Nondestructive Assessment of Plastic Elbows Using Torsional Waves: Numerical and Experimental Investigations

This work addresses numerical and experimental investigations on the wave propagation and diffusion of the torsional mode T(0,1) in polyvinyl-chloride (PVC) structures with curved components. The wave finite element method (WFEM) is used to determine dispersion characteristics of the waves traveling in a PVC elbow, and to compute reflection and transmission coefficients from a defect with various sizes and positions in the elbow. The effect of size and location on the wave diffusion properties are examined. Numerical results underscore the sensitivity of the diffusion coefficients with respect to frequency and to the defect geometry. These results are firstly compared to experimental tests carried out using an appropriate test-rig for torsional-wave generation and detection. The experiments consist in evaluating the wave attenuation engendered by the material damping, as well as comparing time responses recorded at different locations for damaged and undamaged curved structures. Finite element simulations are also performed and their results are compared to the WFEM ones. The results bring out some substantial observations on the defect's detectability in such a structure, and the comparison of WFEM to experiments and FE shows a good agreement.