The use of non-collinear mixing for nonlinear ultrasonic detection of plasticity and fatigue

Abstract

This letter reports on the application of the non-collinear mixing technique to the ultrasonic measurement of material nonlinearity to assess plasticity and fatigue damage. Non-collinear mixing is potentially more attractive for assessing material state than other nonlinear ultrasonic techniques because system nonlinearities can be both independently measured and largely eliminated. Here, measurements made on a sample after plastic deformation and on a sample subjected to low-cycle fatigue show that the non-collinear technique is indeed capable of measuring changes in both, and is therefore a viable inspection technique for these types of material degradation.

2D finite element modeling of the non-collinear mixing method for detection and characterization of closed cracks

“…The method is applied in the case of a closed crack embedded in an elastic solid which behavior is considered linear. The application of the non-collinear mixing method for a classical bulk nonlinearity (already studied and showed in [26,27,28,30]) is beyond the scope of this paper. In this study, the interface is modeled by a unilateral contact with Coulomb's friction and the resolution is evaluated in the time domain.…”

“…To enforce the frequency separation of longitudinal waves with respect to other harmonic contributions due to material nonlinearity or experimental devices, it is possible to use different frequencies associated with different angles of incidence. In [26], the same angles and frequencies were used for both incident shear waves. A technique was used to eliminate the underlying experimental system nonlinearity by subtracting the sum of the responses to each of the incident waves excited separately (without any interaction).…”

“…More recently, the scattered wave has been used to evaluate plastic deformation in an aluminum solid [26]. The method has also been successfully applied to the evaluation of physical aging of PVC [28] and the evaluation of a diffusion welding interface in titanium [29].…”

Acoustic nonlinearity parameters for transversely isotropic polycrystalline materials

“…Some examples include small amplitude waves in an initially stressed solid, 1-8 finite amplitude interactions between two or more waves, [9][10][11][12] and harmonic waves generated from a finite amplitude fundamental wave. [13][14][15][16][17][18] In an experimental setting, these examples open the door for correlating the nonlinear elastic properties of the solid to wave measurements.…”

Nonlinear phased array imaging

“…Nonlinear ultrasonic methods have been proposed for years as a technique to increase sensitivity to damage 1,2,3 . These have shown significant increase in sensitivity to fatigue state and the ability to detect previously invisible features such as closed cracks.…”