Three‐dimensional fiber orientation in vibration welded joints of glass fiber reinforced polyamide‐6

Abstract A technique was developed to obtain the three‐dimensional distribution of fiber orientation in vibration‐welded joints of polyamide‐6 (PA‐6) reinforced with 30 wt% glass fibers. The heat‐affected zone (HAZ) of fiber‐reinforced PA‐6 was successfully revealed by polishing and etching the vibration welded joints. Examination with the polarized light microscope in the reflection mode showed detailed microstructure domains, including the bulk crystalline zone and the HAZ. Experimental elliptical fiber cross‐section images were used to obtain second order orientation tensors, thus providing a quantitative description of the three‐dimensional fiber orientation distribution. The fibers in the HAZ were reoriented towards the squeeze flow direction, when compared with the bulk phase. Low welding pressure does not necessarily produce a more favorable fiber orientation in the tensile direction than high welding pressure. High welding pressure and low amplitude promote fiber reorientation in both the squeeze flow and tensile (weld thickness) directions. Overall, it was found that, at 30% fiber content, vibration‐welded joints of injection molded fiber‐reinforced PA‐6 are weaker than vibration‐welded joints in unreinforced injection molded samples. The fibers in the former do not undergo sufficient reorientation to influence weld strength in the tensile direction. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers