High Tensile Rate Research Articles

Coupling effect of temperature and strain rate on mechanical properties and deformation mechanisms of Cr26Mn20Fe20Co20Ni14 high-entropy alloy

It is proposed that high-entropy alloys (HEAs) with face-centered cubic (FCC) structure possess superior strength-ductility synergy at low temperature or high tensile rate, attributing to enhanced twinning ability. In present work, the coupling effects between low temperature and high strain rate on the mechanical properties and deformation mechanisms of the Cr26Mn20Fe20Co20Ni14 HEA were investigated. Compared with that at room temperature (RT) with a strain rate of 10−3 s−1, the HEA exhibits enhanced strength but sacrificial ductility at liquid nitrogen temperature (LNT) with a higher strain rate of 10−1 s−1. Investigation of the microstructures reveals that twinning and stacking fault dominate the deformation at RT with a strain rate of 10−3 s−1. At LNT and 10−1 s−1, the deformation is inhomogeneous, characterized by local twinning and dislocation planar slip as well as relatively less HCP phase transformation. Moreover, numerous cracks induced by weakened interfaces and high flow stress at LNT lead to premature fracture.

Monotonic tension behavior of 2D woven oxide/oxide ceramic matrix composites at ultra-high temperature

The research on mechanical behavior and failure analysis of oxide/oxide CMC at ultra-high temperatures can broaden its application scope. The present work studied monotonic tension behavior of the oxide/oxide CMC at 800 °C∼1200 °C and two tensile rates (i.e. 5 mm/min and 0.5 mm/min). The uniaxial tensile test, fracture morphology characterization and finite element analysis were preformed to reveal the deformation and failure mechanisms of the oxide/oxide CMC at ultra-high temperature. The results show that the mechanical properties of the oxide/oxide CMC are sensitive to the temperatures and tensile rates. The stress-strain curves are almost linear at the high tensile rate and nonlinear at the low tensile rate. The ultimate tensile strength decreases significantly at low tensile rate and for temperatures higher than 1100 °C. The mechanical properties of the material are principally determined by oxide fiber/oxide matrix interface strength under low temperature and high-stress conditions, while by interlayer bonding strength under high temperature and low-stress conditions.

Synthesis, microstructure and mechanical properties of partially biobased biodegradable poly(ethylene brassylate-co-ε-caprolactone) copolyesters

High-molecular-weight poly(ethylene brassylate-co-ε-caprolactone) copolyesters within a wide composition range were prepared via triphenyl bismuth catalyzed copolymerization of ethylene brassylate (EB) and ε-caprolactone (ε-CL) in bulk. Microstructural analysis of the resulting copolyesters demonstrated that the comonomer units were completely random distribution. DSC and WAXD recognized that the copolyesters cocrystallize within the lattices analogous to either of the parent homopolymers. It confirmed the isodimorphism behavior with a pseudo-eutectic point of melting temperatures as well as lattice spacings at 75 mol% ε-CL units. The crystal cell would be stretched in one dimension rather than expanding in both dimensions with the incorporation of comonomer units according to the result of WAXD. The mechanical properties of the copolyesters are well tunable by the composition, and its trend is consistent with the isodimorphism behavior, in particular, the maximum elongation at break over 2000% is located at the pseudo-eutectic point. The intralamellar shear occurred at the low tensile rate while both intralamellar shear and interlamellar shear occurred at high tensile rate. The copolymers exhibit excellent hydrolytic stability.

Mechanical properties of gold twinned nanocubes under different triaxial tensile rates

The gold twinned nanocubes under different triaxial tensile rates are explored by molecular dynamics simulation. Hydrostatic stress and Mises stress are defined in order to understand triaxial stresses. Twin boundaries prevent dislocations between twin boundaries from developing and dislocation angles are inconspicuous, which causes little difference between triaxial stresses. The mechanical properties of the nanocubes under low and high tensile rates are different. The curves of nanocubes under high tensile rates are more abrupt than those under low tensile rates. When the tensile rate is extremely big, the loadings are out of the nanocubes and there are not deformation and fracture in the internal nanocubes.

Effect of aging treatment on hydrogen embrittlement of PH 13-8 Mo martensite stainless steel

The effect of aging treatment on hydrogen embrittlement of PH 13-8 Mo steel was investigated by tensile tests. The specimens were electrochemically hydrogen-charged in 0.5mol/L NaOH solution with 1g/L CH4N2S at room temperature for 24h, and then were tensioned to fracture at different tensile rates. The results show that hydrogen slightly increases the tensile strength of the steel at high tensile rate (20mm/min), but decreases the tensile strength at low tensile rate (0.5mm/min and 0.03mm/min). In the range of temperature from 540°C to 750°C, the specimen aged at 650°C has the highest resistance to hydrogen embrittlement, which can be attributed to reverted austenite. At tensile rate of 0.03mm/min, the SEM fractograph reveals quasi-cleavage and intergranular fracture mode for hydrogen-charged specimens aged at 540°C, 600°C,700°C and 750°C while dimple-type fracture mode for hydrogen-charged specimens aged at 650°C.

Working Load on Specimen in Rapid-Fracture Toughness Test

In order to evaluate dynamic fracture toughness of structural steel, three point bending (3 PB-COD) or compact tension (CT) test is usually carried out by using drop weight or high tensile rate testing machine.Since, in static test, applied load to the specimen can easily measured exactly by load cell of test system, but in dynamic test it is difficult to get or decide working load on test specimen because the effect of acceleration affects on the output of load cell in test system.In this paper, the estimation of working load on test specimen was investigated applying a simple mass and spring model to the loading system of test equipment.

Stress Corrosion Cracking of Alpha Titanium Alloys at Room Temperature

Abstract Transgranular stress corrosion cracks are formed in Ti-5Al-2.5Sn alloy immersed in a 3 percent NaCl aqueous solution when tensile specimens are dynamically strained over a narrow range of rates. Metallographic evidence suggests that the critical process during crack propagation is entry of hydrogen into the alloy at the crack tip immediately following creation of fresh metal surface. Fractographic examination reveals that cracks propagate by a discontinuous cleavage mechanism. As each incremental growth is arrested, the embrittlement process resumes. Ductile fracture is observed in specimens strained (a) at high tensile rates because there is insufficient time for embrittlement to occur, and (b) at low tensile strain rates because repassivation occurs more readily and hydrogen entry is substantially reduced. In methanolic solutions containing HCl, an identical cleavage crack propagation process is observed. In addition, a slow intergranular dissolution mechanism is found in alloys susceptible and nonsusceptible to cleavage-type failure. This is initiated in specimens that have regions of high residual stress, e.g., sheared edges and continues until the mechanical strength of the alloy is reduced to a very low value. During this process hydrogen is picked up by the metal. Clevage has been observed in specimens broken in air after exposure. Vacuum annealing substantially reduces but does not eliminate this slower form of attack by removing initiation sites. Anodic polarization at low current densities produces extremely severe intergranular attack. The significance of dislocation arrangements, mechanical properties, and electrochemical reactions at the crack tip are discussed in detail. In particular, it is suggested that cathodic polarization can prevent cracking by forming films which reduce the rate of hydrogen ingress. In 10N HCl solutions, cathodic polarization does not prevent cracking.