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Three-dimensional interactions of multiple frictionless punches pressed onto elastic half-space are considered. A method of analysis, inspired by similar ideas for interacting cracks [Kachanov, M., 1987. Int. J. Solids Struct. 23(1) 23–43], is suggested. The surface displacements of individual punches are interrelated via transmission factors that give the average surface displacements induced by a considered punch at sites of other punches. The method is extended to tilted punches. Comparison with available numerical results shows that the method has higher accuracy than other analytical methods. [ABSTRACT FROM AUTHOR]

Abstract: We discuss computation of compliance/stiffness contribution tensors of an inhomogeneity of non-ellipsoidal shape and the difficulties that may be encountered in this context. These issues are illustrated on the example of one specific shape factor: concavity–convexity of the inhomogeneity shape. It is found, in particular, that the effect of the concavity factor depends on the specific constraint imposed. If the inhomogeneity volume is kept constant, then its compliance contribution rapidly increases with increasing concavity; on the computational side it leads to difficulties related to unusually high requirements to the accuracy of the computed volume averages quantities. If, on the other hand, the characteristic dimensions (for example, the distance between the farthest points) are kept constant, then the dependence of the compliance contribution on the concavity factor is almost linear. [Copyright &y& Elsevier]

Experimental observations suggest that for perfectly-plastic materials containing pores, the (small) strain at which significant macroscopic yielding occurs is relatively insensitive to porosity, for volume fractions below approximately 15–20% (although the yield stress drops significantly with increasing porosity). Another observation is that, at these porosity levels, the stress–strain curve remains approximately linear almost up to the yield point. Based on these observations, Sevostianov and Kachanov constructed yield surfaces that explicitly reflect the shapes of the pores and their orientation. The underlying microscale mechanism is that local plastic “pockets” near pores blunt the stress concentrations; as a result, they remain limited in size and well contained in the elastic field until they connect and almost the entire matrix plasticizes within a narrow interval of stresses that can be idealized as the yield point. The present paper provides direct insight into the micromechanics of poroplasticity through direct microscale numerical simulation. Besides confirming the basic microscale mechanism, these simulations reveal that the reduction of the macroscopic poroplastic yield stress is approximated quite closely by 1−v2 times the dense nonporous yield stress, where v2 is the volume fraction of the pores. [Copyright &y& Elsevier]

The incremental normal compliance of a contact of "irregular" (non-elliptical) shape between two elastic half spaces is considered. The contact is modeled as external crack. An approximate expression for the stress intensity factor (SIFs) around its boundary, in conjunction with Rice (1975) theorem that interrelates SIFs and crack compliances, are used to evaluate the crack compliance. The results cover a broad class of contact shapes, including – but not limited to - all convex ones. Bounds, similar to Hill's comparison theorem in micromechanics, are formulated for the compliances of contacts. The cross-property elasticity-conductivity relation yields similar results for contact conductance. The methodology is illustrated on several examples. • A methodology for evaluation of contact compliances by treating contacts as external cracks is suggested. • Compliances of contacts of irregular shapes are evaluated. • Rigorous bounds for contact compliances are derived. [ABSTRACT FROM AUTHOR]

• Cracks of "zig-zag" shapes consisting of two rectilinear links are considered. • Their compliances and stress intensity factors and far field asymptotics are examined. • A simple and reasonably accurate computational procedure is developed. Cracks of kinked, or "zig-zag" shapes (that are common in brittle materials, particularly in polycrystalline ones) consisting of two rectilinear links are considered. Their compliances, as well as stress intensity factors, are examined using a simple and reasonably accurate procedure that is based on approximating the original configuration by rectilinear cracks separated by a very small ligament. Full stress fields and their far-field asymptotics are also examined. [ABSTRACT FROM AUTHOR]

Effective properties of short fiber reinforced composite material containing internal defects are considered. A new method of evaluation of the elastic properties deterioration due to microcracks/microvoids is suggested. It is based on the explicit correlations between two groups of anisotropic effective constants—thermal conductivities and elastic stiffnesses—established for such composite materials. Theoretical estimates are in a good agreement with obtained experimental data. [Copyright &y& Elsevier]

In literature on the effective properties of composites, one-particle homogenization schemes have been developed alongside with solutions for periodic arrangements of inhomogeneities (starting with the pioneering work of Lord Rayleigh, 1892). It has often been claimed that the two approaches are, to some extent, equivalent. These claims have been based, mostly, on the fact that in the case of cubic arrangement of spherical particles the two approaches, indeed, yield close results. The present work shows that the mentioned case (that is the simplest, and very special one) constitutes an exception: generally, application of one-particle homogenization schemes to periodic composites may generate very large errors. • Comparative analysis of effective conductivities of periodic and random composites is provided. • It is shown that materials with cubic arrangement of particles can be modeled using one-particle approximations. • Generally, application of one-particle homogenization schemes to periodic composites may generate very large errors. [ABSTRACT FROM AUTHOR]

Abstract The compliance contribution of a penny-shaped crack having multiple contacts between crack faces is analyzed. In order to reduce the number of parameters involved, regular lattices of circular contacts are considered. It is found, in particular, that, at the same total area of contacts, a large number of small contacts produces stronger stiffening effect than a small number of large contacts; hence the total contact area is not the parameter controlling the crack compliance contribution. The effects of contacts on both the normal and the shear crack compliances are found to be very close. In the case of moderately non-regular contact lattices, the results were found to be only marginally different from the results for regular ones. Results are conveniently expressed in terms of "Holm's radius"—the radius of a single contact that would have produced the same effect. Being applied to multiple cracks with contacts, our results yield the "adjusted", for the presence of contacts, value of crack density. [ABSTRACT FROM AUTHOR]

• Monitoring the lifetime, using changes in the elastic anisotropy and the increase of the α ′-phase. • High-accuracy acoustic monitoring, based on monitoring wave velocity ratios and α ′-phase. • Extraction of information on the past loading history (strain range and the number of cycles N). Low-cycle fatigue of metastable austenitic steel is studied experimentally, by combining high-accuracy acoustic monitoring of elastic anisotropy and eddy current monitoring of volume fraction of the martensite. This combined approach allows estimation of fatigue life as well as the information on the past loading history. At the microstructural level, the data allow one to identify the end of the incubation stage and the onset of active growth of the martensitic α ′ phase. Changes of elastic anisotropy and their dependence on the strain range, as well as their linkage to underlying micromechanics, are discussed. [ABSTRACT FROM AUTHOR]