A new NDT: Evaluation of plastic strains in bulk from displacements on surfaces (Q1071555)

Non-destructive testings (NDT) of materials available at this time are methods to observe microstructures, residual stresses and defects of materials located near free surfaces. However, no NDT have been available for measurements of plastic deformations in bulk accumulated by loading processes. This short note proposes a new non-destructive testing (NDT) to evaluate plastic strains in the bulk of materials caused by any loading, simply from measurements of surface displacements in plane. The surface displacements in plane are relative (differential) displacements of points on free surfaces after unloading measured from a state before the loading has been applied. The measurement may be performed by holography for instance. The principle of the present method is based upon an inverse usage of the boundary integral equation method (BIEM). The fictitious body forces due to plastic strains are sources of boundary values of displacements and tractions on interfaces in BIEM. Inversely, under some conditions, the fictitious body forces are determined from the boundary values of displacements. Consequently, the associate plastic strains can be evaluated.