Search

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]

This paper investigated the dynamic mechanical properties of CO2-cured foam concrete under varying conditions, focusing on the effects of foam admixture and fiber reinforcement. The study tends to enrich the knowledge regarding the performance of CO2-cured foam concrete under different loading rates, especially in relation to density and matrix strength. The foam admixture of the specimens ranges from 26% to 55%, achieving density from 600 kg/m3 to 1,000 kg/m³. The specimens were loaded at strain rates from 80 s-1 to 398 s-1. Experimental results revealed the dynamic elastic modulus, dynamic compressive strength, and Dynamic Increase Factor (DIF) showed a strong correlation with the foam admixture and density. In addition, the incorporation of polypropylene (PP) fibers effectively improved the mechanical behavior of the foam concrete, achieving up to a 17% increase in dynamic compressive strength. This comprehensive analysis highlights the critical role of foam admixture and fiber reinforcement in determining the dynamic properties of CO2-cured foam concrete and provides valuable insights for optimizing the dynamic performance of foam concrete in various construction applications. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the dynamic mechanical properties of coal and rock under deep water conditions. The research employs an enhanced Split Hopkinson Pressure Bar (SHPB) testing system. Five sets of dynamic impact experiments were conducted on coal samples under varying loading conditions to analyse the changes in dynamic strength, energy dissipation, fractal dimension and other characteristics of coal samples under different water content states were analyzed. The experimental results demonstrate that: (1) Under specific strain rate conditions, the dynamic strength of saturated coal samples is lower than that of natural coal samples. As the strain rate gradually increases, the bonding force generated by free water and the Stefan effect jointly act, and the peak strength of saturated coal samples under high strain rate loading conditions is higher than that of natural coal samples. (2) Under certain strain rate conditions, the absorption energy of saturated coal samples is approximately 10% to30% lower than that of natural coal samples, and deformation hysteresis phenomenon occurs in natural coal samples, thereby improving the dynamic strength of natural coal samples relative to saturated coal samples; (3) The fractal dimension of saturated coal samples with a specific strain rate under three-dimensional dynamic static combination loading is higher than that of natural coal samples, and the percentage of small particle coal samples with debris is higher than that of natural coal samples; Finally, based on the HJC model, some coal samples were selected to simulate the coal rock failure characteristics during the triaxial loading process using ANSYS/LS-DYNA, and their stress–strain curves and failure morphology diagrams were obtained. The discrepancy between the numerical simulation and the experimental results was less than 10%, thereby further elucidating and corroborating the coal failure process and dynamic mechanical characteristics. [ABSTRACT FROM AUTHOR]

Metals manufactured by selective laser melting (SLM) with different directions exhibit different mechanical properties. This study conducted dynamic and static mechanical tests using a universal testing machine and split-Hopkinson bar (SHPB). The mechanical properties of 18Ni300 with 0° and 90° build directions manufactured by SLM were compared, and the micro-structure properties of the two build directions were analysed by metallographic tests. The Johnson–Cook (J-C) constitutive model was fitted according to the experimental results, and the obtained constitutive parameters were verified by numerical simulations. The results revealed that the constitutive model could predict the mechanical properties of 18Ni300 in a dynamic state. The build direction had little influence on the mechanical properties in a static state, but there was a significant difference in the dynamic state. The difference in the dynamic compressive yield strength of the 18Ni300 material manufactured by SLM with two build directions was 9.8%. The SLM process can be improved to produce 18Ni300 with uniform mechanical properties by studying the reasons for this difference. [ABSTRACT FROM AUTHOR]

This study investigates the dynamic mechanical properties of red sandstone under normal and acidic conditions with varying pH levels using the Split Hopkinson Pressure Bar (SHPB) technique. By integrating fractal theory and energy dissipation theory, the study reveals the changing patterns of fractal dimension and dissipated energy density of red sandstone in acidic environments. The test results indicate that as the impact air pressure increases, the strain rate, compressive strength, and maximum strain of the red sandstone show an upward trend, demonstrating a noticeable hardening effect of the strain rate. The physicochemical effects of acid corrosion lead to a deterioration in the mechanical properties of red sandstone, with a more pronounced deterioration as acidity levels increase. Furthermore, the fractal dimension of crushed red sandstone shows a direct positive relationship with the strain rate, while the average fragmentation block size decreases with increasing strain rate and the fractal dimension increases. Under acid corrosion, the fractal dimension increases, the average fragmentation block size decreases, and the dissipated energy density decreases. These findings offer a scientific foundation for the design and protection of underground geotechnical structures in acid-prone regions. [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]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The surrounding rock of a tunnel is subjected to cyclic impacts from different directions in tunnel engineering construction, resulting in directional damage to the rock mass. To investigate the impact direction effects on damage, a split Hopkinson pressure bar (SHPB) system was utilized to conduct cyclic impact tests on marble. The dynamic mechanical response of the marble was analyzed under different impact directions and loadings. Additionally, the P-wave velocity and pore distribution of damaged marble under different modes were obtained. The results showed that the P- wave velocity of marble decreased with the increasing impact times and loadings, while the porosity increased. The P-wave velocity of marble in Mode I was generally lower than that in Mode II, while the porosity was higher than that in Mode II. At an impact loading of 98 MPa, the porosity of marble subjected to three impacts was 3.21% and 1.98% under Modes I and II, respectively. The micropores showed a decreasing trend with impact times in Mode I, and the proportion of medium pores increased in both modes. In terms of dynamic properties, the dynamic peak strength and elastic modulus of marble declined with increasing damage. The degradation effect of Mode I on marble was significantly greater than that of Mode II, and it intensified with the increasing number of impacts and loadings. The difference in mechanical parameters and absorbed energy of marble under different impact modes increased with impact times and loadings. The energy absorption ratio of marble under Mode I was superior to that under Mode II. Additionally, a correction function was incorporated into the damage constitutive model to portray the compaction phase of marble. The improved model can accurately depict the mechanical response of marble under different modes. Finally, the damage anisotropy ratio (DAR) was defined based on P-wave velocity to characterize damage anisotropy, and the mechanism of damage anisotropy of marble under different impact modes was discussed. Highlights: Dynamic compression tests were conducted on marble under different impact directions and loadings ultilizing an SHPB system. The directional effects of the P-wave velocity and pore characteristics of marble under different impact modes were obtained. The dynamic mechanical response of the marble and the differences in response under different impact modes were analyzed in depth. The damage anisotropic characteristics of marble under different impact modes were investigated, and the directional effect on the damage mechanism was discussed. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to investigate the dynamic mechanical properties of coal and rock under deep water conditions. The research employs an enhanced Split Hopkinson Pressure Bar (SHPB) testing system. Five sets of dynamic impact experiments were conducted on coal samples under varying loading conditions to analyse the changes in dynamic strength, energy dissipation, fractal dimension and other characteristics of coal samples under different water content states were analyzed. The experimental results demonstrate that: (1) Under specific strain rate conditions, the dynamic strength of saturated coal samples is lower than that of natural coal samples. As the strain rate gradually increases, the bonding force generated by free water and the Stefan effect jointly act, and the peak strength of saturated coal samples under high strain rate loading conditions is higher than that of natural coal samples. (2) Under certain strain rate conditions, the absorption energy of saturated coal samples is approximately 10% to30% lower than that of natural coal samples, and deformation hysteresis phenomenon occurs in natural coal samples, thereby improving the dynamic strength of natural coal samples relative to saturated coal samples; (3) The fractal dimension of saturated coal samples with a specific strain rate under three-dimensional dynamic static combination loading is higher than that of natural coal samples, and the percentage of small particle coal samples with debris is higher than that of natural coal samples; Finally, based on the HJC model, some coal samples were selected to simulate the coal rock failure characteristics during the triaxial loading process using ANSYS/LS-DYNA, and their stress–strain curves and failure morphology diagrams were obtained. The discrepancy between the numerical simulation and the experimental results was less than 10%, thereby further elucidating and corroborating the coal failure process and dynamic mechanical characteristics.

Abstract The environment of deep in-situ occurrence is complex, and secondary dynamic disasters occur frequently. Exploring the dynamic constitutive models of coal at different depths is the foundation for deep resource development, which can help promote the safe and efficient mining of coal resources at different depths and reveal the mechanism of sudden dynamic disasters. Dynamic mechanical testing of coal at different depths of the Pingdingshan mine (China) was carried out using a split Hopkinson pressure bar system with confining pressure. On the basis of statistical damage theory, dynamic constitutive models of coal at different depths were explored, and the theoretical models were compared and verified using the experimental results. An expression relating to the infinitesimal element strength of coal and loading rate was derived, and the parameters σ 1dp , E d , and ε 1dp were determined. Inversion verification of the model showed that the experimental results agree well with the theoretical results prior to the peak stress. These research results are expected to be applied to the exploitation of deep resources, laying a foundation for the law of deep earth science and the construction of deep engineering.

To investigate the dynamic tensile mechanical properties of red sandstone under varying impact pulse widths and amplitudes, we employed the response surface methodology to examine the dynamic response characteristics of sandstone under different bullet lengths and impact velocities. Subsequently, a dynamic damage constitutive model for sandstone was developed. Macroscopic and microscopic features of sandstone were analyzed through digital image correlation (DIC) and scanning electron microscopy (SEM) experiments. Additionally, ANSYS software was utilized to analyze stress wave characteristics under controlled shock waves and the impact of geological factors on rock fracturing effects. The findings revealed the following. First, the length and impact velocity of bullets exhibit an interactive effect on the tensile response characteristics of sandstone. Peak load, energy consumption rate, and energy density display a positive correlation with bullet velocity. Second, according to the DIC results, the fractal dimension of the crack is negatively correlated with the length of the bullet during equal energy impacts. Third, microscopic failure modes included fractures along particle cementation and through particles, with section roughness decreasing as bullet length increased under equivalent energy impacts. Fourth, a dynamic damage constitutive model (R2 ≥ 0.84) was established based on the Zhu-Wang-Tang (Z-W-T) model and Drucker-Prager (D-P) criterion, clarifying model parameters and influence rules. Fifth, under controlled shock waves, the pulse width facilitates crack propagation, while the pulse amplitude initiates crack formation. Optimal rock breaking efficiency is achieved when stress waves exhibit a large pulse width and low radiation values, meeting specific threshold conditions.

In order to study the effect of basic roof period pressure on the dynamic characteristics of impact pillar, one-dimensional dynamic and static combined loading SHPB experimental device is used to carry out dynamic impact experiment on the impact sandstone pre-treated by cyclic loading and unloading. In the experiment, three different axial cycle thresholds are pre-set: 6, 12, 18 MPa, and then carry out dynamic compression experiments under different impact pressure conditions. The dynamic mechanical response, energy evolution and fragmentation distribution characteristics of impact sandstone under different cycle thresholds and impact pressure are discussed. The results show that the dynamic stress-strain curve of rock samples can be divided into elastic stage, yield stage and failure stage. The initial stage of dynamic stress-strain curve is almost straight line, and there is no fracture compaction stage in static uniaxial compression. The average dynamic compressive strength, the average dynamic elastic modulus and the average dynamic deformation modulus first increase and then decrease with the increase of the cyclic threshold. The average dynamic peak strain decreases first and then increases with the increase of cycle threshold. The average dynamic compressive strength, average dynamic elastic modulus and average dynamic deformation modulus of rock samples at the critical threshold are the largest, and the average dynamic peak strain is the smallest. The density of reflected energy and dissipated energy decreases first and then increases with the increase of the cycle threshold. The transmission energy increases first and then decreases with the increase of the cycle threshold. At the critical threshold, the density of reflected energy and dissipated energy is the smallest and the transmitted energy is the largest. There are four kinds of failure modes of rock samples under impact load: crushing failure, rock fragmentation, rock side spalling and rock splitting. Under each impact pressure, the fractal dimension of rock samples decreases first and then increases with the increase of cycle threshold, and increases nonlinearly with the increase of dissipated energy density. The densification of impact rock is better, the intensity of impact failure is weaker, the fragmentation degree is larger, the dissipated energy density is smaller, and the fractal dimension is smaller. The research results show that when the basic roof period pressure is less than the damage threshold value of the impact pillar, the periodic pressure can improve the rock density and affect the damage degree of the dynamic impact.

Additive manufacturing high-strength steel has a unique manufacturing process and has broad application prospects in military equipment, aerospace, and other fields, but it is often threatened by dynamic loads such as explosion and high-speed impact during use, which has attracted wide attention. In this paper, the dynamic impact of additive manufacturing high-strength steel LMD-BK and wrought high-strength steel BK was carried out at strain rates of 1000 s−1–5000 s−1 by the Split-Hopkinson pressure bar (SHPB) test, respectively, and the differences in the dynamic mechanical properties of the two were investigated under the impact of different strain rates. Using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) micro-observation techniques, the microstructure morphologies of LMD-BK and BK before and after dynamic impact were characterized, and the microstructure evolution mechanism of the two was investigated. The results show that both LMD-BK and BK are strain rate sensitive, and the dynamic compressive strength increases and then decreases with the increase of strain rate, with a maximum at 2000 s−1 and a minimum at 1000 s−1. The maximum and minimum values of dynamic compressive strength for LMD-BK are 1978 MPa and 1757 MPa, respectively; for BK, the maximum and minimum values of dynamic compressive strength are 1389 MPa and 1329 MPa, respectively. The final strain of the material increases as the strain rate increases. At the same strain rate, the final strain of BK is always larger than that of LMD-BK. With the increase in strain rate, the impact work absorbed by the material increases, and at the same strain rate, LMD-BK can absorb more impact work than BK. Microscopic observations show that after dynamic impact, LMD-BK undergoes fragmentation of the columnar structure and compression of the cellular structure to form a deformation localization zone. These results are of great significance for the study of dynamic mechanical properties and microstructure evolution mechanism of high-strength steel made by additive manufacturing under extreme environments such as explosion and high-speed impact.

Abstract This paper presents the investigation of the dynamic mechanical properties of coal rock under complex stress conditions at depth, based on the improved Separate Hopkinson Pressure Bar Test System. A total of 15 groups of coal samples were used to perform dynamic impact tests under different conditions. The changing rules of dynamic strength, crushing, fractal dimension and damage modes of coal under different stress conditions were analyzed. A total of nine groups of coal samples were selected for numerical simulation using ANSYS/LS-DYNA. The results show that: (1) The stress–strain curves of coal specimens under different strain rates, different confining pressures and axial pressures have basically the same trend and the curves show a certain jump forward. (2) The peak dynamic stress of the coal specimens increased linearly with the increase of strain rate and confining pressure, and the ambient pressure limited the expansion of internal cracks of the coal specimens under impact loading. Based on the experimental and simulated data, the maximum relative errors between the experimental and simulated data were determined to be 2.9578% for Group A, 6.177% for Group B, and 6.382% for Group C, respectively. (3) The damage modes of the coal samples under the three-dimensional dynamic-static combined loading were mainly “X” type and “conical” shear damage. The fractal dimension increases with the increase of strain rate, decreases with the increase of confining pressure, and first decreases and then increases with the increase of axial pressure. This research achievement can provide theoretical support for the prevention of dynamic disasters in deep coal mine engineering.

This study attempts to investigate the dynamic tensile mechanical properties of sandstone under freeze-thaw cycle by using the split Hopkinson pressure bar (SHPB)test system to perform dynamic splitting tests on sandstone samples with freeze-thaw cycle 0, 10, 20 and 40 times at different impact speeds.Also adopting the high-speed digital image correlation (DIC), we observed the dynamic tensile failure process of the specimen, where we analyzed the strength characteristics, deformation process and failure form of frozen sandstone under dynamic tensile stress in different freeze-thaw cycles.Results show that 1)the dynamic tensile σ-t curves of frozen sandstone and ordinary sandstone exhibit similar patterns of stress variation under different freeze-thaw cycles, which can be divided into four stages: low speed growth section, high speed growth section, peak plateau section and decreasing section; 2)the peak tensile stress increases linearly with the increase of stress loading rate; 3)the peak tensile stress of frozen rock has a certain freeze-thaw cycle effect, and there is a strong correlation between the peak tensile stress and the number of freeze-thaw cycles.The dynamic tensile strength of frozen rock increases first and then decreases as the number of freeze-thaw cycles increases.Under the same impact pressure, the frozen rock specimen shows certain freeze-thaw cycle effect as the tensile strain at the center shows N=40>20>0>10 under 4 kinds of freeze-thaw cycles.

Due to their exceptional impact resistance, ceramics are extensively used in various fields. However, unavoidable pores, microcracks, and inherent defects can degrade the performance of ceramic materials. A damage model of SiC ceramics under passive confining pressure was constructed based on the Lemaitre strain equivalence principle and the Weibull distribution function. This paper presented a dynamic damage model for SiC ceramics subjected to passive confinement pressure based on the principles of damage mechanics. Additionally, the split Hopkinson pressure bar device was employed to investigate the compressive strength and damage evolution of SiC ceramics at various shock pressures and confinement degrees. The experimental results indicate that constraints can reduce the damage to ceramics. The metal sleeve increased stiffness when compressing the ceramic material, allowing the specimen to convert from brittle–plastic–brittle. When sufficient constraints can be provided, the peak strain decreases gradually with the increase of the impact air pressure. Experimental data showing good agreement with the proposed model validated and analyzed the established model. Thinner boundary constraints cannot maintain the stability of ceramic structures, thicker boundaries do not significantly improve performance, and thicker boundaries can cause more weak areas. This paper provides guidance for the design of encapsulated ceramic composite armor by quantitatively studying the constraint thickness. [ABSTRACT FROM AUTHOR]

In engineering, soft rock is often damaged by dynamic loads such as dynamic compaction, vibrating compaction and blasting, resulting in varying degrees of damage. To understand the compressive response, fracture characteristics and energy dissipation characteristics of red bed soft rock under different dynamics, we carried out a series of dynamic impact tests by the separated Hopkins pressure bar system. The experimental results show that the dynamic peak stress, critical strain and toughness of red bed soft rock increase with the increase in strain rate with the increase in strain rate, which ranges from 37 to 102 s−1. Specifically, the dynamic compressive strength of red bed soft rock at 98 s−1 is 4.63 times that of the quasi-static average. As the strain rate increases, the fracture characteristics: integrity, slightly split and pulverized, and the size of fragments decrease and the number of fragments increases. When the strain rate exceeds the critical value 72 s−1, the fracture characteristics are pulverized. The energy dissipation density increases with the strain rate and increases faster when the strain rate exceeds the critical value. The energy utilization first increases and then decreases, when the strain rate is 88 s−1, the maximum utilization rate is 38%. [ABSTRACT FROM AUTHOR]

Fracture within the rock is one of the main factors leading to rock destabilization and has a significant effect on the stability of the project. In this study, sandstone is used as a research target, specimens with crack inclination angles of 0°, 30°, 45°, 60°, and 90° are prefabricated, and the split Hopkinson pressure bar (SHPB) impact test of sandstone with cracks is carried out based on digital image recognition technology to explore the dynamic damage characteristics of the specimens with five angles. The basic mechanical parameters of sandstone are tested to determine the RHT model intrinsic parameters, and the numerical computational RHT model of sandstone containing crack defects is established, which is verified in comparison with the test to analyze the validity of the model. Finally, the failure characteristics of the numerical model under initial stress were carried out. The study shows the following: with the increase in the fracture angle, the dynamic compressive strength and deformation modulus are distributed in a slanting V-shape, and the inclination angle of 45° is the smallest. The strain rate and energy dissipation rate are distributed in a slanting N-shape, and the inclination angle of 45° is the largest. The transmittance shows a decreasing trend, which is the opposite of the reflectivity pattern. The crack angle determines the location and direction of the initial crack, which affects the failure mode. In addition, the parameters of the RHT constitutive model suitable for sandstone are obtained, and the damage and strength patterns of the established RHT model are highly consistent with the laboratory test results. The damage range of numerical models for crack defects with different inclination angles is negatively correlated with confining pressure values and positively correlated with axial pressure values. The damage zones are symmetrically distributed approximately perpendicular to the direction of cracks, and the confining pressure has a contributing role in the peak of the element stresses; however, the axial compression has no contribution in the peak of the element stresses. [ABSTRACT FROM AUTHOR]

This paper demonstrates the importance of a proper contact algorithm selection when a constitutive model is correlated and validated, especially in the case of brittle materials. A parametric study is carried out to study the influence of contact parameters on the outcomes of the numerical simulations of a dynamic compression test. The split Hopkinson pressure bar (SHPB) model is developed, and sandstone rock is considered as a representative material having considerably different properties compared to SHPB bars. The finite element method (FEM) and smoothed particle hydrodynamics (SPH) were used to simulate specimen behaviour using a LS-Dyna solver. Two contact types based on the penalty method are analysed: nodes to surface (FEM and SPH) and surface to surface (FEM only). Furthermore, three approaches of contact stiffness calculation are used for each contact type. The waveform data and failure patterns are then compared among all simulated cases and the corresponding experimental outcomes. It is found that the soft constraint stiffness (SOFT = 1) provides the best outcomes, especially in the case of one-way contact, and is nearly insensitive to stiffness scaling parameters. By contrast, standard (SOFT = 0) and segment-based (SOFT =2) approaches require a substantial effort in adjusting the stiffness scaling parameters to obtain satisfactory results. This paper provides valuable guidance for correlating and validating parameters of constitutive models for rock and other brittle materials in the SHPB test. [ABSTRACT FROM AUTHOR]

The multi-jointed rock mass (MJRM) in mining, tunnel and underground engineering is prone to fracture and destabilization under the disturbance of blasting-induced dynamic wave. Study on dynamic mechanical properties of the MJRM under impact loading contributes to improving the stability of rock mass during engineering activities. A continuous-discrete coupling numerical model is developed to reproduce the laboratory Split Hopkinson Pressure Bar (SHPB) tests. The stress–strain relationship, crack types, joint penetration modes and energy dissipation characteristics of the MJRM at different joint inclination angles (α) are analyzed. Then the effects of the loading rate, number of joints, joint spacing (d) and joint stiffness on the dynamic peak strength and elastic modulus of the MJRM are discussed. It is revealed that the dynamic peak strength and elastic modulus of the MJRM are affected by the joint inclination angles, number of joints, joint spacing and joint stiffness, while the loading rate has little effect on the dynamic elastic modulus of the MJRM. The cracks generated at the joint tip do not appear to have enough time to expand under the impact loading. The main cause of the MJRM failure is the generation of the extensive micro-cracks that penetrate into each other and eventually connect with the joints to form the failure path. [ABSTRACT FROM AUTHOR]

Thin Spray-On Liner (TSL) has been widely used in underground engineering support such as mining due to its convenient operation and good support effect. The TSL applied to the rock is inevitably affected by dynamic loads from excavation. In order to study the support effect of TSL on a rock under dynamic load, a series of uniaxial compression experiments under static and dynamic loads are carried out on the TSL-coated specimen, and the costing thickness is 1 mm, 3 mm and 5 mm, respectively. The results showed that the TSL can improve the strength and peak strain of sandstone, and the degree of improvement is more obvious with the increase of costing thickness under static and dynamic load, and the loading rate of the dynamic load is about 70 ∼ 110 s−1. It was also found that the dynamic strength increases exponentially with strain rate, with the costing thickness increases, the strain rate index of sandstone increases. The good bonding ability and tensile properties of TSL ensure support to rock. Application of TSL can delay the time for cracks to appear in the specimen and increase the energy required for the failure of the specimen. The phenomenon was also simulated using ABAQUS, and the simulations show that TSL provides passive support that the pressure of TSL gradually increases with the deformation of the sandstone during the impact, and can delay the failure time of the specimen and reduce the number of cracks. That is consistent with the experiment. [ABSTRACT FROM AUTHOR]

Impact tests on post-fire concrete confined by Carbon Fiber-Reinforced Polymer/Plastic (CFRP) sheets were carried out by using Split Hopkinson Pressure Bar (SHPB) experimental setup in this paper, with emphasis on the effect of exposed temperatures, CFRP layers and impact velocities. Firstly, according to the measured stress-strain curves, the effects of experiment parameters on concrete dynamic mechanical performance such as compressive strength, ultimate strain and energy absorption are discussed in details. Additionally, temperature caused a softening effect on the compressive strength of concrete specimens, while CFRP confinement and strain rate play a hardening effect, which can lead to the increase in dynamic compressive strength by 1.8 to 3.6 times compared to static conditions. However, their hardening mechanisms and action stages are extremely different. Finally, nine widely accepted Dynamic Increase Factor (DIF) models considering strain rate effect were summarized, and a simplified model evaluating dynamic compressive strength of post-fire concrete confined by CFRP sheets was proposed, which can provide evidence for engineering emergency repair after fire accidents. [ABSTRACT FROM AUTHOR]

High-strength engineered geopolymer composite (EGC) materials exhibit excellent mechanical properties under quasistatic loading, thus showing great potential in military and civilian facilities subjected to impact or explosive loading. However, its dynamic mechanical response under high-speed loading is not fully understood. In this study, dynamic compressive test was performed on EGC with PE fiber contents of 0%, 0.5%, 1.0%, 1.5%, and 2.0% using the Split Hopkinson Pressure Bar (SHPB) test. The results indicated that EGC reinforced with 1.5% fiber exhibited optimal static and dynamic mechanical performance. In the strain rate range of 181 s−1 to 201 s−1, when the fiber content increased from 1.0% to 1.5% and 2.0%, the dynamic compressive strength of the EGC increased by 24.3%, 28.8%, and 44.0%, respectively, compared to the matrix without fiber. Dynamic parameters of the EGC, including dynamic compressive strength, dynamic increase factor, and impact toughness, showed sensitivity to strain rates and increased with strain rate. A modified model, incorporating the fiber bridging effect, was proposed based on the CEB-FIP model, providing important guidance for practical engineering applications. [ABSTRACT FROM AUTHOR]

A mechanical property experiment was carried out on steel-polypropylene fiber-reinforced concrete after elevated temperatures by using a 50 mm diameter SHPB apparatus. The regulations of compressive strength, elastic modulus, Poisson's ratio, and other mechanical properties under six heating temperature levels (normal temperature, 100 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and three impact pressures (0.3 MPa, 0.4 MPa, 0.5 MPa) were studied. Using ANSYS/LS-DYNA 19.0 numerical simulation software and LS-PrePost post-processing software, numerical simulation analysis was conducted on the dynamic Hopkinson uniaxial impact compression and uniaxial dynamic impact splitting mechanical experiments of C40 plain concrete and steel-polypropylene hybrid fiber concrete. The results show that the dynamic compressive strength of hybrid fiber concrete with the optimal dosage reaches its maximum at a temperature group of 200 °C, and the dynamic compressive strength of hybrid fiber concrete with the optimal dosage increases by 97.1% compared to C40 plain concrete at a temperature group of 800 °C. The impact waveform and stress-strain curve results of the numerical simulation are very similar to the experimental results. The errors in calculating the peak stress and peak strain are within 6%, which can truly and accurately simulate the static mechanical properties and failure process of hybrid fiber-reinforced concrete. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of accurately determining the arrival time of stress wave signals in SHPB test data processing. To eliminate human error, we introduce the time-window energy ratio method and evaluate six filters for noise reduction using box fractal dimensions. A mathematical model is established to optimize the stress equilibrium and impact process, which is solved using particle swarm optimization, resulting in the PSO-TWER method. We explore the impact of inertia weight and calculation methods on optimization outcomes, defining a stress equilibrium evaluation index. The results indicate that time-window length significantly affects arrival-time outputs, and the dynamic inertia weight factor enhances optimization convergence. The method accurately determines arrival times and effectively screens test data, providing a robust approach for SHPB test data processing. [ABSTRACT FROM AUTHOR]

To study the propagation and evolution of one-dimensional elastoplastic waves within the system under rectangular, trapezoidal, and half-sine incident waves, leveraging elastoplastic incremental wave theory and numerical simulation calculations, the research qualitatively investigates the distribution and evolution of the stress field within the specimen, the impact of Bar 2 parameters, and the deformation characteristics of Bar 2 under these three types of incident waves. The findings indicate: Regardingthe overall stress uniformity of Bar 2 during the entire loading phase, the rectangular incident wave is the most effective, while the half-sine and trapezoidal waves are more advantageous for analyzing the stress conditions in Bar 2 during the early loading phase. The diameter and dimensionless density of the specimen significantly influence the stress non-uniformity, showing an approximate negative and positive correlation, respective. [ABSTRACT FROM AUTHOR]

Incorporating masks into building materials offers a potential solution to the environmental threat of disposable masks with promising material performance. However, research on their dynamic properties is lacking to further determine the application range of the new composite. This study addresses this gap by shredding face masks into strips and incorporating them into mortars at varying volume ratios. The integrity and compactness of the mortar was measured and characterized by P-wave velocity, while dynamic compression properties were explored using a split Hopkinson pressure bar (SHPB) system. Subsequently, sieve analysis was conducted on the fractured specimens. The results indicate that incorporating masks generally improves the mortar integrity and the fragmentation after impacting. The dynamic uniaxial compression strength (DUCS) decreased for all mixing designs compared to plain ones under a constant loading rate. Meanwhile, the dissipated energy density showed a similar trend to the P-wave velocity, exhibiting less pronounced enhancement at higher loading rates. According to the dynamic characteristics, a dynamic constitutive model based on the Lemaitre principle and Weibull distribution of damage is developed and validated. The test results are further understood through the perspective of the mechanism of mask inclusion. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mining Science & Technology is the property of Journal of Mining Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigated the dynamic mechanical properties of CO2-cured foam concrete under varying conditions, focusing on the effects of foam admixture and fiber reinforcement. The study tends to enrich the knowledge regarding the performance of CO2-cured foam concrete under different loading rates, especially in relation to density and matrix strength. The foam admixture of the specimens ranges from 26% to 55%, achieving density from 600 kg/m3 to 1,000 kg/m3. The specimens were loaded at strain rates from 80 s-1 to 398 s-1. Experimental results revealed the dynamic elastic modulus, dynamic compressive strength, and Dynamic Increase Factor (DIF) showed a strong correlation with the foam admixture and density. In addition, the incorporation of polypropylene (PP) fibers effectively improved the mechanical behavior of the foam concrete, achieving up to a 17% increase in dynamic compressive strength. This comprehensive analysis highlights the critical role of foam admixture and fiber reinforcement in determining the dynamic properties of CO2-cured foam concrete and provides valuable insights for optimizing the dynamic performance of foam concrete in various construction applications.

Engineering cementitious composites (ECC) is an innovative high performance engineering structural material with high ductility, high toughness, and unique multiple cracking characteristics. Currently, most of the fibers used in ECC are expensive Kuraray PVA fibers produced in Japan. More and more researchers are using Polyethylene (PE) fibers made in China with low cost, high strength and high elastic modulus to replace Kuraray PVA fibers. However, the finer diameter and hydrophobicity make it difficult for the PE fibers to be distributed in the matrix evenly. In addition, most research currently focuses on the static performance of PE-ECC, with limited research on its dynamic performance. In this study, PE-ECC with different fiber contents was prepared with a high-power, high-speed mixer. Compressive tests, tensile tests and split Hopkinson pressure bar (SHPB) impact compression tests on the specimens were conducted to study their static and dynamic performance. The results indicated that increasing the fiber content can improve the mechanical properties of PE-ECC when the fiber volume fraction is low. Further increasing the volume fraction of fibers will affect the uniform distribution of fibers, leading to a decrease in the mechanical properties of PE-ECC and an increase in the discreteness of test results. Considering the difficulty of fiber dispersion and mechanical properties, it is recommended that the content of PE fibers should not exceed 2.25%. The research results of this paper may provide a reference for the promotion and application of PE-ECC, especially in the field of collision protection.

Polyurea (PU) materials are widely used in civil and military fields owing to their excellent weather, wear and corrosion resistance, impact resistance and energy absorption ability. In this study, polyurea nanocomposites integrated with polydopamine functionalized graphene oxide (GO@PDA) were reported. The functionalization of graphene oxide (GO) with polydopamine was achieved under mild conditions to optimize the dispersion and interfacial compatibility of GO within the PU matrix, thereby reinforcing the mechanical properties of PU materials. The quasi-static and dynamic compressive behaviors of PU nanocomposites under various strain rates (0.001–7000 s−1) were comprehensively investigated through a universal testing machine and split Hopkinson pressure bar (SHPB), respectively. Results revealed a significant enhancement in the strain-rate sensitivity, flow strength, yield strength, and strain energy density with the increasing strain rate and GO@PDA content. Particularly, at a strain rate of 7000 s−1, GO@PDA1.0%/PU nanocomposite exhibited a remarkable increase of 33% and 54% in flow strength and yield strength, respectively. This remarable enhancement was closely related with the effective dispersion and superior interfacial compatibility between GO@PDA and PU matrix. Eventually, to offer a comprehensive understanding of the mechanical behavior of PU nanocomposites, a visco-hyperelastic intrinsic model was employed to accurately capture the mechanical response under various strain rates.

Rock mass in tunnel, underground chamber and other underground engineering is inevitably affected by multiple blasting impact, rock mass cracking and failure are often affected by these damaged rock mass, so it is meaningful to study the rock mass affected by dynamic damage. To explore the influence of cyclic impact on the internal structure of marble, NMR (Nuclear Magnetic Resonance) technique was adopted to test the marble. It was found that the impact would rise the porosity of marble, and the pore size distribution would also change greatly. Then uniaxial compression experiments were conducted on core samples. The results show that the impact will cause significant damage to the marble, and the mechanical properties of the marble will be obviously degraded. With the increase of impact times, the peak strength and tangential deformation modulus tend to decrease. The impact effect promotes the initiation and development of rock microcracks, pushes forward the development of the compaction stage, and increases the strain at the full compaction point. In addition, the damage constitutive model with the combination of different disturbances and loads was constructed in stages according to the principle of statistics, and the experimental results were used to verify the damage constitutive model. The crack closure and failure of the samples subjected to different impact times were well reflected in the model, and the practical significance of the parameters in the model was analyzed. The failure mode of the sample subjected to different impact times is discussed and verified by acoustic emission technology.

In this work, a Cu–10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology. Physical properties of the alloy, including density, microstructure, melting point, and constant-volume specific heat, are tested. Via the split Hopkinson pressure bar (SHPB) and flyer-plate impact experiments, the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298–823 K and under strain rates of 1 × 10−3–5.2 × 103 s−1, and the Hugoniot relationship at impact pressures of 1.46–17.25 GPa and impact velocities of 108–942 m/s is obtained. Evolution of the Cu–10Ta microstructure that occurs during high-strain-rate impact is analyzed. Results indicate that the Cu–10Ta alloy possesses good thermal stability, and at ambient temperatures of up to 50% its melting point, stress softening of less than 15% of the initial strength is observed. A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate. Under strong impact, the copper phase is identified as the primary source of plastic deformation in the Cu–10Ta alloy, while significant deformation of the high-strength tantalum particles is less pronounced. Furthermore, the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact. Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.

In order to explore the enhancement effect of hybrid fiber content on the mechanical properties of cemented tailings backfill, three kinds of fiber materials were selected for slump, uniaxial compression and SHPB impact tests. The test results show that the fiber material has a great influence on the fluidity of the filling body. The higher the fiber content is, the weaker the fluidity is, and the polypropylene fiber has the most significant influence on the fluidity. The improvement of dynamic and static mechanical properties of filling body by hybrid fiber is affected by the content of hybrid fiber. In a certain range, with the increase of fiber content, it shows a trend of increasing first and then decreasing. The 0. 4% mass fraction of polypropylene fiber has the most significant increase in the early compressive strength of the filling body. At the standard curing age of 28 days, the improvement of dynamic and static mechanical properties of filling body by steel fiber is greater than that of the other two fibers. The hybrid fiber with a total fiber content of 1. 4% 1. 5% has the largest increase in the dynamic compressive strength of the filling body, and the increase is greater than that of higher or lower fiber content. At the same average strain rate, with the increase of the hybrid fiber content, the reflection energy and absorption energy of the filling body decrease first and then increase, and the transmission energy increases first and then decreases. The test results show that the appropriate amount of hybrid fiber can effectively improve the mechanical properties of the filling body, which is conducive to the safety of filling mining, and has a certain guiding role in the design of mine filling body materials. [ABSTRACT FROM AUTHOR]

In this work, a Cu–10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology. Physical properties of the alloy, including density, microstructure, melting point, and constant-volume specific heat, are tested. Via the split Hopkinson pressure bar (SHPB) and flyer-plate impact experiments, the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298–823 K and under strain rates of 1 × 10−3–5.2 × 10³ s−1, and the Hugoniot relationship at impact pressures of 1.46–17.25 GPa and impact velocities of 108–942 m/s is obtained. Evolution of the Cu–10Ta microstructure that occurs during high-strain-rate impact is analyzed. Results indicate that the Cu–10Ta alloy possesses good thermal stability, and at ambient temperatures of up to 50% its melting point, stress softening of less than 15% of the initial strength is observed. A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate. Under strong impact, the copper phase is identified as the primary source of plastic deformation in the Cu–10Ta alloy, while significant deformation of the high-strength tantalum particles is less pronounced. Furthermore, the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact. Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure. [ABSTRACT FROM AUTHOR]

Rocks containing flaws around rock structures are often subjected to complex temperatures and geological conditions. This study investigates the mechanical behavior of heat-treated rock samples with a flaw under ungrouted and grouted conditions subjected to dynamic loading. Rock samples were prepared from two different types of rocks, model rock and natural marble, with an existing flaw at a fixed orientation under three different infill conditions, i.e., ungrouted, cement grouted, and epoxy grouted. Samples were initially heat treated to a temperature between 30 and 650 °C for 0–15 h and then subjected to dynamic loading using Split Hopkinson Pressure Bar (SHPB). A high-speed camera was coupled with SHPB to record the progressive failure process of these samples, and Digital Image Correlation (DIC) captured the strain evolution. It was observed that the strength and stiffness of samples remained constant up to a certain temperature, namely transition temperature (i.e., 100–150 °C and 500–650 °C for model rock and marble, respectively) and then reduced significantly. The presence of grouts improved the mechanical behavior of samples significantly. However, their efficiency was dependent on the degree and duration of heating. Epoxy grout was observed to have superior efficiency compared to cement grout at lower degrees and lesser durations of heating which reverses for their higher magnitudes. Except for the epoxy-grouted samples at low temperatures, fracture initiation took place from the flaw tips in all other samples. Fracturing was dominated by tensile cracks at lower degrees and lesser duration of heating which changes to shear cracks-dominated mechanism, especially for porous model rock with the increasing degree and duration of heating. Highlights: Grouts were efficient in improving the dynamic response of jointed rocks with efficiency dependent upon the heat treatment of samples. Crack initiation and progression for grouted samples depend on grout strength, degree and duration of heating. Crack initiation and progression for ungrouted samples depend on the degree and duration of heating. Epoxy grout was more efficient for lower degree and duration of heating while cement grout was for higher ones. The transition from tensile-dominated fracturing to shear-dominated fracturing with increasing duration and degree of heating with more dominant effect on porous model rocks as compared to crystalline marble. [ABSTRACT FROM AUTHOR]

Water content plays a significant role in the dynamic mechanical properties of rocks in hydraulic, deep underground, and mining engineering. However, the previous study generally concentrated on the oven-dried and water-saturated rock with spherical pores. Therefore, this study aims to investigate the impact of different water saturation levels and microstructure on the dynamic mechanical properties of artificial porous rock (APR) with multi cracks. The specimens with six water saturation levels (100%, 80%, 60%, 40%, 20%, and 0%) were tested under various loading rates using a split Hopkinson pressure bar (SHPB). The obtained results include the typical failure modes, stress–strain curves, dynamic uniaxial compressive strength (DUCS), fragmentation performance, and energy dissipation. The findings indicate that the DUCSs of unsaturated specimens initially increase with water saturation (20% ~ 80%) but subsequently decrease to the lowest value under fully saturated conditions. The dissipated energies of wet specimens are higher than that of dry specimens. Moreover, the dry specimen is prone to fail in a rock burst pattern, whereas the wet specimens exhibit a pulverization pattern. In addition, the corresponding water-effect mechanisms are discussed based on the microstructure of the APR. [ABSTRACT FROM AUTHOR]