Study of a three point-bending specimen for shear characterisation of sandwich cores

A sandwich beam loaded in three-point bending (TPB) was employed for the shear characterization of foam cores destined to structural sandwich application. In the design of the specimen, particular care was taken to avoid measurement errors deriving from the flexural component of the displacement and from the de Saint Venant's effects, yet retaining the simplicity in the formulae for data reduction. Using the new method, experimental tests were carried out on a PVC foam 55 Kg/m3 in density. For comparison, shear characterization tests were also performed according to ISO 1922. The results obtained demonstrate that, when the core shear modulus is considered, TPB and ISO 1922 can provide practically coincident results. However, TPB yielded a shear strength about 20% higher than the ISO Standard, together with a shear strain at failure that is 10% lower. The failure modes observed suggest that the core shear behavior is better represented by TPB, whereas ISO 1922 is unsuitable to correctly measure the core shear strength.