Comparative studies of the constitutive models for tungsten heavy alloy (95W-3.5Ni-1.5Fe) at high strain rates

The plastic behaviors’ description of a tungsten heavy alloy (95W-3.5Ni-1.5Fe) at temperatures of 298–773 K and strain rates of 0.001–11,000 s−1 is systematically studied based on four constitutive models, that is, Zerilli-Armstrong model, modified Zerilli-Armstrong model, Mechanical Threshold Stress model, and modified Mechanical Threshold Stress model. The quasi-static compression experiments using an electronic universal testing machine and the dynamic compression experiments using a split Hopkinson pressure bar apparatus are employed to obtain the true stress–strain curves at a total of three temperatures (298 K, 573 K, and 773 K) and a wide range of strain rates (0.001–11,000 s−1). The parameters of the four constitutive models are obtained by the above fundamental experimental data and Grey Wolf Optimizer. The correlation coefficient and average absolute relative error are used to evaluate the predicted performance of these models. Modified Mechanical Threshold Stress model is found to have the highest predicted performance in describing the flow stress of the 95W-3.5Ni-1.5Fe alloy. Eventually, two compression experiments whose loading conditions are not in the fundamental experiments are conducted to validate the four models.

Low temperature super ductility and threshold stress of an ultrafine-grained Al–Zn–Mg–Zr alloy processed by equal-channel angular pressing

Low temperature tensile and impression creep tests were carried out on an ultrafine-grained 7xxx series Al–4.8Zn–1.2 Mg–0.14Zr (wt%) alloy, which can be deformed for maximum elongation of about 200% at 150 °C. The characteristics of the deformation process, such as the strain rate sensitivity (SRS) and activation energy (Q) were determined by considering also the effect of threshold stress. Relatively high SRS of $$\sim$$ ∼ 0.35 and low activation energy of $$\sim$$ ∼ 92 kJ/mole were obtained, confirming the super ductility of the investigated ultrafine-grained alloy in the low temperature region between 140 and 160 °C. Graphical abstract

Relationship Between Intrinsic Threshold Stress Intensity And Near-Tip Residual Stress: A Reference Material Property

The relationship between intrinsic, closure-free threshold stress intensity and near-tip residual stress, characterizes the effect of load magnitude as well as load history on near-threshold fatigue crack growth rates. It serves as a reference against which precise closure data can be extracted from growth rates to calibrate analytical estimates. These possibilities were subjected to rigorous experimental verification involving threshold and near-threshold fatigue response under overloads, underloads with load-shedding on a steel prone to oxide debris formation. The study reveals why conventional load shedding practice to characterize threshold stress intensity is prone to yield unconservative and misleading results.

The investigation of artificial and natural defects on the fatigue strength of vacuum-assisted high pressure die cast AlSi9Cu3(Fe) aluminum alloy

AlSi9Cu3(Fe) vacuum-assisted high pressure die cast (VPDC) specimens were investigated by experimental fatigue test and fracture mechanics approach. The aims of the investigations were (i) to evaluate the fracture resistance and (ii) to indirectly determine the threshold stress intensity value (ΔKth) of casting alloy in uniaxial tension. The specimens were sorted into two groups: specimens with different size (0.01-0.40 mm2) natural defects, and specimens an additional artificial blind hole. The fatigue strength region was tested at R=-1 stress ratio to 107 number of cycles to fracture. The fracture mechanics approach was applied to study the behavior of the small cracks by Kitagawa diagram, the defect size was taken into account by the Murakami’s (√area) parameter. The fatigue strength values were 104.7 MPa for smooth specimen, 92.7 MPa for specimen with D0.3 artificial hole, and 87.2 MPa for specimen with D0.6 artificial hole at the prescribed cycles, respectively.

High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.