364 results
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2. Line creep in paper peeling.
- Author
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Rosti, Jari, Koivisto, Juha, Traversa, Paola, Illa, Xavier, Grasso, Jean-Robert, and Alava, Mikko J.
- Subjects
- *
FRACTURE mechanics , *CREEP (Materials) , *AVALANCHES , *STRAINS & stresses (Mechanics) , *STRENGTH of materials , *STRUCTURAL failures - Abstract
The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with non-local elasticity, and study various measures of the experimental avalanche-avalanche and temporal correlations such as the autocorrelation function of the released energy and aftershock activity. From all these we conclude, that internal avalanche dynamics seems to follow “line depinning”-like behavior, in rough agreement with the depinning model. Meanwhile, the correlations reveal subtle complications not implied by depinning theory. Moreover, we also show how these results can be understood from a geophysical point of view. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
3. Effect of creep-fatigue loading condition on crack tip fields of grade 91 steel at crack initiation and growth.
- Author
-
Jung, Hyun-Woo, Kim, Yun-Jae, and Takahashi, Yukio
- Subjects
FRACTURE mechanics ,STEEL fracture ,STEEL fatigue ,STRAINS & stresses (Mechanics) ,FATIGUE cracks ,FINITE element method ,ECCENTRIC loads - Abstract
In this paper, the effect of creep-fatigue loading condition on crack tip deformation and stress fields of Grade 91 steel at 600 °C at crack initiation and growth is studied. By using finite element debond analysis method, creep-fatigue crack growth tests using C(T) specimens under various load ratios and hold times are simulated, and the effect of creep-fatigue load ratio and hold time on the crack opening profile, equivalent stress, crack-opening stress and triaxiality at crack initiation and growth is presented. It is found that the crack tip deformation and stress fields under tension–compression creep-fatigue loading are overall different from those under tension-tension creep-fatigue and pure creep loading, due to re-sharpening of the crack tip. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
4. Singularities of an inclined crack terminating at the bi-material interface in a Reissner plate.
- Author
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Zhang, Zhaojun, Gao, Haiyang, and Yao, Weian
- Subjects
INTERFACES (Physical sciences) ,FRACTURE mechanics ,MONOTONIC functions ,STRAINS & stresses (Mechanics) ,MATHEMATICAL singularities ,NUMERICAL calculations - Abstract
On the basis of Reissner's plate theory, the stress singularities at the tip of an arbitrarily inclined semiinfinite crack terminating at the interface of two dissimilar materials are investigated in the present paper. Using the eigenfunction expansion method, the eigenequation of the corresponding problem is derived explicitly by directly solving the governing equations of Reissner's plate theory in terms of three generalized displacement components. In this paper, the focus is on the calculation of the singularity order as a fundamental quantity in fracture mechanics. The singularity orders of the moments and shear force at the crack tip are determined by the dominant eigenvalues whose real parts lie between 0 and 1. The influences of the bi-material parameters and the crack inclination angle on the moment and shear force singularity orders are discussed in detail. Specifically, the variations of the shear force singularity order with the bi-material parameter and the crack inclination angle are examined in detail. It is proved that the shear force singularity order is a completely monotonic function of the bi-material parameter and the inclination angle. Some numerical results are given in order to prove the validity of the present study. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
5. Self-similarity in concrete fracture: size-scale effects and transition between different collapse mechanisms.
- Author
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Carpinteri, Alberto and Puzzi, Simone
- Subjects
FRACTURE mechanics ,CRACKING of concrete ,DEFORMATIONS (Mechanics) ,METAL fractures ,STRAINS & stresses (Mechanics) ,STRENGTH of materials ,STRUCTURAL failures - Abstract
Since the pioneering paper by Mandelbrot (Nature, 308:721–722, 1984) on the fractal character of the fracture surfaces in metals, the fractal aspects in the deformation and failure of materials have been investigated by several Researchers (see the reviews by Bouchaud (J Phys Condens Matter, 9:4319–4344) and Carpinteri et al. (Appl Mech Rev, 59:283–305, 2006)) and the attempts to apply fractals to fracture have grown exponentially. Aim of this paper is 2-fold: on one hand, it summarizes in a detailed yet concise fashion the major results of the fractal approach to the scaling of mechanical properties in solid mechanics; on the other hand, it reports some recent results concerning the size effect in the failure of reinforced concrete (RC) beams. These recent findings clearly show that the picture of the size-scale effects is much more complex when interaction among different collapse mechanisms occurs. The consequences on the size-scale effects are discussed in detail. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
6. Multiple cohesive crack growth in brittle materials by the extended Voronoi cell finite element model.
- Author
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Shanhu Li and Ghosh, Somnath
- Subjects
BRITTLENESS ,FRACTURE mechanics ,MATERIAL fatigue ,STRENGTH of materials ,STRESS concentration ,STRAINS & stresses (Mechanics) ,FINITE element method - Abstract
This paper is aimed at modeling the propagation of multiple cohesive cracks by the extended Voronoi cell finite element model or X-VCFEM. In addition to polynomial terms, the stress functions in X-VCFEM include branch functions in conjunction with level set methods and multi-resolution wavelet functions in the vicinity of crack tips. The wavelet basis functions are adaptively enriched to accurately capture crack-tip stress concentrations. Cracks are modeled by an extrinsic cohesive zone model in this paper. The incremental crack propagation direction and length are adaptively determined by a cohesive fracture energy based criterion. Numerical examples are solved and compared with existing solutions in the literature to validate the effectiveness of X-VCFEM. The effect of cohesive zone parameters on crack propagation is studied. Additionally, the effects of morphological distributions such as length, orientation and dispersion on crack propagation are studied. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
7. Analysis of micro--macro material properties and mechanical effects of damaged material containing periodically distributed elliptical microcracks.
- Author
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Tetsuji Kato and Toshihisa Nishioka
- Subjects
STRESS concentration ,SOLIDS ,NUMERICAL analysis ,STRENGTH of materials ,STRAINS & stresses (Mechanics) ,FRACTURE mechanics - Abstract
The existence of numerous microcracks causes changes in the stiffness or fracture toughness of materials. In this paper, the manifestations of mechanical properties in the damaged materials caused by the microcracks are evaluated by the present homogenization method based on the superposition method together with the VNA solution. Moreover, it is known that the stress concentration at the macrocrack tip decreases due to the stress relaxation effect caused by the existence of the microcracks. In order to evaluate the manifestations of mechanical behavior, the mechanical effects of the existence of the microcracks on the macrocrack, the component separation method for mixed-mode stress intensity factors of the macrocrack in the damaged materials is newly developed in this paper. Various numerical analyses are successfully conducted for the two topics, the mechanical properties of the damaged materials and the mechanical behavior of the macrocrack in the damaged materials. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
8. On the three-dimensional problem of an interface crack under uniform heat flow in a bimaterial periodically-layered space.
- Author
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Kaczyński, Andrzej and Matysiak, Stanislaw J.
- Subjects
STRAINS & stresses (Mechanics) ,DEFORMATIONS (Mechanics) ,FRACTURE mechanics ,STRENGTH of materials ,MATERIAL fatigue ,MATHEMATICAL models - Abstract
This paper deals with the study of thermal stresses due to a plane crack lying on an interface in a microperiodic two-layered composite under a uniform perpendicular heat flow. An approximate analysis is carried out within the framework of linear stationary thermoelasticity with microlocal parameters. Taking this approach, a general method of solving the resulting boundary-value problem is presented. Effective results have been achieved through the use of suitable potential solutions and reducing the thermal crack problem to its skew-symmetric isothermal mechanical counterpart. An illustrative example is given in the paper by considering an insulated stress-free penny-shaped crack. For this problem the solution is obtained in terms of elementary functions and discussed from the point of view of fracture theory. [ABSTRACT FROM AUTHOR]
- Published
- 2003
9. On the direct numerical simulation of plane-strain fracture in a class of strain-limiting anisotropic elastic bodies.
- Author
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Mallikarjunaiah, S. and Walton, Jay
- Subjects
STRAINS & stresses (Mechanics) ,COMPUTER simulation ,ANISOTROPY ,CAUCHY problem ,QUASISTATIC processes ,FRACTURE mechanics - Abstract
In this paper, using a special class of nonlinear response relations between linearized strain and Cauchy stress tensors, we study a quasi-static mixed-mode (combination of mode-I and mode-II) fracture boundary value problem. A special subclass of such relations are strain-limiting in which the strains are guaranteed to be uniformly bounded in the neighborhood of crack-tip. In this article, we consider a finite element method based direct numerical simulation (DNS) of plane-strain mixed-mode fracture in a class of strain-limiting, transversely isotropic elastic bodies. We study the numerical solution of a nonlinear fracture boundary value problem with displacement as the primary unknown. The linearized version of the strong form was derived using damped Newton's method and the corresponding weak formulation was solved using a conforming finite element method. The results of this DNS indicate that even very near the crack tip, both stress and strain remain much smaller in magnitude than the corresponding predictions from the linearized elastic fracture mechanics (LEFM). While away from strain concentrating crack-tip region, the solution to the nonlinear, strain-limiting model agrees closely with the LEFM solution. This supports recent asymptotic theoretical studies of anti-plane and plane-strain fracture boundary value problems. Further, we also study the behavior of cleavage stress in the neighborhood of crack-tip. The numerical results indicate that the cleavage stress is largest along a line directly ahead of the crack-tip in agreement with the classical LEFM solution for pure mode I loading. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
10. Crack initiation in single lap joints: effects of geometrical and material properties.
- Author
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Weißgraeber, Philipp, Felger, Julian, Talmon l'Armée, Andreas, and Becker, Wilfried
- Subjects
CRACK initiation (Fracture mechanics) ,LAP joints ,STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,BRITTLE fractures ,ADHESIVE joints - Abstract
Brittle failure of adhesively bonded single lap joints is considered in this paper. A coupled stress and energy criterion in the framework of finite fracture mechanics is employed to study crack initiation by means of a numerical model presented by Hell et al. (Eng Fract Mech 117:112-126, ). Two different formulations of the coupled criterion are compared and the effect of geometrically nonlinear bending deformation of the adherends is analysed. A comparison to experimental results on the effect of the overlap length for single lap joints with composite adherends is given, showing a very good agreement of the failure load predictions. A detailed study of the effects of the geometrical and material parameters of a single lap joint configuration is given. As the energy release at crack formation is considered, the size effect of the adhesive layer thickness is covered correctly. The paper closes with an analysis of the effect of the unbonded adherend length. An approximate explicit expression for a minimum unbonded adherend length is given, which is required to optimize joint designs and to allow for the study of individual parameter effects in numerical and experimental studies. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
11. On characteristic lengths used in notch fracture mechanics.
- Author
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Pluvinage, G. and Capelle, J.
- Subjects
FRACTURE mechanics ,MICROSTRUCTURE ,STRAINS & stresses (Mechanics) ,MECHANICAL behavior of materials ,NOTCH effect ,MATERIAL plasticity - Abstract
In this paper, four kinds of characteristic length parameters used in a local notch fracture criterion are presented: (1) a characteristic length $${\uprho }_{\mathrm{c}}$$ generally connecting to the notch radius, (2) a characteristic distance $$\hbox {X}_{\mathrm{c}}$$ considered as intrinsic to material and connected to the microstructure, (3) a critical distance $$\hbox {d}_{0}$$ considered as intrinsic to material and connected to the fracture process zone, (4) an effective distance $$\hbox {X}_{\mathrm{ef}}$$ considered as a characteristic of the stress distribution. Each approach is discussed. The paper ends with the author's opinion about the different methods. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
12. Crack growth simulation for arbitrarily shaped cracks based on the virtual crack closure technique.
- Author
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Liu, Yan-Ping, Li, Guo-Qing, and Chen, Chuan-Yao
- Subjects
FRACTURE mechanics ,COMPUTER simulation ,CRACK closure ,APPROXIMATION theory ,STRAINS & stresses (Mechanics) ,CRACK propagation (Fracture mechanics) - Abstract
In this paper, crack growth simulation for arbitrarily shaped cracks was investigated based on the virtual crack closure technique. During simulations, the crack front was represented by an approximated zigzag line which had the same general shape as the given crack. For this approximated zigzag crack front, a modified approach was developed to determine the required nodal forces, virtually closed area and displacement opening. After the strain energy release rate G was calculated, crack growth was governed by the fracture criterion G/ G
C = 1 at all the crack tip nodes. The important features of the proposed approach are that (i) a simple stationary finite element mesh can be used for arbitrarily shaped cracks and (ii) adaptive re-meshing technique is avoided in studying crack growth. Three cases having different initial crack shapes are presented to assess the validity of this approach and to evaluate the ease of use in tracking crack growth. Reasonable agreement between the present study and other approaches are obtained. The shape changes during crack propagation can also be tracked with ease. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
13. On Influence of Non-Singular Stress States on Brittle Fracture.
- Author
-
Gardeazabal, David, He, Zhuang, and Kotousov, Andrei
- Subjects
BRITTLE fractures ,STRAINS & stresses (Mechanics) ,ELASTICITY ,FRACTURE mechanics ,PARAMETER estimation ,AXIAL loads ,FRACTURE toughness - Abstract
In the case of sufficiently brittle material the use of stress intensity factor as a fracture parameter alone is well justified within the Linear-Elastic Fracture Mechanics. This is because the singular stress field associated with the stress intensity factor is dominant near the crack tip. However, there are numerous experimental evidences that the critical stress intensity factor to cause fracture initiation (or fracture toughness) can be affected by the specimen geometry as well as loading conditions. To address this issue a number of twoparameter criteria have been proposed in the past, which often utilise non-singular terms of the classical asymptotic expansion of the stress field near the crack tip. Therefore, there is a problem of the selection of an appropriate parameter in addition to the stress intensity factor, which could account for various effects induced by the specimen geometry and loading on initiation of brittle fracture. This short paper demonstrates that brittle fracture conditions can be successfully predicted with various two-parameter criteria, and there are no clear advantages in the use of T-stress as the additional parameter in fracture criterion, in comparison with the next non-singular term, A
1 , of the asymptotic expansion. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
14. Ductile fracture prediction and forming assessment of AA6061-T6 aluminum alloy sheets.
- Author
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Nguyen, Hao H., Nguyen, Trung N., and Vu, Hoa C.
- Subjects
DUCTILE fractures ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,POROSITY ,POROUS materials - Abstract
In this paper, an extension to a modified Gurson porous ductile material model, namely the Dung’s model, is introduced to investigate ductile fracture processes of AA6061-T6 aluminum alloy sheets. The combined Dung–Hill48 model accounts for anisotropic hardening effects of the matrix material. The constitutive model is implemented as a user-defined material subroutine in ABAQUS/Explicit to predict ductile fracture and formability of the aluminum alloy sheets. Ductile fracture predictability of the model comes from the description of void growth in an anisotropic strain hardening material. After being calibrated the model is applied to establish a fracture plastic strain–triaxiality relation using only tensile test data of smooth and R-notched specimens. Calculations of forming limits from seven deep drawing simulations with Nakajima specimens estimate the formability of the material. Influence of the material anisotropy on the obtained forming limit diagram is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
15. On the description of ductile fracture in metals by the strain localization theory.
- Author
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Morin, David, Hopperstad, Odd Sture, and Benallal, Ahmed
- Subjects
DUCTILE fractures ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,COMPUTER simulation ,METALS - Abstract
Numerical simulations based on the bifurcation and imperfection versions of the strain localization theory are used in this paper to predict the failure loci of metals and applied to an advanced high strength steel subjected to proportional loading paths. The results are evaluated against the 3D unit cell analyses of Dunand and Mohr (J Mech Phys Solids 66(1):133–153,
2014 . doi:10.1016/j.jmps.2014.01.008) available in the literature. The Gurson porous plasticity model (Gurson in J Eng Mater Technol 99(1):2–15,1977 . doi:10.1115/1.344340) is used to induce strain softening and drive the localization process. The effects of the void growth, void nucleation and void softening in shear are investigated over a large range of stress triaxialities and Lode parameters. A correlation between the imperfection and bifurcation results is established. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
16. Analysis and design of dual-phase steel microstructure for enhanced ductile fracture resistance.
- Author
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Gerbig, Daniel, Srivastava, Ankit, Osovski, Shmuel, Hector, Louis G., and Bower, Allan
- Subjects
DUCTILE fractures ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,MICROSTRUCTURE ,FERRITES ,MARTENSITE - Abstract
The goal of this paper is to predict how the properties of the constituent phases and microstructure of dual phase steels (consisting of ferrite and martensite) influence their fracture resistance. We focus on two commercial low-carbon dual-phase (DP) steels with different ferrite/martensite phase volume fractions and properties. These steels exhibit similar flow behavior and tensile strength but different ductility. Our experimental observations show that the mechanism of ductile fracture in these two DP steels involves nucleation, growth and coalescence of micron scale voids. We thus employ microstructure-based finite element simulations to analyze the ductile fracture of these dual-phase steels. In the microstructure-based simulations, the individual phases of the DP steels are discretely modeled using elastic-viscoplastic constitutive relations for progressively cavitating solids. The flow behavior of the individual phases in both the steels are determined by homogenizing the microscale calibrated crystal plasticity constitutive relations from a previous study (Chen et al. in Acta Mater 65:133–149,
2014 ) while the damage parameters are determined by void cell model calculations. We then determine microstructural effects on ductile fracture of these steels by analyzing a series of representative volume elements with varying volume fractions, flow and damage behaviors of the constituent phases. Our simulations predict qualitative features of the ductile fracture process in good agreement with experimental observations for both DP steels. A ‘virtual’ DP microstructure, constructed by varying the microstructural parameters in the commercial steels, is predicted to have strength and ductile fracture resistance that is superior to the two commercial DP steels. Our simulations provide guidelines for improving the ductile fracture resistance of DP steels. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
17. Dissipation during crack growth in a viscoelastic material from a cohesive model for a finite specimen.
- Author
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Ciavarella, M.
- Subjects
- *
FRACTURE mechanics , *VISCOELASTIC materials , *COHESIVE strength (Mechanics) , *CRACK propagation (Fracture mechanics) , *STRAINS & stresses (Mechanics) , *ENERGY dissipation - Abstract
In the present paper, we extend results recently given by Ciavarella et al. (J Mech Phys Solids 169:105096, 2022) to show some actual calculations of the viscoelastic dissipation in a crack propagation at constant speed in a finite size specimen. It is usually believed that the cohesive models introduced by Knauss and Schapery and the dissipation-based theories introduced by de Gennes and Persson-Brener give very similar results for steady state crack propagation in viscoelastic materials, where usually only the asymptotic singular field is used for the stress. We show however that dissipation and the energy balance never reach a steady state, despite the constant propagation crack rate and stress intensity factor. Our loading protocol permits a rigorous solution, and implies a short phase with constant specimen elongation rate, but then possibly a very long phase of constant or decreasing elongation, which differs from typical experiments. For the external work we are therefore unable to use the de Gennes and Persson-Brener theories which suggested that the increase of effective fracture energy would go up to the ratio of instantaneous to relaxed modulus, at very fast rates. We show viscoelastic dissipation is in general a transient quantity, which can vary by orders of magnitude while the stress intensity factor is kept constant, and is largely affected by dissipation in the bulk rather than at the crack tip. The total work to break a specimen apart is found also to be possibly arbitrarily large for quite a large range of intermediate crack growth rates. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
18. The most dangerous flaw orientation in brittle materials and structures.
- Author
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Salvadori, A. and Giacomini, A.
- Subjects
BRITTLE material fracture ,MECHANICAL loads ,TENSILE tests ,STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,BRITTLE fractures - Abstract
In the present paper a sheet of material is considered. It is loaded by uniaxial tensile stress and contains a random distribution of flaw orientations, with the flaws thought of as flat pre-cracks of comparable length, and with all crack planes being oriented perpendicular to the faces of the sheet. Intuition suggests that the most likely flaw to initiate fracture, which will be termed the 'most dangerous defect', lies orthogonally to the major load axis. The purpose of the present paper is to show that such an assumption is incorrect. Neither the most dangerous defect nor the first increments of crack growth will be oriented perpendicularly to the stress direction (nor will they be co-planar with the orientation of the most critical flaw). [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
19. Numerical simulation of the fracture process in concrete resulting from deflagration phenomena.
- Author
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Fukuda, Daisuke, Moriya, Kazuma, Kaneko, Katsuhiko, Sasaki, Katsuya, Sakamoto, Ryo, and Hidani, Keitaro
- Subjects
COMPUTER simulation ,FRACTURE mechanics ,CONCRETE ,ELECTRIC discharges ,NITROMETHANE ,STRAINS & stresses (Mechanics) ,FINITE element method - Abstract
This paper investigated the mechanism of fracture in concrete due to the deflagration phenomenon. For this purpose, the electric discharge impulse crushing method was selected, with liquid nitromethane (NM) taken as the deflagration agent. Employing this technique, NM is set inside charge holes and initiated by electric discharge. The pressure generated by the deflagration of NM in a steel chamber was modeled using the Jones-Wilkins-Lee equation of state. The modeled and measured pressures agreed well and the applicability of the pressure model was validated. Then, assuming controlled splitting along the expected fracture surface in concrete, dynamic fracture process analysis (DFPA) based on two-dimensional dynamic finite element method was conducted. The results showed that fracture patterns predicted in the DFPAs agreed well with those obtained from experiments. The mechanism of fracture in concrete due to deflagration was then discussed in terms of the fracture process in the controlled splitting. Owing to stress interference from each charge hole, compressive stress zones (CSZs) formed above and below the middle regions between charge holes where maximum and minimum principle stresses were both in compression. The CSZs was found to be important in obtaining a flatter fracture surface in the case of controlled splitting. In conclusion, the proposed method was shown to be useful for the investigation of the fracture mechanism in the case of the use of deflagration agents and could be useful for the design optimization of such controlled splitting. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
20. Crack propagation criteria in three dimensions using the XFEM and an explicit-implicit crack description.
- Author
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Baydoun, M. and Fries, T.
- Subjects
CRACK propagation (Fracture mechanics) ,FINITE element method ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,BENDING (Metalwork) ,TORSION ,FORCE & energy - Abstract
This paper studies propagation criteria in three-dimensional fracture mechanics within the extended finite element framework (XFEM). The crack in this paper is described by a hybrid explicit-implicit approach as proposed in Fries and Baydoun (Int J Numer Methods Eng, ). In this approach, the crack update is realized based on an explicit crack surface mesh which allows an investigation of different propagation criteria. In contrast, for the computation of the displacements, stresses and strains by means of the XFEM, an implicit description by level set functions is employed. The maximum circumferential stress criterion, the maximum strain energy release rate criterion, the minimal strain energy density criterion and the material forces criterion are realized. The propagation paths from different criteria are studied and compared for asymmetric bending, torsion, and combined bending and torsion test cases. It is found that the maximum strain energy release rate and maximum circumferential stress criterion show the most favorable results. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
21. On the Relationship Between the H-Tensor and the Concentration Tensor and Their Bounds.
- Author
-
Zohdi, T.
- Subjects
COMPOSITE materials ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,VOLUMETRIC analysis ,HYDROGEN bonding - Abstract
For composite materials, two quantities that are useful for characterizing the contribution of inhomogeneities in a matrix material to the overall properties are (1) the individual H-tensor, H, which describes the contribution of a single inhomogeneity and (2) the overall strain concentration tensor, which describes the relationship between the overall volumetric strain to the average strain of all of the inhomogeneities. In this paper, we develop a relationship expressing the overall H-tensor, $${\mathcal{H}}$$ , in terms of the overall strain concentration tensor. An important feature of the derivation is that it allows for rigorous upper and lower bounds on the overall H-tensor. In the special case that the inhomogeneities are all the same, with the same orientation, then $${\mathcal{H} = {\bf H}_i}$$ , and the results derived for $${\mathcal{H}}$$ also hold for H. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
22. Matrix form near tip solutions of interface corners.
- Author
-
Hwu, Chyanbin
- Subjects
STRESS intensity factors (Fracture mechanics) ,PREDICTION theory ,STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,COMPARATIVE studies ,NUMERICAL analysis ,STRENGTH of materials ,DEFORMATIONS (Mechanics) - Abstract
In this paper, the stresses near the tip of interface corners are expressed in matrix power function form. To make this matrix power function form valid for all possible cases of interface corners, all kinds of singularities including oscillatory and logarithmic singularity are discussed in this paper. The coefficient vector of this matrix power function form solution is then defined as a vector of stress intensity factors along the radial direction. Since the stress intensity factors are functions of radial direction, the maximum stress intensity factor of a certain radial direction may be useful for the fracture prediction of interface corners. This new definition of stress intensity factors is applicable for all possible singular orders-repeated or distinct, real or complex, and keeps the same unit for all possible interface corners. Therefore, it will be helpful for bridging the problems of cracks, corners, interface cracks and interface corners. Finally, the matrix form solutions are reduced to the scalar form solutions for two special cases. One is a special case of corner angles-cracks, and the other is a special case of anisotropic materials-isotropic materials. Through this reduction, new scalar form analytical solutions are obtained and specialized further to compare with the existing analytical solutions. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
23. Crack propagation in elastic solids using the truss-like discrete element method.
- Author
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Kosteski, Luis, Barrios D'Ambra, Ricardo, and Iturrioz, Ignacio
- Subjects
CRACK propagation (Fracture mechanics) ,ELASTICITY ,COMPUTER simulation ,STRAINS & stresses (Mechanics) ,CRYSTAL lattices ,FRAGMENTATION reactions ,FRACTURE mechanics - Abstract
The crack propagation simulation is still an open problem in the mechanical simulation field. In the present work this problem is analyzed using a version of truss-like Discrete Element Method, that here we called DEM. This method has been used with success in several applications in solid mechanical problems where the simulation of fracture and fragmentation is relevant. The formulation of DEM explaining the way the process of rupture could be simulated in consistent form is showed. Also are described details about how the dynamical fracto-mechanical stress intensity factors are computed. The main aim of this paper is to show the ability of this method in simulating fracture and crack propagation in solids, for this, three examples with different levels of complexity are analyzed. The obtained results are presented in terms of the variation of dynamic stress intensity factor in the fracture process, the stress map and geometric configuration on different steps in the simulation of the fracture process, the crack speed and the energetic balance during all the process. These results are compared with experimental and numerical results obtained by other researchers and published in recognized scientific papers. Final commentaries about the performance of the version of lattice model considered are carried out. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
24. Analytical solution for propagation of hydraulic fracture with Barenblatt's cohesive tip zone.
- Author
-
Mokryakov, Vyacheslav
- Subjects
FRACTURE mechanics ,HYDRAULICS ,MATHEMATICAL models ,PRESSURE ,STRAINS & stresses (Mechanics) ,FLUID mechanics ,ROCK mechanics - Abstract
In the paper, a model of a hydraulic fracture with a tip cohesive zone according to the Barenblatt's approach is considered. The particular case of inviscid fracturing fluid and impermeable rock is studied analytically. Dependencies on time of the fracture length, injection pressure, and fracture opening at the wellbore are obtained, and compared with the corresponding dependencies for a brittle (elliptic-tip) hydraulic fracture. It is proved that on the assumption of finiteness of the cohesive stresses action range, the cohesive zone length cannot also exceed a certain limit value. The limit form of the cohesive zone is obtained, and the limit fracture toughness is evaluated. It is shown that effective fracture toughness tends to the limit value as power function of fracture length with index −1/2. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
25. Bimaterial Four Point Bend Specimen with Sub-Interface Crack.
- Author
-
Marsavina, Liviu and Piski, Timea
- Subjects
FINITE element method ,NUMERICAL analysis ,STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,DEFORMATIONS (Mechanics) - Abstract
Asymmetric four point bend specimens are often used for determination mode II fracture toughness. Different corrections were proposed to classical solution of Stress Intensity Factors for this specimen. This paper provides a solution for a bi-material four point specimen with sub-interface crack. The solutions were obtained using Finite Element Analysis, and the effect of crack distance to interface, crack length and materials combination were investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
26. Studies of dynamic crack propagation and crack branching with peridynamics.
- Author
-
Youn Doh Ha and Bobaru, Florin
- Subjects
FRACTURE mechanics ,DEFORMATIONS (Mechanics) ,BRITTLENESS ,STRAINS & stresses (Mechanics) ,STRESS waves - Abstract
In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement ( m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons. We also analyze the influence of the particular shape of the micro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well as it obtains crack propagation speeds that compare well, qualitatively and quantitatively, with experimental results published in the literature. The branching patterns also correlate remarkably well with tests published in the literature that show several branching levels at higher stress levels reached when the initial notch starts propagating. We notice the strong influence reflecting stress waves from the boundaries have on the shape and structure of the crack paths in dynamic fracture. All these computational solutions are obtained by using the minimum amount of input information: density, elastic stiffness, and constant fracture energy. No special criteria for crack propagation, crack curving, or crack branching are used: dynamic crack propagation is obtained here as part of the solution. We conclude that peridynamics is a reliable formulation for modeling dynamic crack propagation. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
27. A finite element modelling for directly determining intensity factors of piezoelectric materials with cracks.
- Author
-
Zongjie Cao and Zhenbang Kuang
- Subjects
PIEZOELECTRIC materials ,FRACTURE mechanics ,FINITE element method ,STRAINS & stresses (Mechanics) ,NUMERICAL analysis ,ELECTRIC potential - Abstract
Recently, authors(Cao et al., Acta Aeronautica et Astronautica Sinica 25(5): 470–472, 2004) extended the singular crack element originally introduced by Wang et al. (Eng Fract Mech 37(6):1195–1201, 1990) for evaluating the stress intensity factors (SIFs). Extensive studies have proved the versatility and accuracy of the element. This study is to show the versatility of the element for piezoelectric materials. In this paper, electric potential and displacement fields near a crack tip of piezoelectric materials are first used to construct a finite element version for directly determining intensity factors of piezoelectric materials with cracks. A singular finite element is constituted and a new method to calculate intensity factors of piezoelectric materials with cracks is obtained without any post-processing procedures. Detailed derivations are given and the results obtained with present method are good agreement with those of theoretical results, the FEM data by ANSYS and singular electromechanical crack tip elements. The results to the different selections of the structural dimensions are carried out. Numerical examples demonstrate the accuracy and validity of the novel element of present method. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
28. Correction to the Crack Extension Direction in Numerical Modelling of Mixed Mode Crack Paths.
- Author
-
Lucht, T. and Aliabadi, M.
- Subjects
STRENGTH of materials ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,BOUNDARY element methods ,MECHANICS (Physics) - Abstract
In order to avoid introduction of an error when a local crack growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction is proposed in connection with crack growth analyzed by the Dual Boundary Element Method (DBEM). The proposed correction procedure and a reference correction procedure already described in the literature are evaluated by solving two different computational crack growth examples. In the two examples it is found that analyses of the crack paths performed with the proposed crack correction procedure using big increments of crack extension are in excellent agreement with analyses of the crack paths performed by using very small increments of crack extension. Furthermore, it is shown that the reference correction procedure has a tendency to overcorrect the crack growth direction if the stop criterion for the iterative correction procedure is not calibrated in each new crack growth analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
29. Determination of the CTOA and J integral by fracture surface topography analysis.
- Author
-
Yuguang Cao and Tanaka, Kiyoshi
- Subjects
FRACTURE mechanics ,DEFORMATIONS (Mechanics) ,STRAINS & stresses (Mechanics) ,ELASTIC solids ,PHYSICS instruments ,FRACTOGRAPHY ,MECHANICS (Physics) - Abstract
In order to investigate the causes of material fracture, a new method is proposed that uses only the fracture surfaces for determining the fracture parameters in terms of the Cract-tip opening angle (CTOA) and the J integral. This method is based on the principle of fracture-surface topography analysis (FRASTA). In FRASTA, the fracture surfaces are scanned by laser microscope and the elevation data is recorded. Based on this recorded elevation data, the J integral can be calculated. The J integral calculated by the new method agrees well with that calculated by the elastic compliance method. FRASTA allows easy determination of the crack opening deformation (CTOA and COA) and the variation in CTOA and COA through specimen thickness. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
30. Some Expressions for the Strain Energy in a Finite Volume Surrounding the Root of Blunt V-notches.
- Author
-
Lazzarin, P. and Berto, F.
- Subjects
BRITTLENESS ,MATERIALS testing ,FRACTURE mechanics ,ELASTICITY ,MATERIAL fatigue ,NOTCH effect ,STRAINS & stresses (Mechanics) - Abstract
The paper gives some closed form expressions for the strain energy averaged in a finite size volume surrounding the root of blunt V-shaped notches under Mode I loading. The control volume, reminiscent of Neuber’s concept of elementary structural volumes, is thought of as dependent on the ultimate tensile strength and the fracture toughness K
IC in the case of brittle or quasi-brittle materials subjected to static loads. Expressions for strain energy density under plane strain conditions and Mode I loading have been derived from an analytical frame recently reported in the literature, which matches Williams and Creager-Paris’ solutions in the particular cases of plates weakened by sharp V-notches or blunt cracks (U-notches), respectively. In order to validate a local-strain-energy based approach, a well-documented set of experimental data recently reported in this journal by Gómez and Elices has been used. Data refer to blunt and sharp V-specimens of PMMA subjected to static tension loads and characterised by a large variability of notch root radius (from 0 to 4.0 mm) and notch angle (from 0° to 150°). Critical loads obtained experimentally have been compared with the theoretical ones, estimated here by keeping constant the mean value of the strain energy in a well-defined small size volume. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
31. T-stress in orthotropic functionally graded materials: Lekhnitskii and Stroh formalisms.
- Author
-
Jeong-Ho Kim and Paulino, Glaucio H.
- Subjects
FUNCTIONALLY gradient materials ,COMPOSITE materials ,MATERIALS ,STRAINS & stresses (Mechanics) ,ARCHITECTURE ,ELASTIC solids ,FLEXURE ,MECHANICS (Physics) - Abstract
A new interaction integral formulation is developed for evaluating the elastic T-stress for mixed-mode crack problems with arbitrarily oriented straight or curved cracks in orthotropic nonhomogeneous materials. The development includes both the Lekhnitskii and Stroh formalisms. The former is physical and relatively simple, and the latter is mathematically elegant. The gradation of orthotropic material properties is integrated into the element stiffness matrix using a ``generalized isoparametric formulation'' and (special) graded elements. The specific types of material gradation considered include exponential and hyperbolic-tangent functions, but micromechanics models can also be considered within the scope of the present formulation. This paper investigates several fracture problems to validate the proposed method and also provides numerical solutions, which can be used as benchmark results (e.g. investigation of fracture specimens). The accuracy of results is verified by comparison with analytical solutions. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
32. A fracture criterion for sharp V-notched samples.
- Author
-
Gómez, F. J. and Elices, M.
- Subjects
STRAINS & stresses (Mechanics) ,DEFORMATIONS (Mechanics) ,FRACTURE mechanics ,STRENGTH of materials ,MATERIAL fatigue ,MATHEMATICAL models - Abstract
The objective of this paper is to show the advantages of the cohesive crack model for predicting fracture of V-notched components. Critical values of the generalized stress intensity factor can be obtained from the knowledge of the material softening function and the elastic parameters, avoiding a cumbersome experimental work. The results were checked successfully against experimental ones, from other authors, in different materials: steel, aluminium, PMMA and PVC. A non dimensional formulation of the fracture criterion for sharp V-notched components was obtained and a simple approximate expression derived for easy appication. [ABSTRACT FROM AUTHOR]
- Published
- 2003
33. Crack onset at a v-notch. Influence of the notch tip radius.
- Author
-
Leguillon, Dominique and Yosibash, Zohar
- Subjects
ELASTICITY ,STRAINS & stresses (Mechanics) ,STRENGTH of materials ,FRACTURE mechanics ,DEFORMATIONS (Mechanics) ,ENGINEERING - Abstract
A criterion to predict crack onset at a sharp notch in homogeneous brittle materials has been presented in a previous paper of one of the authors. It is reviewed and improved herein. It fulfils both the energy and the strength criteria and takes an Irwin-like form involving the generalized intensity factor of the singularity governing the elastic behaviour in the vicinity of a notch tip. The prediction agrees fairly well with the experiments although it slightly underestimates the experimental measures. A cause of this discrepancy can be that a small notch tip radius blunts the sharp corner. It is analysed in this paper by means of matched asymptotics involving 2 small parameters: a micro-crack increment length and the notch tip radius. A correction is brought to the initial prediction and a better agreement is obtained with experiments on PMMA notched specimens. Experiments performed on a stiffer material (Alumina/Zirconia) show that it is less sensitive to small notch tip radii. A remaining small discrepancy between experiments and predictions can be due to some non linear behaviour of the materials near the notch tip. In addition, without new developments, the method allows to determine the stress intensity factor at the tip of a short crack emanating from a sharp or a rounded v-notch. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
34. Application of peridynamic stress intensity factors to dynamic fracture initiation and propagation.
- Author
-
Panchadhara, Rohan and Gordon, Peter
- Subjects
STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,CRACK initiation (Fracture mechanics) ,FRACTURE toughness ,MECHANICAL loads - Abstract
A non-local formulation of the classical continuum mechanics theory called peridynamics is used to study initiation and propagation of dynamic fractures. The purpose of this study is twofold. First, we introduce a new post-processing technique to estimate stress intensity factors using peridynamic data. Second, the peridynamic stress intensity factors are used to study the influence of loading rate on key aspects of dynamic fracture. In particular attention is focused on examining the influence of loading rate and material properties on time to fracture and the local stress state at the fracture tip during initiation and propagation. In the first part of the paper emphasis is placed on using stress intensity factors to verify the numerical method. Simulations are performed on simplified test cases and the results are compared to relevant experimental and numerical studies found in the literature. Peridynamic stress intensity factors are then used to demonstrate the influence of loading rate on fracture initiation and propagation. To this end simulations are performed by partially loading the internal surfaces of a notch at various loading rates and monitoring the stress intensity at the tip of the notch. For each loading rate, the stress intensity factor increases smoothly to a value above the input fracture toughness at which point initiation occurs. After initiation, the stress intensity factor remains nearly constant in time. It is shown that the stress intensity factor at initiation and the time to fracture depend on the loading rate. Predictions show that the critical stress intensity is insensitive to loading rate when the fracture initiation time is below a material-dependent characteristic time scale. As loading rate increases, the time to fracture decreases and stress intensity at initiation increases markedly. The characteristic time-scale is shown to be only dependent on the material stiffness and independent of the strength of the singularity at the fracture tip. In our simulations, increasing the loading rate resulted in fracture branching. Also, the fracture speed increases with loading rate. However, the dynamic stress intensity factor of a propagating fracture is shown to be independent of loading conditions for a linear peridynamic solid with rate-independent input fracture toughness. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
35. On the anti-plane state of stress near pointed or sharply radiused notches in strain limiting elastic materials: closed form solution and implications for fracture assessements.
- Author
-
Zappalorto, M., Berto, F., and Rajagopal, K.
- Subjects
STRAINS & stresses (Mechanics) ,NOTCH strength ,FRACTURE mechanics ,SURFACE cracks ,ELASTICITY - Abstract
In this paper a comprehensive investigation is carried out with regard to the state of the stress and strain in the neighbourhood of notches in bodies subjected to an anti-plane state of shear stress, within the context of a strain limiting theory of elasticity. Taking advantage of a unified analytical framework, the strain-limiting theory of elasticity is used to determine the full stress and strain field close to a pointed or radiused notch with any notch opening angle. An extensive discussion is provided that highlights the main features of stress and strain distributions, and the implications of the new theory for fracture assessments. In particular, it is proved that the obtained stress and strain solution predicts finite strains at the notch tip and allows the intensity of the stress field to be written as a function of the elastic Notch Stress Intensity Factor $$K_{3}$$ , as in the case of conventional linearized elasticity theory. This makes the strain limiting elasticity an excellent vehicle for justifying theoretically a K based-approach to the fracture of brittle elastic solids, within the context of a self consistent theory, unlike the classical linearized theory that predicts singularities for the strain at crack tips. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
36. Cracks at rounded V-notch tips: an analytical expression for the stress intensity factor.
- Author
-
Sapora, A., Cornetti, P., and Carpinteri, A.
- Subjects
FRACTURE mechanics ,NOTCHED bar testing ,STRAINS & stresses (Mechanics) ,MECHANICAL loads ,FINITE element method ,BRITTLE fractures ,FRACTURE toughness - Abstract
An analytical expression for the stress intensity factor related to a crack stemming from a blunted V-notch tip is put forward. The analysis is limited to mode I loading conditions, as long as the crack length is sufficiently small with respect to the notch depth. The proposed formula improves significantly the predictions of a recently introduced relationship, by considering a notch amplitude dependent parameter. Its values are estimated through a finite element analysis: different notch amplitudes, ranging from $$0^{\circ }$$ to $$180^{\circ }$$ , and different crack length to root radius ratios, ranging from 0 to 10, are taken into account. The evaluation of the apparent generalized fracture toughness according to equivalent linear elastic fracture mechanics concludes the paper. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
37. Cohesive model approach to the nucleation and propagation of cracks due to a thermal shock.
- Author
-
Cyron, Christian, Marigo, Jean-Jacques, and Sicsic, Paul
- Subjects
COHESIVE strength (Mechanics) ,FRACTURE mechanics ,THERMAL shock ,NUCLEATION ,SURFACE energy ,STRAINS & stresses (Mechanics) - Abstract
This paper studies the initiation of cohesive cracks in the thermal shock problem through a variational analysis. A two-dimensional semi-infinite slab with an imposed temperature drop on its free surface is considered. Assuming that cracks are periodically distributed and orthogonal to the surface, at short times we show that the optimum is a distribution of infinitely close cohesive cracks. This leads us to introduce a homogenized effective behavior which reveals to be stable for small times, thanks to the irreversibility. At a given loading cracks with a non-cohesive part nucleate. We characterize the periodic array of these macro-cracks between which the micro-cracks remain. Finally, for longer times, the cohesive behavior converges towards that from Griffith's evolution law. Numerical investigations complete and quantify the analytical results. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
38. Cohesive crack, size effect, crack band and work-of-fracture models compared to comprehensive concrete fracture tests.
- Author
-
Hoover, Christian and Bažant, Zdeněk
- Subjects
COHESIVE strength (Mechanics) ,SURFACE cracks ,FRACTURE mechanics ,BRITTLE materials ,TENSILE strength ,SEPARATION (Technology) ,STRAINS & stresses (Mechanics) - Abstract
The simplest form of a sufficiently realistic description of the fracture of concrete as well as some other quasibrittle materials is a bilinear softening stress-separation law (or an analogous bilinear law for a crack band). This law is characterized by four independent material parameters: the tensile strength, $$f'_t$$ , the stress $$\sigma _k$$ at the change of slope, and two independent fracture energies-the initial one, $$G_f$$ and the total one, $$G_F$$ . Recently it was shown that all of these four parameters can be unambiguously identified neither from the standard size effects tests, nor from the tests of complete load-deflection curve of specimens of one size. A combination of both types of test is required, and is here shown to be sufficient to identify all the four parameters. This is made possible by the recent data from a comprehensive test program including tests of both types made with one and the same concrete. These data include Types 1 and 2 size effects of a rather broad size range (1:12.5), with notch depths varying from 0 to 30 % of cross section depth. Thanks to using identically cured specimens cast from one batch of one concrete, these tests have minimum scatter. While the size effect and notch length effect were examined in a separate study, this paper deals with inverse finite element analysis of these comprehensive test data. Using the crack band approach, it is demonstrated: (1) that the bilinear cohesive crack model can provide an excellent fit of these comprehensive data through their entire range, (2) that the $$G_f$$ value obtained agrees with that obtained by fitting the size effect law to the data for any relative notch depth deeper than 15 % of the cross section (as required by RILEM 1990 Recommendation), (3) that the $$G_F$$ value agrees with that obtained by the work-of-fracture method (based on RILEM 1985 Recommendation), and (4) that the data through their entire range cannot be fitted with linear or exponential softening laws. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
39. Determination of History of Dynamic Stress Intensity Factor at Low Impact Velocities using Reduced Record of Experimental Forces in Three Point Bend Test.
- Author
-
Balachandran, R. and Maiti, S. K.
- Subjects
STRAINS & stresses (Mechanics) ,STRESS intensity factors (Fracture mechanics) ,FRACTURE mechanics ,TIMOSHENKO beam theory ,VIBRATION (Mechanics) - Abstract
The paper examines the possibility of reducing the efforts for data collection through impact testing of three point bend specimens for determining the variation of the dynamic SIF (DSIF) with time. In modelling, the specimen is represented by two Timoshenko beams connected by a rotational spring. The DSIF variation with time is obtained through forced vibration analysis by treating the beam as a free-free system under the action of the experimentally measured striker force and the anvil reactions. The anvil reactions can correspond to any specimen in a batch of specimens differing slightly in length or crack size. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
40. Fracture characterization of high-density polyethylene pipe materials using the $$J$$ -integral and the essential work of fracture.
- Author
-
Elmeguenni, M., Naït-Abdelaziz, M., Zaïri, F., and Gloaguen, J.
- Subjects
FRACTURE mechanics ,POLYETHYLENE ,TENSILE strength ,CRACK propagation (Fracture mechanics) ,BENDING strength ,NECKING (Engineering) ,STRAINS & stresses (Mechanics) - Abstract
In this paper, fracture mechanics concepts are reviewed and their relevance to examine the toughness of highly deformable materials such as high-density polyethylene (HDPE) pipe materials is discussed. Using two different specimen configurations (single edge notched bending and compact tension), it was found that the $$J-R$$ approach is unable to give pertinent indications on fracture toughness of HDPE. Alternatively, applying the essential work of fracture approach to double edge notched tension specimen, seems a more appropriate way to measure the fracture strength of HDPE and therefore to analyze the fracture process of such materials. Nevertheless, the severe necking occurring at the crack tip and in the plastic zone makes difficult the crack growth measurement, which clearly depends on the strain state and on the stress triaxiality level. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
41. Derivation of constraint-dependent J- R curves based on modified $$T$$ -stress parameter and GTN model for a low-alloy steel.
- Author
-
Wang, J., Wang, G., Xuan, F., and Tu, S.
- Subjects
CONSTRAINTS (Physics) ,STRAINS & stresses (Mechanics) ,LOW alloy steel ,FRACTURE mechanics ,CRACK propagation (Fracture mechanics) ,MECHANICAL loads ,DUCTILE fractures - Abstract
In this paper, a modified load-independent $$T$$ -stress constraint parameter $$\tau ^{*}$$ was defined. The $$\tau ^{*}$$ of specimens with different crack-tip constraint levels at different $$J$$ -integrals was calculated, and its load-independence has been validated. Based on the modified constraint parameter $$\tau ^{*}$$ and the numerically calculated J- R curves by using the Gurson-Tvergaard-Needleman (GTN) model for the SENB specimens with different $$a/W$$ , the equations of constraint-dependent J- R curves for the A508 steel were obtained. The predicted J- R curves using the equations essentially agree with the experimental and calculated J- R curves. The transferability of the constraint-dependent J- R curves to the CT, SENT and CCT specimens was validated. The results show that the modified constraint parameter $$\tau ^{*}$$ and the GTN model can be effectively used to derive the constraint-dependent J- R curves for ductile materials. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
42. Calculation method for maximum low-cycle fatigue loads using FRASTA reconstruction data.
- Author
-
Cao, Yu-guang, Zhang, Shi-hua, and Tanaka, Kiyoshi
- Subjects
SURFACE topography ,FATIGUE cracks ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,FAILURE analysis ,MATERIAL plasticity - Abstract
A new method is proposed to calculate the load on a specimen during a fatigue failure using a post-mortem analysis of the fracture surfaces. This method uses the fracture-surface topography analysis to infer the plastic strains that have developed during the failure. That is, based on the previously proposed simple bar hypothesis, the fracture surfaces can be assumed to be composed of independent rectangular bars. After dividing the plastic deformation into single bars, the original lengths of these bars are calculated and then the global strains of these bars during the course of failure are calculated. According to the relationship between true stress and true strain for the material, the normal stress on the cross section of each bar is determined. Adding all loads on all bars together provides the total applied load of the specimen. As illustrations, the method is applied to fracture surfaces obtained from double-edge notched specimens made of two kinds of metallic alloy, broken under low-cycle fatigue. Results show that the calculated maximum fatigue load is almost equal to that recorded during testing. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
43. Stress-Strain Behaviour Simulation of Vanadium Microalloyed Steel with the Internal Defects During two Different Heating Strategies.
- Author
-
Kvičala, Miroslav, Frydrýšek, Karel, and Hendrych, Aleš
- Subjects
HEATING of steel ,VANADIUM alloys ,STRAINS & stresses (Mechanics) ,SIMULATION methods & models ,MICROALLOYING ,CRACK propagation (Fracture mechanics) ,FRACTURE mechanics ,MECHANICAL properties of metals - Abstract
This paper is focused on the explanation of a linkage between two different heating strategies and a grow of the internal casting defects, that are already present in continuously cast blooms made from vanadium micro-alloyed Cr-Mo steel. Internal defects initiation and propagation can be associated to unsuitable casting and heating conditions. Small casting voids surrounded by ferrite-bainite network enriched by carbides forming elements produce perfect conditions for crack grow during the bloom straightening, heating in the soaking pit and/or heat treatment. Moreover, we simulated the stress-strain behaviour of continuously cast round bloom during heating in soaking pit using the FEM software. It is shown that optimized heating strategy led to significantly lower rates of the plastic strain as a crucial value for the crack propagation. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
44. A multi-scale approach to bridge microscale damage and macroscale failure: a nested computational homogenization-localization framework.
- Author
-
Coenen, E., Kouznetsova, V., Bosco, E., and Geers, M.
- Subjects
FRACTURE mechanics ,STRUCTURAL failures ,BRIDGES ,MICROSTRUCTURE ,DEFORMATIONS (Mechanics) ,CRACK propagation (Fracture mechanics) ,COHESIVE strength (Mechanics) ,STRAINS & stresses (Mechanics) - Abstract
This paper presents a multi-scale modelling approach for bridging the microscale damage and macroscale failure. The proposed scheme evolves from a classical computational homogenization scheme (FE) towards a discontinuity enriched framework. The classical homogenization approaches typically rely on the separation of scales principle, which is violated as soon as a strain localization band develops within a microstructural volume element (MVE). The newly developed scheme resolves this limitation by considering the bifurcation of the microscale deformation into a continuum 'bulk' part and a localization related part. The most distinct feature of the proposed framework is that both, the local macroscale traction-opening response of the cohesive crack and the stress-strain response of the surrounding 'bulk', are obtained from a single MVE analysis. The discontinuity enriched macroscale description is formulated to accommodate for the micro-macro coupling. The macroscale boundary value problem and the corresponding implementation are detailed for the use within the embedded discontinuities approach. The presented multi-scale method is demonstrated on a numerical example of a cohesive crack propagation in a macroscopic double notch specimen, with underlying voided microstructure. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
45. Numerical analysis of dynamic crack propagation in rubber.
- Author
-
Elmukashfi, Elsiddig and Kroon, Martin
- Subjects
CRACK propagation (Fracture mechanics) ,NUMERICAL analysis ,STRAINS & stresses (Mechanics) ,RUBBER ,FINITE element method ,FRACTURE mechanics ,VISCOELASTICITY ,STRENGTH of materials - Abstract
In the present paper, dynamic crack propagation in rubber is analyzed numerically using the finite element method. The problem of a suddenly initiated crack at the center of stretched sheet is studied under plane stress conditions. A nonlinear finite element analysis using implicit time integration scheme is used. The bulk material behavior is described by finite-viscoelasticity theory and the fracture separation process is characterized using a cohesive zone model with a bilinear traction-separation law. Hence, the numerical model is able to model and predict the different contributions to the fracture toughness, i.e. the surface energy, viscoelastic dissipation, and inertia effects. The separation work per unit area and the strength of the cohesive zone have been parameterized, and their influence on the separation process has been investigated. A steadily propagating crack is obtained and the corresponding crack tip position and velocity history as well as the steady crack propagation velocity are evaluated and compared with experimental data. A minimum threshold stretch of 3.0 is required for crack propagation. The numerical model is able to predict the dynamic crack growth. It appears that the strength and the surface energy vary with the crack speed. Finally, the maximum principal stretch and stress distribution around steadily propagation crack tip suggest that crystallization and cavity formation may take place. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
46. T-stress evaluations of an interface crack in the materials with complex interfaces.
- Author
-
Yu, Hongjun, Wu, Linzhi, and Li, Hui
- Subjects
STRAINS & stresses (Mechanics) ,FRACTURE mechanics ,NUMERICAL analysis ,FINITE element method ,COMPLEXITY (Philosophy) ,SYMMETRY (Physics) - Abstract
This paper develops an interaction integral method for extracting the T-stress of an interface crack in the materials with complex interfaces. In numerical computations, the interaction integral should be converted into an equivalent domain formulation to ensure numerical precision. It can be found that the present domain formulation does not contain any terms related to material interfaces, namely, the interaction integral is domain-independent for material interfaces. As a deduction, the present interaction integral can be used to solve the T-stress for a crack located on a curved interface effectively. Combined with the extended finite element method, the interaction integral method is employed to solve several interface crack problems. Good accuracy can be obtained for the interface fracture of a typical bimaterial strip. Meanwhile, it can be noted that the T-stress converges to a stable value only when the integral domain reaches up to an enough size. Since it is extremely difficult to select a large enough integral domain without any interfaces for the materials with complex interfaces, the domain-independence of the present interaction integral for interfaces is practical significant. Due to this point, the interaction integral method will become a quite reliable and convenient technique to solve the T-stress of an interface crack in the materials with complex interfaces. Finally, the interfacial fracture problem is investigated for several representative centrosymmetric structures formed by two constituent materials. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
47. Pressure stimulated electrical emissions from cement mortar used as failure predictors.
- Author
-
Triantis, D., Stavrakas, I., Kyriazopoulos, A., Hloupis, G., and Agioutantis, Z.
- Subjects
MORTAR ,FRACTURE mechanics ,CEMENT ,STRAINS & stresses (Mechanics) ,RELAXATION phenomena ,CREEP (Materials) ,ELECTRIC properties of materials ,MATERIALS compression testing ,HIGH pressure (Technology) - Abstract
The electrical signals emitted during the application of uniaxial compressive mechanical stress upon cement mortar specimens are observed and discussed in this paper. This work discusses the electrical signals that are detected when the specimens are excited by a stepwise uniaxial stress increase from a low level ( σ) to a higher level ( σ) at a fast or slow rate and consequently remain at a high pressure regime for a long time. When maintaining constant mechanical stress for a long time, creep phenomena are evident in the specimen and the corresponding electrical emissions are recorded and analyzed. The characteristics of the electrical signal give clear information regarding the breaking stress ( σ) of the material. The electrical emission recordings are of great interest when the applied σ is located in the vicinity of the failure stress; the emitted electrical current increases greatly due to the sequential formation and propagation of cracks that occurs in this stress region. Thus, by correlating the strain rate variations to the electrical emissions this methodology can be used to predict failure due to compressive stress in cement mortars. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
48. Time-domain BEM for transient interfacial crack problems in anisotropic piezoelectric bi-materials.
- Author
-
Lei, Jun and Zhang, Chuanzeng
- Subjects
FRACTURE mechanics ,TIME-domain analysis ,BOUNDARY element methods ,NUMERICAL integration ,STRAINS & stresses (Mechanics) ,ELECTRIC displacement ,PIEZOELECTRIC materials ,MECHANICAL behavior of materials ,ANISOTROPY - Abstract
A time-domain boundary element method (BEM) together with the sub-domain technique is applied to study transient response of interfacial cracks in piecewise homogeneous, anisotropic and linear piezoelectric bi-materials under electrical and mechanical impacts. The present time-domain BEM uses a quadrature formula for the temporal discretization to approximate the convolution integrals and a collocation method for the spatial discretization. Quadratic quarter-point elements are implemented at the tips of the interface cracks. To determine the real or complex dynamic stress intensity factors and the dynamic electrical displacement intensity factor of the interfacial cracks, an explicit extrapolating formula in a typical state of the crack plane perpendicular to the poling direction is presented in this paper. Numerical examples are presented; and the effects of the load combination and material combination on dynamic intensity factors and dynamic energy release rate are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
49. A damage model for crack prediction in brittle and quasi-brittle materials solved by the FFT method.
- Author
-
Li, Jia, Tian, Xiao-Xiao, and Abdelmoula, Radhi
- Subjects
FRACTURE mechanics ,BRITTLENESS ,FOURIER transforms ,PREDICTION models ,NUMERICAL analysis ,STRAINS & stresses (Mechanics) ,COMPUTER simulation - Abstract
In this paper, we present a damage model and its numerical solution by means of Fast Fourier Transforms (FFT). The FFT-based formulation initially proposed for linear and non-linear composite homogenization (Moulinec and Suquet in CR Acad Sci Paris Ser II 318:1417-1423 ; Comput Methods Appl Mech Eng 157:69-94 ) was adapted to evaluate damage growth in brittle materials. A non-local damage model based on the maximal principal stress criterion was proposed for brittle materials. This non-local model was then connected to the Griffith criterion with the aim of predicting crack growth. By using the proposed model, we carried out several numerical simulations on different specimens in order to assess the fracture process in brittle materials. From these studies, we can conclude that the present FFT-based analysis is capable of dealing with crack initiation and crack growth in brittle materials with high accuracy and efficiency. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
50. A non-singular boundary integral formula for frequency domain analysis of the dynamic T-stress.
- Author
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Phan, A.-V.
- Subjects
BOUNDARY element methods ,GALERKIN methods ,FRACTURE mechanics ,STRAINS & stresses (Mechanics) ,FOURIER transforms ,NUMERICAL analysis ,ASYMPTOTIC expansions - Abstract
A non-singular 2-D boundary integral equation (BIE) in the Fourier-space frequency domain for determining the dynamic T-stress (DTS) is presented in this paper. This formulation, based upon the Fourier transform of the asymptotic expansion for the stress field in the vicinity of a crack tip, can be conveniently implemented as a post-processing step in a frequency-domain boundary element analysis of cracks. The proposed BIE is accurate as it can be directly collocated at the crack tip in question. The technique is also computationally effective as it simply requires a similar computing effort as that used in determining the dynamic stress components at an interior point of a domain. Five numerical examples involving both straight and curved cracks are studied to validate the proposed technique. For the frequency domain analysis of the DTS in these examples, the exponential window method is employed to obtain its time history. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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