Finite element investigation of “cradle tests” for the mechanical characterization of pultruded rods under compression

The development of hierarchical composites using pultruded rods as a primary building block is ongoing. These new composites, thanks to the nature of their constituent, offer more freedom of design as three-dimensional structures compared to the two-dimensional layer-by-layer composites. Getting a good understanding, and therefore characterisation of these building blocks becomes crucial before using them in hierarchical structures. However, it is expensive to perform many tests by following a trial-and-error approach. Modelling those tests therefore becomes useful as it allows the users to get a first estimation of the possible output of an experiment. These models are even more crucial when they aim to represent the complex behaviour of a system, as is the case with compression of Fibre Reinforced Polymers (FRPs): the shear instability, the buckling, twisting and rotations resulting from compression loads are not trivial to predict, neither are the limitations of the test method used. A model of a modified four-point bend test is presented, with its limits as well as its potential for improvement.