Post-stretching induced stress redistribution in Fibre Metal Laminates for increased fatigue crack growth resistance

Post-stretching is a potential method to change the unfavorable residual stress system in fibre metal laminates (FMLs). During post-stretching of the material, the metal layers will be strained into the plastic region of the stress–strain curve, while the fibre layers remain elastic. After unloading, the residual stress system due to curing will be reduced or even reversed dependent on the amount of stretching. In the past, the classical laminate theory (CLT) has been modified, incorporating the thermal expansion for the application to FMLs. Furthermore, a fatigue crack growth prediction model has been developed based on this extended theory. Here, this classical laminate theory is further extended to calculate the stress redistribution after stretching the uni-directional laminates (ARALL and GLARE). This paper present the method to calculate the residual internal stress distribution in the fibre direction.For the validation of the post-stretching formulations, fatigue crack growth tests on GLARE1-2/1, 3/2, 4/3, 5/4-0.3 have been performed. Good agreement has been obtained.