Split Hopkinson Pressure Bar Device Research Articles

Research on microplastic deformation of Inconel718 under the conditions of high temperature and high strain rate

The compression experiments of the nickel-based superalloy Inconel718 were carried out with the help of split Hopkinson pressure bar device, and the microstructure evolution law in the compression deformation of the alloy was studied by means of optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dislocation theory, a three-dimensional discrete dislocation dynamics model is established. By simulating the dynamic evolution of the discrete dislocation, the interaction of the dislocation itself and the formation of the dislocation microstructure were captured, and further explore the microplastic deformation process of Inconel718. The results show that deformation conditions significantly affect the rheological behavior and dynamic recrystallization behaviour. The cross slip of dislocations is closely related to temperature and strain rate, which in turn affect the dislocation configuration. The deformation mechanism of Inconel718 under the conditions of high temperature and high strain rate is jointly dominated by dislocation slip and twin deformation. As the temperature increases, the average Schmidt factor increases, and more dislocation slip systems are activated. As the strain rate increases, the number of deformation twins increases, while the thickness of deformation twins decreases.

Dynamic mechanical response and failure characteristics of coal and rock under saltwater immersion conditions

The stability of coal and rock masses in water-rich mines is affected by both mine water erosion and dynamic disturbances. Thus, it is necessary to study the dynamic mechanical response and failure characteristics of coal and rock under the combination of saltwater and a high strain rate. To this end, a split Hopkinson pressure bar device was employed to investigate the effects of impact velocity, water content, and immersion liquid on the dynamic mechanical behaviours of coal and rock. The results revealed that the weakening effect of saltwater on the dynamic mechanical properties of coal and rock is much greater than that of distilled water. With increasing moisture content, the dynamic compressive strength of the coal specimens decreases monotonically, while that of the rock shows a trend of first increasing and then decreasing. The failure process and destruction of coal and rock are comprehensively affected by both the external impact load and the physical and mechanical properties of the material. The degree of damage of the coal and rock specimens increases with increasing impact velocity and water content. Moreover, the influence of various factors on the impact fracture mechanism of coal and rock under saltwater immersion conditions was revealed. These findings are highly important for the design and maintenance of underground coal and rock building structures.

Dynamic failure behaviour of sandstone with various weak-filling joints using the Brazilian disc method

Rock masses contain joints often filled with low-strength materials like mud and gum. The instability mechanism of a filled jointed rock mass under dynamic loads is complex, posing challenges for disaster control. Splitting tests were conducted using a split Hopkinson pressure bar (SHPB) device and a high-speed camera to investigate the effects of weak-filling joints at various angles on the failure mechanism and mechanical properties of sandstone. The typical failure processes, splitting mechanical properties, and fracture morphologies were analysed. The results indicated that as the joint angle increased from 0° to 90°, the crack coalescence pattern of the jointed sample under static and dynamic splitting loads evolved from complete separation along the bonding surfaces to shear-slippage failure along the direction of the joint angle and tensile-shear failure with a dominant zigzag track, ultimately leading to typical tensile failure. Under dynamic loads, filled joints reduced brittleness of the samples, contrary to the behaviour observed under static loads. Peak load and displacement were proportional to joint angle and impact gas pressure, respectively. The fracture surface morphology precisely reflected the macroscopic fracture mechanism at the microscopic scale.

Dynamic compressive behavior of steel fiber synergistically reinforced cellular concrete under high strain-rate loading

To better understand the reinforcement and toughness effects of steel fibers, a 75-mm split Hopkinson pressure bar (SHPB) device was used to test the uniaxial dynamic compression properties of steel fiber synergistically reinforced cellular concrete (SFSRCC) under high strain rates. The dynamic compression performance characteristics of the SFSRCC, including the stressstrain curve, dynamic strength, impact toughness and failure mode, were analyzed. The results showed that the dynamic strength, peak strain and impact toughness of SFSRCC increase with increasing strain rate. Compared with that of cellular concrete (SAP10S0), a higher steel fiber volume ratio corresponded to a greater enhancement in the dynamic performance characteristic indices of the SFRCC. The maximum increases were 138.4%, 180.0% and 280.0% for the DIF, peak strain, and impact toughness, respectively. The damage degree of the SFSRCC specimen decreased with increasing fiber content, and a larger area of residual "core retention" was observed, which indicated that the impact resistance of the SFSRCC with a high fiber content was improved. An empirical formula that can accurately characterize the dynamic strength increase factor (DIF) of SFSRCC with high strain rates was proposed, and the prediction results obtained by using the DIF of the SFSRCC were highly consistent with the test results, which confirmed its effectiveness. To further quantify the strain rate enhancement effect and fiber content for the reinforcement and toughening ability of SFSRCC, the relationships between the peak strength/peak strain/impact toughness and strain rate and between the DIF increment ratio/strain energy density increment ratio and fiber volume fraction were determined. In conclusion, the dynamic compression performance characteristics of SFSRCC can be enhanced by incorporating an appropriate quantity of steel fibers with a dynamic impact load.

Dynamic impact experimental and global cohesive element method to shale fracture characterization

The fracture behavior and various of mechanical mechanisms of shale are greatly influenced by the bedding surface. To study the effects of bedding angles on the crack propagation patterns and dynamic fracture properties, the shale notched semi-circular bend (NSCB) specimens were studied by the modified split Hopkinson pressure bar (SHPB) device, three-dimensional digital image correlation (3D-DIC) system with the high-speed (HS) photography and ABAQUS finite element software. The research results showed that at the same impact velocity, the 30°, 45° and 60° beddings played an obvious deflexion effect on the shale crack propagation. However, the 0° and 90° bedding did not deflect the crack propagation. The dynamic fracture toughness of shale NSCB specimens increased with the increase of impact loading rate but the increase magnitude decreased with the higher impact rate. The kinetic energy during specimen fracture was calculated by the extracting displacement data from the 3D-DIC, and it was found that the kinetic energy accounted for less than 6% of the absorbed energy during the dynamic compression of the shale. The crack propagation characteristics of ABAQUS simulation was approximately consistent with the experimental results. It is conducive to the study of shale gas fracturing and the formation of complex seam networks in shale and it is of great research significance for the efficient extraction of shale gas.

Dynamic constitutive model of saturated saline frozen soil under uniaxial impact loading

The soil matrix, salt crystals, ice crystals, and pore solutions constitute the composite geological material of saturated saline frozen soil. The destruction mode and dynamic constitutive model of saturated saline frozen soil need to be studied because infrastructure construction is increasingly being extended to regions with saturated saline frozen soil. Based on the split Hopkinson pressure bar device, uniaxial impact compression tests were conducted on frozen soil samples with different salt contents under different strain rates. The strain rate of saturated saline frozen soil must be emphasized based on the results. The gradient of the elastic segment and maximum stress of the soil are negatively correlated with the salt content increase. To further explore the failure mechanism, the study examined the damage and failure behavior of saturated saline frozen soil, along with the absorption energy in the failure process. According to the test results, the saturated saline frozen soil was similar to a particle-reinforced composite. Subsequently, the debonding damage of the ice–salt eutectic and the mechanical–chemical damage of the soil matrix were considered. The test results could be predicted accurately from the results of the model, verifying that the influences of the salt content and strain rate are reasonably considered by the constructed model.

Dynamic responses of laminated and graded ZrC-Mo composites

It is of great significance to investigate the dynamic responses of functionally graded materials (FGMs). A series of experiments are conducted to evaluate the dynamic behaviors of the laminated and graded ZrC-Mo composites with three graded exponents (i.e., 0.69, 1.35, and 2.70) by the split Hopkinson pressure bar (SHPB) device. The graded composites with an exponent of 0.69 show the highest strength and best performances of the three. It results from the formation of local stress-transferring structures and the interaction of the ZrC component and Mo component. Based on the digital imaging correlation (DIC) method, different evolutions of local strains in the ZrC-rich and the Mo-rich regions are analyzed by changing the gradient directions of the composites. The transmission behaviors of stress waves in the laminated and graded composite with multi-interfaces are investigated theoretically. The finite element method (FEM) is used to evaluate influences of the plasticity of metal component, and the transmitted coefficient in theory is employed to optimize and evaluate the laminated and graded structures. It also indicates the special role of loading frequency. These results might be helpful for a profound understanding of the internal wave propagation and guide the structural designing optimization.

Stress overshoot and its evolution of ceramsite concrete with freeze–thaw cycles under impact loading

In the present study, the impact characteristics of ceramsite concrete after freeze–thaw cycles are studied. The split Hopkinson pressure bar (SHPB) device is applied to conduct impact compression tests on ceramsite concrete samples with different volume fractions and freeze–thaw cycles under different strain rates. The performed analyses show that there is an obvious stress overshoot evolution after the peak stress of the stress–strain curve. The obtained results show that the stress and damage evolution of the stress overshoot platform has an obvious strain rate effect. It is found that with an increase in freeze–thaw cycles, freeze–thaw damage increases, while the magnitude of platform stress and overshoot stress decreases. The volume fraction of ceramsite affects the evolution of the stress overshoot platform. It is pointed out that the physical nature of the plateau trend originates from the competition between the effects of damage softening and secondary strain strengthening. The dynamic constitutive relationship of ceramsite concrete considering the influence of freeze–thaw cycles and damage evolution is established. The performed analyses demonstrate that the theoretical model can be applied to accurately analyze the stress–strain characteristic curve of ceramsite concrete. The results demonstrate that the impact failure images obtained from the finite element method are good consistent with the experimental results.

A statistical bonded particle model study on the effects of rock heterogeneity and cement strength on dynamic rock fracture

AbstractNumerical modelling and simulation can be used to gain insight about rock excavation processes such as rock drilling. Since rock materials are heterogeneous by nature due to varying mechanical and geometrical properties of constituent minerals, laboratory observations exhibit a certain degree of unpredictability, e.g. with regard to measured strength and crack propagation. In this work, a recently published heterogeneous bonded particle model is further developed and used to investigate dynamic rock fracture in a Brazilian disc test. The rock heterogeneities are introduced in two steps—a geometrical heterogeneity due to statistically distributed grain sizes and shapes, and a mechanical heterogeneity by distributing mechanical properties using three Weibull distributions. The first distribution is used for assigning average bond properties of the grains, the second one for the intragranular bond properties and the third one for the bond properties of the intergranular cementing. The model is calibrated for Kuru black diorite using previously published experimental data from high-deformation rate tests of Brazilian discs in a split-Hopkinson pressure bar device, where high-speed imaging was used to detect initiations of cracks and their growth. A parametric study is conducted on the Weibull heterogeneity index of the average bond properties and the grain cement strength and evaluated in terms of crack initiation and propagation, indirect tensile stress, strain and strain rate. The results show that this modelling approach is able to reproduce key phenomena of the dynamic rock fracture, such as stochastic crack initiation and propagation, as well as the magnitude and variations of measured quantities. Furthermore, the cement strength is found to be a key parameter for crack propagation path and time, overloading magnitudes and indirect tensile strain rate.

Experimental study on dynamic properties of flax fiber reinforced recycled aggregate concrete

Recycling waste concrete is critical to land use and reduction of landfills. It is a good option to recycle the waste coarse aggregates from it and add them to the concrete matrix. Due to the existence of new and old interface transition zones (ITZs), the quasi-static compressive strength of recycled aggregate concrete is lower than that of natural aggregate concrete, which limits the widespread application of recycled aggregate concrete. In order to improve its engineering application of recycled aggregate concrete, the dynamic compressive properties were studied. Thus, based on a Split Hopkinson Pressure Bar (SHPB) device, the effects of strain rate and recycled coarse aggregate (RCA) replacement ratio on the failure mode, dynamic compressive strength, critical strain and toughness were investigated. It was found that increasing the strain rate led to the aggravation of the specimen damage and growth of the dynamic compressive strength, toughness and critical strain. At a high strain rate, the strain rate effect changed the failure mode of recycled aggregate concrete. This reduced the performance difference between recycled and natural aggregate concrete, in terms of the dynamic compressive strength. The recycled aggregate concrete had a similar toughness to the natural aggregate concrete. Although the growth of the RCA replacement ratio decreased the dynamic compressive strength and increased the critical strain, it had a little effect on the toughness. In order to reduce the brittleness of the recycled aggregate concrete and improve its deformability, non-synthetic, green and low-consumption flax fibers were incorporated into the concrete matrix, and its dynamic compressive behaviors were studied experimentally accordingly. Tests verified that the addition of flax fibers significantly reduced the damage and increased the critical strain. Especially when the strain rate was greater than 200 s-1, flax fiber reinforced recycled aggregate concrete exhibited a superior energy consumption ability. Based on the experimental data, empirical equations were proposed to describe the dynamic compressive strength, critical strain and toughness at different strain rates.

Valorization of Air-Cooled EAF Manganese Slag in Comminution Processes: an Investigation into the Breakage Characterization

In recent years, slag, a residue from pyrometallurgical processes, has become more attractive in circular economy frameworks to increase the efficient use of resources throughout the life cycle of steel products and help in the reduction of carbon emissions. Its applicability is strongly dependent on the particle size, and therefore, the optimization of breaking processes should be approached by increasing the knowledge of the dynamics of slag to promote fracture. Increasing the knowledge on the mechanical response of manganese slag opens up the potential for the development of cost-effective numerical models, e.g., constitutive models based on inverse engineering calibration frameworks or digital twins. In this study, rate-dependent tests of manganese slag have been performed using a split Hopkinson pressure bar device for testing its dynamic mechanical response. In order to obtain information about the crack initiation and fracture process, 2D ultra-high speed imaging was implemented with a sampling frequency of 663,200 fps for diametrically loaded specimens. Full-field deformation measurements using digital image correlation (DIC) techniques showed a staggered fracture process where failure points on mechanical response curves vary due to the internal events happening in the material. Localized frictional occurrences and inertial effects acting inside the pre-cracked matrix have a strong effect on the global mechanical response, and therefore, a great variability of strengths was obtained.

Experimental Investigation on the Influence of Wave Impedance on Dynamic Mechanical Response of Granites undergone High Temperature.

Wave impedance is an important physical quantity to characterize the dynamic properties of materials. To explore the influence of wave impedance on the dynamic mechanical response of rock, the granite samples with a wave impedance gradient change are obtained by changing the heating temperature, and the impact compression test is carried out by using a split Hopkinson pressure bar (SHPB) device. The stress wave propagation law, dynamic stress-strain relationship, and fracture characteristics of rocks with different wave impedances are studied comparatively, and the influence mechanism of wave impedance on the dynamic mechanical response of rocks is comprehensively analyzed from two aspects of material properties and dynamics. The results show the following: (1) Under the action of the same incident wave, the reflected wave amplitude, transmission wave takeoff time, peak stress, peak strain, and equivalent average size of fragments of granite samples with different wave impedances are significantly different. (2) As the heating temperature increases, the wave impedance of granite continuously decreases and the degree of damage intensifies. Within the high-temperature treatment range of 400 to 600 °C, there is a damage wave impedance threshold between 7854 and 3081 g·cm-3·m·s-1. Below this wave impedance, granite will appear to have significant damage deterioration. (3) Under the same incident wave, the strain rate and loading rate of granite samples show negative correlation and positive correlation with wave impedance, respectively. There is a progressive relationship between rock wave impedance, stress wave propagation, strain rate history/stress history, and dynamic mechanical response.

Damage constitutive model of lunar soil simulant geopolymer under impact loading

Lunar base construction is a crucial component of the lunar exploration program, and considering the dynamic characteristics of lunar soil is important for moon construction. Therefore, investigating the dynamic properties of lunar soil by establishing a constitutive relationship is critical for providing a theoretical basis for its damage evolution. In this paper, a split Hopkinson pressure bar (SHPB) device was used to perform three sets of impact tests under different pressures on a lunar soil simulant geopolymer (LSSG) with sodium silicate (Na2SiO3) contents of 1%, 3%, 5% and 7%. The dynamic stress–strain curves, failure modes, and energy variation rules of LSSG under different pressures were obtained. The equation was modified based on the ZWT viscoelastic constitutive model and was combined with the damage variable. The damage element obeys the Weibull distribution and the constitutive equation that can describe the mechanical properties of LSSG under dynamic loading was obtained. The results demonstrate that the dynamic compressive strength of LSSG has a marked strain-rate strengthening effect. Na2SiO3 has both strengthening and deterioration effects on the dynamic compressive strength of LSSG. As Na2SiO3 grows, the dynamic compressive strength of LSSG first increases and then decreases. At a fixed air pressure, 5% Na2SiO3 had the largest dynamic compressive strength, the largest incident energy, the smallest absorbed energy, and the lightest damage. The ZWT equation was modified according to the stress response properties of LSSG and the range of the SHPB strain rate to obtain the constitutive equation of the LSSG, and the model's correctness was confirmed.

Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage

In order to study the effect of the freeze-thaw cycle on the integrity and dynamic mechanical performance of rubber concrete, the wave speed of rubber concrete specimens with 10% rubber volume was measured by a nonmetallic ultrasonic detector. The impact tests were also performed on rubber concrete specimens with different numbers of freeze-thaw cycles (0, 25, 50, 75, 100, and 125) at different impact air pressures (0.3, 0.4, 0.5, and 0.6 MPa) using a 74 mm diameter split Hopkinson pressure bar (SHPB) device, peak stress, ultimate strain dynamic intensity enhancement factor (DIF), and energy absorption effect. The results show that with the increase of freeze-thaw cycles, the wave speed decreases, and the freeze-thaw action will damage the rubber concrete and reduce the longitudinal wave velocity. Under the same freeze-thaw cycles, with the rise of strain rate, the peak stress, limit strain, DIF, and absorbed energy increase, and there is an obvious strain rate effect; under the pressure of 0.6 MPa, the peak stress of 25, 50, 75, 100, and 125 freeze-thaw cycles decreases by 25.1%, 37.1%, 46%, 52.5%, and 54.8%. With the increase of the freeze-thaw cycles, the peak stress of the specimen decreases, and the decrease gradually decreases. After the number of cycles exceeds 100, the stress decrease of the specimen is no longer obvious, the limit strain increases, and the absorbed energy decreases. The freeze-thaw environment significantly reduces the strength and integrity of rubber concrete specimens.

Dynamic compressive behavior of polyethylene fiber reinforced high strength and high ductility concrete over wide ranges of strain rate

High strength and high ductility concrete (HSHDC) possesses extraordinary mechanical properties, including high compressive strength (123.3 MPa), high tensile strength (9.1 MPa), and ideal tensile strain capacity (6.6%), and exhibits promising application prospects in structures against dynamic loadings. This study systematically explored the dynamic compressive behavior of Polyethylene (PE) fiber reinforced HSHDC over wide ranges of strain rates (10−5–102 s−1) using the hydraulic servo-controlled testing machine and split Hopkinson pressure bar device. The dynamic stress-strain relations and failure patterns of HSHDC were obtained, based on which the dynamic compressive strength, peak compressive strain, and specific energy absorption (SEA) were analyzed in detail. It indicated that the compressive strength increased moderately at low strain rates (2.4 × 10−5–2.4 × 10−2 s−1) and obviously at high strain rates (105.8–258.8 s−1) with the increase of strain rate. To describe the dynamic compressive strength, several dynamic increase factor (DIF) formulae in the literature were evaluated, and an experimentally fitted DIF formula was proposed. The peak compressive strain remained almost constant at low strain rates, while it decreased significantly with the increase of strain rate at high strain rates. Besides, the dynamic SEA shows a bilinear growth law with the increasing strain rate and has a more obvious strain rate effect than the dynamic compressive strength. Finally, a nonlinear viscoelastic constitutive model was established, which satisfactorily predicts the compressive stress-strain relationship of HSHDC at different strain rates.

Study on the impact resistance of steel fiber-reinforced self-compacting concrete after high temperature

The present study explored the dynamic mechanical properties of steel fiber-reinforced self-compacting concrete (SFRSCC) after a high temperature. The impact test was conducted using a φ80 mm split Hopkinson pressure bar (SHPB) device, with a focus on the factors of influence and the regularity of steel fiber content (0.5 %, 1.0 %, and 1.5 %), impact strain rate (55 s−1, 90 s−1, and 140 s−1), and temperature (20 °C, 300 °C, 600 °C, and 900 °C) on the failure form, dynamic strength, impact toughness, and dynamic increase factor (DIF-σ) of SFRSCC after high-temperature exposure, and the mechanism analysis based on the results of the SEM examination. The impact test results revealed the following: (1) With the increase in the steel fiber (SF) content, the dynamic strength (fp) of the SFRSCC exhibited a further evident growth trend after high temperature compared to that at normal temperature reaching 105 % and the toughness index also increased by more than 20 %. (2) While the effect of SF content on DIF-σ of SFRSCC was not significant under normal temperature conditions after high-temperature exposure, the DIF of SFRSCC can increase by over 40 % with the increase of SF content. In addition, the strain rate effect was also further significant, and the DIF-σ can increased by about 30 % after high-temperature treatment compared to normal temperature. (3) A prediction formula was proposed for DIF-σ of SFRSCC after high temperature, and the results were in good agreement with the results of the impact test. This prediction formula can better provide theoretical data support for disaster prevention and reduction in subsequent projects. The findings of the present study would serve as a valuable reference for subsequent research on the impact resistance of SFRSCC after high-temperature exposure.

Dynamic Mechanical Properties and Damage Evolution Characteristics of Beishan Deep Granite under Medium and High Strain Rates.

To study the dynamic mechanical properties and damage evolution mechanism of Beishan deep granite under medium and high strain rates, dynamic mechanical tests for the deep granite specimens with different strain rates were conducted using the split Hopkinson pressure bar (SHPB) device. The improved Zhu-Wang-ang (ZWT) dynamic constitutive model was established, and the relationship between strain rate and strain energy was investigated. The test results show that the strain rate in the dynamic load test is closer to the strain rate in the rock blasting state when the uniaxial SHPB test is applied to the granite specimens in a low ground stress state. Peak stress has a linear correlation with strain rate, and the dynamic deformation modulus of the Beishan granite is 152.58 GPa. The dissipation energy per unit volume and the energy ratio increase along with the strain rate, whereas the dissipation energy per unit volume increases exponentially along with the strain rate. There is a consistent relationship between the damage degree of granite specimens and the dissipation energy per unit volume, which correspond to one another, but there is no one-to-one correspondence between the damage degree of granite specimens and the strain rate. To consider the damage and obtain the damage discount factor for the principal structure model, the principal structure of the element combination model was improved and simplified using the ZWT dynamic constitutive model. The change of damage parameters with strain rate and strain was obtained, and the dynamic damage evolution equation of Beishan granite was established by considering the damage threshold.

Mechanical properties and failure characteristics of anisotropic shale with circular hole under combined dynamic and static loading

In deep hard rock mines, the drilling and blasting method is mainly used for mining, which results in a complex environment of high static stress and frequent dynamic disturbance in some underground engineering surrounding rocks for a long time. In addition, a large number of underground engineering are in the geological tectonic zone with poor stability, which often triggers rock disasters when stress waves propagate to the bedding. Therefore, it is significant to study the failure process and mechanism of underground engineering in bedded rock masses under combined dynamic and static loading. In this study, a combined dynamic and static impact experiment was conducted on circular-hole-containing shale specimens with different bedding angles using a modified split Hopkinson pressure bar (SHPB) device, and the damage process was recorded using Digital Image Correlation (DIC) technique. The experimental results show that the stress-strain curves of shale specimens under combined dynamic and static conditions include three stages elasticity, yielding, and failure. With the increase of the bedding angle, the dynamic strength and Young's modulus of the specimens showed a trend of decreasing and then increasing, with obvious anisotropy. However, with the increase of pre-static load, the dynamic strength and Young's modulus of the specimens showed a tendency to increase first and then decrease. In addition, repeated refraction (transmission) and reflection of the stress wave between the beddings and the stress concentration phenomenon of the circular holes resulted in different failure characteristics of the specimens with different bedding angles.

Application of metaheuristic optimization algorithms-based three strategies in predicting the energy absorption property of a novel aseismic concrete material

This study aims to predict the energy absorption property of a novel aseismic concrete material made of rubber, sand and cement. To investigate the energy absorption property of this novel aseismic concrete material, the energy transmission rate (ETR) was calculated by using the Split-Hopkinson Pressure Bar (SHPB) device. Furthermore, some prediction models were developed to predict the ETR in order to estimate it in the field and other laboratory environments. Therefore, six metaheuristic optimization algorithms-based three strategies (i.e., evolutionary algorithms: Differential evolution (DE) and Human felicity algorithm (HFA); physical algorithms: Nuclear reaction optimization (NRO) and Lightning search algorithm (LSA); swarm intelligence algorithms: Harris Hawks optimization (HHO) and Tunicate swarm algorithm (TSA)) and random forest (RF) model were combined to generate various hybrid prediction models for forecasting the ETR. The results indicated that the TSA-RF model has the best performance for predicting the ETR in both the training phase (RMSE: 1.5388 and R2: 0.9349) and the testing phase (RMSE: 1.6083 and R2: 0.9165). The sensitive analysis results demonstrated that cement is the most important parameter for predicting the ETR, but the rubber showed the largest negative correlation with the ETR. As a result, the application of artificial intelligence in ETR prediction has been proven to be feasible, this work can provide a novel idea for the development of aseismic materials in tunnel engineering.

Experimental study on dynamic mechanical properties and damage characteristics of coral reef limestone

The coral reef limestone (CRL) in this study is characterized by well-developed pores, varied density range, and obvious growth line. To investigate the dynamic mechanical properties and damage characteristics of CRL, a series of impact experiments were conducted by employing a split Hopkinson pressure bar (SHPB) device. The effects of growth line inclination, strain rate and density on the dynamic mechanical properties of CRL were analyzed, and their damage characteristics were estimated by a quantitative analysis of the failure patterns. The results show that the stress–strain curve of CRL has a longer elastic stage and a shorter failure stage compared with porous rock-like materials, the porous properties of CRL are not obvious. The dynamic peak stress of CRL with the same density decreases gradually with the increasing growth line inclination. The strain rate effect of dynamic peak stress of CRL has a dependent on density, and the correlation between dynamic peak stress and strain rate becomes more obvious for CRL with higher density. The dynamic peak stress of CRL increases exponentially with increasing density, and density shows a much greater effect on peak dynamic stress compared with the growth line inclination. In addition, CRL exhibits distinct failure patters and fragment morphology from terrigenous rocks. CRL has an obvious fractal characteristic with fractal dimension of 2.09–2.76, which is influenced by growth line inclination, strain rate and density consistent with dynamic strength.