Fiber Bragg grating detection of gel time and residual strain of curing in epoxy resins

Abstract

AbstractThe curing shrinkage of epoxy resin can generate residual strains and internal stresses that reduce the material's strength and life. In this paper, a thermocouple‐compensated fiber grating detection method for the gel time and residual strain in epoxy resin is proposed. The strain evolution and glass transition temperature of E51/W93 epoxy systems with different Al2O3 contents cured at 30°C are detected by fiber Bragg gratings and DSC tests. The generation mechanism of residual strain in epoxy resin filled with Al2O3 fillers is studied. The gel time, gel temperature and residual strain of epoxy resin can be measured by this method. The results show that the cure shrinkage of epoxy is affected by chemical shrinkage, thermal expansion or shrinkage, and demolding, resulting in residual strain of the material after curing. Moreover, the glass mold has a great interference with the curing shrinkage of epoxy. The Al2O3 filler can prolong the gel time of E51/W93 epoxy systems, and reduce the exothermic peak temperature of curing. When the content of Al2O3 filler exceeds 44.44 wt.%, the low proportion of epoxy and the thermal conductivity of the filler make the curing shrinkage of epoxy during the heating stage mainly affected by chemical shrinkage. The glass transition temperature of the epoxy with Al2O3 content of 70.59 wt.% is the maximum, and the residual strain is at a low level. This method is helpful to analyze the curing shrinkage characteristics of materials, and is of great significance for evaluating the properties of epoxy cured products and guiding the optimization of material parameters.Highlights A method for measuring the gel time and residual strain of curing in epoxy resin is proposed. The study focuses on the detection of key parameters during the curing of epoxy resins with different Al2O3 contents. The aim is to analyze the curing shrinkage and residual strain generation mechanism of epoxy resin filled with different contents of Al2O3.