Tensile and Compressive Properties of Mg-3Al-2Zn-2Y Alloy at Different Strain Rates

The tensile and compressive properties of Mg-3Al-2Zn-2Y alloy at room temperature at strain rates in the range of 0.001-1400 s^?1 and 0.001-4800 s^?1, respectively, were investigated. The ultimate strength in tension tests has positive effect to strain rate, while that in compression tests has positive effect at strain rates in the range of 0.001-1800 s^?1 and negative effect when the strain rate increases to 4800 s^?1. The strain rate sensitivity of ultimate strength is different for tension and compression. To both tension and compression, the density of dislocation increases with increasing of strain rate and parallel dislocations come being at high strain rate. A large number of twins appear when the strain rate increases to certain degree. The fracture characteristics change from quasi-cleavage to ductile fracture as tensile strain rate increases, while the compression strain rate has little influence on the fracture characteristics.     

Effect of Dynamic Change in Strain Rate on Mechanical and Stress Corrosion Cracking Behavior of a Mild Steel

The current work analyzes the effect of the dynamic change in strain rate during tensile loading of a mild steel on its mechanical and stress corrosion behavior in 3.5 wt.% NaCl solution. The sample experiences high strain rate (10^?2 s^?1) up to 10, 15 and 20% of total deformation and then very low strain rate of 10^?6 s^?1 till fracture without any unloading in between. The behavioral characteristics of the steel under these circumstances are found to be different from that exhibited during complete loading till fracture both at high and slow strain rates separately. Total strain increases with the increase in the strain at which change in strain rate happens, and this is attributed to the generation of large number of dislocations at higher strain rate and subsequently release of dislocation at low strain rate during change over due to more time available for dynamic recovery. This observation is common for both in air and corrosive environment. One unique observation in this study is the higher total strain and lower strength observed during dynamic change in strain rate in the corrosive environment compared to that in air, which is attributed to the hydrogen-induced plasticity mechanism.     

A Modified Constitutive Equation for Aluminum Alloy Reinforced by Silicon Carbide Particles at Elevated Temperature

In this paper, the constitutive relationship of an aluminum alloy reinforced by silicon carbide particles is investigated using a new method of double multivariate nonlinear regression (DMNR) in which the strain, strain rate, deformation temperature, and the interaction effect among the strain, strain rate, and deformation temperature are considered. The experimental true stress-strain data were obtained by isothermal hot compression tests on a Gleeble-3500 thermo-mechanical simulator in the temperature range of 623-773 K and the strain rate range of 0.001-10 s^?1. The experiments showed that the material-softening behavior changed with the strain rate, and it changed from dynamic recovery to dynamic recrystallization with an increase in the strain rate. A new constitutive equation has been established by the DMNR; the correlation coefficient (R) and average absolute relative error (AARE) of this model are 0.98 and 7.8%, respectively. To improve the accuracy of the model, separate constitutive relationships were obtained according to the softening behavior. At strain rates of 0.001, 0.01, 0.1, and 1 s^?1, the R and AARE are 0.9865 and 6.0%, respectively; at strain rates of 5 and 10 s^?1, the R and AARE are 0.9860 and 3.0%, respectively. The DMNR gives an accurate and precise evaluation of the flow stress for the aluminum alloy reinforced by silicon carbide particles.     

Environmental embrittlement of two-phase Fe30Ni20Mn35Al15

It is shown that the ductility of lamellae-structured Fe₃₀Ni₂₀Mn₃₅Al₁₅ (in at. %), which consists of B2 and f.c.c. phases, is influenced by testing environment. Tensile tests performed in air at strain rates ranging from 3 × 10^?6 to 3 × 10^?1 s^?1 showed that the elongation to fracture and ultimate tensile strength (UTS) increased with increasing strain rates below 3 × 10^?3 s^?1, and were independent of strain rate at ～10.5% and 840 MPa for strain rates ≥ 3 × 10^?3 s^?1. In order to understand this strain-rate sensitive behavior, tensile tests were also performed in either dry oxygen or 4% hydrogen + nitrogen at different strain rates. The elongation and UTS in oxygen were insensitive to strain rate and close to those tested at 3 × 10^?3 s^?1 in air, whereas the elongation in hydrogen was 4% for strain rates ≤3 × 10^?3 s^?1 and increased to ～10.8% at 3 × 10^?1 s^?1. The reduction of ductility in air and hydrogen-charged environment at low strain rate is attributed to hydrogen embrittlement.     

Flow Behavior and Mechanical Properties of a High Silicon Steel Associated with Dynamic Strain Aging

Flow behavior of two grades of steel including a high silicon (HS) steel and a plain low carbon steel as the reference were considered in this work. Tensile testing at temperatures varying between 25 and 550?°C and different strain rates in the range of 4?×?10^?5 to 0.1?s^?1 were conducted and the mechanical properties, such as elongation at fracture point and strain rate sensitivity were then determined. It is observed that for both steels, dynamic strain aging occurs in the employed deformation conditions, however, the region of serrated flow and the type of the serration were somehow different. For the case of the HS steel, the serrated flow region is shifted to the higher temperatures and also, the activation energy for appearance of dynamic strain aging increases as well.     

Increase in the plasticity of molybdenum after high-rate deformation under pressure

The dependence of the plasticity of polycrystalline molybdenum on the strain rate has been studied after deformation performed under pressure and at an ambient temperature of 293 K. The samples were deformed in tensile tests. The strain rate of tensile deformation and the pressure in each experiment are constant. The range of the strain rate is 8.3 × 10^?7 to 8.3 m/s and the pressure is 0.1–500 MPa. At a pressure of ambient atmosphere, molybdenum at a strain rate less than 200 s^–1 in value (10^2.3 s^–1) fractures in a brittle manner with zero residual strain. The brittle fracture of the working part of a cylindrical sample occurs simultaneously in several places. The molybdenum plasticity decreases in the range of low strain rates regardless of the pressure and, on the contrary, plasticity under pressure increases in the range of high strain rates. The strain rate of tensile deformation at which the dependence of the plasticity on the strain rate under pressure changes is 8.3 × 10^–4 m/s (a strain rate of 0.25 s^–1). The high plasticity of molybdenum after deformation under pressure is observed at high strain rates.     

Hot Deformation Behavior and Processing Maps of 2099 Al-Li Alloy

Hot deformation behavior and processing maps of the 2099 Al-Li alloy are investigated by tensile test at the temperature range from 250 to 450 °C and the strain rate range from 0.001 to 5.0 s^?1. The typical true stress-true strain curves show that the flow stress increases with increasing the strain rate and decreasing the deforming temperature. All curves exhibit rapid work hardening at an initial stage of strain followed by remarkable dynamic softening. Based on the flow stress behavior, the processing maps are calculated and analyzed according to the dynamic materials model (DMM). The processing maps exhibit an instability domain in the temperature and strain rate ranges: T = 250-260 °C and \(\dot{\upvarepsilon }\)  = 0.1-0.5 s^?1. The maps also exhibit an optimum hot working condition in the stability domain that occurs in the temperature of 400 °C for a strain rate of 0.001 s^?1 and having a maximum efficiency of 60%. The microstructural examinations exhibit the occurrence of dynamic recovery (DRV) during hot deformation of the 2099 alloy which is the dominant softening mechanism in the alloy. The fracture behavior changes from a brittle fracture to a ductile fracture as strain rate decreases and temperature increases.     

High temperature deformation and processing map of a NiTi intermetallic alloy

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s^?1 to 1 s^?1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s^?1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s^?1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s^?1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s^?1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s^?1 and at temperature of 1100 °C and all range of strain rates.     

原位TiB2颗粒增强7075铝基复合材料的热压缩变形行为和显微组织演变

采用等温热压缩实验研究不同变形条件下(变形温度300～450℃、应变速率0.001～1 s?1)原位TiB2颗粒增强7075铝基复合材料的热成形行为、损伤机制和显微组织演变.结果表明,复合材料在低温和高应变速率下的主要损伤机制是颗粒断裂和界面脱粘,而在高温和低应变速率下主要是基体的韧窝断裂.此外,复合材料在高温、低应变...     

Deformation behavior and mechanisms of Ti- 1023 alloy

1 Introduction Beta titanium alloys offer a variety of microstructural morphologies and associated mechanical property variations thus giving considerable latitude in microstructure design. They are the most versatile class of titanium alloys and offer th…     

Tensile behavior of a free-standing Pt-aluminide (PtAl) bond coat

The tensile behavior of a high activity stand-alone Pt-aluminide (PtAl) bond coat was evaluated by the micro-tensile test method at various temperatures (room temperature to 1100 °C) and strain rates (10^?5 s^?1–10^?1 s^?1). At all strain rates, the stress–strain behavior of the stand-alone coating was significantly affected by the variation in temperature. The stress–strain response was linear, indicating brittle behavior, at temperatures below the brittle–ductile transition temperature (BDTT). The coating exhibited appreciable ductility (up to 2%) above the BDTT. The strength (both yield stress and ultimate tensile strength) of the coating decreased and its ductility increased with increasing temperature above the BDTT. The tensile behavior of the coating was sensitive to strain rate in the ductile regime, with its strength increasing with increasing strain rate at any given temperature. The BDTT of the coating was found to increase with increasing with increasing strain rate. The coating exhibited two distinct mechanisms of deformation above the BDTT. The transition temperature for the change of deformation mechanism also increased with increasing strain rate.     

The high-speed deformation behavior of TRIP steels

The high-speed deformation behavior of TRIP steel was investigated at strain rates ranging from 10⁻² s⁻¹ to 10³ s⁻¹. The effects of metallurgical factors, such as the rolling direction, thickness, and gage length, on the tensile properties at various strain rates were evaluated. The ultimate tensile strength, uniform elongation, strain rate sensitivity, absorbed energy, and strain-hardening exponent are reported. In general, the strength increases and the ductility decreases as the strain rate increases. The samples with a high amount of retained austenite had two distinct regions of strain rate sensitivity, showing high strain rate sensitivity over a strain rate of 10² s⁻¹. The tensile properties were not affected by the gage length and thickness of the tensile samples; however, the rolling direction of the tensile samples affected the UTS values slightly. The absorbed energy of the TRIP steel greatly exceeded that of HSLA steel.     

Influence of strain rate on microstructure and formability of AZ31B magnesium alloy sheets

The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^?4, 10^?3, 10^?2, 10^?1 s^?1 at 200 °C. The results show that the volume fraction of dynamic recrystallization grains increases and the original grains are gradually replaced by recrystallization grains with the strain rate decreasing. A larger elongation and a smaller r-value are obtained at a lower strain rate, moreover the erichsen values become larger with the strain rate reducing, so the formability improves. This problem arises in part from the enhanced softening and the coordination of recrystallization grains during deformation.     

Strain-dependent constitutive analysis of hot deformation and hot workability of T4-treated ZK60 magnesium alloy

The hot deformation behavior of T4-treated ZK60 magnesium alloy was investigated in a compression test conducted with a thermo-mechanical simulator at a temperature range of 523 K to 673 K and a strain rate of 0.001 s^?1 to 1 s^?1. The results show that the flow stress increases as the deformation temperature decreases and the strain rate increases. Strain-dependent constitutive relationships were developed using regression method and artificial neural network, and good agreements between the experimentally measured values and the predicted ones were achieved. The work hardening analysis and onset of dynamic recrystallization (DRX) were investigated. The processing map reveals a domain of DRX at the temperature range of 620–673 K and strain rate range of 0.001–0.01 s^?1, with its peak efficiency of 32% at 623 K and 0.001 s^?1, which are the optimum values of the parameters for hot working of the T4-treated ZK60 alloy. The strain level has a great effect on the processing maps and lower temperatures and higher strain rates should be avoided during hot working processes. DRX model indicates that DRX of ZK60 alloy is controlled by the rate of nucleation, which is slower than the rate of migration.     

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10^?5, 1.25 × 10^?4, 2.5 × 10^?3, and 1.25 × 10^?2 s^?1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10^?3 s^?1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10^?5 s^?1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10^?3 s^?1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.     

Strain rate sensitivity of nanocrystalline Au films at room temperature

The effect of strain rate on the inelastic properties of nanocrystalline Au films was quantified with 0.85 and 1.76 μm free-standing microscale tension specimens tested over eight decades of strain rate, between 6 × 10^?6 and 20 s^?1. The elastic modulus was independent of the strain rate, 66 ± 4.5 GPa, but the inelastic mechanical response was clearly rate sensitive. The yield strength and the ultimate tensile strength increased with the strain rate in the ranges 575–895 MPa and 675–940 MPa, respectively, with the yield strength reaching the tensile strength at strain rates faster than 10^?1 s^?1. The activation volumes for the two film thicknesses were 4.5 and 8.1 b³, at strain rates smaller than 10^?4 s^?1 and 12.5 and 14.6 b³ at strain rates higher than 10^?4 s^?1, while the strain rate sensitivity factor and the ultimate tensile strain increased below 10^?4 s^?1. The latter trends indicated that the strain rate regime 10^?5–10^?4 s^?1 is pivotal in the mechanical response of the particular nanocrystalline Au films. The increased rate sensitivity and the reduced activation volume at slow strain rates were attributed to grain boundary processes that also led to prolonged (5–6 h) and significant primary creep with initial strain rate of the order of 10^?7 s^?1.     

Effects of the Strain Rate and Temperature on the Microstructural Evolution of Twin-Rolled Cast Wrought AZ31B Alloys Sheets

This article investigates the effects of the strain rate and temperature on the microstructural evolution of twin-rolled cast wrought AZ31B sheets. This was achieved through static heating and through tensile test performed at strain rates from 10^?4 to 10^?1 s^?1 and temperatures between room temperature (RT) and 300 °C. While brittle fracture with high stresses and limited elongation was observed at the RT, ductile behavior was obtained at higher temperatures with low strain rates. The strain rate sensitivity and activation energy calculations indicate that grain boundary diffusion and lattice diffusion are the two rate-controlling mechanisms at warm and high temperatures, respectively. An analysis of the evolution of the microstructure provided some indications of the most probable deformation mechanisms in the material: twinning operates at lower temperatures, and dynamic recrystallization dominates at higher temperatures. The static evolution of the microstructure was also studied, proving a gradual static grain growth of the AZ31B with annealing temperature and time.     

Tensile characterization and constitutive modeling of AZ31B magnesium alloy sheet over wide range of strain rates and temperatures

Magnesium alloys are an ideal candidate due to their low density in comparison to aluminum and steel alloys when designing a vehicle with lower weight and therefore, reduced fuel consumption. It is important to characterize the strain rate sensitivity of any material that will be used in a structure which can undergo high rate deformation (as in an automobile crash) as well as during high velocity forming processes such as electromagnetic or electrohydraulic forming. Tensile tests for AZ31B magnesium alloy sheet at different strain rates were carried out using different testing techniques: (i) quasi-static strain rates tests were conducted in a range between 10⁻³ and 10⁻¹ s⁻¹ using a conventional electro-mechanical tensile testing apparatus; (ii) intermediate strain rates tests at 4.0 × 10¹ to 10² s⁻¹ using an instrumented falling weight apparatus; and (iii) high strain rates at 0.5 × 10³ to 1.5 × 10³ s⁻¹ using a tensile split Hopkinson bar. Furthermore, quasi-static and high strain rate tests were also performed for different temperatures, from room temperature up to 250 °C. Strain rate and temperature effects are also discussed for rolling and transverse direction, to identify the variation of sheet properties with loading direction. Finally, the constitutive fitting of the stress-strain curves to the widely employed Johnson-Cook material model equation is evaluated and also a new model is proposed based on a modified J-C model to account for the variation of strain hardening with strain rate.     

Hot deformation and processing maps of as-sintered CNT/Al-Cu composites fabricated by flake powder metallurgy

The deformation behaviors of as-sintered CNT/Al-Cu composites were investigated by isothermal compression tests performed in the temperature range of 300?550 °C and strain rate range of 0.001?10 s^?1 with Gleeble 3500 thermal simulator system. Processing maps based on dynamic material model (DMM) were established at strains of 0.1?0.6, and microstructures before and after hot deformation were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). The results show that the strain has a significant influence on the processing maps, and the optimum processing domains are at temperatures of 375?425 °C with strain rates of 0.4?10 s^?1 and at 525?550 °C with 0.02?10 s^?1 when the strain is 0.6. An inhomogeneous distribution of large particles, as well as a high density of tangled dislocations, dislocation walls, and some sub-grains appears at low deformation temperatures and strain rates, which correspond to the instability domain. A homogeneous distribution of fine particles and dynamic recrystallization generates when the composites are deformed at 400 and 550 °C under a strain rate of 10 s^?1, which correspond to the stability domains.     

Development of high strain rate equations for stainless steels

The dynamic response of four types of stainless steel sheet was investigated at different strain rates from 10⁻² up to 10³ s⁻¹. The results from the tensile tests were used to evaluate the parameters in three different multiplicative strain rate equations of the type used in crashworthiness calculations. A new type of sigmoid constitutive equation is proposed for one grade of stainless steel.