Numerical simulations of non-destructive testing procedure by shearography and thermography

Abstract

The intrinsic structure of composites can lead to defects decreasing their reliability and their in-mission security. Numerical simulations aiming to improve and support defect detection are envisaged in this work. More precisely, shearography and thermography as non-destructive detection methods are being modeled here. Two defect types are considered: delamination and porosity.

Detection is investigated with external thermal excitation, leading to thermal and mechanical analysis in simulations. Firstly, an overview of composites, their defects and non-destructive techniques is addressed. Secondly, prerequisites for simulations like governing equations and assumptions made, the heater characterization, and the numerical scheme used for the transient thermal problem resolution are exposed. Then, defect numerical models are constructed and studied. Delamination and porosity are the two types of defects considered. Numerical models for the delamination covered true delamination and artificial delamination like the physic insert and flat bottom hole models. The porosity model is represented by a few flat bottom holes localized in a small region. Finally, an experimental approach compared with numerical results is used as a validation method.

Different delamination models are developed and they show pretty well concordances between them, except for the Teflon layer (type of physic insert) model for which the mechanical response was not expected or at least, suggests a further study to determine its validity. The porosity model showed difficulties in this kind of defect detection. Finally, the experimental approach enabled to see that numerical and experimental results were similar but that some efforts on parameter updating remain to be made. Mainly the characterization of the lamp that irradiates a highly non-homogeneous flux.