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This study aims to investigate the crashworthiness properties of thin-walled foam-filled Auxetic metal/composite cellular tubes under quasi-static and low-velocity impact axial loading. The specimens were fabricated using thin-walled steel tubes and Glass Fiber Reinforced Composite (GFRC) laminates. The crashworthiness characteristics including peak load, absorbed energy, specific absorbed energy, and failure mechanisms of the hybrid structures were studied and compared with individual hollow section and foam-filled Auxetic tubes. In addition, detailed FE simulations were performed using LS-DYNA software, which was verified by the experiments. [ABSTRACT FROM AUTHOR]

A variety of energetic material (EM) devices could be designed more efficiently with a more rapid protocol of modeling and testing if computational tools are more predictive. Drop weight impact tester (DWIT) is widely used to experimentally study energetic material response to impact. Drop weight impact on a thin layer of RDX powder is studied here and computationally modeled to compute the likelihood of EM powder ignition from low‐speed impact. The overall objective is to develop a thermomechanical‐based FEM methodology that can qualitatively predict ignition‐likelihood to study iginition mechanics in EM powders and understand how anvil properties and striker impact conditions influence it. The mechanical confinement conditions offered by an anvil and striker type, influence energy transmission and heat localization within the energetic powder. Efficiently modeling both the bulk behavior and the mesoscopic behavior, such as, localized shear and particle‐to‐particle frictional heating, is necessary to design insensitive EM‐devices. A 3D finite element modeling (FEM) approach is described that more accurately models the impact conditions than previously developed 2D models. The results are compared with the experimental results and the 2D simulations. A continuum‐based explicit FEM can only simulate the bulk‐behavior of the powder. To accurately predict hot‐spot ignition mechanisms, meso‐scale multi‐particle models of the EM is needed. For computational efficiency, hybrid models that combines continuum and multi‐particle FEM (MPFEM) were utilized. The computed temperature profiles are compared for two anvil types and demonstrates that an assessment of ignition likelihood is viable with the hybrid methodologies proposed. [ABSTRACT FROM AUTHOR]

To investigate the propagation mechanisms of stress waves and the characteristics of crack distribution in tunnel structures subjected to explosive effects, an experimental model simulating rock mass using cement mortar was employed. Blasting experiments were conducted at various vertical locations relative to the tunnel. Utilizing ultra-dynamic strain monitoring alongside high-speed digital image recognition, we captured in real time the dynamic evolution of stress waves as well as the precise initiation and expansion paths of cracks. A comprehensive analysis was performed on both stress wave propagation and damage patterns within the refuge structure. Furthermore, the reliability of our numerical simulation algorithm was validated through an examination of fluid-structure coupling algorithms. The results indicated that peak strains at monitoring points within the tunnel increased as detonation points approached it, leading to heightened structural damage. Numerical simulations demonstrated a strong correlation between observed peak strains at critical locations and corresponding damage data from our experimental model. Additionally, it was found that decreasing height between detonation points and the tunnel resulted in increased dynamic response parameters—such as overpressure, velocity, and acceleration—at monitoring sites within the tunnel, thereby exacerbating damage to key areas including vaults and footwall structures. To mitigate potential structural instability within refuges, a full-section molded concrete lining support system was implemented along with supplementary anchor (mesh) spraying in critical regions to ensure long-term operational safety. [ABSTRACT FROM AUTHOR]

The main cause of damage to maize during harvesting and processing is impact damage. This study aimed to investigate the evolution of impact damage to maize kernels under different impact velocities and orientations. Based on the damage characteristics observed in impact tests, an elastoplastic model has been established to accurately simulate the damage behaviour of maize kernels. The microscopic impact behaviour of maize kernels was presented by the finite element method. The results indicated that there were differences in the evolution of damage for different damage morphology in maize kernels. The nature of surface damage was the diffusion and reflection of stress waves, while the nature of local breakage was the concentration of tiny cracks and the release of elastic potential energy. The nature of fracture was the combined effect of compressive and tensile stresses. Meanwhile, under the surface damage, the maximum stresses in the contact area of maize kernels subjected to front orientation were 20.08 MPa, 10.71 MPa for side orientation, and 13.56 MPa for bottom orientation. Under the local breakage, the front orientation with the highest number of cracks occurred at a velocity of 27.3 m s−1, while for the side orientation, it occurred at 24.6 m s−1, and for the bottom orientation, it occurred at 26.2 m s−1. The results can be extended to the study of impact damage in irregularly shaped grains, which was beneficial for controlling product quality and optimising the design of relevant mechanical parameters in agricultural engineering and food engineering fields. [Display omitted] • Damage morphology of maize kernels was summarised. • Evolution rules of damage in multi-orientation maize kernels were explored. • Impact dynamic response of multi-orientation maize kernels was obtained. • Differences in impact damage of multi-orientation maize kernels were compared. [ABSTRACT FROM AUTHOR]

This work studies numerically the development of adiabatic shear banding (ASB) during high strain-rate compression of AISI 1045 steel. Plane strain and cylindrical axisymmetric compressions are simulated in LS-DYNA, considering rectangular and cylindrical steel samples, respectively. Also, a parametric analysis in height-to-base ratio is conducted in order to evaluate the effect of geometry and dimensional ratio of the sample on ASB formation. Doubly structural-thermal-damage coupled finite element models are developed for the numerical simulations, implementing the thermo-viscoplastic Modified Johnson–Cook constitutive relation and damage criterion, while further damage-equivalent stress and strain fields are introduced for the damage coupling. The simulations revealed that plane strain compression promotes more ASB formation, providing lower critical strain for ASB initiation and wider and stronger ASBs compared with axisymmetric compression. Further, X-shaped ASBs initially form during plane strain compression, while as deformation increases, they transform into S-shaped ASBs in contrast to axisymmetric compression, where parabolic ASBs are developed. Also, a lower height-to-base ratio leads to greater ASB propensity, reducing critical strain in axisymmetric compression. Finally, thermal softening is found to precede damage softening and dominate the ASB genesis and its early evolution, while in contrast damage softening drives later ASB evolution and its transition to fracture. [ABSTRACT FROM AUTHOR]

This study conducts a numerical investigation into the response of a honeycomb sandwich structure cube under internal blast. Three different types of honeycomb core structures with varying numbers of sides were designed to withstand internal blast loads. Numerical simulations were performed using LS-DYNA, applying the same material and volume for the honeycomb core to evaluate the effect of core geometry. Both the honeycomb and steel cube were meshed with shell elements using a default element formulation, with the back plate defined as a fixed support to induce uniform deformation. The Johnson--Cook Material Model was applied for material behavior. Results indicated that as the number of sides of the honeycomb core increased, the front plate experienced less damage, demonstrating improved blast resistance. These findings suggest that optimizing the geometry of honeycomb cores can enhance the energy absorption capacity of structures, making them suitable for protective applications in blast-resistant designs. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of a blast-resistant design of reinforced concrete panels with a novel auxetic reinforcement layout inspired by auxetic materials, which have a negative Poisson's ratio, i.e., shrink under compression and expand under tension. A series of two-way supported panels reinforced with re-entrant auxetic-shaped rebars were numerically tested under a TNT explosion. The high-fidelity multi-physics explicit solver of LS-DYNA was utilized to analyze the efficiency of the proposed design. Firstly, the incident pressure of a TNT explosion data and the structural response of a conventional reinforced concrete panel under a TNT explosion were successfully validated by comparing with the experimental and empirical results. Secondly, the blast-resistant capacity of the proposed model was evaluated in comparison to two different conventional designs. Moreover, a parametric study was carried out to reveal the driving parameters of the newly proposed auxetic-shaped reinforcement design. It has been proved that the proposed auxetic reinforcement layout significantly reduces the spalling radius and increases the energy absorption capacity of panels. As a result of the parametric study, the increased reinforcement volume ratio was ineffective on the spalling radius, although the cell size of auxetic reinforcement was found to be quite effective for the blast-resistant design of concrete panels. Overall, the proposed re-entrant auxetic reinforced panel performed far better than conventional designs under blast load. With the recent developments in 3D printing technology, the proposed auxetic reinforcement layout is a strong candidate to deal with blast-resistant designs of concrete panels. [ABSTRACT FROM AUTHOR]

Cellular materials such as aluminum and polyurethane foams are recognized for their effectiveness in energy absorption. They commonly serve as crushable cores in sacrificial cladding for blast mitigation purposes. This study delves into the effectiveness of autoclaved aerated concrete (AAC), a lightweight, porous material known for its energy-absorbing properties as a crushable core in sacrificial cladding. The experimental set-up features a rigid frame made of steel measuring 1000 × 1000 × 15 mm3 with a central square opening (300 × 300 mm2) holding a 2 mm thick aluminum plate representing the structure. The dynamic response of the aluminum plate is captured using two high-speed cameras arranged in a stereoscopic configuration. Three-dimensional digital image correlation is used to compute the transient deformation fields. Blast loading is achieved by detonating 20 g of C4 explosive set at 250 mm from the plate's center. The study assesses the mineral foam's absorption capacity by comparing out-of-plane displacement and mean permanent deformation of the aluminum plate with and without the protective solution. Six foam configurations (A to F) are tested experimentally and numerically, varying in the foam's free space for expansion relative to its total volume. Results show positive protective effects, with configuration F reducing maximum deflection by at least 30% and configuration C by up to 70%. Foam configuration influences energy dissipation, with an optimal lateral surface-to-volume ratio (ζ) enhancing protective effects, although excessive ζ leads to non-uniform foam crushing. To address the influence of front skin deformability, a non-deformable front skin has been adopted. The latter demonstrates an increased effectiveness of the sacrificial cladding, particularly for ζ values above the optimal value obtained when using a deformable front skin. Notably, using a non-deformable front skin increases maximum deflection reduction and foam energy absorption by up to approximately 30%. [ABSTRACT FROM AUTHOR]

Exploiting a sharply-dipping thin vein mine is a challenging task because of the troubles in ore drawing and functioning large-scale mining tools in the limited underground space. Thus, considerations are mandatory to assume an effective mining technique that is able to handle unequal boundaries of this kind of orebody, providing a high recovery rate while lessening preparations before/after stoping and ore dilution. This paper analyses the medium-deep hole blasting of sharply inclined thin vein mines under different blasting factors using LS-DYNA. The links between blasting factors and over-under-excavation percentage of blasting, blasting cracks' density and nearby rock particles' vibration velocity are proven in the current research. Results show that segmental blasting is not much different from one-time blasting in the whole center section in terms of the blasting effect, but its impact on nearby rock is smaller. Two types of holes were designed in W- and X-type, and the distance between the holes were selected to be 0.8, 0.9, 1 m, with total 6 hole types. The effective stresses and displacements at the key monitoring points of the modeled nearby rock were analyzed by W- and X-types of hole placement. Compared with X-type holes, the effective stresses and displacements of W-type holes are smaller, indicating that W-type holes cause less damage to nearby rock. Based on the cumulative damage cloud map, it was concluded that the 0.8 m hole spacing had a larger influence on nearby rock, and that 0.9 m hole spacing was selected considering the factors of blasting effectiveness and resource recovery efficiency. Finally, this mining technique has the potential to be broadly employed to exploit related orebodies. [ABSTRACT FROM AUTHOR]

The performance of multi‐layer ceramic/composite ballistic armor consisting of Alumina, Carbon fiber, and Ultra High Molecular Weight Polyethylene (UHMWPE) under the impact of 7.62 × 51 M61 caliber armor‐piercing (AP) bullets was examined by experimental and finite element methods. The alumina ceramic thickness used in the experiments is 12 mm. The composite structure thickness used in all samples is 10 mm. Explicit dynamic analyses were also conducted using the Ls‐Dyna to verify the experimental studies. The analysis results were compared with experimental studies and evaluated by considering the damage status of the bullet and armor. According to ballistic test results, partial penetration was observed in all armor produced. The front ceramic layer caused corrosion of the bullet, and a mushrooming effect occurred on it. The carbon fiber layer has dramatically helped as an alternative or support to UHMWPE. Since the results obtained with the carbon fiber ratios used remain within the standards, it will not pose a problem regarding usage. On the contrary, using carbon fiber, which is relatively easier to produce and supply than UHMWPE and more economically suitable, will provide more significant benefits. Experimental and numerical studies have revealed consistent results for all armors. Highlights: The effect of a 7.62 × 51 armor‐piercing bullet on ceramic/composite armor was examined.Carbon fiber and UHMWPE hybrid structure was created in different thicknesses.The carbon fiber layer has dramatically helped as an alternative or support to UHMWPE.Using carbon fiber, which is relatively easier to produce and supply than UHMWPE and is more economically suitable.Experimental and numerical studies have revealed consistent results for all armors. [ABSTRACT FROM AUTHOR]

It is well‐known that shear failure is a collapse mechanism that is the riskiest, fastest, and catastrophic and occurs with no visible signs of damage or prior warning for RC beams. Therefore, to prevent brittle shear failure, the RC beams should include sufficient shear reinforcement, such as stirrups, and be designed to have sufficient shear capacity. However, the RC beams' shear capacity becomes inadequate for various reasons. One of these reasons may be the acting of the impulsive impact load, which is uncommon and disregarded in the design phase on the RC beams. An experimental program was conducted to examine the impact behavior and failure mode of shear‐deficient RC beams in the scope of the present study. Besides, it aims to investigate the effectiveness of the strengthening method using CFRP strips in improving the general behavior, failure mode, and performance of shear‐deficient RC beams exposed to impact load. The time histories of the accelerations, displacements, impact loads, and strains in the CFRP strips were measured. They were interpreted how they are affected by experimental variables examined in the experimental study. Furthermore, the finite element model of the specimens was generated in the LS‐DYNA software, and the experimental and numerical results were compared by performing finite element analysis in terms of failure modes and general behavior. [ABSTRACT FROM AUTHOR]

Vaginal childbirth is the final phase of pregnancy when one or more fetuses pass through the birth canal from the uterus, and it is a biomechanical process. The uterine active contraction, causing the pushing force on the fetus, plays a vital role in regulating the fetus delivery process. In this project, the active contraction behaviors of muscle tissue were first modeled and investigated. After that, a finite element method (FEM) model to simulate the uterine cyclic active contraction and delivery of a fetus was developed in LS-DYNA. The active contraction was driven through contractile fibers modeled as one-dimensional truss elements, with the Hill material model governing their response. Fibers were assembled in the longitudinal, circumferential, and normal (transverse) directions to correspond to tissue microstructure, and they were divided into seven regions to represent the strong anisotropy of the fiber distribution and activity within the uterus. The passive portion of the uterine tissue was modeled with a Neo Hookean hyperelastic material model. Three active contraction cycles were modeled. The cyclic uterine active contraction behaviors were analyzed. Finally, the fetus delivery through the uterus was simulated. The model of the uterine active contraction presented in this paper modeled the contractile fibers in three-dimensions, considered the anisotropy of the fiber distribution, provided the uterine cyclic active contraction and propagation of the contraction waves, performed a large deformation, and caused the pushing effect on the fetus. This model will be combined with a model of pelvic structures so that a complete system simulating the second stage of the delivery process of a fetus can be established. [ABSTRACT FROM AUTHOR]

The commercialization and the subsequent widespread adoption of self-driving electric cars have allowed environmentally friendly vehicles to have more interior space than traditional gas-powered vehicles, which has, in turn, led to a growing demand for space utilization of vehicle interiors. A monopost seat is an innovative, lightweight seat designed to maximize space utilization under the seat, with the insertion of a monopost columnar structure between the monopost seat guide rail and the floorboard. However, compared to standard seats, a monopost seat leaves room for improvement when it comes to safety considerations. In our previous study, dynamic simulations of a monopost seat were performed using LS-DYNA. The results revealed that the upper slide rail was the most vulnerable component. In this study, optimal designs were generated to make the upper sliding rail more stable and lighter. To this end, PIAnO, a comprehensive optimal design program, was employed to combine the orthogonal array design of experiments with metamodel-based optimal design methods to deliver the best possible model. A series of simulations confirmed the safety of the new model, which was a significantly improved version of the existing design in terms of stability and weight. [ABSTRACT FROM AUTHOR]

This paper explores the performances of a finite element simulation including four concrete models applied to a full-scale reinforced concrete beam subjected to blast loading. Field test data has been used to compare model results for each case. The numerical modelling has been, carried out using the suitable code LS-DYNA. This code integrates blast load routine (CONWEP) for the explosive description and four different material models for the concrete including: Karagozian & Case Concrete, Winfrith, Continuous Surface Cap Model and RiedeleHiermaiereThoma models, with concrete meshing based on 10, 15, and 20 mm. Six full-scale beams were tested: four of them used for the initial calibration of the numerical model and two more tests at lower scaled distances. For calibration, field data obtained employing pressure and accelerometers transducers were compared with the results derived from the numerical simulation. Damage surfaces and the shape of rupture in the beams have been used as references for comparison. Influence of the meshing on accelerations has been put in evidence and for some models the shape and size of the damage in the beams produced maximum differences around 15%. In all cases, the variations between material and mesh models are shown and discussed. [ABSTRACT FROM AUTHOR]

In the current study, an experimental setup consisting of smoothbore 30-caliber powder gun was employed to launch spherical projectiles (3 g/ϕ9) in the ballistic range of velocities from 500 to 1700 m/s and obliquity (0, 33 and 65°), impacting 2 mm thin Steel 1006 target plates. Crater dimensions (major and minor dia.) obtained from series of FE simulations run for the above configuaration was validated by corresponding experimental data. Subsequently, a fullscale 3D FE model considering 8-noded hexahedral elements was used to discretize SS304 conical projectiles (replacing spherical projectile) with various apex angles viz. 40°, 60°, 80° and 100° impacting on single (3 mm) and double layer (1.5 mm each) steel 1006 targets (replacing 2 mm target) in LS dyna. The material behavior was characterized using J–C strength and damage models, along with Gruneisen Equation of State. An erosion algorithm was used in the explicit FE code LS-DYNA to remove undesirable elements. In the next stage, Adam and Nadam optimizers have been employed in ANN models developed using Python code within the Tensor-Flow framework. The Keras Tuner library in the Tensor-Flow framework was used for hyper parameter tuning. The ANN models trained using simulation data successfully predicted the residual KE of conical projectiles with intermediate apex angles of 90°, 70°, and 50° across twelve different impact scenarios. The models with Adam and Nadam optimizers achieved mean squared error (MSE)/coefficient of determination (R2)/mean absolute percentage error (MAPE) values of 109.44/0.998/6.72 and 91.19/0.998/7.76, respectively.Article Highlights: Simulation data has good agreement within ± 10% with data generated from Ballistic experiments highlighting robustness and accuracy of the FE model used in the study. The novel approach of integrating simulation results with ANN models satisfactorily predicted the residual kinetic energy of projectiles. Keras Tuner library in the Tensor Flow framework automatically predicted optimal sets of hyper parameters for ANN models. This study proved that, Adam and Nadam optimisers in ANN modelling are ideal for regression problems involving ballistic studies. Hybrid approach involving FEA, ANN and ballistic experiments is first of its kind in predicting the damage of double layer targets. [ABSTRACT FROM AUTHOR]

Abstract To investigate the propagation mechanisms of stress waves and the characteristics of crack distribution in tunnel structures subjected to explosive effects, an experimental model simulating rock mass using cement mortar was employed. Blasting experiments were conducted at various vertical locations relative to the tunnel. Utilizing ultra-dynamic strain monitoring alongside high-speed digital image recognition, we captured in real time the dynamic evolution of stress waves as well as the precise initiation and expansion paths of cracks. A comprehensive analysis was performed on both stress wave propagation and damage patterns within the refuge structure. Furthermore, the reliability of our numerical simulation algorithm was validated through an examination of fluid-structure coupling algorithms. The results indicated that peak strains at monitoring points within the tunnel increased as detonation points approached it, leading to heightened structural damage. Numerical simulations demonstrated a strong correlation between observed peak strains at critical locations and corresponding damage data from our experimental model. Additionally, it was found that decreasing height between detonation points and the tunnel resulted in increased dynamic response parameters—such as overpressure, velocity, and acceleration—at monitoring sites within the tunnel, thereby exacerbating damage to key areas including vaults and footwall structures. To mitigate potential structural instability within refuges, a full-section molded concrete lining support system was implemented along with supplementary anchor (mesh) spraying in critical regions to ensure long-term operational safety.

This paper explores the performances of a finite element simulation including four concrete models applied to a full-scale reinforced concrete beam subjected to blast loading. Field test data has been used to compare model results for each case. The numerical modelling has been, carried out using the suitable code LS-DYNA. This code integrates blast load routine (CONWEP) for the explosive description and four different material models for the concrete including: Karagozian & Case Concrete, Winfrith, Continuous Surface Cap Model and Riedel–Hiermaier–Thoma models, with concrete meshing based on 10, 15, and 20 mm. Six full-scale beams were tested: four of them used for the initial calibration of the numerical model and two more tests at lower scaled distances. For calibration, field data obtained employing pressure and accelerometers transducers were compared with the results derived from the numerical simulation. Damage surfaces and the shape of rupture in the beams have been used as references for comparison. Influence of the meshing on accelerations has been put in evidence and for some models the shape and size of the damage in the beams produced maximum differences around 15%. In all cases, the variations between material and mesh models are shown and discussed.

Numerical simulations were conducted to validate computational and constitutive models for steel materials through dynamic material tests involving both tension and compression. These simulations involved the numerical modeling of the split Hopkinson pressure bar (SHPB) apparatus, with the appropriate loading applied directly in compression and indirectly in tension. To induce a tensile wave within the specimen, a shoulder, such as a coupler or collar, was interposed between the bars. The simulations were carried out using the LS-DYNA finite element code. In these numerical simulations of the SHPB tests, the MAT-15 Johnson–Cook material model was applied to represent mild steel. The resulting stress–strain relationships obtained under both compression and tension conditions were subsequently compared to corresponding experimental data. The primary objectives of these simulations were to determine the optimal placement of strain gauges on both the input and output bars of the tensile SHPB setup. Additionally, the simulations aimed to assess the influence of the gauge length-to-diameter ratio on the behavior of the mild steel specimen subjected to dynamic tension and compression. The results showed that the pulse produced due to the mechanical mismatch of the element at boundaries can be avoided using the length of the input bar smaller than the output bar. Further, the location of the strain gauge in the case of the output bar should be toward the output bar-shoulder interface, while in the case of the input bar, it should be considered at the center of the span of the bar. [ABSTRACT FROM AUTHOR]

Abstract In the current study, an experimental setup consisting of smoothbore 30-caliber powder gun was employed to launch spherical projectiles (3 g/ϕ9) in the ballistic range of velocities from 500 to 1700 m/s and obliquity (0, 33 and 65°), impacting 2 mm thin Steel 1006 target plates. Crater dimensions (major and minor dia.) obtained from series of FE simulations run for the above configuaration was validated by corresponding experimental data. Subsequently, a fullscale 3D FE model considering 8-noded hexahedral elements was used to discretize SS304 conical projectiles (replacing spherical projectile) with various apex angles viz. 40°, 60°, 80° and 100° impacting on single (3 mm) and double layer (1.5 mm each) steel 1006 targets (replacing 2 mm target) in LS dyna. The material behavior was characterized using J–C strength and damage models, along with Gruneisen Equation of State. An erosion algorithm was used in the explicit FE code LS-DYNA to remove undesirable elements. In the next stage, Adam and Nadam optimizers have been employed in ANN models developed using Python code within the Tensor-Flow framework. The Keras Tuner library in the Tensor-Flow framework was used for hyper parameter tuning. The ANN models trained using simulation data successfully predicted the residual KE of conical projectiles with intermediate apex angles of 90°, 70°, and 50° across twelve different impact scenarios. The models with Adam and Nadam optimizers achieved mean squared error (MSE)/coefficient of determination (R2)/mean absolute percentage error (MAPE) values of 109.44/0.998/6.72 and 91.19/0.998/7.76, respectively.

Abstract Deep coal‐rock formations are subjected to complex stress environments characterized by high static stresses and dynamic disturbances. To study the damage, fracture, and energy evolution characteristics of coal‐rock under dynamic–static combined loading, a new multiscale constitutive model for coal‐rock under dynamic–static combined loading is proposed based on micromechanics, and it is implemented into the LS‐DYNA solver. A numerical model of coal‐rock Split Hopkinson Pressure Bar under dynamic–static combined loading is established using LS‐DYNA, and research on the mechanical and energy evolution characteristics of coal‐rock under one‐dimensional and three‐dimensional dynamic–static combined loading is conducted. The results show that under one‐dimensional dynamic–static combined loading, with the increase of precompression, the dynamic peak stress linearly decreases while the combined peak stress linearly increases, and the dissipated energy of the specimen shows a decreasing trend. The fracture patterns of the coal‐rock specimen include internal shear fracture and external tensile fracture, and eventually, these two modes of fracture intersect to form macroscopic mesh cracks. As the axial pressure increases, the degree of specimen fragmentation gradually increases. Under three‐dimensional dynamic–static combined loading, with the increase of preconfining pressure, the stress–strain curve of the specimen will transition from “stress drop” to “stress rebound” after the peak. The peak stress increases with the increase of confining pressure, and the energy dissipation density of the specimen increases first and then decreases with the increase of confining pressure. With the increase of confining pressure, the hoop deformation of the specimen plays a constraining role, and the degree of specimen fracture gradually weakens, and the time of fracture occurrence gradually delays. The research results contribute to revealing the mechanical and energy mechanisms of rockburst disasters in deep coal mines.

Copyright of Industria Textila is the property of Institutul National de Cercetare-Dezvoltare pentru Textile si Pielarie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The threat of rockfall impacting bridges in mountainous areas poses a great risk to the safety of passing trains. This study delves into the dynamics of rockfall impact and its implications on the interaction between train vehicles and bridges. Leveraging LS-DYNA, this study first captured the force–time history of rockfall impact on bridge structures. Subsequently, there was a comparison with the impact forces generated at various speeds with those predicted by established formulas, validating the accuracy of simulations. Employing BANSYS software, the dynamic responses of both bridge structures and the vehicle–bridge coupling system to falling rocks were analyzed. The investigation encompassed parameters such as impact speed, position, and train location. The findings reveal that escalating impact speeds correlate with increased average and maximum impact forces from falling rocks. Notably, the average impact force does not linearly correspond with rock speed and often exceeds values calculated by conventional formulas. Impact position minimally affects maximum impact force, yet alterations in position prolong impact duration, consequently reducing average impact force. Rockfall-induced impacts precipitate notable spikes in train lateral acceleration, lateral wheelset force, wheel unloading rate, and derailment coefficient, albeit with a comparatively lesser impact on vertical acceleration. Increasing impact speed and altering position intensifies the vehicle’s response, particularly when the train is in close proximity to the impact site. [ABSTRACT FROM AUTHOR]

Deep coal‐rock formations are subjected to complex stress environments characterized by high static stresses and dynamic disturbances. To study the damage, fracture, and energy evolution characteristics of coal‐rock under dynamic–static combined loading, a new multiscale constitutive model for coal‐rock under dynamic–static combined loading is proposed based on micromechanics, and it is implemented into the LS‐DYNA solver. A numerical model of coal‐rock Split Hopkinson Pressure Bar under dynamic–static combined loading is established using LS‐DYNA, and research on the mechanical and energy evolution characteristics of coal‐rock under one‐dimensional and three‐dimensional dynamic–static combined loading is conducted. The results show that under one‐dimensional dynamic–static combined loading, with the increase of precompression, the dynamic peak stress linearly decreases while the combined peak stress linearly increases, and the dissipated energy of the specimen shows a decreasing trend. The fracture patterns of the coal‐rock specimen include internal shear fracture and external tensile fracture, and eventually, these two modes of fracture intersect to form macroscopic mesh cracks. As the axial pressure increases, the degree of specimen fragmentation gradually increases. Under three‐dimensional dynamic–static combined loading, with the increase of preconfining pressure, the stress–strain curve of the specimen will transition from "stress drop" to "stress rebound" after the peak. The peak stress increases with the increase of confining pressure, and the energy dissipation density of the specimen increases first and then decreases with the increase of confining pressure. With the increase of confining pressure, the hoop deformation of the specimen plays a constraining role, and the degree of specimen fracture gradually weakens, and the time of fracture occurrence gradually delays. The research results contribute to revealing the mechanical and energy mechanisms of rockburst disasters in deep coal mines. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High voltage electrical pulse fracturing technology based on electrohydraulic effect is a new type of rock mass fracturing technology. This technique is characterized by its safety, high efficiency, environmental friendliness and controllable energy usage. It holds a significant potential for its application in the stress control of surrounding rock in coal mines because the complex stress conditions present in underground rock mass. To further investigate the cracking effect of the technology on hard rock mass under different surrounding rock stress conditions, the numerical simulation of high voltage electric pulse rock mass cracking was carried out on the rock sample based on the RHT damage constitutive model by LS-DYNA. The processes of damage evolution and effective stress evolution inside the rock mass were collected. The cracking characteristics and crack propagation mechanism of the rock mass were analyzed. The numerical simulation overcomes the problem that it is difficult to effectively monitor the internal rock mass during the cracking process due to the fast discharge process and large electromagnetic interference in the indoor test. The self-developed high-voltage electrical pulse rock fracturing test platform was used to carry out the high voltage electrical pulse rock fracturing test under different surrounding rock stress conditions, and the reliability of the numerical simulation results was verified by the obtained rock surface fracture characteristics. The following conclusions are obtained: ① The numerical model of LS-DYNA high voltage electric pulse rock mass fracturing is established based on the RHT constitutive model. The equivalent parameters for the numerical simulation are derived according to the energy equivalent relationship between explosive blasting and high voltage electric pulse. The reliability of these parameters is confirmed by comparing the laboratory tests results with the numerical simulation results. ② By analyzing the crack propagation on the upper surface of specimens, it reveals that the crack will deflect in the direction of the maximum compressive initial stress. Initially, the total length of the crack first decreases gradually during this process. As the angle between all cracks and the maximum initial compressive stress becomes less than 45°, the total crack length begins to increase gradually. ③ Numerical simulations demonstrate that the dynamic stress resulting from high voltage electric pulse discharge is much greater than the initial stress in the surrounding rock during the early stages of fracturing. Dynamic stress plays a leading role in rock failure in this process. As the dynamic stress quickly diminishes during propagation, the initial surrounding rock stress is gradually close to the dynamic stress and finally dominates the initiation and propagation of cracks. The results indicate that surrounding rock stress plays a crucial role in determining the development and expansion characteristics of rock mass cracks. It notably influences the direction of crack expansion. When the high voltage electric pulse fracturing technology is used to crack the deep rock mass, the stress state of the rock mass should be considered. The scientific fracturing scheme should be formulated to achieve an efficient fracturing of the rock mass. The research results provide a reliable numerical simulation method for high voltage electric pulse rock fracturing and a reference for the formulation of deep rock mass fracturing scheme.