Infrared detection of thermomechanical coupling in solids

The thermal effects due to thermomechanical coupling in solids have been identified within the general framework of the thermodynamics of irreversible processes based on internal variables. The paper aims to illustrate the use of infrared thermography as a nondestructive, real-time and noncontact technique to detect, observe and evaluate the evolution of temperature changes caused by the diverse processes of irreversible physical phenomena. The results obtained highlight the advantages of differential infrared thermography. This technique minimizes the thermal noise in real or industrial environments and thus facilitates the detection, discrimination and interpretation of the diverse dissipative phenomena involved in these nonlinear coupled thermomechanical effects within the framework of a consistent theoretical background. Stress and strain concentrations in loaded materials and structural components occur and result in localized forces that are sufficient to promote plasticity and/or inelasticity. At the structural level, breakdown appears as microcracking and possibly slippage at component interfaces. In addition to traditional techniques of mechanical strength evaluation, it provides a ready evaluation of a limit of acceptable damage under service loading beyond which the material will be rapidly destroyed, or of fatigue resistance under cyclic excitations or dynamic solicitations. Finally this paper suggests various potential applications of the thermal scanning technique in diverse engineering domains: detection of fluid leakage, nondestructive testing using thermal conduction phenomena, elastic stress measurements, localization of dissipative phenomena and rapid evaluation of fatigue limit for industrial materials.