Microplane constitutive model and metal plasticity

Abstract

The microplane model is a versatile constitutive model in which the stress-strain relations are dermed in tenns of vectors rather than tensors on planes of all possible orientations, called the microplanes, representative of the microstructure of the material. The microplane model with kinematic constraint has been successfully employed in the modeling of concrete, soils, ice, rocks, fiber composites and other quasibrittle materials. The microplane model provides a powerful and efficient numerical tool for the development and implementation of constitutive models for any kind of material. The paper pres-ents a review of the background from which the microplane model stems, highlighting differences and similarities with other approaches. The basic structure of the microplane model is then presented, to-gether with its extension to fmite strain defonnation. Three microplane models for metal plasticity are introduced and discussed. They are compared mutually and with the classical Jrflow theory for incre-mental plasticity by means of two examples. The first is the material response to a nonproportional loading path given by uniaxial compression into the plastic region followed by shear (typical of buck-ling and bifurcation problems). This example is considered in order to show the capability of the mi-croplane model to represent a vertex on the yield surface. The second example is the 'tube-squash ' test of a highly ductile steel tube: a finite element computation is run using two microplane models and the Jrflow theory. One of the microplane models appears to predict more accurately the final shape of the deformed tube, showing an improvement compared to the J2-flow theory even when the material is not SUbjected to abrupt changes in the loading path direction. This review article includes 114 references.