Achieving high strength without sacrificing its transparency during ultrasonic spot joining polymethyl methacrylate

As a widely used ophthalmic material, the usage of polymethyl methacrylate (PMMA) inevitably involves joining multiple components into large parts. This brings a problem of maintaining the transparency of PMMA at the joined region. Ultrasonic spot joining is used to join PMMA in this work. Different input energies are applied to achieve tight bonding and guarantee the joint transparency. Results show that low input energies of 50 J, 100 J and 200 J achieve limited bonding but can maintain good transparency of the joint. Bonding area increases obviously with increasing the input energy to 400 and 800 J but the joint transparency decreases due to the thermal degradation. The hardness of PMMA seldom decreases after joining. Joint with good strength and transparency is obtained using input energy of 200 J. [Display omitted] •Bonding first starts at the overlap edge due to stronger vibration.•High input energy causes thermal degradation, decreasing the joint transparency.•Ultrasonic vibration hardly changes the hardness of PMMA.•Joint with high strength and good transparency is obtained using 200 J.•Ultrasonic spot joining fabricates PMMA joint stronger than other methods.