Failure Mechanisms Of Structures Research Articles

Experimental and Meshless Numerical Simulations on the Crack Propagation of Semi-Circular Bending Specimens Containing X-Shaped Fissures Under Three-Point Bending.

Cracks in rock and concrete have a great adverse effect on the stability of engineering structures; however, there are few studies on X-shaped fissures which widely exist in rock and concrete structures. Based on this background, three-point bending fracture tests of SCB specimens containing X-shaped fissures are carried out. The momentum equations in the SPH method are improved, and the crack propagations of SCB specimens under three-point bending are simulated. The results show that cracks grow simply along the vertical direction in the sample with no X-shaped fissures, and the existence of an X-shaped fissure changes the crack growth path and final failure modes of the SCB samples. The crack propagation simulation results are consistent with the experimental results, which verifies the rationality of the improved SPH method. The load-displacement curves mainly present three typical stages: the initial compaction stage, linear elastic deformation stage, and failure stage. The peak load decreases first then increases with an increase in eccentricity. With an increase in X-shaped fissure length and decrease in X-shaped fissure angle, the peak load decreases. The damage counts remain at 0 at the initial loading stage, corresponding to the initial compaction stage and the linear elastic deformation stage, and increase sharply at the later loading stage, corresponding to the failure stage, which is consistent with the experimental results. The influence mechanisms of X-shaped fissures on the crack propagation paths are discussed; the existence of different X-shaped fissure morphologies aggravate the tensile stress concentration at specific positions, leading to different crack propagation modes in the experiments. The research results can provide a certain reference for understanding the failure mechanisms of engineering structures containing X-shaped fissures and promote the applications of the SPH method into the simulations of cross-fissure crack propagations.

The water weakening effect on the progressive slope failure under excavation and rainfall conditions

The water weakening effect refers to the gradual deterioration of soil mechanical properties under long-term saturation. This paper analyzed the impact of water weakening on slope stability under alternating excavation and rainfall. The field investigation speculated shale hydration as the cause of overall slope instability. The mechanical parameters of hydrated shale were determined by the parameter inversion and empirical estimation methods. The simulations were used to restore the process of parameter weakening and slope failure, and confirmed the fact that hydration causes landslide. Furthermore, the failure mechanism of slope and support structure under hydration were investigated. The results show that the mechanical parameters of the slope decreased linearly, whereas the plastic strain–time and total displacement-maximum shear stress curves of the hydrated shale exhibited three stages: slow initial growth, rapid growth in the middle term, and rapid increase in the later period; the rate of slope deformation and the factor of safety reduction also gradually increase over time; under middle stage of hydration, the middle to rear of shale were extruded, while the front first underwent tensile shear deformation, forming a plastic zone of at rear and front excavated slope; In the late stage, hydrated shale quickly reaches its yield limit (maximum shear stress of 270 kPa), the middle and rear shale is damaged and compresses the front, causing it to transform from tensile shear to compressive shear failure. The plastic zone in the rear extends forward and connects with the front ones, forming an overall landslide. Besides, preventing deep landslides caused by hydration through waterproofing, drainage, protection, and support for excavated slopes has proven difficult. Therefore, it is necessary to redesign treatment schemes based on the characteristics of stress, strain, and seepage.

Failure Mechanism and Structural Optimization of the Primary Support Structure for Expressway Tunnel in Soft Rock: A Case Study

When the highway tunnel crosses the soft rock, the primary support structure often fails and damages because it cannot withstand the excessive surrounding rock pressure. For the Magu tunnel in Yunnan Province, which is in the upper hard and lower soft stratum, the surrounding rock deformation is large, and the primary support structure occurs spray concrete cracking, steel arch frame twisting deformation. According to the convergence constraint curve, this paper proposes to adopt the primary support optimization design scheme of "shortening the bench length + optimizing the length and arrangement of anchor rods". According to the numerical simulation results of FLAC3D, the important indexes such as deformation convergence, surrounding rock stress, anchor axial force and thickness of plastic zone in different excavation support conditions are analyzed. The conclusions are as follows: 1. The soft rock at the foot of the benches does not provide sufficient support resistance, resulting in large settlement and convergence deformation that can cause the primary support structure to fail and become damaged. 2. The length of the middle bench and the primary support strength and stiffness contribute most to the deformation. 3. The deformation control effect of the short anchor rods on the surrounding rock is relatively weak. Increasing the length of anchor can better play the role of anchor suspension enhancement and give full play to the surrounding rock's own bearing capacity. Finally, the deformation of the tunnel is under control after adopting the optimized primary support structure, which ensures the smooth construction.

Insights into Cation Migration and Intermixing in Advanced Cathode Materials for Lithium‐Ion Batteries

AbstractCathode materials are the core components of lithium‐ion batteries owing to the determination of the practical voltage and effective energy of the battery system. However, advanced cathodes have faced challenges related to cation migration and cation intermixing. In this review, the study summarizes the structural failure mechanisms due to the cation mixing of advanced cathodes, including Ni‐rich and Li‐rich layered cathodes, spinel, olivine, and disordered rock‐salt materials. This review starts by discussing the structural degradation mechanisms caused by cation intermixing in different cathodes, focusing on the electronic structure, crystal structure, and electrode structure. Furthermore, the optimization strategies for effective inhibition of cation migration and rational utilization of cation mixing are systematically encapsulated. Last but not least, the remaining challenges and proposed perspectives are highlighted for the future development of advanced cathodes. The accurate analysis of cation migration using advanced characterization, precise control of material synthesis, and multi‐dimensional synergistic modification will be the key research areas for cation migration in cathodes. This review provides a comprehensive understanding of cation migration and intermixing in advanced cathodes. The effective inhibition of cation migration and the rational utilization of cation intermixing will emerge as pivotal and controllable factors for the further development of advanced cathodes.

A Review of Stability of Dam Structures in Coal Mine Underground Reservoirs

Coal has remained the primary component of China’s energy structure, and high-intensity extraction has continued in the central and western coal-producing regions of China. In contrast to the abundant coal resources, water resources have become extremely scarce in these regions, creating a conflict between coal resource extraction and water resource conservation. The coal mine underground reservoir (CMUR), as a typical technology for combined coal and water extraction and water-preserving coal mining, has been applied in numerous mines in central and western China. This effectively alleviates water resource shortages and achieves the goal of water resource conservation. The CMURs utilizes the goaf created by longwall mining as the water storage space. The reservoir dam structure comprises coal pillars, which serve as protective coal pillars in the mining area, and artificial dam structures that filled the gaps between these coal pillars. The stability of the dam structure under the complex stress effects of hydraulic coupling has been identified as the key to maintaining the safe operation of the CMUR. The mechanical properties, stress field, fracture field, and seepage field (“three fields”) change mechanisms, as well as the research results on size optimization of coal pillar dams and artificial dams in CMURs, were systematically reviewed. The core content included the instability and failure mechanisms of dam structures under the comprehensive coupling effects of factors such as dry–wet cycles of mine water, long-term immersion, chemical effects of high-salinity water, dynamic and static loads, and cyclic loads. This paper is considered to have certain reference value for the study of the stability of dam structures in CMURs and to provide some guidance for the safe operation of CMURs.

Enhanced compressive mechanical properties of different topological lattice structures fabricated by additive manufacturing

This study focuses on the mechanical properties of 316 L stainless steel lattice structures. Three types of lattice structures with varying topology cells were designed and fabricated by additive manufacturing (AM) techniques. The experimental test and numerical simulation were employed to investigate compressive response and failure mechanisms of lattice structures. The results indicate that decreasing the porosity or unit cell size of lattice structures can significantly improve mechanical performance. Furthermore, it is noted that lattice structures with face-centered cubic with(vertical) Z-struts (FCCZ) cells exhibit the highest elastic modulus, compressive strength, and energy absorption, along with distinct failure modes in comparison to other types of lattice structures.

Performance of reinforced concrete slabs subjected to simultaneous fire and blast loads

Reinforced concrete (RC) slabs might experience severe damage from multiple hazards such as fire, explosion, and impact during their service life. RC slabs under independent or sequential hazard such as fire or blast loading have been intensively investigated. In reality, fire and explosion often occur simultaneously instead of occurring one after the other as assumed in some previous studies. Simultaneous actions of thermal loading and blast loading on structures are likely to generate different responses or even different response modes and failure mechanisms of structures as compared to independent or sequential actions of the two loads on structures. However, very limited study has been conducted to investigate the performance of RC slabs under simultaneous fire and blast loads. This study investigates the dynamic performance of RC slabs subjected to concurrent fire and blast loads, considering the simultaneous actions of thermal-induced stress, deformation, material deterioration and blast loading. The numerical model is first calibrated with the test results of RC slab under fire or blast loading. With the calibrated numerical model, the effect of thermal stress induced by fire loading on the blast performance is investigated. The influences of fire duration before the occurrence of explosion, as well as the blast loading scenarios and RC slab parameters on the structural responses are investigated. The dynamic responses induced by blast loading after the fire action as usually assumed in the literature are also calculated and compared with those obtained from simultaneous fire and blast loads. Their implications on representing the effects of coupled concurrent fire and blast loads on structural performances are discussed.

Introduction to the special issue on failure mechanism in advanced materials and structures

Introduction to the special issue on failure mechanism in advanced materials and structures

For the regeneration of spent graphite: The exploring of structural failure mechanism about commercial graphite

Along with the wide application of electric automobiles, the great “wave” of recycling for lithium-ion batteries would be upcoming due to their limited cycling lifespan. As the main components but without valuable elements, spent graphite suffers from effective recycling manners. Although the regeneration method has been deemed as a promising manner, the clarifying of their failure mechanism is prerequisite to the exploring of regeneration methods. Herein, commercial graphite with different healthy states is prepared through the disassembling of cells at different cycles. Assisted by the detailed structural analysis, the systematic failure process is clearly illustrated. At initial cycling, the shuttling of lithium ions renders the decomposing of unstable carbon atoms and some weak interlayer structures. With further cycling, the interlayer architecture and large-size grains were further damaged, to form small-size grains, accompanying enhanced anisotropy, finally resulting in the increasing internal resistance. Moreover, owing to the ion-diffusion behaviors, graphite sheets have an obvious moving, resulting in the transformation from 2H-phase to 3R-phase with the decreasing of energy-storage activity. Thus, from the perspective of internal structure, the decreasing of graphitized grains and the formation of 3R-phase served as crucial failure factors. Given this, the work is anticipated to illustrate the failure mechanism of graphite, meanwhile offering the basic regeneration direction of spent graphite samples.

Ultimate strength failure mechanism and optimization design of marine composite deck grillage structures with opening

In this paper, the ultimate bending strength and the failure mechanism of the marine composite deck grillage structure are experimentally and numerically investigated, before the optimization design is conducted to enhance the ultimate bearing capacity. The ultimate strength experiment of the composite deck grillage structure is first carried out. Based on the improved progressive failure method and the cohesive damage theory, the numerical simulation considering fiber failure, matrix failure, shear failure and adhesive layer failure is conducted and the predicted strains, load–displacement curves, and failure modes of the specimen are compared with the experimental ones to verify the accuracy of the present method. Both experimental and predicted results show that the stiffeners and the laminated deck near the opening are the stress concentration areas, and the matrix failure is main failure mode. The optimization results show that the suitable panel thickness can reduce the stress concentration effect and avoid premature fracture in localized areas due to stress concentration. The increase of the stiffener heights can significantly increase the ultimate strength and the bending stiffness. These findings can provide support for the design of composite deck grillage structures in ships.

Representation of Thermomechanical Damage in Fiber-Reinforced Ceramic Composites at High Thermal Gradients

Ceramic matrix composites (CMCs) are the core strategic materials for the thermal structure of new-generation hypersonic aircraft. The unclear understanding of the cross-scale thermomechanical behavior and failure mechanism of materials and structures in high-temperature transient environments is a key scientific issue that restricts the reliable design and safe operation of hypersonic aircraft. In this study, a high-temperature test module in a supersonic wind tunnel with integrated various test systems was independently designed to systematically investigate the thermal mechanical damage evolution of CMCs used in astronautics applications under high-temperature transient conditions. Furthermore, a numerical method for fluid-heat-solid coupling based on an iterative solution strategy was developed and compared with an algorithm based on a wall modification strategy in terms of computational efficiency and accuracy. Besides, a comparative analysis was conducted with the temperature field distribution of the sample obtained in the hypersonic wind tunnel integration test to verify the correctness of the developed thermal-fluid-solid coupling calculation method. Finally, through thermoelastic coupling computational models, the high-thermal-gradient-induced thermomechanical damage mechanism of the CMCs was revealed, providing support for further optimizing the material system and thermal structure design of the CMCs.

Microcracking in On-Chip Interconnect Stacks: FEM Simulation and Concept for Fatigue Test

The semiconductor industry is continuing the scaling down of both device and on-chip interconnect features, for performance and economic reasons. This trend has implications for the design of guard ring structures, i.e. metallic non-functional structures in the back-end-of-line (BEoL) stack designed to be efficient to stop microcracks. In this work, we present a sample design for an in situ experiment to study mechanical degradation and failure mechanisms of crack stop structures in the BEoL stack, to ensure the mechanical robustness of microchips for future technology nodes. Additional finite element method (FEM) simulations provide supplementary understanding of the crack kinetics. To examine the effects of mechanical loading on crack stop elements of the BEoL stack, a novel sample geometry for an in situ fatigue experiment using x-ray microscopy was developed. The x-ray microscope (ZEISS Xradia 800 Ultra) enables high-resolution imaging of the 3D-patterned sample structures and defects such as microcracks. The tailored sample geometry allows the application of a tensile load to a BEoL specimen by a lever mechanism. The feasibility of the sample design is shown by mode-I loading of a pure interconnect sample. Post-mortem analysis by scanning electron microscopy (SEM), confirming planar microcrack propagation from the notch through the dielectric layer with small deflections of the crack path near cone shaped copper vias. FEM simulations focusing on the stress-strain fields around a crack tip indicate the beginning of copper plasticity as major mechanism starting the redirection of cracks due to resulting material compression in front of the obstacle.

Study on Damage and Failure Mechanism of Steel Structure Affected by Temperature

Study on Damage and Failure Mechanism of Steel Structure Affected by Temperature

Analysis of compressive failure mechanism of concrete and grouting cubes by Peridynamics

The structural failure forms and mechanisms of plain concrete, grout, and different aggregate concrete under the action of pressure have been puzzling the engineering and academic circles. To provide more favorable analytical means and theoretical support for structural damage and failure, this paper first adopts the experiments to analysis the compressive failure trend of cubic specimens of concrete and grout, and combines the results with the three-dimensional Peridynamics theory (PD) analyzed the damage trend and failure mechanism of the same tests with the same parameters under load. From the comparison, we can conclude that PD could truly analyze the failure mechanism of three-dimensional structures and was superior to the tests. Meanwhile, we also found that different number and position pebbles have a great influence on the failure path and damage mechanism of concrete.

Structural Evolution and Fracture Mechanism of WC-Particle-Reinforced FeCoCrNiMn High-Entropy Alloy Coatings

A hard-particle-reinforced high-entropy alloy (HEA) coating shows significant potential for tribological applications, but relatively little work on the fracture mechanism of the coating has been reported. In this work, the FeCoCrNiMn HEA coatings, doped with varying contents of WC, were fabricated using a plasma surfacing technique. The structure, mechanical properties, and fracture behaviors of these coatings were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), and hardness and tensile tests. The addition of WC particles significantly altered the growth mode of the coating texture from large coarse grains to fine grains. The coating without WC doping had a hardness of 198.8 ± 15.6 HV, a yield strength of 225 MPa, a tensile strength of 478 MPa, and a strain of 53.7%. The hardness, yield strength, tensile strength, and strain were 222.3 ± 34.4 HV, 353 MPa, 704 MPa, and 42.6% for the coating with 10% WC doping and 355.6 ± 51.6 HV, 454 MPa, 627 MPa, and 9.4% for the coating with 20% WC doping. Meanwhile, the coating with 40% WC doping showed the greatest hardness of 514.9 ± 48.1 HV and had the highest yield strength of 457 MPa, but its tensile strength and strain decreased to 517 MPa and 2.7%, respectively. In this article, the detailed structural evolution, strengthening, and fracture failure mechanisms of the coatings are discussed systematically.

Failure mechanisms and process defects of 3D-printed continuous carbon fiber-reinforced composite circular honeycomb structures with different stacking directions

3D printing of continuous carbon fiber-reinforced composites relieves molds in composite manufacturing and gives flexibility to the design of lightweight and robust circular honeycomb structures. Nevertheless, how process defects affect the failure mechanisms of 3D-printed continuous carbon fiber-reinforced honeycomb structures remains undisclosed. To advance this research area, it requires a comprehensive investigation of the failure mechanisms and process defects of 3D-printed continuous carbon fiber-reinforced composite circular honeycomb structures (CCFRCCHSs), with particular attention to the influence of stacking orientations. In this study, 3D printing has been introduced to fabricate CCFRCCHSs using the identical composite material and geometry but different stacking orientations. Both in-plane and out-of-plane quasi-static compression experiments were carried out on these CCFRCCHSs. The mechanical properties and failure mechanisms were investigated through experimental analysis and cross-section observation, from which the microscopic voids and weak interfaces were identified as the dominating factors influencing the failure modes of CCFRCCHSs. This study provides insights into the association between process defects and failure mechanisms of 3D-printed CCFRCCHSs with different stacking directions, which offers guidance for the design of lightweight and robust composite circular honeycomb structures.

An insight into the mechanical behavior and failure mechanisms of T-stiffened composite structures with through-interface debonding defects

A robust 3D finite element model framework was established to capture the mechanical behavior and failure mechanisms of intact and through-interface debonding T-stiffened composite structures based on the progressive damage model and the cohesive zone model. Meanwhile, specimens with and without interface debonding defects were fabricated to validate the reliability and robustness of the proposed modeling framework. Finally, a parametric study was conducted on the types of interfacial debonding to further explore the effect on the buckling load, delamination initiation load, and ultimate load-carrying capacity of the composite stiffened structure. The results indicate that the load-carrying capacity of both single interface defects and double interface defects decreases gradually with increasing defect length and converges to a constant value. The reductions were 28.31% and 47.68%, respectively, compared to the intact structure. Interestingly, interfacial debonding has the most significant effect on the ultimate load at the 1/4 position. Moreover, interface debonding defects not only severely weaken the ultimate load-carrying capacity of the structure but also significantly alter the post-buckling path and failure mechanism, resulting in distinct degrees of deformation and damage morphology.

Failure Mechanism and Structural Safety Assessment of the Primary Support Structure of Soft Rock Tunnel: A Case Study

Based on a soft rock tunnel in a mountainous area of northwest Yunnan Province, a refined numerical model of different support forms considering structural interaction is established to comprehensively evaluate the structural failure mechanisms and mechanical responses of different support forms. Research shows that compared to steel rib structures, the axial force and bending moment of sprayed concrete structures is larger under different combinations of support structures. Compared with a single-layer support structure, the stress distribution at each position of the double-layer I-shaped steel structure is more uniform, and the sprayed concrete structure only experiences compression damage at the corner of the side wall. As the strength of sprayed concrete increases, the stress distribution of sprayed concrete at the arch waist becomes more uniform. The stress concentration state of sprayed concrete at the corner of the tunnel wall and the plastic yield state of the steel rib structure have also been improved. The higher the concrete strength, the lower the stress ratio on the steel rib’s inner and outer sides.

Discrete element analysis on impact failure mechanism of “Zhengzhou 7.20” catastrophic flood for coal gangue railway subgrade

Limited research has been conducted on the failure mechanism of coal gangue railway subgrade structures during catastrophic flood disasters, including the impact of varying flood impact heights and load sizes. This study investigates the process and mechanism of coal gangue railway subgrade failure in the coal mining subsidence area, in conjunction with the “7.20” catastrophic flood in Zhengzhou. First, various factors such as impact forms, impact height, flow velocity, water depth, and wave height are considered, and a wave-water flow coupling calculation method is proposed to determine the catastrophic flood load acting on inclined slopes. The maximum impact load calculated is then applied to simulate the impact process of the catastrophic flood using Particle Flow Code 2D. As the flood-related parameters increase, the maximum impact load on the subgrade slope also increases, leading to the breakdown of the subgrade and causing fatal damage. Finally, the failure process of the coal gangue railway subgrade under the impact and scour of a catastrophic flood is divided into three stages: erosion weakening, potential failure surface formation, and overall failure. The main failure mechanisms of each stage are revealed. These research result findings offer valuable insights for the design of railway subgrade reinforcement under catastrophic flood conditions.

Low‐velocity impact response of 3D carbon fiber reinforced polymer auxetic lattice structures

AbstractIn this paper, low‐velocity impact properties and impact damage responses of a novel type of 3D hybrid auxetic structures made from carbon fiber‐reinforced polymer (CFRP) laminates were investigated experimentally and numerically. The structures were first fabricated with three different rib's width ratios t1/t0, and then impacted with three different impact energies of 30, 40, and 50 J using a drop tower impact system equipped with a cylindrical impactor. The finite element (FE) models were built in ABAQUS/Explicit, and the Hashin criteria were applied to predict the failure of the structures. The contact force histories, energy histories, displacements, and failure modes were compared between the experiment and FE simulation at all three impact energy levels. The failure morphologies and mechanisms were obtained and studied. The impact testing results suggest that the 3D auxetic structure with a higher t1/t0 ratio can lead to higher peak contact force and sustain higher impact energy. The failure of the structure starts from the middle area and propagates to the upper and lower areas. This research provides a better understanding of the impact responses and failure modes of the 3D auxetic lattice structure, which can promote the potential applications of the auxetic materials.Highlights Drop weight low‐velocity impact responses of 3D novel hybrid auxetic lattice structures are investigated through both experiment and finite element simulation. The effects of structural parameters on the impact performance of the 3D auxetic structures at different impact energy levels are analyzed. The failure morphologies and mechanisms of the 3D auxetic structures are studied.