On the determination of edge stresses in layered composites

For test specimens built up symmetrically from 16 layers of fiber reinforced material the stress distributions are claculated under axial and thermal loads. Though the stresses are assumed constant in the axial direction volume elements are necessary to include interlaminar shear and peeling stresses. But the number of degrees of freedom and the bandwidth of the system matrix can be kept relatively low. The results show quite distinct stress peaks at layer interfaces, and it was found that even with 16 quadratic elements over the layer thickness these values have not reached an acceptable accuracy. The convergence behavior gives rise to the conjecture, that infinite stresses may occure at those points. Making use of the subtructure technique a few examples with different stacking sequences were analyzed. The results are compared to obtain a set-up with small edge stresses. (orig.)