Fatigue properties of vibration welded nylon 6 and nylon 6,6 butt joints

The fatigue properties of vibration welded butt joints in two commonly used thermoplastics, nylon 6 and nylon 6,6, are examined in this paper. Plaques were welded at 212 Hz and at an amplitude of 1.8 mm. to a weld penetration of 1.5 mm. Dog-bone coupons were machined from the welded plaques and then fatigue cycled at frequencies ranging from 3 to 10 Hz with a stress ratio of R=0.1 in load control. All coupons failed by fatigue initiated at the weld. Stress-life data were generated for high pressure and low pressure welding conditions. They all appear to have similar fatigue behaviour with the exception of nylon 6 welded in high pressure. The temperature rise in the weld region during testing was found to be insignificant and no physical thermal damage was observed. Vibration welding of these materials appears to be viable for structural applications requiring fatigue resistance.