Numerical study on how heterogeneity affects ultrasound high harmonics generation

Finite element models with explicitly modelled mesoscale heterogeneity in material are introduced to numerically investigate the correlation between the ultrasonic higher harmonics and plastic deformation. The model predicts the changes of the second- and third-harmonics due to the plastic deformation in materials without the microstructural information and state variables at each loading step. The numerical predictions of ultrasonic higher harmonics change agree with the experimental data on Aluminium 1100. The numerical model is extended to study the effect of heterogeneity characteristics, including volume fraction, size and strength deviation, on the higher harmonics. The numerical studies consistently show that the third-harmonics is more sensitive than the second-harmonics to the level of plastic deformation for all heterogeneity characteristics. Moreover, among the heterogeneity characteristics considered, the material strength deviation of heterogeneity from the bulk affects the changes of higher harmonics the most. The numerical observations are discussed and compared with experimental results provided in the literature.