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The cluster down-the-hole hammer reverse-circulation drilling technology is an attractive approach for achieving a high rate of penetration (ROP) through the \"small hole drilling, large hole enlarged\" construction method. However, limited research has been conducted on the mechanism of button rock-breaking mechanism under enlarged impact conditions. In this investigation, the crater dimensions and volume, debris particle size, and micro-strain curves of granite with different ratio ( k ) of enlarged-hole to pilot-hole diameter under the impact of a nine-buttons drill bit were investigated by drop hammer impact test. A dynamic damage numerical model for button and rock under impact load was established, and the stochastic initiation process of cracks under button impact was developed through the incorporation of cohesive elements at a global level. Impacts of k- value, lithology, and lateral inclination on the characteristics and quantity of cracks, bit–rock interaction (BRI) curves, and energy consumption in median cracks ( l m ) and well-wall cracks ( l w ) were investigated. The results indicate a high degree of volumetric fragmentation and substantial axial compression at k  = 2–3, resulting in a competitive performance in rock-breaking. When k  = 3, the highest number of cracks occurs, along with maximum crack width and minimal propagation of l w . The BRI curves for granite and limestone demonstrate similar shapes across different lithologies, with the highest number of cracks occurring at k  = 3. The BRI curve of sandstone demonstrates a higher penetration depth and a lower impact force compared to the other two rock types. When k  = 3 and the button inclination angle is 15°, the maximum number of cracks and crack size are achieved, while maintaining a small value for l w , leading to an optimal rock-breaking effect and well-wall stability. Highlights The effect of ratio ( k ) of enlarged-hole to pilot-hole diameter on rock-breaking was discussed Crater and debris dimensions and degree of axial compression were notably larger at k  = 3 As the k -value increases, the energy used for rock fragmentation decreases The number and width of cracks reached a maximum at k =3 with minimal well wall fracture When k =3 and the impact angle is 15°, the maximum number of cracks and crack size were achieved

The mechanical performance of all‐lightweight concrete (ALC) structures can be significantly improved through the incorporation of steel fibers. However, research on the dynamic response of steel fiber–reinforced all‐lightweight concrete (SFALC) structures under impact loading remains limited. This study systematically investigates the impact resistance of SFALC beams reinforced with flat and corrugated steel fibers through drop hammer impact tests. Five SFALC beams were specifically designed and tested to analyze the effects of different fiber geometries on their impact performance. Experimental results demonstrate that both flat and corrugated steel fibers enhance the structural stiffness, mitigate crack initiation and propagation, shorten the duration of the initial impact peak, and reduce peak and residual displacements, thereby improving overall damage resistance. Notably, corrugated steel fibers exhibit superior efficacy in mitigating impact‐induced damage, reducing peak impact force, and enhancing the structural integrity of the beams compared to flat fibers. As the impact velocity increases, both types of specimens exhibit pronounced local punching failure. However, beams reinforced with corrugated steel fibers experience significantly reduced punching damage, indicating superior impact resistance. These findings provide valuable insights into optimizing the design of high‐performance ALC structures for impact‐resistant applications.

Current research on crashworthiness predominantly concentrates on the design of thin-walled structures for frontal collisions, while studies on side impacts remain comparatively sparse. Functionally graded lattice structures have emerged as a promising solution for lightweight and energy-efficient design. In this study, a novel B-pillar configuration was developed by replacing the conventional reinforcement plate with a functionally graded lattice-filled dual-hat beam. The bending energy absorption behavior was evaluated through numerical simulations and validated by drop hammer impact tests. A surrogate model was constructed using design of experiments, and multi-objective optimization was performed via the NSGA-II algorithm. The final optimal design parameters were t 1  = 0.93 mm, t 2  = 1.01 mm, t 3  = 1.92 mm, and ϖ = 1.344. The optimized B-pillar achieved an intrusion of 65.344 mm, an intrusion velocity of 1395.41 mm/s, and a total mass of 5.975 kg. These correspond to a 31.01% mass reduction, with 8.26% and 25.69% decreases in maximum intrusion and intrusion velocity, respectively, compared to the original design. The discrepancy between the optimization predictions and post-optimization simulation results was less than 15%, confirming the accuracy and robustness of the optimization framework. The results demonstrate significant improvements in both crashworthiness and lightweight performance under side-impact conditions.

Honeycomb aluminum structures are used in energy-absorbing constructions in military, automotive, aerospace and space industries. Especially, the protection against explosives in military vehicles is very important. The paper deals with the study of selected aluminum honeycomb sandwich materials subjected to static and dynamic compressive loading. The used equipment includes: static strength machine, drop hammer and Split Hopkinson Pressure Bar (SHPB). The results show the influence of applied strain rate on the strength properties, especially Plateau stress, of the tested material. In each of the discussed cases, an increase in the value of plateau stresses in the entire strain range was noted with an increase in the strain rate, with an average of 10 to 19%. This increase is mostly visible in the final phase of structure destruction, and considering the geometrical parameters of the samples, the plateau stress increase was about 0.3 MPa between samples with the smallest and largest cell size for the SHPB test and about 0.15 MPa for the drop hammer test.

To solve the problem of low energy release efficiency of fluoropolymer-based reactive materials, four PTFE (Polytetrafluoroethylene) -based reactive structural materials with different contents were prepared by adding traditional energetic materials (RDX, 1,3,5-Trinitrohexahydro-1,3,5-triazine) and alloy metals (aluminum magnesium, aluminum magnesium zinc). In addition, in order to reduce the high cost of the existing high-speed impact energy release testing device, the formulation optimization of PTFE-based aluminum alloy reactive material was efficiently carried out using a small-scale drop hammer impact test in this paper. The self-designed impact energy release testing device was established for the overpressure measurement of PTFE-based aluminum alloy reactive materials. The impact response processes of PTFE-based aluminum alloy reactive material were recorded with high-speed photography. The energy release characteristics were quantified using overpressure measurements. Based on the chemical reaction properties and microstructural characterization of the PTFE-based reactive materials, the ignition mechanism of aluminum alloy reactive materials was analyzed under drop hammer impact load. The results show that the quantitative characterization of the overpressure changes of reactive materials in a quasi-enclosed space before and after reaction can reflect their energy release efficiency under low-velocity impact by using the drop hammer impact energy release testing device. The order of impact response overpressure values for four PTFE-based reactive materials has been conducted. The aluminum alloy reactive material containing RDX explosive has the highest overpressure value and the highest energy release efficiency in terms of drop hammer impact response. Based on the ignition mechanism and energy release characteristics of these four PTFE-based reactive materials, it was found that the addition of alloy metal powder can reduce impact sensitivity, but when activated, it can effectively enhance the damage effect.

The investigation of wave propagation in the geological environment is warranted, and will ultimately help to provide a better understanding of the response of subsoil to excitation. Frequently utilized physical modeling represents a simplification of the global natural system for the needs of the investigation of static and dynamic phenomena with regard to the time domain. The determination of appropriate model materials is probably the most important task for physical model creation. Considering that subsoil represents a crucial medium for wave propagation, an evaluation of suitable model materials was carried out. A plate load test with a circular plate is a non-destructive method for determining the static bearing capacities of soils and aggregates, which are usually expressed by the deformation modulus Edef,2 (MPa) and the static modulus of elasticity E (MPa). A lightweight deflectometer test was used to characterize the impact modulus of deformation Evd (MPa), which is determined based on the pressure under the load plate due to the impact load. A representative propagation of the load–settlement curve for the PLT and the acceleration–time curve for the hammer drop test were investigated. The calculated E values were found to be in the interval between 2.6 and 5.7 kPa, and depending on the load cycle, the values of E ranged from 2.6 to 3.1 kPa. The modulus E from the hammer drop test was significantly larger than the interval between 10.6 and 40.4 kPa. The values of the dynamic multiplier, as a ratio of the hammer drop value to the PLT value, of the modulus E ranged from 4.1 to 13.0. The output of the plate load testing was utilized for the calibration of the finite element method (FEM) numerical model. Both the physical and numerical models showed practically ideal linear behavior of the mass. However, the testing of gelatin-like materials is a complex process because of their viscoelastic nonlinear behavior.

Crack development initiated from nonpersistent joints in rock mass plays a key role in the instability of rock structures. In particular, the dynamic behavior of nonpersistent discontinuities can result in the coalescence and failure of rock structures. The effect and contribution of such joint parameters on rock structures’ failure under impact loading have not been thoroughly investigated by researchers. In this paper, 68 concrete Brazilian disks, manufactured to include several nonpersistent joints and joint sets, are subjected to impact loading to explore the impact of joint continuity factor, joint spacing, bridge angle, and loading direction on the required dynamic energy for crack initiation (DECI) and coalescence (DECC). Artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and its combination with particle swarm optimization (PSO) and genetic algorithm (GA) have been developed to predict the energy indexes. The performance of the models was evaluated using statistical indicators. The results show that intelligent methods can predict both energy indexes and that their outputs are consistent with laboratory results. The R -squared index for the test data of the ANN, ANFIS, and ANFIS-PSO/GA models to predict DECI parameters is 0.97, 0.96, 0.96, and 0.97, respectively, and for DECC is 0.98, 0.96, 0.96, and 0.93, respectively. The ANN have the best performance for the test data based on all statistical indexes. In addition, multiple parametric sensitivity analysis shows that both the joint continuity and joint spacing have the most significant effect while bridge angle and loading direction have the minimal effect on the energy indexes.

PTFE/Al reactive material is an energetic material that releases energy under impact conditions, resulting in a wide range of application prospects. In order to improve its damage ability—considering the higher heat of the reaction per unit mass when Ni2O3 is involved in the aluminothermic reaction—we designed and studied PTFE/Al/Ni2O3, a reaction material based on polytetrafluoroethylene (PTFE). We also designed two other kinds (PTFE/Al, PTFE/Al/CuO) for comparative study, with the mass fraction of the metal oxides added at 10%, 20%, and 30%, respectively. The quasi-static compression properties and impact initiation behavior of the material were investigated by a universal material testing machine and a drop hammer test. The reaction process of different materials under a high strain rate was recorded using a high-speed camera. The results show that with the increase in Ni2O3 content, the strength of the PTFE/Al/Ni2O3 reactive material shows an increasing trend followed by a decreasing trend. Among the three reactive materials, when the content of Al/Ni2O3 reaches 30 wt.%, the reaction duration is the longest (at 4 ms) and the reaction fireball is the largest. The addition of Ni2O3 is helpful to improve the reactivity and reaction duration of the PTEF/Al reactive material.

The drop hammer impact test was carried out to investigate the dynamic response of closed-cell Al foams. A relatively reasonable method was also developed to evaluate the velocity sensitivity of cellular material. The typical impact load–displacement curve exhibited two stages containing the initial compression stage and the progressive crushing stage. Three compressive damage behaviors and four failure modes of closed-cell Al foams were revealed, while the effect of velocity on the impact properties and the energy absorption capacity of different specimens were investigated. The results showed that the specific energy absorption of the specimens increased with the increasing density of the specimen and the impact velocity. However, the specimens with higher specific energy absorption seemed not to indicate better cushioning performance due to the shorter crushing displacement. In addition, the uniaxial impact simulation of two-dimensional (2D) Voronoi-based foam specimens was conducted at higher impact velocities. The simulation results of impact properties and deformation behavior agreed reasonably well with the experimental results, exhibiting similar velocity insensitivity of peak loads and deformation morphologies during uniaxial impact.

Metal/fluoropolymer materials are typical reactive materials. Polytetrafluoroethylene (PTFE)/Al/CuO reactive materials were studied in this research. Scanning electron microscopy (SEM), quasi-static compression, the Split Hopkinson pressure bar test, and the drop hammer test were used to study the mechanical properties and induced reaction characteristics of the reactive materials with different Al/CuO thermite contents and different particle sizes. SEM images of the samples demonstrate that the reactive materials were mixed evenly. The compression test results show that, if the particle size of PTFE was too small, the strength of reactive materials after sintering was reduced. After sintering, with the increase in the content of Al/CuO thermite, the strength of the micro-sized PTFE/Al/CuO firstly increased and then decreased. The Johnson–Cook constitutive model can be used to characterize the reactive materials, and the parameters of the Johnson–Cook constitutive model of No. 3 reactive materials (PTFE/Al:Al/CuO = 3:1) were obtained. The reliability of the parameters was verified by numerical simulation. Drop hammer tests show that the addition of Al/CuO aluminothermic materials or the use of nano-sized PTFE/Al reactive materials can significantly improve the sensitivity of the material. The research in this paper can provide a reference for the preparation, transportation, storage, and application of reactive materials.