Investigation of the transient fracture behavior of carbon fiber reinforced polymer fibers in ultrasonic-assisted machining

Abstract

With the wide application of carbon fiber reinforced polymer (CFRP), machining-induced damage has received increasing attention. Due to the anisotropy of the fibers, the fiber fracture mode directly affects the performance of CFRP parts. Surface quality is closely related to the fiber fracture mode. This paper focuses on analyzing the fracture modes of CFRP fibers under ultrasonic-assisted machining (UAM). By conducting conventional machining (CM) and UAM experiments, combining scanning electron microscope (SEM) images, the relationships between cutting forces, surface roughness, fiber orientation, and fracture modes are analyzed. Compared to CM, UAM reduced cutting forces by 22%–63%, surface quality was improved by 36%, fibers predominantly fractured in a shear mode, and the fiber orientation effect was reduced by 42.4%. As cutting speed increased, cutting forces were reduced by 29.2%; however, excessively high speeds resulted in increased surface roughness and a greater fiber orientation effect. Increased ultrasonic amplitude led to 31.8% increase in cutting forces, 59.5% improvement in surface quality, and 67.5% reduction in the fiber orientation effect. Decomposing Acoustic emission (AE) signals using wavelet packet. The frequency bands for bending fracture and shear fracture were found to be 75–200 kHz and 375–475 kHz respectively. Moreover, the energy distribution in these frequency bands under different machining methods was analyzed to judge the fiber fracture behavior of CFRP. This research provides data support for optimizing the precision machining process of CFRP and enriches the AE database on fiber fracture modes, contributing to the improvement of accuracy and efficiency in non-destructive testing techniques. Highlights: Study of the connection between force, AE, roughness and fiber fracture behavior. UAM improves the percentage of fiber shear fracture. Characteristic frequency ranges of different fiber fracture modes have been determined. UAM inhibits the orientation effect of fibrous fibers. Cutting force and roughness exhibit two cycles within fiber direction ranging from 0 to 360°.