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In this paper, a Zr–5W alloy was fabricated via casting. In order to obtain the mechanical properties of the material, quasi-static compression tests at room temperature and split Hopkinson pressure bar tests at various temperatures were carried out. The x-ray diffraction result showed that the main components of the alloy were αZr and W2Zr, where αZr is the matrix and W2Zr is the reinforcement. The metallographic characterization results showed that there were two main forms of W2Zr in the material, namely, large particle boundary and small diffuse submicrometer precipitates. The reinforcements of both distributions have the effect of increasing the strength of the material, but the small submicrometer W2Zr precipitates would cause microcrack nucleation during the late plastic deformation stage, resulting in damage softening. In order to make theoretical calculations of the mechanical properties of materials, the Johnson–Cook (JC) constitutive model and Zerilli–Armstrong (ZAM) constitutive model of the material were obtained. It was found that the JC constitutive model had poor consistency in describing material properties. Although the consistency of the ZAM constitutive model was higher than that of the JC constitutive model, it still had obvious shortcomings. Combined with the deformation mechanism of the alloy, a modified constitutive relation was established by adding damage softening terms based on the hexagonal close-packed metal constitutive model inferred by the kinetics of heat-activated dislocations. The relative error results of all working conditions show that the correlation consistency of the improved constitutive model in this paper is significantly better than that of JC constitutive and ZAM constitutive. [ABSTRACT FROM AUTHOR]

A promising solution to reduce energy usage and mitigate the wear of drilling and comminution tools during mining operations involves inducing vibrations within the piezoelectric phases dispersed in the structure of rocks using alternating current (AC). This paper presents experimental evidence of AC-induced weakening of Kuru granite, manifested as improvements in rock drillability and reductions of strength. Sievers' J-miniature drill tests were used to assess surface drillability. The impact of AC treatment on the quasi-static strength of granite was assessed via three-point bending and indirect tension Brazilian disk tests. The influence of AC treatment on the dynamic tensile strength of the rock was determined using split Hopkinson bar tests, with the fragmentation process captured using in situ ultra-fast synchrotron X-ray phase contrast imaging. The quasi-static tests revealed no reduction in rock strength after the AC treatment. In contrast, reductions of 25% in hardness and 18% in dynamic tensile strength were observed. Fragmentation patterns differed between treated and non-treated rocks, with treated specimens exhibiting reduced macrocrack formation during loading. Highlights: Diverse experiments confirm that alternating current excitations weaken Granite. Sievers' J-tests evidenced enhanced drillability of Granite after the alternating current treatment. Exposure to alternating currents decreased the tensile strength of Granite in dynamic Brazilian disc experiments. Treated Brazilian disc specimens showed lower energy absorption during dynamic loading. Synchrotron X-ray phase contrast images revealed reduced crack branching of treated granite specimens during dynamic loading. [ABSTRACT FROM AUTHOR]

Self-compacting concrete (SCC) is widely used in reinforced concrete buildings, owing to its ability to consolidate by weight and its lack of requirement for external vibration. Reinforced concrete buildings can be subjected to high strain rate loading during the early days of construction or in their service life. Thus, it is critical to understand the behaviour of concrete under high strain rate loadings at different ages. Minimal studies have previously focused on the early-age behaviour of concrete under high strain rates. This study tries to fill this gap. It focuses on the behaviour of M40 grade SCC under three levels of strain rate loading at ages of 1, 3, 7, 14 and 28 d. The split-Hopkinson pressure bar (SHPB) was used to test 45 SCC specimens of diameter 100 m and thickness 50 mm at high strain rates, ranging from 30 s−1 to 110 s−1, and the determined compressive strength, peak strain and elastic modulus results are compared with quasistatic test results of SCC specimens. The dynamic increase factor (DIF) determined in the SHPB experiment is compared with the CEB-fib code model. The results indicate that the DIF reduces as the concrete's strength and age increase. [ABSTRACT FROM AUTHOR]

The thermo-mechanical stress, which was a combination of thermal stress from rapid temperature changed and dynamic mechanical stress from scrap impact, accelerated the damage to MgO–C refractories during service. The influence of graphite content (8 wt% and 16 wt%), heat treatment temperature, and oxidation level (partially oxidized or not) on dynamic mechanical stress damage behavior was investigated using the Split-Hopkinson pressure bar test at various loading velocities. The results indicated the SHPB test could form dynamic stress, and the parameters obtained post-test could characterize the dynamic mechanical properties of MgO–C refractories. Furthermore, all of the specimens' dynamic compressive strength clearly demonstrated the strain rate hardening effect; this phenomenon was particularly evident in the low-graphite specimens. Additionally, the thermally treated specimens dissipated impact energy by destroying the whole volume, whereas the oxidized specimens suffered damage layer by layer, and the specimens' dynamic mechanical characteristics were weakened by oxidization or heat treatment. [ABSTRACT FROM AUTHOR]

Microcapsule-based self-healing concrete (MSC) has been widely studied, with a focus on static behavior and self-healing effectiveness. However, the dynamic mechanical properties of MSC have rarely been studied. This study presents a mesoscale numerical investigation of the dynamic compressive behavior of MSC under impact loading. In mesoscale, MSC is regarded as a four-phase composite material mainly composed of coarse aggregates, interface transition zones, cement mortar, and microcapsules. A pseudo 3D numerical model is constructed by combining a slice of a detailed mesoscale model with a homogenous 3D model. The mesoscale MSC slice models with different mass fractions of microcapsules (0%, 2%, 5%, and 8%) are constructed. Different coarse aggregate shapes (i.e., circles, ellipses, and polygons) are considered. The uniaxial dynamic compressive behaviors of MSC materials under loads of different strain rates are numerically simulated and compared with those from split Hopkinson pressure bar tests previously done by the authors. The comparison results show that the present mesoscale model can accurately predict the compressive strength and failure mode of MSC. The effects of the microcapsules ratio and strain rate on the dynamic strength are studied. Results show that the MSC compressive strength decreases with the increase in microcapsules and increases with the increase in strain rate. The dynamic increase factor (DIF) of the specimen is jointly contributed by the material DIF, inertial constraints, and heterogeneity. Different aggregate shapes have little effect on the simulation results of MSC behavior. The obtained dynamic mechanical properties of MSC may assist in designing MSC to resist collisions or explosions. [ABSTRACT FROM AUTHOR]

The development of electronic fuze has placed higher demands on encapsulation resins, which are required to provide not only insulation and protection, but also higher impact resistance and good electromagnetic shielding performance. A new composite material consisting of hollow glass microspheres (HGM) and modified epoxy resin was developed. This material exhibits significant electromagnetic shielding capabilities for terahertz (THz) waves, as well as superior impact energy absorption properties. Bisphenol A‐type epoxy resin (E‐44) was modified using Al(OH)3, red phosphorus, carbon black, and SiO2, and the material properties were optimized by adjusting the HGM content. The electromagnetic shielding effectiveness and impact energy absorption of the composite material in the THz band were comprehensively tested using THz time‐domain spectroscopy and split Hopkinson pressure bar testing systems. Additionally, a comprehensive evaluation of the mechanical and dielectric properties, thermal conductivity, and thermal stability of the material was conducted. The results showed that the electromagnetic shielding effect of 60 vol.% HGM hybrid‐modified resins was the best, reaching 43.78 dB. The 20 vol.% HGM hybrid‐modified resins not only has a specific absorption energy of 18.51 J/cm3, but also has the best overall performance. This work has advanced the design and development of multifunctional and impact‐resistant potting epoxy resins. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are widely utilized in aerospace, medical devices, and automotive industries, renowned for their superior mechanical properties and high-temperature resistance. Despite these advantages, the thermomechanical coupling behavior of CF/PEEK under dynamic loading conditions is not well understood. This study aims to explore the thermomechanical coupling effects of CF/PEEK at elevated strain rates, employing Hopkinson bar impact tests and scanning electron microscopy (SEM) for detailed characterization. Our findings indicate that an increase in temperature led to significant reductions in the yield strength, peak stress, and specific energy absorption of CF/PEEK, while fracture strain had no significant effect. For instance, at 200 °C, the yield strength, peak stress, and specific energy absorption decreased by 39%, 37%, and 38%, respectively, compared to their values at 20 °C. Furthermore, as the strain rate increased, the yield strength, peak stress, specific energy absorption, and fracture strain all exhibited strain-hardening effects. However, as the strain rate further increased, above 4000 s−1, the enhancing effect of the strain rate on the yield strength and peak stress gradually diminished. The interaction of the temperature and strain rate significantly affected the mechanical performance of CF/PEEK under high-speed impact conditions. While the strain rate generally enhanced these properties, the strain-hardening effect on the yield strength weakened as the temperature increased, and both the temperature and strain rate contributed to the increase in specific energy absorption. Microdamage mechanism analysis revealed that interface debonding and sliding between the fibers and the matrix were more pronounced under static compression than under dynamic compression, thereby diminishing the efficiency of stress transfer. Additionally, higher temperatures caused the PEEK matrix to soften and exhibit increased viscoelastic behavior, which in turn affected the material's toughness and the mechanisms of stress transfer. These insights hold substantial engineering significance, particularly for the optimization of CF/PEEK composite design and applications in extreme environments. [ABSTRACT FROM AUTHOR]

Highlights The present study investigates the quasi‐static and dynamic mechanical properties of the composite laminates reinforced by flax hybridized with E‐glass and/or carbon fabrics. Epoxy resin was used as the polymeric matrix. Three different hybrid composite laminates were prepared: Glass/flax (HGF), carbon/flax (HCF), and carbon/glass/flax (HCGF) composite laminates. Non‐hybrid flax composite laminate (NHF) was prepared as a reference material. The quasi‐static mechanical properties were investigated by performing tensile and flexural tests. The dynamic mechanical behavior was evaluated using the split Hopkinson pressure bar test and dynamic mechanical analysis technique. The results showed that hybridizing flax with glass and/or carbon fibers significantly enhanced both the quasi‐static and dynamic mechanical properties of the composite system. Due to hybridization, the tensile strength increased from 50.5 MPa for NHF to 71.5, 162, and 107 MPa for HGF, HCF, and HCGF, respectively. Similarly, the flexural strength increased from 33.4 MPa for NHF to 104, 149, and 112 MPa for HGF, HCF, and HCGF, respectively. All the composite laminates showed a strain rate‐dependent behavior when tested using the SHPB test. Moreover, the dynamic compressive strength was substantially improved due to hybridization. DMA results showed that hybridization significantly improved the storage modulus and loss modulus of hybrid composites. Polymer composites reinforced with flax fabric hybridized with glass and/or carbon fabrics were fabricated. The fabricated hybrid composites were subjected to quasi‐static mechanical tests (tensile and flexural) and dynamic mechanical tests (DMA and SHPB). The hybridization approach was effective in improving the static and dynamic mechanical properties of hybrid composites. The static and dynamic behavior of hybrid composites can be tailored by controlling the type of synthetic fibers hybridized with natural ones. [ABSTRACT FROM AUTHOR]

The split-Hopkinson pressure bar technique is widely used to determine the dynamic mechanical behavior of materials. However, spike-like stress features appear in the initial stress behavior of ultra-soft materials tested with a split-Hopkinson bar. These features are not intrinsic characteristics of the materials. Potential causes were investigated through experiments and numerical simulations. It was found that the spike feature represents derived stress resulting from the radial inertia effect during dynamic loading. In this work, we propose and experimentally verify effective methods to reduce this effect. The influences of density, strain acceleration, ratio between inner and outer diameter, and Poisson's ratio on the radial inertia effect were investigated. The spike stress was found to change linearly with density and strain acceleration but decrease significantly when the inner/outer diameter ratio was below 0.3, after which it remained nearly constant. A parabolic stress distribution was observed along the radial direction due to the Poisson effect, especially when the ratio exceeded 0.3, leading to higher spike stress. Finally, suggestions were proposed as experimental guidance when testing ultra-soft materials. [ABSTRACT FROM AUTHOR]

The bar properties (elastic modulus, density, Poisson's ratio, and sound speed) necessary for exploiting bar impact tests were calibrated via two methods called the 1D method (which combines the iterative dispersion correction with 1D approximation) and 3D method (which resorts to the simulation-based reverse engineering of the strain profile in a circular 3D bar). The two methods cross-verified one another for a maraging steel bar with 19.1 mm in diameter. This paper also considers the method of calibrating measured strain and finally presents a method of determining the impact velocity with reference to a reliably measured strain profile for a bar calibrated via the 1D method. [ABSTRACT FROM AUTHOR]

Concrete structures, such as armories, military bunkers, and petrochemical facilities, are susceptible to explosive loads during service. The superior mechanical properties of ultrahigh-performance concrete enable structures built with it to endure explosive loads. This study aims to characterize the behavior of ultrahigh-performance concrete at different ages, namely, 1, 3, 7, 14, and 28 days, at different strain rates. The compressive stress–strain response of ultrahigh-performance concrete is studied at static and high-strain-rate loading. The high-strain-rate response is characterized using a split-Hopkinson pressure bar of 100-mm diameter. The influence of age on strength, dynamic increase factor strain rate, elastic modulus, peak strain, and energy absorption are discussed. When tested at the same striker velocity, the dynamic increase factor and strain rate of ultrahigh-performance concrete of similar specimen size decrease with age. The elastic modulus and energy absorption increase from 1 to 14 days. There is no significant change in these quantities between 14 and 28 days. The strength, elastic modulus, and energy absorption increase with increasing strain rate for all ages. Experimental data are validated using the Tedesco model and current standards for stress, strain, and elastic modulus. The model from the standards overestimates strength, whereas the Tedesco model predicts strength conservatively. [ABSTRACT FROM AUTHOR]

The possibility of increasing the static and dynamic strength of the aluminum-magnesium alloy AMg4.5 is shown by using methods of severe plastic deformation, a combination of annealing and additional deformation of ultrafine grained alloy. The strength properties of the material are evaluated using a structural-temporal approach to the analysis of experimental data on the dynamic tension of small samples obtained on split-Hopkinson pressure bar. [ABSTRACT FROM AUTHOR]

Basalt fibre reactive powder concrete (BFRPC) was prepared by incorporating basalt fibres (BFs) instead of steel fibre into reactive powder concrete. In this study, the impact resistance of BFRPC was experimentally and numerically analysed at different strain rates (101–102 s−1). The 75 mm dia. split-Hopkinson pressure bar was used for impact compression tests and the finite-element software LS- Dyna was used for numerical simulation analysis. The results showed that the high-strength BFRPC has an obvious strain rate effect and the dynamic increase factor (DIF) of compressive strength increases logarithmically with strain rate. Meanwhile, the parameters of the Comité Euro-international du Béton (CEB) model were refitted and the relationship between strain rate and DIF was established. By using the Holmquist–Johnson–Cook material constitutive model (HJC model), the stress–strain curves and failure patterns obtained were consistent with the experimental results. The incorporation of BFs significantly improves the deformation properties of BFRPC. [ABSTRACT FROM AUTHOR]

The effects of different flyash content, steel fibre content and water-binder ratio on the dynamic compressive strength of alkali-activated slag high performance concrete (ASHPC) were studied. When flyash and water-binder ratio rose, the dynamic compressive strength of ASHPC fell by 27.3% and 23.5%, respectively, and increased by 81.6% when steel fibre content increased. The dynamic elastic modulus rises by 35.0% with an increase in steel fibre content and falls by 48.0% and 65.6%, respectively, with an increase in flyash content and water-binder ratio. The toughness conversion ratio and pre-peak toughness ratio dropped by 34.1% and 9.5%, respectively, whereas the post-peak toughness ratio rose by 36.4% with an increase in flyash content. The test block's pre-peak toughness ratio and toughness conversion ratio increased by 12.7% and 60.0%, respectively, with an increase in steel fibre , whereas the post-peak toughness ratio declined by 31.0%. With the increase of water-binder ratio, the pre-peak toughness ratio and toughness conversion rate of the test block increased by 31.0 % and 132 %, respectively, and the post-peak toughness ratio decreased by 42.8 %. The energy absorption and reflection rise while the energy transmission falls as flyash concentration and the water-binder ratio rise. The transmission energy rises as the amount of steel fibre grows, while the energy absorption and reflection fall. [ABSTRACT FROM AUTHOR]

This work explores the dynamic fracture characteristics of recycled tyre polymer (RTP) fibre reinforced concrete after exposure to 20, 105, 250, 400 and 600 °C. Split Hopkinson pressure bar tests were performed to characterize the dynamic compressive properties under strain rates of 40–120 s−1, in terms of the failure mode, strain-stress response, dynamic strength, dynamic increase factor (DIF), peak strain and energy absorption capacity. Results indicate that the failure pattern varies from splitting failure to core failure, and finally to pulverization failure due to strain rate effect, regardless of exposure temperatures. The dynamic strength and DIF are enhanced by strain rate effect but drop by 56.1% and 23.9% at 600 °C, respectively, while no explosive spalling occurs because of the thermal expansion of RTP fibres. The temperature-dependent dynamic fracture mechanism is closely related to the physicochemical reactions in the concrete matrix, bridging or rupture of RTP fibres and breaking of coarse aggregates. [ABSTRACT FROM AUTHOR]

In order to study the brittleness characteristic of the rock failure process, firstly, the brittleness characteristic coefficient of rock is established based on the back–front stage of the stress‐strain curve. Second, the brittleness characteristic coefficient of rocks at high temperatures (T = 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, and 800°C) was obtained by impact compression of the Hopkinson pressure bar test system. Thirdly, the brittleness characteristic coefficient was verified by the microscopic characteristics of the fragments under SEM. Finally, the temperature effect of the brittleness characteristic coefficient was analyzed by the principal component analysis method. The results show that the brittleness failure characteristic coefficient based on the postfrontal phase of the stress‐strain curve can accurately describe the brittleness change characteristics of high‐temperature rock under the Hopkinson shock. The higher the temperature of sandstone, the weaker the brittleness. At the same time, the microstructure of sandstone shows that the failure process is intergranular failure‐intergranular failure + transgranular failure‐transgranular failure, which effectively confirms the change characteristics of the brittleness characteristic coefficient during the failure process of sandstone. Using principal component analysis, it is found that the main internal factors for the change of the brittleness characteristic coefficient of sandstone are the deformation of brittle feldspar under heat and the energy dissipation of sandstone influenced by the thermal expansion of quartz. [ABSTRACT FROM AUTHOR]

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An experimental design method is proposed to guide the selection of specimen dimension and split Hopkinson pressure bar apparatus. This method is applicable to the woven composite with modulus independent of strain rate. This method can predict the maximum specimen dimension at the desired strain rate under the maximum strike velocity of the apparatus. Based on the proposed design method, the in‐plane dynamic compressive behavior of 2D plain weave carbon/aramid hybrid composite was obtained. The strength exhibited sensitive to strain rates. The nonlinear constitutive model described the dynamic constitutive relationship effectively. The distribution of delamination failure significantly influenced the final failure shape of the specimens through the high‐velocity camera. Microscopic observations indicated that carbon fiber yarns and aramid fiber yarns exhibited different fracture modes. Highlights: An experimental design method applicable to woven composites in dynamic tests.Negative correlation between strength and strain rate of hybrid composites.The validity of the nonlinear constitutive model to dynamic property.The effect of hybridization and strain rates on damage modes. [ABSTRACT FROM AUTHOR]

The research on fracture mechanisms of brittle materials is extremely difficult such as the determination of the energy absorption modes and the geometric characteristics of debris. In this paper, a dynamic experimental fragment recovery device was developed to study the facture characteristics of A99 ceramics (the mass of Al2O3 accounts for 99%) based on the Split‐Hopkinson pressure bar (SHPB) experiments, in which the energy absorption mechanism was revealed. A three‐view characterization method was developed to obtain the geometric characterization formula under various strain rate; therefore, the geometric parameters of the fragments can be quickly characterized. The failure mode was investigated in correlation between strain rate and micro‐cracks. It was found that the shape of the strain rate controlled the proportion of dissipated energy. At a lower strain rate the fragment was prone to needle shape, while at a higher strain rate (above 2001 s−1) the proportion of dissipated energy increased to 72% and the fragment shape tended to be nearly spherical. A formula based on strain rate was proposed to characterize the geometric parameters of the fragments without the need of geometry dimensions; therefore, the fragment rate can be quickly obtained, which could provide guidance for the design of ceramics parts. [ABSTRACT FROM AUTHOR]

The presence of frozen clay as a natural protective material makes it a crucial layer of defense against potential impacts in various engineering projects. Studying the strength and deformation characteristics of frozen clay is, therefore, particularly important. In this study, static mechanical tests, the Hopkinson impact test, and fly-plate tests were conducted on frozen clay to identify its mechanical properties under an impact load. The uniaxial compression strength, flexural strength, and elastic modulus displayed a linear increase with the change in temperature. The fractal dimension was used to describe the failure characteristics of frozen clay, yielding values ranging from 1.5691 to 1.8785. At the same temperature, the fractal dimension exhibited a strain rate effect as the strain rate increased. A light gas gun system was then used to conduct fly-plate tests on frozen clay at varying temperatures (−3, −20 °C, and ordinary temperature). The impact process was meticulously analyzed, considering factors such as shock wave velocity, particle velocity behind the shock wave, impact pressure, and volume strain. Moreover, our investigation plotted the D–u (volume strain–particle velocity) and P–μ shock (impact pressure–shock wave velocity) adiabatic curves. Notably, we observed that samples with a higher initial strength exhibited an increased resistance to compression under an identical initial density and moisture content, resulting in a discernible leftward shift of the P–μ curve. The results provide a theoretical basis and technical support for similar projects in the future. [ABSTRACT FROM AUTHOR]

The dynamic stress–strain response of a material can be described by a number of different models of varying fidelity. However, an individual model's ability to replicate the dynamic stress–strain response of a material can be hindered by experimental variability. Reification, an approach to fusing models and experimental data with inherent scatter, is presented. It is then used to determine the optimum parameters of the Johnson–Cook (JC) and Zerilli–Armstrong (ZA) models using a fusion of Split-Hopkinson Pressure Bar (SHPB) data and the JC and ZA models fit to the SHPB data using a traditional approach. The output of the fused model is a dataset that represents a "best-guess" sampling of the possible stress–strain response of a high strength steel. In the present work, the dynamic response of a newly developed steel, AF9628, is evaluated. Under the reification framework, the experimental variability and limitations of the mathematical model expressions are addressed by the optimized sampling of data and combined fitting process. The JC and ZA models are then re-fit to partitions of the fused dataset, which bound the responses of the traditionally fit JC and ZA models. The behavior of the re-fit models and the traditionally fit models are compared via a simulated Taylor anvil test. [ABSTRACT FROM AUTHOR]

Compared with a large number of studies on the magnetic field properties of sintered NdFeB, the study on its dynamic mechanical behavior is insufficient, which restricts the further development of materials in a dynamic environment. To break through the above situation, the dynamic mechanical property of sintered NdFeB materials is discussed based on the split-Hopkinson pressure bar (SHPB) experimental principle. The experimental data show that the material has obvious strain rate correlation characteristics at medium and high strain rates. To describe the dynamic behavior characteristics of material so as to better guide engineering practice, a new dynamic compression damage constitutive model of sintered NdFeB is proposed. The damage is defined on the basis of Weibull distribution. In addition, the wing crack growth model considering the crack gap is established. Thus the damage evolution model can be obtained. Combining the damage evolution model with Zhu-Wang-Tang (ZWT) constitutive model, the dynamic damage ZWT constitutive model of sintered NdFeB under one-dimensional impact load is constructed. The key parameters of the model are identified according to the experimental data and the non-linear phenomenon of the stress-strain curve of sintered NdFeB under one-dimensional impact load can be well explained. [ABSTRACT FROM AUTHOR]

Ductile materials exhibit rate-dependent behaviors when subjected to different loading rates, particularly during impact and explosion events. In order to investigate the high strain rate behaviors of metal materials, a phase field model considered the rate-dependent threshold for effective plastic work is proposed. And the presented model couples the influences of the stress triaxiality and Lode angle parameter on failure behaviors. Later, a single element is modeled to demonstrate the impacts of the model in predicting stress-strain relations under varying loading rates. To illustrate the impacts of the Lode angle parameter on load-displacement responses, rectangular notch specimens are used. Next, the presented model is employed to mimic the shear fracture of hat-shaped specimens at different strain rates based on the split Hopkinson pressure bar tests, and the model parameters are calibrated by comparing the strain waveforms between the simulations and experiments. The numerical results indicate the developed model is capable of accurately reproducing the shear ductile fracture of the hat-shaped specimens under high strain rates. [ABSTRACT FROM AUTHOR]

To study the dynamic mechanical properties and failure characteristics of intersecting jointed rock masses with different joint distributions under confining pressure, considering the cross angle α and joint persistence ratio η, a numerical model of the biaxial Hopkinson bar test system was established using the finite element method–discrete-element model coupling method. The validity of the model was verified by comparing and analyzing it in conjunction with laboratory test results. Dynamics-static combined impact tests were conducted on specimens under various conditions to investigate the strength characteristics and patterns of crack initiation and expansion. The study revealed the predominant factors influencing intersecting joints with different angles and penetrations under impact loading. The results show that the peak stress of the specimens decreases first and then increases with the increase of the cross angle. When α < 60°, regardless of the value of η, the dynamic stress of the specimens is controlled by the main joint. When α ≥ 60°, the peak stress borne by the specimens decreases with increasing η. When α < 60°, the initiation and propagation of cracks in the cross-jointed specimens are mainly controlled by the main joint, and the final failure surface of the specimens is composed of the main joint and wing cracks. When α ≥ 60° or η ≥ 0.67, the secondary joint guides the expansion of the wing cracks, and multiple failure surfaces composed of main and secondary joints, wing cracks, and co-planar cracks are formed. Increasing lateral confinement significantly increases the dynamic peak stress able to be borne by the specimens. Under triaxial conditions, the degree of failure of the intersecting jointed specimens is much lower than that under uniaxial and biaxial conditions. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effects of sandstone ring specimens with different inner diameters on dynamic compression mechanical characteristics after dry and wet circulation. To carry out our study, we subjected a sandstone ring specimen with a 50 mm outer diameter and a 0~25 mm inner diameter to 10 cycles of dry and wet circulation. Afterward, we recorded the specimen's basic physical parameters and used a split-Hopkinson pressure bar (SHPB) test device to perform an impact compression test. Following dry and wet circulation, our results showed that the mass loss rate increased and the volume expansion rates and density decreased with the increase in the inner diameter of the sandstone ring sample. Simultaneously, with the increase in the inner diameter of the specimen ring, the dynamic compressive strength of the specimen presented an exponential negative correlation, the dynamic elastic modulus presented a quadratic negative correlation, and the dynamic peak strain presented a quadratic positive correlation. Concurrently, the average particle size of the specimen decreased, and the degree of breakage increased with the increase in the sandstone sample's inner diameter. Regarding the energy analysis performed in this study, the sandstone ring sample's energy dissipation increased, and its kinetic performance evidently weakened with the increase in the ring sample's inner diameter. The results of this study have certain reference values for the construction and maintenance of natural cavity rock and underground hard rock roadways. [ABSTRACT FROM AUTHOR]

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock's fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock's dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone's dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits "double peak" characteristics; when it exceeds 30°, a "single peak" waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone's fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space. [ABSTRACT FROM AUTHOR]

The features of the fracture of the aluminum alloy AMg4.5 under dynamic tension according to the Kolsky methods using Split-Hopkinson pressure bar are considered. Experimental and theoretical data of strength characteristics of the alloy in the initial coarse-grained and ultrafine-grained states are presented. It is shown that the high degree of deformation of the material obtained in the process of severe plastic deformation by torsion under high pressure has a negative effect on the dynamic strength of the material. [ABSTRACT FROM AUTHOR]

Helicoidal composite has been found naturally existing in many species of crustaceans and it has recently raised a significant amount of interests among researchers due to its great impact performance resulted from unique fiber layup architecture. This work is focused on developing a novel bio-inspired helicoidal thermoplastic composite and studying its mechanical behaviors under different testing conditions. Continuous glass fiber reinforced polypropylene composite preforms were used for compression molding the helicoidal structure with a pitch angle of 16.3° and nonlinear pitch angle. Composites with conventional fiber layups such as 0/90 and quasi-isotropic layup sequences were also prepared and tested for comparison purpose. Various tests at different strain rates, including quasi-static test (flexural test and compression after impact test), low strain rate test (Izod impact test and drop tower impact test), and high strain rate test (Split Hopkinson pressure bar test), were performed to evaluate the mechanical properties of the helicoidal composites and conventional composites. The helicoidal composites showed twisting fracture pattern for deflecting cracks involving more areas for energy absorption in addition to common failure mechanisms in the Izod impact test. It was also found that the helicoidal composite showed considerably higher damage tolerance than the conventional composites in high strain rate scenarios. [ABSTRACT FROM AUTHOR]

The investigation of inhomogeneous materials under dynamic conditions presents several challenges, particularly with regard to testing the dynamic properties of concrete, which requires the use of a large-scale split-Hopkinson pressure bar (SHPB). The present study aims to address these challenges by designing and calibrating a 155 mm diameter SHPB. The design and construction of the apparatus are described, and its data processing, including wave pulse dispersion correction, is assessed to ensure accurate representation of stress and deformation conditions. The apparatus is validated through experiments on brittle (confined concrete) and ductile (copper) specimens. The results demonstrate the ability of SHPB to characterize the dynamic properties of large-scale specimens and to correct dispersed signals in the bar, allowing for the accurate determination of specimen surface pulses. Validity of the results is confirmed through one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) wave analyses. Therefore, the 155 mm diameter SHPB setup has shown excellent performance in deriving the dynamic properties of large-diameter specimens. This study provides evidence to support the conclusion that the utilization of a 155 mm SHPB setup enables the experimental assessment of dynamic properties in large-diameter specimens. This conclusion is directly supported by the analysis of test data obtained from confined concrete samples and copper materials. [ABSTRACT FROM AUTHOR]

In this study, ventilated cavitating flow characteristics around an axisymmetric projectile are investigated by combining experiments and numerical simulations. Experiments were carried out with a Split–Hopkinson pressure bar launch system and the pressure-equaling exhaust technology. Modular projectiles are designed to experimentally investigate the influence of head shape and ventilatory volume on flow characteristics. Large eddy simulation model is applied to obtain more flow field information. Compared with the conical head projectile, the hemispherical head projectile has a thinner attached cavity and more local detachment of the cavity. The statistical structure of the velocity and pressure fluctuations are analyzed by combining histograms and Q–Q diagrams. The results show that the pressure drag is dominant in the total drag and the periodic pulsation of the tail cavity and the stable vortex structure at the tail cause the variation of drag. The larger cavity volume changes the actual shape of the projectile, making the drag of the conical head projectile higher. The evolution characteristics of the cavitating flow field around the projectile with different ventilatory volumes are obtained, and the relationship between pressure fluctuation and chamber volume is derived. It is found that the reentrant jet causes a reverse flow at the nozzle, which leads to local pressure rise at the same interval. The above research work could contribute to the design and flow control of the ventilated cavity body. [ABSTRACT FROM AUTHOR]

Featured Application: This work has the potential to be applied to deep rock engineering under the coupling environment of groundwater, geothermal and in situ stress fields. In order to study the dynamic properties of temperature–water-coupled sandstone under axial pressure, impact compression tests were carried out on sandstone samples after temperature–water coupling under eight types of axial pressure (0.5~4.0 MPa) loading as well as no axial pressure loading by using the split-Hopkinson pressure bar (SHPB) test set. The results showed that the mass, volume, and density of the sandstone specimens increased by 0.57%, 0.37%, and 0.20%, respectively, after temperature–water coupling. With increasing axial pressure, the dynamic compressive strength of temperature–water-coupled sandstone samples decreased as a linear function, the dynamic strain increased as a quadratic function, the dynamic modulus of elasticity decreased as a quadratic function, and the average strain rate increased as an exponential function, indicating a strong strain rate effect. From the energy point of view, as the axial pressure increases, the absorption energy of the sample increases, the reflection energy gradually decreases, the crushing degree of the sample increases, and the size of the broken pieces decreases; the average particle size of the sandstone sample pieces decreases quadratically with the increase in the absorption energy and linearly with the increase in the axial pressure. [ABSTRACT FROM AUTHOR]

This paper demonstrates the application of the Johnson–Holmquist II (JH-2) model with correlated and validated parameters to simulate the behavior of a sandstone. The JH-2 model is used to simulate various tests, including single-element tests, structural quasi-static uniaxial and triaxial compression tests, and the split Hopkinson pressure bar test. Additionally, the model is used to simulate drop-weight impact test using a ball bearing and two loading scenarios involving small-scale blasting and projectile impacts. Quantitative and qualitative comparisons demonstrate that the JH-2 model agrees well with both experimental and analytical results. Limitations of the model are also highlighted, particularly for quasi-static problems, as the model was originally developed for high-strain-rate simulations. Ultimately, this study demonstrates that the JH-2 rock constitutive model can obtain reasonable results for a material other than the material for which the model was originally correlated and validated. This paper provides valuable guidance for modeling and simulating sandstone and other rock materials subjected to dynamic loadings. [ABSTRACT FROM AUTHOR]

In this work, we investigated the impact of moisture content on the dynamic mechanical properties of precast concrete members. The dynamic splitting impact test was applied to concrete specimens with different moisture contents using the split-Hopkinson pressure bar (SHPB) with a diameter of 75 mm. Further, variation laws of the waveform, stress–strain curve, damage pattern, dynamic splitting tensile strength (DSTS), strain rate, and damage evolution were analyzed. Experimental results indicate that specimen fragmentation degree increases with moisture content. The DSTS exhibited a "softening in the water" phenomenon when the moisture content was low, resulting in a decrease in strength. However, when the moisture content was high, the strength displayed a strengthening phenomenon, owing to the adhesion of internal pore water. The dynamic strength of the specimens is the macroscopic manifestation of the dynamic balance between the strain effect and moisture content. To model the effect of moisture content and strain rate, a viscoelastic damage constitutive model based on Weibull distribution was proposed and validated, considering the influence of water content and residual strength. The established model can reflect the damage stress–strain relationships of concrete with varying moisture contents under the impact load. The variation laws of associated parameters, such as Weibull distribution parameters, viscosity coefficient, and damage variables, were analyzed to explore the damage mechanism. From the experimental study, it can be concluded that moisture content is closely related to the specimens' damage pattern, and the dynamic performance of concrete, both of which can be captured by the proposed viscoelastic damage model. [ABSTRACT FROM AUTHOR]

Alkali-activated concrete (AAC) features excellent mechanical properties and sustainability. The incorporation of crumb rubber (CR), recycled concrete aggregates (RCAs), and recycled steel fibers (RSFs) can further enhance environmental sustainability. This paper mainly investigated the dynamic behaviors of a novel rubberized AAC incorporating RCAs and RSFs (RuAAC) through Split-Hopkinson Pressure Bar (SHPB) tests. The variables included three types of RSF content (1%, 2% and 3%), five types of rubber content (0%, 5%, 20%, 35% and 50%) and five impact pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa and 0.9 MPa). Dynamic stress–strain curves, dynamic strength, the dynamic increase factor (DIF), impact toughness and the synergistic effects of RSF and CR were discussed. The results show that increasing RSF and CR contents could improve the impact resistance of RuAAC under impact loading. The RuAAC exhibited significant strain rate sensitivity, and the sensitivity increased with larger contents of RSF and CR. The increase in strain rate sensitivity was more pronounced with higher CR contents, which was reflected in larger dynamic increase factor (DIF) values. Under high impact pressure, the impact toughness was obviously enhanced with higher RSF contents, while the contribution of increased CR content to impact toughness was not apparent, which may be attributed to the fact that this study only calculated the integral under the dynamic stress–strain curve before the peak stress to determine impact toughness, neglecting the potential contribution of CR particles after the peak point. The obvious strain sensitivity exhibited by the RuAAC in the SHPB tests indicated superior impact performance, making it particularly suitable for architectural structures prone to seismic or explosive impacts. [ABSTRACT FROM AUTHOR]

Constitutive relations for slip and deformation twinning behaviors of a number of metals, including α-titanium, copper, α-iron, and tantalum materials, are described over a very large range in imposed strain rates. The focus is on application to higher-rate Taylor (solid cylinder) impact tests, split-Hopkinson pressure bar measurements, and shock as compared with ramp-type isentropic compression tests and including simulations of the corresponding dislocation-based deformation behaviors. [ABSTRACT FROM AUTHOR]

This research article investigated the stress-state and strain-rate-dependent mechanical properties and failure of alumina ceramic. Compression–shear testing was carried out using a split-Hopkinson pressure bar under equivalent strain rates ranging from 1 0 1 s−1 to 1 0 3 s−1. Ultra-high-speed images coupled with digital image correlation were used to investigate the in situ time-evolving strain field and the failure process (e.g., crack growth). Experimental results showed equivalent strength reduced from 4.27 ± 0.23 GPa for the uniaxial compression tests to 3.75 GPa and 2.00 GPa for compression–shear tests across the strain rates and shear angles (5 ° to 25 °), with the strength decreasing with an increasing shear angle. The crack speed ranged from 908 m/s to 3208 m/s across the range of strain rates and shear angles, with a positive correlation noted for crack speeds with strain rate and increasing sensitivity with an increasing shear angle. The extent of localization of shear strain in alumina under compression–shear deformation was observed to be strain-rate-dependent, and it increased with an increasing strain rate of deformation. Furthermore, axial and shear strain localization increased with the increasing shear angle, contributing to local shear failure before the complete failure of the specimen. Overall, this paper provides new insights and measurements of the strain-rate-dependent and shear-dependent strength and crack speeds of alumina under compression–shear loading, and these serve as vital inputs for future computational model development and validation. [ABSTRACT FROM AUTHOR]

The stability of the cemented paste backfill is threatened by the dynamic disturbance during the excavation of the surrounding ore body. In this paper, the computerized tomography (CT) and Split Hopkinson Pressure Bar (SHPB) tests were conducted to explore the initial pore distribution characteristics of the cemented tailings backfill (CTB) and the development of the crack under low impact amplitude. SHPB tests were conducted with impact amplitudes of 34, 37, and 39 mV, respectively. Results show that the initial pores of CTB were steadily distributed with the height of CTB. The CTB contained many initial pores with similar pore size distribution characteristics, and the largest number of pores is between 0.1 and 0.3 mm. Most of the cracks in CTB after low impact amplitude develop and expand along the initial pores, and the damage of CTB mainly exists in shear cracks. A dependence has been established that the dynamic uniaxial compressive strength of the CTB increases, the total crack volume first increases and then decreases, and the number of cracks increases as the impact amplitude increases. The research results can provide a valuable reference for the dynamic performance of CTB under low impact amplitude and the design of mining backfill. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of different materials has been widely studied using the split Hopkinson pressure bar (SHPB) testing. The striker bar's velocity (SV) and the incident bar's impact surface are well known to have a significant impact on producing a clear signal in the compressive SHPB studies. Several times, the shape of the incident strain signal differs from an ideal state, and the reason is difficult to find. In this paper, a parametric investigation of such understudied instances is carried out utilising Abaqus software for finite element analysis (FEA). The numerically obtained incident strain pulse for a perfectly aligned SHPB setup with different SV was validated experimentally on compressive SHPB apparatus. The numerical output was found to have good agreement with experimental results. Further, plots of incident strain were evaluated numerically for Sv (10, 15, 20, 25 and 30 in m/s) which was used for polynomial fitting using MATLAB's curve fitting tool. A similar method was adopted for symmetrically plane non-parallel impact surface on the incident bar. The angles chosen for FEA calculations were 5°, 10°, 15° and 20°. Filleted impact surface with radius (r) 1.5, 3, 4.5 and 6 mm was also studied. The study of the variation of impact surface shape was done at a striker velocity of 25 m/s. It was observed from this study that when striker velocity increases, the absolute magnitude of incident strain at peak increases while rise time remained constant. In turn, when the symmetrically non-parallel plane surface angle and fillet radius grow, the absolute value of incident strain at peak almost stays the same but the rising time lengthens. This study can help understand the nature and discrepancy of the incident strain signal obtained in the compressive SHPB setup and find its root cause. [ABSTRACT FROM AUTHOR]

The laminated metal materials are widely used in military, automobile and aerospace industries, but their dynamic response mechanical behavior needs to be further clarified, especially for materials with joint interface paralleling to the loading direction. The mechanical properties of TA2/Q345 (Titanium/Steel) laminated metal of this structure were studied by using the split Hopkinson pressure bar (SHPB). To shed light on the stress-state of a laminated metal with parallel structure, the relative non-uniformity of internal stress R(t) was analyzed. The mechanism of deformation compatibility of welding interface was discussed in detail. The current experiments demonstrate that in the strain rate range of 931–2250 s−1, the discrepancies of the internal stress in specimens are less than 5%, so the stress-state equilibrium hypothesis is satisfied during the effective loading time. Therefore, it is reasonable to believe that all stress–strain responses of the material are valid and reliable. Furthermore, the four deformation stages, i.e., the elastic stage, the plastic modulus compatible deformation stage, uniform plastic deformation stage and non-uniform plastic deformation stage, of the laminated metal with parallel structure were firstly proposed under the modulating action of the welding interface. The deformation stages are helpful for better utilization of laminated materials. [ABSTRACT FROM AUTHOR]

Experiments and peridynamic simulations of the split-Hopkinson pressure bar (SHPB) have been conducted to investigate the dynamic mechanical behaviors of magnesium aluminate (Mg-Al) spinel. The high-speed camera and scanning electron microscopy were used to observe the failure process and the fracture surface. In our modified model, the crystal orientation and grain boundary strength were explicitly quantified, accompanied by the dual-horizon peridynamic technique, resulting in high calculation accuracy and efficiency. Then effects of the stress state and strain rate on the failure mechanism of spinel have been investigated with the damage evolution process. Micro-pores tend to be generated at the intersection of grain boundaries, while cracks will propagate along these micro-pores, leading to trans-granular and inter-granular failures. Finally, the microstructure effects on the mechanical properties of spinel have been systemically investigated. The strength and distribution of grain boundaries were found to significantly affect the strength and crack propagation of Mg-Al spinel. [ABSTRACT FROM AUTHOR]

The mechanical properties of water-rich coal and rock in a subzero environment are very different from those at room temperature, which causes many unexpected hazards for projects. In this study, coal and rock samples subjected to the coupled effects of water, temperature, and dynamic loads were taken as the research object, and the discussion was shaped around their mechanical properties. The crack evolution trend and different gradient impact velocities were determined using a split-Hopkinson pressure bar (SHPB). Multiple fractals were based on high-speed digital image correlation (HS-DIC) technology and the quality-screening method; the evolution trend of the surface cracks in the crushing process and the distribution characteristics of the specimen fragments after crushing were examined from the perspective of fractals. This provided a powerful supplement to the existing research system on the problem of mining via the freezing method, and it accounted for the shortcomings of the existing research to a certain extent. In this research, the results mainly showed four points: (1) The coal samples were determined to have a wave velocity between 1.68 and 2.01 km/s, while the rock samples were between 2.24 and 2.61 km/s. Under the same conditions, the rock's resistance to deformation and damage was greater than that of coal. (2) In the saturated state, the plastic strength of the coal and rock samples was greater than that in the dry state, due to the strengthening of their internal stresses caused by the presence of fissure water. (3) With decreasing temperature, the degree of the dynamic compression factor of coal and rock showed a trend of initially increasing, then decreasing, and then increasing. With the increase in the loading rate, the destruction of the coal and rock was more intense, and the destruction process was accelerated. (4) After the saturated coal and rock samples were frozen, their interiors were affected by the dual factors of contraction under the influence of temperature and expansion under the influence of the freezing expansion force. The internal fissures closed or shrank, and the water in the pores turned into ice, leading to an increase in pore volume. [ABSTRACT FROM AUTHOR]

Compared with most dynamic tests, point load test is widely used in engineering practice because of its wide requirements for test conditions. In offshore mining engineering, the surrounding rock is affected by dynamic load impact and corrosion of various aqueous solutions for a long time. Therefore, it is of great significance to study the influence of hydrochemical corrosion on dynamic mechanical properties of rock to ensure the stability of surrounding rock. In this paper, a large number of dynamic point load and dynamic uniaxial compression tests were carried out on the granite mined from a large mine by using the Split Hopkinson pressure bar test device after the corrosion of pH values of 2, 5, and 7 solutions, respectively. Based on the energy theory, the crushing energy consumption in the test process is analyzed, and finally the fitting formula of the dynamic compressive strength and the crushing energy consumption in the dynamic point load test is obtained through fitting analysis. The results show that when the crushing energy consumption in the dynamic point load test is used to estimate the dynamic compressive strength, a certain crushing energy consumption (the final value of this test is 70 J in this paper) is more accurate, and it can estimate the dynamic compressive strength under various corrosion conditions under this crushing energy consumption. However, with the change of crushing energy consumption in the dynamic point load test, this transformation relationship is no longer accurate, and it is necessary to modify this transformation relationship with corrosion condition as the influencing factor. This conclusion can provide reference for obtaining the dynamic compressive strength of rocks under different corrosion conditions in engineering field in the future. [ABSTRACT FROM AUTHOR]

The problem of the determination of material strength properties through the Kolsky experimental technique is considered. Small size specimens of M1 copper alloy are tested on a split Hopkinson pressure bars equipment. The experimental data of tensile tests observed under both dynamic and quasi-static conditions are analysed within the framework of the incubation time criterion and the Sign-Perturbed Sums method. It is shown that the influence of a test performance error is considered in the data treatment procedure based on the developed method. [ABSTRACT FROM AUTHOR]

In order to explore the size effect of the mechanical and damage characteristics of coal measure sand stones under dynamic load, uniaxial impact compression tests were carried out on coal-bearing sand stones with a diameter of 50 mm and a length–diameter ratio of L/R = 0.5, 0.8, 1, 1.2, 1.5, 1.8, and 2 by using the Hopkinson pressure bar test system. The size effect law of the mechanical properties and energy dissipation of coal-bearing sandstone under a high strain rate were investigated. Then, the mercury injection test was carried out on the fragments at different positions, and the electron microscope scanning test was carried out on the fragments near the end of the transmission rod. Based on the area damage definition method and normalization treatment, the integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, was established. The results showed that the peak strength and dynamic elastic modulus of coal measure sandstone increased first and then decreased with the increase in length–diameter ratio under impact compression load, and they reached the maximum when the length–diameter ratio was 1.2. The dynamic peak strain increased gradually with the increase in length–diameter ratio. The energy of coal-bearing sandstone showed strong size effect, that is, the total absorbed energy, elastic energy, and dissipated energy increased with the increase in length–diameter ratio, and the size effect of total absorbed energy was the most obvious. Under the same impact pressure, the porosity of coal-bearing sand stones with seven kinds of length–diameter ratios near the incident end was roughly the same. But when the length–diameter ratio was greater than 0.5, the porosity decreased gradually with the increase in the distance from the incident end. And the larger the length–diameter ratio, the more obvious the decreasing trend. When the length–diameter ratio was smaller, the size of the holes and cracks and the cluster density were larger. The integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, showed that the larger the length–diameter ratio, the better the relative integrity of coal-bearing sandstone. [ABSTRACT FROM AUTHOR]

In this study, hemihydric phosphogypsum (HPG) was used to partially replace cement to prepare phosphogypsum-based concrete (PGBC). A split-Hopkinson pressure bar (SHPB) system was used to perform dynamic compression tests on PGBC in the strain rate range from 136 s−1 to 432 s−1. The effects of the strain rate on the dynamic compressive performances, impact toughness, and failure modes of the PGBC with different HPG replacement rates (30%, 35%, 40%, 45%, and 50%) were quantitatively discussed. The results showed that, like plain concrete, PGBC exhibited a significant strain rate effect and its dynamic compressive mechanical properties increased with the increase in the strain rate. The dynamic compressive mechanical properties of concrete were weakened by HPG replacement, but the strain rate sensitivity of concrete was improved when HPG was replaced. The dynamic compressive strength and dynamic modulus of elasticity of the PGBC approximately followed a trend of first increasing and then decreasing with the increase in the HPG replacement rate. [ABSTRACT FROM AUTHOR]

When a vehicle leaves the road, crash barriers stop it and prevent significant damage to the vehicle, its environment, and the occupants. Typically, such protection systems are made of simple steel, but fiber-reinforced composites can efficiently absorb and dissipate the impact energy at high-risk locations. In order to design such protective systems, material parameters under dynamic loading are necessary. Here, split Hopkinson pressure bar tests with unidirectional glass-fiber-reinforced epoxy of 58% glass fiber content are performed. The elastic response at strain rates between 300/s and 700/s in the loading direction parallel and perpendicular to the fiber is determined. From the measured data, a model of the time dependence of the elastic modulus is derived to enable the design engineer to lay out protective systems made of such GFRPs. [ABSTRACT FROM AUTHOR]

Full understanding of dynamic mechanical characteristics of coal samples under true triaxial condition is of great significance for preventing and controlling deep coal and rock dynamic disasters. The results of this study showed that the transmission amplitude decreases with the increase in σ1 and increases with the increase in the impact velocity. The peak stress and absorbed energy of coal decreased with the increase in σ1 under true triaxial conditions. Under uniaxial and true triaxial conditions, the peak stress and absorbed energy of coal increased with the increase in impact velocity, and the stress change under true triaxial conditions was more sensitive to the action of dynamic load. Compared with uniaxial impact, the damage degree of coal sample under true triaxial condition was lower. The fractal dimension of broken blocks increased linearly with the increase in σ1 and dynamic load, indicating that the degree of broken coal was intensified. This study effectively reveals the failure mechanism of coal under unequal static load and dynamic load. [ABSTRACT FROM AUTHOR]

A novel cellular concrete with millimeter-level pores fabricated with superabsorbent polymers and fiber is introduced. Porous structure with reinforcement of fiber are adopted to improve crack resistance and shock-absorbing ability. To investigate the dynamic mechanical performance of fiber-reinforced cellular concrete, quasistatic compression and split Hopkinson pressure bar tests with strain rate from 15 to 90 s−1 were conducted. Three different fiber volume fractions (0.2%, 0.6%, and 1%), and two types of fibers (polypropylene fiber and basalt fiber (BF)) were adopted. Along with two levels of porosities (20% and 60%), total of 12 mix designs of cellular concrete to three-level axial impacting. The research results show that the novel cellular concrete is sensitive to high strain rates, demonstrating increasing dynamic compressive strength, dynamic elastic modulus, dynamic increase factor (DIF), and peak toughness with the increase in strain rate. In addition to the inertia effect, the locally enhanced porous structure and fiber structure can change the stress field and crack path, along with the energy consumption of deformation and cracks in the pores. The amount of fiber, physicochemical property, distribution, and shape amplify or dampen through its thickening effect, interface reaction, and stress transmission. Recommended fiber types and dosages were proposed to improve strength, stiffness, and toughness. BF showed an enhanced performance in terms of strength, modulus, and sharp strain-rate effect. Rules of DIFs were also studied. Awareness of the dynamic properties provides a foundation for proper design of structural members and increases the use of cellular concrete. [ABSTRACT FROM AUTHOR]

Understanding the dynamic failure mechanism of rocks subjected to chemical corrosion is very important. However, the previous works mainly focused on static damage rather than dynamic pulverization with chemical corrosion. In this study, Split Hopkinson Pressure Bar (SHPB) impact tests are performed to study the dynamic mechanical properties and energy evolution of granite after chemical corrosion. The XRD and SEM analyses are employed to reveal the chemical reaction processes and corrosion mechanisms. Moreover, the fractal dimension is applied to determine the failure pattern of granite. The experimental results show that the acidic environment causes muscovite, albite, and microcline to generate SiO2 (quartz), and the newly generated SiO2 has a weak pressure-bearing capacity. As corrosion progressed, micro-particles accumulate on the surface and cause stress concentrations, which implies a decrease in dynamic properties. Chemical corrosion causes internal microcracks to propagate, and more energy is absorbed when they coalesce under the dynamic impact. The chemical solution enters the inside of specimens through the surface cracks for further reaction, which causes the failure pattern to change from splitting failure to crushing failure. The findings can fill in the gap in the chemical corrosion mechanism of granite subjected to dynamic impact. Highlights: Split Hopkinson Pressure Bar tests are performed to study the dynamic mechanical properties of granite after chemical corrosion. The XRD and SEM analyses are employed to reveal the chemical reaction processes and corrosion mechanisms. The acidic environment causes muscovite, albite, and microcline to generate SiO2, and the generated SiO2 has a weak load-bearing capacity. Chemical corrosion causes microcracks to propagate, and more energy is absorbed when they coalesce under the dynamic impact. [ABSTRACT FROM AUTHOR]

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