Dynamic Response Mechanism Research Articles

Dynamic compressive response and fracture mechanisms of ZrB2–SiC ceramic based on discrete element method

AbstractTo investigate the dynamic compression behaviors of fracturing and damage evolution of ZrB2–SiC ceramic, this paper proposes a discrete element method to carry out the dynamic compressive behavior of ZrB2–SiC ceramic. This study is based on three‐dimensional discrete element‐finite difference coupling modeling to realize the reproduction of the splitting Hopkinson pressure bar experiment process. Micro‐parameters of the linear parallel bond model are obtained by calibrating dynamic compression strengths, stress–strain curves, and fracture characteristics of ZrB2–SiC ceramic. The dynamic compressive stress–strain curve can be divided into four stages according to the microcrack evolution and acoustic emission: stage I, linear elastic stage; stage II, microcrack initiation and then stable development stage; stage III, increment stage of microcracks before peak strength; stage IV, increment stage of microcracks after peak strength. The dynamic damage evolution with strain shows a Weibull distribution. The shape and scale parameters change with strain rate. In addition, under the dynamic compression, crack initiation stress, fracture pattern, and fragment size distribution of the ZrB2–SiC ceramic composite exhibited a significant strain‐rate dependence.

Interleaved Buck-Type Rectifier With Pseudo-DC-Link Capacitors for Automatic Current Balancing

This article presents an interleaved buck-type rectifier with pseudo-dc-link capacitors featuring automatic current balancing, soft-switching operation, efficient ac-dc conversion, and tight output regulation. The ac-input-current-synchronized modulation scheme that hybridizes for cycle-by-cycle phase-shift and duty ratio adjustment is adopted for zero-voltage switching (ZVS) operation and output regulation. In addition, the pseudo-dc-link capacitors facilitate the convergence and current balancing between output inductors. Mathematical models are provided to quantitatively describe the mechanism of current balancing, steady-state performance, and dynamic response. A lab prototype is built, and the experimental results are provided to verify the features.

Dynamic response mechanism analysis of hinged FBG acceleration sensor

Considering the influence of the adhesive layer and hinge structure on the dynamic response effect of the hinged fiber Bragg grating (FBG) acceleration sensor, a multi-degree-of-freedom series vibration model and a transfer function were established based on the system dynamic equation. The stiffness calculation formulas of the hinge and adhesive layer were derived based on Castigliano’s second theorem. The results demonstrated that the response time of the sensor could significantly lag when the elastic modulus of the adhesive layer is lower than a certain critical value. The most crucial parameter affecting the dynamic response performance of the sensor is hinge thickness. The jagged oscillations in the sensor response signals can be reduced with the appropriate increase in the thickness, width, and semi-minor axis of the hinge as well as by reducing the semi-major axis of the hinge. However, it could also lead to an increase in the resonance frequency and a decline in sensitivity.

Habitat change and interspecific associations mediate the response of riparian ground-dwelling arthropod assemblages to flooding in the Three Gorges Reservoir

Seasonal water level fluctuation is a typical characteristic of reservoirs created by dams on rivers. Due to their important roles in connecting ecological processes between riparian zones and adjacent uplands or waterbodies, ground-dwelling arthropods are essential components for maintaining riparian ecosystem health. However, the dynamic characteristics and response mechanisms of ground-dwelling arthropod assemblages to seasonal water level fluctuations have not been clearly established. We investigated ground-dwelling arthropods before and after summer floods (along with the influence of planned winter impoundment) in the drawdown zone of the Three Gorges Reservoir. Redundancy analysis and examination of interspecific associations were conducted to explore driving mechanisms for variations in these arthropod assemblages. Our results demonstrated that: i. floods are dominant mediating factors for variations in ground-dwelling arthropod assemblages in riparian zones; ii. species composition and abundances of ground-dwelling arthropod assemblages were in a state of dynamic change under the influence of floods; iii. Interplay of habitat modifications and interspecific associations influenced the composition as well as the distribution of ground-dwelling arthropods. We suggest that ground-dwelling arthropods are sensitive indicators for riparian ecosystem health and are valuable for evaluating work on the conservation and management of riparian zones.

Numerical simulation on crushing and breakages of particles in a sphere-chain under impact loading

To improve the study of dynamic mechanical response of granular materials under impact load, sphere-chain as a specific granular material, are taken as the research object. The crushing and breakages of particles in sphere-chain were numerically simulated in the frame of the ANSYS/LS-DYNA software to identify the dynamic response mechanism of granular materials with different sizes and numbers particles under impact loading. The simulated breaking process and strain changes were compared with the test results to verify the feasibility of the numerical simulation. The displacement and stress evolution law of sphere-chain under axial impact loading is analyzed. The results show that the fracture process and strain variation of the sphere-chain obtained by the numerical simulation are consistent with the test results. The fracture propagation is generated from the contact point and intersects the other contact point, And the degree of breaking is the top, bottom and middle pellet from large to small. Large compressive displacement and compressive stress appear at the contact point and its vertical axial line, while tensile displacement and tensile stress appear on the surface. The degree of breaking is positively correlated with the number of pellets and negatively correlated with the size of pellets.

Dynamic Response Mechanism of Silt Ground under Vibration Load

The frequent vibration loads during the operation of trains can cause vibration deformation of the tunnel structure and surrounding weak strata, thereby endangering the safe operation of trains. The purpose of this paper is to study the dynamic response of surrounding soil layers caused by train vibrations through the finite difference method with FLAC3D. Based on existing research, we studied the artificially deterministic exciting force function. Then, we simulated the tunnel working conditions of a train with a 3D model, and applied the artificially deterministic exciting force function to the tunnel model. To study the vibration caused by trains in silty soil, we divided the trains into two cases, one-way and two-way. We compared the displacement–time curves of one-way and two-way trains. When the horizontal distance between the monitoring point and the vibration source increases, the peak value of the displacement–time curve decreases. As the speed of the train increases, the peak value of the displacement–time curve increases. The vertical displacement of the ground under the dynamic load of the two-way train is greater than that of the one-way train. In the acceleration–time curve, there is a lag in the ground acceleration response. The faster the speed of the subway train, the greater the peak value of the acceleration–time curve. This study can provide a guide for the evaluation and prevention of ground vibration subsidence and uneven subsidence of strata in the silt area of the Yellow River Region.

Finite element analysis on impact response and damage mechanism of composite laminates under single and repeated low-velocity impact

Aerospace composite structures are subjected to not only single but also repeated low-velocity impact during service conditions. In this paper, the dynamic mechanical response and damage mechanism characterization of composite laminates under single and repeated low-velocity impact are investigated numerically by considering the thickness effect. A progressive damage finite element model is developed in ABAQUS with the help of a user-defined material subroutine. The Hou failure criteria are applied to simulate the intra-layer damage, while the cohesive zone model is adopted to describe the inter-layer damage. The validated model is used to study the effect of thickness. The composite plates with three kinds of thickness are analyzed and discussed in terms of contact force, central displacement, energy absorption and internal damage in detail. The numerical results indicate that for both single and repeated impact, the impact response parameters vary linearly with thickness for the chosen plates. Moreover, the damage patterns are inconsistent with each other in that the dominant damage mode changes from intra-laminar damage to inter-laminar damage as the thickness increases owing to the better load-bearing capacity of the thicker layer.

Accident dynamic response and injury mechanism of the collision accident between right-turning truck and cyclist straight

The proportion of accident between right-turning truck and cyclist straight is smaller than other types of collision accidents. But it is far likely for cyclists to suffer severe injury when it happens. In this paper, we pay attention to the effects of four parameters (truck speed, collision angle, friction coefficient, and truck driver's reaction time) on the dynamic response process and the injury level of cyclist of the accident between right-turning truck and cyclist straight. We found that all the parameters have a great impact on those. Two types of dynamic response processes exist. In step one and step two, the injury values of cyclist were all below their threshold when the truck speed was less than 27 km/h. But when the truck speed is greater than or equal to 27 km/h, the injury value of the chest is higher than 60 g. Meanwhile, HIC and the resultant acceleration of the chest increase with truck speed. Most of the injury value of the crushed part exceeds the fixed value when step three happened. So, slowing down the truck speed and reducing the possibility of cyclist being crushed can improve the safety level of cyclists.

Changes in thermophysical and thermomechanical properties of thermally treated anisotropic shale after water cooling

Shale gas has become the development focus of many countries recently for its strategic importance, and the deep shale gas extraction is becoming a priority worldwide. Water-based drilling and fracturing fluid can inevitably lead to an intense heat exchange on deep high-temperature shale reservoirs, thus understanding the changes in thermophysical and thermomechanical properties of deep shale reservoirs after being subjected to water cooling is essential. In this present work, the changes in thermophysical and thermomechanical properties of thermally treated shale specimens (25–200 ℃) with five kinds of bedding plane inclinations (BPI) of 0°, 30°, 45°, 60° and 90° after water cooling are researched in the lab. Results illustrate that as temperature increases, the density and P-wave velocity obviously decrease and the porosity increase for shale specimens with the five different BPI after thermal treatment and water cooling. Dynamic uniaxial compression strength of all the specimens after thermal treatment and water cooling decreases gradually with increasing temperature, while the static one increases except for specimens with the BPI of 60°. The dynamic and static strength anisotropy of specimens became more obvious with increasing temperature, but the treatment temperature does not act well in changing the anisotropic evolution trend under the two conditions. In the end, the overall response of anisotropic shale after thermal treatment and water cooling is discussed by the results of scanning electron microscope (SEM) and ABAQUS numerical simulation, and the mechanism of dynamic and static strength response is systematically revealed. The findings are hoped to provide theoretical guidance and technical support for the deep shale gas extraction.

Morphology-Evolved Succulent-like FeCo Microarchitectures with Magnetic Configuration Regulation for Enhanced Microwave Absorption.

The regulation of magnetic configuration through diverse morphologies to achieve a rapid magnetic response has attracted considerable academic favor on account of the unique application prospects in various fields. Herein, porous FeCo alloys with morphology evolved from spheres to succulent-like microstructures are successfully constructed via a facile hydrothermal reaction-hydrogen reduction synthetic strategy. A multiple balance/competition mechanism is proposed, including the coexistence of the dissolution-precipitation balance of hydroxides and the dissociation-stability balance of coordination compounds, the Fe3+-Co2+ competition, and the precipitation-coordination reaction contest. As the morphology evolves to a succulent-like assembly, the multidomain features with a stable combination of vortex states and the violent motion of magnetic vectors contribute to the improvement of magnetic storage capacity and loss capability, which are evidenced by the off-axis electron holography and micromagnetic simulation. Consequently, the succulent-like FeCo exhibits enhanced permeability and microwave absorption performance. The effective absorption bandwidth reaches 5.68 GHz, and the maximum reflection loss is elevated to -53.81 dB. This work sheds considerable insight into the microstructure regulation with an application in microwave absorption and offers guidance in research for the topological magnetic configuration and dynamic response mechanism of magnetic alloys.

Shaking Table Test Study on Dynamic Response of Bedding Rock Slope with Weak Rock

A shaking table model test was conducted to study the dynamic response and failure mechanism of a bedding rock slope with weak rock layer based on the “Xiaguiwa” landslide in the Jinsha River basin of Sichuan-Tibet. The influence of schist-like weak rock layer on bedding rock slope is considered. The test results show that the Peak Ground Acceleration (PGA) amplification coefficient varies rhythmically from the inside to the surface of the slope, and 0.3 g and 0.6 g are the slope appears cracking and instability. schist-like weak rock layer makes the seismic wave enhance obviously, but in the slope flexure position, the seismic wave near the weak rock layer is slightly weakened instead, and the maximum displacement often occurs above the weak rock layer. the “bucking” occurs at 1/4 of the slope height, and the fracture degree at the middle and lower part of the slope is greater than that at the middle and upper part, and the slope damage surface appears to be “concave at the top and convex at the bottom”. The damage process of the model slope is divided into four stages. The model test results reflect the influence of the weak rock layer on the seismic dynamic response and damage process of the bedding rock slope.

Dynamic response and damage mechanism of parallel wire cables under contact explosion

With the global threat of terrorism on the rise, the protection of important infrastructure such as cable-stayed bridges from terrorist assaults has become a major concern. In cable-stayed bridge designs, the cables are crucial load-carrying components, and their failure could result in the progressive collapse of the bridge with catastrophic results. However, there is very limited understanding of the blast effects on cables. This paper presents a study on the blast performance of parallel wire cables under contact explosions. Field blast tests were conducted on four identical parallel wire cable specimens with varying charge weights and prestress levels. Arbitrary-Lagrangian-Eulerian (ALE) algorithm is utilized to develop the numerical model in LS-DYNA. The numerical model is then validated and further used to investigate the damage mechanism of the cable under contact explosions. The results indicate that the damage process of cables under contact blasts can be divided into three stages: Compression, divergence, and stretching. The wires arranged in angular points facing the detonation are particularly vulnerable, and high-density polyethylene (HDPE) is prone to be pelted off by explosive pressure. Parametric analyses were carried out to investigate the influences of charge weight and prestressing force on the damage degree of cables. The relationship between the TNT equivalent and the number of fracture wires is derived from the parametric analysis results. Furthermore, the prestress is found to have a considerable impact on the degree of cable damage induced by contact explosions. Taking prestress into account, a damage evaluation method for blast-damaged cables is proposed.

Tensile mechanical behavior and fracture characteristics of sandstone exposed to freeze-thaw treatment and dynamic loading

Rock masses in high-elevation or cold areas are vulnerable to the joint results of freeze-thaw (F-T) action and dynamic loading, it is thus significant to evaluate the tensile mechanical behavior and fracture characteristics of F-T treated rocks under dynamic loading. In this study, based on the split-Hopkinson pressure bar (SHPB) device, the dynamic flattened Brazilian disc (FBD) tests are performed on sandstone to investigate the degradation mechanism of dynamic tensile response and fracture characteristics of rock induced by F-T treatment. Recur to high-speed photography and digital image correlation (DIC) technique, 3D scanning and scanning electron microscope (SEM), the macroscopic and microscopic fracture characteristics of F-T treated sandstone are comprehensively observed and discussed. Experimental results show that the dynamic tensile strength of sandstone constantly decreases with increasing F-T cycles at a specified loading rate. The failure mode of FBD specimen gradually transforms from slash mode to ‘Y’-shaped mode and then to ‘X’-shaped mode with increasing loading rates. 3D scanning results show that the roughness of the central fracture surface of FBD specimen decreases with increasing loading rate or freeze-thaw cycles. Furthermore, both microscopic tensile and shear fracture patterns are observed by SEM, and it is found that the trans-granular (TG) fracture become more prevalent under higher loading rate or higher freeze-thaw cycles. In addition, some hidden connection between microscopic fracture mechanism and macroscopic mechanical properties of F-T treated sandstone is analyzed and discussed.

Dynamic response and failure mechanisms of a laser-fabricated flexible thin film strain gauge

Increasing demand for smart devices has spurred the development of advanced sensors with smaller and more adaptable form factors. The integration of thin film technology into sensors such as strain gauges has the potential to reduce their size and allow for the use of new manufacturing techniques. However, fabrication of reliable thin film strain gauges remains a challenge. Here, we demonstrate the manufacture of a 1025 Ω flexible thin film strain gauge using a UV laser patterning process and evaluate its dynamic tensile response. The strain gauges exhibit a sensitivity comparable to conventionally fabricated commercial alternatives, and can reliably survive 106 cycles up to 1750 µε. Above this strain level, several failure mechanisms are identified, with unique electrical responses corresponding to physical damage observed on the strain gauges. These findings provide a guide to diagnose thin film strain gauge failures, demonstrate an unconventional fabrication technique, and show their potential for use in long-term dynamic load sensing applications.

Soil microbial ecological effect of shale gas oil-based drilling cuttings pyrolysis residue used as soil covering material

The residue derived from oil-based drilling cutting pyrolysis could be used as paving materials. Some petroleum hydrocarbons remain in the residue after pyrolysis and cause severe environmental pollution. In this study, the soil column leaching experiments were carried out under different leaching amounts, and the vertical migration characteristics of petroleum hydrocarbons in soil and the dynamic response mechanism of microorganisms to petroleum hydrocarbons were analyzed. The result showed that the soil pH value and water content with different leaching amounts did not differ significantly, but the vertical migration ability of each petroleum hydrocarbon component was different. In petroleum hydrocarbon contaminated soil, the relative abundance of Proteobacteria maintained a high level (23.6%–60.7%). At the genus level, the relative abundance of Massilia decreased with the leaching amount increased. According to PICRUSt, Monooxygenase [EC: 1.14.13.-] played a significant role in petroleum hydrocarbon degradation. While Long-chain-fatty-acid-CoA ligase [EC: 6.2.1.3] had the highest relative abundance. By studying the influence of shale gas oil-based drilling cuttings pyrolysis residue on soil physical and chemical properties and soil microorganisms, this work provides scientific ecological assessment for the resource application of pyrolysis residue.

Dynamic Response and Failure Mechanism of Concrete Arch Dams under Extreme Loadings: A Solid Foundation for Real-World Actions to Reduce Dam Collapse Losses during Wartime or Terrorist Attacks

With massive energy demands, the majority of developing countries are at a critical juncture in their industrial development. Their energy structure, on the other hand, is relatively specific and heavily reliant on fossil fuels, resulting in significant environmental pollution. As a result, the development of clean energy is on the horizon, which is related not only to whether developing countries can build a resource-saving and environmentally friendly society but also to whether they can achieve socially sustainable development. As a significant clean energy source, not only does hydropower play an important role in the development of an energy-efficient and environmentally friendly green economy, but it also has numerous benefits such as shipping, irrigation, flood control, and water supply. So, hydropower development is critical for developing countries to adjust their energy structures, achieve regional development balance, and ensure river defense safety. However, precision guidance technology is maturing around the world. If one side’s water-retaining dam is accurately blasted in the event of a full-scale war or local conflict, it may cause significant economic and human losses. Dam safety and protection from strong explosions deserve special attention given the obvious seriousness of the consequences. It is critical to improve the anti-explosion safety of major hydraulic structures by revealing the dynamic response behavior, damage mechanism, and dam characteristics under explosion impact loads, as well as evaluating the dam’s condition after extreme loads. In the critical work of disaster prevention and mitigation, this is crucial to our social and economic development. This study is not only a key technical problem and an important strategic task in hydraulic structure construction, but it may also serve as a guideline for governments to take effective measures to reduce the loss of dam break under special circumstances.

Dynamic response and failure mechanism characterization of composite‐metal sandwich structures under slamming impact utilizing CEL method

AbstractSlamming is a complicated fluid–structure coupling process accompanied with complex transfer of load and energy, which may pose a significant risk to the overall safety of structure. This paper aims to evaluate the dynamic response and elucidate the failure mechanism of composite‐metal sandwich structures under slamming impact. Firstly, a reliable numerical simulation process is established based on CEL method in ABAQUS/Explicit combining with a VUMAT subroutine, whose effectiveness is verified through the comparison with published experimental results. Subsequently, dynamic response of the sandwich structures is investigated considering the influence of slamming velocity and material constituent. Meanwhile, damage evolution and critical failure mechanism are assessed through progressive damage analysis. Results show that CF‐Al‐CF case owns the best mechanical performance and the latest ultimate failure moment. The overall performance of sandwich structure is mainly dependent on the mechanical properties of skin. Additionally, damage of Al‐CF‐Al case is more sensitive to the variation of velocity compared with that of CF‐Al‐CF and Al‐Al‐Al cases, which indicates that the ductility of core is responsible for ultimate damage. Moreover, extensively distributed matrix tension damage can be identified as the critical damage mode, which may further cause debonding damage and even fiber fracture.

Shock compression of nanoporous silicon carbide at high strain rate

The dynamic material response and void collapse mechanisms of nanoporous silicon carbide (SiC) under shock compression are systematically investigated by large scale molecular dynamic simulations. The effects of shock intensity are revealed by varying shock particle velocities (Up) from 1.0 to 3.5 km/s. The influences of different void sizes in samples are evaluated as well. Results show that the void collapse mechanism is highly related to the impact velocity. Under low and medium impact velocities (1.0 km/s, 1.5 km/s, 2.0 km/s, respectively), the atoms in the earliest collapse region flow vertically and decompose the voids into two sub-voids. Besides, a theoretical model is applied to explain the earliest collapse region at low impact velocity. Meanwhile, the internal jetting dominates the void collapse under high impact velocities (2.5 km/s, 3.0 km/s, 3.5 km/s, respectively), making the voids horizontally filled. In addition, the formation mechanism of hotspot is revealed, which is determined by the void collapse modes. Larger voids are more likely to collapse when subjected to the same impact velocity. The nanoporous SiC samples with larger voids can better weaken the stress wave by converting the mechanical energy into thermal energy. The results provide deep insights into void collapse in SiC and promote the designs of advanced nanoporous ceramics in the application of shock-protect system under extreme conditions.

On the evolution mechanism of permeability during gas drainage: Insights from deformation field, gas pressure field and temperature field

Permeability is an important factor affecting efficient gas drainage, ensuring coal mine process safety, ecological environment protection and clean energy capture. We develop a gas drainage physical simulation device with multi-physical coupling to study the dynamic response mechanism of permeability during gas drainage and explore the basic relationship between the interaction between boreholes and permeability during parallel borehole drainage. By installing 48 pressure sensors, 14 temperature sensors, and 9 displacement sensors in a test box, gas drainage tests of parallel boreholes with spacings of 250, 504, and 784 mm were carried out. The results show that during gas drainage in parallel boreholes, the dynamic evolution law of permeability in different spatial positions of the coal reservoir has apparent differences. The permeability near the borehole area exhibits a fast decline rate and a large recovery amplitude, and vice versa. The gas pressure, coal deformation, and coal temperature influence the periodical permeability evolution. In the early stage of drainage, gas pressure and coal temperature play a leading role in reducing permeability. In the middle and late stages, coal deformation slowly increases permeability. When the borehole spacing was 250 mm, the permeability decay rate and rebound rate were high with interaction between the boreholes; a drainage superposition area makes the permeability spatial variation difference between the boreholes significant. A correlation is observed between borehole spacing, gas migration rate, and permeability. The study is expected to have a substantial guiding significance for efficient gas drainage, decreasing greenhouse gas emissions, and improving coal mine process safety.

Failure Mechanism and Dynamic Response Characteristics of Loess Slopes Under the Effects of Earthquake and Groundwater

A large-scale shaking table test was conducted with simulated earthquakes and groundwater to study the dynamic response and instability mechanism of a loess slope with a saturated bottom. By examining the acceleration, dynamic pore water pressure, corresponding soil pressure and observed macroscopic failure behaviour of the slope under different shaking intensities, the dynamic responses of acceleration and pore water pressure of the loess slope were analysed. By comparing the time history curve of acceleration with the time history curves of pore water pressure and surrounding soil pressure, we found that the instability failure of the slope was first due to the continuous vibration that caused the local structure of the slope soil to be damaged, forming locally saturated soil and the rise in the groundwater table during shaking. Then, the saturated soil liquefied under the action of strong vibration, and the liquefied soil mass slid under the action of a high-intensity earthquake force. Finally, the acceleration and spectral characteristics of the pore water pressure changed sharply with a shift in the predominant frequency at the liquefied locations under a high shaking intensity. The significant changes in dynamic pore water pressure mainly occurred when the shaking components in the low-frequency bands below 1 Hz. This implied that the shift in the frequency mainly resulted from the damage in the structure of the loess slope after high-intensity shaking. These results help us better understand the triggering mechanism and failure mechanism of saturated loess slopes during the Minxian-Zhangxian earthquake.