CONTROLLING THERMAL-STRESSES IN COMPOSITES BY MEANS OF FIBER PRESTRESS

A new method of applying a prestress to the fibers in composite lamina tes prior to and during cure is described, and several [0(p)/90](T) la minates produced at varying prestress levels are discussed. Experiment al measurements described in this paper confirm that fiber prestressin g can reduce or eliminate residual thermal stresses. This is evidenced by a reduction in the thermal warpage of unsymmetric [0(p)/90](T) lam inates. An existing thermal analysis of unsymmetric laminates (develop ed by Hyer) is modified slightly in this paper to account for fiber pr estressing, and is then used to predict out-of-plane deformations of t he [0(p)/90](T) panels. Measurements compare well with theory. Specime ns machined from the prestressed panels were also subjected to tensile loadings and inspected for matrix cracks in the 90 degrees ply. It wa s found that fiber prestressing greatly reduced matrix cracking in [0( p)/90](T) specimens, but had little effect on [0/90(p)](T) specimens.