Development of a New Method for Residual Stress Analysis on Fiber Reinforced Plastics with Use of Digital Image Correlation

In scope of the investigation of residual stresses the hole drilling method is an accepted method. The method is though not applicable for materials with high anisotropic behavior. Therefore a new algorithm is derived which allows the calculation of residual stresses in laminates made of unidirectional layers. Also the strain gauges deliver only strains on the areas where the strain gauges are applied. With the use of a high resolution imaging system and digital image correlation this area and the informational output can be widely improved. First, the derivation of the residual stress analysis algorithm is presented. For this an adequate finite element model, which is modeling the cooldown process as well as the drilling process, is set up and the surface strains are extracted. Based on this information an algorithm is derived and presented. Within the derivation a change of the layup, a possible change of the cooldown process and a variation of the drilling steps can be investigated. In consequence the input parameters of the algorithm can vary dependent on these factors. Second, the new optical testing setup with refinements to be able to measure the small deformations within micro-strains on the specimen’s surface is prepared and the concept presented. To solve the problem of casting shadows of the drill a special camera setup is being used.