Joining fibre reinforced sustainable thermoplastic composites using the welding process

Joining carbon fibre reinforced thermoplastic composites (CFRTPs) by the welding process is becoming an attractive technique due to its exceptional surface preparation savings over adhesive bonding, and uniform stress transfer over metallic drilling and riveting. To ensure the initiative of ‘applying right process to right material’, welding using both resistance heating and Infra-red (IR) heating were both studied simulatively and experimentally in this work. The characterisation of heat-transfer within the resistively welded region was firstly investigated using Finite Element Analysis (FEA), which determined the key parameters of power density and clamping distance for a high-quality weld. Experiments were carried out in a Single Lap Joint (SLJ) configuration, and the resultant strengths under tensile loading have demonstrated a competitive capability to an aerospace-grade of ~ 42.8 MPa. The follow-up FEA results suggested splitting the heating element into separate elements could effectively improve thermal uniformity and reduce the temperature difference from 171 °C to 101 °C. Such a heating element formed with a thickness of ~2 μm was then accomplished by an inkjet printing technology. In IR welding, a heat-transfer simulation utilising a constant beam power firstly predicted the temperature development in the welding zone. In addition, the model evaluated the actual emissivity (ε=0.84) of a Low Melting PAEK composite to the designated IR emitters for consequent studies. A follow-up model combining the physics of heat transfer and the surface-to-surface radiation was then carried out. By optimising the power density and IR emitter positions, a weldable process window and thermal uniformity less than 121 °C was determined. The optimised welded SLJ under lab-scale experiments proved a comparable lap shear strength ~ 37.3 MPa to the earlier resistance-welding works. The research found the benefits that IR welding is of a high heating coverage towards composite substrates, while RW impose the considerable controllability of thermal behaviour, which indicates a combination of both techniques for joining large-scale composite structures in industrial-scale applications.

Citation

Pu, J. (2025). Joining fibre reinforced sustainable thermoplastic composites using the welding process [Unpubished doctoral thesis]. University of Chester.

Publisher

University of Chester

URI

https://chesterrep.openrepository.com/handle/10034/629963

Type

Thesis or dissertation