A BIAXIAL TENSION-COMPRESSION TEST METHOD FOR COMPOSITE LAMINATES

Development of a test system and associated experimental procedure for evaluating the strength of composite laminates under an in-plane biax ial tension-compression (BTC) stress state is presented. A description of the BTC test system and specimen is given. Flexible end reinforcem ents which do not transfer transverse external loads were used to elim inate stress concentrations caused by tensile grips and prevented the edges of the laminates from being crushed in compression. A relatively homogeneous statically determinant biaxial tension-compression stress field can be achieved in the gage section and the effects of a range of biaxial tension or compression stresses on the shear failure behavi or can be easily studied. A commercial fiberglass fabric/epoxy laminat e, G-10, is available in sheet and tubular forms and was used to evalu ate the BTC specimen and test fixture. Results from this specimen desi gn have the same strength as tubular specimens. Under a biaxial tensio n-compression loading condition, failure strength in one direction is not affected by applying a second transverse load. The in-plane shear cut-off predicted by most anisotropic strength criteria for composite laminates under a biaxial tension-compression stress state is not obse rved in G-10 composite laminates.