Search Results (75)

Temperature and strain rate play a crucial role in determining the mechanical properties of metals. These critical parameters are typically assessed using the split Hopkinson pressure bar (SHPB) test. However, previous studies have seldom considered the coupled influence of temperature and strain rate on dynamic mechanical behavior, thereby reducing the accuracy of constitutive models. To accurately characterize the dynamic mechanical behavior of 34CrNi3MoA low-alloy steel, a new constitutive model combining temperature and strain rate was developed. Firstly, SHPB experiments under varying temperatures and strain rates were designed to obtain actual stress–strain curves. The results indicate that the mechanical properties of 34CrNi3MoA low-alloy steel are significantly influenced by both temperature and strain rate. True stress has a significant temperature-softening effect within the temperature range of 25 °C to 600 °C, while the flow stress in the yield stage increases with rising strain rate. Secondly, a novel constitutive model was established by integrating a correction function. The model comprises three components: a strain rate-strengthening function influenced by temperature, a temperature-softening function influenced by strain rate, and a strain-hardening correction function accounting for the coupling of temperature and strain rate. Comparing the mean relative error, the new model significantly improves accuracy compared to the original Johnson–Cook (J-C) model. Full article

In order to correctly measure the shock wave pressure generated by a near-field explosion, and while considering the limitations of the measurement and calibration method of the current bar pressure sensor, an improved shock wave pressure measurement method was designed based on a bar pressure sensor combined with photon Doppler velocimetry (PDV) and strain measurement. By measuring the strain on the pressure bar and the particle velocity on the rear-end face, the shock wave pressure applied on the front-end face of the pressure bar was calculated based on one-dimensional stress wave theory. On the other hand, a calibration method was designed to validate the reliability of the test system. Based on the split-Hopkinson pressure bar (SHPB) loading experiment, the transmission characteristics of stress wave in the bar and the accuracy of the system test results were verified. The results indicated that the stress wave measurement results were consistent with the one-dimensional elementary theoretical calculation results of stress wave propagation in different wave-impedance materials, and the peak deviation measured by PDV and strain measurement method was less than 1.5%, which proved the accuracy of the test method and the feasibility of the calibration method. Full article

The pull-back method for determining dynamic tensile strength assumes one-dimensional stress wave propagation and material homogeneity. This study validates these assumptions for unidirectional reinforced concrete (UDRC) through experiments and numerical simulations. Split Hopkinson pressure bar tests were conducted on plain concrete, plain UDRC, and deformed UDRC specimens containing a central 6 mm steel bar. Ultra-high-speed digital image correlation at 500,000 fps enabled precise local strain rate measurements (3 s⁻¹ to 55 s⁻¹) at fracture locations. Finite element simulations revealed that while reinforcement induces localized multi-axial stresses near the steel–concrete interface, the bulk concrete maintains predominantly uniaxial stress conditions. Experimental results showed less than 1% variation in pull-back velocity between specimen types. Statistical analysis confirmed a unified strain rate-strength relationship: ${\sigma }_{\mathrm{spall}}=4.1+4.7{log}_{10}\left(\dot{\epsilon }\right)$$\mathrm{M}\mathrm{Pa}$, independent of reinforcement configuration (ANCOVA: $p=0.2182$ for interaction term). The dynamic tensile strength is governed by concrete matrix properties rather than reinforcement type. These findings are the first to experimentally and numerically validate the pull-back method’s applicability to UDRC systems, establishing that dynamic tensile failure is matrix-dominated and enabling simplified one-dimensional analysis for reinforced concrete under impact. Full article

To quantitatively describe the damage degree and failure process of the cemented backfill (CB) under dynamic loading, this paper performed numerical split Hopkinson pressure bar (SHPB) impact experiments on CB samples using the ANSYS/LS-DYNA. The damage pattern and failure process of CB samples with four mix ratios (cement-to-sand (c/s) ratios of 1:4, 1:6, 1:8, and 1:10) at different impact velocities (v) (1.5, 1.7, 1.8, and 2.0 m/s) were numerically investigated using the micro-crack density method to define the damage variable (d). The results revealed that the use of a waveform shaper in the numerical simulation yielded a more ideal rectangular wave to ensue uniform stress distribution across the sample’s plane without stress concentration. Numerical simulations effectively depicted the dynamic failure process of the CB, with the overall failure trend exhibiting edge spalling followed by the propagation and interconnection of internal cracks. When the v increased from 1.7 m/s to 1.8 m/s, the d increased by more than 10%. As the v increased from 1.5 m/s to 2.0 m/s, the d for c/s ratios of 1:4, 1:6, 1:8, and 1:10 ranged from 0.238 to 0.336, 0.274 to 0.413, 0.391 to 0.547, and 0.473 to 0.617, respectively. A significant “leap” phenomenon in damage was observed when the c/s ratio changed from 1:6 to 1:8. Full article

This study investigates damage characteristics of red sandstone under dynamic loads to clarify the effects of construction disturbances and blasting on the stability of surrounding rock during mountain tunnel construction in water-rich strata. Dynamic impact experiments at various loads were conducted using the Split Hopkinson Pressure Bar (SHPB) instrument, complemented by simulations of the fracturing process in saturated sandstone using finite element software. This analysis systematically examines the post-fracture granularity mass fraction, stress-strain curves, peak stress-average strain rate relationship, and fracture patterns. The dynamic response mechanism of red sandstone during the process of tunnel blasting construction was thoroughly investigated. Experimental results reveal that the peak stress and failure strain exhibit strain rate dependency, increasing from 45.65 MPa to 115.34 MPa and 0.95% to 5.23%, respectively, as strain rate elevates from 35.53 s⁻¹ to 118.71 s⁻¹. The failure process of red sandstone is divided into four stages: crack closure, nearly elastic phase, rapid crack development, and rapid unloading. Dynamic peak stress and average strain rate in sandstone demonstrate an approximately linear relationship, with the correlation coefficient being 0.962. Under different impact loads, fractures in specimens typically expand from the edges to the center and evolve from internal squeezing fractures to external development. Peak stress, degree of specimen breakage, and energy dissipation during fracturing are significantly influenced by the strain rate. The numerical simulations confirmed experimental findings while elucidating the failure mechanism in surrounding rocks under varying strain rates. This work pioneers a multiscale analysis framework bridging numerical simulation with a blasting construction site, addressing the critical gap in time-dependent deformation during tunnel excavation. Full article

During deep mining engineering, coal bodies are subjected to complex geological stresses such as periodic roof pressure and blasting impacts, which may induce mechanical property deterioration and trigger severe rock burst accidents. This study systematically investigated the mechanical characteristics and failure mechanisms of coal under strain rates on two orders of magnitude through quasi-static cyclic loading–unloading experiments and split Hopkinson pressure bar (SHPB) tests, combined with acoustic emission (AE) localization and crack characteristic stress analysis. The research focused on the differential mechanical responses of coal-rock masses under distinct stress environments in deep mining. The results demonstrated that under quasi-static loading, the stress–strain curve exhibited four characteristic stages: compaction (I), linear elasticity (II), nonlinear crack propagation (III), and post-peak softening (IV). The peak strain displayed linear growth with increasing cycle, accompanied by a failure mode characterized by oblique shear failure that induced a transition from gradual to abrupt increases in the AE counts. In contrast, under the dynamic loading conditions, there was a bifurcated post-peak phase consisting of two unloading stages due to elastic rebound effects, with nonlinear growth of the peak strain and an interlaced failure pattern combining lateral tensile cracks and axial compressive fractures. The two loading conditions exhibited similar evolutionary trends in crack damage stress, though a slight reduction in stress occurred during the final dynamic loading phase due to accumulated damage. Notably, the crack closure stress under quasi-static loading followed a decrease–increase pattern with cycle progression, whereas the dynamic loading conditions presented the inverse increase–decrease tendency. These findings provide theoretical foundations for stability control in underground engineering and prevention of dynamic hazards. Full article

In complex geological environments, the discontinuous dynamic response behavior of jointed rock masses under the coupled effects of in situ stress and transient dynamic disturbances significantly exacerbates the risk of surrounding rock instability. This study establishes three-dimensional numerical models of various jointed rocks under uniaxial–biaxial–triaxial split Hopkinson pressure bar (SHPB) experimental systems through the coupling of the finite difference method (FDM) and discrete element method (DEM). The models adhere to the one-dimensional stress wave propagation assumption and satisfy the dynamic stress equilibrium requirements, demonstrating dynamic mechanical responses consistent with physical experiments. The results reveal that the synergistic–competitive effects between joint configuration and initial pre-compression jointly dominate the dynamic mechanical response of rocks. Multiaxial pre-compression promotes the development of secondary force chain networks, enhances rock impact resistance through multi-path stress transfer mechanisms, significantly improves strain energy storage density during peak stages, and drives failure modes to evolve from macroscopic through-going fractures to localized crushing zones. The spatial heterogeneity of joint configurations induces anisotropic characteristics in principal stress fabric. Single joint systems maintain structural integrity due to restricted weak plane propagation, while cross/parallel joints exhibit geometrically induced synergistic propagation effects, forming differentiated crack propagation paths that intensify frictional and kinetic energy dissipation. Through cross-scale numerical model comparisons, the evolution of force chain fabric, particle displacement distribution, microcrack propagation, and energy dissipation mechanisms were analyzed, unveiling the synergistic regulatory effects of the stress state and joint configuration on the rock dynamic response. This provides a theoretical basis for impact-resistant structure optimization and dynamic instability early warning in deep engineering projects involving jointed surrounding rock. Full article

The Split-Hopkinson pressure bar (SHPB) test is a commonly accepted experiment to investigate the material behavior under high strain rates. Due to the low impedance of soft materials, here, the test has to be performed with plastic bars instead of metal bars. Such plastic bars have a certain viscosity and require a correction of the measured signals to account for the attenuation and dispersion of the transmitted waves. This paper presents a signal correction method based on a spectral decomposition of the strain-wave signals using Fast Fourier Transform and additional applied strain gauges in the experimental setup. The concept can be used to adapt the pulses and to concurrently validate the measurement method, which supports the evaluation of the experiment. Our investigation is carried out with a Split-Hopkinson pressure bar setup of PMMA bars and silicon-like specimens produced by the 3D printing process of digital light processing. Full article

Mastering the dynamic mechanical behaviors of pre-stressed fractured rocks under repeated impact loads is crucial for safety management in rock engineering. To achieve this, repeated impact loading experiments were performed on produced fractured samples exposed to varying pre-applied axial and confining pressures using a split Hopkinson pressure bar test system in combination with a nuclear magnetic resonance imaging system, and the dynamic failure mechanism and fractal features were investigated. The results indicate that the dynamic stress–strain curves exemplify typical class II curves, and the strain rebound progressively diminishes with growing impact times. The impact times, axial pressure, and confining pressure all significantly affect the dynamic peak strength, average dynamic strength, dynamic deformation modulus, average dynamic deformation modulus, maximum strain, and impact resistance performance. Moreover, under low confining pressures, numerous shear cracks and tensile cracks develop, which are interconnected and converge to form large-scale macroscopic fracture surfaces. In contrast, specimens under a high confining pressure primarily experience tensile failure, accompanied by localized small-scale shear failure. Under low axial pressure, some shear cracks and tensile cracks emerge, while at high axial pressure, anti-wing cracks and secondary coplanar cracks occur, characterized predominantly by shear failure. In addition, as the confining pressure grows from 8 to 20 MPa, the fractal dimensions are 2.44, 2.32, 2.23, and 2.12, respectively. When the axial pressures are 8, 14, and 20 MPa, the fractal dimensions are 2.44, 2.46, and 2.52, respectively. Overall, the degree of fragmentation of the sample decreases with growing confining pressure and grows with rising axial pressure. Full article

Stress wave dispersion can result in the loss or distortion of critical high-frequency data during high-strain-rate material tests or blast loading experiments. The purpose of this work is to demonstrate the benefits of correcting stress wave dispersion in split-Hopkinson pressure bar experiments under various testing situations. To do this, an innovative computational algorithm, $\mathtt{SHPB}\text{\_}\mathtt{Processing}.\mathtt{py}$, is created. Following the operational run through of $\mathtt{SHPB}\text{\_}\mathtt{Processing}.\mathtt{py}$’s capabilities, it is used to process test data acquired from split-Hopkinson pressure bar tests on aluminium, sand and kaolin clay samples, under various testing conditions. When comparing dispersion corrected and simple time shifting data obtained from SHPB experiments, accounting for dispersion removes spurious oscillations and improves the inferred measurement at the front of the specimen. The precision of the stress and strain results gathered from its application emphasises its importance through the striking contrast between its application and omission. This has a significant impact on the validity, accuracy and quality of the results. As a result, in the future, this tool can be utilised for any strain rate testing situation with cylindrical bars that necessitates dispersion correction, confinement, or stress equilibrium analysis. Full article

Obtaining reliable dynamic mechanical properties through experiments is essential for developing and validating constitutive models in material selection and structural design. This study introduces a dynamic tensile method using a modified M-type specimen loaded by a split Hopkinson pressure bar (SHPB). A closed M-type specimen was thus employed. Finite element simulations and experiments were used to validate the design of the M-type specimen, which was fabricated using 17-4PH (precipitation hardening) stainless steel powder with a 3D (three-dimensional) selected laser melting (SLM) printer. After verifying force balance and uniform deformation in the tensile region, tensile tests were conducted across strain rates from quasi-static to a strain rate of 5900 s⁻¹. The results demonstrated that this method effectively assessed the dynamic tensile behaviors of stainless steel at high strain rates, and achieved both ultra-high strain rates and large plastic deformation. Full article

To improve the safety and stability of tunnel structures, developing grouting materials suitable for cold regions with excellent performance is crucial. Herein, waterborne polyurethane (WPU) was used to modify cement grouting materials. Through orthogonal testing analysis, the optimal mixing ratio of the modified cement grouting materials was determined to be as follows: a water–cement ratio of 0.5, hydroxypropyl methyl cellulose (HPMC) content of 0.05%, WPU content of 5%, water-reducing agent (WRA) content of 0.2%. Furthermore, the dynamic mechanical properties of grouting concretion stones were studied. The influence of various external parameters on the compressive strength of the grouting concretion stones cured for different ages was evaluated. The influence degree of stone particle size on the dynamic compressive strength of the grouting stone body was d_{5–10 mm} > d_{5–20 mm} > d_{5–30 mm}. The split Hopkinson pressure bar experiment was performed to show that for the same strain rate, the absorbed energy and energy utilization rate first increase and then decrease with increasing stone particle size. When the stone particle size was 5–20 mm, the absorption energy and energy utilization rate of the grouting stone body were the highest. Full article

Open-pit coal mining offers high resource recovery, excellent safety conditions, and large-scale production. However, the process generates significant dust, leading to occupational diseases such as pneumoconiosis among miners and adversely affecting nearby vegetation through dust deposition, which hinders photosynthesis and causes ecological damage. This limits the transition of open-pit mining to a green, low-carbon model. Among these processes, blasting generates the most dust and has the widest impact range, but the specific amount of dust generated has not yet been thoroughly studied. This study integrates indoor experiments, theoretical analyses, and field tests, employing the Split Hopkinson Pressure Bar (SHPB) system to conduct impact loading tests on coal–rock samples under pressures ranging from 0.13 MPa to 2.0 MPa. The results indicate that as the impact load increases, the proportion of large-sized blocks decreases while smaller fragments and powdered samples increase, signifying intensified sample fragmentation. Using stress wave attenuation theory, this study translates indoor impact loadings to field blast shock waves, revealing the relationship between blasting dust mass fraction and impact pressure. Field tests at the Haerwusu open-pit coal mine validated the formula. Using image recognition technology to analyze post-blast muck-pile fragmentation, the estimated dust production closely matched the calculated values, with an error margin of less than 10%. This formula provides valuable insights for estimating dust production and improving dust control measures during open-pit mine blasting operations. Full article

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

This paper comprehensively investigates the dynamic mechanical properties of concrete by employing a 75 mm diameter Split Hopkinson Pressure Bar (SHPB). To be detailed further, dynamic compression experiments are conducted on coral aggregate seawater concrete (CASC) to unveil the relationship between the toughness ratio, strain rate, and different strength grades. A three-dimensional random convex polyhedral aggregate mesoscopic model is also utilized to simulate the damage modes of concrete and its components under varying strain rates. Additionally, the impact of different aggregate volume rates on the damage modes of CASC is also studied. The results show that strain rate has a significant effect on CASC, and the strength grade influences both the damage mode and toughness index of the concrete. The growth rate of the toughness index exhibits a distinct change when the 28-day compressive strength of CASC ranges between 60 and 80 MPa, with three times an increment in the toughness index of high-strength CASC comparing to low-strength CASC undergoing high strain. The introduction of pre-peak and post-peak toughness highlights the lowest pre-to-post-peak toughness ratio at a strain rate of approximately 80 s⁻¹, which indicates a shift in the concrete’s damage mode. Various damage modes of CASC are under dynamic impact and are consequently defined based on these findings. The LS-DYNA finite element software is employed to analyze the damage morphology of CASC at different strain rates, and the numerical simulation results align with the experimental observations. By comparing the numerical simulation results of different models with varying aggregate volume rates, it is reported that CASC’s failure mode is minimized at an aggregate volume rate of 20%. Full article