Shear Strength of Vibration Welded Lap Joints

Discontinuously reinforced thermoplastic composites are used in a wide variety of automotive applications due to their excellent mechanical properties and low processing cost. The mechanical properties of these short/long fiber reinforced materials can be improved by using continuous fibers. However, processing these continuously reinforced composites is more difficult due to the inextensible nature of the fibers. It is possible to combine the ease of processing of discontinuously reinforced thermoplastics with the superior mechanical properties of continuously reinforced materials by creating a hybrid part. The two different materials can be married using a number of technologies such as overmoulding and joining. In this research, vibration welding is used to join polypropylene reinforced with continuous glass fibers to other polypropylene compounds. Lap and T-style joints have been made using an instrumented linear vibration welder. The effects of weld parameters such as weld area, weld pressure and meltdown have been assessed using a compression shear test. This work is one of the first to assess relatively large surface area lap joints. The results show that shear stresses of the order of 15 MPa are attainable for a wide variety of processing conditions.