The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Ronald J Omalley - One of the best experts on this subject based on the ideXlab platform.
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inverse finite element modeling of the barreling effect on experimental stress strain curve for high temperature steel Compression test
Journal of Materials Processing Technology, 2017Co-Authors: X Wang, H Li, K Chandrashekhara, S A Rummel, Semen Naumovich Lekakh, D C Van Aken, Ronald J OmalleyAbstract:Abstract Thermomechanical properties used in the modeling of steel forming processes that are determined using high temperature cylindrical coupon Compression Testing are subject to errors due to barreling of the test specimen. Barreling caused by the friction between specimen and platens reduces the accuracy of the mechanical property determination. In this study, Gleeble hot Compression Testing was conducted to investigate material behavior for a low carbon structural steel over a range of temperatures (from 900 °C to 1200 °C) and strain rates (from 1 s−1 to 30 s−1). An inverse method combined with finite element analysis was developed to correct the experimental stress-strain curves for the observed barreling effect to obtain the actual stress-strain curves for the material. In deformation simulations, the revised stress-strain curves produced barreling shape predictions that agreed well with the barrel shapes observed in experiments. A comprehensive parametric study based on the revised stress-strain curves was performed to study barreling for a range of friction coefficients, temperatures, and strain rates. Results showed that the magnitude of barreling increases with increasing friction coefficient. For a specific friction coefficient, the magnitude of the barreling decreases with increasing temperature and varies non-linearly with strain rate.
Guoqiang Li - One of the best experts on this subject based on the ideXlab platform.
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thermomechanical behavior of thermoset shape memory polymer programmed by cold Compression Testing and constitutive modeling
Journal of The Mechanics and Physics of Solids, 2011Co-Authors: Guoqiang Li, Wei XuAbstract:Abstract Programming is a key process for thermally activated stress or strain recovery of shape memory polymers (SMPs). Typically, programming requires an initial heating above the glass transition temperature ( T g ), subsequent cooling below T g and removal of the applied load, in order to fix a temporary shape. This work adopted a new approach to program thermoset SMPs directly at temperatures well below T g , which effectively simplified the shape fixing process. 1-D Compression programming below T g and free shape recovery of a thermoset SMP were experimentally investigated. Functional stability of the shape fixity under various environmental attacks was also experimentally evaluated. A mechanism-based thermoviscoelastic–thermoviscoplastic constitutive model incorporating structural and stress relaxation was then developed to predict the nonlinear shape memory behavior of the SMP trained below T g . Comparison between the prediction and the experiment showed good agreement. The structure dependence of the thermomechanical behavior of the SMP was further discussed through a parametric study per the validated constitutive model. This study validates that programming by cold-Compression is a viable alternative for thermally responsive thermoset SMPs.
Wei Xu - One of the best experts on this subject based on the ideXlab platform.
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thermomechanical behavior of thermoset shape memory polymer programmed by cold Compression Testing and constitutive modeling
Journal of The Mechanics and Physics of Solids, 2011Co-Authors: Guoqiang Li, Wei XuAbstract:Abstract Programming is a key process for thermally activated stress or strain recovery of shape memory polymers (SMPs). Typically, programming requires an initial heating above the glass transition temperature ( T g ), subsequent cooling below T g and removal of the applied load, in order to fix a temporary shape. This work adopted a new approach to program thermoset SMPs directly at temperatures well below T g , which effectively simplified the shape fixing process. 1-D Compression programming below T g and free shape recovery of a thermoset SMP were experimentally investigated. Functional stability of the shape fixity under various environmental attacks was also experimentally evaluated. A mechanism-based thermoviscoelastic–thermoviscoplastic constitutive model incorporating structural and stress relaxation was then developed to predict the nonlinear shape memory behavior of the SMP trained below T g . Comparison between the prediction and the experiment showed good agreement. The structure dependence of the thermomechanical behavior of the SMP was further discussed through a parametric study per the validated constitutive model. This study validates that programming by cold-Compression is a viable alternative for thermally responsive thermoset SMPs.
Jing Zhou - One of the best experts on this subject based on the ideXlab platform.
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Constitutive behavior and microstructure evolution of the as-extruded AE21 magnesium alloy during hot Compression Testing
Journal of Alloys and Compounds, 2015Co-Authors: Li Ping Wang, Jurek Duszczyk, G. Fang, M A Leeflang, L.-x. Wang, Jing ZhouAbstract:Magnesium alloys containing rare earth elements possess improved corrosion resistance and mechanical properties and therefore have great potential for a wide range of applications including biomedical applications. Hot forming is meant not only for shaping but also for microstructure modification and performance enhancement. It is of great importance to define optimum forming conditions on the basis of a fundamental understanding of the response of magnesium alloys to deformation. The present study aimed at characterizing the hot deformation behavior of the as-extruded AE21 magnesium alloy by performing isothermal Compression tests over a temperature range of 350–480°C and a strain rate range of 0.001–10s−1. Flow stress data obtained were intended for establishing a constitutive equation, which would be indispensable for the prediction of the response of the material to hot deformation, for example, by means of numerical simulation. The true stress–strain curves obtained from the experiments were analyzed, considering different mechanisms of microstructure evolution operating during Compression Testing at different stages. The Sellar and Tegart model was used to establish the constitutive equation of the alloy during the steady-state deformation. The differences in activation energy value between the present as-extruded magnesium alloy and other wrought magnesium alloys were found and attributed to materials processing history. The Zener–Hollomon parameter was used to correlate the deformation condition with the response of the material to deformation, reflected in the shape of the true stress–strain curve. Microstructure observations indicated that kink bands played an important role in determining the shape of the flow stress–strain curve of the as-extruded AE21 magnesium alloy.
T Meinander - One of the best experts on this subject based on the ideXlab platform.
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dynamic Compression Testing of a tunable spring element consisting of a magnetorheological elastomer
Smart Materials and Structures, 2007Co-Authors: M Kallio, Tomi Lindroos, S Aalto, E Jarvinen, T Karna, T MeinanderAbstract:Magnetorheological elastomers (MRE) are interesting candidates for active vibration control of structural systems. In this study, spring elements consisting of magnetorheological elastomer were prepared and tested in dynamic Compression to study the changes in their stiffness and vibration damping characteristics under the influence of a magnetic field. Aligned and isotropic magnetorheological elastomer composites were prepared using room temperature vulcanizing silicone elastomer as the matrix material and carbonyl iron as the magnetizable filler. Aligned MREs were prepared by curing the material under an external magnetic field. Aligned MREs were tested and the results were compared with isotropic composites with no preferred orientation. The mechanical properties of the MREs were tested in cyclic Compression passively and with increasing magnetic flux density. The influence of the Testing frequency and strain amplitude on the dynamic stiffness and damping properties was studied. It was noted that when measured in a magnetic field both the dynamic spring constants and the loss factor values of aligned MREs were increased compared to the zero-field values. The dynamic stiffness of aligned MREs increased with increasing Testing frequency and it was tunable with magnetic flux density in the studied frequency range. The loss factor of aligned MREs was also tunable with the magnetic flux density but the absolute values also depend on the Testing frequency. The dynamic stiffness of the aligned MREs measured in Compression decreased with increasing strain amplitude, but the damping properties were not affected similarly. On the basis of these results, MREs are applicable as tunable spring elements for active vibration control.