Crystalline damage development during martensitic transformations

Abstract

A recently developed thermo-mechanical model [1] is presented that can be used to simulate the interactions between martensitic phase transformations and crystalline damage growth at the austenitic grain level. Subgrain information is included in the model via the crystallographic theory of martensitic transformations, see also [2,3]. The state of transformation for the individual transformation systems is represented by the corresponding volume fractions. The state of damage in the austenite and the martensitic transformation systems is reflected by the corresponding damaged volume fractions. The thermodynamical forces energetically conjugated to the rate of volume fraction and the rate of damaged volume fraction are the driving forces for transformation and crystalline damage, respectively. The model is used to analyse three-dimensional boundary value problems that are representative of microstructures appearing in multiphase carbon steels assisted by transformation-induced plasticity. The numerical integration of the model is performed within a finite deformation framework, using a fully implicit Euler backward method. The consistent tangent is computed numerically by consistent linearization of the updated stress, see also [4]. The analyses show that the growth of damage effectively limits the elastic stresses developing in the martensitic product phase, where the maximum value of the stress strongly depends on the toughness of the martensite. Furthermore, the generation of crystalline damage delays the phase transformation process, and may arrest it if the martensitic product phase is sufficiently brittle. The response characteristics computed with the phase-changing damage model are confirmed by experimental results.Aerospace Engineerin