Anisotropy And Localization Of Plastic Deformation

Present developments in materials science, mechanics and engineering, as well as the demands of modern technology, result in a new and growing interest in plasticity and in bordering domains of the mechanical behavior of materials. This growing interest is attested to by the success of both The International Journal of Plasticity, which after its inception rapidly became the leading journal for plasticity research, and the series ofInternational Symposia on Plasticity and Its Current Applications, which is now the premier international forum for plasticity research dissemination. The First International Symposium on Plasticity and Its Current Applications was conceived and organized by Professor Akhtar S. Khan, and was held at the University of Oklahoma (Norman, Oklahoma, USA) from July 30 to August 3, 1984. It was attended by over one hundred scientists from fifteen countries. "Plasticity '89: the Second International Symposium on Plasticity and Its Current Applications" was held at Mie University (Tsu, Japan) from July 31 to August 4, 1989; this symposium was co-chaired by Professors Khan and Tokuda. The main emphasis of this meeting was on dynamic plasticity and micromechanics, although it included other aspects of plasticity as well. It was attended by over two hundred researchers from twenty-three nations.

Proceedings of the IUTAM-ISIMM Symposium, held in Nottingham, U.K., 30 August--3 September 1994

The classical, phenomenological theory of plastically anisotropic materials has passed a long way: from the work of von Mises presented in 1928, and the HilI formulation given in 1948, to the latest papers on large elastic-plastic deformations of anisotropic metal sheets. A characteristic feature of this approach is a linear flow rule and a quadratic yield criterion. Mathematical simplicity of the theory is a reason of its numerous applications to the analysis of engineering structures during the onset of plastic deformations. However, such an approach is not sufficient for description of the metal forming processes, when a metal element undergoes very large plastic strains. If we take an initially isotropic piece of metal, it becomes plastically anisotropic during the forming process, and the induced anisotropy progressively increases. This fact strongly determines directions of plastic flow, and it leads to an unexpected strain localization in sheet elements. To explain the above, it is necessary to take into account a polycrystalline structure of the metal, plastic slips on slip systems of grains, crystallographic lattice rotations, and at last, a formation of textures and their evolution during the whole deformation process. In short, it is necessary to introduce the plasticity of crystals and polycrystals. The polycrystal analysis shows that, when the advanced plastic strains take place, some privileged crystallographic directions, called a crystallographic texture, occur in the material. The texture formation and evolution are a primary reason for the induced plastic anisotropy in pure metals.

The main scope of this Cargese NATO Advanced Study Institute (June 5-17 2000) was to bring together a number of international experts, covering a large spectrum of the various Physical Aspects of Fracture. As a matter of fact, lecturers as well as participants were coming from various scientific communities: mechanics, physics, materials science, with the common objective of progressing towards a multi-scale description of fracture. This volume includes papers on most materials of practical interest: from concrete to ceramics through metallic alloys, glasses, polymers and composite materials. The classical fields of damage and fracture mechanisms are addressed (critical and sub-critical quasi-static crack propagation, stress corrosion, fatigue, fatigue-corrosion . . . . as well as dynamic fracture). Brittle and ductile fractures are considered and a balance has been carefully kept between experiments, simulations and theoretical models, and between the contributions of the various communities. New topics in damage and fracture mechanics - the effect of disorder and statistical aspects, dynamic fracture, friction and fracture of interfaces - were also explored. This large overview on the Physical Aspects of Fracture shows that the old barriers built between the different scales will soon "fracture". It is no more unrealistic to imagine that a crack initiated through a molecular dynamics description could be propagated at the grain level thanks to dislocation dynamics included in a crystal plasticity model, itself implemented in a finite element code. Linking what happens at the atomic scale to fracture of structures as large as a dam is the new emerging challenge.

This volume covers topics involving large plastic deformation of metallic materials. These proceedings offer an overview of the synergism achieved by combining microstructural characterization and understanding, mechanical modelling and experiments, numerical analysis and computation.