Interface mechanical problems are of paramount importance in engineering and materials science. Traditionally, due to the complexity of modelling their mechanical behaviour, interfaces are often treated as defects and their features are not explored. In this study, a different approach is illustrated, where the interfaces play an active role in the design of innovative hierarchical composites and are fundamental for their structural integrity. Numerical examples regarding cutting tools made of hierarchical cellular polycrystalline materials are proposed, showing that tailoring of interface properties at the different scales is the way to achieve superior mechanical responses that cannot be obtained using standard materials

The fracture properties of thin aluminum inclusions embedded in anisotropic paperboard composites, of interest for food and beverage packaging industry, can be determined by performing tensile tests on non-conventional heterogeneous specimens. The region of interest of the investigated material samples is monitored all along the experiment by digital image correlation techniques, which allow to recover qualitative and quantitative information about the metal deformation and about the evolution of the damaging processes leading to the detachment of the inclusion from the surrounding laminate composite. The interpretation of the laboratory results is supported by the numerical simulation of the tests.

This paper summarises an attempt of estimating macro-, micro-, and nano-hardness of metallic materials through conventional elasto-plastic finite element (FE) analyses. In more detail, to verify if the classical FE method can successfully be used for such a purpose, initially a series of hardness testes were carried out on three metallic materials characterised by a different elasto-plastic behaviour, i.e., aluminum alloy 7075-T6, low-carbon steel BS970-En3B, and, finally, austenitic steel AISI 316L. Subsequently, by making the indentation force vary in the range 490 N-490 µN, Vickers hardness was estimated from elasto-plastic FE models done by using, to calibrate the mechanical properties of the investigated metals, the corresponding monotonic stress-strain curves experimentally determined by testing samples having both conventional size and, for austenitic steel AISI 316L, gauge length size equal to approximately 100 µm. The systematic comparison between experimental results and numerical simulations suggests that the increasing of the measured hardness value with the decreasing of the indenter size may directly be ascribed to the role played by the actual morphology of the material being tested. In particular, it is seen that conventional elasto-plastic continuum mechanics is no longer adequate to estimate metallic material hardness as the size of the indented surface approaches the average size of the grains. Finally, in order to overcome the above limitation by allowing the classical elasto-plastic FE approach to be used also to estimate nano-hardness, a simple engineering method is proposed and subsequently validated through the generated experimental results.

The ductile fracture occurs mainly in three stages i.e. void nucleation, void growth and the void coalescence. The present work focuses on the study the coalescence of existing micro void in a ductile material, mild steel. The specimen with holes in square array at various angle to load axis have been tested. The holes were machined in the specimen and assuming those hole as the voids. The growth and coalescence behaviours during tensile straining were observed both in macro and micro levels. Since the existing facility is not adequate to make hole size in micron, this work has been carried out by making hole upto 500 micron. The results are compared with other specimen with bigger size hole and without any hole. Also the effects of micro voids (present in the material) on the progress of crack have been studied. It is found that with same amount of voids, present in different positions, the mechanical properties of the material are altered.

The Equal Channel Angular Pressing is a hardening treatment with which ductile metals can be processed to refine their grain and sub-grain structure. This process enhances the mechanical strength of metals in terms of tensile strength, stress-controlled fatigue strength, and fatigue crack growth resistance. In this paper the authors draw a review of the major results of a wide research activity they carried out on a copper microstructure processed by Equal Channel Angular Pressing. The essential results are that tensile and fatigue strengths of the so obtained refined structure are improved by a factor of two with respect to the original coarse-grained metal. The fatigue crack initiation mechanism and the stability of the refined microstructure under cyclic loading are topics also discussed, evidencing the essential role of the process and of the material parameter, as the content of impurities in the microstructure. In this review, the authors also underline some critical aspects that have to be more investigated.