On the Sandwich Plate Twist Test for Shear Testing

This work examines the viability of the sandwich twist (anticlastic) test as a means to determine the in-plane and transverse shear properties of the face sheets and core in sandwich materials through analysis and testing. The contribution of core transverse shear to the total compliance of the specimen is quantified for different material systems and the adequacy of classical laminated plate theory (CLPT) as a data reduction method for such a test is examined. Parametric studies are conducted using finite element analysis (FEA) to examine the influence of transverse shear deformation on the plate compliance and propose some guidelines for specimen design. It is shown that CLPT greatly underestimates the plate compliance, except when very stiff cores and compliant face sheets are used, as a result of transverse core shear deformation. A shear correction factor is proposed to correct the CLPT compliance for transverse shear deformation of the core. For sandwich panels with compliant cores, the shear correction factor may be used to determine transverse shear modulus of the core.