Non Linear Spectroscopy for Damage Detection on Aerospace materials

Abstract

The research activities of this work concentrated on nonlinear material properties in presence of damages or defects. In particular the attention is focused on the low velocity impact damages on laminated composite materials and on the development of new methodology for non destructive damage detection.

Low velocity impact damage morphology is characterized by contact surfaces and open cracks, thus the scope of this work is to study the nonlinear wave propagation and acoustic contacts nonlinearity in damaged medium.

The work has been inspired by recent studies about nonlinear behaviour of contact surfaces in geomaterials, which contain a large number of discontinuities, and the non linear spectroscopy methodologies able to measure nonlinear properties induced by this class of defects.

Hysteretic model called PM-space has been proposed to characterize nonlinear behaviour of damage in homogeneous medium and used in FE in house code to simulate wave propagation effects. Numerical results shows nonlinearities such as harmonics generation and wave’s modulation strictly connected with damaged material model, which acts as the only nonlinear source in the medium.

Based on the numerical results an experimental campaign has investigated the nonlinear spectroscopy methodology: Nonlinear Resonance Ultrasound Spectroscopy (NRUS) and Nonlinear Wave Modulation Spectroscopy (NWMS) and their ability to measure phenomena such as harmonics generation, wave modulation and dependency of resonance frequency in damaged laminated composite. The results proposed are very promising as the nonlinear properties are well correlated to the damage presence and severity.

Same techniques have been also applied to study clamping condition on intact samples. Results presented show that weak bond can also generate nonlinearities such as sidebands in agreement evidence provided in literature.

In addition a damage localization technique has been established and results compare against thermal base methodology (Active Pulse Thermography and Thermosonics) are in good agreement.

Date of Award	1 Nov 2010
Original language	English
Awarding Institution	University of Bath
Supervisor	Michele Meo (Supervisor)