Abstract:

To improve the mechanical properties of fiber⁃reinforced thermoplastic composites， ultrasonic assisted injection molding experiments were carried out for rectangular flat parts based on polyamide 6 （PA6） reinforced by glass fiber （GF）. Ultrasonic vibration was applied in the following two situations： （1） filling stage， （2） filling and packing stages. X⁃ray diffraction， scanning electron microscopy， Fourier⁃transform infrared spectroscopy， and tensile experiments were performed to investigate the effects of ultrasonic application time and ultrasonic power on the crystallinity and mechanical performance of the parts， the orientation degree of glass fibers， and the bonding strength between glass fibers and the matrix. The changes in the internal crystallinity and mechanical properties of the parts subjected to ultrasonic vibration after water absorption were also studied. The results indicated that crystallinity of the parts was significantly improved by applying ultrasonic vibration with a power of 400 W. When 560 W ultrasound was applied， both the orientation morphology of glass fiber and the bonding strength between the matrix and fibers were improved. Moreover， the tensile strength and bending strength of the parts molded by applying ultrasound during the filling stage were increased by 11.9 % and 10.1 %， respectively. However， the mechanical properties of the parts tended to drop with continuously increasing the ultrasonic power. After absorbing water， the parts showed a decrease in the crystallinity and mechanical properties. Such a reduction could be depressed by introducing ultrasonic vibration into the molding process of the parts.

Key words: ultrasonic vibration, glass?fiber?reinforced polyamide 6, condensed matter structure, crystallinity, mechanical property