Product PerformanceDeformation of reinforced polymer bearing elements on full-scale compressive strength and creep tests under yielding conditions

Ultra high molecular weight polyethylene (UHMWPE) reinforced with a carbon fibre/epoxy ring (hybrid polymer pad) is used as bearing elements in a ball-joint for rotation of a storm surge barrier, requiring high strength and dimensional stability. The concave bearing surfaces contain 500 pads with diameter 250 mm incorporated in machined holes. As they are used as functional parts, high deformation will cause failure due to loss of clearance between the convex and concave surfaces. The applicability of general models for deformation of polymers to present structural design is limited, as they are based on material models and the effect of reinforcements should be verified. For optimisation and reliability, the present study focuses on a component test with a simulation of the real contact situation as closely as possible. From local analysis of the bearing elements, each polymer pad is loaded at 150 MPa, well above the polyethylene yield strength of 21 MPa. Full-scale experimental tests show two important details for stable deformation and life-time functionality, i.e. the clearance between the hybrid UHMWPE pad and its sample holder and the cold flow of a polymer lip over the carbon fibre ring for avoiding contact between the reinforcing ring and the convex counterface. Therefore, different geometries are evaluated with a total deformation of 10% during compression and 0.5% during subsequent creep. After recovery, a permanent deformation less than 1% is measured. For cold flow of the polymer lip, both the lip diameter and lip thickness should be controlled. Finally, a loading capacity of 400 MPa is determined for a hybrid UHMWPE pad.