Evidence of dissipative and growing nonlinearity in Lamb waves due to stress-relaxation and material degradation in composites

Subir Patra; Hossain Ahmed; Mohammadsadegh Saadatzi; Sourav Banerjee

doi:10.1016/j.ultras.2019.01.002

Evidence of dissipative and growing nonlinearity in Lamb waves due to stress-relaxation and material degradation in composites

Ultrasonics. 2019 Jul:96:224-231. doi: 10.1016/j.ultras.2019.01.002. Epub 2019 Jan 14.

Authors

Subir Patra¹, Hossain Ahmed¹, Mohammadsadegh Saadatzi¹, Sourav Banerjee²

Affiliations

¹ Integrated Material Assessment and Predictive Simulation Laboratory (i-MAPS), Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, United States.
² Integrated Material Assessment and Predictive Simulation Laboratory (i-MAPS), Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, United States. Electronic address: banerjes@cec.sc.edu.

PMID: 30712780
DOI: 10.1016/j.ultras.2019.01.002

Abstract

Experimentally observed dissipated nonlinearity in Lamb wave propagation in composites due to stress-relaxation is reported herein. It was found that the stress relaxation in composite is inherently coupled with the second order nonlinear parameter derived from the Lamb wave modes. Due to the combined effect of internal stresses and damage accumulation in composites, the second harmonic frequency was found to be shifted towards the lower frequency with increasing amplitude, which was partially recovered and shifted back during the stress relaxation. A comprehensive fatigue experiment was conducted on ASTM standard composite specimens with fatigue loading sequences and relaxation, while the guided Lamb wave signals were collected using piezoelectric sensors integrated with the specimens. A remarkable ∼27% reduction of acoustic nonlinearity was observed during relaxation. Rate and degree of relaxation were found to be the function of number and frequency of loading cycles and inherently correlated with the remaining strength of the composites.