Split Hopkinson Pressure Bar System Research Articles

The investigation on Johnson-Cook model and dynamic mechanical behaviors of ultra-high strength steel M54

Ultra-high strength steel M54 has been considered as promising candidates for structural applications in spacecraft and aircraft, because of its excellent static and dynamic characteristics. Numerical simulation is widely accepted as an effective way to help understand the dynamic response to structures under impact loadings. In this study, the Johnson-Cook (J-C) constitutive parameters and failure parameters used in ANSYS were accurately determined by fitting static and dynamic experimental data. Based on the obtained experimental results, the good combination of ultra-high strength and good elongation under quasi-static condition was ascribed to its special chemical composition, the microstructure of ultrafine lath martensite with high dislocation density, ultra-high martensite content, uniform distribution of nano-sized M2C carbides and the existence of reverted austenite films. The dynamic compressive properties at high strain rates were investigated systematically by split Hopkinson pressure bar (SHPB) system. A remarkable strain rate strengthening effect came into evident on flow stress of the steel. The dynamic strengthening mechanisms were considered as fine-grain strengthening, substructure strengthening, and dislocation strengthening. Also, adiabatic shear behaviors of the steel under dynamic compressive tests were investigated. The results demonstrated that the strain rate was a key basis to judge stability of the M54 steel under impact loading. Recrystallization mechanism was responsible for the appearance of fine equiaxed grains within adiabatic shear bands (ASBs). The evolution of the ASBs was simultaneously revealed. The obtained experimental results and established J-C constitutive model could enhance the scientific understanding of dynamic mechanical behaviors of the M54 steel and provide reliable constitutive parameters for better guiding relevant engineering applications.

Temperature effect on dynamic compression performance of random fibrous composites in the TTT and IP directions

This study examines the effect of temperature on the dynamic compressive performance of random fibrous (RF) composites at temperatures up to 1273 K in the through-the-thickness (TTT) and the in-plane (IP) directions, using an improved high-temperature split Hopkinson pressure bar (SHPB) system. The results revealed that in the IP direction, the RF composite presented a shear fracture mode below 1073 K and initiated multiple major cracks in the specimens at 1273 K. However, the composite showed a layered fracture mode in the TTT direction from 288 to 1273 K. The dynamic strength in both directions showed a consistent trend when observed under static loading below the critical temperature. The change in the strain-rate sensitivity (SRS) of the dynamic strength was insignificant for temperatures below the transition temperature of viscous-flow and brittle deformation of the RF composite. However, above the transition temperature, the SRS of the dynamic strength became significant.

High strain-rate compression behavior of polymeric rod and plate Kelvin lattice structures

The compressive high strain-rate behavior of polymeric Kelvin lattice structures with rod-based or plate-based unit cells was investigated through experimental techniques and finite element simulations. Polymeric lattice structures with 5x5x5 unit cell geometries were manufactured on the millimeter scale using vat polymerization additive manufacturing and tested at low (0.001/s) and high (1000/s) strain-rates. High strain-rate experiments were performed and validated for a viscoelastic split-Hopkinson (Kolsky) pressure bar system (SHPB) coupled with high-speed imaging and digital image correlation (DIC). Experimental results at both low and high strain-rates show the formation of a localized deformation band which was more prevalent in low relative density specimens and low strain-rate experiments. Strain-rate effects of lattice specimens strongly correlate with effects of the base polymer material; both bulk polymer and lattice specimen demonstrated strain-rate hardening, strain-rate stiffening, and decreased fracture strain under dynamic loading. Results show mechanical failure properties and energy absorption depended strongly on the relative density of the lattice specimen and exhibited distinct scaling between relative density and geometry type (rod, plate) and loading rate. High relative density plate-lattices demonstrated inferior mechanical properties to rod-lattices; however, there exists a critical relative density for a given mechanical property (17%–28%) below which plate-lattices outperform rod-lattices of similar mass. High strain-rate explicit finite element simulations were performed and showed good agreement with the mechanical failure trends and deformation modes observed in the experiments.

Study on the effects of joints orientation and strength on failure behavior in shale specimen under impact loads

As an anisotropic and jointed material, shale has been extensively investigated due to the rich unconventional gas reserved in the shale rock mass. In the process of hydraulic fracturing in jointed shale, joints may significantly affect hydraulic crack behavior under dynamic disturbance loads, such as crack propagation direction, speed and distance, which has a great effect on the efficiency of hydraulic fracturing and gas production. Therefore, it is of great significance to study crack dynamic propagation characteristics in shale with different orientation joints and dynamic strength. Impacting experiments were conducted on the single cleavage triangle (SCT) shale specimens with joint orientation 0°, 30°, 45°, 60° and 90°, respectively. A modified split Hopkinson pressure bar (SHPB) system was applied and AUTODYN code was used to simulate crack dynamic fracture behavior. For the case of a single joint and multiple parallel joints, crack propagation directions and trajectories were numerically analyzed. The experimental and numerical results indicate that joints have a great influence on crack dynamic propagation direction. In addition, the crack propagation speed of shale is positively related to the loading rate under dynamic loads. If joints are considered as thin layer material, dynamic tensile strength and elastic modulus of joints have a great effect on dynamic crack propagation behavior under impact loads.

A modified triaxial split Hopkinson pressure bar (SHPB) system for quantifying the dynamic compressive response of porous rocks subjected to coupled hydraulic-mechanical loading

A modified triaxial split Hopkinson pressure bar (SHPB) system for quantifying the dynamic compressive response of porous rocks subjected to coupled hydraulic-mechanical loading

Experimental Study on Dynamic Mechanical Properties and Fracturing Behavior of Granite CSTFBD Specimens in SHPB Tests

Abstract The purpose of this paper is to study the dynamic fracture mechanics characteristics and fracturing behavior of cracked-straight-through flattened Brazilian disk specimens using the Split Hopkinson Pressure bar system. The researchers also used Particle Flow Code 2D for simulating the crack process and achieved consistent outcomes. In this experiment, rock specimens were made from Beijing Fangshan granite. The results of the experiment determined the effects of impact pressures and loading angles on the crack mode and mechanical properties of the specimens. These specimens have attained the stress equilibrium state prior to failure. With greater impact pressure, there will be faster changes in the corresponding equivalent tensile stress, while the peak value remains relatively high under the same loading angle. With different loading angles, the change rate of the equivalent tensile stress remains the same; however, the time required to reach the maximum stress becomes different. For a 30° loading angle, the energy dissipation ratio in accordance with the same impact pressure is lower than compared to that of a 0° loading angle. In this experiment, several cracks have been produced under a different range of impact pressures and loading angles, which can be classified into six types. They include two types of tensile cracks, shear cracks, and tensile-shear cracks. At a 0° loading angle, mode I fracture occurs, and at 15° and 30° loading angles, a mixed-mode I-II fracture occurs on the specimen. Furthermore, triangular fracture zones occur on the two end faces of the specimens under the loading force due to the concentration of local stress during the force process.

Strain characteristics and energy dissipation laws of gas-bearing coal during impact fracture process

To reveal fracture mechanism of gas-bearing coal subjected to complex geology environment, the impact dynamics experiments were conducted to study energy characteristics based on split Hopkinson pressure bar (SHPB) system. The incident, reflected and transmission strain were collected to calculate various energy. It was found reflected strain was always larger than transmission strain. Therefore, the reflected energy was generally higher than transmission energy under different loading conditions, but they were smaller than incident energy. With time evolution, both elastic deformation and dissipative energy experienced slow increase, rapid increase, peak point and decrease stage regardless of loading conditions. Before macro failure, micro-meso fractures had changed drasticly, which also involved intense energy conversion. So dissipative energy peak was earlier than that of elastic deformation energy. Due to pre-damage of static load and weakening effects of gas, the dissipative energy decreased with their increases (static load from 2.00 to 9.00 MPa and gas pressure from 0.25 to 1.50 MPa) during impact fracture process. However, at high confining pressure and dynamic load environment, the impact failure of gas-bearing coal exhausted massive energy. These energy characteristics will provide guidances to prevent and control disaster during coal mining and coal seam gas (CSG) exploitation in deep area.

Experimental Investigation on the Energy Properties and Failure Process of Thermal Shock Treated Sandstone Subjected to Coupled Dynamic and Static Loads

Thermal shock (TS) is known as the process where fractures are generated when rocks go through sudden temperature changes. In the field of deep rock engineering, the rock mass can be subjected to the TS process in various circumstances. To study the influence of TS on the mechanical behaviors of rock, sandstone specimens are heated at different high temperatures and three cooling methods (stove cooling, air cooling, and freezer cooling) are adopted to provide different cooling rates. The coupled dynamic and static loading tests are performed on the heated sandstone through a modified split Hopkinson pressure bar (SHPB) system. The influence of heating level and cooling rate on the dynamic compressive strength, energy dissipations, and fracturing characteristics is investigated based on the experimental data. The development of the microcracks of the sandstone specimens after the experiment is analyzed utilizing a scanning electron microscope (SEM). The extent of the development of the microcracks serves to explain the variation pattern of the mechanical responses and energy dissipations of the specimens obtained from the loading test. The findings of this study are valuable for practices in rock engineering involving high temperature and fast cooling.

Deformation and Failure Properties of High-Ni Lithium-Ion Battery under Axial Loads.

To explore the failure modes of high-Ni batteries under different axial loads, quasi-static compression and dynamic impact tests were carried out. The characteristics of voltage, load, and temperature of a battery cell with different states of charge (SOCs) were investigated in quasi-static tests. The mechanical response and safety performance of lithium-ion batteries subjected to axial shock wave impact load were also investigated by using a split Hopkinson pressure bar (SHPB) system. Different failure modes of the battery were identified. Under quasi-static axial compression, the intensity of thermal runaway becomes more severe with the increase in SOC and loading speed, and the time for lithium-ion batteries to reach complete failure decreases with the increase in SOC. In comparison, under dynamic SHPB experiments, an internal short circuit occurred after impact, but no violent thermal runaway was observed.

Influence of bedding anisotropy on the dynamic fracture behavior of layered phyllite

Layered phyllite, a typical anisotropic rock caused by the existence of beddings, is common in rock engineering. To evaluate the influence of beddings and loading rates on the dynamic fracture behavior of layered phyllite, notched semicircular bending (NSCB) specimens were measured using a split-Hopkinson pressure bar (SHPB) system. Static fracture testing using a servo-controlled material testing system was also conducted for comparison. The results of this study indicate that three typical fracture paths can be found for NSCB specimens under both static loading and dynamic loading. The fracture path evidently exhibits dependence on the loading rate. For specimens under static loading, dominated fractures are more likely to propagate along the bedding planes while the dominated fractures tend to ignore bedding planes as the loading velocity increases. Consequently, the fracture length ratio along the bedding plane is considerably lower under dynamic loading than under static loading. Anisotropic effects on static and dynamic fracture toughness are evident; however, the anisotropy of fracture toughness decreases as impact velocity increases. The results of this study confirm that a reduced fracture length ratio along the bedding plane induced by an increase in loading rate weakens the dependence of dynamic fracture toughness on anisotropy.

Effect of microwave treatment on the thermal properties and dynamic splitting behavior of red sandstone

Microwave energy is a promising application in future rock breakage operations in the civil, mining, processing, and space industries. Rock engineering projects frequently experience mechanical vibration and blasting impacts. Thus, understanding the dynamic fracturing behavior of microwave-treated rock is essential for its future application in microwave-assisted mechanical rock breakage. A customized industrial microwave system with a multimode resonant cavity was used to heat red sandstone at different microwave power levels (up to 4 kW) for a constant exposure time (4 min). The rock surface temperature distribution after microwave treatment was measured by an infrared camera. Dynamic splitting tests were conducted using a split Hopkinson pressure bar (SHPB) system in combination with a high-speed camera. Experimental results indicate that the rock dynamic splitting strength is negatively related to the microwave power, and the maximum reduction is 47.8%. Microwave treatment induced an obvious nonuniform temperature distribution and C-shaped surface cracks on disc specimens. During the dynamic splitting test, the crack induced by dynamic loading always initiates from the crack tip induced by microwave irradiation and then propagates along the loading diameter. The distribution of the inner high-temperature zone in the disc specimen is symmetric along the horizontal centerline of the disc specimen.

Experimental study on dynamic notch fracture toughness of V-notched rock specimens under impact loads

In this study, the dynamic notch fracture toughness of V-notched rock specimens was investigated. V-notched semicircular bend specimens made of a medium-grained granitic rock called Fangshan granite were subjected to tests using a split Hopkinson pressure bar (SHPB) system combined with an ultrahigh-speed camera. First, an empirical formula was derived using dimensional analysis to calculate the fracture parameters of sharp V-notches, and the dynamic notch fracture toughness was calculated using dynamic forces obtained from the SHPB tests and the empirical formula. Second, full-field displacement fields generated during the dynamic fracture process were measured using the digital image correlation (DIC) method, and the notch fracture toughness was extracted using the displacement fields at the V-notch tip. Third, the experimental results obtained using the empirical formula were compared with the DIC results and subsequently validated using a modified mean stress criterion. The proposed methods have significant applications in the fracture assessment of rock structures weakened by notches.

The numerical simulation of large diameter split Hopkinson pressure bar and Hopkinson bundle bar of concrete based on mesoscopic model

In the comparison of Hopkinson bundle bar (HBB) system and the large diameter split Hopkinson pressure bar (SHPB) system, the influence of bar diameter on the dispersion effect of the one-dimensional longitudinal wave is analyzed theoretically firstly. Three trapezoidal loads with different peak values are applied to the elastic bars with two types of sections to investigate the stress wave propagation. Then, based on the fractal characteristics of concrete aggregate, the 3D realistic mesoscopic model is constructed as numerical models. And the dynamic responses of concrete under two kinds of test systems have been compared and analyzed. The results show that, the HBB system can more effectively reduce the lateral dispersion in the stress wave propagation and is beneficial to maintain the waveform than the large diameter SHPB system. The large diameter SHPB simulated results based on the 3D realistic mesoscopic model are consistent with the experimental results, which verify the feasibility of the mesoscopic model. The HBB system can obtain the similar simulated results as the large diameter SHPB system, such as the similar waveform with the double peak phenomenon of the reflection wave. However, there is a significant difference in the failure pattern of the specimens under two test systems, which is caused by the boundary effect of the hexahedron specimen in the HBB system. In conclusion, the HBB system can also carry out the dynamic mechanical properties of concrete-like materials. Moreover, HBB system can obtain more detailed information, reflecting the difference of local mechanical properties of concrete. Although there are still some deficiencies, it can still provide additional ideas for related researchers.

Experimental and Numerical Investigation on the Dynamic Failure Envelope and Cracking Mechanism of Precompressed Rock under Compression-Shear Loads

The complex response of underground geomaterials subjected to dynamic disturbance arises from the microstructure redistribution under high in- situ stress and the resulting fracture behaviors at multiaxial stress states. Inclined specimens were employed in an axially constrained split Hopkinson pressure bar (SHPB) system to achieve a combination of compression-shear stress states and static-dynamic loads. The loading rate under investigation ranged from 500 to 4,000 GPa/s, along with the axial prestress of 7, 21, 35, 49, and 63 MPa on specimens with an inclination of 0°, 3°, 5°, and 7°. The modified SHPB experimentation and discrete-element method modeling were implemented to unravel the combined effects of the loading rate, preload, and stress path on the failure mechanism of sandstone specimens involving the failure strength and envelope, fracturing pattern, fragmentation, and microcracking process. The positive rate dependence of the failure strength and Drucker–Prager envelope was observed. The preload showed double effects on the failure strength, indicated by an upper bound of the failure envelope as it expanded with the increasing preload. The microdamage accumulated during preloading and the global stress field collectively influenced the failure pattern of the inclined specimen, altering from a shear fracturing mode under dynamic loading or high-preload static-dynamic loading to an axial splitting mode near the specimen surface under low-preload static-dynamic loading.

High-Temperature Compressive Response of SiCp/6092Al Composites under a Wide Range of Strain Rates.

The high-temperature dynamic compressive properties of a 30 vol.% SiCp/6092Al composite, fabricated using powder metallurgy, were experimentally investigated using the split Hopkinson pressure bar system with an electric furnace. Three different ambient temperatures, namely, room temperature, 200 °C, and 350 °C, were adopted, and the dynamic tests of the composite specimens were conducted at strain rates ranging from 1500 to 4500 s−1. The experimental results showed that the flow stress of the composite was generally insensitive to strain rates at room temperature. However, the composite started exhibiting different strain-rate-dependent behaviors as the temperature increased, and the flow stress nonlinearly varied with increasing temperature. In addition, the microscopic images of the specimens showed that the microscopic failure mechanisms of the composite were greatly influenced by the ambient temperature and strain rate. Specifically, the percentage of failed particles decreased with rising temperature and the dominating failure mode of particles changed significantly as the strain rate increased.

Experimental and numerical investigation of model I dynamic fracture toughness of 95W-3.5Ni-1.5Fe alloy using the semi-circular bend specimens

Semi-circular bend specimens are used to measure the brittle materials' fracture toughness, such as brittle metals, rocks, and ceramic materials. The quasi-static and dynamic model I fracture toughness of tungsten heavy alloy, a typical brittle metal material, are measured using the semi-circular bend specimens under quasi-static compression and dynamic impact loadings. For quasi-static cases, the specimens are loaded on a universal testing machine with a constant loading speed. While for dynamic cases, the specimens are executed on a modified split Hopkinson pressure bar system with the impact pressures from 0.2 to 0.4 MPa. The results show that the dynamic fracture toughness of tungsten alloy increases with the increase of the loading rate. Further, a rate-dependent bilinear traction-separation law is introduced to explain the dynamic fracture behaviors of tungsten alloy. The parameters of the rate-dependent law are obtained from the experiments and the finite element simulations. Finally, the dynamic simi-circular bend simulations using the cohesive element with rate-dependent cohesive law are established to simulate the crack propagation, and the simulation results are in good agreement with the test data.

SHPB experimental method for ultra-soft materials in solution environment

Biological soft tissues usually perform physiological functions in solutions, and the mechanical properties of the bio-soft matters in air and solution may differ from that in solution, but the measurement technique of the dynamic mechanical properties of ultra-soft materials in solution is still an unexplored realm. In order to develop a feasible method to test ultra-soft materials in solution by the split Hopkinson pressure bar (SHPB) technique, this paper uses the liquid silicone rubber (LSR) whose property is seldom affected by water and the purified water as a testing material and a solution, respectively. The double-striker electromagnetic driving SHPB system, which has been designed for ultra-soft materials, is adopted to carry out dynamic test for LSR in solution, meanwhile the testing process was recorded by a high-speed digital camera. The tests include three cases named as: Specimen in air, No specimen in water, Specimen in water. Specimen in air was set as a reference; No specimen in water was used to learn the mechanism of load transferring of the water and to set the correction of the effect of the water; Specimen in water was the standard test in water whose results must be modified for the characterization of materials. The high-speed images show that the water may be regarded as a steady flow until the constant strain rate loading ended. Based on such phenomenon and the unchanged volume of specimen and by simplifying the description of the flow field, a data correcting method was set up on the basis of the deduction of both the specimen deformation and fluid flow field to modify the experimental result tested in water. According to the comparison, experimental result in air shows good agreement with corrected result in solution, indicating the feasibility of our recommended method for the SHPB tests in solution. In this way, our research is of great significance in laying an important foundation in the new academic field of the dynamic mechanical behaviors of bio-soft matters in solution.

Influence of geometric parameters of surface electrode on electromechanical response of PDMS under impact loading

In order to clarify the electromechanical coupling characteristics of polymer materials and extend their applications in MEMS (Micro-electromechanical Systems), electromechanical responses of PDMS (Polydimethylsiloxane) with different electrodes and thicknesses under different loading conditions have been performed experimentally and numerically. Basic electrical parameters measurement and quasi-static tensile experiment of PDMS specimens were conducted. Furthermore, the dynamic mechanical properties and polarization voltage of PDMS with different electrodes and thicknesses under different loading conditions have been studied by Split Hopkinson Pressure Bar (SHPB) system integrating with electrical output measuring system. Beyond that, Abaqus/Explicit numerical simulation of PDMS specimen under different loading conditions was carried out based on Yeoh viscoelastic model and Prony series, then the strain gradient and the flexoelectric coefficients were obtained. The results show that the maximum stress of PDMS increases with increasing of loading speed and decreases with increasing of thickness, the maximum polarization voltage increases with increasing of strain rate, the maximum polarization voltages of PDMS with “C” electrode and “+” electrode are about 14 times of that with circular electrode, the flexoelectric coefficients of PDMS are within the range of 10−11–10−9C/m.

Dynamic mechanical properties and microstructure evolution of AlCoCrFeNi2.1 eutectic high-entropy alloy at different temperatures

The dynamic mechanical properties of the AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) fabricated by drop-casting (DC) and suction-assisted casting (SC) are investigated under different strain rates and temperatures using Split Hopkinson Pressure Bar (SHPB) system. Microstructure analysis is conducted through SEM, EBSD and TEM to reveal the deformation and fracture mechanisms of the present EHEA. The yield strength and flow stresses for both the DC alloy and SC alloy increase with increasing strain rate, but decrease with increasing temperature. A mixture of ductile and brittle fracture morphologies exists in both the DC and SC EHEAs. Moreover, the SC alloy displays more shear dimples on the fracture surface, while brittle fracture features become dominant for the DC alloy. Abundant accumulation of dislocations in the quasi-static test produces slip traces in the FCC lamellar phase which further enhances the plasticity of the SC alloy. Meanwhile, the dislocation cells formed by high-density dislocation tangles at high strain rates, leading to apparent work hardening and strain rate sensitivity of the SC alloy. The adiabatic shear band (ASB) forms in the SC alloy before shear failure and the adjacent twisted and curved lamellar structures play a significant role in preventing shear localization. Overall, the SC alloy exhibits a stronger strain rate effect and better ductility than the DC alloy.

Laser-based additively manufactured bio-inspired crashworthy structure: Energy absorption and collapse behaviour under static and dynamic loadings

The progress of additive manufacturing (AM) technique broadens the conceivement and adoption of new types of lattice structures effectively. A new lattice structure, drawing on inspiration from nature, was developed and manufactured via selective laser melting (SLM) to explore the effects of printing parameters on densification and mechanical performance. Compressive experiments were conducted by universal testing machine and Split Hopkinson Pressure Bar (SHPB) system to assess energy absorption and collapse behaviour of bio-inspired structures subjected to static and dynamic load. Each deformation evolution was captured and the digital image correlation (DIC) method was adopted to analyze the strain distribution in the compressive process. The observations reveal that the bio-inspired structure possesses a steady deformation mode under static and dynamic loading, which exhibits a promising prospect for impact resistant applications. Furthermore, energy absorption of this bio-inspired structure displayed some sensitiveness to the rate of strain. Finally, finite element analysis based on Johnson-Cook constitutive model was performed as well to simulate the static and dynamic response of the bio-inspired structure. The finite element outcomes remarkably coincide with the outcomes of experiments.