The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
J L Martin - One of the best experts on this subject based on the ideXlab platform.
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Loss of strength in Ni3Al at elevated temperatures
Philosophical 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
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about the determination of the thermal and Athermal Stress components from Stress relaxation experiments
Acta 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 - One of the best experts on this subject based on the ideXlab platform.
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Deformation in Zr–1Nb–1Sn–0.1Fe using Stress relaxation technique
Materials 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.
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Deformation behavior of tantalum and a tantalum tungsten alloy
International 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 - One of the best experts on this subject based on the ideXlab platform.
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Micro-grinding Temperature Prediction Considering the Effects of Crystallographic Orientation and the Strain Induced by Phase Transformation
International 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.
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Grain size sensitive–MTS model for Ti-6Al-4V machining force and residual Stress prediction
The 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.
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Force prediction in micro-grinding maraging steel 3J33b considering the crystallographic orientation and phase transformation
The 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.
Noriyuki Tsuchida - One of the best experts on this subject based on the ideXlab platform.
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Effects of Temperature and Strain Rate on Stress-Strain Curves for Dual-Phase Steels and Their Calculations by Using the Kocks-Mecking Model
Isij International, 2012Co-Authors: Noriyuki Tsuchida, Yoshimasa Izaki, Tomoyuki Tanaka, Kenzo FukauraAbstract:Effects of temperature and strain rate on Stress-strain curves for two types of dual-phase (DP) steel with different carbon contents were investigated from the viewpoints of tensile tests and the Kocks-Mecking (KM) model based on thermal activation theory. In the tensile tests, flow Stress increased but elongation decreased with decreasing temperature or increasing strain rate. Uniform elongation for each DP steel was almost independent of deformation temperature between 123 and 373 K. In the comparison of strain rate sensitivity exponent (m), the m-value increased with decreasing the volume fraction of martensite. The calculated true Stress-true strain curves by using the KM model agreed with the measured ones at various temperatures and strain rates for the DP steels. In terms of the parameters for the KM model, the Athermal Stress and mechanical threshold Stresses were different between the two types of DP steel. This seems to be associated with the difference of volume fractions of ferrite and martensite.
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Effect of ferrite grain size on tensile deformation behavior of a ferrite-cementite low carbon steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Noriyuki Tsuchida, Yo Tomota, H. Masuda, Yasunori Harada, Kenzo Fukaura, Kotobu NagaiAbstract:Abstract Stress–strain curves for ferrite-cementite (FC) steels with ferrite grain sizes between 0.47 and 13.6 μm were studied by tensile tests with strain rates of 103, 100, and 3.3 × 10−4 s−1 at 296 K. The Stress–strain curves for the FC steels are categorized into two different types. In one type, the Luders deformation is interrupted due to the onset of necking, and in the other type, the Luders band propagates throughout the gage section of a tensile specimen followed by work-hardening. The lower yield and flow Stresses increase while uniform and total elongations decrease with a decrease in ferrite grain size. The effect of ferrite grain size on flow Stress is hardly dependent on strain rate. These experimental results reveal that the grain refinement strengthening contributes mainly to an increase in the Athermal Stress component.
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Flow Stress Analysis using the Kocks–Mecking Model for Ferrite–Cementite Steels with Various Ferrite Grain Sizes
Isij International, 2008Co-Authors: Noriyuki Tsuchida, Kotobu Nagai, Kenzo Fukaura, Yo TomotaAbstract:True Stress (σ)–true strain (e) curves were calculated by using the Kocks–Mecking (KM) model for the ferrite–cementite steels with various ferrite grain sizes between 0.47 and 13.6 μm. In the KM model, the effect of ferrite grain size on flow Stress is described by the Athermal Stress component that follows the Hall–Petch equation. The effects of temperature and strain rate on flow Stress, which are correlated with the thermal Stress component, are independent of the ferrite grain size. The calculated σ–e curves by using the KM model agree with the measured ones at various temperatures and strain rates including the high-speed tensile test with a strain rate of 103 s−1. From the calculations based on a micromechanic model, it is found that the volume fraction of second phase affects the grain size dependence in multi-phase steels. The m-value showing strain rate sensitivity for the external Stress was decreased with a decrease in grain size and that for the thermal Stress was independent of grain size.
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Application of the Kocks–Mecking model to tensile deformation of an austenitic 25Cr–19Ni steel
Acta Materialia, 2001Co-Authors: Noriyuki Tsuchida, Hideaki Moriya, Yo Tomota, Osamu Umezawa, Kotobu NagaiAbstract:Abstract Stress–strain relationships obtained by tensile test below room temperature for an austenitic 25Cr–19Ni steel were analyzed by using the Kocks–Mecking model to make clear the effects of temperature and strain rate on flow Stress. A temperature range used here is between 77 and 296 K, a strain rate range between 10−9 and 10−2 s−1 and true strain below 0.2, where structure evolution depends on strain but scarcely on temperature and strain rate. This means that work-hardening rate is almost independent of test temperature and strain rate in the above ranges. Crosshead-arresting tests were performed to obtain flow Stresses at 10−9 s−1 and the results suggested that the Athermal Stress could hardly be determined from the measurement of Stress relaxation behavior at low temperatures. Flow curves obtained by the above deforming conditions are successfully described by using the Kocks–Mecking model with minor modifications. That is, we have claimed that the work-hardening consists of the thermal Stress and the Athermal Stress. It should be noted that the flow curves for as hot-rolled specimens and for annealed specimens can be well simulated by changing the Athermal Stress.
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Description of Stress-strain Curves Based on Thermal Activation Models for a Ti–Fe–O Alloy at 77 to 296 K with Strain Rates from 10-9 to 10-2 sec-1
Isij International, 2000Co-Authors: Noriyuki Tsuchida, Hideaki Moriya, Yo Tomota, Osamu Umezawa, Kotobu NagaiAbstract:Using two thermal activation models for dislocation motion, we analyzed experimental data for a Ti-Fe-O alloy. One is the Kocks-Mecking model and the other is the Ogawa model. These two models differ from each other in the determination of Athermal Stress component and the modeling of work hardening. The Kocks-Mecking model is found to describe well the measured flow curves in a temperature range between 77 and 296 K and in a strain rate range between 10 -5 and 10 -2 sec -1 . The so-called base curve is found to be a flow curve at the strain rate of approximately 10 -9 sec - 1 by the calculations using the Kocks-Mecking model. In actual, the strain rate of 10 -9 sec -1 is approximately the minimum strain rate obtained by the crosshead displacement dwell test. The Ogawa model was found to be insufficient to describe the above flow curves for the Ti-Fe-O alloy.
Kotobu Nagai - One of the best experts on this subject based on the ideXlab platform.
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Effect of ferrite grain size on tensile deformation behavior of a ferrite-cementite low carbon steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Noriyuki Tsuchida, Yo Tomota, H. Masuda, Yasunori Harada, Kenzo Fukaura, Kotobu NagaiAbstract:Abstract Stress–strain curves for ferrite-cementite (FC) steels with ferrite grain sizes between 0.47 and 13.6 μm were studied by tensile tests with strain rates of 103, 100, and 3.3 × 10−4 s−1 at 296 K. The Stress–strain curves for the FC steels are categorized into two different types. In one type, the Luders deformation is interrupted due to the onset of necking, and in the other type, the Luders band propagates throughout the gage section of a tensile specimen followed by work-hardening. The lower yield and flow Stresses increase while uniform and total elongations decrease with a decrease in ferrite grain size. The effect of ferrite grain size on flow Stress is hardly dependent on strain rate. These experimental results reveal that the grain refinement strengthening contributes mainly to an increase in the Athermal Stress component.
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Flow Stress Analysis using the Kocks–Mecking Model for Ferrite–Cementite Steels with Various Ferrite Grain Sizes
Isij International, 2008Co-Authors: Noriyuki Tsuchida, Kotobu Nagai, Kenzo Fukaura, Yo TomotaAbstract:True Stress (σ)–true strain (e) curves were calculated by using the Kocks–Mecking (KM) model for the ferrite–cementite steels with various ferrite grain sizes between 0.47 and 13.6 μm. In the KM model, the effect of ferrite grain size on flow Stress is described by the Athermal Stress component that follows the Hall–Petch equation. The effects of temperature and strain rate on flow Stress, which are correlated with the thermal Stress component, are independent of the ferrite grain size. The calculated σ–e curves by using the KM model agree with the measured ones at various temperatures and strain rates including the high-speed tensile test with a strain rate of 103 s−1. From the calculations based on a micromechanic model, it is found that the volume fraction of second phase affects the grain size dependence in multi-phase steels. The m-value showing strain rate sensitivity for the external Stress was decreased with a decrease in grain size and that for the thermal Stress was independent of grain size.
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Application of the Kocks–Mecking model to tensile deformation of an austenitic 25Cr–19Ni steel
Acta Materialia, 2001Co-Authors: Noriyuki Tsuchida, Hideaki Moriya, Yo Tomota, Osamu Umezawa, Kotobu NagaiAbstract:Abstract Stress–strain relationships obtained by tensile test below room temperature for an austenitic 25Cr–19Ni steel were analyzed by using the Kocks–Mecking model to make clear the effects of temperature and strain rate on flow Stress. A temperature range used here is between 77 and 296 K, a strain rate range between 10−9 and 10−2 s−1 and true strain below 0.2, where structure evolution depends on strain but scarcely on temperature and strain rate. This means that work-hardening rate is almost independent of test temperature and strain rate in the above ranges. Crosshead-arresting tests were performed to obtain flow Stresses at 10−9 s−1 and the results suggested that the Athermal Stress could hardly be determined from the measurement of Stress relaxation behavior at low temperatures. Flow curves obtained by the above deforming conditions are successfully described by using the Kocks–Mecking model with minor modifications. That is, we have claimed that the work-hardening consists of the thermal Stress and the Athermal Stress. It should be noted that the flow curves for as hot-rolled specimens and for annealed specimens can be well simulated by changing the Athermal Stress.
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Description of Stress-strain Curves Based on Thermal Activation Models for a Ti–Fe–O Alloy at 77 to 296 K with Strain Rates from 10-9 to 10-2 sec-1
Isij International, 2000Co-Authors: Noriyuki Tsuchida, Hideaki Moriya, Yo Tomota, Osamu Umezawa, Kotobu NagaiAbstract:Using two thermal activation models for dislocation motion, we analyzed experimental data for a Ti-Fe-O alloy. One is the Kocks-Mecking model and the other is the Ogawa model. These two models differ from each other in the determination of Athermal Stress component and the modeling of work hardening. The Kocks-Mecking model is found to describe well the measured flow curves in a temperature range between 77 and 296 K and in a strain rate range between 10 -5 and 10 -2 sec -1 . The so-called base curve is found to be a flow curve at the strain rate of approximately 10 -9 sec - 1 by the calculations using the Kocks-Mecking model. In actual, the strain rate of 10 -9 sec -1 is approximately the minimum strain rate obtained by the crosshead displacement dwell test. The Ogawa model was found to be insufficient to describe the above flow curves for the Ti-Fe-O alloy.