SHAPE-MEMORY - A NEW CONCEPT OF EXPLANATION AND OF MATHEMATICAL-MODELING .1. MICROMECHANICAL EXPLANATION OF THE CAUSALITY IN THE SM PROCESSES

The shape memory effect and pseudoelasticity that are observed typical ly with some binary and ternary alloys are explained on the basis of i nteraction of the sets of different atoms of the elements constituting the alloy. The concrete discussion is limited to binary alloys only, assuming that the processes in ternary alloys are similar in principle , but substantially more complicated and therefore difficult to be mod elled. The differing thermal expansions of the two elements present in a binary alloy are assumed to be the cause of the changes of energy o f the interatomic forces with changing temperature. Cooling of such an alloy in austenitic state leads to an increase of this energy, then t he energy is partly dissipated and the structure of the alloy transfor ms to a martensitic one; the metastable austenitic configuration chang es into the lower energy martensitic structure. The mechanism of the t ransformation consists in the following variations of the interatomic distances: the distances between the differing atoms in the binary all oy (pairs with the smallest distances and with the strongest bonds) re main nearly unchanged, whereas the distances between atoms of the same element (pairs with larger distances and with weaker bonds) do change with martensitic transformation substantially, which leads to the low ering of the bond energy. It is shown that this understanding of the p rocess agrees with a number of observed phenomena and it opens the pos sibility of modelling the shape memory effect and pseudoelasticity by a continuum model consisting of two continuous infrastructures corresp onding to the two sets of atoms present in the binary alloy.