Investigation of non-uniform gelation effects on residual stresses of thick laminates based on tailed FBG sensor

Due to the appearance of temperature gradient and non-uniform gelation, fully understanding of residual stresses is even more complex in thick laminates. In this paper, basic mechanisms of cure process were presented firstly. Then, experimental investigation of the non-uniform gelation was carried out together with characterization of necessary material properties. Tailed FBG sets were applied to monitor the cure of thick laminates with temperature gradient. The non-uniform gelation and chemical shrinkage gradient were captured successfully. Lastly, FEM analysis integrating thermal-chemical sub-model and stress-displacement sub-model was carried out to reveal the development of residual stresses. It is demonstrated that the high temperature layer gelled earlier and showed more chemical shrinkage. The chemical strain gradient would introduce compression internal stresses in prior gelled layer and introduces tensile internal stresses in later gelled layer. For the case studied here, transverse residual stress generated by non-uniform chemical shrinkage is small. The strategy used here is promising to estimate the residual stresses for more complex cases further.