Papers by Keyword: Brittle-Ductile Transition

Abstract: The paper presents a comparative analysis of the dynamic loading of a polymethyl methacrylate (PMMA) target by a polyethylene (PE) projectile exposed to laser radiation with similar initial energy characteristics of the projectile and the laser pulse. The similarities and differences in the mechanisms of the target's response and its destruction to high-speed mechanical and laser action are shown. A higher efficiency of laser irradiation in the destruction of PMMA was found, and the conditions for the transition of the fracture mechanism from brittle to elastic-plastic were shown.

Abstract: The brittle to ductile failure mode transition and the formation of adiabatic shear bands (ASB) of polypropylene were observed at high strain rate impact loading. The dynamic experiments were conducted using a split Hopkinson pressure bar (SHPB) set-up with hat-shaped specimens. The post-test observations of the recovered specimens were performed by polarized light microscopy. The mechanical behaviors of specimens are strongly influenced by temperature, the strength of specimen decreases with increasing temperature. Furthermore, the specimen fractures as a brittle solid at room temperature (20°C), while at a high temperature (100°C), the specimen fractures on a ductile model. At high temperature impact tests, shear bands are observed in the shear zone of the hat-shaped specimen, and the cracks formed at the corners propagate along the shear bands.

Abstract: The toughness of blends composed of PA6 and acrylonitrile-butadiene-styrene (ABS) compatibilized by using styrene-maleic anhydride (SMA) as a compatibilizer was measured over a wide temperature region. The addition of SMA results in a significant increase of the PA6 phase viscosity due to the in situ formation of graft polymers during the melt processing, and the significant change in viscosity ratio between the PA6 and ABS due to the formation of SMA-g-PA6 graft polymer may be prevent the coalescence of the dispersed phase. All results in this paper were consistent, and showed the good interaction between PA6 and ABS, which were proved by the morphology and mechanical properties of the blends.

Abstract: Based on reciprocating electroplated diamond wire saw (REDWS) slicing experiments, a study on REDWS machining brittle-ductile transition of single crystal silicon was introduced. The machined surfaces and chips were observed by using Scanning Electron Microscope (SEM), and some experimental evidences of the change of material removal mode had been obtained. The experimental results indicate there is a close relationship between material removal mode and the ratio r value of ingot feed speed and wire speed, through controlling and adjusting the r value, the material removal mode can be complete brittle, partial ductile and near-ductile removal.

Abstract: Based on impulse theories and indentation fracture mechanics, the motion model of the contact between abrasive particle and workpiece in workpiece two-dimension ultrasonic vibration grinding (WTDUVG) was analyzed, and the critical condition of ultrasonic vibration grinding brittle-ductile transition was analyzed theoretically, furthermore the critical cutting depths of a grain under different grinding conditions were obtained by Matlab programs. In this work, the ultrasonic vibration and conventional diamond grinding of Al2O3/ZrO2 nanoceramics were performed in order to investigate the effect of workpiece ultrasonic vibration on the brittle-ductile transition mechanism, the effect of grit size, worktable speed and grinding depth on the critical depth of cut were studied by grinding experiments. the micro-topography of the grinding surface was observed by AFM and SEM. Experiment indicated that only when the grinding depth less than critical grinding depth, ductile regime grinding of ceramics can be realized, the appropriate grinding parameter on surface finish are suggested.

Abstract: Hardness, elastic modulus and scratch resistance of single silicon wafer are measured by nanoindentation and nanoscratching using a nanoindenter. Fracture toughness is measured by indentation using a Vickers indenter. The results show that the hardness and elastic modulus at a peak indentation depth of 100 nm are 12.6 and 166.5 GPa respectively. These values reflect the properties of the silicon wafer, the bulk material. The fracture toughness value of the silicon wafer is 0.74 Mpa·m1/2. The material removal mechanisms are seen to be directly related to the normal force on the tip. The critical load and scratch depth estimated from the scratch depth profile after the scratching and the friction profile are 138.64 mN and 54.63 nm respectively. If the load and scratch depth are under the critical values, the silicon wafer will undergo plastic flow rather than fracture. The critical scratch depth is different from that calculated from the formula of critical-depth-of-cut described by Bifnao et al and some reasons are given.

Abstract: According to the size effect theory established on the concept of geometrically necessary dislocations and results of nano-indentation experiments, a novel brittle-ductile mechanism of ultra-precision turning of single crystal silicon is proposed. The accurate critical chip thickness is firstly calculated on the basis of theoritical analysis. A macro-micro cutting model is created based on the brittle-ductile transition mechanism. Finally, the results of study are testified through experiments.

Abstract: One of the remarkable achievements of nanotechnology is the ability to achieve nanometric surface finishes in single-point diamond turning of high-precision components for complex optical surfaces. A better understanding of the surface generation mechanisms is of prime importance for the development for the prediction of the surface roughness. This paper presents a study of mechanisms of nano-surface generation in single-point diamond turning of various types of materials.

Abstract: Formation, propagation and length of crack and hardness of single silicon wafer were investigated at different temperatures by means of Vickers indentation, using lower temperature testing unit with semiconductor refrigerating chip and higher temperature testing unit with closed electric furnace. The results show that the hardness of single silicon wafer decreases with the increase of temperature, while the length of crack increases with the increase of temperature. Ductile-brittle transition of the single silicon wafer can occur at different temperatures with the increase of load. When the load is smaller and temperature is lower, no cracks can be found.

Abstract: The physical model of fixed-abrasive diamond wire-sawing monocrystalline silicon was founded to analyze the elastic deformation of the wire, supposing that every grit was connected to the surface of the wire by a spring. Ignoring lateral vibration of the wire, the geometrical model of wire-sawing was founded; the average cut depth of single grit was calculated theoretically. Based the indentation fracture mechanics and investigations on brittle-ductile transition of machining monocrystalline silicon, the removal mechanism and surface formation was studied theoretically. It shows that in the case of wire-sawing velocity of 10m/s or higher, infeed velocity of 0.20mm/s and diamond grain size of 64μm or smaller, the chip formation and material removal is in a brittle regime mainly, but the silicon wafer surface formation is sawed in a ductile regime. The size of the abrasives, the wire-saw velocity and infeed velocity can influence the sawing process obviously.