Papers by Keyword: Adiabatic Shear

Abstract: A method for building the constitutive relationship based on the J-C model and hardness is presented through considering the influence of hardness on the yield strength and the tensile strength. A constitutive relationship of hardened AISI 1045 is built by this method and the adiabatic shear critical cutting conditions of three kinds of hardness AISI 1045 steel are prediction through a model building by the linear pertubation analysis which considering the influence of compression stress of the primary shear zone, the cutting conditions and the constitutive relationship. For proving the prediction results, some orthogonal cutting experiments are performed to get the critical cutting conditions of adiabatic shear. The comparison shows that the prediction results are consistent with that of experiments.

Abstract: The main characteristic of hard turning process is easy to produce serrated chip. The chip deformation will impact greatly turning process. It is very important to analysis the chip formation and morphology during precision turning process of hardened steel. The deformation mechanism of serrated chip formation process and its chip morphology of chips produced during precision turning process of the hardened steel GCr15 is studied in hard cutting experiment by the methods such as numerical simulation of two-dimensional finite element analysis of turning, chip cross-sectional microscopic analysis and other methods .High speed precision turning of hardened steel GCr15 produces morphology of continuous chip and serrated chip; Serrated chip has the typical characteristics of the adiabatic shear slip after section such as apical surface of the serrated chip is composed of multilayer rolling dentate shear plane, a single surface of one tooth is not smooth, but no crack. Extrusion grooves is produced from tooth root to tip; Intensive slip line on serrated chip cross-section can be saw by microscopic observation; Fracture surface of the serrated chip presents small tumor tissues. The results show that the reason of hardened GCr15 steel forming serrated chip is periodic adiabatic shear fracture, and the research provides a theoretical reference application of hard turning technology.

Abstract: Dynamic compression test on TC6 titanium alloy samples have been done by using a split Hopkinson bar process and extra circuit under conditions of room temperature and high strain-rate. The effect of impressed-current on sensitivity of adiabatic shear of TC6 titanium alloy has been studied. It is shown that the impressed-current can reduce the sensitivity of adiabatic shear of TC6 titanium alloy under the condition of high strain-rate. Free electron in the samples will do direct move and take heat away from high localized area to decrease the effect of the heat. The result will help to delay formation of the adiabatic shear band. So, that is reducing the sensitivity of adiabatic shear of TC6 titanium alloy.

Abstract: As the deformation of chip increases with cutting speed, the morphology of chip changes from continuous to serrated type. It is supposed that serrated chips generate due to adiabatic shear instability in the primary deformation zone. A new analytical model for predicting adiabatic shear critical condition in orthogonal cutting is proposed by considering cutting conditions and properties of workpiece material. It is found that the influence of shear strain on the onset of adiabatic shear could be neglected. The shear strain rate and temperature, however, play a leading role on the onset of adiabatic shear. At lower cutting speed the shear strain rate plays a dominant role while at higher cutting speed the situation is just the reverse. With the increase of cutting speed, the yield stress, material characteristic constant and uncut chip thickness will facilitate adiabatic shear instability, while the coefficient of strain rate hardening, coefficient of strain hardening, coefficient of thermal softening, thermal diffusivity and tool rake angle have negative effect on adiabatic shear instability.

Abstract: Orthogonal cutting experiments of Fe-36Ni invar alloy are performed. The change of chip morphology with cutting conditions are investigated through metallurgical observation, and the critical cutting speed of adiabatic shear for Fe-36Ni invar alloy at different cutting depths and rake angles are given. In addition, the characteristic of chip deformation before the occurrence of adiabatic shear is also analyzed. The results show that the critical cutting speed decreases with the increase of cutting depth and hardness, but increases with the increase of rake angle. The deformation coefficient tends to a constant value with the increase of cutting speed.

Abstract: Precision Hard Cutting process is easy to generate periodic saw chip. So it is significant to research characteristics of chip formation. Based on DEFORM software platform and FEM, the behavior of adiabatic shear in cutting deformation zone is simulated, simulation results show that the formation of saw chip is due to plastic instability occurred in the shear plane resulting concentrated shear slip; chip cross-sectional microscopic analysis is used to analyzed chip morphology, microscopic observation results show that with the increase of cutting parameters, the degree of segmentation increases and the cutting speed is the most significant factor. The boundary is determined between the continuous chip and saw chip, with increase of workpiece hardness, critical cutting parameters of generating saw chip reduce. The results can provide a reasonable amount of reference data for choosing cutting parameters of high-speed hard cutting.

Abstract: Orthogonal cutting experiments of Fe-36Ni invar alloy are performed to investigate the influence of cutting conditons on adiabtic shear, which occurs in the process of chip formation of many materials. It is found that the cutting speed, cutting depth and rake angle all have influence on adiabatic shear and there is a critical cutting speed at which the adiabatic shear appears. By metallurgical observation, the critical cutting speed under different cutting depth and rake angles are given. A model based on linear pertubation analysis is used to predict the adiabatic shear critical ctting conditions of Fe-36Ni invar alloy. The comparison of prediction results and that of expriments shows that this prediction model is available.

Abstract: Orthogonal cutting experiments of hardened AISI1045 steel(45HRC) are performed to investigate the influence of cutting conditions on adiabatic shear which occurs in the process of chip formation of many materials. It is found that the cutting speed, cutting depth and rake angle all have influence on adiabatic shear and there is a critical cutting speed at which the adiabatic shear appears. By metallurgical observation, the critical cutting speed under different cutting depths and rake angles are given. A model based on linear pertubation analysis is used to predict the adiabatic shear critical cutting conditions of hardened AISI 1045 steel. The comparison of prediction results and that of expriments shows that this prediction model is valid.

Abstract: A deep understanding of adiabatic shear fracture (ASF) during serrated chip formation is essential to explore the material removal mechanism of high speed cutting (HSC). This paper aims to reveal the microscopic details of ASF in serrated chips. The material to investigate was AISI 1045 steel of different hardness grades, and the micro-structural analysis was conducted using optical and scanning electronic microscopes. The investigation showed that at the hardness of HRC50, most fractured surfaces were covered by a large number of dimples elongated along the shear direction, indicating that the fundamental cause of the serrated chip generation is the deformation localization of the adiabatic shear followed by ductile damage fracture in primary shear zones. The higher the material hardness is, the easier the adiabatic shear and ductile fracture take place. A new model was then proposed to interpret the ductile fracture due to adiabatic shear governed by the nucleation, growth and coalescence of micro-voids during serrated chip formation.

Abstract: A model is presented for the prediction of critical cutting conditions of adiabatic shear in orthogonal high speed cutting. Considering the influence of compression stress, a critical criterion of adiabatic shear in orthogonal high speed cutting is given by linear perturbation on the compress-shear deformation continuum mechanics basic equations of the primary shear zone. Combining with the relationship of cutting conditions and deformation ones, also the materials constitutive realtionship, a pridiction model, which expressed by cutting conditions and materials properties is established. As an example, the adiabatic shear critical conditions of AISI 1045 steel are predicted, and cutting experiments are performed. The prediction results are consistent with that of experiments.