Dynamic Elastic Limit Research Articles

The Dynamic Properties of Low-Alloyed Copper Alloys with a Submicrocrystalline Structure Obtained by High-Strain-Rate Deformation

Abstract—The mechanical properties of alloys Cu–0.03 wt % Zr and Cu–0.10 wt % Cr with a submicrocrystalline structure formed during dynamic channel-angular pressing and subsequent annealing. The properties of the alloys were studied under shock compression conditions with a pressure of 4.7–7.0 GPa and a deformation rate of (1.3–3.2) × 105 s–1. It is shown that grain grinding from 200–400 to 0.3–1.0 microns increases the dynamic elastic limit and the dynamic yield strength of the Cu–0.03% Zr alloy by 1.9 and 1.8 times, respectively, but reduces the shear strength by 1.4 times. Subsequent annealing at 400 and 450°C can increase the characteristics of the elastic-plastic transition by 3.0 and 3.7 times, respectively, and increase the shear strength to the level of a large-crystal analog. It is determined that the dispersion of the Cu–0.10% Cr alloy structure to 1.0–5.0 microns increases not only the dynamic elastic limit and dynamic yield strength by 3.7 and 2.6 times, respectively, and the shear strength by 1.5 times, compared with its value in the coarse-grained state.

Behavior of Zr–1Nb alloy in coarse- and ultrafine-grain states under laser-induced shock wave loading

The work is devoted to the study of the Zr-1Nb alloy in coarse-grained and ultrafine-grained states under laser-induced shock-wave loading. This material is of interest due to the application for the manufacture of shells for fuel elements of nuclear reactors. The properties of this alloy in the ultrafine-grained state is attracted for the reliability improvement of fuel rods in wide range of load intensity. Shock wave loading was carried out using a Beamtech SGR-Extra-10 high-energy nanosecond laser. The free surface velocity profiles were registered by the VISAR system. Mechanical characteristics are obtained using velocity profiles. It is shown that the spall strength and dynamic elastic limit for the coarse-grained state are higher than for the ultrafine-grained state. In general, the Zr-1Nb alloy in the ultrafine-grained state is more susceptible to spall fracture, including laser shock peening. Numerical simulation of the process under study has been carried out using statistically based nonlinear model of solid with defects and finite element method to describe the deformation behavior and fracture of the material under shock-wave loading. Simulation results are qualitatively consistent with experiments in the prediction of the conditions of spall failure.

Mechanical properties of submicrocrystalline aluminium matrix composites reinforced by “in situ” graphene through severe plastic deformation processes

The method of high-resolution scanning and transmission electron microscopy was used to investigate the features of the formation of the structure and deformation behavior of a composite material based on aluminum with microadditions of graphene under severe plastic deformation by the dynamic channel-angular pressing method. It was found that an aluminum-graphene composite with a submicrocrystalline structure with the hardness 2.5 times higher than in the as-cast state forms in the deformation process. For the first time, the dynamic properties of the composite were measured under loading by plane shock waves at a speed of 5.0·105 s-1. Comparison with the dynamic characteristics of a coarse-crystalline composite showed an increase in the dynamic elastic limit and dynamic yield stress by 1.8–2.0 times.

Dynamic Strength of Submicrocrystalline and Nanocrystalline Copper Obtained by High-Strain-Rate Deformation

Abstract—The dynamic properties of commercial copper (99.8 wt % purity) with a submicrocrystalline and nanocrystalline structure obtained by high-strain-rate deformation using the dynamic channel-angular pressing (DCAP) method have been studied in this work. The tests were carried out under conditions of shock compression at a pressure of 5.6−6.8 GPa at a strain-rate of (0.9−2.0) × 105 s–1. The analysis of the evolution of the structure and mechanical properties, namely, the dynamic elastic limit, dynamic yield stress, and the spall strength of copper before and after DCAP in different regimes, made it possible to evaluate the influence of the dispersity and imperfection of the crystal structure on its resistance to the high-strain-rate deformation and fracture. It has been shown that the grain refinement from 100 to 0.5−1.0 μm increased the dynamic elastic limit and the dynamic yield stress of copper by six times, but only slightly decreased the spall strength. The further refinement of the structure (up to 0.05−0.40 μm) increases the spall strength of copper by 1.4 times as compared to its value in the initial coarse-grained state.

The Influence of the Cobalt Content on the Strength Properties of Tungsten Carbide Ceramics under Dynamic Loads

Based on the registration and analysis of the full wave profiles, the Hugoniot elastic limit and spall strength of ceramics based on tungsten carbide with different cobalt content are measured. We also study the influence of the cobalt content on the mechanical characteristics of tungsten carbide such as hardness, fracture strength, Young’s modulus, shear modulus, and sound velocity. It is shown that in the process of spalling, the failure stresses grow and the dynamic elastic limit decreases almost linearly within the scatter of their values with growing cobalt content; moreover, the value of the Hugoniot elastic limit is abruptly practically halved as the cobalt content grows from 0 to 2 wt %.

Dynamic properties of reactor steels Kh16N15M3T1 and Kh13V2 under shock-wave loading of submicrosecond scale

Kh16N15M3T1 and Kh13V2 reactor steels were investigated. The study was carried out using a light-gas gun with the deformation velocities ranging from 4·104 to 3·106 s-1 and shock-loading pulses in 0.05-1 μs duration range. Dependences of the spallation strength and dynamic elastic limit in a wide temperature range are obtained. The recovered specimens were used to carry out the metallography analysis.

Incipience and development of spall fracture in 30KHGSA steel, α↔ε transformation, spall fracture and damage recovery

Results of investigation into strength and elasto-plastic properties of 30KhGSA steel are presented. The investigation was performed with planar samples using submicrosecond shockwave length technique. Shockwave amplitude varied in the range from 4 to 26 GPa and controlled with 0.2% accuracy. Steel sample temperature varied in the range from-90 °C to 670 °C. Stress wave profiles in the samples were registered with VISAR and PDV interferometers having nanosecond time resolution and measurement error better than 0.8%. Special attention was payed to the study of spall fracture incipience and development processes as well as damage recovery (healing), and shockwave passing through the damaged region in steel samples. Relaxation characteristics of dynamic elastic limit were determined. Spall strength magnitude versus strain rate and temperature characteristics was determined. The impact of polymorphic α↔ε transition in 30KhGSA steel on spall strength was studied.

Peculiarities of the elastic-plastic transition and failure in polycrystalline vanadium under shock-wave loading conditions

Specific features in the deformation of polycrystalline vanadium under shock-wave loading conditions have been studied by experimental and theoretical methods. Analysis of the full wave profiles was used to determine the dynamic elastic limit and spall fracture stress in a range of stain rates of 105–107 s−1. The laws of elastic–plastic transition at the shock-wave front, mechanisms of elastic precursor relaxation, and spall fracture development are discussed.

Resistance of submicrocrystalline aluminum alloys to high-rate deformation and fracture after dynamic channel angular pressing

A comparative study of the deformation behavior of submicrocrystalline (formed by dynamic channel angular pressing) and coarse-grained commercial aluminum alloys (AMts and V95), and commercial aluminum A7 has been performed under impact compression conditions. Dynamic elastic limit (Hugoniot elastic limit) σHEL, yield strength Y, and spall strength σsp at a deformation rate of (1.2–3) × 105 s−1 were determined by analyzing the experimental velocity profiles of the free surface of samples. It has been found that the dynamic elastic limit and yield strength increase after all the materials studied have transformed into a submicrocrystalline state (crystallite size of 200–700 nm). Submicrocrystalline alloy V95 has the highest value of Y and submicrocrystalline aluminum A7 has the lowest one. The effect of grain size on spall strength is ambiguous. The values of σsp for submicrocrystalline alloys are 1.32–1.36 GPa. The submicrocrystalline V95 alloy and commercial A7 aluminum demonstrate a decrease in the spall strength, whereas the spall strength of the alloy AMts slightly increases with decreasing grain size.

Influence of the temperature-induced martensitic-austenitic transformation on the strength properties of high-alloy steels under dynamic loading

The dynamic elastic limit and spall strength of high-alloy chromium-manganese-nickel steel in the martensitic-austenitic transformation induced by a change in the temperature from −120 to 200°C is measured by recording the complete wave profiles with a VISAR laser interferometer and subsequently analyzing them. The spall strength of the investigated steel in the martensitic phase is found to be 25–30% higher than the strength of steel in the austenitic phase. In this case, the strength decreases in a stepwise manner in a narrow temperature range approximately from −50 to 20°C, where, apparently, basic changes in the internal structure of steel occur due to the martensitic-austenitic transformation. The measured values of the dynamic elastic limit of high-alloy steel have a sufficiently large scatter and hardly decrease with increasing temperature without any features associated with the martensitic-austenitic transformation of the structure.

Deformation of zirconium – niobium alloy E635 in sub-microsecond shock waves

Strength characteristics of zirconium - niobium alloy E635 were measured under shock - wave loading conditions at normal and elevated temperatures and results of these measurements are presented. Measurements were taken in conditions when samples were impacted by plane shock waves with the pressure up to 13 GPa and duration from ∼0.05 μs up to 1 μs. Free-surface velocity profiles were recorded with the help of VISAR and PDV laser Doppler velocimeters having nanosecond time resolution. Evolution of elastic precursors with samples thickness varying from 0.5 up to 8 mm is also considered. Measured attenuation of the elastic precursor was used to determine plastic strain rate behind the precursor front. Temperature effect on the value of dynamic elastic limit and spall strength at normal and elevated temperatures is studied. This work is implemented with the support of the State Atomic Energy Corporation “Rosatom” under State Contract H.4x.44.90.13.1111.

High strain rate deformation and fracture of the magnesium alloy Ma2-1 under shock wave loading

This paper presents the results of measurements of the dynamic elastic limit and spall strength under shock wave loading of specimens of the magnesium alloy Ma2-1 with a thickness ranging from 0.25 to 10 mm at normal and elevated (to 550°C) temperatures. From the results of measurements of the decay of the elastic precursor of a shock compression wave, it has been found that the plastic strain rate behind the front of the elastic precursor decreases from 2 × 105 s−1 at a distance of 0.25 mm to 103 s−1 at a distance of 10 mm. The plastic strain rate in a shock wave is one order of magnitude higher than that in the elastic precursor at the same value of the shear stress. The spall strength of the alloy decreases as the solidus temperature is approached.

Ceramics based on partly stabilized zirconium dioxide: technology, structure, properties, and behavior under dynamic action

Technology is described for manufacturing dense ceramic from very fine powder based on zirconium dioxide partly stabilized with yttrium oxide. Some engineering properties of the manufactured ceramic are defined. Its microstructure and phase composition are studied. Ceramic properties with impact-wave loading are studied, and values of dynamic elastic limit and spalling strength are obtained.

A ceramic based on partially stabilized zirconia: Synthesis, structure, and properties under dynamic load

A ceramic based on zirconia partially stabilized by yttrium oxide has been prepared. The main properties of the prepared ceramic have been characterized: density, ultimate strength under twisting, microhardness, elasticity coefficients, etc. The microstructure and phase composition of the ceramic and its phase transformations under mechanical action have been studied. The properties of the ceramics under dynamic load have been studied, and the values of the dynamic elastic limit and splitting strength have been obtained. The results have been compared with the literature data.

Behavior of the nickel-titanium alloys with the shape memory effect under conditions of shock wave loading

The behavior of the Ti51.1Ni48.9 and Ti49.4Ni50.6 alloys with shape memory effects has been studied under submicrosecond shock wave loading in the temperature range from −80 to 160°C, which includes both the regions of the stable state of the specimens in the austenite and martensite phases and the regions of thermoelastic martensitic transformations. The grain size of the studied alloys varies from initial values 15–30 to 0.05–0.30 μm. The dependences of the dynamic elastic limit on the temperature and on the elemental composition are similar to the dependences of the yield stress of these alloys under low strain rate loading. The rarefaction shock wave formation as a consequence of the pseudoelastic behavior of the alloy during a reversible martensitic transformation has been revealed. A decrease in the grain size leads to an increase in the dynamic elastic limit and decreases the temperatures of martensitic transformations.

Spall fracture in sapphire

The dynamic tensile strength of sapphire has been studied under conditions of impact loading in the region of dynamic (Hugoniot) elastic limit (HEL). In the absence of inelastic deformation, the spall strength of sapphire strongly depends on the loading time and exhibits a tendency to decrease with increasing compressive stress in the incident impulse. The development of inelastic deformation leads to the complete loss of material resistance to the tensile straining.

Dynamic yielding of single crystal Ta at strain rates of ∼5 × 105/s

A magnetic loading technique was used to produce planar ramp loading of [100] and [110] orientations of single crystal tantalum to peak stresses of either ∼18 or ∼86 GPa for applied plastic strain rates of about 2 × 106/s. It was found that the dynamic elastic limit varied only slightly for factor-of-2 changes in the resulting elastic strain rates near 5 × 105/s. For wave propagation in the [100] direction, the dynamic elastic limit varied from 4.18–3.92 GPa for corresponding sample thicknesses of 0.625–1.030 mm and exhibited a slight rate dependence for the strain rate region studied. For [110] compression, the elastic limit was essentially independent of propagation distance, but exhibited a significant sample-to-sample variation; the elastic limit for this orientation varied from 2.49–3.18 GPa over sample thicknesses of 0.702–1.023 mm, with an average and standard deviation for the data of 2.93 ± 0.27 GPa. There was no apparent rate dependence in this case for the strain rates examined.

Resistance to deformation and fracture of aluminum AD1 under shock-wave loading at temperatures of 20 and 600°C

The results of measurements of the dynamic elastic limit and spall strength under shock-wave loading of aluminum samples AD1 of thicknesses between 0.5 and 10.0 mm at room temperature and at temperature increased up to 600°C are presented. The anomalous thermal hardening of aluminum under high strain rate has been confirmed. An analysis of the decay of precursors at temperatures of 20 and 600°C has shown that the change in the main mechanism of drag of dislocations occurs at a strain rate equal approximately to 5 × 103 s−1, which agrees with the results of measurements by the Hopkinson split bar method. The results of measurements of the spall strength in a wide range of strain rates add the previously obtained data and agree with them.

Elastic-plastic phenomena in ultrashort shock waves

A physical model of shock-wave phenomena in metals irradiated by a femtosecond laser pulse has been developed. The use of the experimental results (reported in S.I. Ashitkov et al., Pis’ma Zh. Eksp. Teor. Fiz. 92, 568 (2010) [JETP Lett. 92, 516 (2010)] together with the molecular dynamics simulation makes it possible to study the elastic properties of aluminum crystals at extreme shear stresses comparable in amplitude with the shear modulus. As a result, the elastic Hugoniot adiabat has been continued to the region of metastable elastic states at very high pressures, which are one or two orders of magnitude higher than the commonly accepted values for the dynamic elastic limit. It has been shown that the ultrashort elastic shock wave of superhigh pressure precedes the formation of the known split-shock wave structure consisting of an elastic precursor and a plastic shock wave.

Thermodynamic Evaluation of the Dynamic Elastic Limit of Metals

Given that the plastic state of substances is similar to the liquid state, the work of plastic deformation is assumed to be proportional to the heat of melting. An equation is derived which relates the dynamic elastic limit to the volume change upon “mechanical melting.” The proportionality coefficient in this equation is determined by the degree of fragmentation of crystalline grains (shock-compression rate). The use of microscopic atomic rigidity characteristics makes it possible to derive a universal formula for calculating the elastic limit with a reasonable accuracy.