Design, simulation and testing of a short fibre reinforced polymer - metal hybrid structure

Polymer Metal Hybrid (PMH) structures are lightweight solutions that combine the ductility of a metal insert with the high specific properties of short fibre reinforced polymers. In this work, the design, simulation and testing of a PMH structure is presented. The structure is meant as a demonstrator for load bearing applications, where at failure large displacements must be ensured without a complete separation in two or more parts. These safety requirements are typical of the automotive applications, like suspension arms. The component studied in this work is a simplified structure inspired by the structure of a car suspension’s control arm. The component is a beam with simplified geometry made of short fibre reinforced polyamide, manufactured by injection moulding. The beam was designed considering a load condition of three-point bending. The metal insert is meant for preventing the separation into two or more pieces after the failure of the composite shell. The shape of the metal insert was defined by topological optimization, with the objective of minimizing its mass and the constraint of preserving a certain fraction of the original stiffness. The design of the reinforced plastic shell was refined by through process modelling, i.e. by simulating the injection moulding process and evaluating the mechanical properties of the material, taking into account the effect of fibre orientation. The fibre orientation is known to affect the stiffness and the strength of SFRP [1, 2]. Based on the distribution of the fibre orientation obtained by the simulation the local properties of the composite material were evaluated using the Digimat software [3]. The part was then manufactured and tested., Static and fatigue tests were conducted considering the design condition of three-point bending, and the results were compared with the numerical simulations carried out with the Abaqus software. Moreover, the components were subjected to creep tests in order to verify the dimensional stability of the PMH structures. In this type of test, the component was subjected to a constant load configuration of three-point bending for long time (at least 500 hours). The maximum deflection of the component was measured as a function of the time. The influence of the temperature on the creep effects was also investigated. The behaviour of the PMH component was compared to the behaviour of the same component made of the same reinforced polyamide material but without the metal insert. The comparison was carried out considering both the static and the dynamic load conditions.