Search Results (385)

To evaluate the influence of fiber content, temperature, and loading rate on the dynamic compression performance of ultra-high performance concrete (UHPC), orthogonal Split Hopkinson Pressure Bar (SHPB) tests were performed on 120 MPa UHPC specimens. Range analysis of the test data reveals that the steel fiber content exerts the largest range on dynamic compressive strength, with loading rate ranking second and temperature having the least effect. A three-dimensional mesoscopic finite element model that accounts for temperature-dependent behavior was developed using a modified Karagozian & Case (K&C) constitutive model together with high-temperature bond–slip degradation curves. The simulated peak stresses are generally higher than the experimental values, with a Root Mean Square Error of 9.02 MPa, a Normalized Root Mean Square Error of 4.65%, and a maximum discrepancy of 10.07%, while the major experimental failure characteristics are reasonably reproduced. Additional numerical simulations indicate that the influence of steel-fiber content becomes increasingly temperature-dependent. Within the experimentally investigated range up to 300 °C, higher fiber content generally improves dynamic response and specimen integrity. At 600~800 °C, the numerical extrapolations suggest that the reinforcing efficiency of steel fibers may be substantially reduced under the assumed temperature-dependent degradation conditions. These high-temperature trends require further experimental validation. Full article

This study presents a systematic investigation into the mechanical responses of two tungsten-based alloys—84W–11.2Ni–4.8Fe and 88W–8.4Ni–3.6Fe—fabricated via selective laser melting (SLM). Quasi-static compression tests using a universal testing machine and dynamic impact experiments employing a split Hopkinson pressure bar (SHPB) were conducted over a temperature range of 298–598 K and strain rates spanning from 1 × 10⁻³ s⁻¹ to 2.3 × 10³ s⁻¹. Both alloys exhibited significant strain-rate hardening and thermal softening effects. Based on the experimental data, a Johnson–Cook (J–C) constitutive model was established. The fidelity of the calibrated model for the 84W alloy was rigorously validated through pulsed X-ray radiography and static armor penetration tests. The SLM-fabricated 84W-shaped charge liner produced a well-collimated jet with a tip velocity of 5101.5 m/s and achieved a penetration depth of 87 mm into rolled homogeneous armor (RHA)-equivalent steel targets. Numerical simulations using the developed J–C model showed close agreement with experimental measurements, with a maximum discrepancy of only 9.19%, thereby confirming the predictive capability of the constitutive model. These results demonstrate that the proposed J–C model can reliably characterize the large-deformation behavior of SLM-processed 84W and 88W liners under the extreme thermomechanical conditions characteristic of shaped charge jet formation—namely high temperature, high pressure, and ultra-high strain rate. Collectively, this work establishes a foundational framework for the application of SLM technology to shaped charge liner design and provides a critical basis for further research into jet formation physics and penetration mechanics of tungsten-based alloys. Full article

To enhance critical infrastructure protection against low-cost UAV impacts, this study proposes a novel ring lattice sandwich structure (RLSS) fabricated via an economical interlocking-assembly-brazing method. Its quasi-static compressive behavior is systematically investigated through experiments, numerical simulations, and theoretical analysis. Theoretical models for relative density and initial yield stress are validated against experiments, with errors of 7.1% and 6.6%, respectively. Quasi-static tests show that the one-layer RLSS exhibits a specific energy absorption (SEA) of 8.67 J/g, while the two-layer structure drops to 5.66 J/g due to inter-layer torsional instability. SHPB impact tests at strain rates of 750–1369 s⁻¹ demonstrate a pronounced strain-rate effect, with dynamic increase factors ranging from 1.14 to 1.43. Numerical simulations accurately reproduce the experimental deformation modes and reveal that multi-layer (2–5 layers) RLSSs reduce SEA by 46.9% compared with the one-layer simulated value of 9.43 J/g. Adding a 0.3-mm inner panel in simulations restores the crushing mode and raises the SEA of the two-layer structure to 7.19 J/g, surpassing the non-panel counterpart (6.03 J/g). Hybrid core configurations provide additional advantages: Mode I (ring–pyramid with inner panel) enhances total energy absorption with a limited ring-layer count, while Mode II (alternating layers) achieves minimal plateau stress fluctuation (PSF = 0.09). These findings confirm that the proposed RLSS, especially when optimized with thin inner panels or hybrid designs, offers great potential as protective cladding against impact and blast threats. Full article

This study systematically investigates the dynamic mechanical behavior and constitutive modeling of low-temperature quenched and tempered 42CrMo steel under high-strain-rate and high-temperature conditions. Dynamic compression tests were performed using a split Hopkinson pressure bar (SHPB) system over a strain rate range of 460–6450 s⁻¹ and a temperature range of 25–800 °C. The results show that the flow stress of quenched 42CrMo steel exhibits significant strain hardening and temperature softening effects, while its strain rate sensitivity is observed to be relatively low, especially under ultra-high-strain-rate conditions. Based on the experimental data, both the Power-Law and Johnson–Cook constitutive models were established. A hardness-based temperature softening coefficient was introduced to convert the experimental stress–strain curves into isothermal stress–strain curves, thereby effectively decoupling the coupled effects of strain rate and temperature. Error analysis indicates that the Power-Law model yields an average fitting error of 1.98%, which is superior to that of the Johnson–Cook model (3.23%), suggesting that the Power-Law model is more suitable for describing the dynamic mechanical behavior of low-temperature quenched and tempered 42CrMo steel. The findings of this study provide a reliable constitutive basis for numerical simulations of low-temperature quenched and tempered 42CrMo steel under extreme thermomechanical coupling conditions, such as high-speed cutting and impact forming. Full article

Overburden rotation and mining disturbance promote deep coal fracture and spalling, potentially inducing dynamic hazards, while the coal–rock thickness ratio largely governs the composite’s dynamic response and failure severity. Based on the geological conditions of a typical deep coal mine, SHPB tests were performed on coal–sandstone composite specimens with four systematically varied coal-to-rock ratios (C:R = 1:0, 2:1, 1:1, and 1:2). High-speed photography and the digital speckle correlation method (DIC) were integrated to capture displacement, strain, energy, and fragmentation fields throughout progressive dynamic compression. Experimental data revealed four findings: (1) Crack development follows a sequential evolution process of initiation, propagation, and failure. Higher impact air pressure accelerates crack development and coalescence, resulting in a higher degree of specimen fragmentation and fewer large blocks. Within the tested range of coal–rock ratios, an increase in the rock proportion accelerates coal fracture, which is attributed to the significantly higher density and hardness of rock compared to coal. (2) Energy evolution consistently follows three stages: absorption, accumulation, and dissipation. Under identical impact pressure, a higher rock ratio elevates equivalent stiffness and wave impedance, leading to monotonic increases in peak stress, peak strain, absorbed energy, and dissipated energy. (3) The fragmentation degree exhibits a pronounced dependence on impact pressure. Specifically, for the pure coal specimen (C:R = 1:0), when the impact pressure increases from 0.3 MPa to 0.7 MPa, the mass percentage of coarse debris (>30 mm) drops from 73.37% to 18.57%, whereas that of fine particles (<4 mm) rises from 15.69% to 35.24%. (4) Under identical impact conditions, a higher rock proportion leads to increasing trends in all measured indicators, including peak stress, strain, and energy accumulation and dissipation, which are consistent with the superior mechanical properties of the rock. Based on these observations, it can be inferred that the wave impedance mismatch and stiffness ratio at the coal–rock interface play a key role in controlling stress wave transmission/reflection and strain incompatibility; however, the individual contribution of each factor warrants further dedicated investigation. Full article

Calcareous sand is widely used in marine and island reef engineering; however, its low strength and severe particle breakage are further exacerbated under dynamic loading, making the dynamic performance of reinforced calcareous sand critical to engineering safety. Nevertheless, research on the dynamic characteristics of EICP/MICP-reinforced calcareous sand remains very limited. The dynamic performance was evaluated using Split Hopkinson Pressure Bar (SHPB) tests, and the results were compared with UCS data to examine the effects of particle gradation and fiber content on both dynamic and static behaviors. The results show that dynamic strength increases with calcium carbonate content (CCC) and impact pressure. Under the same CCC, the dynamic strength is consistently higher than the static strength, with a maximum difference of up to 2.5 MPa. Fiber incorporation significantly enhances structural integrity, and SEM analysis reveals that this improvement stems from effective bonding between fibers and cementitious materials. Based on the static and dynamic test results, the optimal mix ratio for EICP-reinforced calcareous sand is determined as 50% coarse sand content and 0.4% fiber content by mass, which provides theoretical support and design parameters for sustainable green reinforcement of calcareous sand foundations in marine and island reef engineering. Full article

Mixed mode I–III fracture commonly occurs in rock masses under complex three-dimensional stress states, yet the combined effects of loading conditions and fracture mode remain unclear. In this study, a heterogeneous sandstone disc model is developed in ABAQUS by coupling the Drucker–Prager elastoplastic model, an equivalent-strain damage model, and cohesive elements. The model is validated against static Brazilian splitting tests and dynamic SHPB tests. ENDB specimens are then employed to investigate mode I, mode III, and mixed mode I–III fracture under static and dynamic loading with offset angles ranging from 0° to 62.5°. As the offset angle increases, crack propagation evolves from straight tensile extension to deflected, twisted, and fragmented patterns dominated by anti-plane shear. Dynamic loading intensifies crack segmentation, localized damage, and transient instability while increasing the peak load, fracture toughness, and fracture energy. In contrast, the effective fracture toughness and fracture energy decrease monotonically with increasing offset angle under both loading conditions. A linear trend consistent with R² > 0.99 is observed between the mode I–III mixing coefficient and the effective fracture toughness based on single-realization simulations, the effective fracture toughness under dynamic loading is approximately 2.22 times that under static loading based on direct comparison of calculated values. These findings improve the understanding of loading-dependent mixed mode I–III fracture in sandstone and provide guidance for rock mass stability assessment. Full article

The dynamic load generated by the fracture of a hard roof significantly disturbed the stability of the surrounding rock in the lower roadway of the study site. This study established a dynamic transmission model of hydraulic fracture mesh and analyzed the influence of the hydraulic fracture mesh parameter on dynamic load attenuation from the perspectives of energy distribution and stress wave attenuation. The SHPB numerical model was established and calibrated based on PFC2D, and the findings were as follows: the hydraulic fracture mesh changes the rock into a discontinuous structure, which hinders the propagation of dynamic load and changes the medium of dynamic load propagation, resulting in part of the dynamic load being reflected and accumulating in the mesh area, causing the rock in the mesh area to break up or making the rock on the side of the hydraulic mesh to slip, which reduces the energy of the dynamic load. Finally, an industrial experiment was conducted on the 10107 working face of Huayuan Coal Mine. Monitoring results showed that the deformation of the roadway sides and roof was reduced by 833 mm and 861 mm, respectively, and the stability of the surrounding rocks of the roadway was effectively improved. Full article

In this study, we explore the static and dynamic mechanical responses of layered cemented backfill subjected to blasting loads. Variable-rate uniaxial compression tests and Split Hopkinson Pressure Bar (SHPB) numerical simulations were performed on specimens with three different interlayer cement-to-tailings ratios. All samples were cured for 28 days before testing. The test results reveal that uniaxial compressive strength rises and then falls with increasing loading rates, and mixed tensile-shear failure dominates quasi-static loading conditions. The interlayer cement-to-tailings ratio dominates the bearing capacity of backfill. At the test loading rate of 0.02 mm/s, lowering the interlayer ratio from 1:4 to 1:8 sharply reduces peak strength from 5.595 MPa to 1.285 MPa, with a total drop of 77.0%. SHPB simulation results show obvious strain-rate hardening under dynamic impact. For samples with an interlayer ratio of 1:4, dynamic compressive strength increases from 5.38 MPa to 6.16 MPa as impact velocity rises from 4 m/s to 13 m/s, a 14.5% improvement caused by rapid compaction of internal micropores. Combining damage mechanics and energy conservation principles, we establish a dynamic damage constitutive model that couples inherent layered interfacial damage with blasting-induced dynamic disturbance. Model predictions match experimental measurements well. The peak strength error is only 1.3% at a loading rate of 0.005 mm/s, and peak deviations for all test cases are controlled within 5.0%. This work quantitatively clarifies the static and dynamic mechanical evolution of layered cemented backfill, and provides solid theoretical support for mixture proportion design and blasting stability assessment in high-stage sequential backfilling mining. Full article

This study investigates the effect of coal gangue aggregate fractal gradation on the dynamic mechanical behavior and impact failure mechanism of cemented coal gangue backfill composites. Four aggregate gradations with different mass fractal dimensions were designed, and static compression and split Hopkinson pressure bar (SHPB) dynamic compression tests were conducted. The effects of fractal dimension and strain rate on stress–strain response, dynamic peak strength, dynamic increase factor (DIF), deformation modulus, energy dissipation, and failure morphology were analyzed. The results show that the composites exhibit a clear strain-rate strengthening effect, with dynamic strength, DIF, and deformation modulus increasing as strain rate increases. Aggregate fractal dimension has a nonlinear regulatory effect on mechanical performance. Among the four tested gradations, the specimen with D_f = 2.41 exhibits the best overall static and dynamic bearing performance, which is attributed to a more continuous coarse-particle skeleton and improved fine-particle filling. When the fractal dimension is too low, insufficient fine-particle filling leads to discontinuous contacts and larger pores; when it is too high, excessive fine particles weaken coarse-particle interlocking and promote matrix-dominated deformation. Energy analysis and failure observations further indicate that an intermediate fractal gradation improves energy absorption and delays unstable crack propagation. These findings provide a reference for gradation optimization and dynamic stability evaluation of coal gangue-based cemented backfill materials. Full article

To investigate the impact resistance of hybrid fiber-reinforced recycled aggregate concrete (RAC) under dry–wet cycles and sulfate attack, hybrid fiber-reinforced recycled aggregate concrete (RAC) was prepared. Dynamic impact compression experiments were conducted using an SHPB test device with a 50 mm diameter. The microstructure of recycled aggregate concrete (RAC) within dry–wet cycles and sulfate attack was examined using SEM. The results indicate that the dynamic compressive strength first rises and then declines with the rise in dry–wet cycles, and increases with the increase in the average strain rate. When the number of dry–wet cycles reaches 16, the dynamic compressive strength reaches its peak, with the B4S6 group achieving a maximum dynamic compressive strength of 59.02 MPa. The dynamic elastic modulus follows a good quadratic parabolic function distribution with respect to the number of dry–wet cycles. Both the incident energy and dissipated energy density initially rise and then reduce with increasing dry–wet cycles. The energy values of RAC with different fiber types follow the order: B4S6 > S6 > B4 > RAC. Under impact loading, the strain rate–strain time history curve of recycled aggregate concrete (RAC) exhibits the change of “increase–decrease–stable–decrease”. With increasing dry–wet cycles, the degree of fragmentation of recycled aggregate concrete (RAC) first increases and then decreases, the fractal dimension first decreases and then increases, and the average particle size first increases and then decreases. SEM results and microscopic reaction mechanisms reveal that in the early stage of dry–wet cycles, sulfate ions generate ettringite and gypsum within the recycled aggregate concrete (RAC), which fill internal cracks and pores, making the concrete denser and enhancing its mechanical properties. Towards the end of the dry–wet cycle, the amount of expansive ettringite and gypsum inside the recycled aggregate concrete (RAC) increases, leading to a sharp increase in pore wall stress, which induces new microcracks in the specimens, manifesting as a decline in mechanical properties at the macroscopic level. Full article

To investigate the dynamic impact performance of carbon fiber reinforced polymer (CFRP)-confined recycled concrete, this study designed four series comprising 80 specimens with parameters including strain rate, recycled coarse aggregate replacement ratio, and number of CFRP confinement layers. Split Hopkinson Pressure Bar (SHPB) impact tests were conducted to analyze the dynamic failure mode, stress–strain responses under dynamic loading, and variation in compressive strength of the CFRP-confined concrete specimens. Additionally, a modified Weibull statistical model and fractal theory were employed to analyze the dispersion characteristics of dynamic compressive strength. The results show that the dynamic compressive strength exhibits clear strain-rate sensitivity. The presence of CFRP confinement does not alter the fundamental shape of the stress–strain curves under different strain rates. The proposed modified Weibull statistical model accurately predicts the distribution of dynamic compressive strength at varying strain rates, with an average prediction error of 3.4% and a maximum error of 5.3%. Fractal dimension can quantitatively characterize the evolution trend and degree of crack-induced damage. Within the strain rate range of 52.85–138.42 s⁻¹, the fractal dimension of unconfined ordinary concrete specimens increases from 1.647 to 2.138; for unconfined recycled concrete, it increases from 1.612 to 2.158. The fractal dimension for CFRP-confined ordinary concrete specimens increases from 1.524 to 1.938, and for CFRP-confined recycled concrete specimens, from 1.503 to 2.019. The fractal dimension increases with the increase of strain rate, reflecting a typical strain rate effect. Full article

Carbon nanotube (CNT)-reinforced composites are promising advanced materials due to their exceptional mechanical properties. This paper presents a comprehensive investigation of the mechanical behavior of CNT/epoxy composites through theoretical modeling and experimental validation. An equivalent cylindrical fiber model was developed to transform CNTs into effective reinforcement phases, enabling the application of classical composite mechanics. Three reinforcement configurations were analyzed: two unidirectional short fiber models (aligned and staggered) and a three-dimensional four-directional braided long-fiber model. The effects of geometric parameters, including the diameter-to-thickness ratio (D/t) and fiber aspect ratio, on the effective elastic moduli were systematically evaluated. Static and dynamic compression experiments were conducted using an MTS 810 testing system and a Split Hopkinson Pressure Bar (SHPB) to examine the influence of loading rate, vacuum treatment, and reinforcement type (CNT, SiC, and hybrid SiC/CNT) on composite strength. The results indicated that 3 wt% CNT reinforcement increases the Young’s modulus by 30% under static loading and enhanced the dynamic compressive strength under impact loading. The vacuum degassing process significantly affected composite quality, with insufficient vacuum leading to strength degradation due to void formation. Theoretical predictions using Mori–Tanaka and dilute methods showed good agreement with experimental results at low reinforcement volume fractions. Scanning electron microscopy revealed uniform CNT dispersion and provided insights into failure mechanisms, including CNT pull-out and breakage. This work contributes to the understanding of structure–property relationships in CNT-reinforced polymer composites and provides guidelines for achieving their optimal design. Full article

In underground engineering, the dynamic failure mechanisms of rock masses containing openings under impact loading are of vital importance. This study systematically investigates the effects of opening shape, size, and orientation on the dynamic behavior of red sandstone. Dynamic impact tests are first performed using a split Hopkinson pressure bar together with high-speed photography and digital image correlation for full-field strain and crack monitoring. A two-dimensional combined finite–discrete element (FDEM) model is then developed to reproduce the dynamic failure process. It is found that the opening size significantly affects the dynamic compressive strength, while the opening shape dictates crack initiation and propagation. Circular openings induce symmetric cracking, square openings cause corner-dominated cracks, and horseshoe-shaped openings produce asymmetric failure whose dominant side depends on the rotation angle. The FDEM model established in this study successfully reproduces the main crack paths and failure modes observed in experiments, which provides a powerful tool for the analysis of rock dynamic failure. Moreover, the results in this study also provide practical engineering guidance for the reinforcement and support measures for different opening shapes. Full article

Dust and coal mine gas in deep mines are highly prone to causing fires, and the cyclic high temperatures generated by such fires are one of the key factors contributing to the instability of deep rock structures. To research the dynamic splitting tensile mechanical properties of sandstone subjected to high-temperature cycling, impact splitting tensile tests were performed on sandstone specimens under normal temperature and after high-temperature cycling treatments ranging from 250 °C to 900 °C using a split Hopkinson pressure bar (SHPB) with increasing cyclic temperature. The average dynamic tensile strength of sandstone specimens declines following a quadratic function, dropping from 18.07 MPa at T = 150 °C to a minimum value of 3.08 MPa, representing a maximum reduction of 82.96%. The dynamic strain and average strain rate exhibit increasing trends following exponential and logarithmic functions, respectively, while the dynamic elastic modulus exhibits a logarithmic declining trend. As the cyclic temperature grows, the degree of fragmentation of the specimens intensifies, transitioning from axial splitting failure to pulverization failure, with fragment size decreasing and fractal dimension exhibiting increasing trends. For temperatures between 450 °C and 600 °C, the dynamic tensile strength, dynamic strain, average strain rate, dynamic elastic modulus, average particle size, and fractal dimension all show a distinct interval behavior. As the cyclic temperature rises, the incident, reflected, and transmitted energies gradually decline. A higher fragmentation energy density corresponds to more severe specimen fragmentation, and the average fragment size follows a negative quadratic relationship with fragmentation energy density, which effectively quantifies the dynamic splitting tensile fragmentation behavior of rock. The findings of this study regarding the dynamic behavior and damage evolution of sandstone under cyclic high-temperature conditions can serve as a reference for assessing rock mass stability in high-temperature applications such as underground engineering and resource development. Full article