Integration of digital shearography and FEM for non-destructive evaluation of internal cracks in GRE pipes

Pipes made of glass fiber-reinforced epoxy (GRE) are often exposed to complex environmental conditions, which can make them prone to internal cracking. Quantitative, non-destructive evaluation of cracks can reduce unintended failures and improve system reliability. The use of digital shearography, a modern non-destructive method based on laser interferometry, in the diagnosis of composite materials has drawn attention in recent years. In this paper, a model for the quantitative evaluation of subsurface cracks in various locations on GRE pipes was developed by integrating the finite element method and shearography with thermal stimulation. The response surface method was used to design the simulations, and the effect of crack dimensions and location on the phase map and out-of-plane surface strain component was investigated. The results demonstrated that the crack placement angle relative to the shearography device is effective on crack detectability due to the change in the actual shearing size. A model was then presented to estimate the length and depth of the crack based on the displacement derivative graph by using analysis of variance and regression techniques. By determining the out-of-plane displacement derivative, the proposed model enables precise estimation of the dimensions and location of subsurface cracks.