High-frequency vibration effects on material removal mechanisms in ultrasonic transverse scratching of carbon fiber reinforced plastics.

This paper represented some fundamental investigations on the potential effects of the high-frequency vibration on material removal mechanisms in ultrasonic transverse scratching of carbon fiber reinforced plastics (CFRPs). It was found that the ultrasonic superimposition brought about the evident reduction of the ductile-brittle transition depth of the unidirectional CFRPs. For the scratched groove generated without ultrasonic, the tensile stress and compressive stress caused by the indenter penetration were respectively responsible for the formations of the radial cracks at the leading edges and the central region. Under the combination of the inertia effects induced by the ultrasonic superposition and the skin-core structure of the carbon fibers, the micro-defects situated at the interior of the fibers were nucleated simultaneously, and their propagations caused the formations of the oblique cracks. Incorporated with the strain rate effects of the materials, a fresh theoretical model was proposed to describe the evolution of the mechanical stress during the scratching process. The fiber fragments induced by the oblique cracks were just concentrated on the top surface of the scratched groove, due to the coupling effects of the small penetration depth of the indenter and the express reduction of strain rate.