Fatigue strength of vibration‐welded unreinforced nylon butt joints

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Abstract
The fatigue properties of vibration‐welded butt joints in two thermoplastics, nylon 6 and nylon 6,6, are examined in this work. Injection molded plaques were welded under high and low pressure conditions 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 welded and unwelded plaques and then fatigue cycled in load control at a stress ratio of R = 0.1. The test frequency ranged from 1 to 10 Hz to avoid hysteretic heating. When the temperature rise in the weld region during testing was insignificant, no physical thermal damage was observed. It was found that the nonwelded specimens have longer fatigue lives than the welded ones, while the welded specimens appear to have similar fatigue behavior, except for nylon 6 welded in high pressure, which was slightly inferior. Vibration welding of these materials appears to be viable for structural applications requiring fatigue resistance. POLYM. ENG. SCI. 45:935–944, 2005. © 2005 Society of Plastics Engineers