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J L Martin – 1st expert on this subject based on the ideXlab platform
Loss of strength in Ni3Al at elevated temperaturesPhilosophical Magazine, 2020Co-Authors: B. Viguier, T. Kruml, J L MartinAbstract:
International audienceThe Stress decrease above the Stress peak temperature (750 K) is studied in single crystals of Ni3(Al,3at%Hf). Two thermally activated deformation mechanisms are evidenced on the basis of Stress relaxation and strain rate change experiments. From 500 to 1070K, the continuity of the activation volume/temperature curves reveals a single mechanism of activation enthalpy 3.8eV/atom and volume 90b3 at 810 K with an Athermal Stress of 330MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores is evidenced through serrated yielding, peculiar shapes of Stress strain curves while changing the rate of straining and Stress relaxation experiments. This complicates the identification of the deformation mechanism which is likely connected with cube glide. From 1070K to 1270K, a high temperature mechanism has an activation enthalpy and volume of 4.8eV/atom and 20 b3 respectively, at 1250 K
about the determination of the thermal and Athermal Stress components from Stress relaxation experimentsActa Materialia, 2008Co-Authors: Tomas Kruml, O Coddet, J L MartinAbstract:
The determination of the thermal and Athermal Stress components using relaxation experiments along a Stress-strain curve is critically evaluated. Short-term Stress-relaxations are performed along the Stress-strain curve of single crystals of Ge at 850 K, Cu, and Ni3Al at 300 K. They are analyzed by three different equations with two or three parameters including the Athermal Stress. The Stress components obtained are compared to the values determined by Stress-reduction experiments considered as the reference method. The relaxation rate is considered successively to be a power function or a hyperbolic sine function of the effective Stress or a hyperbolic decrease of Stress with time is assumed. It is shown that the three methods overestimate or underestimate the Stress components depending on the material and deformation conditions. The error can be as large as about 100%. Reasons for the inadequacy of short-term relaxation experiments for the determination of the Stress components are discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Rajeev Kapoor – 2nd expert on this subject based on the ideXlab platform
Deformation in Zr–1Nb–1Sn–0.1Fe using Stress relaxation techniqueMaterials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: Rajeev Kapoor, Shashikant L. Wadekar, J.k. ChakravarttyAbstract:
Abstract Deformation behavior of Zr–1Nb–1Sn–0.1Fe was studied using the Stress relaxation technique. Stress relaxation experiments were carried out over a range of temperatures (296–765 K) and for strains up to 0.12. The Stress–time data were analyzed to obtain the activation volume and enthalpy. It was found that in the strain rate range of 10 −4 –10 −6 s −1 and in the temperature range of 296–570 K, the activation volume and enthalpy do not vary with strain. From this and the magnitude of the activation volume and its variation with thermal Stress, either the Peierls Stress or the dislocation–interstitial interaction is the rate controlling short range barrier to dislocation motion. The time independent Stress component obtained using decremental unloading technique, called here as the remnant Stress, was observed to have a large temperature dependence. By using a relation in which the activation free energy is a function of thermal Stress, it was found that, in general, the remnant Stress cannot be used to represent the Athermal Stress.
Deformation behavior of tantalum and a tantalum tungsten alloyInternational Journal of Plasticity, 2001Co-Authors: Sia Nemat-nasser, Rajeev KapoorAbstract:
Abstract A comparative study of the deformation behavior of tantalum and a tantalum 2.5 wt.% tungsten alloy is carried out. High strain-rate experimental data are used to develop phenomenological constitutive relations. The temperature and the strain-rate sensitivity of the flow Stresses are compared. It is observed that although the flow Stress for the Ta–2.5%W alloy is greater than that of Ta, the corresponding temperature and strain-rate sensitivity is less pronounced. Ta–2.5%W experiences a solid-solution softening, wherein the Athermal Stress component has increased, while the thermal component has decreased by the alloying.
Steven Y. Liang – 3rd expert on this subject based on the ideXlab platform
Micro-grinding Temperature Prediction Considering the Effects of Crystallographic Orientation and the Strain Induced by Phase TransformationInternational Journal of Precision Engineering and Manufacturing, 2019Co-Authors: Man Zhao, Xia Ji, Steven Y. LiangAbstract:
This paper proposes a physical-based model to predict the temperature in the micro-grinding of maraging steel 3J33b with the consideration of material microstructure and process parameters. In micro-grinding, the effects of crystallography on the grinding machinability become significant, since the depth of cut is of the same order as the grain size. In this research, the Taylor factor model for multi-phase materials is proposed to quantify the crystallographic orientation (CO) with respect to the cutting direction by examining the number and type of activated slip systems. Then, the flow Stress model is developed, in which both the Athermal Stress resulted from the COs and the strain induced by the phase transformation are taken into account. On the basis of the flow Stress model, the grinding forces are predicted followed by the calculation of the grinding heat. In the investigation, the triangular heat flux distribution and the reported energy partition model are applied in the calculation of workpiece temperature. Furthermore, the temperature model is validated by conducting an orthogonal-designed experiment, with the predictions of the maximum temperature in good agreement with the experimental data. Moreover, the predictive data is compared with the predictions resulted from the two other previously reported models. The results indicate that the proposed temperature model with considering the effect of CO and the phase transformation improved the prediction accuracy of the micro-grinding temperature.
Grain size sensitive–MTS model for Ti-6Al-4V machining force and residual Stress predictionThe International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Yanfei Lu, Peter Bocchini, Hamid Garmestani, Steven Y. LiangAbstract:
Material properties are significantly influenced by the parameters of the machining process. The accurate prediction of machining force and residual Stress reduces power consumption, enhances material properties, and improves dimensional accuracy of the finished product. Traditional method using the finite element analysis (FEA) costs a significant amount of time, and the archived mechanical threshold Stress (MTS) model without consideration of microstructure of the material yields inaccurate result. In this paper, a grain size–sensitive MTS model is introduced for the machining process of Ti-6Al-4V. A grain size–sensitive term is introduced to the modified MTS model to account for evolution of the grain size. The grain size–sensitive MTS model takes the microstructure of the Ti-6Al-4V into consideration for the calculation of machining force and residual Stress. The grain size–sensitive term is introduced into the Athermal Stress component using the initial yield Stress, strain hardening coefficient, and the Hall-Petch coefficient. The analytical result is compared with those of experimental studies and the traditional Johnson-Cook model to prove the validity in the prediction of machining force and residual Stress. The proposed model explores a new area for calculating cutting forces and residual Stress.
Force prediction in micro-grinding maraging steel 3J33b considering the crystallographic orientation and phase transformationThe International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Man Zhao, Xia Ji, Steven Y. LiangAbstract:
In micro-grinding, the effects of crystallography on grinding force become significant since the depth of cut is of the same order as the grain size. In this research, the Taylor factor model for multi-phase materials is proposed based on the previously reported Taylor factor model for monocrystalline material. Based on this model, the flow Stress model is developed, which takes both the effect of CO on the Athermal Stress and the Stress induced by the phase transformation into account. Based on the flow Stress model, the predictive model of chip formation force is proposed by adapting parallel-sided shear zone theory. The rubbing force is modeled by applying Waldorf’s worn tool theory. Furthermore, the plowing force is predicted based on previously reported model by the authors. Subsequently, a comprehensive model of the micro-grinding force is proposed by considering mechanical-thermal loading, the effects of crystallography, and phase transformation. Finally, the model is validated by conducting an orthogonal-designed experiment with the result proving that the prediction of the model is capable to capture the magnitude and trend of the experimental data. Moreover, the proposed analysis are compared with the predictions of two other previously reported models with the result, indicating that the model that considers the effect of CO and the phase transformation improves the accuracy of the micro-grinding force.