Impact Compressive Properties of Polyurethane Foams with 3D Continuous Fibre Reinforcement

<p>Flexible and rigid polyurethane foams are used in applications subjected to impact loads. Integrating a three-dimensional, continuous fibre reinforcement meets high requirements for stiffness and strength. A fundamental comparison of the impact compressive properties was carried out for contributing to a reasonable choice between these variants. A rigid and flexible foam with a bulk density of 85 kg/m³ each was investigated with and without reinforcement by a warp-knitted spacer fabric. The material testing was conducted using a drop weight tester in accordance with a German standard. Three impacts are applied by a hammer with a flat surface larger than the area of the sample plate. Different impact energies were investigated and the deformation behaviour was analysed using a high-speed camera. Much higher energy absorptions at low deformations were found with rigid foam. Peak stresses and decelerations were lower with flexible foam if the load did not densify the material. Reinforcing the foams leads to an anisotropic deformation and improves the impact compressive properties, especially in the case of the flexible variant. The four materials analysed had a similar rebound and largely maintained their performance when subjected to the repeated impact load.</p>