Monitoring Elastoplastic Deformation in Ductile Metallic Materials Using Sideband Peak Count-Index Technique

Ductile metallic materials such as aluminum alloy, brass, and steel are widely used in engineering structures. Monitoring elastoplastic deformation in these materials is important for structural health monitoring (SHM) to ensure the safety of structures made of metallic materials. This article presents a newly developed and promising nonlinear ultrasonic (NLU) technique called sideband peak count-index (or SPC-I) for monitoring the early stages of elastoplastic deformation in ductile metallic alloy Al6061. Experimental results presented in this article show that the elastic range of the Al6061 SPC-I values shows slight changes due to the inherent inhomogeneities (imperfect grain boundaries or dislocations at the grain boundaries under loadings) of Al6061. Then the SPC-I value changes rapidly as the material enters the plastic range zone. Compared to the linear ultrasonic (LU) parameters (wave velocity and attenuation changes), the SPC-I shows a noticeable advantage (higher sensitivity) for monitoring the early stages of the elastoplastic deformation in these ductile metallic specimens investigated in this study. It is concluded that the SPC-I technique is useful for monitoring deformations in ductile metallic materials, especially in their plastic zone. This work extends the applicability of the SPC-I technique for monitoring elastoplastic deformations in metallic specimens that have not been reported in earlier works and can provide some guidelines for SHM related to elastoplastic deformation in metallic structures.