Micro-steel fiber reinforced ultra high strength concrete (MSFRHSC) has been extensively utilized in protective structural engineering due to its enhanced mechanical properties. The addition of steel fibers effectively alleviates the intrinsic brittleness of concrete while simultaneously improving compressive strength and fracture energy. This study investigates the anti-penetration performance of MSFRHSC through experimental and numerical approaches. MSFRHSC specimens with optimized mix ratios were prepared, achieving compressive strengths of up to 150 MPa. A series of penetration tests were conducted using W18Cr4V high-speed steel projectiles launched via a gas gun at three typical design impact velocities of 480 m/s, 650 m/s, and 770 m/s. The morphological characteristics of the penetration trajectory, the damage characteristics and the relationship between projectile velocity and target penetration depth was obtained and analyzed. Then, finite element simulations were conducted with Holmquist-Johnson-Cook (HJC) constitutive model representing the MSFRHSC material. The simulated penetration depths and damage morphologies showed good agreement with the experimental results. The high-speed penetration process and penetration mechanism of MSFRHSC were obtained and analyzed. In addition, a comparative analysis was conducted on the penetration resistance of MSFRHSC with different fiber content and the same strength plain concrete, revealing the influence pattern by which the addition of steel fibers enhances the toughness of concrete and thereby improves its penetration resistance. Finally, parametrical analysis were conducted, an empirical function relating penetration depth to impact velocities (300 similar to 800 m/s) was derived. The findings provide valuable insights for the application of MSFRHSC in impact-resistant structures and offer a reliable reference for finite element modeling of projectile penetration.

Cold launch systems require environmentally friendly, safe, and energy-efficient propulsion methods to meet modern operational demands. High-pressure CO2 expansion presents a promising alternative due to its significant volume expansion, environmental compatibility, and high energy density. In this work, a CO2 phase transition driven launch system was proposed and a comprehensive theoretical and CFD model were developed. Firstly, a MATLAB-based zero-dimensional model is built to predict system behavior. Then, a launch system is constructed and high-speed launch tests are successfully performed. Launch velocity of 109 m/s is achieved for a 650 kg projectile, with a maximum cylinder pressure of 5.06 MPa. The experimental results agree well with numerical predictions, with pressure and velocity errors of only 0.98% and 2.34%, respectively. Furthermore, a computational fluid dynamics (CFD) system is established. The simulation results further verify the correctness of experimental system and theoretical model. The pressure error is only 0.59%, and the launch speed error is 1.60%. In addition, parametric analysis based on the zero-dimensional model shows that projectile mass and CO2 mass significantly affect the pressure and launch velocity. The preliminary chamber volume has a minor effect on the launch velocity but a notable influence on the cylinder pressure. Reducing the preliminary chamber volume from 75 L to 60 L increases the launch velocity by 0.18% and decreases the maximum pressure by 1.78%. In conclusion, this study pioneers the use of a phase transition unit as the core propulsion mechanism in a CO2 phase transition driven projectile system and provides a reference for future large-scale launch studies.

Driven by the requirements of lightweight design and efficient impact protection, biomimetic hexagonal honeycomb structures have been widely used for energy absorption. However, their dynamic response and energy absorption behavior in underwater environments remain insufficiently understood. To address this gap, this study investigates the impact response and deformation mechanisms of aluminum honeycomb structures under fully submerged conditions relevant to marine engineering. We fabricated honeycomb cores from 5052-H18 aluminum alloy and developed a custom fixture for fluid-structure interaction tests under underwater drop hammer impact conditions. Using force sensors and high-speed photography, we characterized the dynamic impact behavior through load-time and velocity-time responses. Results demonstrate that drainage holes in the support plate serve a dual function: they enable the structure to maintain stable deformation and absorb energy underwater while also significantly enhancing energy absorption capacity. Specifically, the mean crushing force increases by 156.5%, and the energy absorption capacity increases by 333% compared to performance in air. This enhancement arises from the plastic deformation of cell walls and the additional energy dissipation induced by fluid-structure interaction. Overall, this study clarifies the dynamic compression behavior of aluminum honeycombs in underwater environments and demonstrates their potential for marine energy-absorption applications.

Non-pyrotechnical connection and separation devices are critical components for spacecraft, but traditional devices exhibit strain rate sensitivity, leading to unlocking forces exceeding design values under dynamic impact. To address this issue, this study proposes a novel shear-type connection and separation device that innovatively transforms axial tensile failure of conventional notched bolts into controlled shear failure via rational geometric design, fundamentally reducing strain rate sensitivity. Quasi-static axial tensile and dynamic impact tests are conducted to evaluate the unlocking forces and fracture modes of the device. Additionally, a finite element model is established and verified using experimental data, and a theoretical prediction model for unlocking force is developed using the least squares method and interpolation polynomial. The results demonstrate that the geometric design effectively reduces strain rate sensitivity, with unlocking forces from static tensile and dynamic impact tests being essentially consistent. The maximum stress occurs on the cross-section containing the center of the preset hole, extending in an “S” shape as the load increases. The theoretical prediction model exhibits high precision, with a goodness of fit greater than 0.9 and prediction errors less than 5%. This research provides a reliable and precise alternative to traditional non-pyrotechnical devices, enhancing the safety and efficiency of aerospace operations by mitigating the impact of strain rate effects on unlocking forces.

Against the backdrop of rising global terrorism and industrial accidents, research on infrastructure safety under blast impact has become critically urgent. As a pivotal approach for investigating dynamic responses and damage characteristics of materials and structures subjected to explosive loading, the equivalent blast-loading techniques, which show safe, efficient, and accurate, have emerged as both a research frontier and challenge. This review synthesizes advancements in equivalent blast-loading techniques for far-field explosion simulation, encompassing explosive-driven shock tubes, high-pressure gas-driven shock tubes, drop-weight impact testing machines, and hydraulically-actuated simulators. While each technique exhibits distinct advantages and limitations in simulating blast shockwaves, all strive to establish controlled and secure experimental environments that reproduce high-velocity air flow fields and pressure waves generated by explosions. Through comparative assessment, their performance in load replication fidelity, applicability, and operational efficiency are elucidated, alongside discussions on implementation challenges and potential. Finally, a novel blast simulation technique leveraging liquid-gas phase-transition-driven expansion is introduced and the follow-up research directions are prospected.

Manufacturing defect in carbon fiber reinforced polymers pose a major challenge to clarification of the weakening mechanism, duo to their various types, shapes, and multi-scale characteristics. In this study, a three-dimensional computed tomography was utilized to create void’s model and then conducts multi-scale analysis using the homogenization method. In details, a mesoscopic model is developed by millimeter-scale voids, where the material properties derived from homogenization calculations of a micro-scale model containing voids, fibers, and resins. Comparing against theoretical calculations and conventional representative volume element methods demonstrates that the proposed multi-scale approach offers higher accuracy in predicting the mechanical behavior of carbon fiber reinforced polymers with voids (the error within 5% of experimental results). Additionally, a significant direction-dependent modulus weakening mechanism caused by voids was revealed, which is determined by distribution laws and morphology of voids, can provide valuable insights for designing and evaluating carbon fiber reinforced polymers structures.

It is very inconvenient and difficult for experiments to manufacture and weld the stiffened plate, especially for scaled-down models used in engineering applications. The present work aims at investigating the equivalent experiment methods for damage evaluation of stiffened plates subjected to blast loading. Initially, two kinds of equivalent methods are presented: mass equivalent and deformation energy equivalent. Then, two sets of blast experiments with different dimensions and explosive weights were conducted to examine the equivalent effect. The damage features of both the stiffened plates and equivalent plates are analyzed. The results show that the deflection values of mass equivalent plate are greater than that of stiffened plates while the energy equivalent plate the opposite. Meanwhile, numerical studies are also conducted and the results are in good agreement with the experiments. In addition, dimensional analysis was introduced and additional numerical simulations with larger dimensions and bigger blast loads were conducted. Both the experimental and numerical results indicate that energy equivalent method is suitable for small deformation problems, while mass equivalent method is appropriate for the strong impact and high inertial effect issues. Furthermore, based on the experimental and numerical data, an engineering design equivalent method for stiffened plate under blast loads was obtained, and a detailed discussion of the design process was provided.

Trapezoidal corrugated sandwich structures are widely used in rail transit and other engineering fields due to their lightweight and high-strength. Particularly during service, body loads are transferred to the sidewalls of the sandwich structure, thereby inducing lateral compression. However, owing to the complex geometric configuration and material composition of trapezoidal corrugated sandwich structures, their mechanical response and damage mechanisms under lateral compression are intricate. In this work, an analysis method combining 3D DIC and FE is proposed to fully elucidate its damage evolution and post-failure mechanism. Four lateral compression tests varying loading directions and displacements were designed. The results indicate that under lateral compression loads in different directions, sandwich structures exhibit differentiated load transfer paths, leading to significant directional dependence in the evolution trends of force-displacement curves after debonding failure. Moreover, the peak bearing capacity of the structure is primarily governed by adhesive layer strength and adhesive uniformity. This work provides a critical theoretical basis for enhancing compressive performance of lightweight sandwich structures.

Compressed-air ejection systems are characterized by short actuation times and high instantaneous flow rates, which subject unmanned aerial vehicles (UAVs) to significant overloads during launch. These conditions impose stringent structural requirements on UAVs, adversely affecting weight and cost control. To achieve a high launch velocity with low overload, this study proposes a multi-chamber ejection method with time-sequenced actuation. This approach is based on an internal ballistics model that incorporates real-gas properties. This approach reduces launch overload while maintaining the required muzzle velocity. An internal ballistics model for UAV compressed-air ejection has been developed and experimentally validated, utilizing real-air properties. Furthermore, a multi-chamber ejection strategy was introduced. Simulations were conducted to analyze the internal ballistic performance of systems with two or three identical or different high-pressure chambers. The results demonstrate that using multiple chambers significantly reduces the maximum overload-by 20.91%, 26.08%, and 33.24% for two identical, two different, and three different chambers, respectively-while achieving the same muzzle velocity as a single-chamber system.

The advancement of rail transportation necessitates energy absorption structures that not only ensure safety but also optimize space utilization,a critical yet often overlooked aspect in existing designs.This study presents a compact energy absorption structure(CE)that integrates the advantages of cutting rings and thin-walled tube modules,offering a solution with the high space utilization and the superior crashworthiness.Through theoretical modeling and experimental validation using a drop-weight test system,we analyzed the dynamic response and energy absorption characteristics of the CE.Comparative analysis with existing structures,namely the cutting shear rings(CSR)energy absorption structure and thin-walled tube structure(TW),revealed that the CE significantly improves specific energy absorption(SEA)by 102.76%and 61.54%,respectively,and optimizes crush force efficiency(CFE)by increasing 8.23%and 5.49%compared to CSR and TW.The innovative design of the CE,featuring deformation gradient and delay response strategies,showcases its potential for practical application in engineering,advancing the field of crashworthiness engineering.

Breakthroughs in highly impact-resistant materials and structures are crucial in engineering fields such as military protection, transportation and architecture. Nevertheless, the resisting efficiency of conventional materials has progressively fallen short of increasing advanced engineering demands. In this study, drawing inspiration from the flexibility and versatility of cutting-edge origami design, a novel metamaterial with enhanced impact resistance capabilities is proposed. The core principle of microstructural design is based on origami kinematics, where the constrained degrees of freedom create interrelated movements and deformations across various components. It gives a triaxial loading-associated energy absorption mechanism where the periodic units of the metamaterial exhibit strong resistance and high internal forces in all directions when subjected to any uniaxial load, resulting in more extensive deformation and strain localization mitigation. For further mechanism analysis, an origami metamaterial specimen is fabricated using Selective Laser Melting (SLM) 3D printing technology with 6061 aluminum alloy. A light-gas gun system is used for the test of specimen impact resistance, resisting high- kinetic-energy projectile above 500J. A corresponding simulation model is also constructed to investigate the impact behavior. The results demonstrate that the origami metamaterial exhibits exceptional impact resistance, e.g., higher ballistic limit and higher specific energy absorption (SEA). Overall, this work reveals a high impact energy absorption mechanism based on origami kinematics, which further contributes to the mechanistic interdisciplinary study of origami geometry and impact dynamics.

Unmanned aerial vehicles (UAVs) have demonstrated immense value in the military sector. This research proposes the use of Trifluoromethane as a novel cold ejection medium. Trifluoromethane, being easily compressible, exhibiting high safety and low infrared characteristics, is well-suited for small-volume high-pressure chambers. The feasibility of Trifluoromethane for UAV ejection has been confirmed through experiment. Furthermore, a thermodynamic numerical model has been established for the ejection medium to investigate the effects of key parameters on ballistic performance. The study’s findings demonstrate that as the volume of the high-pressure chamber increases, the ejection velocity of the UAV is enhanced, but the improvement slows down. Meeting the ejection velocity specifications for the UAV, reducing the volume of the high-pressure chamber can lower the peak pressure within the low-pressure chamber. An increase in the release pressure of the high-pressure chamber can enhance the ejection velocity, but the improvement slows down. Lowering this pressure can effectively reduce the UAV’s acceleration. There is a maximum valve diameter beyond which the ejection velocity remains constant, however, the peak acceleration can still increase. Enlarging the volume of the low-pressure chamber can effectively reduce the UAV’s peak acceleration. This study provides a safe and efficient technical solution for the cold ejection of large UAVs.

Internal explosions are more complicated and destructive than external explosions. It is hard to give accurate predictions of the internal blast load by existing simplified models. In the present work, a fast calculation method for the shock wave of internal blast within a confined space was developed. Firstly, the theoretical bases of this method, the reflection addition rules and the image burst theory, were introduced and validated. Then, the concept of the influence region of image burst for internal blast calculation was proposed, and the detailed calculation method for internal blast load was presented. In addition, the internal blast loads inside a typical cubic structure and a tunnel model were calculated using this developed method, respectively. Moreover, comparison studies between the calculated results and experimental data as well as numerical simulation results were conducted. It was found that the results of the fast calculation model are in good agreement with those of the blast experiment and fine numerical simulation, but the fast calculation takes only less than 2 min. Finally, the advantages and defects of the present method were discussed and further study advices were suggested to improve the accuracy.

Large ships and submarines are the main equipment and mobile platforms supporting three-dimensional naval space operations. However, with the increasing damage power and strike accuracy of warheads, plus the diversity of destroying elements, their living environment is facing increasingly severe threats. It is thus necessary to work on the damage and protection of naval vessels subjected to blast loading. The blast-induced damage and protection of naval vessels is an interdisciplinary issue that involves the integration of explosion mechanics, fluid mechanics, structural mechanics, materials science and other disciplines in which many challenges are yet to be addressed. In view of some of the key issues involved, this paper systematically summarizes the research progress on blast load characteristics, damage mechanisms and protection technologies and equipment at home and abroad in recent years. The shortcomings of the current research are pointed out and the development trends of ship explosion damage and protection are predicted. This study can provide valuable references for future research on the efficient damage and protection of naval vessels.

It is widely known that the demand for structures with excellent energy absorption capacity is paramount in numerous engineering applications. In this study, combined with the structure properties of cutting shear rings energy absorption structure (CSR) and thin-walled tube structure (TW), a cutting and thin-walled tube combined energy absorption structure (CTE) suitable for long and narrow limited space is proposed. To investigate the effects of geometric parameters on the properties of the three structures, a numerical model of the CTE is established and compared with the results of drop-weight test. Then the energy absorption properties of the three structures are compared with the evaluation indexes. The results show that the error between the theoretical model of the three structures and the test is less than 10%. Compared with the CSR and the TW, the specific energy absorption (SEA) of the CTE increases by 102.76% and 61.54%, and the peak-to-average ratio (PAR) decreases by 12.85% and 8.77%. Combined with the idea of gradient layout and delayed start, the modular design of the CTE structure acquires lower PAR. In addition, modular CTE structure for drop-weight test is carried out, and the experimental results show that the CTE shows three response modes during deformation. Compared with ring mode, diamond mode is equipped with higher SEA and PAR.

Understanding the near-field characteristics of leakage is essential for safety distance calculations and risk assessment of emergency response to a pipeline leakage. This paper presents a small-scale experiment and computational fluid dynamics model designed to investigate the transient characteristics of near-field parameters. The study also analyzes the effects of leakage orifice diameter on the transient characteristics of the near-field. The results show that a pipeline leak starts with the formation of a compression wave, which causes the air at the front of the stream to be compressed, heated and pressurized. CO2 is then released at high pressure, creating a strong expansion wave that keeps the fluid pressure below local atmospheric levels. For full-hole and large-hole leaks, the temperature drop and rate show a negative linear correlation with the size of the leak hole. Conversely, for small hole leaks with the ratio of hole diameter to pipe diameter values below 0.2, the temperature drop shows an opposite trend. As the ratio of hole diameter to pipe diameter values increases, the maximum diameter of the barrel drum-shaped disk gradually increases, but the maximum expansion angle of the jet decreases. It is hoped that this work will contribute to the improvement of research models that assess the consequences of potential high-pressure pipeline rupture scenarios.

Fiber-reinforced composite tubes have remarkable advantages in energy absorption due to the high specific strength, stiffness, and fracture energy, etc. While, the energy absorption capacity is severely dominated by buckling deformation. To this end, the buckling behaviors and corresponding mechanism of CFRP (carbon fiber reinforced polymer) tubes are systematically investigated in this work. Furthermore, an advanced bionic method referring to bamboo and human bones is adopted to improve the buckling. To effectively analyze the buckling, drop weight impact experiments and corresponding numerical simulations are carried out. The results show that the specific energy absorption (SEA) of CFRP tubes is significantly affected by the diameter-to-height ratio and fiber ply direction, and the influencing mechanism is excessive buckling caused by the geometric characteristics and brittle failure of CFRP. At last, the SEA of CFRP tubes were improved through bio-inspired multi-layered metal/composite hybrid, where the buckling is suppressed reasonably well. The conclusions drawn would be inspiring or guiding the optimal design of high energy-absorbing composite tubes in engineering application.

The vapor-liquid equilibrium (VLE) state of CO2 commonly appears in pipelines for its transport, refrigeration systems, and large-scale trans-critical cycle systems. However, the behavior of sudden leaks in such systems remains unclear, which poses a challenge in assessing the risk of leakage. This work is focused on the decompression behavior of VLE state CO2 with different volume fractions of vapor phases in high-pressure pipeline leakage, specifically with the development of a computational fluid dynamics (CFD) model with a nonequilibrium phase transition and the real gas model. The results suggest that the Peng-Robinson Equation of State (PR EoS) is more conservative in predicting the degree of superheat than that of Span-Wagner (S-W) EoS and GERG-2008 EoS. Moreover, it is found that the initial volume fraction of the vapor phase in VLE state CO2 plays a crucial role in determining the characteristics of sudden leakage, such as pressure, temperature, and decompression wave speed both inside and outside the pipe. However, the position of the Mach disk remains unaffected by the initial volume fraction of the vapor phase. The initial vapor volume fraction of 0.2 has the most significant impact on the transient behaviors of the leakage, that is, the speed of the initial decompression wave is approximately 1.46 times slower than that of pure liquid CO2, the pressure and temperature start to decrease approximately 0.46 ms after those of pure liquid CO2, which is about 5.1 times later. Additionally, the peak pressure of the near-field jet is 6.3% higher and the maximum velocity is 11.4% higher than that of pure liquid CO2. It hopes that this work will contribute to the improvement of research models that assess the consequences of potential high-pressure pipeline rupture scenarios.

Accidental leakage poses a significant safety concern for carbon capture, utilization, and storage (CCUS) projects. Understanding the near-field characteristics of leakage is essential for dispersion studies, safety distance calculations, and risk assessment of emergency response to a pipeline leakage. This paper presents a small-scale CO2 pipeline leakage experiment designed to investigate the transient characteristics of near-field parameters, including temperature, pressure, and jet structure. The study also analyzes the effects of factors such as initial pressure, initial temperature, and leakage orifice diameter on the transient characteristics of the near-field. The experimental results demonstrate that lower initial temperatures lead to higher near-field pressure peaks, while larger orifice diameters result in larger near-field pressure peaks. Furthermore, a larger hole diameter combined with a lower initial temperature and higher initial pressure leads to the negative pressure region in the near-field being farther away from the leakage opening. In the liquid state, the near-field temperature is lower compared to the gaseous state due to the strong liquid-gas flash evaporation. When different orifice diameters are used for depressurization, larger diameters cause a more significant drop in near-field temperature. The study also reveals that the effect of initial temperature on the jet structure is less significant compared to the effect of initial pressure. The primary objective of the experiment was to collect near-field leakage data and analyze the characteristics of near-field leakage. It is hoped that this work will contribute to the improvement of research models that assess the consequences of potential high-pressure pipeline rupture scenarios.

The Carbon dioxide (CO2) phase transition blasting is a state-of-the-art technology in fields of geotechnical, geological, and mining engineering, due to its advantages of high safety, environmental friendliness (Non-toxic and smoke-free), and cost-effective design benefited from the low-temperature characteristics. However, the evolution mechanism of CO2 within the pressure vessel before the blasting is still not clearly revealed. To address this issue, a phase-diagram-formulated Equation of State (EOS) is proposed to describe the phase evolution and mechanical behaviors of CO2. Furthermore, a fluid-solid coupling simulation model is established using the Euler grid-based Finite Element Method (FEM). The simulation model is validated through CO2 phase transition blasting experiments and then used for the mechanism analysis. The results reveal that the initial rapid rise, further slow increase, and extremely rapid decline of the pressure evolution in the vessel are dominated by the combination of heat absorption and external work, the phase transition of CO2, and the failure of the rupture disc, respectively. In addition, the influence laws of combustion agent energy, environment temperature and rupture disc strength on the blasting are systematically investigated. The final conclusions may provide useful insights for the design of CO2 phase transition blasting and the development of eco-friendly blasting technologies.