Compression Split Hopkinson Pressure Bar Research Articles

Establishing of Constitutive Equation of ZGMn13 Steel and Cutting Simulation Test

Constitutive equation of material has an important influence on the simulation results in the finite element simulation. In this paper, Johnson-Cook constitutive equation parameters of the high manganese steel ZGMn13 have been derived from the data of compression tests and split Hopkinson pressure bar test. Based on this equation, the finite element simulation of ZGMn13 steel cutting has been done. This Johnson-Cook constitutive model of high manganese steel ZGMn13 can accurately describe the plastic behavior of the material.

Dynamic Impact Response of Inconel 718 Alloy under Low and High Temperatures

Dynamic impact response of Inconel 718 alloy is studied at temperatures ranging from −150 to 550°C and strain rates in the range of 1000 to 5000 s−1 using a compressive split Hopkinson pressure bar. It is found that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The highest work hardening rate is observed in the specimen at the lowest temperature (−150°C) and the highest strain rate (5000 s−1). However, the work hardening rate is weakened by the deformation-induced temperature rise under high strain and strain rate conditions. The strain rate sensitivity increases with increasing strain rate, but decreases with increasing temperature. The activation energy varies as a function of the strain rate and temperature, and has a maximum value of 40 kJ/mol. The greatest thermal softening effect occurs at the highest strain rate of 5000 s−1 and temperatures in the range −150∼25°C. The microstructural observations confirm that the mechanical response of the Inconel 718 specimens is directly related to the effects of the strain rate and temperature on the evolution of the impacted microstructure.

Increased accuracy of SHPB test apparatus to better evaluate naval steels

The use of high strength steel alloys for shipbuilding applications has increased in recent years in an effort to decrease costsassociated with the manufacture (i.e. material and welding costs) and operation (i.e. fuel economy) of naval vessels. The use ofthinner hull plate has implications for many design criteria, including high strain rate (impact and shock loading) performance.Increasingly, numerical modeling is being used to simulate high strain rate loading events on naval vessels, such as collisions and weapons attacks, with a goal of assessing operational limits. Accurate and reliable high strain rate material data must be used to ensure the accuracy of the numerical models. Confidence in measured data can only be achieved if the potential sources of errorin the measurement system have been eliminated, minimized or characterized. The mechanical behavior of three naval alloys, MIL S-16216K (HY-80), ASTM A517 grade F and CSA G40-21 350WT cat 5 were quantified under high strain rate (103s-1) compression using a Split Hopkinson Pressure Bar (SHPB) apparatus. A systematic error analysis was conducted on the SHPB apparatus to identify potential sources of error in the test set-up, data acquisition and data processing. The identified sources of error were then eliminated, minimized or compensated for, in order to improve the accuracy of the testing apparatus. SHPB compression data are compared to quasi-static tensile behavior. Metallography was conducted before and after high strain rate testing in order to investigate the deformation mechanisms that occurred in the alloys during the high strain rate loading events.

High strain rate mechanical behavior of epoxy under compressive loading: Experimental and modeling studies

Investigations on high strain rate behavior of epoxy LY 556 under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the experimental investigations. The studies are presented in the strain rate range of 683–1890 per second. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. Further, an analytical method is presented based on variable rate power law for the prediction of compressive strength at high strain rate loading for epoxy LY 556. Using the analytical method, high strain rate compressive stress–strain behavior is presented up to strain rate of 10,000 per second.

Numerical Simulation of Double Specimens in Split Hopkinson Pressure Bar Testing

The split Hopkinson pressure bar (SHPB) is the most commonly used technique to characterize the dynamic behaviour of materials at very high strain rates. However, a classic single specimen test only generates a single stress-strain curve at the average strain rate of the test. This paper proposes three arrangements on the use of double specimens in SHPB compression testing. All waves propagating along the bars have been used to analyse the dynamic behaviour of the specimens. To simulate the test and predict its dynamic performance, an axisymmetric finite element analysis using LS-DYNA was conducted for the experiment using 13 mm bar diameter. The validity of the simulations was checked with experimental data from normal SHPB testing. Based on the simulations, the modified techniques are achievable and at least two stress-strain curves of materials can be extracted without violating the requirement of a valid SHPB test.

Adiabatic shearing behaviour of unweldable Al–Sc alloy under extremely high shear loading

The present study applies a compressive type split Hopkinson pressure bar to investigate the adiabatic shear behaviour of unweldable Al–Sc alloy under high strain rates ranging from 3·0 × 105 to 6·3 × 105 s–1. The effects of the strain rate on the shear stress, adiabatic shear band characteristics, and fracture features of the unweldable Al–Sc alloy are systematically examined. The results show that both the shear stress and the strain rate sensitivity increase with increasing the strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. Moreover, the distortion angle and the magnitude of the local shear strain near the shear band both increase with increasing the strain rate. At a strain rate of 3·0 × 105 s–1, the fracture surface is characterised by multiple transgranular clearage fractures. However, for strain rates greater than 4·5 × 105 s–1, the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the ductility of the unweldable Al–Sc alloy improves with increasing the strain rate.

Impact deformation behaviour of Ti–6Al–4V alloy in the low-temperature regime

The impact response of Ti–6Al–4V alloy is investigated using a compressive split-Hopkinson pressure bar at strain rates of 1.0 × 10 3 s −1, 3.0 × 10 3 s −1 and 4.3 × 10 3 s −1 and temperatures of −150 °C, 0 °C and 25 °C, respectively. It is shown that for a constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, while the activation volume decreases. Meanwhile, for a constant strain rate, the activation volume increases with increasing temperature, while the flow stress, work hardening rate and strain rate sensitivity decrease. Scanning electron microscopy (SEM) observations reveal that the fracture surfaces are characterised by a transgranular dimpled structure, indicating that Ti–6Al–4V alloy has excellent ductility. The density of the dimples increases with an increasing strain rate or increasing temperature. Transmission electron microscopy (TEM) observations show that the dislocation density increases with an increasing strain rate, but decreases with an increasing temperature. The linear correlation between the square root of the dislocation density and the true stress confirms the existence of a Bailey–Hirsch type relationship. Finally, the strengthening effect observed at higher strain rates and lower temperatures is attributed to a greater dislocation density.

Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s −1 are illustrated and then compared with statically determines stress–strain curve (1.0 × 10 −3 s −1). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.

Effects of prestrain on high temperature impact properties of 304L stainless steel

The effects of prestrain, strain rate, and temperature on the impact properties of 304L stainless steel are investigated using a compressive split-Hopkinson pressure bar. The impact tests are performed at strain rates ranging from 2000 to 6000 s−1 and temperatures of 300, 500, and 800 °C using 304L specimens with prestrains of 0.15 or 0.5. The results show that the flow stress, work-hardening rate, and strain rate sensitivity increase with increasing strain rate or decreasing temperature. As the prestrain increases, the flow stress and strain rate sensitivity increase, but the work-hardening rate decreases. The temperature sensitivity increases with an increasing strain rate, temperature, and prestrain. Overall, the effects of prestrain on the impact properties of the tested specimens dominate those of the strain rate or temperature, respectively. Finally, optical microscopy observations reveal that the specimens fracture primarily as the result of the formation of adiabatic shear bands.

High temperature microstructural evolution of 304L stainless steel as function of pre-strain and strain rate

304L stainless steel specimens are pre-strained to 0.15 or 0.5 and are then deformed at strain rates ranging from 2000 s −1 to 6000 s −1 at temperatures of 300 °C, 500 °C and 800 °C using a compressive split-Hopkinson pressure bar. The results show that for both values of the pre-strain, the flow stress increases with increasing strain rate, but reduces with increasing temperature. At deformation temperatures of 300 °C or 500 °C, the flow stress in the 0.5 pre-strained specimen is higher than that in the specimen pre-strained to 0.15. However, at a temperature of 800 °C, the two specimens exhibit a similar level of flow stress. Transmission electron microscopy (TEM) observations reveal that the strengthening effect observed in the specimens deformed at 300 °C or 500 °C is the combined result of dislocations, mechanical twins and martensite transformation. However, at a deformation temperature of 800 °C, the strengthening effect is the result primarily of dislocation multiplication. The volume fraction of martensite transformation decreases with increasing strain rate and temperature. In addition, both the dislocation density and the twin density increase with increasing strain rate, but decrease with increasing temperature. Finally, the quantitative analysis results indicate that the flow stress varies with the square root of the dislocation density, the twin density and the volume fraction of martensite, respectively.

Impact deformation behaviour and dislocation substructure of Al–Sc alloy

This paper employs a compressive split-Hopkinson pressure bar to investigate the impact deformation behaviour of Al–Sc alloy under high strain rates of 1.2 × 10 3 s −1, 3.2 × 10 3 s −1 and 5.8 × 10 3 s −1, respectively, and temperatures of −100 °C, 25 °C and 300 °C. It is shown that for a constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, while the activation volume decreases. Conversely, for a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the activation volume increases. It is found that the impact deformation behaviour of Al–Sc alloy can be accurately described using the Zerilli–Armstrong constitutive equation. Optical microscopy (OM) observations reveal that the specimens fail principally as the result of an adiabatic shearing mechanism. Furthermore, scanning electron microscopy (SEM) observations show that the fracture surfaces are characterised by a dimple-like structure, which indicates a ductile failure mode. Transmission electron microscopy (TEM) observations indicate that the dislocation density and cell size are related to the strain rate, flow stress and temperature. Finally, the TEM observations suggest that the strengthening effect observed in the deformed Al–Sc alloy is the result of Al 3Sc precipitates within the matrix and at the grain boundaries, which suppress dislocation motion and prompt an increase in the work hardening stress.

Stress–strain behavior of composites under high strain rate compression along thickness direction: Effect of loading condition

Investigations are carried out on the behavior of typical plain weave E-glass/epoxy; plain weave carbon/epoxy; satin weave carbon/epoxy; and satin weave carbon – plain weave E-glass and epoxy hybrid composites under high strain rate compressive loading along thickness direction. Compressive split Hopkinson pressure bar apparatus was used for the studies. Two loading cases, namely, specimen not failed and specimen failed during loading are investigated. The special characteristics of specimen not failed case are presented. For this case, the specimens are under compressive strain initially and are under tensile strain during the later part of loading. The induced tensile strain is higher than the induced compressive strain. This could lead to failure of specimen/structure under tensile strain even though the applied load is compressive.

Comparative study of dynamic impact properties and microstructures of weldable and unweldable aluminium–scandium (Al–Sc) alloys

The dynamic deformation behaviours of two Al–Sc alloys, one weldable and one unweldable, are investigated at strain rates ranging from 1·2 × 103 to 5·9 × 103 s–1 and temperatures of –100, 25 and 300°C respectively, using a compressive split Hopkinson pressure bar. The fracture features and microstructures of the impacted specimens are examined using scanning electron microscopy and transmission electron microscopy respectively. The stress–strain relationships indicate that for both alloys, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. Moreover, the flow stress, work hardening rate and strain rate sensitivity are higher in the unweldable Al–Sc alloy than in the weldable alloy. In both alloys, the activation volume is dominated by a thermally activated mechanism and increases as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. In describing the plastic deformation behaviour of the two Al–Sc alloys using the Zerilli–Armstrong fcc constitutive model, the error between the predicted flow stress and the measured stress is found to be <5%. The scanning electron microscopy observations reveal that the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of a ductile fracture mode. The dimple like structures on the fracture surfaces of the unweldable Al–Sc alloy are shallower than those on the fracture surfaces of the weldable Al–Sc alloy, which indicates that the weldable Al–Sc alloy has a better ductility than the unweldable Al–Sc alloy. The transmission electron microscopy images show that the microstructures of the two alloys contain different types of precipitates. Specifically, the unweldable Al–Sc alloy contains both Al3Sc and Al2Cu particles, whereas the weldable Al–Sc alloy contains Al3Sc precipitates only. These particles prevent dislocation motion, and therefore prompt a significant strengthening effect. The transmission electron microscopy observations also reveal that in both alloys, the dislocation density increases with increasing strain rate, but decreases with increasing temperature. Furthermore, it is found that the dislocation density of the unweldable Al–Sc alloy is higher than that of the weldable Al–Sc alloy. In other words, the dislocation cells in the unweldable Al–Sc alloy are smaller than those in the weldable Al–Sc alloy. Thus, it is inferred that the unweldable Al–Sc alloy has a higher flow stress than the weldable Al–Sc alloy.

Strain rate and temperature effects on dynamic properties of high-strength weldable aluminum-scandium alloy

The dynamic mechanical behavior, fracture characteristics, and microstructural evolution of high-strength weldable aluminum-scandium (Al–Sc) alloy were investigated using a compressive split Hopkinson pressure bar at strain rates of 1.3 × 103, 3.6 × 103, and 5.9 × 103 s−1, respectively, and temperatures of −100, 25, and 300 °C. The results showed that the flow stress, work hardening rate, and strain rate sensitivity increase with increasing strain rate but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Moreover, the fracture strain decreases with increasing strain rate and decreasing temperature. It was shown that the Zerilli–Armstrong face-centered-cubic (fcc) constitutive equation provides accurate predictions of the mechanical response of the Al–Sc alloy under the considered strain rate and temperature conditions. Scanning electron microscopy observations revealed that the fracture surfaces of the impacted specimens are characterized by transgranular dimpled features, which are indicative of a ductile failure mode. Moreover, transmission electron microscopy observations indicated the presence of both fine and coarse randomly dispersed precipitates within the matrix and at the grain boundaries. It was found that an increasing strain rate reduces the size of the dislocation cells within the impacted Al–Sc microstructure and therefore increases the dislocation density. However, at higher temperatures, the dislocations are annihilated, leading to a reduction in the dislocation density and a corresponding increase in the dislocation cell size. The variations observed in the size and density of the dislocation cells were found to be consistent with the dynamic tendencies noted in the stress–strain response of the Al–Sc alloy.

SHPB圧縮実験法標準化案の提示とその問題点

The standardization of the split Hopkinson pressure bar compression test is attempted to determine stress-strain curves at high constant strain rates, say 1000 s-1, for four types of sheet metal specimen under conditions of uniaxial stress using an extrapolation method. The extrapolation method which is a variant of the well-known Cook and Larke extrapolation method has been established for determining curves of dynamic resistance to homogeneous deformation, i.e., intrinsic stress-strain curves. We use laminated circular plate specimens with four initial ratios of constant diameter to height that is equal to the thickness multiplied by the number of the plate laminated. It is also shown that one of eight striker bars with different kinds of tapered cylindrical shapes enables constant strain rate testing throughout the deformation of specimens. The analysis of the experimental results is conducted as follows: First, the mean stress containing friction effects are graphed against strain. Secondly, curves are cross-plotted with the mean stress as the ordinate and current diameter/height (d/h) ratio as the abscissa for various strains. The extrapolation of a curve back to zero d/h in the figure is expected to be the intrinsic flow stress free of the effect of friction.

Hybrid composites under high strain rate compressive loading

Hybrid composites consist of two or more types of fibres and/or matrices in a composite. By combining two or more types of fibres, it is possible to club advantages of both the fibres while simultaneously mitigating their less desirable qualities. Investigations on high strain-rate behaviour of a typical hybrid composite under compressive loading are presented. The hybrid composite is made using satin weave carbon and plain weave E-glass with epoxy resin. Studies were also carried out on satin weave carbon/epoxy and plain weave E-glass/epoxy. Compressive split Hopkinson pressure bar (SHPB) apparatus was used for the studies. Compressive properties were evaluated along all the three principal directions in the strain-rate range of 546–1503 s −1. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. The explanation for this is provided based on stress wave attenuation studies.

Impact mechanical response and microstructural evolution of Ti alloy under various temperatures

A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of a Ti alloy (Ti–1.1Mo–5.2Zr–2.9Al–0.35Fe–0.05N–0.20 O–0.02H in wt.%) deformed at strain rates ranging from 8 × 10 2 s −1 to 8 × 10 3 s −1 and temperatures between 25 °C and 900 °C. In general, the results indicate that the mechanical behaviour and microstructural evolution of the alloy are highly sensitive to both the strain rate and the temperature conditions. The flow stress curves are found to include both a work-hardening region and a work-softening region. The strain rate sensitivity parameter, β, increases with increasing strain and strain rate, but decreases with increasing temperature. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result primarily of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. Correlating the mechanical properties of the current Ti alloy with the TEM observations, it is concluded that the precipitation of α phase dominates the fracture strain. TEM observations reveal that the amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions.

Impact Response and Microstructural Evolution of Biomedical Titanium Alloy under Various Temperatures

A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behavior and microstructural evolution of biomedical Ti alloy deformed at strain rates ranging from 8 × 102 s−1 to 8 × 103 s−1 at temperatures between 25 °C and 900 °C. In general, the results indicate that the mechanical behavior and microstructural evolution of the alloy are highly sensitive to both the strain rate and the temperature conditions. The flow-stress curves are found to include both a work-hardening region and a work-softening region. The strain-rate-sensitivity parameter, β, increases with increasing strain and strain rate but decreases with increasing temperature. The activation energy varies inversely with the flow stress and has a low value at high deformation strain rates and low temperatures. Microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result primarily of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. Correlating the mechanical properties of the biomedical Ti alloy with the TEM observations, it is inferred that the precipitation of α phase dominates the fracture strain. Transmission electron microscope observations reveal that the amount of α phase increases with increasing temperature below the β-transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain observed under the current loading conditions.

The strain rate and temperature dependence of microstructural evolution of Ti–15Mo–5Zr–3Al alloy

A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 102 s−1 to 8 × 103 s−1 and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions.

Effects of strain rate and temperature on mechanical behaviour of Ti–15Mo–5Zr–3Al alloy

This study uses the compressive split-Hopkinson pressure bar to investigate the mechanical behaviour of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8×10 2 to 8×10 3 s −1 and temperatures between 298 and 1173 K. The results indicate that the mechanical behaviour of the alloy is highly sensitive to both the strain rate and the temperature. The flow stress curves are found to include a work hardening region and a work softening region. The strain rate sensitivity parameter, m , increases with increasing strain and strain rate, but decreases with increasing temperature. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. Correlating the mechanical properties of the Ti alloy with the transmission electron microscope (TEM) observations, it is concluded that the precipitation of α phase dominates the fracture strain. TEM observations reveal that the amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 973 K and results in the minimum fracture strain observed under the current loading conditions.