Determination of plastic deformation with variable ultrasonic excitation positions

For highly stressed mechanical components, information regarding the beginning of plastic deformation is of enormous importance. Therefore, nondestructive testing and structural health monitoring techniques are essential to examine said components and to make statements concerning the mechanical integrity. In this work, dislocation theory was extended and combined with ultrasonic wave excitation to obtain dislocations in isotropic materials. In the analytical derivation, the ultrasonic longitudinal waves were sent in different propagation directions relative to the uniaxial tensile load. The derived nonlinearity coefficients enabled the investigation as a function of these angles. The evaluated coefficient behaviour allows for statements about the position of the ultrasonic excitation relative to the tensile load to be made. Furthermore, a signature could be derived from which the degree of plasticity can be determined if a reference measurement is available. The newly derived coefficients and their behaviour make it possible to efficiently detect the beginning of plastic deformation and to predict the position of the applied load vector.