Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

Abstract

The heterogeneity and anisotropy of fibre-reinforced polymer matrix composites results in a highly complex mechanical response and failure under multiaxial loading states. Among the different biaxial testing techniques, tests with cruciform specimens have been a preferred option, although nowadays, they continue to raise a lack of consensus. It is therefore necessary to review the state of the art of this testing methodology applied to fibre-reinforced polymers. In this context, aspects such as the specific constituents, the geometric design of the specimen or the application of different tensile/compressive load ratios must be analysed in detail before being able to establish a suitable testing procedure. In addition, the most significant results obtained in terms of the analytical, numerical and experimental analyses of the biaxial tests with cruciform specimens are collected. Finally, significant modifications proposed in literature are detailed, which can lead to variants or adaptations of the tests with cruciform specimens, increasing their scope.

Keywords: biaxial loading; cruciform specimen; failure theories; fibre-reinforced polymer; finite element method; multiaxial; tensile/compressive loading; testing facility.

Figure 1

Triaxial testing facility at University of Castilla-La Mancha (UCLM, Spain): (a) triaxial testing machine. (b) CFRP cruciform specimen being tested under biaxial tensile–tensile loading.

Figure 2

Schematisation of the most frequently used geometrical features in cruciform specimens: (a) Single radius corner. (b) Double radii filleted corner. (c) Elliptical corner. (d) Slotted arms.

Figure 3

Gauge zone designs frequently found in literature: (a) Squared central zone. (b) Circular central zone. (c) Rhomboidal central zone. (d) Double tapering.

Figure 4

3D model of a quarter of cruciform specimen presenting different techniques for thickness tapering: (a) Stepped transition. (b) Linear reduction. (c) Curved transition.

Figure 5

3D model of the anti-buckling device developed by Serna Moreno and Horta Muñoz [82].