Processing and characterization of the thermoplastic composites manufactured by ultrasonic vibration–assisted automated fiber placement

To obtain the autoclave-level mechanical properties using in situ consolidation of thermoplastic composites by automated fiber placement (AFP) with high efficiency is the focus of recent research. Different heat resources were utilized to pursue improved mechanical properties and deposition rates but yet not very satisfactory. In this article, E-glass fiber/polypropylene laminates, manufactured by ultrasonic vibration–assisted AFP (UAFP) and autoclave, were compared by means of mechanical properties and crystallization. The interfacial bonding mechanism was analyzed theoretically based on the principle of ultrasonic heating and the autohesion. The orthogonal tests were designed to study the effect of the process parameters on the interlaminar shear strength (ILSS), including the ultrasonic amplitude, layup speed, and pressure, to optimize the manufacturing process of specimens. The mechanical tests and differential scanning calorimetry (DSC) were utilized to evaluate the ILSS, mode I interlaminar fracture toughness G IC, impact toughness, and degree of crystalline of laminates from hot-press and UAFP. The experimental results indicate that the ILSS of the specimens from UAFP can match with the hot-press specimens. The G IC and the impact toughness of the UAFP specimens are 59.9% and 20.1% lower than the hot-press ones, respectively, which are due to the lower degree of crystalline caused by the higher cooling rate during the UAFP process. The results of DSC show that the crystallinity of specimens made from UAFP is only 38.5%, whereas the 49.2% crystallinity is tested for the hot-press.