Thermomechanical Analysis of the Cyclic Behavior of Materials

The cyclic behavior of materials often shows stabilized hysteretic responses. The present paper aims at highlighting the advantages of combining digital image correlation (DIC) and infrared thermography (IRT) to identify the energy nature of such hysteresis loops. Dissipative mechanisms are generally responsible for the mechanical energy lost in the stress-strain loop, reflecting irreversible material degradation. Thermodynamic analysis of the cyclic responses however revealed that such hysteresis areas may not only be induced by intrinsic dissipation but also by internal energy variations (stored energy) and/or by strong thermomechanical coupling effects associated with heat diffusion. From an experimental standpoint, kinematic data obtained by DIC techniques were used to estimate a stress-strain response and then compute the volume deformation energy within a hysteresis loop. Moreover, thermal images produced by an infrared camera were used to estimate the distribution of heat sources generated by the deformation. These sources may be due to dissipative and/or thermomechanical coupling effects. Several application examples were chosen to illustrate the diversity of mechanisms that induce hysteretic responses.