Search Results (394)

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

To address the damage and failure of electromechanical structures such as Printed Circuit Board (PCB) modules and battery assemblies under multiple impacts, this study combined experimental and modeling approaches to quantitatively investigate the influence of target material mechanical properties on impact acceleration characteristics. Quasi-static tensile/compression tests, split-Hopkinson pressure bar dynamic compression tests, and sequential multiple-target impact experiments were conducted on nine metallic materials, providing constitutive parameters and impact response data. Variance analysis revealed that material type significantly affected acceleration characteristics (p ≤ 1.62 × 10⁻⁵), whereas the target position in the impact sequence was statistically insignificant (p ≥ 0.89). Quantitative prediction models were established for different acceleration characteristics: Ridge regression (α = 0.1) was employed for Peak 1–Peak 3, Duration 1, and Duration 3, while linear regression was used for Duration 2. The results quantitatively demonstrated that the elastic modulus was positively associated with both peak acceleration and duration, while dynamic compressive yield strength exhibited a significant negative influence. This work establishes a preliminary quantitative predictive framework that provides guidance for target material selection in sequential multiple-target impact experiments and offers an experimental approach for generating tunable overload responses in high-intensity impact testing of electromechanical components. 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

Cemented backfill (CTB) in mining operations is frequently exposed to blasting-induced dynamic disturbances. These disturbances compromise CTB stability. This study employed split Hopkinson pressure bar (SHPB) tests, scanning electron microscopy (SEM), and high-speed imaging to characterize dynamic mechanical response and failure modes of CTB. The results showed that dynamic compressive strength (DCS) increased with impact load. However, damage severity also increased with load. High-speed imaging of crack evolution yielded fractal dimensions between 0.5 and 1.3. Higher fractal dimensions correlated with more extensive macroscopic cracking and greater CTB damage. They also indicated an increased probability of CTB failure and loss of load-bearing capacity. Microstructural observations identified ettringite (AFt) and C-S-H gel as the principal hydration products that provided cohesion and strength. However, pervasive microcracks and micropores accounted for the CTB’s low inherent strength. The findings suggest that reducing dynamic loads during mining operations can mitigate damage to CTB. Full article

This study investigates the flow stress behavior of Z-shaped steel wire used in cable sealing applications, over a temperature range of 20–500 °C and a strain rate range of 10⁻⁴ to 3000 s⁻¹. The primary objective is to establish reliable constitutive data to support accurate numerical simulations in relevant engineering contexts. To this end, quasi-static tensile tests, high-temperature tensile tests, and high-strain-rate dynamic compression tests were conducted using a high–low temperature electronic universal testing machine and a split Hopkinson pressure bar system. The true stress–strain responses were obtained, and the corresponding mechanical properties were systematically analyzed. Experimental results show that at room temperature (20 °C) and within the low strain rate range (10⁻⁴–10⁻¹ s⁻¹), the flow stress is insensitive to strain rate variations. However, following yielding, the slope of the flow stress curve increases noticeably with accumulating strain, indicating deformation behavior governed predominantly by strain hardening. Under high-strain-rate conditions at room temperature (20 °C, 10² to 10³ s⁻¹), the yield stress increases with increasing strain rate, revealing a pronounced strain rate sensitivity. At elevated temperatures combined with a low strain rate (300–500 °C, 10⁻³ s⁻¹), both the yield stress and the overall flow stress decrease markedly as the temperature rises, demonstrating significant thermal softening behavior. The microstructure and fracture of Z4 steel wire were observed by SEM to systematically investigate the effects of strain rate and temperature on its microstructural characteristics, thereby revealing the micro-mechanism of the material’s flow stress. Based on these experimental observations, a Johnson–Cook constitutive model was developed for the Z-shaped steel wire used in cable sealing applications. Validation results confirm that the model accurately captures the flow stress evolution of the material under coupled temperature and strain rate conditions. Full article

This study investigates the influence of nano-alumina (nano-Al₂O₃) on the compressive properties and damage mechanisms of epoxy matrix composites across a wide strain rate range. Composites with varying nano-Al₂O₃ contents (0, 1, 3, 5, 10, 15 wt%) were tested under quasi-static (0.001~0.1 s⁻¹) and dynamic (2500~4800 s⁻¹) conditions using a universal testing machine and a Split Hopkinson Pressure Bar, respectively. The phase, the microstructure, and their effects on macro-mechanical performance and micro-damage were characterized by XRD, SEM, and TEM. Results indicate that the incorporated nano-Al₂O₃ is highly crystalline, single-phase lamellar α-Al₂O₃. Its addition significantly modulates the compressive properties, with effects dependent on both content and strain rate. Under quasi-static compression, yield strength increased monotonically with nano-Al₂O₃ content at 0.1 and 0.01 s⁻¹, reaching a maximum increase of ~9.5% at 15 wt%. However, at 0.001 s⁻¹, optimal strength occurred at 10 wt%, beyond which agglomeration caused degradation. Dynamic tests revealed a positive strain rate effect. The 10 wt% composite exhibited optimal overall performance, combining high peak stress and a stable stress plateau, whereas the 15 wt% sample showed higher peak stress but poor post-peak load-bearing capacity. Microstructural analysis showed that 10 wt% nano-Al₂O₃ dispersed uniformly, enhancing toughness by inhibiting crack propagation via interfacial bonding and microstructural refinement. In contrast, at 15 wt%, particle agglomeration induced interfacial defects, promoting debonding and brittle fracture. This work provides insights into the wide-strain-rate mechanical behavior of nanoparticle-reinforced polymers and supports the design of high-performance, impact-resistant epoxy composites. Full article

To elucidate the dynamic impact response mechanism and energy evolution principles of coal–rock composites, dynamic impact tests were conducted on coal–medium sandstone and medium sandstone–medium sandstone composites at varying impact velocities utilizing a split Hopkinson pressure bar (SHPB) test system. The failure modes of the specimens, characteristics of stress wave propagation, dynamic stress–strain correlations, and energy dissipation properties were extensively analyzed. The results indicate that, when impact velocity increases, the failure mechanism of the composites shifts from shear slip to crushing failure. The dynamic response demonstrates a pronounced strain rate impact, and the failure energy threshold significantly escalates. Full article

The synergistic deformation and energy dissipation of backfill–surrounding rock composite structures under impact loading remain poorly understood, despite the frequent exposure of deep mine backfilled stopes to dynamic disturbances such as blasting and seismicity. In this study, Split Hopkinson Pressure Bar (SHPB) tests were conducted at a fixed impact pressure of 0.2 MPa on single-material specimens and bonded backfill–rock composite cylinders, with loading applied from both the backfill end and the surrounding rock end. Single backfill specimens exhibited dominant reflected energy (~90%) and low crushing energy consumption (<20%), whereas composite specimens displayed characteristic “double-peak” or “flat-peak” stress–strain signatures with peak strengths exceeding that of standalone backfill. When loading was directed from the high-strength surrounding rock into the backfill, the reflected energy ratio decreased to 60–80% and crushing energy consumption increased to 20–30%, demonstrating a loading-direction-dependent energy dissipation mechanism. These results provide a quantitative reference for optimizing blast sequence design in backfilled stopes. Full article

The discrete element method (DEM) is widely used to simulate concrete failure, but calibrating its mesoscopic dynamic parameters is computationally expensive due to the high-dimensional parameter space. This study proposes a physics-informed active learning framework to autonomously calibrate these parameters under impact loads. An FDM-DEM coupled split Hopkinson pressure bar model is established to simulate macroscopic dynamic compressive responses. Subsequently, a Plackett–Burman experimental design reduces the parameter optimization space from 16 to 8 core dimensions. A multi-layer perceptron surrogate model is then constructed. By comparing two heuristic active sampling strategies, results indicate that a parameter priority-guided strategy incorporating physical priors significantly outperforms a mid-value exploration strategy. The proposed approach achieves coefficients of determination exceeding 0.9 for predicting multiple macroscopic dynamic indicators on an independent testing set. Building upon this forward mapping, a robust inverse parameter prediction mechanism is established, achieving a closed-loop reconstruction of 0.8662. This framework provides a reliable, data-efficient, and automated pathway for calibrating complex multiphase particulate systems. Full article

Deciphering the dynamic fracture evolution of rock masses, particularly the interaction between dynamic stress waves and localised weak interlayers, is essential for optimising dynamic rock excavation in mining engineering. To systematically explore how these structural planes halt propagating cracks and generate a dynamic shielding effect, this study integrated Split Hopkinson Pressure Bar experiments, Digital Image Correlation techniques, and computational modeling. The findings demonstrate that altering the geometric orientation of the soft layer dictates the ultimate failure pattern. While an orthogonal interface (i.e., an interface with 0° inclination perpendicular to the loading direction) allows a tension-driven crack to cleave directly through the entire composite specimen, introducing an inclined obliquity of 15° forces the advancing fracture to deviate and permanently halt inside the soft stratum. Macroscopically, this barrier capability is validated by a rapid decrease in fracture speed, which drops abruptly by 75.5% upon encountering the inclined zone. Microscopic numerical evaluations confirm that this fracture arrest originates from wave mode conversion at the misaligned boundary. The angled interface forces incoming compressional pulses to transform into intense shear stresses, promoting extensive fracture. Substantial energy dissipation within the interlayer fully deprives the primary crack of the tensile stress required for propagation, effectively confining the stress-propagated hard rock within an energy shadow zone and suppressing further fragmentation. Full article

To further improve the mechanical properties of shotcrete in coal mine roadways, end-hooked steel fibers and chopped basalt fibers were selected. Based on the optimal mix ratios identified in existing research, steel–basalt hybrid fiber shotcrete (SBFC) specimens were prepared. Dynamic impact tests under different impact loads and various hybrid fiber contents were conducted using an SHPB. The microstructure was characterized using SEM and XRD. The results show that the dynamic compressive stress–strain curve of steel–basalt hybrid fiber shotcrete can be classified as elastic deformation stage, plastic yield stage, and post-peak failure stage. The incorporation of hybrid fibers reduces the elastic deformation and plastic yield stage, and the post-peak failure stage under active confining pressure shows elastic aftereffect characteristics. The dynamic compressive strength, dynamic elastic modulus, and deformation modulus increase with the increase in impact pressure and fiber content. When there is no confining pressure, the maximum dynamic compressive strength, dynamic elastic modulus, and modulus of deformation of SBFC4 reached 53.1 ± 2.2 MPa, 4.51 ± 0.3 GPa, and 2.55 ± 0.1 GPa, respectively, representing increases of 37.20%, 264.01%, and 59.37% compared with the control group. The dynamic compressive strength increases with the average strain rate, demonstrating a favorable strain rate effect. The energy–time history curves can be roughly divided into initial, growth, and stable stages. Under the same impact load conditions, as the fiber content gradually increases, the incident energy, dissipated energy, and energy utilization rate of the specimens all show a gradual upward trend. SEM and XRD results show that steel fibers and basalt fibers maintain good bonding with the cement matrix, contribute to the formation of gel and crystalline products within the specimens, effectively delay the initiation and propagation of cracks, and thereby improve the mechanical properties of the concrete specimens. Full article

To overcome the low strength of conventional polytetrafluoroethylene/aluminum (PTFE/Al) reactive materials and the insufficient reaction efficiency of aluminum, this study introduces highly reactive aluminum–cerium alloys (Al-Ce-1#, -2#, and -3#, with Ce contents of 30, 50, and 70%, respectively; the primary phase in Al-Ce-3# is Al₂Ce) with a multiscale structural design (comprising both micron-sized and nano-sized particles) into an ammonium perchlorate (AP) matrix. Al/AP reactive materials and Al-Ce/AP reactive materials with varying Ce contents were prepared. The thermal decomposition characteristics, dynamic mechanical properties, and impact ignition behavior were systematically investigated using differential scanning calorimetry (DSC) and split Hopkinson pressure bar (SHPB) experiments. The results demonstrate that the addition of Al₂Ce significantly alters the thermal decomposition process of AP, substantially lowering its decomposition temperature (by approximately 69 °C) and promoting concentrated exothermic decomposition. SHPB tests reveal that Al₂Ce/AP composites exhibit higher dynamic yield strength and flow stress than the Al/AP, accumulating faster strain energy density under impact loading, which indicates a more violent fragmentation failure mode. This enhanced mechanical failure behavior, which provides highly reactive interfaces and promotes hotspot formation, synergizes with the catalytic effect of Al₂Ce on AP decomposition. Together, these mechanisms jointly improve the impact ignition sensitivity of the material, significantly lowering its ignition threshold and shortening its combustion duration. This study confirms that Al₂Ce/AP is a novel reactive material combining excellent dynamic mechanical properties with outstanding impact reactivity, providing theoretical and technical support for the application of highly reactive rare-earth aluminum alloys in aluminum-based reactive materials. Full article

To explore the dynamic mechanical performance of metal rubber (MR) under high-speed impact loading, cylindrical solid MR specimens with spring coil outer diameters of 2–4 mm and relative densities of 0.2–0.35 have been prepared, and dynamic compression tests have been carried out utilizing the split Hopkinson pressure bar (SHPB) device at strain rates of 400–1000 s⁻¹. The dynamic stress–strain response of MR has been systematically analyzed, and the influences of strain rate, spring coil outer diameter, and relative density on its dynamic elastic modulus and energy absorption properties have also been quantitatively investigated. The results reveal that the dynamic stress–strain relationship of MR under high-speed impact presents significant nonlinearity and distinct strain rate effect. MR specimens with higher relative density, smaller spring coil outer diameter, or higher strain rate exhibit a larger dynamic elastic modulus, while those with higher relative density, larger spring coil outer diameter, or lower strain rate achieve higher energy absorption efficiency. A modified dynamic constitutive model for MR based on the Sherwood-Frost model has been developed by incorporating strain rate, relative density, and spring coil outer diameter as key influencing variables. The results show that the maximum mean relative error between the predicted and experimental data is less than 20%, indicating a favorable accuracy and reliability of the constitutive model. The proposed model can effectively characterize and predict the dynamic mechanical behavior of MR under high-speed impact loading conditions, providing a reliable theoretical basis for the engineering application of MR in impact-resistant structures. Full article