Simultaneous measurements of effective chemical shrinkage and modulus evolution during polymerization

An integrated measurement technique is proposed to measure the effective chemical shrinkage and the modulus of polymeric materials simultaneously, as a function of time, during polymerization (evolution history). The method is based on a fiber Bragg grating (FBG) sensor. A polymer is cured around a glass FBG and the Bragg wavelength (BW) shift is continuously documented while polymerization progresses at the curing temperature. Based on the theoretical relationship between the BW shift and the stress field in the FBG, the measured BW shift is used to determine the evolving effective chemical shrinkage and the modulus. The results can be employed to predict curing-induced residual stresses in geometrically-complex packaged assemblies. The proposed method is implemented on a high temperature curing epoxy.