Analysis of a mini-sandwich compression test specimen

Mini-sandwich compression specimens have been analyzed by using a rule-of-mixtures approach and a finite element method which takes into account the mechanical and non-mechanical loadings. The results of stress analysis are illustrated for an (ASA4/3501-60/3501-6]_s specimen and an (AS4/APC-2)/APC-2]_s specimen as examples. Both specimen configurations contain face sheets consisting of two plies of O° orientation. The compressive strengths of these two unidirectional composites were computed from the experimentally measured strengths of the mini-sandwich specimen and the stress state predicted by the present analysis. The present result shows that a rule-of-mixtures approach can cause considerable error in the interpretation of the compressive strength of unidirectional face sheets. Procedures for the accurate determination of the compressive strengths of the face sheets for mini-sandwich specimens are presented. A simplified non-linear approach reveals that it is important to consider the final tangent or secant material properties rather than the initial material properties to obtain accurate stress distributions of the specimen prior to failure.