Dissipative properties of materials with thermoelastic martensite conversion

Conclusion

Internal friction in metallic materials experiencing a thermoelastic martensite conversion under conditions of a monotonically changing thermodynamic stimulus is determined by two main factors: irreversible processes involving growth of crystals of the new phase, and cyclical motion of the phase boundaries under the action of applied periodic stresses. While the losses caused by irreversible processes decrease with increase in loading amplitude, depending on the type of conversion the amplitude dependence of the background component of internal friction may be of a complex nonmonotonic character, with a maximum in losses at certain oscillation amplitudes. At low amplitudes sections of the boundary unattached to defects perform cyclical motions like membranes, and the losses due to the thermal conversion effect may produce a significant contribution to the overall damping level only at the membrane resonant frequencies. For amplitudes exceeding the critical boundary detachment stress internal friction increases, passes through a maximum, and then decreases anew. The amplitude dependence of internal friction behaves in a similar manner in the process of creation and subsequent collapse of crystals of the new phase in the field of an external periodic load.