Residual Stress Measurements to Aid Manufacturing of Aerospace Composite Materials

Composite materials are increasingly being used for aerospace and structural applications due to the many advantages they offer including reduced weight, improved mechanical properties, and reduced maintenance schedules. Although composites have significant structural benefits, they are not immune from the effects of manufacturing residual stress, which occur due to a mismatch of matrix and fiber thermal expansion coefficients and chemical cure shrinkage of the matrix material. The performance of composite materials is affected by residual stress including: fiber debonding, matrix cracking, fiber breakage, and delamination. In addition, residual stresses also influence the dimensional distortion or spring back that is often experienced post cure. To effectively understand and predict residual stress effects on performance of composite materials, accurate and reliable residual stress data are required. Few methods currently exist for the measurement of residual stresses in composites and none have accuracy and repeatability in the full range of aerospace composite materials suitable for understanding material performance. This program will work to develop an advanced method for residual stress measurement in composite materials.