Thermal effects on thermoplastic composites welded joints: A physical and mechanical characterisation

The use of high performance thermoplastic composites (TPCs) in the aviation industry has increased over the last years. TPCs have significant advantages such as superior damage tolerance, excellent chemical resistance and the ability to be welded. To date, mechanical fastening, primarily, and adhesive bonding are the two traditional joining methods used in aviation industry. However, welding of TPCs has attracted significant attention due to its advantageous qualities such as the very short cycle times and the minimised stress concentrations. Most of the research published on welding of TPCs concerns process optimization and the evaluation of the mechanical performance at room temperature (RT) conditions. However, aircraft operate in a wide range of temperatures, typically between -50 °C to 70 °C and depending on the conditions, even up to 93 °C. Considering the temperature dependency of polymer composites properties, the weld performance of TPCs at low and high temperatures needs to be addressed. To the author’s knowledge, prior to the year 2014 there was no available literature assessing the influence of temperature on the mechanical performance of TPCs welded joints and since then, only a few publications have addressed this topic. The primary objective of this thesis was to not only fill the literature gap but also to obtain deeper knowledge and clear understanding of the behaviour of thermoplastic composites welded joints at low and high temperatures. In other words, to understand the phenomena dictating the weld performance which, in turn, would pave the way for further improvement of material properties and weld design.