Mechanical properties of vibration welded short- and long-glass-fiber-reinforced polypropylene

The tensile properties of vibration welded polypropylene plates were measured as a function of glass fiber content (30 and 40 wt%), glass fiber length (short- and long-fiber compounds), weld pressure (1–5 MPa), meltdown (0.5 and 2 mm) and type of faying surface (welding along either molded or machined edges). When plates were welded along their molded-edges, weld strengths were observed to be in the range of 15–30 MPa depending on the welding parameters and material type. The weld strength was observed to decrease with increasing fiber content for all materials and welding conditions studied. If, however, the plates were welded along machined edges, it was possible to obtain weld strengths that approached those of the bulk composite material. Weld strengths of over 70 MPa were observed for 40% long-glass-fiber-reinforced polypropylene compounds welded under conditions of low pressure. This was not observed for any short-fiber or 30% long-fiber polypropylene compounds. Possible causes for this high weld strength are discussed.