Papers by Keyword: Strain Rate Sensitivity (SRS)

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Authors: Li Yuan Qin, Jian She Lian, Long Zhe Quan, En Chen Jiang
Abstract: A fully dense nanocrystalline Ni-Co alloy with 18 nm grain size exhibited high strength of about 2200 MPa and ductility of 8.19.2% at strain rates of 1.04×10-5 to 1.04 s-1 and room temperature. The alloying of Co element induces the grain refinement, solid solution hardening and decrease of stacking fault energy should contribute to the favorable combination of mechanical performance. The obvious distinctions of fracture-surface morphologies with strain rate alteration were attributed to underlying deformation mechanism transition. The high strain rate sensitivity exponent and small activation volume indicate that grain boundary activity may be expected in this alloy.
Authors: Chris H.J. Davies
Abstract: Samples of extruded magnesium alloy AZ31 (nominally 3 wt% Al, 1 wt% Zn, 0.3 wt% Mn, with the balance magnesium) were tested in uniaxial compression at temperatures from room temperature to 200°C. Monotonic and strain rate jump tests were conducted, and strain rate sensitivity, and activation volume were determined. At the lower temperatures tested, strain rate sensitivity was found to increase with strain to a limiting value, whereas at 200°C strain rate sensitivity initially followed a similar trend, but did not reach a limit within the bounds of the test. The effect of temperature on strain rate sensitivity was minor up to 150°C. Activation volume decreased with stress by roughly an order of magnitude over the course of the tests. An analytical model was modified to incorporate strain rate sensitivity, and it is shown that the evolution of material by twinning into an orientation favourable for slip is principally responsible for the trend in strain rate sensitivity with increasing strain.
Authors: P. Tasnádi, András Juhász, Nguyen Q. Chinh, I. Kovács
Authors: Hai Yan Zhu, Ying Chen Zhang, Jing Zou, Hong Yan Wu, Y.P. Qiu
Abstract: The purpose of the present work is to investigate the microstructural deformation of the montmorillonite (MMT) particles/polypropylene (PP)/polylactic acid (PLA) nanocomposite filaments infused with plasma treated MMT. The activation volumes of the MMT/PP/PLA nanocomposite filaments ranging from 31.4572 to 151.2100 (nm)3 estimated by the Eyring’s equation quantitatively revealed that the plasma treated MMT acted as obstacles to dislocation motion during microstructural plastic deformation mechanisms. DSC analysis showed marked increases in glass transition temperature (Tg), indicating the plasma treated MMT could effectively help resist the free crankshaft movement of the macromolecular chain in the nanocomposite filaments. In addition, the MMT/PP/PLA nanocomposite filaments developed intercalated structures which had been examined by SEM.
Authors: Shao Wei Hu
Abstract: Discontinuous yield of material as Jerky flow was explained. Then, the strain rate sensitivity (SRS) and instability criterion was given out. Some tests were carried out at constant stress rate, so Jerky flow is manifested as a discontinuity in the stress-strain curves in form of strain bursts. Finally, the dynamic behaviors of specimens during instability of thermal origin were simulated with COLSYS software, whose results are good with test ones.
Authors: Jing Nan Huang, Ying Chen Zhang, Hai Yan Zhu, Hong Yan Wu, Y.P. Qiu
Abstract: In the current study the role of plasma treated nano titanium dioxide particles and strain rate on the tensile properties of plasma treated nano TiO2 particles/PP/PLA nano-composites filaments (PTNTOPPCF) was studied. The experiments included tensile tests and differential scanning calorimetry (DSC). The addition of the plasma treated nano titanium dioxide particles into PP/PLA caused a change in Young's modulus and yield stress of the composites. Strain rate sensitivity of the PTNTOPPCF changed as plasma with and without oxygen treated nano titanium dioxide particles was added to it with different percentage of weight. It was increased with more PLA, MAH, and higher flow rate of oxygen. Activation volumes ranged in 4−40(nm)3 for true nanocrystalline material estimated by the Eyring equation, which were changed un-monotonically with oxygen plasma treatment.
Authors: Y.B. Chun, Chris H.J. Davies
Abstract: Measurements of strain rate sensitivity (SRS) provide a key link between dislocation-based interpretations of plastic deformation and macroscopic measurements made in mechanical tests. It is well known that plastic deformation of hexagonal close-packed (hcp) metals is achieved not only by dislocation glide but also by twinning and that the atomic rearrangement underlying the latter mode is different from that of slip. This leads to an expectation that co-activation of twinning may affect SRS of hcp metals. This assumption was tested in the present work where strain rate jump tests in both tension and compression were conducted on highly textured AZ31 plate. It was found that the SRS of the alloy in tension decreased with strain whereas that in compression increased with strain, exhibiting negative values at low strain and positive values at higher strain. Microstructure analyses revealed that the strain regimes where negative SRS or decreasing trend in SRS with strain was observed correspond to extensive twinning, implying a negative SRS of twinning. It is concluded that dislocation model alone cannot explain the strain rate dependence of flow stress in metals whose deformation is assisted by twinning.
Authors: Bing Zhe Bai, Han Zhang
Abstract: Two novel methods of obtaining microduplex structures, ferrite plus spherical carbides, in ultrahigh strength steels (~2000MPa) are introduced. One is through an adequate deformation just below the austenite-ferrite equilibrium transformation temperature (i.e. Ae3 temperature, ~983K) followed by water quenching. The adequate deformation directly leads to the formation of a (ferrite plus spherical carbides) microduplex structure. The microstructure evolution during the deformation includes pearlite transformation, cementite spheroidization and ferrite recrystallization. The other is through an adequate deformation above Ae3 temperature (~1003K) followed by water quenching to produce martensite firstly and then obtain a (ferrite plus spherical carbides) microduplex structure during warm deformation of martensite. Microstructural analysis on the microduplex structure shows that submicron carbides are located at ferrite grain boundaries while nanometer ones are dispersed inside ferrite grains. This kind of carbide distribution may suppress the coarsening of ferrite grains and form a dynamic equilibrium of ferrite grain size on a specific deformation condition. The strain rate sensitivity of the (ferrite plus spherical carbides) microduplex structures is about 0.4 at 973K and strain rate of 10-4s-1.
Authors: Lothar W. Meyer, Matthias Hockauf, Anton Hohenwarter, Steffen Schneider
Abstract: A tungsten heavy alloy (92%W, Ni-Co matrix) is subjected to severe plastic deformation (SPD) by high pressure torsion (HPT) at room temperature up to equivalent strains of 0.7, 5.3, 10.7 and 14.3. The microstructure and the mechanical properties are investigated by cylindrical compression samples at quasi-static and dynamic loading. The harder spherical W particles are homogeneously deformed within the softer matrix, becoming ellipsoidal at medium strains and banded at high strains without shear localization or fracture. Results of quasi-static loading show that the strength is approaching a limiting value at strains of ~10. At this strain for the matrix a grain size of ~80 nm and for W a cell size of ~250 nm was observed, suggesting strain concentration on the matrix. The initial yield stress of 945 MPa for the coarse-grained condition is increased thereby to an ultimate value of 3500 MPa, while a peak stress of ~3600 MPa is reached. Such remarkably strength has never been reported before for pure W or W-based composites. The strain hardening capacity as well as the strain rate sensitivity is reduced drastically, promoting the early formation of (adiabatic) shear bands.
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