RESIDUAL THERMAL STRAIN OF METALS IN HEATING-COOLING CYCLES

Metallic samples subjected to heating-cooling cycles undergo a permane nt change in their length. The difference between the initial length a nd the length at the end of the cycle (residual strain) depends on the maximum temperature attained duping the cycle. This dependence of res idual strain on the maximum temperature of the cycle is similar for al l of the examined metals (polycrystalline copper, aluminium, iron, gol d, lead and single-crystal copper). Upon further increasing this tempe rature, the metal residual strain changes from positive to negative va lues. The temperature at which the maximum positive residual strain oc curs is characteristic for each metal. The value of the residual strai n and the temperature at which it changes its sign depend on the previ ous thermal history of the metal.