DETERMINATION OF RESIDUAL SHEAR STRESSES IN COMPOSITES BY A MODIFIED LAYER-REMOVAL METHOD

The layer-removal method is often used for measurement of internal str esses in homogeneous polymeric materials. In order to extend the use o f the method to laminated composites containing shear stresses, certai n refinements are needed. These include (i) determination of twisting moments, (ii) use of varying material properties (elastic moduli) thro ugh the thickness of the composite plate, (iii) use of geometric non-l inear analysis accounting for large deformations, and (iv) measurement not only of normal curvatures but also twisting curvatures and normal and shear strains. These refinements are necessary, because a non-sym metric laminate is created when layers are removed, which shows large (twisting) curvatures. The modified layer-removal method was theoretic ally validated on a typical compression-moulded continuous fibre lamin ate (polyetherimide/glass) and a typical injection-moulded short fibre -reinforced laminate (polycarbonate/glass). The modified method produc ed good results and the need to use the modified layer-removal analysi s is clearly demonstrated. (C) 1998 Chapman & Hall.