| Summary: | Composite structures have been becoming increasingly popular in multiple industries such as
the automotive, marine and aerospace sectors, due to its ability to be lightweight yet retaining
its specific stiffness properties. Moreover, thermoplastics have been highly preferred due its
resin having the ability to become softer once heated, while retaining its properties after cooling
down. This makes them the perfect candidate for the ultrasonic welding joining method. Not
only does ultrasonic welding provide excellent bonding between joints, it is also cost and time
effective compared to other joining processes. Elium® is a novel acrylic thermoplastic resin
that was utilized in this project, a first of its kind resin that that is able to cure at room
temperature.
The objective of this final year project was to investigate the welding characteristics of fully
and hybrid thermoplastic composites manufactured using novel resin Elium®. The
thermoplastic composite parts were manufactured at laminate scales using vacuum assisted
resin infusion process, and trials of ultrasonic welding were performed thereafter. Lap shear
tests were then conducted in order to determine the weld strength of each of the different
configurations, as well as in-depth and scanning electron microscopy (SEM) to understand the
weld characteristics and failure mechanisms behind a good or bad welded samples. Samples
were also adhesively joined and tested in order to compare between both joining methods.
From the results of ultrasonic welding, weld PES/EL_PES/EL had the highest maximum LSS
of 4.94MPa in pure thermoplastic configurations, while weld C-UHMWPE/EL_C-UHMWPE/EL had the highest maximum LSS of 8.99MPa in hybrid thermoplastic
configurations. This shows a 45% improvement in weld strength when using hybrid
configurations. Moreover, most configurations from adhesive joining and ultrasonic welding
joining methods show similar LSS results, with the exception of adhesive C-UHMWPP/EL_C-UHMWPP/EL. Fiber pullout, fiber imprints, rough surfaces and shear cusps were observed
from failure surfaces of samples and SEM investigation, indicating strong bonds between
adherends. Hybrid thermoplastic fibers are looking promising in several applications and
industries. Although ultrasonic welding is challenging to use for thermoplastic fibers, it is
definitely a good alternative for adhesive joining if the welding parameters are well optimized.
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