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M Rahman - One of the best experts on this subject based on the ideXlab platform.
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Effect of Dry Cutting on Force and Tool Life When Machining Aerospace Material
World Academy of Science Engineering and Technology International Journal of Mechanical Aerospace Industrial Mechatronic and Manufacturing Engineering, 2010Co-Authors: Kumaran Kadirgama, M Rahman, M. M. Noor, Khaled Abou-el-hossein, H.h. Habeeb, Bashir Mohamad, Rosli Abu BakarAbstract:Cutting fluids, usually in the form of a liquid, are applied to the Chip Formation Zone in order to improve the cutting conditions. Cutting fluid can be expensive and represents a biological and environmental hazard that requires proper recycling and disposal, thus adding to the cost of the machining operation. For these reasons dry cutting or dry machining has become an increasingly important approach; in dry machining no coolant or lubricant is used. This paper discussed the effect of the dry cutting on cutting force and tool life when machining aerospace materials (Haynes 242) with using two different coated carbide cutting tools (TiAlN and TiN/MT-TiCN/TiN). Response surface method (RSM) was used to minimize the number of experiments. ParTiAlN Swarm Optimisation (PSO) models were developed to optimize the machining parameters (cutting speed, federate and axial depth) and obtain the optimum cutting force and tool life. It observed that carbide cutting tool coated with TiAlN performed better in dry cutting compared with TiN/MT-TiCN/TiN. On other hand, TiAlN performed more superior with using of 100 % water soluble coolant. Due to the high temperature produced by aerospace materials, the cutting tool still required lubricant to sustain the heat transfer from the workpiece.
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Study of the temperature and stress in nanoscale ductile mode cutting of silicon using molecular dynamics simulation
Journal of Materials Processing Technology, 2007Co-Authors: X. P. Li, M RahmanAbstract:Abstract In nanoscale cutting of brittle materials, it has been found that there is a brittle–ductile transition when the cutting tool edge radius is reduced to nanoscale and the undeformed Chip thickness is smaller than the tool edge radius. In order to understand the mechanism of the brittle–ductile transition, the cutting characteristics, such as stress and temperature in the cutting region, have to be investigated. However, since the machining size is very small, on the nanoscales, it's very difficult to measure the temperature and stress in the Chip Formation Zone experimentally. In this study, the molecular dynamics (MD) method is employed to model and simulate the nanoscale ductile mode cutting of monocrystalline silicon wafer. The MD simulation results show that the temperature rise in the cutting Zone will affect the diamond tool. In the cutting process, the thrust force is larger than the cutting force. As the tool cutting edge radius increases, the shear stress in the workpiece material around the cutting edge will decrease. When the shear stress is so low that it is insufficient to sustain dislocation emission in the Chip Formation Zone, crack propagation becomes dominating. Consequently, the Chip Formation mode changes from ductile to brittle.
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High-pressure phase transFormation as the mechanism of ductile Chip Formation in nanoscale cutting of silicon wafer:
Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2007Co-Authors: X. P. Li, M RahmanAbstract:AbstractIn nanoscale cutting of silicon wafer, it has been found that under certain conditions ductile mode Chip Formation can be achieved. In order to understand the mechanism of the ductile Chip Formation, experiments and molecular dynamics (MD) simulations have been conducted in this study. The results of MD simulations of nanoscale cutting of silicon showed that because of the high hydrostatic pressure in the Chip Formation Zone, there is a phase transFormation of the monocrytslline silicon from diamond cubic structure to both β silicon and amorphous phase in the Chip Formation Zone, which results in plastic deFormation of the workpiece material in the Chip Formation Zone, as observed in experiments. The results further showed that although from experimental observation the plastic deFormation in the ductile mode cutting of silicon is similar to that in cutting of ductile materials, such as aluminium, in ductile mode cutting of silicon it is the phase transFormation of silicon rather than atomic dislo...
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Characteristics of dynamic hard particles in nanoscale ductile mode cutting of monocrystalline silicon with diamond tools in relation to tool groove wear
Wear, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:Abstract In nanoscale ductile mode cutting of the monocrystalline silicon wafer, micro/nano groove wear on the diamond cutting tool flank face is often observed, which is beyond the understanding based on conventional cutting processes because the silicon workpiece material is monocrystalline with the hardness lower than that of the diamond cutting tool at room temperature. From the investigation of such a phenomenon, a concept of “dynamic hard particles” generated in the Chip Formation Zone as a result of silicon phase transFormation from monocrystalline to amorphous was proposed. It was believed that the “dynamic hard particles” caused the groove wear at the tool flank. In this study, the characteristics of such “dynamic hard particles” and their relationship with the diamond tool groove wear have been investigated through molecular dynamics (MD) simulation of nanoscale ductile mode cutting of monocrystalline silicon with diamond tools. The results show that during the cutting process, due to the workpiece material phase transFormation from monocrystalline to amorphous, which results in the existence of silicon atom groups with shorter bond lengths in the Chip Formation Zone, “dynamic hard particles” having a dynamic and uneven distribution over the entire Chip Formation Zone are formed. The distribution changes over time and cutting stages. When the cutting runs into a steady state, the “dynamic hard particles” are mostly distributed in the lower portion of Chip Formation Zone, contributing directly to three body abrasions on the tool flank face, causing groove wear at tool flank. The dynamic distribution of the “dynamic hard particles” also causes the uncertainty of the groove wear locations at the tool flank.
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Characteristics of ductile mode Chip Formation in nanoscale cutting of brittle materials
International Journal of Abrasive Technology, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:In this paper, a comprehensive study of the machining characteristics of nanoscale ductile mode cutting of brittle materials is presented, covering the critical cutting conditions for the ductile mode of Chip Formation, cutting conditions for crack initiation in the Chip Formation Zone, effect of the cutting edge radius, machined workpiece surface and subsurface damage, effect of ultrasonic vibration assistance, mechanism of nanoscale ductile mode Chip Formation, cutting forces, tool wear and dynamic hard particles in the Chip Formation Zone. Systematic experiments for nanoscale cutting of a number of brittle materials, including tungsten carbide, silicon and glass, are conducted and Molecular Dynamics (MD) modelling and simulation for nanoscale cutting of monocrystalline silicon are carried out. The results are shown in detail in the paper.
Xiaoping Li - One of the best experts on this subject based on the ideXlab platform.
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Characteristics of dynamic hard particles in nanoscale ductile mode cutting of monocrystalline silicon with diamond tools in relation to tool groove wear
Wear, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:Abstract In nanoscale ductile mode cutting of the monocrystalline silicon wafer, micro/nano groove wear on the diamond cutting tool flank face is often observed, which is beyond the understanding based on conventional cutting processes because the silicon workpiece material is monocrystalline with the hardness lower than that of the diamond cutting tool at room temperature. From the investigation of such a phenomenon, a concept of “dynamic hard particles” generated in the Chip Formation Zone as a result of silicon phase transFormation from monocrystalline to amorphous was proposed. It was believed that the “dynamic hard particles” caused the groove wear at the tool flank. In this study, the characteristics of such “dynamic hard particles” and their relationship with the diamond tool groove wear have been investigated through molecular dynamics (MD) simulation of nanoscale ductile mode cutting of monocrystalline silicon with diamond tools. The results show that during the cutting process, due to the workpiece material phase transFormation from monocrystalline to amorphous, which results in the existence of silicon atom groups with shorter bond lengths in the Chip Formation Zone, “dynamic hard particles” having a dynamic and uneven distribution over the entire Chip Formation Zone are formed. The distribution changes over time and cutting stages. When the cutting runs into a steady state, the “dynamic hard particles” are mostly distributed in the lower portion of Chip Formation Zone, contributing directly to three body abrasions on the tool flank face, causing groove wear at tool flank. The dynamic distribution of the “dynamic hard particles” also causes the uncertainty of the groove wear locations at the tool flank.
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Characteristics of ductile mode Chip Formation in nanoscale cutting of brittle materials
International Journal of Abrasive Technology, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:In this paper, a comprehensive study of the machining characteristics of nanoscale ductile mode cutting of brittle materials is presented, covering the critical cutting conditions for the ductile mode of Chip Formation, cutting conditions for crack initiation in the Chip Formation Zone, effect of the cutting edge radius, machined workpiece surface and subsurface damage, effect of ultrasonic vibration assistance, mechanism of nanoscale ductile mode Chip Formation, cutting forces, tool wear and dynamic hard particles in the Chip Formation Zone. Systematic experiments for nanoscale cutting of a number of brittle materials, including tungsten carbide, silicon and glass, are conducted and Molecular Dynamics (MD) modelling and simulation for nanoscale cutting of monocrystalline silicon are carried out. The results are shown in detail in the paper.
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Crack initiation in relation to the tool edge radius and cutting conditions in nanoscale cutting of silicon
International Journal of Machine Tools & Manufacture, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:Abstract In cutting of brittle materials, experimentally it was observed that there is a ductile–brittle transition when the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius of the zero rake angle. However, how the crack is initiated in the ductile–brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has not been fully understood. In this study, the crack initiation in the ductile–brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has been simulated using the Molecular Dynamics (MD) method on nanoscale cutting of monocrystalline silicon with a non-zero edge radius tool, from which, for the first time, a peak deFormation Zone in the Chip Formation Zone has been found in the transition from ductile mode to brittle mode cutting. The results show that as the undeformed Chip thickness is larger than the cutting edge radius, in the Chip Formation Zone there is a peak deFormation depth in association with the connecting point of tool edge arc and the rake face, and there is a crack initiation Zone in the undeformed workpiece next to the peak deFormation Zone, in which the material is tensile stressed and the tensile stress is perpendicular to the direction from the connecting point to the peak. As the undeformed Chip thickness is smaller than the cutting edge radius, there is no deFormation peak in the Chip Formation Zone, and thus there is no crack initiation Zone formed in the undeformed workpiece. This finding explains well the ductile–brittle transition as the undeformed Chip thickness increases from smaller to larger than the tool cutting edge radius.
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Molecular dynamics modelling and simulation of nanoscale ductile cutting of silicon
Journal of Computer Applications in Technology, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:A simulation system for nanoscale ductile mode cutting of monocrystalline silicon has been developed in thi study using the Molecular Dynamics (MD) method for better understanding of the ductile mode cutting mechanism. In the model of this simulation system, the initial atom positions of silicon workpiece material are arranged according to the crystal lattice structure, the atomic interactive actions of silicon are based on the Tersoff potential, the diamond cutting tool is assumed to be undeformable, the tool cutting edge is realistically modelled to have a finite radius, and the motions of the atoms in the Chip Formation Zone are determined by Newton's equations of motion. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the results of experimental cutting tests to substantiate the developed simulation system and the results show a good agreement with analytical findings.
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Study of the mechanism of nanoscale ductile mode cutting of silicon using molecular dynamics simulation
International Journal of Machine Tools & Manufacture, 2007Co-Authors: Xiaoping Li, M RahmanAbstract:Abstract In cutting of brittle materials, it was observed that there is a brittle-ductile transition when two conditions are satisfied. One is that the undeformed Chip thickness is smaller than the tool edge radius; the other is that the tool cutting edge radius should be small enough—on a nanoscale. However, the mechanism has not been clearly understood. In this study, the Molecular Dynamics method is employed to model and simulate the nanoscale ductile mode cutting of monocrystalline silicon wafer. From the simulated results, it is found that when the ductile cutting mode is achieved in the cutting process, the thrust force acting on the cutting tool is larger than the cutting force. As the undeformed Chip thickness increases, the compressive stress in the cutting Zone decreases, giving way to crack propagation in the Chip Formation Zone. As the tool cutting edge radius increases, the shear stress in the workpiece material around the cutting edge decreases down to a lower level, at which the shear stress is insufficient to sustain dislocation emission in the Chip Formation Zone, and crack propagation becomes dominating. Consequently, the Chip Formation mode changes from ductile to brittle.
Andrew A O Tay - One of the best experts on this subject based on the ideXlab platform.
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Crack initiation in relation to the tool edge radius and cutting conditions in nanoscale cutting of silicon
International Journal of Machine Tools and Manufacture, 2007Co-Authors: M. B. Cai, X. P. Li, M Rahman, Andrew A O TayAbstract:In cutting of brittle materials, experimentally it was observed that there is a ductile-brittle transition when the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius of the zero rake angle. However, how the crack is initiated in the ductile-brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has not been fully understood. In this study, the crack initiation in the ductile-brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has been simulated using the Molecular Dynamics (MD) method on nanoscale cutting of monocrystalline silicon with a non-zero edge radius tool, from which, for the first time, a peak deFormation Zone in the Chip Formation Zone has been found in the transition from ductile mode to brittle mode cutting. The results show that as the undeformed Chip thickness is larger than the cutting edge radius, in the Chip Formation Zone there is a peak deFormation depth in association with the connecting point of tool edge arc and the rake face, and there is a crack initiation Zone in the undeformed workpiece next to the peak deFormation Zone, in which the material is tensile stressed and the tensile stress is perpendicular to the direction from the connecting point to the peak. As the undeformed Chip thickness is smaller than the cutting edge radius, there is no deFormation peak in the Chip Formation Zone, and thus there is no crack initiation Zone formed in the undeformed workpiece. This finding explains well the ductile-brittle transition as the undeformed Chip thickness increases from smaller to larger than the tool cutting edge radius. © 2006 Elsevier Ltd. All rights reserved.
E. Uhlmann - One of the best experts on this subject based on the ideXlab platform.
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Cutting Simulation with Consideration of the Material Hardening in the Shear Zone of AISI1045
Procedia CIRP, 2017Co-Authors: E. Uhlmann, Steffen Henze, Katrin Brommelhoff, Walter ReimersAbstract:Abstract By the use of high energy synchrotron X-ray diffraction it was possible to determine the stress state in the Chip Formation Zone during orthogonal cutting of AISI1045. The analysis of the diffractograms showed a hardening of the material during the movement through the shear Zone. For this reason nano indentation experiments on prepared Chips have been carried out. With these experiments, the material hardening has been confirmed. The nano indentation experiments were reproduced by FEM simulations and it was possible to determine flow curves of the hardened material above the shear Zone based on existing flow curves of AISI1045. Thus, cutting simulations have been carried out, which considered the material hardening in the shear Zone. The simulation results were then compared with the results of the in-situ strain measurements.
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influence of the built up edge on the stress state in the Chip Formation Zone during orthogonal cutting of aisi1045
Procedia CIRP, 2015Co-Authors: E. Uhlmann, Steffen Henze, Katrin BrommelhoffAbstract:Abstract In-situ strain measurements with high energy synchrotron radiation during orthogonal cutting of AISI1045 were carried out. Thereby it was possible to determine the stress state in the Chip Formation Zone during the cutting process. As such, observations regarding the Formation of built-up edges during the cutting process have been made. The Formation of a built-up edge on the cutting tool is a common phenomenon during cutting of mild steel and other ductile materials, in particular at low cutting speeds. This may result in increased tool wear and a decrease in the resulting surface quality. By analyzing the Chip roots of the in-situ experiments, it was possible to determine the geometry of the built-up edges on tools with a rake angle of γ = 0° and cutting edge radii of r β = 30 μm and r β = 60 μm. Using the obtained data a simulation model which represents the built-up edge could be established with two versions of the built-up edge: a solid one as part of the rigid tool and an elastic one in front of the tool. Using FEM cutting simulations with and without built-up edges, it was possible to show the influence of a built-up edge on the Chip Formation and the stress state in the Chip Formation Zone. With this data, a comparison of the results of the cutting simulations with those of the in-situ experiments was conducted.
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space resolved microstructural characteristics in the Chip Formation Zone of orthogonal cut c45e steel samples characterized by diffraction experiments
Journal of Materials Processing Technology, 2013Co-Authors: Katrin Brommelhoff, E. Uhlmann, Steffen Henze, Robert Gerstenberger, Torben Fischer, Norbert Schell, Walter ReimersAbstract:Abstract Diffraction experiments with high energy synchrotron X-radiation were performed during orthogonal cutting of the steel C45E. The development of the microstructure was analysed by means of the evolution of integral X-ray peak intensities and FWHMs (Full Width at Half Maxima) at different measuring positions in the Chip Formation Zone. Measuring positions were chosen around the primary and secondary shear Zones and behind the cutting edge, to represent positions with a different degree of deFormation. The results were compared to observations made from optical microscopy on the Chip root samples. A strong change of the microstructure was observed during Chip Formation in dependence on the measuring position, namely a strong reduction of domain sizes and a reorientation which results in a bcc shear texture, which is described with the ideal textures ( 1 1 0 ) [ 0 0 1 ] and ( 1 1 2 ¯ ) [ 1 1 1 ] . The shear direction determined by optical microscopy could be brought into agreement with the shear direction observed in the 1 1 0 X-ray pole figure.
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An extended shear angle model derived from in situ strain measurements during orthogonal cutting
Production Engineering, 2013Co-Authors: E. Uhlmann, R. Gerstenberger, W. Reimers, T. Fischer, S. Henze, K. Brömmelhoff, N. SchellAbstract:There are numerous cutting models which describe the Chip Formation process. However, they are based on a number of simplifying assumptions. In order to verify these assumptions and to get a better understanding of the cutting process, the different stress states in the Chip Formation Zone were determined by means of diffraction experiments with monochromatic high-energy synchrotron X-radiation during orthogonal, quasistatic cutting of the material C45E. The results from the experiments are compared with simulated stresses. The experimental data indicate that the assumption of a free Chip flow according to the shear angle model of Opitz and Hucks is not valid. The model was therefore extended considering the normal stresses in direction of the Chip flow.
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In situ strain measurement in the Chip Formation Zone during orthogonal cutting
Production Engineering, 2011Co-Authors: E. Uhlmann, R. Gerstenberger, S. Herter, T. Hoghé, W. Reimers, B. Camin, R. V. Martins, A. Schreyer, T. FischerAbstract:The strain and stress state in the Chip Formation Zone determines the Chip Formation. However, it is difficult to obtain experimental data about the strain/stress fields during machining. For this reason, present Chip Formation models highly simplify the Chip Formation process. In order to extend the knowledge regarding the Chip Formation mechanisms, an experimental method for the in situ measurement of the elastic deFormations within the Chip Formation Zone during the cutting process has been developed. Using these deFormations, the stress state can subsequently be calculated. The method is based on X-ray diffraction using high-energy synchrotron X-radiation during machining the workpiece in an orthogonal cutting process under quasistatic experimental conditions. The diffraction patterns are captured with a 2D detector. A comparison of the experimentally determined stresses at different measuring positions within the Chip Formation Zone with results from a FEM cutting simulation shows a good qualitative and partially also quantitative consistency. Possibilities for the further performance increase of the method are identified so that the method can be used for the verification and extension of existing Chip Formation models in future.
X. P. Li - One of the best experts on this subject based on the ideXlab platform.
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High-pressure phase transFormation as the mechanism of ductile Chip Formation in nanoscale cutting of silicon wafer:
Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2007Co-Authors: X. P. Li, M RahmanAbstract:AbstractIn nanoscale cutting of silicon wafer, it has been found that under certain conditions ductile mode Chip Formation can be achieved. In order to understand the mechanism of the ductile Chip Formation, experiments and molecular dynamics (MD) simulations have been conducted in this study. The results of MD simulations of nanoscale cutting of silicon showed that because of the high hydrostatic pressure in the Chip Formation Zone, there is a phase transFormation of the monocrytslline silicon from diamond cubic structure to both β silicon and amorphous phase in the Chip Formation Zone, which results in plastic deFormation of the workpiece material in the Chip Formation Zone, as observed in experiments. The results further showed that although from experimental observation the plastic deFormation in the ductile mode cutting of silicon is similar to that in cutting of ductile materials, such as aluminium, in ductile mode cutting of silicon it is the phase transFormation of silicon rather than atomic dislo...
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Study of the temperature and stress in nanoscale ductile mode cutting of silicon using molecular dynamics simulation
Journal of Materials Processing Technology, 2007Co-Authors: X. P. Li, M RahmanAbstract:Abstract In nanoscale cutting of brittle materials, it has been found that there is a brittle–ductile transition when the cutting tool edge radius is reduced to nanoscale and the undeformed Chip thickness is smaller than the tool edge radius. In order to understand the mechanism of the brittle–ductile transition, the cutting characteristics, such as stress and temperature in the cutting region, have to be investigated. However, since the machining size is very small, on the nanoscales, it's very difficult to measure the temperature and stress in the Chip Formation Zone experimentally. In this study, the molecular dynamics (MD) method is employed to model and simulate the nanoscale ductile mode cutting of monocrystalline silicon wafer. The MD simulation results show that the temperature rise in the cutting Zone will affect the diamond tool. In the cutting process, the thrust force is larger than the cutting force. As the tool cutting edge radius increases, the shear stress in the workpiece material around the cutting edge will decrease. When the shear stress is so low that it is insufficient to sustain dislocation emission in the Chip Formation Zone, crack propagation becomes dominating. Consequently, the Chip Formation mode changes from ductile to brittle.
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The mechanism of ductile Chip Formation in cutting of brittle materials
The International Journal of Advanced Manufacturing Technology, 2007Co-Authors: X. P. Li, S. Y. LiangAbstract:A theoretical analysis for the mechanism of ductile Chip Formation in the cutting of brittle materials is presented in this paper. The coexisting crack propagation and dislocation in the Chip Formation Zone in the cutting of ductile materials are examined based on an analysis of the geometry and forces in the cutting region, both on Taylor’s dislocation hardening theory and the strain gradient plasticity theory. It was found that the ductile Chip Formation was a result of large compressive stress and shear stress in the Chip Formation Zone, which shields the growth of pre-existing flaws by suppressing the stress intensity factor K _ I . Additionally, ductile Chip Formation in the cutting of brittle materials can result from the enhancement of material yield strength in the Chip Formation Zone. The large compressive stress can be generated in the Chip Formation Zone with two conditions. The first condition is associated with a small, undeformed Chip thickness, while the second is related to the undeformed Chip thickness being smaller than the radius of the tool cutting edge. The analysis also shows that the thrust force F _ t is much larger than the cutting force F _ c . This indicates that large compressive stress is generated in the Chip Formation Zone. This also confirms that the ductile Chip Formation is a result of large compressive stress in the Chip Formation Zone, which shields the growth of pre-existing flaws in the material by suppressing the stress intensity factor K _ I . The enhancement of material yield strength can be provided by dislocation hardening and strain gradient at the mesoscale, such that the workpiece material can undertake the large cutting stresses in the Chip Formation Zone without fracture. Experiments for ductile cutting of tungsten carbide are conducted. The results show that ductile Chip Formation can be achieved as the undeformed Chip thickness is small enough, as well as the undeformed Chip thickness is smaller than the tool cutting edge radius.
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Crack initiation in relation to the tool edge radius and cutting conditions in nanoscale cutting of silicon
International Journal of Machine Tools and Manufacture, 2007Co-Authors: M. B. Cai, X. P. Li, M Rahman, Andrew A O TayAbstract:In cutting of brittle materials, experimentally it was observed that there is a ductile-brittle transition when the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius of the zero rake angle. However, how the crack is initiated in the ductile-brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has not been fully understood. In this study, the crack initiation in the ductile-brittle mode transition as the undeformed Chip thickness is increased from smaller to larger than the tool cutting edge radius has been simulated using the Molecular Dynamics (MD) method on nanoscale cutting of monocrystalline silicon with a non-zero edge radius tool, from which, for the first time, a peak deFormation Zone in the Chip Formation Zone has been found in the transition from ductile mode to brittle mode cutting. The results show that as the undeformed Chip thickness is larger than the cutting edge radius, in the Chip Formation Zone there is a peak deFormation depth in association with the connecting point of tool edge arc and the rake face, and there is a crack initiation Zone in the undeformed workpiece next to the peak deFormation Zone, in which the material is tensile stressed and the tensile stress is perpendicular to the direction from the connecting point to the peak. As the undeformed Chip thickness is smaller than the cutting edge radius, there is no deFormation peak in the Chip Formation Zone, and thus there is no crack initiation Zone formed in the undeformed workpiece. This finding explains well the ductile-brittle transition as the undeformed Chip thickness increases from smaller to larger than the tool cutting edge radius. © 2006 Elsevier Ltd. All rights reserved.