Thermoplastics reinforced with random glass mat have high strength and
stiffness; the fibers dominate the mechanical behavior of these compo
sites. The results of this investigation have shown that fibers are in
effective for reinforcing hot-tool and vibration welded butt welds. Th
e maximum weld strengths attained with GMT are comparable to the stren
gths of good welds of the unfilled material. The optimum hot-tool weld
ing parameters;for the reinforced materials are different from those f
or the unfilled material. Unfilled polypropylene is easier to weld tha
n unfilled polyamide. This characteristic is also true of the reinforc
ed materials. In vibration welding, high welding pressures and high am
plitudes result in lower mechanical properties. The optimum penetratio
n depends on the fiber content of the bulk material. This penetration
dependence is different from that for unfilled thermoplastic, for whic
h the mechanical properties are independent of the penetration once a
steady state has been attained.