by Goldstein, Robert V.

DOI: 10.1007/s10704-008-9252-0
Online Date: 7/31/2008
Print publication date: 3/1/2008
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by Makhutov, N. A.; Gadenin, M. M.

The equations of an elasto-plastic static and cyclic deformation at high temperature, force and deformation criteria of quasistatic and fatigue failures, criterion of initiation and propagation of cracks, features of the equations for linear and nonlinear fracture mechanics are described. The mechanics of a nonlinear deformation and fracture is used for calculations of strength, life-time and crack resistance of constructions at high temperature.

DOI: 10.1007/s10704-008-9230-6
Online Date: 7/29/2008
Print publication date: 3/1/2008
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by Kashtanov, A. V.; Petrov, Yu. V.; Pugno, N.; Carpinteri, A.

A new approach describing the dynamic fracture as a process of nucleation and subsequent propagation of a nonlinear wave of microfracture is proposed. The equation describing the microfracture evolution is derived from the transfer equation and a stochastic diffusion-type description of damage redistribution. The physical meaning of the corresponding parameters is clarified by the mass conservation and the incubation time criterion of fracture. Finally the process of dynamic macrocrack nucleation is simulated.

DOI: 10.1007/s10704-008-9223-5
Online Date: 7/29/2008
Print publication date: 3/1/2008
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by Reyes, E.; Casati, M. J.; Gálvez, J. C.

This paper presents a numerical procedure for mixed mode fracture of brickwork masonry. The model is an extension of the cohesive model prepared by the authors for concrete, and takes into account the anisotropy of the material. After the crack path is obtained, an interface finite element (using the cohesive fracture model) is incorporated into the trajectory. Such a model is then implemented into a commercial code by means of a user subroutine, consequently being contrasted with experimental results. Fracture properties of masonry are independently measured for two directions on the composed masonry, and then input in the numerical model. This numerical procedure accurately predicts the experimental mixed mode fracture records for different orientations of the brick layers and two homothetic sizes on masonry panels.

DOI: 10.1007/s10704-008-9243-1
Online Date: 7/29/2008
Print publication date: 5/1/2008
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by Rungamornrat, Jaroon; Mear, Mark E.

A weakly singular, symmetric Galerkin boundary element method (SGBEM) is established to compute stress and electric intensity factors for isolated cracks in three-dimensional, generally anisotropic, piezoelectric media. The method is based upon a weak-form integral equation, for the surface traction and the surface electric charge, which is established by means of a systematic regularization procedure; the integral equation is in a symmetric form and is completely regularized in the sense that its integrand contains only weakly singular kernels of $${\mathcal{O}(1/r)}$$ (hence allowing continuous interpolations to be employed in the numerical approximation). The weakly singular kernels which appear in the weak-form integral equation are expressed explicitly, for general anisotropy, in terms of a line integral over a unit circle. In the numerical implementation, a special crack-tip element is adopted to discretize the region near the crack front while the remainder of the crack surface is discretized by standard continuous elements. The special crack-tip element allows the relative crack-face displacement and electric potential in the vicinity of the crack front to be captured to high accuracy (even with relatively large elements), and it has the important feature that the mixed-mode intensity factors can be directly and independently extracted from the crack front nodal data. To enhance the computational efficiency of the method, special integration quadratures are adopted to treat both singular and nearly singular integrals, and an interpolation strategy is developed to approximate the weakly singular kernels. As demonstrated by various numerical examples for both planar and non-planar fractures, the method gives rise to highly accurate intensity factors with only a weak dependence on mesh refinement.

DOI: 10.1007/s10704-008-9242-2
Online Date: 7/18/2008
Print publication date: 5/1/2008
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by Weber, W.; Steinmann, P.; Kuhn, G.

The continuous growth of 3D cracks under cyclic loading conditions is considered within a discrete simulation procedure. It is performed within the framework of linear elastic fracture mechanics. An incremental procedure is applied to consider the non-linear behavior of crack growth within the simulation. In each increment the direction and magnitude of the crack propagation for each point along the crack front are needed to define the new crack front. Within the present context the crack deflection results from the maximum tangential stress criterion and the crack extension is obtained by the evaluation of a crack propagation rate. To simulate the crack propagation as exactly as possible the evolution of the stress field between two consecutive crack fronts is taken into account. The analysis of the changing stress field is utilized for optimization of the predicted crack fronts. The whole procedure is realized in terms of a predictor–corrector scheme. Numerical examples are presented to demonstrate the benefits of this concept.

DOI: 10.1007/s10704-008-9241-3
Online Date: 7/17/2008
Print publication date: 2/1/2008
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by Papadopoulos, G. A.; Badalouka, B.; Souyiannis, J.

Patch repair of cracked structures has become a rapidly grown technology. The major function of a repair is to reduce the stress intensity factor at the crack-tip. Calculation of stress intensity factor of a repaired crack has been performed by analytical and numerical methods. However, these methods are based on simplifying assumptions regarding material behavior and repair conditions. In the present paper an experimental and an numerical determination of mode-I stress intensity factor (SIF), K_I at the tip of an edge crack reinforced with bonded patches is undertaken by using the optical method of caustics and the finite element analysis (FEA). The experimental method of caustics is simple in its application and has successfully been used for the solution of a host of crack problems of engineering importance. The experimental results are compared with the corresponding one obtained by FEA. The program ANSYS 11 was used for the FEA. The cracked used plates were made of Lexan (PCBA) and the patches were made of Plexiglas (PMMA).

DOI: 10.1007/s10704-008-9240-4
Online Date: 7/15/2008
Print publication date: 2/1/2008
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by Mikulik, Zoltan; Kelly, Donald W.; Prusty, B. Gangadhara; Thomson, Rodney S.

The behaviour of a composite test specimen with an embedded delamination subjected to transverse tension has been investigated through experimental testing and finite element (FE) analyses. The testing program consisted of specimens in two geometrical configurations; square and rectangular delamination. The initiation and growth of the delamination was numerically predicted by fracture mechanics. FE models were analysed with both MSC.Nastran and Abaqus FE codes. The MSC.Nastran model was used to calculate strain energy release rates employing a crack tip element methodology. The Abaqus model was evaluated using the virtual crack closure technique. Both approaches accurately predicted failure initiation locations as observed in the test specimens. Failure loads were also well predicted. The mode mix at the crack tip in the proposed specimen was found to be similar to the mode mix expected in a conventional in-plane compression specimen.

DOI: 10.1007/s10704-008-9220-8
Online Date: 7/10/2008
Print publication date: 2/1/2008
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by Zhang, H.; Ravi-Chandar, K.

In this series of papers, we investigate the mechanics of deformation localization and fragmentation in ductile materials. The behavior of ductile metals at strain rates between 4000 and 15,000 s⁻¹ is considered. The expanding ring experiment is used as the primary tool for examining the material behavior in this range of strain rates. In Part I, the details of the experiment and the experimental observations on Al 6061-O were reported. Statistics of necking and fragmentation were evaluated and the process was modeled through the idea of the Mott release waves both from necking and fragmentation. Finally, it was shown that the strain in the ring in regions that strained uniformly never exceeded the necking strain. In the present paper, Part II, we address the issue of strain hardening and strain-rate sensitivity. Specifically, we examine different materials—Al 1100-H14, and Cu 101—in order to determine the role of material constitutive property on the dynamics of necking. These experiments reinforce the conclusion presented in Part I that the onset of necking essentially terminates the possibility of further straining in other parts of the ring and even more importantly that there is no influence of material inertia on the strain at the onset of necking in this wide range of materials. Furthermore, the effect of aspect ratio of the specimen is evaluated; this reveals that as the aspect ratio increases beyond about five, in addition to or instead of diffuse necking, localization into the sheet necking mode is observed; in this mode, the effect of ring expansion speeds is demonstrated to result in an increase of the strain at the onset of localization. In addition, an absolute size effect is observed: larger specimens exhibit localization at larger strain levels. These observations are explained in terms of plastic wave propagation and reproduced with finite element simulations. In future contributions as part of this sequel, we will explore the effect of other geometrical constraints and the effect of a compliant cladding or coating on the development of necking and fragmentation.

DOI: 10.1007/s10704-008-9233-3
Online Date: 7/8/2008
Print publication date: 3/1/2008
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by Lurie, S. A.; Belov, P. A.

In the paper the higher-order theory of continuous media with conserved dislocations is developed to describe the spectrum of cohesion and superficial phenomena. A new kinematic interpretation of dislocations is offered, that reflects the connection of dislocations with distortion, with change in volume (porosity), and with twisting. The main aim of the paper is to receive the strong theoretical justification for famous hypothesis of Barenblatt about cohesion field near top of crack. A new variants of the fracture criterions are discussed that based on the of the theory of media with microstructures, connection of the length of the cohesion interaction zone (a new physical constant) with parameters of the fracture mechanics is established.

DOI: 10.1007/s10704-008-9225-3
Online Date: 7/8/2008
Print publication date: 3/1/2008
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