Investigation of the Residual Stress State in an Epoxy Based Specimen

Abstract. Process induced residual stresses may play an important role under service loading
conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal
stress level. Therefore, the developed numerical models have to be validated with the experimental
observations. In the present work, the formation of the residual stresses/strains are captured from
experimental measurements and numerical models. An epoxy/steel based sample configuration is
considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling
process with a diameter of 5 mm is subsequently applied to the specimen and the released strains
after drilling are measured using the Digital Image Correlation (DIC) technique. The material
characterization of the utilized epoxy material is obtained from the experimental tests such as
differential scanning calorimetry (DSC) for the curing behavior, dynamic mechanical analysis
(DMA) for the elastic modulus evolution during the process and a thermo-mechanical analysis
(TMA) for the coefficient of thermal expansion (CTE) and curing shrinkage. A numerical process
model is also developed by taking the constitutive material models, i.e. cure kinetics, elastic
modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element
method. The measured and predicted in-plane residual strain states are compared for the
epoxy/metal biaxial stress specimen.