristina

    2015-01-01

    Abstract: A pseudo-mechanism for the production of coke during the thermal cracking of a Colombian heavy crude oil was proposed based on thermal cracking experiments carried out at TGA and at horizontal tube furnace at atmospheric conditions. In-situ combustion (ISC) is a thermal method that improves the recovery of heavy crude oils and involves complex phenomena such as heat and mass transfers, low-temperature oxidation of the liquid phase (LTO), and cracking reactions that yield coke, a car...

  7. Crack Width Analysis of Steel Fiber Reinforced Concrete Elements

    Directory of Open Access Journals (Sweden)

    Darius Ulbinas

    2011-04-01

    Full Text Available The article investigates the effectiveness of steel fiber reinforcement in RC concrete members in regard to ordinary reinforcement. The advantages and disadvantages of different shapes of steel fibers are discussed. The algorithm for calculating crack width based on EC2 and Rilem methodologies is presented. A comparison of theoretical and experimental crack widths has been performed. The relative errors of crack width predictions at different load levels were defined.Article in Lithuanian

  8. Crack Width Analysis of Steel Fiber Reinforced Concrete Elements

    OpenAIRE

    Darius Ulbinas; Gintaris Kaklauskas

    2011-01-01

    The article investigates the effectiveness of steel fiber reinforcement in RC concrete members in regard to ordinary reinforcement. The advantages and disadvantages of different shapes of steel fibers are discussed. The algorithm for calculating crack width based on EC2 and Rilem methodologies is presented. A comparison of theoretical and experimental crack widths has been performed. The relative errors of crack width predictions at different load levels were defined.Article in Lithuanian

  9. Study on Crack Patterns of a Reinforced Building

    OpenAIRE

    PERALTA, Raquel. Maria; TOKUHIRO, Ikuo; トクヒロ, イクオ; 徳広, 育夫

    1992-01-01

    The present work results from the observation of some crack patterns, which occurred in several construction elements of a reinforced concrete building located in the Sakurajima area. The following two studies were made: (I)-The crack patterns produced in the largest slab of second floor. The causes of the cracks in the slab were analyzed on the basis of four specific considerations of Japanese method of calculation (AIJ:Architectural Institute of Japan) and of German method of calculation (D...

  10. Crack propagation under conditions of low cycle fatigue

    International Nuclear Information System (INIS)

    A literature review is given of convenient concepts describing the mechanical behaviour of a cracked body under cyclic loading. Only the range of high growth rates is considered. However, caused by large scale yielding in this range, the application of linear elastic fracture mechanics is no longer possible. Mechanical parameters which control fatigue crack growth are a modified stress intensity factor, the J-integral, the crack tip opening displacement and a suitable strain amplitude. (orig.) With 20 figs

  11. Evolution Procedure of Multiple Rock Cracks under Seepage Pressure

    OpenAIRE

    Taoying Liu; Ping Cao; Hang Lin

    2013-01-01

    In practical geotechnical engineering, most of rock masses with multiple cracks exist in water environment. Under such circumstance, these adjacent cracks could interact with each other. Moreover, the seepage pressure, produced by the high water pressure, can change cracks’ status and have an impact on the stress state of fragile rocks. According to the theory of fracture mechanics, this paper discusses the law of crack initiation and the evolution law of stress intensity factor at the tip of...

  12. Crack instability in a fully ductile pipe system

    International Nuclear Information System (INIS)

    The problem of crack instability is examined, with the following results (a) the conventional SHA defined collapse locus is a conservative assessment of the pipe loading capability within the plastic range; (b) a large safety margin exists considering actual loads, even if secondary loads are included; (c) a parameter is defined which gives the rate of hinge rotation increment with respect to crack extension; (d) comparisons with tearing moduli are given, showing that the crack is generally stable. (orig.)

  13. The influence of cracking on safety of concrete gravity dams

    OpenAIRE

    Adamič, Andrej

    2014-01-01

    In the thesis, the influence of cracking on safety of concrete gravity dams has been analysed. This influence has been studied on the case study of hydroelectric power plant Moste. The mechanical analysis has been performed with a computer program CADAM. The safety of the Moste dam has been analysed for various load combinations, drainage systems, crack heights, and values of horizontal ground accelerations. It has been proved that cracking has an important influence on safety of Moste concre...

  14. Directional crack propagation of granular water systems.

    Science.gov (United States)

    Mizuguchi, Tsuyoshi; Nishimoto, Akihiro; Kitsunezaki, So; Yamazaki, Yoshihiro; Aoki, Ichio

    2005-05-01

    Pattern dynamics of directional crack propagation phenomena observed in drying process of starch-water mixture is investigated. To visualize the three-dimensional structure of the drying-fracture process two kinds of experiments are performed, i.e., resin solidification planing method and real-time measurement of water content distribution with MR instruments. A cross section with polygonal structure is visualized in both experiments. The depth dependency of cell size is measured. The phenomenological model for water transportation is also discussed. PMID:16089617

  15. Fatigue crack growth in additive manufactured products

    Directory of Open Access Journals (Sweden)

    A. Riemer

    2015-10-01

    Full Text Available Additive Manufacturing (AM is a new innovative technique that allows the direct fabrication of complex, individual, delicate and high-strength products, based on their 3D data. Selective Laser Melting (SLM is one of the AM processes that generates metallic components layer by layer using powder-bed technique. The irradiation and consequent melting of metallic powder is realised by the laser source. Employing SLM, especially complex and individual products, such as implants or aerospace parts, are well suited for economic production in small batches. The first important issue in this work was to analyse the fatigue crack growth (FCG in titanium alloy Ti-6-4 and stainless steel 316L processed by SLM. As a first step, stress intensity range decreasing tests were performed on SLM samples in their “as-built” condition. The next step was to adopt measures for optimisation of fatigue crack growth performance of SLM parts. For this purpose various heat treatments such as stress relief annealing and hot isostatic pressing (HIP were applied to the CT specimens. Finally, the strong impact of heat treatment on the residual lifetime was demonstrated by numerical fatigue crack growth simulations. For this purpose, the hip joint implant consisting of Ti-6-4 and processed by SLM was taken into account. It was found that residual stresses have a strong influence on the crack growth in Ti-6-4, while the influence of the micro-pores on the threshold values remains low. In contrast the results for 316L show that its fracturemechanical behaviour is not affected by residual stresses, whereas the microstructural features lead to modification in the da/dN-K-data. The second fundamental aim of this work was to demonstrate the possibilities of the SLM process. For that reason, the individually tailored bicycle crank was optimised regarding its weight and local stresses and finally manufactured using the SLM system. The iterative optimisation procedure was based on

  16. Crack Detection by Digital Image Processing

    DEFF Research Database (Denmark)

    Lyngbye, Janus; Brincker, Rune

    It is described how digital image processing is used for measuring the length of fatigue cracks. The system is installed in a Personal, Computer equipped with image processing hardware and performs automated measuring on plane metal specimens used in fatigue testing. Normally one can not achieve...... a resolution better than that of the image processing equipment. To overcome this problem an extrapolation technique is used resulting in a better resolution. The system was tested on a specimen loaded with different loads. The error σa was less than 0.031 mm, which is of the same size as human measuring...

  17. Crack Length Detection by Digital Image Processing

    DEFF Research Database (Denmark)

    Lyngbye, Janus; Brincker, Rune

    1990-01-01

    It is described how digital image processing is used for measuring the length of fatigue cracks. The system is installed in a Personal Computer equipped with image processing hardware and performs automated measuring on plane metal specimens used in fatigue testing. Normally one can not achieve...... a resolution better then that of the image processing equipment. To overcome this problem an extrapolation technique is used resulting in a better resolution. The system was tested on a specimen loaded with different loads. The error σa was less than 0.031 mm, which is of the same size as human measuring...

  18. Formation mechanism of cracks in saturated sand

    Institute of Scientific and Technical Information of China (English)

    Xiaobing Lu; Zhemin Zheng; Yongren Wu

    2006-01-01

    The formation mechanism of "water film" (or crack) in saturated sand is analyzed theoretically and numerically.The theoretical analysis shows that there will be no stable "water film" in the saturated sand if the strength of the skeleton is zero and no positions are choked.It is shown by numerical simulation that stable water films initiate and grow if the choking state keeps unchanged once the fluid velocities decrease to zero in the liquefied sand column.The developments of "water film" based on the model presented in this paper are compared with experimental results.

  19. Fictitious Crack Model of Concrete Fracture

    DEFF Research Database (Denmark)

    Brincker, Rune; Dahl, H.

    1989-01-01

    , and an alternative energy formulation is given so that it is possible to distinguish between stable and unstable situations. The reformulated substructure method is implemented on computer to give a multilinear stress crack opening displacement relation for the material in the fracture zone, and some qualitative......The substructure method introduced by Petersson is reformulated for the three-point bending specimen in order to obtain complete load-displacement relations without significant truncation. The problem of instability caused by the linearization of the softening in the fracture zone is discussed...

  20. Crack detection by mobile photothermal probe

    Energy Technology Data Exchange (ETDEWEB)

    Bodnar, J.L.; Egee, M.; Menu, C. [Faculte des Sciences, Reims (France); Blanc, A. le; Besnard, R. [CEA, Saclay (France); Sellier, J.Y. [Intercontrole, Rungis (France)

    1994-12-31

    Within the frame of a previous study, encouraging results were obtained regarding the detection of microcracks by Photo Thermal Radiometry under sinusoidal excitation. However, the used method was too slow for an industrial application. It was therefore necessary to consider faster means of analysis. Such is the object of the present study. The authors show that, by using a mobile photothermal probe displaced relatively to the sample, it is possible to rapidly detect opened or non opened cracks, of a few tens of micrometers wide, and a few hundred of micrometers deep.

  1. Pressure tubes cracking due to DHC mechanism

    International Nuclear Information System (INIS)

    Zr-2.5wt%Nb alloy, used in fabrication CANDU and RMBK pressure tubes, fulfils the requirements of a material to be used under specific thermal, mechanical, irradiation and corrosion environment conditions in a nuclear reactor. Despite these advantages, the structural integrity of this assembly can be affected under certain conditions (stress, temperature, hydrogen concentration above the terminal limit of solubility), the crack initiation and propagation process being the mechanism responsible of this behaviour. During their operation the pressure tubes are susceptible to a stable cracking process referred to as Delayed Hydride Cracking (DHC). This phenomenon is one of the most important factors responsible for the degradation of these reactor components. The hydrogen concentration and the stress distribution are the parameters affecting this mechanism, leading to an embrittlement effect of the material, to a loss in the ductility and in the fracture toughness. Therefore, the structural integrity and the in-service lifetime are affected. The pressure tubes fabricated from zirconium alloy occlude exothermically hydrogen during manufacture and during operational service. When the concentration in solution exceeds the TLS (Terminal Limit of Solubility), the excess hydrogen precipitates as platelets of hydride. These hydrides are generally brittle in nature and therefore they cause a structural embrittlement, a loss of ductility and fracture toughness. Under certain thermo-mechanical conditions, the hydrides oriented after the fabrication process in the circumferential direction, tend to reorient. This phenomenon is responsible for a time-dependent failure through the hydride zone and it will arrest in the ductile zirconium matrix. This paper presents the experimental results obtained as a part of the IAEA Co-ordinated Research Project on 'Hydrogen and Hydride Induced Degradation of the Mechanical and Physical Properties of Zirconium-based Alloys', included like a

  2. A Novel Tetrathiafulvalene Building Block

    DEFF Research Database (Denmark)

    Jeppesen, Jan Oskar; Takimiya, Kazuo; Thorup, Niels;

    1999-01-01

    Efficient synthesis of a novel tetrathiafulvalene building block. 2,3-bis(2-cyanoethylthio)-6,7-bis(thiocyanato-methyl)tetrathiafulv alene (7) useful for stepwise and asymmetrical bis-function-alization is reported.......Efficient synthesis of a novel tetrathiafulvalene building block. 2,3-bis(2-cyanoethylthio)-6,7-bis(thiocyanato-methyl)tetrathiafulv alene (7) useful for stepwise and asymmetrical bis-function-alization is reported....

  3. Statistical cryptanalysis of block ciphers

    OpenAIRE

    Junod, Pascal; Vaudenay, Serge

    2007-01-01

    Since the development of cryptology in the industrial and academic worlds in the seventies, public knowledge and expertise have grown in a tremendous way, notably because of the increasing, nowadays almost ubiquitous, presence of electronic communication means in our lives. Block ciphers are inevitable building blocks of the security of various electronic systems. Recently, many advances have been published in the field of public-key cryptography, being in the understanding of involved securi...

  4. NANOSTRUCTURES OF FUNCTIONAL BLOCK COPOLYMERS

    Institute of Scientific and Technical Information of China (English)

    Guojun Liu

    2000-01-01

    Nanostructure fabrication from block copolymers in my group normally involves polymer design, synthesis, selfassembly, selective domain crosslinking, and sometimes selective domain removal. Preparation of thin films with nanochannels was used to illustrate the strategy we took. In this particular case, a linear triblock copolymer polyisopreneblock-poly(2-cinnamoylethyl methacrylate)-block-poly(t-butyl acrylate), PI-b-PCEMA-b-PtBA, was used. Films, 25 to50μm thick, were prepared from casting on glass slides a toluene solution of PI-b-PCEMA-b-PtBA and PtBA homopolymer,hPtBA, where hPtBA is shorter than the PtBA block. At the hPtBA mass fraction of 20% relative to the triblock or the total PtBA (hPtBA and PtBA block) volume fraction of 0.44, hPtBA and PtBA formed a seemingly continuous phase in the matrix of PCEMA and PI. Such a block segregation pattern was locked in by photocrosslinking the PCEMA domain. Nanochannels were formed by extracting out hPtBA with solvent. Alternatively, larger channels were obtained from extracting out hPtBA and hydrolyzing the t-butyl groups of the PtBA block. Such membranes were not liquid permeable but had gas permeability constants ~6 orders of magnitude higher than that of low-density polyethylene films.

  5. CRACK PROPAGATION IN STRUCTURES SUBJECTED TO PERIODIC EXCITATION

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In the present paper, a simple mechanical model is developed to predict the dynamic response of a cracked structure subjected to periodic excitation, which has been used to identify the physical mechanisms in leading the growth or arrest of cracking. The structure under consideration consists of a beam with a crack along the axis, and thus, the crack may open in Mode Ⅰ and in the axial direction propagate when the beam vibrates. In this paper, the system is modeled as a cantilever beam lying on a partial elastic foundation, where the portion of the beam on the foundation represents the intact portion of the beam. Modal analysis is employed to obtain a closed form solution for the structural response. Crack propagation is studied by allowing the elastic foundation to shorten (mimicking crack growth) if a displacement criterion, based on the material toughness, is met. As the crack propagates, the structural model is updated using the new foundation length and the response continues. From this work, two mechanisms for crack arrest are identified. It is also shown that the crack propagation is strongly influenced by the transient response of the structure.

  6. A Calculation Model for Corrosion Cracking in RC Structures

    Institute of Scientific and Technical Information of China (English)

    Xu Gang; Wei Jun; Zhang Keqiang; Zhou Xiwu

    2007-01-01

    A novel calculation model is proposed aiming at the problem of concrete cover cracking induced by reinforcement corrosion. In this article, the relationship between the corrosion depth of the bar and the thickness of the rust layer is established. By deducing the radial displacement expression of concrete, the formula for corrosion depth and corrosion pressure before cracking is proposed. The crack depth of cover in accordance with the maximum corrosion pressure is deduced; furthermore, the corrosion depth and corrosion pressure at the cracking time are obtained. Finally, the theoretical model is validated by several experiments, and the calculated values agree well with the experiment results.

  7. Three-dimensional characterization of stress corrosion cracks

    DEFF Research Database (Denmark)

    Lozano-Perez, S.; Rodrigo, P.; Gontard, Lionel Cervera

    2011-01-01

    Understanding crack propagation and initiation is fundamental if stress corrosion cracking (SCC) mechanisms are to be understood. However, cracking is a three-dimensional (3D) phenomenon and most characterization techniques are restricted to two-dimensional (2D) observations. In order to overcome...... the best spatial resolution. To illustrate the power of these techniques, different parts of dominant stress corrosion cracks in Ni-alloys and stainless steels have been reconstructed in 3D. All relevant microstructural features can now be studied in detail and its relative orientation respect...

  8. Microscopic study of mode I crack tip deformation

    Institute of Scientific and Technical Information of China (English)

    Deshun Fan; Caifu Qian; Zhongjun Jiang

    2005-01-01

    By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.

  9. Crack detection in circular cylindrical shells using differential quadrature method

    International Nuclear Information System (INIS)

    The differential quadrature method combined with an evolutionary optimization algorithm has been proposed for crack detection in cylindrical shell structures. The circumferential crack, which is assumed to be open, is modeled by the extended rotational spring. A crack with finite length divides the shell into four segments. The governing differential equations of motion of the shell are formulated based on Flugge's shell theory. Applying differential quadrature to the differential equations of each segment and the corresponding boundary and continuity conditions results in an algebraic system of equations. Then, an eigenvalue analysis is performed to obtain the natural frequencies of the cracked shell. To identify the crack parameters, an optimization problem is defined and minimized by Bees algorithm, a swarm-based evolutionary optimization technique. The integrity and applicability of the proposed method is confirmed by some experimental case studies. The results show that the crack statuses are predicted well. -- Highlights: • The problem of crack detection in cylindrical shell structures is investigated. • To do this, the differential quadrature method and bees algorithm has been used. • Numerical and experimental studies on the cracked free–free shells were conducted. • The results showed that the crack locations, sizes and depths were predicted well

  10. NSTS Orbiter auxiliary power unit turbine wheel cracking risk assessment

    Science.gov (United States)

    Cruse, T. A.; Mcclung, R. C.; Torng, T. Y.

    1992-01-01

    The present investigation of turbine-wheel cracking problems in the hydrazine-fueled APU turbine wheel of the Space Shuttle Orbiter's Main Engines has indicated the efficacy of systematic probabilistic risk assessment in flight certification and safety resolution. Nevertheless, real crack-initiation and propagation problems do not lend themselves to purely analytical studies. The high-cycle fatigue problem is noted to generally be unsuited to probabilistic modeling, due to its extremely high degree of intrinsic scatter. In the case treated, the cracks appear to trend toward crack arrest in a low cycle fatigue mode, due to a detuning of the resonance model.

  11. Fatigue crack propagation in turbine disks of EI698 superalloy

    OpenAIRE

    A.A. Shanyavskiy

    2013-01-01

    In-service fatigue cracking of turbine disks of EI698 superalloy is discussed based on crack growth analyses. In the bolt joint for disks to shaft connecting there is high level of stress-state, which directed to earlier in-disks fatigue crack origination in low-cycle-fatigue regime. Fracture surface pattern such as fatigue striations were used for their spacing measurement and crack growth duration estimating. Developed disk tests on a special bench by the equivalent program to in-service cy...

  12. MICROMECHANICS ANALYSIS ON EVOLUTION OF CRACK IN VISCOELASTIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    张双寅

    2002-01-01

    A preliminary analysis on crack evolution in viscoelastic materials was presented Based on the equivalent inclusion concept of micro mechanics theory, the explicit expressions of crack opening displacement δ and energy release rate G were derived,indicating that both δ and G are increasing with time. The equivalent modulus of the viscoelastic solid comprising cracks was evaluated. It is proved that the decrease of the modulus comes from two mechanisms: one is the viscoelasticity of the material; the other is the crack opening which is getting larger with time.

  13. Interaction between collinear periodic cracks in an infinite piezoelectric body

    Institute of Scientific and Technical Information of China (English)

    CUI Zhi-jian; HU Hong-ping; YANG Feng

    2008-01-01

    The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping technique, the general periodic solutions for collinear cracks are obtained. The stress intensity factors and the size of saturation strips are derived analytically, and their dependencies on the ratio of the periodicity on the half-length of the crack are analyzed in detail. Numerical results show the following two facts. (1) When h/l>4.0, the stress intensity factors become almost identical to those of a single crack in an infinite piezoelectric body. This indicates that the interaction between cracks can be ignored in establishing the criterion for the crack initiation in this case. (2) The speed of the saturation strip size of periodic cracks approaching that of a single crack depends on the electric load applied at infinity. In general, a large electric load at infinity is associated with a slow approaching speed.

  14. Penny-shaped interfacial crack between dissimilar magnetoelectroelastic layers

    Institute of Scientific and Technical Information of China (English)

    Yan-Song Li; Zeng-He Xu; Wen-Jie Feng

    2011-01-01

    A penny-shaped interfacial crack between dissimilar magnetoelectroelastic layers subjected to magnetoelectromechanical loads is investigated, where the magnetoelectrically impermeable crack surface condition is adopted.By using Hankel transform technique, the mixed boundary value problem is firstly reduced to a system of singular integral equations, which are further reduced to a system of algebraic equations. The field intensity factors and energy release rate are finally derived. Numerical results elucidate the effects of crack configuration, electric and/or magnetic loads, and material parameters of the magnetoelectroelastic layers on crack propagation and growth. This work should be useful for the design of magnetoelectroelastic composite structures.

  15. Identification of breathing cracks in a beam structure with entropy

    Science.gov (United States)

    Wimarshana, Buddhi; Wu, Nan; Wu, Christine

    2016-04-01

    A cantilever beam with a breathing crack is studied to detect and evaluate the crack using entropy measures. Closed cracks in engineering structures lead to proportional complexities to their vibration responses due to weak bi-linearity imposed by the crack breathing phenomenon. Entropy is a measure of system complexity and has the potential in quantifying the complexity. The weak bi-linearity in vibration signals can be amplified using wavelet transformation to increase the sensitivity of the measurements. A mathematical model of harmonically excited unit length steel cantilever beam with a breathing crack located near the fixed end is established, and an iterative numerical method is applied to generate accurate time domain dynamic responses. The bi-linearity in time domain signals due to the crack breathing are amplified by wavelet transformation first, and then the complexities due to bi-linearity is quantified using sample entropy to detect the possible crack and estimate the crack depth. It is observed that the method is capable of identifying crack depths even at very early stages of 3% with the increase in the entropy values more than 10% compared with the healthy beam. The current study extends the entropy based damage detection of rotary machines to structural analysis and takes a step further in high-sensitivity structural health monitoring by combining wavelet transformation with entropy calculations. The proposed technique can also be applied to other types of structures, such as plates and shells.

  16. Pressure Pulsation Signal Analysis for Centrifugal Compressor Blade Crack Determination

    Directory of Open Access Journals (Sweden)

    Hongkun Li

    2014-01-01

    Full Text Available Blade is a key piece of component for centrifugal compressor. But blade crack could usually occur as blade suffers from the effect of centrifugal forces, gas pressure, friction force, and so on. It could lead to blade failure and centrifugal compressor closing down. Therefore, it is important for blade crack early warning. It is difficult to determine blade crack as the information is weak. In this research, a pressure pulsation (PP sensor installed in vicinity to the crack area is used to determine blade crack according to blade vibration transfer process analysis. As it cannot show the blade crack information clearly, signal analysis and empirical mode decomposition (EMD are investigated for feature extraction and early warning. Firstly, signal filter is carried on PP signal around blade passing frequency (BPF based on working process analysis. Then, envelope analysis is carried on to filter the BPF. In the end, EMD is carried on to determine the characteristic frequency (CF for blade crack. Dynamic strain sensor is installed on the blade to determine the crack CF. Simulation and experimental investigation are carried on to verify the effectiveness of this method. The results show that this method can be helpful for blade crack classification for centrifugal compressors.

  17. Vibrational analyses of cracked pre-twisted blades

    Science.gov (United States)

    Chen, L. W.; Jeng, C. H.

    1993-01-01

    A finite element model is utilized to analyze the vibrational behavior of a pre-twisted rotating blade with a single edge crack. This model can satisfy both geometric boundary conditions and natural boundary conditions of the blade. The effects of the transverse shear deformation, rotary inertia and the pre-twisted angle are taken into account. The influences of the crack location and the crack size on natural frequencies, buckling loads and dynamic instability regions are studied. It is found that a crack has great influences on these dynamic characteristics of the rotating blade.

  18. Effect of CTE on Fatigue Cracking of Stainless Steel Vessels

    International Nuclear Information System (INIS)

    Visual examination of lithium hydride reactor vessels revealed cracks that were adjacent to welds. Most cracks were parallel to the weld in the bottom portion of the vessel. Sections were cut out of the vessel containing these cracks and examined using the metallograph, scanning electron microscope, and microprobe to determine the cause of cracking. most of the cracks originated on the outer surface just outside the weld fusion line in the heat affected zone and propagated along grain boundaries. Crack depth of those sections examined ranged from about 300 to 500(micro)m. Other cracks were reported to have reached a maximum depth of 0.32-cm (0.125-inch). The primary cause of cracking was the creation of high tensile stresses associated with the CTE differences between the filler metal and the base metal during operation of the vessel in a thermally cyclic environment. This failure mechanism could be described as creep-type fatigue whereby crack propagation might have been aided by the presence of brittle chromium carbides along the grain boundaries, which is indicative of a slightly sensitized microstructure

  19. Adolescent PTSD and developmental consequences of crack dealing.

    Science.gov (United States)

    Weisman, G K

    1993-10-01

    The effect of crack dealing on emotionally disturbed adolescents in two African-American inner-city communities is examined and illustrated by case examples. Crack dealing was most often found to have dynamics and consequences separate from those of crack use. These include post-traumatic stress disorder and other significant emotional disturbances arising from the violence associated with crack dealing, and the shaping of adolescent identity by the associated culture of violence and guns. Implications for school drug abuse education are explored. PMID:8267095

  20. NONLINEAR DYNAMICS OF A CRACKED ROTOR IN A MANEUVERING AIRCRAFT

    Institute of Scientific and Technical Information of China (English)

    LIN Fu-sheng 林富生; MENG Guang 孟光; Eric Hahn

    2004-01-01

    The nonlinear dynamics of a cracked rotor system in an aircraft maneuvering with constant velocity or acceleration was investigated. The influence of the aircraft climbing angle on the cracked rotor system response is of particular interest and the results show that the climbing angle can markedly affect the parameter range for bifurcation, for quasi-periodic response and for chaotic response as well as for system stability. Aircraft acceleration is also shown to significantly affect the nonlinear behavior of the cracked rotor system, illustrating the possibility for on-line rotor crack fault diagnosis.

  1. Stress corrosion cracking of zirconium in nitric acid

    International Nuclear Information System (INIS)

    The susceptibility of zirconium and its common alloys to stress corrosion cracking (SCC) in nitric acid was investigated by slow strain-rate and constant deflection techniques. Cracking occurred at 250C over a wide range of acid concentrations and electrochemical potentials. The crack velocity increased slightly with increasing temperature. The failure mode was transgranular and the morphology was similar to SCC failures of zirconium alloys in other environments. The fracture was very orientation-dependent suggesting that it occurs on a single crystallographic plane in the material. The results of the study are not consistent with a hydrogen mechanism for cracking

  2. Adolescent PTSD and developmental consequences of crack dealing.

    Science.gov (United States)

    Weisman, G K

    1993-10-01

    The effect of crack dealing on emotionally disturbed adolescents in two African-American inner-city communities is examined and illustrated by case examples. Crack dealing was most often found to have dynamics and consequences separate from those of crack use. These include post-traumatic stress disorder and other significant emotional disturbances arising from the violence associated with crack dealing, and the shaping of adolescent identity by the associated culture of violence and guns. Implications for school drug abuse education are explored.

  3. A Zener-Stroh crack interacting with an edge dislocation

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    A Zener-Stroh crack interacting with an edge dislocation is studied.The crack faces are assumed to be traction free.The applied 'generalized loading' for crack is the initial displacement jump and the intervention of the edge dislocation.Through decomposing the problem into two subsimple problems,using the superposition principle,its solution is obtained.To demonstrate both the validity of the solution and its potential application,two simple examples related to the crack stress intensity factors are pre...

  4. Crack path simulation for cylindrical contact under fretting conditions

    Directory of Open Access Journals (Sweden)

    R.A. Cardoso

    2016-02-01

    Full Text Available In this work different strategies to estimate crack path for cylindrical contacts under fretting conditions are carried out. The main goal is to propose and to evaluate methodologies not only to estimate the direction of crack initiation but also the subsequent propagation in its earlier stages, where the stress field is multiaxial, non-proportional and decays very fast due to the proximity with the contact interface. Such complex conditions pose a substantial challenge to the modelling of crack path. The numerical simulations are provided by a 2D Finite Element Analysis taking into account interactions between the crack faces. The results show that, under fretting conditions, models based on the critical plane method are not effective to estimate the crack initiation orientation, while models based on a so called “critical direction” applied along a critical distance provide better results. Regarding the subsequent crack propagation orientation, it was possible to see that stress intensity factor based models where one considers an infinitesimal virtual crack emerging from an original preexistent crack are powerful mechanisms of crack orientation estimation.

  5. Environment sensitive cracking in light water reactor pressure boundary materials

    International Nuclear Information System (INIS)

    The purpose of the paper is to review the available methods and the most promising future possibilities of preventive maintenance to counteract the various forms of environment sensitive cracking of pressure boundary materials in light water reactors. Environment sensitive cracking is considered from the metallurgical, mechanical and environmental point of view. The main emphasis is on intergranular stress corrosion cracking of austenitic stainless steels and high strenght Ni-base alloys, as well as on corrosion fatigue of low alloy and stainless steels. Finally, some general ideas how to predict, reduce or eliminate environment sensitive cracking in service are presented

  6. Modified strip saturation model for a cracked piezoelectric strip

    OpenAIRE

    R.R. Bhargava; A. Setia

    2008-01-01

    Purpose: The investigations aim to propose a model for arresting an electrical opening of a crack which weakensa narrow, poled and infinite piezoelectric strip. The edges of the strip are subjected to uniform, constant anti-planestresses and in-plane electrical displacements.Design/methodology/approach: The loads applied at the edges of the strip open the crack in a self-similar fashion.Consequently at each tip of the crack a saturation zone protrudes. To stop the crack from further opening t...

  7. Control of thermal cracking and waterproof of J-PARC

    International Nuclear Information System (INIS)

    The switchyard structure of Japan Proton Accelerator Research Complex (J-PARC) is a concrete structure with high performance of execution and waterproof. High performance of waterproof was secured by prevention work of thermal cracking, waterproof in the exterior surface and construction joint, and increasing water-tightness. Many measures to the thermal cracking and increase of water-tightness of concrete decreased the cracks introducing to leakage water. Work process, items for waterproof, example of results of temperature analysis and distribution of thermal cracking index, placing of concrete, and results of measures are stated. (S.Y.)

  8. Eshelby tensor for a crack in an orthotropic elastic medium

    Science.gov (United States)

    Gruescu, Cosmin; Monchiet, Vincent; Kondo, Djimedo

    2005-06-01

    In the present Note, we provide new analytical expressions of the components of Hill tensor P (or equivalently the Eshelby tensor S) associated to an arbitrarily oriented crack in orthotropic elastic medium. The crack is modelled as an infinite cylinder along a symmetry axis of the matrix, with low aspect ratio. The three dimensional results obtained show explicitly the interaction between the primary (structural) anisotropy and the crack-induced anisotropy. They are validated by comparison with existing results in the case where the crack is in a symmetry plane. To cite this article: C. Gruescu et al., C. R. Mecanique 333 (2005).

  9. AN ANALYSIS OF 3D FINITE CRACKED BODIES

    Institute of Scientific and Technical Information of China (English)

    Tao Weiming; Guo Yimu; Cao Zhiyuan

    2001-01-01

    The new-type traction boundary integral equations developed by Hu and with no hyper singular integral are applied to analysis of 3D finite cracked bodies. A numerical algorithm for general 3D problems and a semi-analytical one for axisymmetric problems are presented. Some examples of thick plates and cylindrical columns including penny-shaped crack(s), and rectangular plates including an elliptical crack normal to the surface are analyzed. The comparison between present results and those in literature shows the high accuracy and effectiveness of the present method.

  10. Fatigue crack closure in submicron-thick freestanding copper films

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Toshiyuki, E-mail: kondo@mech.eng.osaka-u.ac.jp; Ishii, Takaki; Hirakata, Hiroyuki; Minoshima, Kohji

    2015-09-03

    The fatigue crack closure in approximately 500-nm-thick freestanding copper films were investigated by in situ field emission scanning electron microscope (FESEM) observations of the fatigue crack opening/closing behavior at three stress ratios of R=0.1, 0.5, and 0.8 in the low–K{sub max} (maximum stress intensity factor) region of K{sub max}<4.5 MPam{sup 1/2}. The direct observation of fatigue cracks clarified that crack closure occurred at R=0.1 and 0.5, while the fatigue crack was always open at R=0.8. Changes in the gage distance across the fatigue crack during a fatigue cycle were measured from the FESEM images, and the crack opening stress intensity factor K{sub op} was evaluated on the basis of the stress intensity factor K vs. the gage distance relationship. The effective stress intensity factor range ΔK{sub eff}=K{sub max}−K{sub op} was then evaluated. The R-dependence of the da/dN vs. ΔK{sub eff} relationship was smaller than that of the da/dN vs. ΔK relationship. This suggests that ΔK{sub eff} is a dominating parameter rather than ΔK in the fatigue crack propagation in the films. This paper is the first report on the presence of the fatigue crack closure in submicron-thick freestanding metallic films.

  11. Fatigue crack closure in submicron-thick freestanding copper films

    International Nuclear Information System (INIS)

    The fatigue crack closure in approximately 500-nm-thick freestanding copper films were investigated by in situ field emission scanning electron microscope (FESEM) observations of the fatigue crack opening/closing behavior at three stress ratios of R=0.1, 0.5, and 0.8 in the low–Kmax (maximum stress intensity factor) region of Kmax<4.5 MPam1/2. The direct observation of fatigue cracks clarified that crack closure occurred at R=0.1 and 0.5, while the fatigue crack was always open at R=0.8. Changes in the gage distance across the fatigue crack during a fatigue cycle were measured from the FESEM images, and the crack opening stress intensity factor Kop was evaluated on the basis of the stress intensity factor K vs. the gage distance relationship. The effective stress intensity factor range ΔKeff=Kmax−Kop was then evaluated. The R-dependence of the da/dN vs. ΔKeff relationship was smaller than that of the da/dN vs. ΔK relationship. This suggests that ΔKeff is a dominating parameter rather than ΔK in the fatigue crack propagation in the films. This paper is the first report on the presence of the fatigue crack closure in submicron-thick freestanding metallic films

  12. Crack opening area estimates in pressurized through-wall cracked elbows under bending

    Energy Technology Data Exchange (ETDEWEB)

    Franco, C.; Gilles, P.; Pignol, M.

    1997-04-01

    One of the most important aspects in the leak-before-break approach is the estimation of the crack opening area corresponding to potential through-wall cracks at critical locations during plant operation. In order to provide a reasonable lower bound to the leak area under such loading conditions, numerous experimental and numerical programs have been developed in USA, U.K. and FRG and widely discussed in literature. This paper aims to extend these investigations on a class of pipe elbows characteristic of PWR main coolant piping. The paper is divided in three main parts. First, a new simplified estimation scheme for leakage area is described, based on the reference stress method. This approach mainly developed in U.K. and more recently in France provides a convenient way to account for the non-linear behavior of the material. Second, the method is carried out for circumferential through-wall cracks located in PWR elbows subjected to internal pressure. Finite element crack area results are presented and comparisons are made with our predictions. Finally, in the third part, the discussion is extended to elbows under combined pressure and in plane bending moment.

  13. ANALYSIS OF CRACK-TIP SINGULARITIES FOR AN INTERFACIAL PERMEABLE CRACK IN METAL/PIEZOELECTRIC BIMATERIALS

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    By modeling metal as a special piezoelectric material with extremely small piezoelectricity and extremely large permittivity, we have obtained the analytical solutions for an interfacial permeable crack in metal/piezoelectric bimaterials by means of the generalized Stroh formalism.The analysis shows that the stress fields near a permeable interfacial crack tip are usually with three types of singularities: r-1/2±iε and r-1/2. Further numerical calculation on the oscillatory index ε are given for 28 types of metal/piezoelectric bimaterials combined by seven commercial piezoelectric materials: PZT-4, BaTiO3, PZT-5H, PZT-6B, PZT-7A, P-7 and PZT-PIC 151 and four metals: copper, silver, lead and aluminum, respectively. The explicit expressions of the crack tip energy release rate (ERR) and the crack tip generalized stress intensity factors (GSIF) are obtained. It is found that both the ERR and GSIF are independent of the electric displacement loading, although they seriously depends on the mechanical loadings.

  14. Crack-tip field on mode Ⅱ interface crack of double dissimilar orthotropic composite materials

    Institute of Scientific and Technical Information of China (English)

    Xue-xia ZHANG; Xiao-chao CUI; Wei-yang YANG; Jun-lin LI

    2009-01-01

    Two systems of non-homogeneous linear equations with 8 unknowns are obtained. This is done by introducing two stress functions containing 16 undetermined coefficients and two real stress singularity exponents with the help of boundary conditions. By solving the above systems of non-homogeneous linear equations, the two real stress singularity exponents can be determined when the double material parameters meet certain conditions. The expression of the stress function and all coefficients are obtained based on the uniqueness theorem of limit. By substituting these parameters into the corresponding mechanics equations, theoretical solutions to the stress intensity factor, the stress field and the displacement field near the crack tip of each material can be obtained when both discriminants of the characteristic equations are less than zero. Stress and displacement near the crack tip show mixed crack characteristics without stress oscillation and crack surface overlapping. As an example, when the two orthotropic materials are the same, the stress singularity exponent, the stress intensity factor, and expressions for the stress and the displacement fields of the orthotropic single materials can be derived.

  15. Experimental determination of the crack driving force J for circumferencially cracked piping elbows

    International Nuclear Information System (INIS)

    In order to study the nocivity of defects on the mechanical behaviour of piping systems, experiments on circumferencially cracked piping components have been conducted. We aimed to compute a value of the so-called ''Jic integral'', which characterizes the capacity to initiate of a pre-existing crack. Using experimental results only, we tried to get rid of the usual formulae hypothesis, based on semi-computed results. Mechanical through-walled defects have been machined in order to represent crack from 600 to 1500 center angle. Bending moment to curvature curves have been outlined and initiation of propagation was determined using electric potential drop technic. Ten in-plan closing tests on austenitic elbows were conducted: 5 in an opening way, 5 in a closing way. J integral value was determined by integration of experimental results. Direct integrations were performed as well as calculations using scaling functions, fitted on the test results. The crack driving force Jic at initiation was slightly greater than other values found in other publications

  16. Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J. [Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 1a, N-7491 Trondheim (Norway); School of Materials Science and Engineering, University of Science and Technology Beijing (USTB), 100083 Beijing (China); Zhang, Z.L., E-mail: zhiliang.zhang@ntnu.n [Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 1a, N-7491 Trondheim (Norway); Ostby, E.; Nyhus, B. [SINTEF, Materials and Chemistry, N-7465 Trondheim (Norway); Sun, D.B. [School of Materials Science and Engineering, University of Science and Technology Beijing (USTB), 100083 Beijing (China)

    2009-12-15

    A strong geometry dependence of ductile crack growth resistance emerges under large scale yielding. The geometry dependence is associated with different levels of crack tip constraint conditions. However, in a recent attempt to identify appropriate fracture mechanics specimens for pipeline steels, an 'independent' relationship between the crack growth resistance curves and crack depths for SENT specimens has been observed experimentally. In this paper, we use the complete Gurson model to study the effects of crack depth and specimen size on ductile crack growth behavior. Crack growth resistance curves for plane strain, mode I crack growth under large scale yielding conditions have been computed. SENB and SENT specimens with three different specimen sizes, each specimen size with three different crack depths, have been selected. It has been found that crack tip constraint (Q-parameter) has a weak dependence on the crack depth for specimens in the low constraint regime.

  17. Zircaloy-4 stress corrosion by iodine: crack kinetics and influence of irradiation on the crack initiation

    International Nuclear Information System (INIS)

    During the PWR power transients, iodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of Zircaloy-4 fuel claddings under Pellet-Cladding Interaction conditions. The primary objective of this study is to distinguish the parameters that contribute to the I-SCC phenomenon in iodized methanol solutions at ambient temperature, on notched tensile specimens, using crack growth rate measurements provided by Direct Current Potential Drop. The results show that for a KI lower than 20 MPa.m1/2, the IG and mixed IG/TG velocity of propagation is a linear function of KI, regardless of the propagation mode. Between 20 and 25 MPa.m1/2, the TG crack growth rate also depends linearly on KI, but increases at a faster rate with respect to KI than during the IG and mixed IG/TG propagation steps. The crack propagation direction and plane (LT and TL) have an impact on the propagation modes, but no impact on the kinetics. The increase of iodine content induces an increase of the crack growth rate for a given KI, and a decrease of the KI, threshold, allowing the crack propagation. This work enables us to quantify the effect of iodine content and of KI on the crack propagation step, propose a propagation law taking into accounts these parameters, and improve the I-SCC description for models. During operation, a zirconium cladding is neutron-irradiated, modifying its microstructure and deformation modes. The second objective of the study is therefore to investigate the impact of these modifications on I-SCC. For that purpose, smooth specimens in recrystallized Zircaloy-4 are proton-irradiated to 2 dpa at 305 C, the microstructure and deformation modes of unirradiated and irradiated Zircaloy-4 are characterized by TEM and SEM, and the influence of these radiation-induced modifications on the I-SCC susceptibility is studied. The Laves phases precipitates are slightly modified by irradiation. The formation of P-type dislocation loops correlated with radiation

  18. Effects of crack tip plastic zone on corrosion fatigue cracking of alloy 690(TT) in pressurized water reactor environments

    Energy Technology Data Exchange (ETDEWEB)

    Xiao, J., E-mail: xiaojunmse@sohu.com [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China); Qiu, S.Y.; Chen, Y. [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China); Fu, Z.H. [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China); School of Material Science and Engineering, Xi Hua University, Chengdu 610039 (China); Lin, Z.X.; Xu, Q. [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China)

    2015-01-15

    Alloy 690(TT) is widely used for steam generator tubes in pressurized water reactor (PWR), where it is susceptible to corrosion fatigue. In this study, the corrosion fatigue behavior of Alloy 690(TT) in simulated PWR environments was investigated. The microstructure of the plastic zone near the crack tip was investigated and labyrinth structures were observed. The relationship between the crack tip plastic zone and fatigue crack growth rates and the environment factor F{sub en} was illuminated.

  19. Skin delivery by block copolymer nanoparticles (block copolymer micelles).

    Science.gov (United States)

    Laredj-Bourezg, Faiza; Bolzinger, Marie-Alexandrine; Pelletier, Jocelyne; Valour, Jean-Pierre; Rovère, Marie-Rose; Smatti, Batoule; Chevalier, Yves

    2015-12-30

    Block copolymer nanoparticles often referred to as "block copolymer micelles" have been assessed as carriers for skin delivery of hydrophobic drugs. Such carriers are based on organic biocompatible and biodegradable materials loaded with hydrophobic drugs: poly(lactide)-block-poly(ethylene glycol) copolymer (PLA-b-PEG) nanoparticles that have a solid hydrophobic core made of glassy poly(d,l-lactide), and poly(caprolactone)-block-poly(ethylene glycol) copolymer (PCL-b-PEG) nanoparticles having a liquid core of polycaprolactone. In vitro skin absorption of all-trans retinol showed a large accumulation of retinol in stratum corneum from both block copolymer nanoparticles, higher by a factor 20 than Polysorbate 80 surfactant micelles and by a factor 80 than oil solution. Additionally, skin absorption from PLA-b-PEG nanoparticles was higher by one order of magnitude than PCL-b-PEG, although their sizes (65nm) and external surface (water-swollen PEG layer) were identical as revealed by detailed structural characterizations. Fluorescence microscopy of histological skin sections provided a non-destructive picture of the storage of Nile Red inside stratum corneum, epidermis and dermis. Though particle cores had a different physical states (solid or liquid as measured by (1)H NMR), the ability of nanoparticles for solubilization of the drug assessed from their Hildebrand solubility parameters appeared the parameter of best relevance regarding skin absorption.

  20. Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

    Science.gov (United States)

    Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

    2016-03-01

    Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

  1. A partly and fully cracked triangular XFEM element for modeling cohesive fracture

    DEFF Research Database (Denmark)

    Mougaard, Jens Falkenskov; Poulsen, Peter Noe; Nielsen, Leif Otto

    2011-01-01

    description as possible on both sides of the crack. The stress accuracy within the crack tip element has been improved to a level, so that the crack tip stresses can be evaluated locally without introducing nonlocal averaging in the surroundings of the crack tip. The partly cracked element can also be applied...

  2. Relationship among Parameters Evaluating Stress Corrosion Cracking

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    @@The threshold stress, σc, for sulfide stress corrosion cracking (SCC) of seven pipeline steels and five other steels, the critical stress, SC, for seven pipeline steels and two drill rod steels with various strengths and the susceptibility to SCC, IRA or σf(SCC)/σf, for four pipeline steels, two drill rod steels and five other steels were measured. The results showed that there are no definite elationships among σc, SC and IRA or σf(SCC)/σf. The threshold stress for hydrogen induced cracking (HIC) during charging with loading in the H2SO4 solution, σc(H), decreased linearly with logarithm of the concentration of diffusible hydrogen c0, i.e., σC(H)=A-B Inc0 for four pipeline steels. σc(H) obtained with a special cathodic current ic, which was corresponding to the diffusible hydrogen concentration during immersing in the H2S solution, were consistent with σc for sulfide SCC for four pipeline steels.Therefore, σc for sulfide SCC can be measured using dynamically charging in the H2SO4 solution with the special cathodic current ic.

  3. Origin of undesirable cracks during layer transfer

    CERN Document Server

    Ponson, Laurent; Atwater, Harry; Ravichandran, Guruswami; Bhattacharya, Kaushik

    2008-01-01

    We investigate the origin of undesirable transverse cracks often observed in thin films obtained by the layer transfer technique. During this process, two crystals bonded to each other containing a weak plan produced by ion implantation are heated to let a thin layer of one of the material on the other. The level of stress imposed on the film during the heating phase due to the mismatch of thermal expansion coefficients of the substrate and the film is shown to be the relevant parameter of the problem. In particular, it is shown that if the film is submitted to a tensile stress, the microcracks produced by ion implantation are not stable and deviate from their straight trajectory making the layer transfer process impossible. However, if the compressive stress exceeds a threshold value, after layer transfer, the film can buckle and delaminate, leading to transverse cracks induced by bending. As a result, we show that the imposed stress \\sigma_m - or equivalently the heating temperature - must be within the ran...

  4. Stochastic modeling of thermal fatigue crack growth

    CERN Document Server

    Radu, Vasile

    2015-01-01

    The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...

  5. Analysis of Crack Tip Stress of Transversal Crack on Slab Corner During Vertical-Horizontal Rolling Process by FEM

    Institute of Scientific and Technical Information of China (English)

    YU Hai-liang; LIU Xiang-hua; WANG Guo-dong

    2008-01-01

    Behavior of transversal crack notched on slab comer during vertical-horizontal rolling process was simula-ted by FEM. The crack tip stress in the whole rolling process was obtained. Influences of the friction coefficient, the initial crack size, the edger roll profile, and the groove fillet radii of grooved edger roll on crack tip stress were ana-lyzed. For vertical rolling, the tension stress appears at crack tip near the slab top surface and the compression stress appears at crack tip near the slab side surface for the flat edger roll; however, the compression stress appears at crack tip near the slab top surface and the tension stress appears at crack tip near the slab side surface in the exit stage for the grooved edger roll. For horizontal rolling, the tension stress appears at crack tip just at the exit stage for the flat edger roll, and the tension stress appears in whole rolling stage; the tension stress value near the slab side surface is much larger than that near the slab top surface for the grooved edger roll.

  6. Crack identification for rotating machines based on a nonlinear approach

    Science.gov (United States)

    Cavalini, A. A., Jr.; Sanches, L.; Bachschmid, N.; Steffen, V., Jr.

    2016-10-01

    In a previous contribution, a crack identification methodology based on a nonlinear approach was proposed. The technique uses external applied diagnostic forces at certain frequencies attaining combinational resonances, together with a pseudo-random optimization code, known as Differential Evolution, in order to characterize the signatures of the crack in the spectral responses of the flexible rotor. The conditions under which combinational resonances appear were determined by using the method of multiple scales. In real conditions, the breathing phenomenon arises from the stress and strain distribution on the cross-sectional area of the crack. This mechanism behavior follows the static and dynamic loads acting on the rotor. Therefore, the breathing crack can be simulated according to the Mayes' model, in which the crack transition from fully opened to fully closed is described by a cosine function. However, many contributions try to represent the crack behavior by machining a small notch on the shaft instead of the fatigue process. In this paper, the open and breathing crack models are compared regarding their dynamic behavior and the efficiency of the proposed identification technique. The additional flexibility introduced by the crack is calculated by using the linear fracture mechanics theory (LFM). The open crack model is based on LFM and the breathing crack model corresponds to the Mayes' model, which combines LFM with a given breathing mechanism. For illustration purposes, a rotor composed by a horizontal flexible shaft, two rigid discs, and two self-aligning ball bearings is used to compose a finite element model of the system. Then, numerical simulation is performed to determine the dynamic behavior of the rotor. Finally, the results of the inverse problem conveyed show that the methodology is a reliable tool that is able to estimate satisfactorily the location and depth of the crack.

  7. Fatigue crack growth behavior of titanium foams for medical applications

    International Nuclear Information System (INIS)

    Research highlights: → Titanium foam with 60% porosity has higher Paris exponent than solid titanium. → High Paris exponents are most likely caused by crack closure and crack bridging. → Solid coating on titanium foam results in lower crack growth than uncoated foam. → The load ratio had a negligible effect on the FCG behavior of both materials. → Medical applications of titanium foams are not limited by their crack growth rate. - Abstract: There is an urgent need to understand the failure behavior of titanium foams because of their promising application as load-bearing implant materials in biomedical applications. Following our recent study on fracture toughness of titanium foams , this paper investigates the mode I fatigue crack propagation in 60% porous open pore titanium foams both with and without solid coated surface. Fatigue crack propagation tests were performed on compact tension specimens at load ratios of R = 0.1 and R = 0.5 and the fracture surfaces were examined using scanning electron microscopy. The crack growth rate, da/dN, versus the stress intensity factor range, ΔK, curves were measured and compared using two different techniques; image processing and compliance methods. The crack extension rates were well described by ΔK, using the Paris-power law approach. Coated and non-coated titanium foams with 60% porosity had a significantly higher Paris exponent than solid titanium, which can be explained by crack closure and crack bridging. It was also shown that the fatigue crack grows along the centerline, following the weakest path throughout the foam. The results obtained from this work provide important information for evaluating the structural integrity of porous titanium components in the future biomedical applications.

  8. Block Matching for Object Tracking

    Energy Technology Data Exchange (ETDEWEB)

    Gyaourova, A; Kamath, C; Cheung, S

    2003-10-13

    Models which describe road traffic patterns can be helpful in detection and/or prevention of uncommon and dangerous situations. Such models can be built by the use of motion detection algorithms applied to video data. Block matching is a standard technique for encoding motion in video compression algorithms. We explored the capabilities of the block matching algorithm when applied for object tracking. The goal of our experiments is two-fold: (1) to explore the abilities of the block matching algorithm on low resolution and low frame rate video and (2) to improve the motion detection performance by the use of different search techniques during the process of block matching. Our experiments showed that the block matching algorithm yields good object tracking results and can be used with high success on low resolution and low frame rate video data. We observed that different searching methods have small effect on the final results. In addition, we proposed a technique based on frame history, which successfully overcame false motion caused by small camera movements.

  9. Cracks propagation by stress corrosion cracking in conditions of Boiling Water Reactor (BWR)

    International Nuclear Information System (INIS)

    This work presents the results of the assays carried out in the Laboratory of Hot Cells of the National Institute of Nuclear Research (ININ) to a type test tube Compact Tension (CT), built in steel austenitic stainless type 304L, simulating those conditions those that it operates a Boiling Water Reactor (BWR), at temperature 288 C and pressure of 8 MPa, to determine the speed to which the cracks spread in this material that is of the one that different components of a reactor are made, among those that it highlights the reactor core vessel. The application of the Hydrogen Chemistry of the Water is presented (HWC) that is one alternative to diminish the corrosion effect low stress in the component, this is gets controlling the quantity of oxygen and of hydrogen as well as the conductivity of the water. The rehearsal is made following the principles of the Mechanics of Elastic Lineal Fracture (LEFM) that considers a crack of defined size with little plastic deformation in the tip of this; the measurement of crack advance is continued with the technique of potential drop of direct current of alternating signal, this is contained inside the standard Astm E-647 (Method of Test Standard for the Measurement of Speed of Growth of Crack by fatigue) that is the one that indicates us as carrying out this test. The specifications that should complete the test tubes that are rehearsed as for their dimensions, it forms, finish and determination of mechanical properties (tenacity to the fracture mainly) they are contained inside the norm Astm E-399, the one which it is also based on the principles of the fracture mechanics. The obtained results were part of a database to be compared with those of other rehearsals under different conditions, Normal Chemistry of the Water (NWC) and it dilutes with high content of O2; to determine the conditions that slow more the phenomena of stress corrosion cracking, as well as the effectiveness of the used chemistry and of the method of

  10. Crack Formation During Hardening in Fibre Reinforced Concrete

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Stang, Henrik

    1996-01-01

    The objective of this project is to establish models for the development of cracks in the early age of fibre reinforced concrete due to restrained shrinkage and temperature variations. These models will be based on measurements of age dependant material properties including the post crack respons...

  11. Nanoscale Electrodes for Flexible Electronics by Swelling Controlled Cracking.

    Science.gov (United States)

    Zhao, Qiang; Wang, Wenjun; Shao, Jinyou; Li, Xiangming; Tian, Hongmiao; Liu, Lu; Mei, Xuesong; Ding, Yucheng; Lu, Bingheng

    2016-08-01

    Nanogap electrodes are realized using pre-patterned electrodes and a swelling controlled cracking method. Parallel fabrication of nanogap electrodes on flexible substrates can be achieved using this method. This swelling-controlled cracking method is promising for fabricating high-performance flexible electronics. UV photodetectors with ZnO nanoparticle-bridged nanogap electrodes exhibit high responsivity and external quantum efficiency.

  12. Subsurface fatigue crack growth in Glare fibre metal laminates

    NARCIS (Netherlands)

    Randell, C.E.

    2005-01-01

    The investigation of the present thesis is concerned with the fatigue crack growth behaviour of part through the thickness cracks in Glare™ fibre metal laminate (FML) subjected to combined tension and bending. An experimental program was executed which required the development of a novel fatig

  13. Laser-Based Instrument Measures Propagation Of Cracks

    Science.gov (United States)

    Lee, Rupert U.; Cox, Robert B.; Youngquist, Robert C.; Sentz, John T.; Rose, Kenneth A.

    1995-01-01

    Report describes use of commerical laser displacement meter to measure propagation of cracks in stainless-steel specimens in stress tests in corrosive (salt-spray) environment. Measurements directed toward determining time from beginning of each test until onset of propagation of crack.

  14. Life and death of a single catalytic cracking particle

    NARCIS (Netherlands)

    Meirer, Florian; Kalirai, Samanbir; Morris, Darius; Soparawalla, Santosh; Liu, Yijin; Mesu, Gerbrand; Andrews, Joy C; Weckhuysen, Bert M

    2015-01-01

    Fluid catalytic cracking (FCC) particles account for 40 to 45% of worldwide gasoline production. The hierarchical complex particle pore structure allows access of long-chain feedstock molecules into active catalyst domains where they are cracked into smaller, more valuable hydrocarbon products (for

  15. On the application of cohesive crack modeling in cementitious materials

    DEFF Research Database (Denmark)

    Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe;

    2007-01-01

    typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model...

  16. The bending of rectangular weakened by a vertical crack

    OpenAIRE

    Babloyan A.H.; Baghdasaryan A.V.

    2008-01-01

    The solution of a problem of elasticity theory for rectangular weakened by a centrally located vertical crack is brought. On the horizontal sides of the rectangular and on the crack faces the stresses are given. On the vertical sides of the rectangular three types of boundary conditions are given.

  17. Near-IR imaging of cracks in teeth

    Science.gov (United States)

    Fried, William A.; Simon, Jacob C.; Lucas, Seth; Chan, Kenneth H.; Darling, Cynthia L.; Staninec, Michal; Fried, Daniel

    2014-02-01

    Dental enamel is highly transparent at near-IR wavelengths and several studies have shown that these wavelengths are well suited for optical transillumination for the detection and imaging of tooth decay. We hypothesize that these wavelengths are also well suited for imaging cracks in teeth. Extracted teeth with suspected cracks were imaged at several wavelengths in the near-IR from 1300-1700-nm. Extracted teeth were also examined with optical coherence tomography to confirm the existence of suspected cracks. Several teeth of volunteers were also imaged in vivo at 1300-nm to demonstrate clinical potential. In addition we induced cracks in teeth using a carbon dioxide laser and imaged crack formation and propagation in real time using near-IR transillumination. Cracks were clearly visible using near-IR imaging at 1300-nm in both in vitro and in vivo images. Cracks and fractures also interfered with light propagation in the tooth aiding in crack identification and assessment of depth and severity.

  18. A circumferential crack in a cylindrical shell under tension.

    Science.gov (United States)

    Duncan-Fama, M. E.; Sanders, J. L., Jr.

    1972-01-01

    A closed cylindrical shell under uniform internal pressure has a slit around a portion of its circumference. Linear shallow shell theory predicts inverse square-root-type singularities in certain of the stresses at the crack tips. This paper reports the computed strength of these singularities for different values of a dimensionless parameter based on crack length, shell radius and shell thickness.

  19. Stereological characterization of crack path transitions in ceramic matrix composites

    Indian Academy of Sciences (India)

    Parag Bhargava; B R Patterson

    2001-04-01

    All ceramic composites involve a mismatch in physical properties the extent of which differs from one composite to another. Mismatch in thermal expansion ( ) and elastic modulus (E) is known to produce stresses that influence the path of a propagating crack. Thus, the relative effect of thermal and elastic mismatch on the crack path is expected to change with change in stress intensity. We propose that the crack path in ceramic composites should undergo a transition with the crack being strongly influenced by the thermal mismatch stresses at low stress intensity and elastic mismatch stresses at high stress intensities. Thus, a material in use under different applications each with its own loading conditions is expected to exhibit different crack propagation tendencies which may be reflected in the – characteristics of the composite material. In the present work several model composites with different combinations of thermal and elastic mismatch have been considered. Cracks propagating at different sub-critical stress intensities (velocities) were generated by a novel indentation technique. Each indentation was performed at a constant displacement rate and a peak load. A range of displacement rates were used to produce cracks propagating at different velocities. The indentations were made using a Vickers indentor fitted in a universal mechanical testing machine. The crack paths in composites were quantified by stereological technique and the proposed theory was verified.

  20. Crack Detectability in Vertical Axis Cooling Pumps During Operation

    Directory of Open Access Journals (Sweden)

    N. Bachschmid

    2004-01-01

    in a position which is rather far away from the crack. 1 × rev., 2 × rev., and 3 × rev. vibration components, which are generally displayed by the machine condition monitoring system and are the most significative symptoms of the presence of a transverse crack in a rotating shaft, are calculated.

  1. Examination of stress corrosion crack tip microstructures in stainless steel

    International Nuclear Information System (INIS)

    Intergranular Stress Corrosion Cracking of austenitic stainless steel components is one of the major materials degradation processes in Boiling Water Reactors (BWRs) and its dependence on the plant water chemistry has been found to be an important factor. Of the contaminants found in BWR water, sulphate ions have been identified as the most aggressive species and their effect has been studied in previous SKI funded work. Sample preparation techniques developed recently allow the examination of stress corrosion microstructures with analysis on the nanometer scale. A sample has been prepared from material tested earlier and studied using advanced electron microscope techniques. Compositional analyses of the crack-wall oxide indicated that it is (Fe,Cr)2O3 and that this oxide incorporates up to 10 % sulphur and some nickel. However, much more sulphur is stored in a nickel sulphide phase that was found precipitated within the crack. The Fe:Cr ratio in the oxide does vary significantly from area to area. In the crack tip region, the crack was found to be following a grain boundary free of carbide precipitates. A single grain boundary precipitate some 60 nm ahead of the visible crack-tip was found and analysed. This precipitate was enriched in nickel and sulphur. Sulphur was also found within a few nanometers of the visible crack tip. The oxides in the crack-tip region were a mixture of Fe2O3 and (Fe,Cr)2O3 and incorporated nickel metal particles up to 100 nm in diameter

  2. A Computer Aided System for Simulating Weld Metal Solidification Crack

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A computer-aided system for simulating weld solidification crack has been developed by which a welding engineer can carry out the welding solidification crack simulation on the basis of a commercial finite element analysis software package. Its main functions include calculating the heat generations of the moving arc, mesh generation, calculating stress-strain distributions with element rebirth technique.

  3. Crack trajectory near a weld: Modeling and simulation

    DEFF Research Database (Denmark)

    Rashid, M.M.; Tvergaard, Viggo

    2008-01-01

    A 2D computational model of ductile fracture, in which arbitrary crack extension through the mesh is accommodated without mesh bias, is used to study ductile fracture near the weld line in welded aluminum plates. Comparisons of the calculated toughness behavior and crack trajectory are made...

  4. Solidification cracking in austenitic stainless steel welds

    Indian Academy of Sciences (India)

    V Shankar; T P S Gill; S L Mannan; S Sundaresan

    2003-06-01

    Solidification cracking is a significant problem during the welding of austenitic stainless steels, particularly in fully austenitic and stabilized compositions. Hot cracking in stainless steel welds is caused by low-melting eutectics containing impurities such as S, P and alloy elements such as Ti, Nb. The WRC-92 diagram can be used as a general guide to maintain a desirable solidification mode during welding. Nitrogen has complex effects on weld-metal microstructure and cracking. In stabilized stainless steels, Ti and Nb react with S, N and C to form low-melting eutectics. Nitrogen picked up during welding significantly enhances cracking, which is reduced by minimizing the ratio of Ti or Nb to that of C and N present. The metallurgical propensity to solidification cracking is determined by elemental segregation, which manifests itself as a brittleness temperature range or BTR, that can be determined using the varestraint test. Total crack length (TCL), used extensively in hot cracking assessment, exhibits greater variability due to extraneous factors as compared to BTR. In austenitic stainless steels, segregation plays an overwhelming role in determining cracking susceptibility.

  5. Fatigue Crack Growth in Bodies with Thermally Sprayed Coating

    Science.gov (United States)

    Kovářík, O.; Haušild, P.; Medřický, J.; Tomek, L.; Siegl, J.; Mušálek, R.; Curry, N.; Björklund, S.

    2016-01-01

    Many applications of thermally sprayed coatings call for increased fatigue resistance of coated parts. Despite the intensive research in this area, the influence of coating on fatigue is still not completely understood. In this paper, the localization of crack initiation sites and the dynamics of crack propagation are studied. The resonance bending fatigue test was employed to test flat specimens with both sides coated. Hastelloy-X substrates coated with classical thermal barrier coating consisting of yttria stabilized zirconia and NiCoCrAlY layers. The strain distribution on the coating surface was evaluated by the Digital Image Correlation method through the whole duration of the fatigue test. Localization of crack initiation sites and the mode of crack propagation in the coated specimen are related to the observed resonance frequency. The individual phases of specimen degradation, i.e., the changes of material properties, crack initiation, and crack propagation, were identified. The tested coatings strongly influenced the first two phases, and the influence on the crack propagation was less significant. In general, the presented crack detection method can be used as a sensitive nondestructive testing method well suited for coated parts.

  6. Diffusion model of delayed hydride cracking in zirconium alloys

    NARCIS (Netherlands)

    Shmakov, AA; Kalin, BA; Matvienko, YG; Singh, RN; De, PK

    2004-01-01

    We develop a method for the evaluation of the rate of delayed hydride cracking in zirconium alloys. The model is based on the stationary solution of the phenomenological diffusion equation and the detailed analysis of the distribution of hydrostatic stresses in the plane of a sharp tensile crack. Th

  7. Development of nondestructive method for prediction of crack instability

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, J.L.; Eylon, D.; Shell, E.B.; Matikas, T.E.

    2000-07-01

    A method to characterize the deformation zone at a crack tip and predict upcoming fracture under load using white light interference microscopy was developed and studied. Cracks were initiated in notched Ti-6Al-4V specimens through fatigue loading. Following crack initiation, specimens were subjected to static loading during in-situ observation of the deformation area ahead of the crack. Nondestructive in-situ observations were performed using white light interference microscopy. Profilometer measurements quantified the area, volume, and shape of the deformation ahead of the crack front. Results showed an exponential relationship between the area and volume of deformation and the stress intensity factor of the cracked alloy. These findings also indicate that it is possible to determine a critical rate of change in deformation versus the stress intensity factor that can predict oncoming catastrophic failure. In addition, crack front deformation zones were measured as a function of time under sustained load, and crack tip deformation zone enlargement over time was observed.

  8. Fracture resistance enhancement of layered structures by multiple cracks

    DEFF Research Database (Denmark)

    Goutianos, Stergios; Sørensen, Bent F.

    2016-01-01

    A theoretical model is developed to test if the fracture resistance of a layered structure can be increased by introducing weak layers changing the cracking mechanism. An analytical model, based on the J integral, predicts a linear dependency between the number of cracks and the steady state...

  9. Development of leak analysis programs from through-wall-crack

    International Nuclear Information System (INIS)

    To introduce Leak-Before-Break (LBB) concept into the piping design standard of the LWR pressure boundary piping, LBB research programs are actively conducted in many nuclear electricity countries. It is one of the most important items to evaluate leak rate through the pipe wall crack to shut down a nuclear power plant safely. At JAERI, a test on the leak rate from a cracked pipe under BWR or PWR operating condition has been carried out from 1987 till 1989. This test is planned to measure the leak flow through circumferential fatigue cracks in 4-, 6-and, 12-inch diameter pipes and through slit specimens. On the other hands, it is necessary to predict and analyse the leak flow through a crack for applying the result of the tests to the structural design standard including the LBB concept. This report describes the some computer programs that calculate crack-opening-area, the crack length, and the flow rate through SCC or fatigue cracks. In these programs, a crack-opening-displacement calculation is available based on modified Tada-Paris equation when pipe geometries and pipe stress conditions are given. The leakage rate calculation is based on Henry's homogeneous nonequilibrium critical flow model and Moody's slip model with several modifications to account for friction and fluid conditions. (author)

  10. Fatigue crack propagation in turbine disks of EI698 superalloy

    Directory of Open Access Journals (Sweden)

    A.A. Shanyavskiy

    2013-04-01

    Full Text Available In-service fatigue cracking of turbine disks of EI698 superalloy is discussed based on crack growth analyses. In the bolt joint for disks to shaft connecting there is high level of stress-state, which directed to earlier in-disks fatigue crack origination in low-cycle-fatigue regime. Fracture surface pattern such as fatigue striations were used for their spacing measurement and crack growth duration estimating. Developed disk tests on a special bench by the equivalent program to in-service cyclic loads have allowed discovering one-to-one correlation between fatigue striation spacing and crack increment in one flight. Number of fatigue striations and beach-marks calculations permitted to estimate crack growth period for the different stages of in-service disks cracking. Equivalent stress level for in-service cracked disks was calculated and compared with stress-level in-tested disks under stress equivalent program to in-service operated cyclic loads. Based on this result non-destructive inspection intervals were discussed and recommended for in-service disks in dependence on number of their flights at the moment of developed inspection to exclude in-flight disks fast fracture.

  11. Near-IR imaging of cracks in teeth.

    Science.gov (United States)

    Fried, William A; Simon, Jacob C; Lucas, Seth; Chan, Kenneth H; Darling, Cynthia L; Staninec, Michal; Fried, Daniel

    2014-02-18

    Dental enamel is highly transparent at near-IR wavelengths and several studies have shown that these wavelengths are well suited for optical transillumination for the detection and imaging of tooth decay. We hypothesize that these wavelengths are also well suited for imaging cracks in teeth. Extracted teeth with suspected cracks were imaged at several wavelengths in the near-IR from 1300-1700-nm. Extracted teeth were also examined with optical coherence tomography to confirm the existence of suspected cracks. Several teeth of volunteers were also imaged in vivo at 1300-nm to demonstrate clinical potential. In addition we induced cracks in teeth using a carbon dioxide laser and imaged crack formation and propagation in real time using near-IR transillumination. Cracks were clearly visible using near-IR imaging at 1300-nm in both in vitro and in vivo images. Cracks and fractures also interfered with light propagation in the tooth aiding in crack identification and assessment of depth and severity. PMID:24817806

  12. Assessment of Hot Crack Properties of Laser Welded Stainless Steel

    DEFF Research Database (Denmark)

    Juhl, Thomas Winther; Olsen, Flemming Ove

    2003-01-01

    measurements for prediction of phases, (3) Various crack tests to assess the crack susceptibility of alloys and (4) A combination of the above for selection of suitable, weldable alloys. The possibility of using such specific methods for alloys and applications has been investigated and recommendations...

  13. Micromechanics of creep fracture : Simulation of intergranular crack growth

    NARCIS (Netherlands)

    Onck, Patrick; Giessen, Erik van der

    1998-01-01

    A computational model is presented to analyze intergranular creep crack growth in a polycrystalline aggregate in a discrete manner and based directly on the underlying physical micromechanisms. A crack tip process zone is used in which grains and their grain boundaries are represented discretely, wh

  14. Cracking in electron beam welding of low alloy steels

    International Nuclear Information System (INIS)

    The study of the cracking in electron beam welding of low alloy steel plates (steel ASTM-A387 gr 22) of high thickness shows that the welding speed to be the essential parameter. A low speed improves the resistance to cracking. The low segregation obtained with this process minimizes the effect of impurities

  15. Hybrid fiber reinforcement and crack formation in Cementitious Composite Materials

    DEFF Research Database (Denmark)

    Pereira, E.B.; Fischer, Gregor; Barros, J.A.O.

    2011-01-01

    The use of different types of fibers simultaneously for reinforcing cementitious matrices is motivated by the concept of a multi-scale nature of the crack propagation process. Fibers with different geometrical and mechanical properties are used to bridge cracks of different sizes from the micro- ...

  16. Predictions for fatigue crack growth life of cracked pipes and pipe welds using RMS SIF approach and experimental validation

    Energy Technology Data Exchange (ETDEWEB)

    Arora, Punit, E-mail: punit@barc.gov.in [Bhabha Atomic Research Centre, Department of Atomic Energy, Maharashtra, Mumbai 400 085 (India); Singh, P.K.; Bhasin, Vivek; Vaze, K.K.; Ghosh, A.K. [Bhabha Atomic Research Centre, Department of Atomic Energy, Maharashtra, Mumbai 400 085 (India); Pukazhendhi, D.M.; Gandhi, P.; Raghava, G. [Structural Engineering Research Centre, Chennai 600 113 (India)

    2011-10-15

    The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel pipes and pipe welds by carrying out analysis/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by using Compact Tension (CT) specimens machined from the actual pipe/pipe weld. Analyses have been carried out to predict the fatigue crack growth life of the austenitic stainless steel pipes/pipes welds having part through cracks on the outer surface. In the analyses, Stress Intensity Factors (K) have been evaluated through two different schemes. The first scheme considers the 'K' evaluations at two points of the crack front i.e. maximum crack depth and crack tip at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (K{sub RMS}) at deepest and surface points. Crack growth and the crack shape with loading cycles have been evaluated. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipe and pipe welds with part through circumferential crack. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (K{sub RMS}) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme. Fatigue crack growth in pipe weld (Gas Tungsten Arc Welding) can be predicted well using Paris constants of base material but prediction is non-conservative for pipe weld (Shielded Metal Arc Welding). Further, predictions using fatigue crack growth rate curve of ASME produces conservative results for pipe and GTAW pipe welds and comparable results for SMAW pipe welds. - Highlights: > Predicting fatigue crack growth of Austenitic Stainless Steel pipes and pipe welds. > Use of RMS-SIF and

  17. Climatological features of blocking anticyclones

    International Nuclear Information System (INIS)

    Several climatological studies have been previously performed using large observational data sets (i.e., 10 years or longer) in order to determine the predominant characteristics of blocking anticyclones, including favored development regions, duration, preferred seasonal occurrence, and frequency of occurrence. These studies have shown that blocking anticyclones occur most frequently from October to April over the eastern Atlantic and Pacific oceans downstream from both the North American and Asian continental regions and the storm track regions to the east of these continents. Some studies have also revealed the presence of a third region block formation in western Russia near 40 degrees E which is associated with another storm track region over the Mediterranean and western Asia

  18. Projectors, Shadows, and Conformal Blocks

    CERN Document Server

    Simmons-Duffin, David

    2012-01-01

    We introduce a method for computing conformal blocks of operators in arbitrary Lorentz representations in any spacetime dimension, making it possible to apply bootstrap techniques to operators with spin. The key idea is to implement the "shadow formalism" of Ferrara, Gatto, Grillo, and Parisi in a setting where conformal invariance is manifest. Conformal blocks in d-dimensions can be expressed as integrals over the projective null-cone in the "embedding space" R^{d+1,1}. Taking care with their analytic structure, these integrals can be evaluated in great generality, reducing the computation of conformal blocks to a bookkeeping exercise. To facilitate calculations in four-dimensional CFTs, we introduce techniques for writing down conformally-invariant correlators using auxiliary twistor variables, and demonstrate their use in some simple examples.

  19. Identification of Micro-cracks to Define Nucleation Stage of Earthquake Occurrence

    Science.gov (United States)

    Fujinawa, Y.; Noda, Y.; Takahashi, K.; Kobayashi, M.; Takamatsu, K.; Natsumeda, J.

    2012-12-01

    Earthquakes are understood to be fracture of crustal rocks or stick slip of neighboring blocks. Preshocks are known to occur generally in the rupture preparatory stage of natural earthquake. And, microcracks are detected in the nucleation stage of accelerated deformation in almost all laboratory experiments. Preshock activity has been found to be less regular to be used for confident predictive purpose. Previous efforts to detect micro-cracks related with natural earthquakes have not succeeded to find particular phenomena to identify the nucleation stage. Here we show that a deep underground electric field measurement using special antenna could detect micro-cracks appearing in the nucleation stage of the Tohoku Earthquake. The measurement method has been proved to be robust to the natural and man-made noises. Whole large pulse-like variations were grouped into three by frequency and waveforms, and found to characterize different phases in the preparatory and after shock processes. Those variations are grouped by time constants: A -type with duration of several to several ten minutes just the same as the pulse-like signals detected previously at the time of volcanic eruption and seismic swarms, B of several hundred Herz, and C of several kiloherz. The B- type variations are sub-grouped into three by waveform: type B-1 of similar to the GUV except in the stepped decay in the relaxation phase after sharp rise, type B-2 of wave packet similar to acoustic emission, and type B-3 of superposition of B-1 and B-2 Different types of electric waveforms are suggested to correspond to crack rupture modes of tensile and shear, and to be generated by confined water movement through the electro-kinetic effects on the ground of previous investigations on laboratory experiments. The second kind of cracks (B-type) is suggested to define the nucleation period: activity increases sharply before the earthquake following the modified Ohmori's law (Figure 1). Field monitoring of micro-crack

  20. Block ground interaction of rockfalls

    Science.gov (United States)

    Volkwein, Axel; Gerber, Werner; Kummer, Peter

    2016-04-01

    During a rockfall the interaction of the falling block with the ground is one of the most important factors that define the evolution of a rockfall trajectory. It steers the rebound, the rotational movement, possibly brake effects, friction losses and damping effects. Therefore, if most reliable rockfall /trajectory simulation software is sought a good understanding of the block ground interaction is necessary. Today's rockfall codes enable the simulation of a fully 3D modelled block within a full 3D surface . However, the details during the contact, i.e. the contact duration, the penetration depth or the dimension of the marks in the ground are usually not part of the simulation. Recent field tests with rocks between 20 and 80 kg have been conducted on a grassy slope in 2014 [1]. A special rockfall sensor [2] within the blocks measured the rotational velocity and the acting accelerations during the tests. External video records and a so-called LocalPositioningSystem deliver information on the travel velocity. With these data not only the flight phases of the trajectories but also the contacts with the ground can be analysed. During the single jumps of a block the flight time, jump length, the velocity, and the rotation are known. During the single impacts their duration and the acting accelerations are visible. Further, the changes of rotational and translational velocity influence the next jump of the block. The change of the rotational velocity over the whole trajectory nicely visualizes the different phases of a rockfall regarding general acceleration and deceleration in respect to the inclination and the topography of the field. References: [1] Volkwein A, Krummenacher B, Gerber W, Lardon J, Gees F, Brügger L, Ott T (2015) Repeated controlled rockfall trajectory testing. [Abstract] Geophys. Res. Abstr. 17: EGU2015-9779. [2] Volkwein A, Klette J (2014) Semi-Automatic Determination of Rockfall Trajectories. Sensors 14: 18187-18210.