Abstract
Metals which are widely used in many types of industries are usually subjected to fatigue and surface corrosion. There is a demand to detect the surface damage caused by fatigue and corrosion at an early stage to ensure the structural integrity. In this paper, a novel nonlinear ultrasonic technique based on the measure of third-order combined harmonic generation, is proposed to detect and locate the surface damage in 6061 aluminum alloy. Third-order combined harmonic generation caused by non-collinear mixing of one longitudinal wave and one transverse wave at different frequencies, is firstly analyzed and experimentally observed. An experimental procedure of nonlinear scanning is proposed for the damage detection and location by checking the variation of frequency nonlinear response. The correlations of nonlinear frequency mixing responses and surface damage in the specimens are obtained. Results show that the nonlinear response caused by fatigue damage and surface corrosion can be identified and located by this method. In addition, this approach can exclude the nonlinearity induced by the instruments and simplify the signal processing.
Highlights
Metallic materials are widely used in various fields such as construction, manufacture, and aerospace applications
Croxford et al reported the use of non-collinear mixing for nonlinear ultrasonic detection of plasticity and fatigue, in which a nonlinear parameter related to the amplitudes of the exciting signals and generated signals was proposed to evaluate the degree of damage
Instead of the measure of second-order combined harmonic waves, this paper focuses on the measure of third-order combined harmonic waves caused by the mixing of one longitudinal wave and one transverse wave
Summary
Metallic materials are widely used in various fields such as construction, manufacture, and aerospace applications. Nonlinear ultrasonic testing based on the second harmonics generation (SHG) has been proposed as a potential method for the detection of micro-defects [4,5,6,7,8] When it comes to surface damages, the use of nonlinear Rayleigh surface wave has been applied to assess the micro-surface damage in metallic materials [9,10,11]. Croxford et al reported the use of non-collinear mixing for nonlinear ultrasonic detection of plasticity and fatigue, in which a nonlinear parameter related to the amplitudes of the exciting signals and generated signals was proposed to evaluate the degree of damage. The variations of acoustic nonlinear parameter via nonlinear scanning in the specimens are used to locate the local surface damage
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