Papers by Keyword: Surface Fracture

Abstract: The mechanical behavior of the surface of metals is strongly affected by surface fracture occurring in the process of mechanical shearing, especially in shaper-type cutting performed for the application of ultra-fine optical manufacturing and several types of nanotechnology. This discussion aims to elucidate the tribological behavior of pure Cu. In ultra-precise cutting, the physics of crystallographic interfaces is extremely important for controlling surface fracture behavior. In this study, surface fracture behavior was evaluated using single crystal copper cut in two different directions (along the (100) and (111) planes). For V-shaped groove cutting, the flat copper surface was cut with a diamond-tip cutting tool (with a V angle of 90°, a rake angle of 0°, and an escape angle of 7°) at a machining speed of 4-4000 mm/min and a cutting depth of 0.2-10 m. The machined surface was observed with a laser scanning microscope and compared with two groove shapes, in which the cutting grooves in the two cutting directions were found to be different. This result was considered to depend on whether the cutting tool moved along the slip planes {111}, which are oriented in the direction. In the case of shallow cutting (under 1 m), the springback behavior became apparent for cutting in the slip plane direction, where the mechanism of this behavior would be associated with the interface between slip-plane fractures created by the cutting tool.

Abstract: Gigacycle fatigue behavior in high-strength steels tested under rotary bending fatigue was summarized in this paper. Characteristic of the very high cycle fatigue is to be caused the transition of fracture mode from surface-induced fracture to subsurface inclusion-induced one. In the vicinity of an inclusion at the origin of internal crack, granular-bright-facet (GBF) area was formed during extremely long fatigue cycles. It was pointed out that the formation of GBF area was an important factor for the control of the internal fatigue fracture in gigacycle regime. The GBF area revealed a very rough granular morphology compared with the area outside the GBF inside the fish-eye zone, and was related to the carbide distribution in the microstructure of the matrix. From the detailed observation of fracture surface and computer simulation by FRASTA method, the GBF area formation mechanism in a gigacycle fatigue regime was proposed as the ‘dispersive decohesion of spherical carbide model’.

Abstract: Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.