Nonlinear resonances in Mn-7 at% Cu

Nonlinear anelasticity in Mn–7 at% Cu is studied by means of resonance curve measurements. Nonlinear resonances, mostly of a soft nature, are observed form room temperature to 238 °C, and the softening is attributed in large part to motion of twin boundaries in the martensite. However, in an intermediate range of temperatures from 50 to 140 °C, hard resonances are observed at moderate strain amplitudes. It is proposed that the hardening arises from the temperaturedependent lattice parameters of the martensite which produces an extra restoring force in the direction opposite to an applied force.