Mathematical Formulation of the α'-Martensite Evolution and its Application in the early Detection of Damage in Sheet Metal, Proceedings of the 14th International Symposium on Plasticity and its Current Applications "Mechanics & Mechanisms of Finite Plastic Deformation", 03.-08.01.2008 in Kona, Hawaii, USA, NEAT PRESS ISBN: 0-9659463-8-X, S. 166-168