Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

The hardening soil model: Formulation and verification

Abstract: A new constitutive model is introduced which is formulated in the framework of classical theory of plasticity. In the model the total strains are calculated using a stress-dependent stiffness, different for both virgin loading and un-/reloading. The plastic strains are calculated by introducing a multi-surface yield criterion. Hardening is assumed to be isotropic depending on both the plastic shear and volumetric strain. For the frictional hardening a non-associated and for the cap hardening an associated flow rule is assumed. First the model is written in its rate form. Therefor the essential equations for the stiffness modules, the yield-, failure- and plastic potential surfaces are given. In the next part some remarks are given on the models incremental implementation in the Plaxis computer code. The parameters used in the model are summarized, their physical interpretation and determination are explained in detail. The model is calibrated for a loose sand for which a lot of experimental data is available. With the so calibrated model undrained shear tests and pressuremeter tests are back-calculated. The paper ends with some remarks on the limitations of the model and an outlook on further developments.

The Heat Developed during Plastic Extension of Metals

Abstract: When a soft metal, such as annealed copper or aluminium, is deformed while cold, either by stretching, hammering, rolling, or other method of ‘‘cold working’’ it hardens; that is, the forces necessary to deform it increase as the amount of plastic deformation increases. The physical state of “cold worked’’ metal is undoubtedly different from that of the metal in its original soft or annealed state, and various explanations have been put forward to account for the difference. Some of these explanations involve the hypothesis that the process of hardening is associated with the formation of amorphous material at the crystal planes where slipping occurs during the deformation. The formation of amorphous material from a crystalline mass would involve a phase change, which would in general be accompanied by a change in the internal energy of the material. It has been suggested that the phase change could detected by measuring the heat evolved during a deformation, and com-ring with the heat equivalent of the work done on the metal by the forces inducing the deformation. Any difference between the two would imply change in the internal energy of the metal. It is curious that very few measurements of this type appear to have been inside. The only reference which we have been able to find occurs in Dr. Rosen-Inde article on “ Metals,” in the 4 Dictionary of Physics,5 where he quotes the previously unpublished observations made by Dr. Sinnat.

Modeling of cyclic ratchetting plasticity, part i: Development of constitutive relations

Abstract: The existing plasticity models recognize that ratchetting direction strongly depends on the loading path, the stress amplitude, and the mean stresses, but their predictions deviate from experiments for a number of materials. We propose an Armstrong-Frederick type hardening rule utilizing the concept of a limiting surface for the backstresses. The model predicts long-term ratchetting rate decay as well as constant ratchetting rate for both proportional and nonproportional loadings. To represent the transient behavior, the model encompasses a memory surface in the deviatoric stress space which recalls the maximum stress level of the prior loading history. The coefficients in the hardening rule, varying as a function of the accumulated plastic strain, serve to represent the cyclic hardening or softening. The stress level effect on ratchetting and non-Masing behavior are realized with the size of the introduced memory surface. Simulations with the model checked favorably with nonproportional multiaxial experiments which are outlined in Part 2 of this paper.