Temperature-Dependent Lap Shear Strength of Adhesively Bonded High-Temperature Resistant Thermoplastics

Abstract

Due to the development of high-temperature resistant thermoplastics, e. g. polyetheretherketone, these plastics have become more attractive for several applications which require good mechanical properties at high service temperatures. In addition to conventional production processes, adhesive bonding is more and more used to build assemblies with a mix of materials to achieve certain product properties. These products are exposed to high temperatures during their product life, driving the need for a thorough understanding of the substrates, adhesives and their bonds. In order to investigate the temperature-dependent behaviour of the mechanical properties of high-temperature resistant joints, different thermoplastics were analysed in shear tension tests. In these tests three substrates (polyetheretherketone, polyetherimide, and polyamide) and two adhesives (one- and two-component epoxy resin) were tested. The tests were performed at four testing temperatures equally spaced between 20 °C and 200 °C to analyse the temperature-dependent material properties. The specimens were built up as a single-lap joint with a constant adhesive thickness. After curing at definite conditions the adhesively bonded joints were tested in a shear tension test. The results of this test are the lap shear strength and failure patterns. The results were correlated with thermal and mechanical properties of substrates and adhesives, e. g. glass transition temperature and Young’s modulus. The experimental analysis reveals a distinct temperature-dependent behaviour of the lap shear strength and failure patterns within the temperature range examined. In general, the lap shear strength decreases with rising testing temperature. Moreover, the failure patterns change from substrate failure to adhesive and cohesive failure of the examined adhesives with rising testing temperature. This implies a significant demand for high-temperature resistant adhesives in the future which can exhibit improved mechanical properties at high temperatures to guarantee an excellent joint between the substrate materials.