A Modified Layer Removal Analysis for the Determination of Internal Stresses in Polymer Composites

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Abstract
The layer removal method is often used for measurement of internal stresses in homogeneous polymer materials. In order to extend the use of the method to polymer composites, certain refinements are needed. These include (1) use of varying mechanical properties (elastic moduli) through the thickness of the composite plate and (2) measurement of not only curvatures but also strains. These refinements are necessary because a nonsymnetric laminate is created when layers are removed. The modified layer removal method was applied to PEI-glass fiber composite cross-ply laminates. The average internal stresses measured within a layer of constant fiber orientation agree well with stress levels predicted by Classical Lamination Theory. The computed stress levels fulfill the condition of stress equilibrium, indicating that the procedure applied in the measurements is correct.