Peak Dynamic Stress Research Articles

Enhancement behaviours of carbon nanotubes reinforced cement based grouting materials under dynamic loading

Carbon nanotubes (CNTs) reinforced cement based grouting material is an important part of green manufacturing industry. Our previous research showed that this material can effectively enhance the impact resistance of rock matrix. In this study, We conducted a comprehensive study and quantitative analysis of the changes in pore structure of this material under impact conditions. Dynamic impact testing and computed tomography (CT) revealed that CNTs significantly increased the cement content in the sample by 79.11%. The CNTs group exhibited higher internal pore density and uniformity, effectively suppressing the formation of dynamic cracks in the sample. Compared to Non-carbon nanotubes (Non-CNTs) cement-based materials, the peak dynamic stress of the CNTs group increased by 4.76% to 21.54%, while the porosity decreased by 57.26%.This study further refined the enhancement behaviors of carbon nanotubes reinforced cement based, and making outstanding contributions to engineering practice.

Investigating the Effects and Mechanisms of Thermal–Vibration-Coupled Stress Relief Treatment on Residual Stress in SiC/Al Composites

Aluminum matrix composites reinforced with particles (PRAMCs) frequently develop considerable residual stresses post-quenching, which can negatively affect fatigue life and dimensional accuracy. Traditional stress relief methods for aluminum alloys are only partially effective. This study examined thermal stress relief (TSR), vibratory stress relief (VSR), and a combined thermal–vibratory stress relief (TVSR) approach for SiC/Al composites. All treatments proved successful in diminishing residual stresses, with the most significant reduction along the direction of peak dynamic stress. Additionally, this study analyzed micro-residual stresses via a macro–micro-residual stress finite element model to understand differences in stress relief outcomes. Optimizing the TVSR process could be key to more effectively reducing residual stresses in SiC/Al composites.

Multiple impact resistance and microstructure of hybrid fiber-reinforced fly ash/slag-based geopolymers after exposure to elevated temperatures

Engineered geopolymer composites (EGC) have garnered significant attention from researchers as a new environmentally friendly building material with superior tensile properties, impact resistance, and high-temperature resistance. This study focuses on the investigation of the dynamic mechanical properties of a hybrid fiber reinforced lightweight EGC containing ceramsite (LW-EGC) after exposure to elevated temperatures and multiple impacts. The effects of temperature, steel fiber content, and ceramsite types were taken into consideration. The analysis encompassed multiple impact stress-strain curves, dynamic peak stress and strain evolution, energy absorption, damage evolution, damage morphology, and microstructure changes following exposure to elevated temperatures. The experimental results revealed a significant decrease in the number of impacts endured by LW-EGC-M as the temperature increased. After 200 °C, the LW-EGC-M experienced 15 impacts, while after 800 °C, it only endured 2 impacts. Both cumulative energy absorption and cumulative damage of LW-EGC exhibited an exponential growth pattern with an increasing number of impacts. Microstructural analysis unveiled the emergence of a new nepheline phase after exposure to elevated temperatures, while the calcite in the matrix demonstrated gradual decomposition. Moreover, elevated temperatures led to a decreased Si/Al ratio in the matrix. The complete melting of PVA fibers after exposure to elevated temperatures resulted in the production of numerous interconnected pores in the matrix, leading to a decline in the mechanical strength of LW-EGC. This phenomenon also contributed to the reduction of internal pore pressures and the release of local vapor pressure generated by elevated temperatures.

Dynamic impact mechanical properties of red sandstone based on digital image correlation method

ABSTRACT In the process of underground blasting excavation, the safety and stability of rock mass are significantly influenced by dynamic load. To study the full-field strain and displacement behaviour of rock materials subjected to dynamic compressive force, the impact tests were done on red sandstone specimens using an electromagnetically driven Hopkinson pressure bar. At the same time, the data were collected by a high-speed camera, and non-contact measurements of the red sandstone were carried out with the digital image correlation method. The resulting images were screened and analysed, based on which the stress-strain curve, full-field strain cloud diagram and displacement cloud diagram were obtained. Results show that the dynamic peak stress increases with the increase of impact velocity. During the impact process, substantial internal uneven deformation occurs in the red sandstone close to the transmission bar’s end face. Under the impact load, the cracks initiate from the upper and lower sides near the transmission bar’s end face, followed by formation of cracks in the middle part. These cracks expand throughout the rock to form through-cracks, eventually resulting in complete failure. For rock materials, the evolution of their strain field during the failure process can reflect the initiation and propagation of their internal cracks. Therefore, the use of digital image correlation method proves effective for studying the deformation and failure mechanisms of rock. The conclusions obtained in this study provide a valuable reference for the macro-meso deformation and failure mechanisms of geotechnical materials.

Influence of Incident Orientation on the Dynamic Response of Deep U-Shaped Cavern Subjected to Transient Loading

In deep rock engineering, caverns are often disturbed by engineering loads from different directions. To investigate the dynamic response of deep U-shaped caverns under different incident orientations, a theoretical solution of the dynamic stress concentration factor along the cavern boundary was derived based on the wave function expansion and conformal mapping method, and the failure characteristics around the cavern were further investigated by PFC2D (Particle Flow Code in two dimensions). As the incident orientation increases from 0° to 90°, the dynamic compressive stress concentration area transforms from both the roof and the floor to the sidewalls, and the peak dynamic stress concentration factor of the roof decreases from 2.98 to −0.20. The failure of the floor converts from dynamic compression shear failure to dynamic tensile failure. Compared to a stress wave incident from the curved boundary, a stress wave incident from the flat boundary causes severer damage. When the stress wave is incident from the sidewall, the cavern with a larger height-to-width (h/w) ratio exhibits severer damage. Conversely, the cavern with a smaller h/w ratio tends to fail as the stress wave is incident from the floor. This paper provides a basic understanding of dynamic responses of the deep U-shaped cavern.

Optimization of steam curing process for Chinese Western and Northeast regions' high‐speed railway concrete prefabricated components

AbstractThis article aims to address the issues of high curing temperatures and thermal damage in the production of prefabricated concrete components for high‐speed railways in high‐altitude and high‐latitude cold regions of China. Various steam‐curing processes for concrete are designed to optimize the high‐quality preparation process of steam‐cured concrete prefabricated components in cold environments. With the goal of controlling the residual expansion deformation and considering the overall impact of curing process on the mechanics, durability, and interface transition zone of steam‐cured concrete, the main conclusions obtained in this study are as follows. Within a pre‐curing time of 3–6 h, when the curing temperature is maintained at 45–60°C, the final residual expansion deformation can be controlled below 300 με. The compressive strength, dynamic elastic modulus, peak stress, water absorption and Chloride ion resistance of steam‐cured concrete show the great improvement under above curing processes. Curing at 80°C should be actively avoided, and it is recommended to adopt a 6 h pre‐curing time with a maximum curing temperature of 45°C, especially for cold regions in China. This study can serve as a valuable reference and provide support for the preparation of prefabricated concrete components in Chinese high‐altitude and high‐latitude areas.

Dynamic mechanical response and crack evolution law of raw coal loaded by dynamic-static coupling under three-dimensional constraints

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

Investigation of dynamic compression properties of lightweight engineered geopolymer composites containing different ceramsites (LW-EGC)

Lightweight engineering geopolymer composites (LW-EGC) can contribute to green building materials products by taking advantage of the advantages of man-made ceramsite and geopolymers. In this paper, an active "sacrifice" method was proposed, which is based on the idea that low elastic modulus ceramsites are preferentially damaged or ruptured during the impact loading process, thus absorbing and dissipating the impact energy. LW-EGC was enhanced by PVA fiber with volume fraction of 2% and multi-walled carbon nanotubes with mass fraction of 0.15%. The dynamic compression properties of LW-EGC containing different ceramsites were studied by using Φ100 mm split Hopkinson pressure bar (SHPB) test device. The compression characteristics of the LW-EGC under an impact load were evaluated, including the strain rate, dynamic stress–strain relationship, elastic modulus, dynamic increase factor (DIF), energy absorption, and failure patterns. The results showed that the dynamic peak stress, dynamic peak strain, DIF, energy absorption and damage degree of LW-EGC all increased with the increase of strain rate, showing obvious strain-rate sensitivity. At high strain rate, the dynamic elastic modulus mainly showed softening effect. At the same strain rate, the impact resistance of LW-EGC-1 containing fly ash ceramsite was the best, and the damage degree of LW-EGC-3 containing shale ceramsite was the lowest. Empirical DIF formulas of the LW-EGC was proposed; the DIF increased approximately linearly with the strain rate in a logarithmic manner.

Effect of high-temperature and strain rate on the mechanical and cracking behaviors of flawed sandstone under dynamic impact loading

A deep understanding of how flawed rock cracks under high temperatures and dynamic impacts is crucial for safe deep rock engineering design and operation. Dynamic impact tests were conducted on sandstones with various flaw inclinations using a Split Hopkinson Press bar (SHPB) system at room temperature and after high-temperature treatment at 600 °C. The results show that the dynamic peak stress and energy consumption of rock were reduced by thermal treatment. The study identified the circular tensile- and compressive-tangential stress zones around the flaw boundary using elastic theory. The strain accumulation zones gradually shift from the tensile- to the compressive-tangential stress zones as the flaw inclination increases, resulting in a larger crack initiation angle and opening displacement, while also constraining the propagation path. Additionally, the high-temperature treatment strengthened the deformation in the circular tensile-tangential stress zone. In contrast to the severe failure of specimens at room temperature, the clear failure pattern of the specimens after high-temperature treatment merely consists of wing cracks. Finally, this study presents a detailed theoretical explanation of the cracking behavior under various conditions, which is consistent with the experimental results. This research enhances the understanding of dynamic crack propagation in deep high-temperature rocks and provides scientific references for engineering safety design and protection.

Three-dimensional numerical simulation of dynamic strength and failure mode of a rock mass with cross joints

To study the dynamic mechanical properties and failure characteristics of intersecting jointed rock masses with different joint distributions under confining pressure, considering the cross angle α and joint persistence ratio η, a numerical model of the biaxial Hopkinson bar test system was established using the finite element method–discrete-element model coupling method. The validity of the model was verified by comparing and analyzing it in conjunction with laboratory test results. Dynamics-static combined impact tests were conducted on specimens under various conditions to investigate the strength characteristics and patterns of crack initiation and expansion. The study revealed the predominant factors influencing intersecting joints with different angles and penetrations under impact loading. The results show that the peak stress of the specimens decreases first and then increases with the increase of the cross angle. When α < 60°, regardless of the value of η, the dynamic stress of the specimens is controlled by the main joint. When α ≥ 60°, the peak stress borne by the specimens decreases with increasing η. When α < 60°, the initiation and propagation of cracks in the cross-jointed specimens are mainly controlled by the main joint, and the final failure surface of the specimens is composed of the main joint and wing cracks. When α ≥ 60° or η ≥ 0.67, the secondary joint guides the expansion of the wing cracks, and multiple failure surfaces composed of main and secondary joints, wing cracks, and co-planar cracks are formed. Increasing lateral confinement significantly increases the dynamic peak stress able to be borne by the specimens. Under triaxial conditions, the degree of failure of the intersecting jointed specimens is much lower than that under uniaxial and biaxial conditions.

Experimental Research on the Impact Resistance Mechanical Properties and Damage Mechanism of Rubberized Concrete under Freeze–Thaw Cycling

To improve the long-term performance of concrete engineering in high-altitude areas, waste tire rubber was added to a concrete mix, and freeze–thaw and impact tests were conducted. The effects of waste tire rubber with different particle sizes (10, 20, 30 mesh) and freeze–thaw cycles (0, 25, 50, 75, 100, 125) on the dynamic mechanical properties of concrete materials were studied. The stress–strain curves, peak stress, and fracture morphology of the specimens were analyzed. The microstructure changes of the specimens were also analyzed using scanning electron microscopy (SEM). The results showed the following: (1) Both macroscopic and microscopic analysis results showed that the internal damage of rubber concrete specimens was smaller after freeze–thawing, and the integrity was better after impact, maintaining a loose but not scattered state. The addition of waste tire rubber significantly improved the material’s impact resistance to a certain extent. (2) As the impact pressure increased, the strain rate of the specimens increased linearly, and the dynamic peak stress was linearly positively correlated with the strain rate. (3) After 125 freeze–thaw cycles, the peak stress of the specimens with 30-mesh added rubber decreased significantly less than that of ordinary concrete under 0.3, 0.45, and 0.6 MPa impact pressure. The dynamic peak stress was higher than that of specimens with 10-mesh and 20-mesh added rubber, and the addition of 30-mesh rubber significantly improved the frost resistance and impact resistance of concrete materials. This study can provide new ideas for the engineering application of rubber concrete.

Dynamic Stress Response in a Novel Prestressed Subgrade under Heavy-Haul Train Loading: A Numerical Analysis

To explore the dynamic transient characteristics induced by passing heavy-haul trains in newly-developed prestressed subgrade, two three-dimensional finite element models were constructed in the time domain using ABAQUS software. These models are categorized as train-track-prestressed subgrade and train-track-unreinforced subgrade. The numerical models also incorporated the vertical track irregularity commonly found in heavy-haul railways. The investigation aims to discern the dynamic stress response differences in both types of subgrades under three distinct train axle loads. Model validation occurred through comparisons with field tests gathered from various heavy-haul railways in China, as well as analogous numerical simulation cases. The findings indicate that track irregularity results in an asymmetric distribution of dynamic stress on the subgrade surface beneath both left and right rails, aligned transversely with the subgrade centerline. Additionally, this asymmetry is notably pronounced. The peak dynamic stress on the subgrade surface beneath the rails for both subgrades increases with escalating train axle loads. However, the prestressed reinforcement structure (PRS) effectively modulates this phenomenon, with the controlling advantage intensifying as train axle load increases. The average dynamic stress level in the prestressed subgrade is marginally lower than in the unreinforced subgrade within the roadbed layer beneath rails. Furthermore, train axle loads amplify the variation level of dynamic stress in the subgrade. However, the variable coefficient of dynamic stress in the prestressed subgrade is less than in the unreinforced subgrade, suggesting that PRS contributes positively to maintaining subgrade dynamic stability. In terms of the longitudinal distribution of peak dynamic stress, both subgrades exhibit normal distribution at varying depths within the roadbed layer. Lastly, the additional dynamic stress in prestressed steel bars also rises with increasing train axle loads. Nonetheless, it remains substantially lower than the static target pre-tensile stress. Moreover, the dynamic responses of prestressed steel bars in different rows attenuate as depth increases away from the subgrade surface. In summary, the study establishes that PRS significantly enhances the dynamic stability of railway subgrade.

Comparative analysis of dynamic mechanical properties of steel fiber reinforced concrete under ambient temperature and after exposure to high temperatures

The dynamic properties of concrete structures after being exposed to high temperatures play a crucial role in post-disaster repair and accident prevention measures. This study examined three different mixture ratios of Steel Fiber Reinforced Concrete (SFRC) with matrix strength of C60 and steel fiber contents of 0%, 1%, and 2%. A Split Hopkinson Pressure Bar (SHPB) with a diameter of 75 mm, along with a heating furnace, was employed to comprehensively investigate the dynamic compression behavior of materials. The specimens were exposed to temperatures ranging from 200 °C to 600 °C. In addition to evaluating the extent of mechanical degradation in SFRC after cooling, auxiliary impact experiments were also carried out at ambient temperature. The experimental data revealed that the dynamic peak stress and peak strain initially increased but eventually decreased as the loading rates continued to rise. The degree of strengthening, toughening, and energy absorption capacity of concrete materials progressively decreased as the escalation of strain rate after the cooling process. Moreover, the inclusion of steel fibers proved effective in preventing cracking and damage to the concrete, preserving the integrity of specimens even at higher temperatures. Simultaneously, the residual stress and deformation capacity of SFRC showed considerable enhancement after exposure to elevated temperatures.

Experiments on the Coal Measures Sandstone’s Dynamic Mechanical Parameter Characteristics under the Combined Action of Temperature and Dynamic Load

This paper conducts impact dynamics experiments on coal measures sandstone in a deep mine via the established dynamic load and temperature split Hopkinson pressure bar (SHPB) experimental system. Firstly, the experimental conditions for the impact dynamics of fine sandstone were determined, with temperatures of 18, 40, 60, 80, and 100 °C, an axial static load range of 1–9 MPa, and a preset bullet incidence velocity of 1.0–5.0 m/s. Secondly, based on the analysis of the basic parameters and physical composition, the dynamic stress and strain responses of fine sandstone under different experimental conditions were obtained, and the change mechanism of its dynamic mechanical process was theoretically analyzed. When the temperature rose from 18 °C to 100 °C, the dynamic peak stress of fine sandstone increased from 36.04 MPa to 73.41 MPa, with an increase of 103.7%. At a temperature of 40 °C, when the axial static load increased from 1 MPa to 9 MPa, the dynamic stress peak of fine sandstone increased from 57.25 MPa to 80.01 MPa, and the corresponding peak strain also showed an increasing trend. The experiment analyzed the variation characteristics of dynamic stress in fine sandstone under the combined action of different strain rates or bullet incidence velocities and different temperatures. In the strain rate range of 47.1 s−1 to 140.9 s−1, there was a significant strain rate effect on the dynamic peak stress and peak strain of fine sandstone, which increased with the increase of strain rate. The study found a polynomial relationship between the dynamic mechanical parameters of fine sandstone and the impact of experimental parameters, with a coefficient of determination greater than 0.9. A dynamic stress constitutive model for fine sandstone under one-dimensional stress state under dynamic load and temperature action was established, and the model validation and parameter determination of dynamic stress changes in fine sandstone under different temperature conditions were carried out. The research results provide a new experimental method for the static and dynamic mechanical analysis of coal and rock masses under complex geological conditions and can provide a basic reference for the prevention and control of dynamic disasters in deep mining processes.

The Static and Dynamic Behavior of Steel Storage Tanks over Different Types of Clay Soil

Steel storage tanks are widely used in different fields. Most of these tanks contain hazardous materials, which may lead to disasters and environmental damage for any design errors. There are many reasons which cause the failure of these tanks such as excessive base plate settlement, shear failure of soil, liquid sloshing, and buckling of the tank shell. In this study, five models of above-ground steel storage tanks resting over different types of clay soils (medium-stiff clay, stiff clay, and very stiff clay soils) are analyzed using the finite element program ADINA under the effect of static and dynamic loading. The soil underneath the tank is truly simulated using a 3D solid (porous media) element and the used material model is the Cam-clay soil model. The fluid in the tank is modeled depending on the Navier–Stokes fluid equation. Moreover, the earthquake record used in this analysis is the horizontal component of the Loma Prieta Earthquake. The analyzed tanks are circular steel tanks with the same height (10 m) and different diameters (ranging from 15 m to 40 m). The soil under the tanks has a noticeable effect on the dynamic behavior of the studied tanks. The tanks resting over the medium-stiff clay (the weakest soil) give a lower permanent settlement after the earthquake because of its low elastic modulus which leads to the absorption of the earthquake waves in comparison to the other types of soil. There are 29.6% and 35.6% increases in the peak dynamic stresses under the tanks in the cases of stiff clay and very stiff clay soils, respectively. The maximum values of the dynamic vertical stresses occur at a time around 13.02 s, which is close to the peak ground acceleration of the earthquake.

Dynamic mechanical properties of ferronickel slag powder-modified soil-cement using split-hopkinson pressure bar testing

Ferronickel slag is an industrial waste, ranking as the fourth largest smelting slag in China, with an annual discharge of about 30 million tons. However, only 8% to 10% of this slag is utilized, leaving a substantial amount of ferronickel slag unutilized. This not only pollutes the environment, but also results in a significant waste of resources. Recycling ferronickel slag wastes allows for the optimum use of resources, which benefits initiatives in ferronickel slag powder production and environmental protection. In light of this, ferronickel slag powder (FSP) and mineral powder (MP) are mixed here to achieve the optimal proportion when incorporated into soil-cement (the mixture is simplified as FSMP) for application in subgrade reinforcement. In the subgrade soil of airport runways, in fact, it often endures the impact of loads, therefore, to study the influence of added ferronickel slag powder on the mechanical behavior of soil-cement after impact compression, the Split-Hopkinson pressure bar (SHPB) testing was conducted on a series of soil-cement samples with varying FSMP replacement ratios (0, 10%, 20%, 30%, 40%, 50%, and 60%). The failure mode, compression after impact (CAI) strength, and dynamic stress–strain relationship of the soil-cement samples were studied. The results indicate that, as the FSMP replacement ratio increases from 0 to 60%, the rate of peak stress growth at 60-day age are 11.39%, 12.08%, 12.57%, 16.11%, −16.83%, and −13.20% respectively. This implies that the dynamic stress first increases as FSMP increases and then decreases after the peak is reached at 40% FSMP replacement. Moreover, as the curing ages, the peak dynamic stress gradually increases. The rate of this increase is significantly higher between the curing age of 7d and 28d than between 28d and M60d. The addition of a suitable amount of ferronickel slag powder can enhance the impact resistance of soil-cement. These findings can serve as a foundation for understanding the application of soil-cement in engineering under impact.

Calculation method of HJC constitutive model parameters of natural joint angle slate

In the course of underground engineering, layered slate is often encountered. Understanding the mechanical characteristics of layered slate is a prerequisite for engineering construction and disaster prevention and mitigation. As a result, at the beginning of a project, a large number of indoor tests are required, which are time-consuming and laborious. In addition, the natural joint angle of the layered slate is random, so it is extremely difficult to establish a database of the mechanical characteristics of layered slate. Hence, it is necessary to find a simple, feasible, and high-precision method to determine the Holmquist–Johnson–Cook (HJC) constitutive model parameters for naturally jointed layered slate with different dip angles. This study first determines the HJC constitutive model parameters of layered slate with five specific joint dip angles (0°, 30°, 45°, 60°, and 90°) through static tests and the split Hopkinson pressure bar (SHPB) test. Furthermore, by employing sensitivity analysis methods, the influence of key parameters of the HJC constitutive model on the dynamic peak stress of slate is determined. Among them, parameters A and B have the most significant impact on stress, exceeding 50%. Thirdly, a nonlinear fitting regression method is used to determine the HJC constitutive model parameters of naturally jointed angular slate. The relationship between the HJC model parameters and the inclination angle of slate joints is derived, and the accuracy of these parameters is verified through numerical simulation methods. The error between the numerical simulation and indoor experiments is within 10%, indicating a high level of simulation accuracy. The research findings provide a highly precise numerical simulation method for similar projects.

Particle size distribution of aggregate effects on the dynamic compressive behavior of cement waste rock backfill

Cement waste rock backfill (CWRB) is an essential component of green mining. Recent studies have demonstrated that the CWRB can slow surface settlement and provide economic advantages. However, there has been only limited research into the susceptibility of CWRB to dynamic impacts such as rock bursts, especially as mining depth increases. This study aims to investigate the dynamic peak stress, elastic modulus, and dissipated energy of CWRB specimens using a split Hopkinson pressure bar system. The results demonstrated that the responses of aggregate with different particle size distributions to the system’s impact strain rate (ISR) were inconsistent. Specifically, the highest dynamic peak stress of 23.71 MPa was achieved for the CWRB (Talbot index = 0.6) at a low ISR (30 s−1–35 s−1) and 62.33 MPa for the CWRB (Talbot index = 0.4) at a high ISR (40 s−1–50 s−1). A strain nephogram and fractal dimension analysis further suggested that the CWRB (Talbot index = 0.4, 0.6) could continue to provide partial compressive resistance after impact. Moreover, a compressive model was developed to determine the “change point” between the low and high ISR. The model indicated that different particle size distributions influenced the porosity, and at a high ISR, the pore structures further worsened the dynamic compressive behavior of CWRB. This study not only enhances our understanding of the compressive performance of CWRB under dynamic impact, but also contributes to the safety and efficiency of filling mining operations. In addition, it offers a theoretical explanation of the effects on the dynamic compressive behavior of CWRB.

Dynamic mechanical behavior and damage properties of SHCC under high strain rate loading

Dynamic mechanical behaviors of strain-hardening cementitious composites (SHCC), considering the influence of strain rates, were investigated using split Hopkinson pressure bar (SHPB). Full-field strain evolution and cracking behavior of SHCC under high strain rate loading were investigated using high-speed digital image correlation (DIC) technology. Additionally, the damage properties of SHCC induced by high strain rate loading were analyzed using X-CT images and SEM observation. The results show that dynamic peak stress, strain, energy absorption capacity and dynamic increase factor (DIF) of SHCC are increased with the increase of strain rate. Full-field strain evolution of SHCC during the SHPB test demonstrates that the expansion in the vertical is larger than compression in the lateral under high strain rate loading. According to the X-CT images, dynamic load with a relatively higher strain rate will induce more fine cracks, and the number of cracks inside the specimen is more than on the surface. Moreover, plastic deformation of PVA fibers occurs under high strain rate loading based on SEM observation.

3D printed bending-stretching coupled non-self-similar hierarchical cellular topology under in-plane loading

Ultralight hierarchical metamaterial is a type of promising structure in aerospace and transportation applications owing to the high stiffness/strength to density ratio. Though some hierarchical topologies with distinct in-plane configurations have been reported, the topology with superior mechanical behaviors under plastic deformation is urgent to be tailored. The present study develops a novel bending-stretching coupled Non-Self-Similar Hierarchical Topology (NSSHT) via additive fabricating methodology, and gives an insight into the mechanical responses and energy absorption capacities. It is identified that the softening post initial peak stress is triggered by the bending of the oblique membrane in the first order unit cell when edge length ratio (γ) is low, while by the initial rotation of second order unit cell when γ is high. Compared to the quasi-static measurements, the dynamic specific initial peak stress of NSSHT with uniform wall thickness (η= 1) was enhanced up to 131.9%. The deformation modes at distinct stress stages are different under quasi-static and dynamic loads. For specific energy absorption capacity, the NSSHT with non-uniform wall thickness behaves better, and the majority is dissipated at stress enhancement stage. The developed novel hierarchical structures enable to provide a wider spectrum of choices for tailoring high-performance lightweight components.