Residual stress evaluation in composites using a modified layer removal method

The layer removal method is often used for measurement of internal stresses in homogeneous polymeric materials. In order to extend the use of this method to laminated composites certain refinements are needed. These include: (i) use of varying material properties (elastic moduli) through the thickness of the composite plate; (ii) use of geometric non-linear analysis to account for large deformations; and (iii) measurement not only of curvatures but also of strains. These refinements are necessary because a non-symmetric laminate is created when layers are removed, which shows large curvatures. The modified layer removal method was theoretically validated on a typical compression-moulded continuous-fibre laminate (PEIiglass) and a typical injection-moulded short-fibre-reinforced laminate (PC/glass). The modified method produced good results and the need to use the modified layer removal analysis is clearly demonstrated.