Determination of chemical cure shrinkage in composite laminates

Residual stresses in composites (microscopic and macroscopic) result from shrinkage of the matrix during cure. It is usual to distinguish between the chemical and thermal components of shrinkage. The former depends on the polymerization reaction, whereas the latter is caused by the difference between the thermal expansion coefficients of the reinforcement and the matrix. A method was developed for determination of the chemical cure shrinkage. A prepreg layer is applied on an identical layer of the same material that has already been cured and postcured. The assembled laminate is then cured, and the resulting warpage is recorded by means of the shadow moire method. The resulting warpage, consisting of elliptical equal deflection contours, is related to the chemical shrinkage.