The Experts below are selected from a list of 118302 Experts worldwide ranked by ideXlab platform
Takeshi Iwamoto - One of the best experts on this subject based on the ideXlab platform.
-
multiscale computational simulation of Deformation Behavior of trip steel with growth of martensitic particles in unit cell by asymptotic homogenization method
International Journal of Plasticity, 2004Co-Authors: Takeshi IwamotoAbstract:Abstract Due to the strain-induced martensitic transformation (SIMT), the strength, ductility and toughness of TRIP (transformation-induced plasticity) steel are enhanced. Such favorable mechanical properties of TRIP steel can be realized by the appropriate combination of the SIMT Behavior and Deformation Behavior of both austenite and martensite. However, since the SIMT and Deformation Behavior of both phases depend strongly on the conditions of the working environment such as temperature, strain rate and stress system, the desired mechanical properties are obtained only in a fairly restricted working environment. On the other hand, martensitic particles of various sizes, shapes and orientations can be observed and are distributed spatially in the microstructure of TRIP steel, therefore it is possible that the mechanical properties of TRIP steel strongly manifest a dependence on the geometrical inhomogeneity and configuration of martensite. If the geometrical configuration and inhomogeneity of martensite can be controlled, we can expect to enhance the mechanical properties of TRIP steel. Here, in order to investigate the effects of the geometrical configuration and inhomogeneity of martensite in the austenitic matrix on the macroscopic Deformation Behavior of TRIP steel, the computational simulation of the Deformation Behavior of TRIP steels with the growth of an ellipsoidal martensitic particle embedded in the center of the austenitic unit cell, is performed using the homogenization technique.
-
computational prediction of Deformation Behavior of trip steels under cyclic loading
International Journal of Mechanical Sciences, 2001Co-Authors: Yoshihiro Tomita, Takeshi IwamotoAbstract:Abstract A constitutive equation accounting for strain rate, temperature and applied stress system dependencies of strain-induced martensitic transformation is given. A series of computational prediction of monotonic and cyclic Deformation Behavior including tension, compression and shearing of typical 304 austenitic stainless steel, have been performed under different environmental temperatures from 77 to 353 K . The effect of stress range, pre-strain, temperature and applied stress system on such responses of TRIP steels as the evolution of martensitic phase, the accumulated plastic strain, and the asymptotic nature of the stress–strain relation with an increase in the number of cycles is clarified. The predictability of the present constitutive model is checked against the experimental results. Furthermore, simulation of the cyclic Deformation Behavior of TRIP steel bars with ringed notch is performed.
W L Chan - One of the best experts on this subject based on the ideXlab platform.
-
size effect on material surface Deformation Behavior in micro forming process
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: J H Deng, W L ChanAbstract:Abstract In micro-forming, when the billet material size is decreased to micro-scale, the mechanical Behaviors of material change and the so-called size effect occurs. The design and fabrication of micro-parts by micro-forming cannot be conducted via leveraging on the knowledge of macro-forming process to micro-forming since the size effect is a barrier to this knowledge transfer. Material surface Deformation Behavior, which plays a significant role on interfacial friction, needs to be investigated in development of micro metal-formed parts. In this study, the effects of specimen size, grain size and asperity size of material on the surface Deformation Behavior have been investigated extensively via compression of pure copper cylinder. It is found that the real contact areas (RCAs) at the tooling-workpiece interface are concentrated at the outer rim, while the close lubricant pockets (CLPs) are located at the inner region. The fraction of RCA does not decrease in proportion to the decrease of specimen size. This leads to the increase of interfacial friction force. Furthermore, it is also observed that the efficiency of lubricant increases with the increase of the asperity size, due to the fact that more lubricant is trapped in the asperity valley resulting in the increase of the CLP fraction. In addition, the research further shows the size effect could affect the surface stress evolution which in turn affects the surface material properties of the formed part. Based on the study of the end surface area of the compressed specimen, it is found that the interfacial friction decreases with the increase of grain size. It is believed that the decrease of friction force is due to the decrease of grain boundary strengthening effect and the increase of the fraction of surface grain to facilitate the material flow.
-
experimental and simulation study of Deformation Behavior in micro compound extrusion process
Materials & Design, 2011Co-Authors: W L ChanAbstract:Abstract In micro-forming process, the prediction of Deformation Behavior is difficult as the conventional material constitutive model is no longer valid when the part geometry is scaled down to micro-level. This is caused by the so-called “size-effect”. It is thus necessary to study the size effect and how it affects the Deformation Behavior in micro-forming process. In this research, a material constitutive model was established based on micro-compression test and its applicability was then studied. To facilitate the research, a flexible tooling set for micro-extrusion was designed and developed first. A modified micro-double cup extrusion test was proposed and the corresponding Finite Element Method (FEM) simulation was conducted. Through experiment and simulation, a set of Deformation load curves were generated so as to provide a reference for calibration of flow stress–strain curve in modeling of micro-extrusion process. The applicability of the calibrated flow stress–strain curve was finally validated by the experimental and simulation results of micro-forward extrusion. It is therefore believed that the flow pattern, the material surface constraint and the material Deformation mode are critical in determination of material flow stress curve. Furthermore, it was found that the change of cup height ratio of the extruded part is not caused solely by the change of friction when the part size is in micro-scale. The material flow stress significantly affects the cup height ratio. These findings provide a basis in understanding of micro-extrusion process.
-
modeling of grain size effect on micro Deformation Behavior in micro forming of pure copper
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: W L Chan, Jianguang LiuAbstract:In micro-scaled plastic Deformation process such as micro-forming, material grain size effect is difficult to reveal and investigate using conventional material models. Finding a way to study and model the grain size effect on micro-scaled Deformation Behavior is a non-trivial issue that needs to be addressed in greater depth. In this study, the grain size effect is investigated through micro-compression of pure copper. The Deformation Behaviors, including inhomogeneous material flow and the decrease of flow stress with the increase of grain size for the same size of specimens, are studied. It is revealed that when the specimen is composed of only a few grains, the grains with different sizes, shapes and orientations are unevenly distributed in the specimen and each grain plays a significant role in micro-scaled plastic Deformation and leads to inhomogeneous Deformation and the scatter of experimental data. Furthermore, it is found that the decrease of flow stress is caused by the dwindling of grain boundary strengthening effect when the grain size is increased. Based on the experiment results and the proposed composite model, the methodologies to estimate grain properties and model grain size effect are developed. Through Finite Element (FE) simulation, the grain size effect on Deformation Behavior and the scatter of flow stress are modeled. The results of the physical experiment and the proposed modeling methodologies provide a basis for understanding and further exploration of micro-scaled plastic Deformation Behavior in micro-forming process.
Peter K Liaw - One of the best experts on this subject based on the ideXlab platform.
-
Deformation Behavior of bulk metallic glasses under a mixed mode i ii loading condition
Intermetallics, 2018Co-Authors: S H Chen, A Domel, Tai Man Yue, Chi Pong Tsui, Kang Cheung Chan, Karin A Dahmen, Peter K LiawAbstract:Abstract Bulk metallic glasses (BMGs) demonstrate different Deformation Behavior under varying loading conditions. In the present work, a Zr57Cu20Al10Ni8Ti5 (atomic percent, at.%) BMG was subjected to a mixed-mode (I/II) loading condition by tailoring double-side notches. The findings show stable plastic-flow plateau stages in the loading-displacement curves, and this phenomenon is different from other notched BMG specimens with predominant-mode-I failure. More importantly, due to the stress concentrations between two notches, most of the slip events with large load drops occur on the fracture plane, resulting in a wide smooth region consisting of several shear steps on the fracture surface. We show that despite different Deformation Behavior, the specimens still display slip-size statistics of the plastic flow, which are similar to those seen in compression tests. The present findings give more insight into the Deformation Behavior/mechanisms of BMGs under varying loading conditions for practical structural applications.
-
fundamental Deformation Behavior in high entropy alloys an overview
Current Opinion in Solid State & Materials Science, 2017Co-Authors: Haoyan Diao, Karin A Dahmen, Rui Feng, Peter K LiawAbstract:Abstract High-entropy alloys (HEAs), as a new class of materials, are nearly equiatomic and multi-element systems, which can crystallize as a single phase or multi-phases. Most of the HEAs described in the literature contain multiple phases (secondary phases, nanoparticles, and so on), rather than a single solid-solution phase. Thus, it is essential to review the typical mechanical properties of both single-phase and multiphase HEAs thoroughly, with emphases on (1) the fundamental physical mechanisms and (2) the difference from conventional alloys. In this paper, mainly based on different mechanical properties, HEAs are classified into four types for the first time, i.e., (a) HEA alloy systems of 3d-transition metals only (Type 1), (b) HEA alloy systems of transition metals with larger atomic-radius elements (Type 2), (c) HEA alloy systems of refractory metals (Type 3), and (4) others (Type 4). Then a number of aspects of mechanical Behavior are reviewed and discussed, including the elastic anisotropy, yield strength, high-temperature performance, serration Behavior, fracture toughness, and fatigue responses, which may serve as a demonstrative summary for the current progress in the scientific research of HEAs. Several mechanisms that quantitatively explain the mechanical properties of single-phase and multiphase HEAs in terms of basic defects (dislocations, twinning, precipitates, etc.) are discussed. A number of future research activities are suggested, based on the emphasis on developing high-performance structural materials. The review concludes with a brief summary of major mechanical properties and insights into the Deformation Behavior of single-phase and multiphase HEAs. The comparison and contrast between HEAs and conventional alloys remain the most compelling motivation for future studies. With the integrated experimental and simulation investigations, a clearer picture of the fundamental Deformation Behavior of single-phase and multiphase HEAs could be explored.
S H Chen - One of the best experts on this subject based on the ideXlab platform.
-
Deformation Behavior of bulk metallic glasses under a mixed mode i ii loading condition
Intermetallics, 2018Co-Authors: S H Chen, A Domel, Tai Man Yue, Chi Pong Tsui, Kang Cheung Chan, Karin A Dahmen, Peter K LiawAbstract:Abstract Bulk metallic glasses (BMGs) demonstrate different Deformation Behavior under varying loading conditions. In the present work, a Zr57Cu20Al10Ni8Ti5 (atomic percent, at.%) BMG was subjected to a mixed-mode (I/II) loading condition by tailoring double-side notches. The findings show stable plastic-flow plateau stages in the loading-displacement curves, and this phenomenon is different from other notched BMG specimens with predominant-mode-I failure. More importantly, due to the stress concentrations between two notches, most of the slip events with large load drops occur on the fracture plane, resulting in a wide smooth region consisting of several shear steps on the fracture surface. We show that despite different Deformation Behavior, the specimens still display slip-size statistics of the plastic flow, which are similar to those seen in compression tests. The present findings give more insight into the Deformation Behavior/mechanisms of BMGs under varying loading conditions for practical structural applications.
-
effect of external disturbances on the strain rate dependent plastic Deformation Behavior of a bulk metallic glass
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: S H Chen, Chi Pong Tsui, T M Yue, K C ChanAbstract:Abstract In this work, the effect of external disturbances on the strain-rate dependent plastic Deformation Behavior of a Zr 57 Cu 20 Al 10 Ni 8 Ti 5 bulk metallic glass (BMG) has been examined by tailoring the geometric confinement, stress gradient, and sample size. With the external disturbances, the fracture strains of the BMG specimens become less dependence on the strain rates, and it is found that the confinement of the propagation of shear bands is the dominant Deformation mechanism. This is different from previous findings in that multiplication of the shear bands also plays a critical role in accommodating the plastic Deformation of BMGs with external disturbances. The present findings not only shed more light on the Deformation mechanisms of BMGs under external disturbances, but also suggest that the use of external disturbances can reduce the dependence of the plastic Deformation Behavior of BMGs on the strain rates.
-
effect of stress gradient on the Deformation Behavior of a bulk metallic glass under uniaxial tension
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: S H Chen, K C ChanAbstract:Abstract In the present study, the stress gradient is shown to significantly affect the Deformation Behavior of a monolithic bulk metallic glass (BMG) at room temperature under tensile loading. It is demonstrated that the stress concentration areas of the BMG specimens facilitate the formation of shear bands, and the presence of “soft” and “hard” regions due to the stress gradient confines the propagation. With these stress gradients, brittle monolithic BMGs exhibit plastic Deformation at the stress concentration areas under tensile loading, and higher orders of stress gradient result in larger confinement for the propagation of shear bands. The findings are significant in controlling the plastic Deformation Behavior of BMGs and in understanding the Deformation mechanisms of monolithic BMGs under complex stress states, which is important for potential engineering applications.
Kyu Cho - One of the best experts on this subject based on the ideXlab platform.
-
high strain rate compressive Deformation Behavior of the al0 1crfeconi high entropy alloy
Materials & Design, 2015Co-Authors: Nilesh Kumar, Rajiv S. Mishra, Q Ying, Xu Nie, Z Tang, P K Liaw, R E Brennan, K J Doherty, Kyu ChoAbstract:Abstract High entropy alloy is a new class of structural metallic materials. No work, so far, has been carried-out to understand high strain-rate plastic Deformation Behavior and resulting microstructure. This work focuses on understanding the Deformation Behavior of an Al0.1CrFeCoNi HEA at high strain-rate (HSR). HSR plastic Deformation in compression mode was carried out using split-Hopkinson pressure bar. The pre- and post-Deformation microstructures were studied using electron microscopes. A high strain-rate sensitivity of yield strength, significant work hardening, and profuse twinning are main characteristics observed during Deformation of the alloy at HSR. Overall, the Deformation Behavior of the alloy was consistent with low stacking fault energy materials.