Failure Mechanisms Of Structures Research Articles

Effects of folded fissure properties on tunnel model failure: Experiments and numerical simulations

Natural folded fissures commonly exist rather than simple straight fissures in rock masses surrounding tunnels. The presence of folded fissures significantly affects the fracture processes and failure modes of tunnel structures, thereby affecting their safety and stability. However, the research in this area is limited. Given this, this study fabricates city-gate section tunnel specimens containing folded fissures of various dip angles (α) and orientation angles (β), utilising 3D sand printing with sand and furan resin as matrix materials. Uniaxial compression fracture tests were conducted at a loading rate of 0.3 mm/min on these specimens using a digital image correlation technique to assess the impact of folded fissures on the mechanical properties and failure modes of the tunnel structures. Additionally, the improved smoothed particle hydrodynamics (SPH) method was used for damage evolution simulations during interactions between folded fissures and tunnels, and the simulation results were compared with the experimental results to verify the correctness of the method. The results show that for folded fissures, wing cracks and anti-wing cracks initiate not only from the ends but also from the bends of the fissures, whereas for straight fissures, they appear only at the fissure ends. Except for β = 0°, the interaction between folded fissures and tunnels generally results in the formation of a crack connecting the folded fissure upper end with tunnel, and the connection position varies with β. Different β values of folded fissures also influence the appearance and morphologies of top major cracks, underside major cracks, side cracks, and corner cracks around tunnels. As α increases, the overlap point of the crack and the tunnel moves from the tunnel corner to the tunnel crown. Moreover, folded fissures significantly affected the peak strength of the tunnel structures. As β increases, the peak strength first decreases, then increases, and finally decreases, reaching a minimum of 3.58 MPa at β = 90°. However, the peak strength differences are not evident under different α values. Finally, the influence of folded fissures on the cracking mechanism of the tunnel models is discussed in detail. This study provides insights into the impact of folded fissures on tunnel fracture modes and offers a reference for the application of SPH to reveal the underlying failure mechanisms of tunnel structures.

Predicting the structural behaviour and failure mechanism of hybrid steel-grout connectors for cross-laminated timber panels using high-fidelity finite-elements modelling

In this paper, a symbiotic experimental and numerical approach is used to determine the structural performance parameters and analyse the failure behaviour of a novel high-performance hybrid steel-grout connector for cross-laminated timber (CLT) panels. The connector is composed of a steel rod, which is embedded into a 3-ply CLT panel with the aid of a thick layer of epoxy-based grout. Material tests on wood from the two lumber grades present in the CLT panels, and on the epoxy-based grout were conducted to provide an insight into their mechanical behaviour. Forty-two monotonic push-out shear tests were conducted on connectors, varying the grout layer diameter thrice and the loading direction twice. A finite-elements (F.E.) model for the connector was developed in the F.E. software ANSYS and calibrated based on experimental observations on materials and connectors. The tested connectors proved to be strong and stiff in both loading directions, with a maximum slip modulus of 111 kN/mm, yield resistance of 177 kN, and maximum resistance of 192 kN. The diameter of the grout was found to significantly influence all three performance parameters, and much so when the connector was loaded in the direction perpendicular to the CLT face layers. The developed F.E model was able to capture the slip modulus, yield resistance, and maximum resistance with an accuracy above 95 %. The F.E. model also sheds light on the structural performance, yield mechanism, and failure propagation for connectors.

Numerical Investigation on Dynamic Response of Carbon Fiber Honeycomb Sandwich Panels Subject to Underwater Impact Load

This study investigates the dynamic response and failure mechanisms of carbon fiber honeycomb sandwich structures under underwater impact loads using finite element numerical simulation. The geometric modeling was performed using HyperMesh, and the dynamic response simulations were carried out in ABAQUS, focusing on honeycomb core configurations with varying edge lengths, heights, and gradient forms. The Hashin damage model was employed to describe the damage evolution of the composite materials. The simulation results revealed that the dynamic response was significantly influenced by the initial shock wave pressure and the geometrical parameters of the honeycomb cells. Larger cell-edge lengths and heights generally resulted in improved energy absorption and reduced rear panel displacement. Among the different configurations, interlayer gradient honeycomb structures demonstrated superior impact resistance compared to homogeneous and in-plane gradient structures, particularly under higher initial shock wave pressures. These findings contribute to optimizing the design of carbon fiber honeycomb sandwich structures for enhanced impact resistance in relevant applications.

Enhancing wear resistance, mechanical properties of composite materials through sisal and glass fiber reinforcement with epoxy resin and graphite filler

This study investigates the mechanical and wears properties of sisal and glass fiber-reinforced epoxy composites with graphite as filler material. We assessed the mechanical properties of the hand-layup-fabricated composite materials, including hardness, tensile strength, flexural strength, and impact strength, by ASTM standards. We also performed wear evaluations using a pin-on-disc apparatus. The results showed that the weight fractions of sisal fiber, glass fiber, graphite, and epoxy resin significantly affected the mechanical properties of the composites. In contrast to composites reinforced with individual fibers, hybrid composites exhibited enhanced mechanical properties. The optimized compositions showed improvements in tensile, flexural, impact, and hardness properties. The wear analysis revealed that a variety of factors, including the weight percentage of reinforcement, sliding velocity, load, and sliding distance, had an impact on the composites' wear resistance. The SEM images provided significant insights into the composite material's micro structural characteristics and failure mechanisms. In general, this research showcases the potential of graphite filler-reinforced sisal and glass fiber epoxy composites for use in applications that demand exceptional abrasion resistance and mechanical strength. Further refinement of the composition and processing methodologies could lead to the development of composites tailored to specific application demands.

Influence of strut angle and radius on the energy absorption and failure mechanisms in 3-strut, 4-strut and 6-strut lattice structures

Abstract 3D-printed truss structures have remarkable potential in the aerospace and weight-critical technologies fields. However, design parameters need to be carefully considered. A low overhang angle or diameter can result in discrepancies. This research presents an approach by examining the effect of strut overhang angle and radius on the mechanical properties of 3-, 4- and 6-strut lattice structures under compressive loading. 1.6- and 2.4-mm diameter struts were designed with 45°, 50°, 55° and 60° overhang angle strut lattices. Experiments were simulated and compared with test results for each parameter. Even if joint regions have little effect on specimens’ density, it has a remarkable effect on mechanical properties of the specimen. To simulate this, many studies were investigated to simulate joint regions. The study’s goal is to deepen the understanding of how design variations in strut lattice structures influence their energy-absorbing characteristic and mechanical behavior, using a combination of static tests and finite element analysis for validation. This insight is crucial for optimizing lattice design to balance weight, strength, and energy-absorbing capacity effectively. The experimental test result and numerical result showed rather good agreement. It is observed that joint regions, overhang angle, and diameters were the main parameters affecting specimens’ mechanical behavior.

Review of Implosion Design Considerations for Underwater Composite Pressure Vessels

The implosion of underwater composite structures is a critical and complex engineering problem, necessitating high-strength, lightweight, and corrosion-resistant materials for deep-sea applications. This manuscript reviews the intricate failure mechanisms of composite structures, focusing on cylindrical structures under extreme underwater conditions. The recent Titan submersible implosion serves as a case study, highlighting the significance of rigorous design considerations. Key topics include material degradation, buckling instability, and material failure, with a detailed analysis of composite layup optimization and manufacturing processes such as filament winding and roll wrapping. The manuscript underscores the need for comprehensive testing, advanced simulation techniques, and monitoring system integration to ensure the safety and effectiveness of composite pressure hulls. Future research should focus on developing more accurate failure models, optimizing manufacturing processes, and enhancing material properties through innovations in composite science to realize the full potential of composite materials in deep-sea applications.

Local high temperature phenomena near the complex interfaces of thermal barrier coatings based on non-Fourier model

Thermal barrier coatings (TBCs) consist of a metal substrate (Sub), a bond coat (BC), and a ceramic top coat (TC). The ceramic coating is a porous dielectric layer with a significant relaxation time that cannot be ignored. In high-temperature environments, an irregularly shaped thermally grown oxide layer (TGO) forms between the BC and the TC. Therefore, using non-Fourier model to describe the thermal contact process of TBCs with complex interface can get more accurate results. However, it is difficult to obtain the analytical solution of this model. This paper introduces a finite volume method based on unstructured meshes to address the non-Fourier heat transfer process in the complex interfaces of multilayer TBCs. The gradient reconstruction technique is employed to calculate the cell derivatives on the surface. The method's reliability is confirmed through a comparison with a two-dimensional analytical solution. The results indicate that the thermal wave travels at a limited speed within the TC layer. After passing through the interface, the thermal wave travels very fast within the BC and Sub layers, due to the influence of thermal wave reflection and superposition, obvious local high temperature will be formed near the interface. In addition, the effects of thermal conductivity, relaxation time and interface shapes on the non-Fourier heat conduction process of TBCs are also discussed. The results of this paper are useful for the structural design and failure mechanism research in TBCs.

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures under laser irradiation

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures are studied under different laser conditions in this paper. Firstly, the damage test of composite honeycomb sandwich structures is conducted. Temperature field and ablation process during laser irradiation are analyzed. Damage morphology and mechanism are verified. Secondly, the influence of laser damage on the bending properties of composite honeycomb panels is studied. Progressive damage process and failure mechanism of honeycomb structures during loading are explored by digital image correlation (DIC) and strain trend. The results show that the temperature at the center point of front surface reaches more than 2000 °C within 1 s under the laser irradiation, while the temperature of back surface exhibits hysteresis. The ablation hole is funnel-shaped and has severe delamination. In the heat affected zone (HAZ), resin matrix has been basically sublimated and oxidized, leaving only carbon fiber bundles and some residual carbon. The honeycomb core in this area has been completely carbonized and deformed. During bending process, the honeycomb core breaks firstly, and strain appears peak at both crack ends, leading the crack extend along both sides. The ultimate load of damaged specimen is 2.35kN, which has a 42.26 % drop compared to that of healthy specimen 4.07kN. Bending properties of specimen are significantly degraded by laser damage.

Bending performance and failure mechanisms of composite sandwich structures with 3D printed hybrid triply periodic minimal surface cores

In this paper, a novel hybrid triply periodic minimal surface (TPMS) core with a nonlinear transition region was designed by combining two types of TPMS (Diamond and Schwarz P) structures using the sigmoid function. The width of the transition region was precisely regulated by adjusting the gradient control parameter r in the sigmoid function. Composite sandwich structures (CSS) were fabricated by bonding two carbon fiber reinforced polymer (CFRP) face sheets to a 3D printed polylactic acid (PLA) core. The bending performance and failure mechanisms of the CSSs with the hybrid TPMS cores were analyzed through three-point bending tests and finite element analysis (FEA). The results indicate that as r increases, the transition region of the hybrid TPMS cores becomes narrower, leading to a gradual decrease in bending strength, bending stiffness, and core shear stress. The failure process of the CSSs in the experiment aligns well with the FEA results. Through comparative analysis of the stiffness-to-weight and strength-to-weight ratios of the CSSs with the native TPMS cores, the hybrid TPMS cores with a wider transition region enhance the structural efficiency of the CSSs, while those with a narrower transition region negatively impact the performance of the CSSs.

Failure analysis of titanium honeycomb sandwich structures subjected to three-point bending in high-temperature condition

In this study, the failure process and failure mechanism of Ti65 titanium sandwich structure subjected to three-point bending under high temperature are explored by the combination method of experimental analysis and numerical prediction. Test results show that the failure modes change and a 50% decrease in the peak compressive load occurs under high temperature. A self-developed parametric finite element model is deployed to recreate the structural details of sandwich honeycomb structures and exhibit the failure process of the titanium sandwich structure under three-point bending. The predicted failure process and critical parameters have excellent consistency with test results.

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.