Monday, 11 October 2004 - 2:40 PM

This presentation is part of : Graduate Student Competition

Continuum Mechanical Approach to Martensite Crystallography

Istemi B. Ozsoy and Valery I. Levitas. Texas Tech University, Department of Mechanical Engineering, Lubbock, TX 79409-1021

A new continuum approach to martensite crystallography is developed for temperature and stress-induced martensitic transformations in elastic and plastic materials. This approach accounts for the internal stresses, interface friction, and nonequilibrium evolution of all crystallographic parameters under multiaxial loading. A representative volume is considered which consists of austenite (A) and twinned martensite (M) divided by a plane interface. The assumption of homogeneous stress and strain fields in A and each M variant is adopted. Plastic slip along slip systems of A and M is taken into account. The stresses and strains in A and each M variant are described by algebraic equations. All crystallographic parameters (volume fractions of each M variant and the orientation of A-M and variant-variant interfaces) are described by thermodynamically consistent kinetic equations. A computational algorithm is developed and the numerical study of fcc®bcc stress-induced transformation is performed. The model is validated by making a comparison with the known crystallographic theories and the theories considering internal stresses. It is obtained that even for the case when the dissipative thresholds for twinning and phase transformation are zero, slip occurs in addition to twinning each of which are considered the alternative mechanisms of plastic accommodation. Transformation surface in a space of principle stresses is found.

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