Papers by Keyword: Strain Rate Sensitivity (SRS)

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Authors: Jon Alkorta, C.J. Luis-Pérez, E.N. Popova, Martin Hafok, Reinhard Pippan, J. Gil Sevillano
Abstract: A commercially pure niobium has been subjected to SPD at room temperature ( ~0.11 TM) via ECAP (90º, route BC) up to 16 passes and via HPT up to shear strains γ =1000. ECAP-ed samples show an equiaxed structure after 8 and 16 passes with a decreasing average grain size. The results show that both the microstructure and mechanical properties of ECAP-ed samples do not reach a steady state up to at least 16 passes. HPT samples show at outer region a finer structural size but similar hardness values at similar equivalent strains. The nanoindentation results show an evident indentation size-effect even for the most deformed samples. The hardness values at the nano level converge for the recrystallized, the ECAP-ed and the HPT samples. This implies that, at the nano level, when the geometrically necessary dislocation density overcomes significantly the (initial) statistically stored dislocation density, hardness depends mainly on the physical intrinsic properties of the material (Burgers modulus, bulk modulus...) and the contribution of bulk mechanical properties (i.e., bulk yield strength) to hardness is smoothed down. Strain-rate sensitivity (SRS) of plastic strength has been also measured by means of rate-jump nanoindentation tests. The SRS is proportional to the inverse of hardness.
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Authors: Ji Kang Zhong, Matthew S. Dargusch, Chris H.J. Davies
Abstract: The hot deformation behaviour of the alpha / beta Ti-6Al-4V alloy was investigated at various temperatures and strain rates by means of compression and torsion tests. As expected, the peak flow stress increased with increasing strain rate and decreased as the initial sample temperature was increased. The different flow behaviours observed are discussed in terms of the volume fraction of each phase. The dual phase Ti-6Al-4V alloy was assumed to be a composite material containing a soft phase and a hard phase. By taking into consideration the phase-to-phase interaction and volume fraction change with temperature, constitutive models are proposed to simulate the deformation behaviours. By application of the rule of mixtures the modelled yield stresses showed good agreement with the experiment results.
879
Authors: J.N. Huang, Ying Chen Zhang, H.Y. Wu, Y.P. Qiu
Abstract: The plasticity of APPJ treatment on microstructure and tensile deformation of carbon nanotube coating basalt fiber in the dynamic states was investigated by specialized tensile testing at room temperature. With the addition of low-temperature helium plasma treatment, Young's modulus and yield stress changed. It was found that micro-structural parameter such as the activation volume was important descriptors for carbon nanotube coating basalt fiber and inter-phase effect on strength. The different APPJ treatments on the carbon nanotube coating basalt fiber showed the change rate sensitivity. Results revealed that APPJ treatment carbon nanotube coating basalt fiber and the inter-phase would enhance the ductility of basalt at room temperature. From the SEM micrographs, an increase in surface roughness has been observed and the degree of fibrillation decreased after helium and oxygen plasma treatment. Contact angle analysis showed taht the treated Basalt filament had lower contact angles than the untreated one. Based on FTIR results, the change of wettability and surface energy depended the amount of polar functional groups on the fiber surface introduced by the treatments.
722
Authors: Jing Zou, Ying Chen Zhang, Hong Yan Wu, Y.P. Qiu
Abstract: The strain rate sensitivity of helium plasma treated Nano Silicon Dioxide particles sol-gel coating Kevlar filaments (HPTNSDPKEVLAR) and concurrent micro-structural evolution. The results of SEM observation and contact angle analysis showed that the treated Kevlar filament had a rougher surface and lower contact angles than the untreated one. According to the FTIR results, the change of wettability was attributable to the amount of polar functional groups on the fiber surface introduced by the treatments. Moreover, the changes of physico-mechanical properties by HPTNSDPKEVLAR were analyzed by using tensile test at different strain rates range from ranging from 0.01 s-1 to 0.6 s-1. It was found that the materials were strain rate sensitive, and both the tensile strength and failure strain increased with increasing strain rate. The dependence of yield stress by HPTNSDPKEVLAR with strain rate followed Eyring’s equation, and may be characterized by implying the similarity in the onset of plastic deformation.
692
Authors: Ying Chen Zhang, J.N. Huang, Hong Yan Wu, Y.P. Qiu
Abstract: The plasticity treatment of APPJ on microstructure and tensile deformation of Nano SiO2 coating Vectran in the dynamic states was investigated by specialized tensile testing at room temperature. With the addition of low-temperature Helium plasma treatment, Young's modulus and yield stress changed. It was found that micro structural parameter such as the activation volume was important to describe the Nano SiO2 coating Vectran and inter-phase strength between filaments and coating. The results of different APPJ treatments on the Nano SiO2 coating Vectran showed the change of the rate sensitivity of the filaments. The flow stress dependence of the strain rate sensitivity indicated that dynamical recover processes associated with the dislocation-dislocation interactions, which develop in the APPJ treatment Nano SiO2 coating Vectran and Vectran after small amount of deformation, leaded to strain localizations and early failure. Results revealed that APPJ treatment Nano SiO2 coating Vectran and the inter-phase would enhance the ductility of Vecetran at room temperature.
700
Authors: Hideaki Tsukamoto, Zhi Gang Dong, Han Huang, Tetsura Nishimura, Kazuhiro Nogita
Abstract: The intermetallics of Cu6Sn5 that are formed at the Sn-based solder/ Cu substrate interface play a significant role in solder joint reliability. The characterization of the mechanical properties of the interface Cu6Sn5 is essential to understand the mechanical performance and structural integrity of the solder joints. In this study, the interface Cu6Sn5 and (Cu,Ni)6Sn5 formed in Sn-Cu and Sn-Cu-Ni ball grid array (BGA) joints were investigated using nanoindentation. The results demonstrated that the strain rate sensitivity and the activation volume of these intermetallics were affected by the reflow times and load conditions. The strain rate sensitivity of Cu6Sn5 and (Cu,Ni)6Sn5 were estimated from 0.023 to 0.105, and the activation volume of Cu6Sn5 and (Cu,Ni)6Sn5 were estimated from 0.128 b3 to 0.624 b3 (b=4.2062x10-9 m) for 1, 2 and 4-reflowed Sn-Cu (-Ni) samples.
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Authors: Tomokazu Masuda, Hiroyuki Toda, Toshiro Kobayashi
Abstract: The strain rate sensitivity of a A6061-T6 aluminum is examined as a function of triaxial stress. The triaxial stress state is changed by changing the notch acuity of notched specimens. Under the high strain rate conditions, increasing triaxiality increases flow stress. Plastic constraint factor decreases in notched specimens under high strain rate conditions. Reduction-of-area in notched specimen increases with increasing strain rate. The relaxation of plastic constraint takes place under high strain rate in the notched specimens. The effects of triaxial stress and strain rate on the fracture surfaces are discussed.
137
Authors: Shan Qing Xu, Dong Ruan, John H. Beynon, Guo Xing Lu
Abstract: The strength enhancement of cellular materials under dynamic compression was experimentally studied in the present paper. A phenomenological model was employed to investigate the entrapped air contribution by introducing a parameter, namely the leaking rate of air. The strength enhancement caused by the entrapped air was then studied for both aluminum honeycombs and foams. It has been found that the pressure change in the entrapped air during dynamic compression is a direct source of strain hardening for aluminum honeycombs whereas it has smaller influence on the strain hardening of aluminum foams. Other sources that might contribute to the strain hardening of cellular materials are also discussed.
522
Authors: B. Yang, Horst Vehoff, Reinhard Pippan
Abstract: A summary of experimental results from nanoindentation, strain rate-controlled tension, in-situ bending and high pressure torsion on bulk electrodeposited nanocrystalline nickel, focusing on the effects of grain size on the mechanical behaviour and deformation mechanisms is presented. The interaction between dislocations and grain boundaries was locally examined by studying the dependence of nanohardness on grain size and indentation size; this is done by always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically. The grain size effects on the different deformation mechanisms of nanocrystalline nickel were revealed by strain rate-controlled tension and nanoindentation experiments, which show that with decreasing grain size the strain rate sensitivity increases and the activation volume decreases, indicating increased grain boundary mediated deformation processes in nanocrystalline nickel. Creep experiments at room temperature revealed that in nanocrystalline nickel grain boundary sliding or diffusion along the interface may dominate at lower stress levels, but with increasing stresses the deformation process is mainly controlled by dislocation creep. In-situ bending experiments in an atomic force microscope revealed directly that grain boundary mediated deformation processes play a significant role in nanocrystalline nickel, which is also supported by the observation of grain coarsening and softening of nanocrystalline nickel caused by high pressure torsion.
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