Residual strain measurement in composites using the cure-referencing method

This paper describes the details of a novel procedure called the cure-referencing method (CRM) to measure the strains associated with residual stresses on the surface of composite panels. The CRM involves the replication of diffraction gratings onto the surface of composite specimens during the autoclave curing cycle. Residual strains associated with the curing process are measured using moire interferometry at room temperature after the specimens have been taken out of the autoclave. The procedures for both the grating replication and the moire interferometry experiment are described in detail. A method of high-temperature moire interferometry was developed to resolve the residual strains due to thermal expansion from those due to chemical matrix shrinkage and stress relaxation. These procedures are demonstrated on unidirectional and multidirectional laminates and on woven textile composites.