TWI Industrial Member Report Summary 508/1995
S M Stevens
Background
Polyetheretherketone (PEEK) is a high performance semicrystalline thermoplastic, which is used, in critical and hostile environments, such as abrasion and chemically resistant linings, pump impellers, and aircraft components. The mechanical properties are influenced by factors such as crystallinity, morphology, and orientation, and are thus likely to be affected by welding. This report describes work that is part of an ongoing project at TWI to generate data on the structural and morphological changes which occur in thermoplastic welds.
Hot plate welds were made in PEEK at hot plate temperatures of 400°C ('optimum' conditions) and 350°C (cold welds) with normal welding pressures, and at 400°C with low welding pressures, in order to produce welds with a range of mechanical properties. Fourier transform infrared (FTIR) microspectrometry was utilised to measure the crystallinity and molecular orientations in these welds, and transmitted light microscopy, and scanning electron microscopy of etched samples, were used to study their morphology. Tensile and tensile-impact tests were carried out; scanning electron microscopy was employed to examine the fracture surfaces of broken test specimens, with transmitted light microscopy to establish where failure occurred.