Study of damage of t-joint components by using different non-destructive techniques

The present research is focused on the use of different non-destructive techniques for detecting damage in CFRP composite structures obtained by an innovative technological process: Automated Fiber Placement. The component was a T-joint stringer adhesively bonded to a skin panel. The aim of the present work is to show the capability of these techniques to provide complementary information for detecting the damage in composites. Automated Fibre Placement consists in an automatic deposing of prepeg or dry plies on a specific mould. The innovation lies in the possibility to reduce the time of the manufacturing process of large and complex structures by using a robotic arm that contemporary deposes fibre tows and pre-polymerizes them. The resulting products present higher quality in terms of surface finish, internal flaws absent and higher mechanical properties. The T-joint component tested in the present research was addressed to both static and cyclic tests. After the damage was induced in the material it was performed a qualitative and quantitative study of the damage by using different nondestructive techniques: Thermoelastic stress analysis (TSA), Ultrasound tests (UT) and displacement/strain measurements provided by strain gages. Processing and post-processing procedures were developed to analyze the data from each tests and finally the comparison of the results allowed a complete characterization and an overview of damage in the component by observing specifically where and when it occurred and how many regions of the component were interested. Finally, dimension, shape and depth where assessed.