A MODIFIED LAYER REMOVAL ANALYSIS FOR THE DETERMINATION OF INTERNAL-STRESSES IN POLYMER COMPOSITES

The layer removal method is often used for measurement of internal str esses in homogeneous polymer materials. in order to extend the use of the method to polymer composites, certain refinements are needed. Thes e include (I) use of varying mechanical properties (elastic moduli) th rough the thickness of the composite plate and (2) measurement of not only curvatures but also strains. These refinements are necessary beca use a nonsymmetric laminate is created when layers are removed. The mo dified layer removal method was applied to PEI-glass fiber composite c ross-ply laminates. The average internal stresses measured within a la yer of constant fiber orientation agree well with stress levels predic ted by Classical Lamination Theory. The computed stress levers fulfill the condition of stress equilibrium, indicating that the procedure ap plied in the measurements is correct.