Composite material characterization through biaxial testing of cruciform specimens

Abstract

Composite materials are applied in a variety of industrial sectors such as aeronautics, marine, construction and energy. The composite components are in general subjected to complex loadings, which lead to multiaxial stress states in the material. To accurately design these composite laminates, failure criteria which are not only verified with uniaxial but also with biaxial test data have to be used. Despite the large demand for this experimental information, there is little existing experimental capability to evaluate the biaxial response of composite materials [1]. One of the techniques to produce biaxial stress states in a composite laminate consists of applying in-plane biaxial loads to a cruciform specimen [2]. Such a test device and a suitable specimen geometry have been developed at the Vrije Universiteit Brussel [3]. As you can see in Figure 1, the specimen has an adapted fillet corner radius and a reduced thickness in the centre to ensure biaxial failure in the gauge section. One of the objectives of biaxial testing is to obtain the failure stresses and strains in order to determine the failure envelopes of a certain material and lay-up. Another aim can be the determination of the mechanical material parameters in one single experimental set-up. It is clear that, due to the complex specimen geometry, the determination of these material characteristics is not straightforward and cannot be obtained as with uniaxial tests.