Search

New experimental data on the dynamic strength of the lead-antimony (2.77%) alloy comprised of different structures formed after thermal treatment in various regimes are presented in this work. The optimal alloy thermal treatment regime (quenching from 250°C) providing the best strength characteristics under explosion or high-speed impact is revealed.

—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.

This paper presents the results of measurements of the spall strength and elastic-plastic proper-ties, under dynamic and static loads, of the high-strength heat-resistant nickel-chromium alloy Inconel 625, obtained by the direct laser deposition method. The structural parameters of the obtained samples and the mechanical properties during static tests were studied. According to our information, anisotropy in the structural parameters operates primarily at the level of plastic deformation of alloys. Shock compression of the additive alloy Inconel 625 samples in the range of 6–18 GPa was carried out using a light-gas gun, both along and perpendicular to the direction of the deposition. The strength characteristics were determined from the analysis of the shock wave profiles, which were recorded using the VISAR laser velocimeter during the loading of samples. It was found that the value of the spall strength of additive samples does not depend on the direction of deposition, and the Hugoniot elastic limit of samples loaded perpendicular to the deposition direction is about ~10% higher. With an increase in the maximum compression stress, the material’s spall strength increases slightly, but for both types of samples, a slight decrease in the Hugoniot elastic limit was observed as the compression stresses increase. On the basis of the measured wave profiles, shock Hugoniots of the samples of the alloy Inconel 625, loaded both along and perpendicular to the direction of deposition, are constructed in this pressure range.

In this work, the critical fracture stresses during spalling of high-strength steel 09CrNi2MoCu samples obtained by direct laser deposition (DLD) were measured under shock compression of up to ~5.5 GPa. The microstructure and mechanical properties of DLD steel samples in the initial state and after heat treatment were studied and compared to traditional hot rolled one. The microstructural features of steel before and after heat treatment were revealed. The heat treatment modes of the deposit specimens on their strength properties under both static and dynamic loads have been investigated. The spall strength of the deposited specimens is somewhat lower than the strength of steel specimens after hot rolling regardless of their heat treatment. The minimum elastic limit of elasticity is exhibited by the deposit specimens. After heat treatment of the deposit samples, the elastic limit increases and approximately doubles. Subsequent heat treatment in the form of hardening and tempering allows obtaining strength properties under Hugoniot loads in traditional hot-rolled products.

Two series of shock-wave experiments have been conducted in order to measure the Hugoniot elastic limit and determine the strain rate dependence of critical fracture stress for tantalum experiencing spall fracture. Tantalum specimens have been preannealed in vacuum at 1000°C. The evolution of elastoplastic compression shock waves at room and elevated up to 500°C temperatures has been presented from complete wave profiles recorded by a VISAR laser Doppler velocimeter. The spall strength dependence on the strain rate during the expansion of the material in a rarefaction wave has been determined.

The dynamic tensile strength (spall strength) of a eutectic bismuth–lead alloy is measured in the solid and liquid states in the temperature range from room temperature to 102°C for the solid phase and in the range 130–150°C for the melt. Melting is found to be accompanied by a decrease in the dynamic tensile strength by almost an order of magnitude. The Hugoniot elastic limit and the spall strength of the alloy in the solid state decrease with increasing test temperature.

In order to determine the compressive and tensile strength of concrete under conditions of explosive loading, and to develop a methodological framework in this regard, three types of concrete have been investigated: concrete with fine-grained granite in the form of crushed stone having a static compressive strength of 47 MPa, the same concrete with the addition of steel fibers and also the same concrete reinforced by steel bars. The samples were rods of 50 and 100 mm diameter and five to ten diameters in length. The compressive fracture occurs at a relatively small distance of propagation of the load pulse along the rod and is accompanied by fast decay. The measurements of parameters of the compression pulse at the end of the fracture zone allowed us to determine the values of the dynamic compressive strength of the concrete while measurements of the free-surface velocity history at long distances were used for determining the dynamic tensile strength or spall strength values. The values of the dynamic compressive strength were found to be 2.5 times higher than the static strength. The steel fibers increased the dynamic compressive strength by about 10%. The obtained values of the dynamic tensile strength are 3–8 times higher than the values of the static tensile strength. The steel fibers increase the tensile strength by 20–50%. The reinforced sample has shown an increase of dynamic tensile strength by a factor of about 30.

The spall strength and dynamic yield stress of polycrystalline hafnium have been measured in a series of plane-wave shock loading experiments using flat sample–transparent window composite targets, with the transparent windows representing polymethyl methacrylate or lithium fluoride plates arranged on the rear side of a hafnium sample. The front side of the target was subjected to shock impact of a copper striker, the rear surface velocity was measured, and the sample was recovered for subsequent metallographic examination. The results were also used for evaluation of the accuracy of spall strength measurements and the analysis of features of high-rate deformation of hafnium.

Using a VISAR laser interferometer , experimental study of the shock compressibility and spall strength of a Kevlar/epoxy composite was performed for two orientations of the fibres. In the experiments, a single stage gas gun (low pressures tests) and explosive driver system (high pressures up to 30 GPa) were used. Hugoniot parameters of Kevlar/epoxy composite were obtained with a kink in the vicinity of 17 GPa which can be associated with a phase transition. It is shown that the shock compressibility and spall strength of composite are almost independent of the fibre orientation. The influence of the anisotropy of the studied material is manifested in the formation of a two-wave configuration at the shock wave propagation along the fibres.

Measurement results for the shock wave compression profiles of 12Cr19Ni10Ti steel and its dynamic strength in the strain rate range 105–106 s−1 are presented. The protracted viscous character of the spall fracture is revealed. With the previously obtained data taken into account, the measurement results are described by a polynomial relation, which can be used to construct the fracture kinetics. On the lower boundary of the range, the resistance to spall fracture is close to the value of the true strength of the material under standard low-rate strain conditions; on the upper boundary, the spall strength is more than twice greater than this quantity. An increase in the temperature results in a decrease in both the dynamic limit of elasticity and the spall fracture strength of steel. The most interesting result is the anomaly in the dependence of the spall fracture strength on the duration of the shock wave compression pulse, which is related to the formation of deformation martensite near the growing discontinuities.

The evolution of elastic-plastic shock compression waves in a VT6 titanium alloy is measured at a distance of 0.16–17 mm at room temperature and 600°C. The results of measuring the decay of an elastic precursors and the compression rate in a plastic shock wave are used to determine the temperature–rate dependences of the flow stress in the strain-rate range 103–107s–1. New data for the spall strength of the alloy at normal and elevated temperatures are obtained.

This paper presents the results of comparative experiments with commercial aluminum AD1 and aluminum A999 of high purity which were designated for measurements of spall strength of these materials at room temperature and at $$640\,^{\circ }\hbox {C}$$ . The measurements confirmed a sharp drop of the spall strength of commercial aluminum when approaching the melting temperature, which probably is associated with an earlier beginning of melting on the grain boundaries with higher concentration of impurities. The pure aluminum A999 maintains high spall strength near the melting temperature.

The results obtained from investigations into the special features inherent in the mechanical characteristics (Hugoniot elastic limit and spall strength) observed under shock-wave loading of Al–Al2O3 composite samples produced by an explosive powder compaction technique are presented. Embedding 10 wt.% of aluminum oxide in the aluminum matrix has been found to increase the Hugoniot elastic limit as opposed to the commercialgrade AD1(Al 1013) aluminum alloy.

Full wave profiles are used to determine the Hugoniot elastic limit and the spall strength of armco iron samples with an as-received structure and the samples recovered after preliminary loading by plane shock waves with an amplitude of 8, 17, and 35 GPa. The measurements are performed at a shock compression pressure below and above the polymorphic a–e transition pressure. Metallographic analysis of the structure of armco iron shows that a developed twinned structure forms inside grains in the samples subjected to preliminary compression and recovered and that the twin concentration and size increase with the shock compression pressure. The spall strength of armco iron under shock loading below the phase transition pressure increases by approximately 10% due to its preliminary deformation twinning at the maximum shock compression pressure. The spallation of samples with various structures at a shock compression pressure above the phase transition proceeds at almost the same tensile stresses. The polymorphic transition in armco iron weakly affects its strength characteristics.

The dynamic tensile strength (spall strength) of tin and lead melts has been measured by a found method. Comparison with similar measurements of the spall strength of these metals at room temperature shows that melting reduces the spall strength by at least an order of magnitude. The spall strength of liquid metals is a smaller fraction of the extremely possible (“ideal”) strength than that for water and organic liquids.

The influence of shock compression on the spall strengths of copper, brass, nickel, stainless steel, armco iron, and titanium nickelide Ti51.1Ni48.9 is studied in the pressure range 2–80 GPa at a strain rate higher than 104 s−1 by recording wave profiles with a VISAR laser velocimeter and subsequent analysis. The strengths of the metals subjected to strong twinning during shock compression are shown to increase with the pressure in a shock wave, and the dependence of the strength on the shock pressure has a threshold character due to thermal softening at the maximum shock wave amplitude. The metals that undergo phase transformations have a more complex relation between the spall strength and the shock compression intensity.

The shock compression wave profiles in three modifications of boron carbide ceramic are studied in the compressive stress range 3–19 GPa. The Hugoniot elastic limit and the spall strength of the materials are determined. It is confirmed that the spall strength of high-hardness ceramic changes nonmonotonically with the compressive stress in a shock wave.

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.

Full wave profiles were monitored by the laser interferometry method by means of a VISAR laser Doppler velocimeter under shock-wave loading of samples of AMg6 aluminum alloy. Analysis of these profiles was used to study the laws of elastic precursor formation and its amplitude variation during elastic–plastic transition front propagation in samples loaded by a shock wave of variable intensity. Critical stresses leading to the spall fracture of samples were determined as dependent on the strain rate under unloading.

This paper presents two examples of significant departures from usual trends of varying the resistance to spall fracture (spall strength) with changing loading history, load duration and peak shock stress. In experiments with vanadium single crystals we observed an important decrease of spall strength when increasing the shock stress. This was interpreted in terms of disruption of the matter homogeneity as a result of its twinning at shock compression. In experiments with 12Kh18N10T austenitic stainless steel we observed a sharp increase of recorded spall strength value when short load pulses of a triangular profile were replaced by shock pulses of long duration having a trapezoidal shape. This anomaly is associated with formation of the deformation-induced martensitic phase.

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.

The results of measurements of shock compression wave profiles for three modifications of carbide ceramics in the stress range 3–19 GPa are presented. The dynamic elasticity and spall strength limits of the materials are determined. It is shown that these characteristics are sensitive to specific characteristics of reaction-sintered ceramics related to technological parameters of the process of their manufacturing. It is confirmed that the spall strength of highly rigid ceramics varies nonmonotonically with increasing compression stress in the shock wave.

The results of measurements of the decay of an elastic precursor in iron at the distances from 0.13 to 10 mm and the spall strength of the samples with such thicknesses have been compared with similar data for the nanometer-scale samples. The decay has been described by a unique dependence whose differentiation gives the relationship between the initial plastic strain rate in the range from 103 to 109 s−1 and the compression stress in the elastic shock wave from 1.5 to 27.5 GPa. The dynamic breaking strength (spall strength) varies in this range of shock-wave load time from 1.5 to 20 GPa.

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.

This paper presents the results of measurements of the strength properties of technically pure tantalum under shock wave loading. It has been found that a decrease in the grain size under severe plastic deformation leads to an increase in the hardness of the material by approximately 25%, but the experimentally measured values of the dynamic yield stress for the fine-grained material prove to be less than those of the initial coarse-grained specimens. This effect has been explained by a higher rate of stress relaxation in the fine-grained material. The hardening of tantalum under shock wave loading at a pressure in the range 40–100 GPa leads to a further increase in the rate of stress relaxation, a decrease in the dynamic yield stress, and the disappearance of the difference between its values for the coarse-grained and fine-grained materials. The spall strength of tantalum increases by approximately 5% with a decrease in the grain size and remains unchanged after the shock wave loading. The maximum fracture stresses are observed in tantalum single crystals.

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.

The dynamic yield strength and tensile (spall) strength of the D16T aluminum alloy are measured when samples are loaded by submicrosecond plane shock waves. The initial (unannealed) and annealed material is studied, and alloy samples subjected to multiple forging at elevated temperatures are also examined. The loading direction with respect to the texture of the material and the shock-compression pulse duration and shape are varied. The difference in the spall strengths measured along the rolling direction and normal to this direction is close to the dynamic yield strength of the material.

The focus of this study is on the deformation mechanisms of high-alloy cast austenitic TRIP/TWIP steel with the nominal composition Fe-16Cr-6Mn-6Ni. Due to its chemical composition, the material exhibits a low stacking-fault energy of 17.5 mJ/m2which facilitates the formation of the deformation-induced γ (fcc) → ε (hep) → α’ (bcc) transformation. Consequently, the steel exhibits a tensile strength of 800 MPa with fracture elongation of 55 % under quasi-static loading. The experiments presented demonstrate the response of this steel to flyer-plate impact (FPI) at room temperature using two different test setups. In the first setup, laser interferometry measurements of the sample free surface were used for determination of the dynamic mechanical properties (Hugoniot elastic limit / HEL. spall strength) after impact with aluminium plates accelerated up to 650 m/s. In the second setup, an experimental shock testing device developed at the Freiberg High-Pressure Research Centre was used for impacting large cylindrical samples without the occurrence of spallation. Subsequently, microstructural investigations were carried out by scanning electron microscopy (SEM) and transmission election microscopy (TEM) in combination with diffraction techniques and magnetic martensite measurements. Their results facilitate the representation of a complete image of deformation mechanisms during shock wave loading.

The Hugoniot elastic limit and spall strength of Ma2-1 magnesium deformable alloy were measured at the sample thickness varied from 0.25 mm to 10 mm at room and elevated temperatures. By means of analysis of decay of an elastic precursor wave it is found that initial plastic strain rate decreases from 2×105 s-1 at distance of 0.25 mm to 103 s-1 at distance of 10 mm. The strain rate in plastic shock wave is by order of magnitude higher at the same value of the shear stress. The spall strength of the alloy grows with increasing the strain rate and decreases with approach to the solidus temperature.

This article reports new experimental results on the mechanical behavior of the Ni48.9Ti51.1 alloy under shock‐wave loading in the temperature range from 213 to 413 K. The samples of NiTi alloy were loaded by impacts of aluminum flyer plates with a thickness of 0.4 mm and an impact velocity of 630±50 m/s. The increase in the yield strength from 0.4 to 2.7 GPa and the spall strength from 1.75 to 3.75 GPa Results indicate that in the range 213 K to 413 K, all values of the spall strength are higher than the values of austenitic NiTi alloys with high contents of nickel. The relationship Us‐up for martensitic NiTi demonstrated no anomaly that was observed with austenitic NiTi alloys.

A series of magnesium single crystals, from 0.2 to 3 mm thick, were shock loaded along specific axes, a and c, of the hexagonal closed packed (hcp) structure. Other experiments involved loading at 45 degrees to these principal axes. Shock compression along the c-axis causes inelastic deformation by means of pyramidal slip and twinning and is associated with the largest Hugoniot elastic limit (HEL) for this material. The low-energy basal slip was activated by shock loading along the inclined direction and has he smallest HEL. In all cases, we observe the decay of the elastic precursor wave and growth of the HEL with increasing temperature. For the c-orientation this change is caused by a decrease of elastic constants, not an increase of shear stress along the pyramidal slip planes. For the other orientations the shear stress on the slip planes increased with temperature. For the inclined shock compression, after the HEL, two plastic waves were found: the stress level of the first plastic wave depends on the ultimate shock stress. Finally, the largest spall strength was along the a-axis and the smallest in the off-axis direction.