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R Narasimhan - One of the best experts on this subject based on the ideXlab platform.
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effect of loading rate on Crack tip fields in three point bend fracture specimen of fcc single crystal
International Journal of Solids and Structures, 2011Co-Authors: P Biswas, R NarasimhanAbstract:Abstract In this work, the effect of impact loading on mode I Stationary Crack tip fields in a three point bend FCC single crystal fracture specimen is investigated using plane strain finite element analysis. The behavior of the single crystal is assumed to be elastic-perfectly plastic. The main objective is to examine the role of material inertia in influencing the stress levels as well as the pattern of slip and kink shear bands around the tip. The results show that under quasi-static loading high stress levels prevail ahead of the notch tip. However, the specimen suffers considerable loss of constraint under dynamic loading, particularly during the initial stages. This increases with loading rate J ˙ . Also significant spread of the plastic zone occurs in the forward sector ahead of the tip under impact loading which is akin to isotropic solids. The pattern of shear bands around the tip in the single crystal also changes with impact velocity. In rate dependent single crystals, a competition between rate sensitivity and material inertia is observed. Thus, while the former enhances the stresses near the tip, the latter tends to reduce them.
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Stationary Crack tip fields in elastic plastic solids an overview of recent numerical simulations
Journal of Physics D, 2009Co-Authors: R Narasimhan, H Y Subramanya, S D Patil, Parag Tandaiya, U RamamurtyAbstract:In this paper, an overview of some recent numerical simulations of Stationary Crack tip fields in elastic-plastic solids is presented. First, asymptotic analyses carried out within the framework of 2D plane strain or plane stress conditions in both pressure insensitive and pressure sensitive plastic solids are reviewed. This is followed by discussion of salient results obtained from recent computational studies. These pertain to 3D characteristics of elastic-plastic near-front fields under mixed mode loading, mechanics of fracture and simulation of near-tip shear banding process of amorphous alloys and influence of Crack tip constraint on the structure of near-tip fields in ductile single crystals. These results serve to illustrate several important features associated with stress and strain distributions near the Crack tip and provide the foundation for understanding the operative failure mechanisms. The paper concludes by highlighting some of the future prospects for this field of study.
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A finite element analysis of small-scale yielding near a Stationary Crack under plane stress
Journal of The Mechanics and Physics of Solids, 2002Co-Authors: R Narasimhan, Ares J. RosakisAbstract:Abstract A detailed finite element analysis of the monotonic loading of a Stationary Crack is performed under Mode I plane stress, small-scale yielding conditions. A small strain, J 2 incremental plasticity theory is employed and both elastic-perfectly plastic and power law hardening materials are considered. Some issues such as the range of dominance of the asymptotic stress and deformation fields and the amount of non-proportional loading near the Crack tip, which have received wide attention in the analogous plane strain problem, are examined. Special attention is devoted to the perfectly plastic idealization by performing a separate singular finite element analysis to clarify some details about the asymptotic stress and deformation fields. The full-field numerical solution is used to simulate synthetic (optical) caustic patterns at different distances from the tip, which are compared with experimental observations and with asymptotic analytical results.
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a finite element analysis of Stationary Crack tip fields in a pressure sensitive constrained ductile layer
International Journal of Solids and Structures, 2000Co-Authors: Roy S Chowdhury, R NarasimhanAbstract:Polymeric ductile adhesive layers joining two elastic adherends is a common feature in various technological applications. Such joints can fail by ductile rupture involving interface debonding and void formation. It has been observed that, unlike in metals, the yield behaviour of polymers is affected by the state of hydrostatic stress. In the present study, the effect of pressure sensitivity of yielding on the stress and deformation fields near a Stationary Crack tip in a constrained adhesive layer is examined. To this end, finite deformation, finite element analyses of a Cracked, sandwiched adhesive layer are carried out under plane strain, small-scale yielding conditions for a wide range of mode mixities. The Drucker-Prager constitutive equations are employed to represent the behaviour of the layer. Both dilational and non-dilational plastic flow are considered. It is found that the stress levels in the layer decrease with increasing pressure sensitivity irrespective of mode mixity. The effect of pressure sensitivity on the notch tip deformation, and near tip plastic mode mixity, is also investigated. Finally, theoretical predictions are made about the variation of fracture toughness with mode mixity due to interface debonding.
A.k. Ghosh - One of the best experts on this subject based on the ideXlab platform.
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An insight of the structure of stress fields for Stationary Crack in strength mismatch weld under plane strain mode-I loading – Part II: Compact tension and middle tension specimens
International Journal of Mechanical Sciences, 2014Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, R. K. Singh, K. K. Vaze, A.k. GhoshAbstract:Abstract In-service inspections of many nuclear power plants have revealed that Cracks are most likely to occur in a weld or in the regions near the weld. In part-I, the problem of a Stationary Crack lying at the centre of a weld in a pure bending specimen SE(PB) was analysed. The detailed structure of the global plastic fields for a deep Crack, under fully plastic condition, was presented. Aspects related to the state of stress at the base-weld interface were discussed. To enhance our understanding of the weld strength mismatch effects, other commonly used fracture specimens, that is, compact tension C(T) and middle tension M(T) specimens having a weld centre Crack were analysed in the present investigation. The influence of weld mismatch on the structure of global stress fields (leading to plastic yielding of the ligament) as well as on the Crack tip constraint was studied. It is demonstrated that, when a Crack is postulated at the centre of a weld, a family of stress fields proposed in part-I for a SE(PB) specimen is applicable to a C(T) specimen also. The studies performed in this article, along with part-I, have established that in comparison to slip line field analysis, the modified upper bound theorem is simple and more general. It is applicable to macroscopically homogeneous materials and can also account for weld mismatch effects.
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An insight of the structure of stress fields for Stationary Crack in strength mismatch weld under plane strain mode-I loading—Part I: Pure bending specimen
International Journal of Mechanical Sciences, 2012Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, A.k. GhoshAbstract:Abstract In-service inspections of many nuclear power plants have revealed that Cracks are most likely to occur in or the regions near the weld. Interfacial Cracks under elastic as well as in elastic–plastic conditions have already been extensively discussed in literature. However, the problem of Crack lying at the centre of weld is less understood. Though several detailed numerical studies have been performed to investigate the influence of weld strength mismatch on Crack-tip stress fields till date, however, the detailed insight of the structure of stress fields under large scale plasticity is still lacking. The present article is intended to bridge that gap. In this work, detailed structure of the global plastic fields which occur in a deeply Cracked (a/W>0.3) mismatch welded pure bending specimen, under fully plastic condition, is presented. Aspects related to the state of stress at the interface of two materials are discussed. It is shown that a family of five fields proposed in this work is adequate to cover all practical cases of weld mismatch. Proposed fields were confirmed by detailed full-field finite element analyses. Excellent agreement is observed between the proposed theoretical solutions and the numerical results.
Ares J. Rosakis - One of the best experts on this subject based on the ideXlab platform.
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A finite element analysis of small-scale yielding near a Stationary Crack under plane stress
Journal of The Mechanics and Physics of Solids, 2002Co-Authors: R Narasimhan, Ares J. RosakisAbstract:Abstract A detailed finite element analysis of the monotonic loading of a Stationary Crack is performed under Mode I plane stress, small-scale yielding conditions. A small strain, J 2 incremental plasticity theory is employed and both elastic-perfectly plastic and power law hardening materials are considered. Some issues such as the range of dominance of the asymptotic stress and deformation fields and the amount of non-proportional loading near the Crack tip, which have received wide attention in the analogous plane strain problem, are examined. Special attention is devoted to the perfectly plastic idealization by performing a separate singular finite element analysis to clarify some details about the asymptotic stress and deformation fields. The full-field numerical solution is used to simulate synthetic (optical) caustic patterns at different distances from the tip, which are compared with experimental observations and with asymptotic analytical results.
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dynamic full field measurements of Crack tip temperatures
Engineering Fracture Mechanics, 2001Co-Authors: Pradeep R Guduru, Ares J. Rosakis, Alan T Zehnder, G RavichandranAbstract:This paper presents a detailed investigation of the evolution of temperature field at the tip of a Stationary Crack subjected to dynamic loading in two different types of steels. A high speed two-dimensional infrared camera was used to image the temperature fields at the Crack tips. In a high strength maraging steel, the thermograms reveal the development of plastic zone and the process of Crack initiation and propagation. In ductile HY100 steel, the thermograms are used to estimate the evolution of J integral and its critical value at Crack initiation. The temperature images are also used to investigate the dominance of HRR field around the Crack tip.
I.a. Khan - One of the best experts on this subject based on the ideXlab platform.
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An insight of the structure of stress fields for Stationary Crack in strength mismatch weld under plane strain mode-I loading – Part II: Compact tension and middle tension specimens
International Journal of Mechanical Sciences, 2014Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, R. K. Singh, K. K. Vaze, A.k. GhoshAbstract:Abstract In-service inspections of many nuclear power plants have revealed that Cracks are most likely to occur in a weld or in the regions near the weld. In part-I, the problem of a Stationary Crack lying at the centre of a weld in a pure bending specimen SE(PB) was analysed. The detailed structure of the global plastic fields for a deep Crack, under fully plastic condition, was presented. Aspects related to the state of stress at the base-weld interface were discussed. To enhance our understanding of the weld strength mismatch effects, other commonly used fracture specimens, that is, compact tension C(T) and middle tension M(T) specimens having a weld centre Crack were analysed in the present investigation. The influence of weld mismatch on the structure of global stress fields (leading to plastic yielding of the ligament) as well as on the Crack tip constraint was studied. It is demonstrated that, when a Crack is postulated at the centre of a weld, a family of stress fields proposed in part-I for a SE(PB) specimen is applicable to a C(T) specimen also. The studies performed in this article, along with part-I, have established that in comparison to slip line field analysis, the modified upper bound theorem is simple and more general. It is applicable to macroscopically homogeneous materials and can also account for weld mismatch effects.
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An insight of the structure of stress fields for Stationary Crack in strength mismatch weld under plane strain mode-I loading—Part I: Pure bending specimen
International Journal of Mechanical Sciences, 2012Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, A.k. GhoshAbstract:Abstract In-service inspections of many nuclear power plants have revealed that Cracks are most likely to occur in or the regions near the weld. Interfacial Cracks under elastic as well as in elastic–plastic conditions have already been extensively discussed in literature. However, the problem of Crack lying at the centre of weld is less understood. Though several detailed numerical studies have been performed to investigate the influence of weld strength mismatch on Crack-tip stress fields till date, however, the detailed insight of the structure of stress fields under large scale plasticity is still lacking. The present article is intended to bridge that gap. In this work, detailed structure of the global plastic fields which occur in a deeply Cracked (a/W>0.3) mismatch welded pure bending specimen, under fully plastic condition, is presented. Aspects related to the state of stress at the interface of two materials are discussed. It is shown that a family of five fields proposed in this work is adequate to cover all practical cases of weld mismatch. Proposed fields were confirmed by detailed full-field finite element analyses. Excellent agreement is observed between the proposed theoretical solutions and the numerical results.
Enrico Radi - One of the best experts on this subject based on the ideXlab platform.
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diffraction of antiplane shear waves and stress concentration in a Cracked couple stress elastic material with micro inertia
Journal of The Mechanics and Physics of Solids, 2019Co-Authors: Andrea Nobili, Enrico Radi, Adam VellenderAbstract:Abstract We investigate diffraction of reduced traction shear waves applied at the faces of a Stationary Crack in an elastic solid with microstructure, under antiplane deformation. The material behaviour is described by the indeterminate theory of couple stress elasticity and the Crack is rectilinear and semi-infinite. The full-field solution of the Crack problem is obtained through integral transforms and the Wiener–Hopf technique. A remarkable wave pattern appears which consists of entrained waves extending away from the Crack, reflected Rayleigh waves moving along the Crack, localized waves irradiating from the Crack-tip with, possibly, super-Rayleigh speed and body waves scattered around the Crack-tip. Interestingly, the localized wave solution may be greatly advantageous for defect detection through acoustic emission. Dynamic stress intensity factors are presented, which generalize to Elastodynamics the corresponding results already obtained in the static framework. The correction brings out the important role of wave diffraction on stress concentration.
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a stedily propagating Crack in planar quasicrystal with fivefold symmetry
ECF17 Brno 2008, 2013Co-Authors: Enrico Radi, Paolo Maria MarianoAbstract:Abstract. A closed-form solution is provided for the stress, strain and velocity fields due to a planar Crack steadily propagating in an elastic quasicrystal with fivefold symmetry at speed lower than the bulk wave-speeds. The case of a semi-infinite rectilinear Crack loaded on its surfaces is considered. The dynamic theory of quasicrystal with inertia forces, but neglecting dissipative phonon activity, is assumed to govern the motion of the medium. Both phonon and phason stress fields display squareroot singular at Crack tip. The energy release rate is positive for subsonic and subRayleigh Crack propagation. The limit case of a Stationary Crack is then recovered as the Crack tip speed becomes vanishing small.
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effects of characteristic material lengths on mode iii Crack propagation in couple stress elastic plastic materials
International Journal of Plasticity, 2007Co-Authors: Enrico RadiAbstract:The asymptotic fields near the tip of a Crack steadily propagating in a ductile material under Mode III loading conditions are investigated by adopting an incremental version of the indeterminate theory of couple stress plasticity displaying linear and isotropic strain hardening. The adopted constitutive model is able to account for the microstructure of the material by incorporating two distinct material characteristic lengths. It can also capture the strong size effects arising at small scales, which results from the underlying microstructures. According to the asymptotic Crack tip fields for a Stationary Crack provided by the indeterminate theory of couple stress elasticity, the effects of microstructure mainly consist in a switch in the sign of tractions and displacement and in a substantial increase in the singularity of tractions ahead of the Crack-tip, with respect to the classical solution of LEFM and EPFM. The increase in the stress singularity also occurs for small values of the strain hardening coefficient and is essentially due to the skew-symmetric stress field, since the symmetric stress field turns out to be non-singular. Moreover, the obtained results show that the ratio η introduced by Koiter has a limited effect on the strength of the stress singularity. However, it displays a strong influence on the angular distribution of the asymptotic Crack tip fields.
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effects of pre stress on Crack tip fields in elastic incompressible solids
International Journal of Solids and Structures, 2002Co-Authors: Enrico Radi, D Bigoni, Domenico CapuaniAbstract:Abstract A closed-form asymptotic solution is provided for velocity fields and the nominal stress rates near the tip of a Stationary Crack in a homogeneously pre-stressed configuration of a nonlinear elastic, incompressible material. In particular, a biaxial pre-stress is assumed with stress axes parallel and orthogonal to the Crack faces. Two boundary conditions are considered on the Crack faces, namely a constant pressure or a constant dead loading, both preserving an homogeneous ground state. Starting from this configuration, small superimposed Mode I or Mode II deformations are solved, in the framework of Biot's incremental theory of elasticity. In this way a definition of an incremental stress intensity factor is introduced, slightly different for pressure or dead loading conditions on Crack faces. Specific examples are finally developed for various hyperelastic materials, including the J2-deformation theory of plasticity. The presence of pre-stress is shown to strongly influence the angular variation of the asymptotic Crack-tip fields, even if the nominal stress rate displays a square root singularity as in the infinitesimal theory. Relationships between the solution with shear band formation at the Crack tip and instability of the Crack surfaces are given in evidence.