Failure Mechanisms Research Articles

Effect of SO2 and NH3 on the corrosion failure of Zn-Al-Mg coatings

This study investigates the corrosion failure mechanism of Zn-Al-Mg (ZAM) coatings in environments containing sulfur dioxide (SO2) and ammonia (NH3) gas through accelerated corrosion tests. A comparison with Galvalume (GL) coatings reveals that ZAM coatings exhibit lower corrosion rates than GL coatings in SO2-containing environments, but display higher corrosion rates in NH3-containing environments. Analysis of the cut-edge corrosion of ZAM-coated steel in these environments reveals noticeable delamination phenomenon, with significant discrepancies observed in the corrosion failure times among different cut-edges of the same sample. This disparity can be attributed to both the uneven distribution of coating caused by processing techniques and the detrimental effects of SO2 and NH3 on the corrosion resistance of surface corrosion products. Notably, the diminished corrosion resistance in NH3-containing environments underscores the pivotal role of environmental factors in coating failure.

Rock damage and fracture characteristics considering the interaction between holes and joints

The work studied the damage and fracture characteristics of granite samples with circular holes and parallel fractures of different lengths under uniaxial compression conditions. Acoustic emission (AE) monitoring and digital image correlation (DIC) were used to analyze the dynamic changes of AE parameters, the evolution characteristics of the deformation field on the sample surface, and the correlation between the fractal dimension and the fracture geometry parameters. A computational model was proposed for evaluating the intensity factor of the fracture tip in a double-fracture structure with holes. The interaction between the fractures was considered to reveal the complex law of the intensity factor and the fracturing angle with the fracture geometry. The changes in AE parameters and fractal dimension indicated the influence of fracture extension on the damage mode of samples. Besides, the fracture length affected the micro-fracture behavior. The surface displacement and strain characteristics of samples revealed the modulation effect of the fracture length on the failure mode. The inclination angle, length, holes, and size of the fractures’ friction coefficient significantly affected the evolution of the intensity factor, which in turn regulated the changes in the fracture angle. The work offers a novel quantitative analytical approach and a theoretical framework for comprehending the damage and failure mechanisms of porous and fractured rocks through extensive experimentation and theoretical analysis. It holds significant practical relevance in geological engineering, mining, and tunnel construction.

Analysis on failure test and evaluation about refueling receptacle of onboard hydrogen system

ABSTRACT As the key component of the onboard hydrogen system, the service life and failure problem of the refueling receptacle easily leads to the hydrogen leakage accident which give rise to the suffocation, the frostbite, the burns, and the impact injuries. The typical hydrogen leakage accidents include the accidental leakage, the ignition, the deflagration, and the explosion. Therefore, the failure test and evaluation problem about the refueling receptacle is focused on. In this paper, the failure test and evaluation about the refueling receptacle covering the vibration resistance performance, the temperature resistance performance, and the durability was studied. First, the failure mechanisms of the refueling receptacle involving the vibration, the temperature, and the durability based on the vehicle operating conditions were clarified. Second, according to the test experience and the vehicle operating condition, the test methods about the failure phenomenon of the refueling receptacle were established, respectively. Finally, the failure test results of the refueling receptacle were analyzed. The failure of the refueling receptacle may caused by the aging and failure of sealing element, the metal creep aging and material damage, the decline in the contact stress at the low-temperature connection, the loose connection, and the internal structural ectopia.

Multi-scale damage characterisation of semi-flexible pavements under freeze-thaw cycles

This study aims to investigate the failure mechanism of semi-flexible pavements (SFP) under freeze-thaw conditions and to provide theoretical support for optimizing the material properties. By simulating the freeze-thaw damage process of SFP in actual service scenarios and combining various experimental methods, the strength characteristics and microstructural change rules of SFP in the freeze-thaw process are systematically analyzed. The study used freeze-thaw tests to simulate the real environment, combined with indirect tensile tests (IDT) and three-point bending tests to evaluate the mechanical properties of SFP. To further investigate the failure mechanism, scanning electron microscopy (SEM) was used to observe the interfacial changes between asphalt and early-strength sulphoaluminate cement (JGM301). Additionally, CT scanning was used to capture the structural changes of SFP during freeze-thaw cycles. The results showed that freeze-thaw cycles significantly and negatively affected the split tensile strength of SFP. SEM observations revealed that cracks appeared at the asphalt-cement interface (ITZ), the cement-SBS bond weakened, and the structure of the cement itself became loose. CT revealed structural changes such as cracking at the interface of the two-phase material, creation of new voids, and linkage of old voids during freeze-thawing of the SFP. In summary, the reduction in adhesion at the cement-asphalt interface and the frost swelling of JGM301 are the main reasons for the damage of SFP in freeze-thaw cycles. This study provides an important basis for an in-depth understanding of the freeze-thaw damage mechanism of SFP and optimization of its performance.

On the strain rate-dependent mechanical behavior of PE separator for lithium-ion batteries

The separator is a critical component for ensuring electrochemical cycling performance and preventing internal short circuits in lithium-ion batteries. For the collision safety of lithium-ion batteries, understanding the rate-dependent mechanical behavior of the separator is essential for battery impact modeling and safety prediction. This study conducts a comprehensive experimental investigation into the strain rate–dependent tensile/compressive behavior and failure mechanism of the polyethylene (PE) separator under quasi-static and dynamic conditions. The combination of deformation images recorded by cameras and post-mortem characterization using SEM was employed to clarify the rate-dependent deformation and fracture mechanism of the separator under both tensile and compressive loading. The experimental results demonstrate a significant strain rate effect on the tensile/compressive mechanical properties and damage/failure behavior of the separator. Furthermore, the effect of the strain rate on the mechanical properties, including the tensile strength, tensile fracture strain, tensile elastic modulus, compressive modulus, yield stress and yield strain of separator, was analyzed and discussed. A significant strain rate-dependent tensile damage and fracture behavior of the separator was observed, where the fracture site exhibited an obvious phase transition and skeletal lamella fracture under extremely high strain rate tensile loading. The separator underwent severe damage under dynamic compressive conditions. The results of this study provide an important basis for the establishment of rate-dependent safety criterion and short circuit prediction of lithium-ion batteries under impact loading, and shed light on understanding separator failure-induced short circuit issues in battery collision safety scenarios.

Mechanical response and failure mechanism of circular inclusion embedded in brittle materials under dynamic impact

Inclusions are prevalent in both natural and synthetic materials. Gaining a comprehensive understanding of their dynamic response and interaction with the surrounding matrix is essential in fundamental mechanics and engineering applications. This study aims to achieve such understanding through theoretical analysis, experimental investigations, and numerical simulations, focusing on the dynamic destruction of inclusions and the underlying mechanisms. Firstly, the circumferential, radial, and shear stresses around elastic heterogeneous inclusions were derived by the wave function expansion and Duhamel integration methods. Subsequently, a set of experiments on sandstone specimens containing three types of inclusions (plaster, epoxy resin, cement) were conducted utilizing the Split Hopkinson Pressure Bar (SHPB) system in conjunction with high-speed photography and Digital Image Correlation (DIC) techniques to obtain the surface deformation of inclusion specimens. Eventually, a series of Finite Element Method (FEM) numerical simulations adopted suitable materials were also carried out to investigate the fracture process of inclusion and matrix under dynamic impact. The results demonstrate that the stress distributions and fracture mode of matrix and inclusion are highly dependent on the physical and mechanical properties of the inclusions and the surrounding matrix, specifically, density ρ, elastic modulus E, Poisson's ratio v, and strength. With an increase in the E and v, there is a reduction in the concentration of circumferential stress, while the radial and shear stresses experience an increase. The experimental and numerical results corroborated the theoretical findings and indicated that the localized dynamic stress concentrations induced by wave scattering around the inclusions directly dominated both local and overall specimen failure. Due to the dissimilarities in elastic parameters and strength between the inclusion and the matrix, the stress state of the inclusion and the interface is not homogeneous. Under dynamic loading, the weaker inclusion experiences tensile cracking at both ends of the loading, and as the mechanical properties (ρ, E, v, and strength) of the inclusion rise, a transition from tensile- hybrid-shear failure occurs within the inclusion. The findings of this study help us understand the dynamic failure mechanisms of dissimilar inclusions in brittle material.

Effect of soil spatial variability on the stability of pipelines under horizontal loading

Submarine pipeline has been utilized more and more widely in offshore oil and gas transportation engineering. Given that these pipelines frequently subject horizontal loading during operation, thus precise predicting their horizontal bearing capacity is essential. However, most previous studies employ deterministic analysis without considering soil spatialvariability. This article introduces a two-dimensional (2D) random finite element analysis to study the horizontal pullout behaviour and failure mechanisms of a pipeline in a spatial variability soil. It is observed that the effect of soil spatial variability on the horizontal bearing capacity factor and failure mechanisms is remarkably substantial, with the distribution of the former showing a close approximation to a log-normal distribution. Furthermore, the average horizontal bearing capacity typically falls below the corresponding deterministic value. Consequently, the deterministic estimation of the horizontal bearing capacity tends to be inflated. Eventually, a reliability-based approach is formulated, where a factor of safety is incorporated to account for the uncertainties arising from spatial variability and ensure a sufficient safety margin. This methodology enables engineers to determine appropriate factor of safety tailored to the specific requirements of each project.

Low cycle fatigue behavior of MAR-M247 nickel-based superalloy from 500 to 900 °C: Analysis of cyclic response, microstructure evolution and failure mechanism

Low cycle fatigue behaviors of MAR-M 247 superalloy were investigated at 500 °C, 700 °C and 900 °C. The detailed deformation mechanisms were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) and the critical resolved stress to active different deformation mechanisms were calculated. The results show that crack propagates along favorable {111} plane at 500 °C, and anti-phase boundary (APB) shearing is the main deformation mechanism. At intermediate temperatures, the cracking mode is similar to 500 °C. The dislocation pinning at L-C lock leads to premature failure. It is difficult for {111} 〈110〉 slip system to shear hard oriented grain with low Schmid factor at 900 °C. Dislocation movement is achieved by Orowan by pass process and thermal activated dislocation climb at high temperature. In addition, the improved life prediction model based on energy method has been constituted and discussed at different temperatures.

A Failure Mechanism of Supports in Weakly Cemented Soft Rock Roadways and the Synergistic Support Design

A Failure Mechanism of Supports in Weakly Cemented Soft Rock Roadways and the Synergistic Support Design

Numerical and experimental investigation of pre-damaged composite stiffened panel under axial compression

The purpose of this paper is to investigate the calculation method and failure mechanisms of composite stiffened panel with pre-damage. The pre-debonding specimen’s failure process is performed by a universal testing machine (UTM) and the failure mechanisms are analyzed using scanning electron microscope (SEM). Together with cohesive zone model (CZM), the finite element method (FEM) is used to simulate the damage evolution of the specimens. In addition, a novel theoretical method is proposed to calculate the bearing capacity of composite stiffened panels. It is found that the failure mode simulated by FEM is consistent with the experimental analysis. Compared with the experimental values, the maximum result error of FEM and theoretical method is 7.9 %. This paper provides a reference for the research of composite stiffened panels with debonding defect.

An elastic-constant stress cohesive zone model for an orthotropic piezoelectric actuator adhesively bonded to a substrate

One of the common failure mechanisms observed in electromechanical systems utilizing actuators, sensors, or flexible electronics is the occurrence of interfacial debonding. In this paper, an elastic-constant stress cohesive zone model is constructed to analyze the interface behavior of piezoelectric actuators used in electromechanical systems when imperfectly bonded to a host medium. The analytical formulation treats the piezoelectric actuator as an orthotropic thin film, employing the membrane assumption. It is assumed that the cohesive zone extends from a point, initially unknown, to the edge of the film. The governing integro-differential equation is solved for various bonding scenarios, including perfect bonding with cohesive zones at the edges, an elastic case with a delaminated zone at the center, and an elastic case with both a delaminated zone at the center and cohesive zones at the edges of the film. Detailed examinations are conducted to explore the effects of stiffness ratio parameters and critical actuating voltage on the stresses within the film and substrate as well as the cohesive zone length. The results indicate that the cohesive zone length covers 45% of the film length when the actuating voltage has a fivefold increase over the critical threshold. For the imperfect bonding, the surface in-plane stress of the substrate exhibits a tensile peak near the boundary of the cohesive zone in addition to compressive singularities at the edges of the film. The shear stress singularity factor has an asymptotic behavior as the actuating voltage goes beyond the critical threshold. The critical actuating voltage reduces by a factor of 5% only if the delamination length does not exceed 70% of the film length.

Effect of microstructural roughness on the performance and fracture mechanism of multi-type single lap joints

Surface roughness of adherends is a crucial factor in determining the performance and failure mechanism of adhesive joints. However, the research dedicated to the examination of fracture mechanism for adhesive joints influenced by surface roughness at microscale is limited. This work conducts systematic experimental and numerical investigations into the effect of microstructural roughness on the performance and fracture mechanism of multi-type adhesive single lap joints (SLJ). The adherend materials are aluminium alloy (Al) and polyphthalamide (PPA), ground into three roughness grades for the fabrication of SLJs using an epoxy adhesive. The mechanical properties of the adhesive, adherends and SLJs derived from experimental studies are utilized to calibrate the microparameters in Discrete Element Method (DEM) models for a numerical analysis. The newly developed DEM models demonstrate efficacy in predicting the performance and capturing the failure modes of multi-type SLJs realistically with distinct microroughness profiles. Finally, the influencing mechanisms of microstructural roughness on the performance of multi-type SLJs are investigated, including the microscale interfacial bonds and mechanical interlockings. The effects of microstructural roughness on the microscale failure mechanisms of multi-type SLJs are also explored and discussed, including the crack initiation, coalescence, and propagation within the adhesive and interface.

Long-term performance of concrete pipes under fatigue traffic loads

In recent years, there has been a concerning increase in road collapses triggered by failures in urban drainage systems. Concrete pipes, commonly uesd in urban drainage pipelines, endure prolonged cyclic loading from traffic above. However, the mechanisms governing the long-term performance and fatigue damage remain unclear. Through conducting fatigue model box tests on concrete pipes, the effects of different fatigue loading cycles on the circumferential strain of concrete pipes were investigated. A fatigue life prediction equation for concrete pipes was proposed, and the crack propagation under various fatigue loading cycles was observed. Additionally, corresponding 3D FE models of concrete pipe-soil interaction with bell-and-spigot joints and gaskets were constructed. These models were used to explore the vertical displacements, circumferential bending moments, and circumferential stresses of the concrete pipes under different fatigue loading cycles, the damage and failure mechanisms of the concrete pipes under fatigue loading were revealed. The results indicate that the potential failure location of concrete pipes is within the inner crown of the bell under the fatigue traffic loads. The circumferential strains and crack propagation exhibiting a three-stage evolution pattern under fatigue loads. The proposed fatigue life prediction equation accurately predicts the remaining life of concrete pipes. Upon reaching 21.89 million loading cycles, the strain at the inner crown of the bell reaches 575.0 με, resulting in complete failure. Cracks on the inner crown of the bell extend inward and to the right from the middle of the joint, forming a channel for crack propagation. The vertical displacements at the crown and the circumferential bending moments of the bell and spigot exhibit rapid increases, stabilization, and subsequent declines with the increasing loading cycles. When concrete pipes undergo fatigue fracture, the maximum vertical displacement and circumferential bending moment at the bell are measured as 2.26 mm and 17.82 kN·m/m, respectively. Stress concentration at the bell and spigot during fatigue loading leads to crack propagation and convergence, causing redistribution of stress fields characterized by an initial increase followed by a decrease in the inner crown and invert of the bell.

Tensile and low-cycle fatigue failure of carbon fiber reinforced aluminium laminates

Fiber metal laminates (FMLs) have emerged as advanced materials for engineering applications due to their high strength-to-weight ratio. This study aims to understand the mechanical response and failure mechanisms of carbon-fiber reinforced aluminium laminates (CARALL) under monotonic and cyclic loading, specifically uniaxial tensile and low-cycle fatigue (LCF) conditions. CARALL, fabricated with alternating (3/2) layers of AA2024-T3 and unidirectional carbon fiber composite, exhibits superior ultimate tensile strength (UTS) compared to AA2024-T3 sheets, with a distinctive three-zone stress-strain curve. The first zone shows elastic strain in both the aluminium alloy and laminate. The second zone features elastic strain in the laminate and plastic strain in the aluminium alloy. In the third zone, surface modifications enhance adhesion, leading to a sudden load drop due to fiber fracture or delamination. Fractographic analysis indicates no significant necking in the laminate, contrasting with the ductile failure of AA2024-T3. The carbon fiber layer exhibits a pure brittle fracture with visible delamination at the interphase of carbon fiber layer and aluminium alloy sheet. Under LCF conditions, the laminate’s cyclic stress response remains stable, with fatigue cracks initiating in the aluminium layers but mitigated by the carbon fibers, leading to cyclic softening. High-magnification images reveal striation marks and transverse micro-cracks in the aluminium, highlighting the complex interaction between aluminium and carbon fiber layers during fatigue.

On-bottom stability of a radial fin integrated surface-laid pipe-section against vertical penetration

This study focuses on the on-bottom stability of surface-laid submarine pipelines during vertical penetration under thermal-induced buckling. Submarine pipelines are susceptible to buckling due to their high slenderness ratio, and the resistance to such displacement relies on pipeline stiffness and soil resistance. To investigate this, laboratory model tests were conducted using a scaled-down pipe section placed on a clay bed. The clay bed was prepared with remoulded Kaolin clay, ensuring uniform moisture content, and the model pipe was scaled down from a typical industry prototype. These tests were conducted in 2D plane strain conditions within a tank, equipped with observation windows to monitor pipe movement and soil behaviour. A significant improvement in the pipe section's penetration resistance and on-bottom stability was observed after incorporating fin in the pipe. The addition of fins altered the earth pressure distribution beneath the vertically loaded pipe, leading to a larger failure mechanism in the adjacent soil. Furthermore, the soil-surface-heaving progressed towards the tank wall with increasing angular distance between the radial fins. Thus, the research demonstrated the effectiveness of radial fins in enhancing the stability and resistance of submarine pipelines against vertical penetration, shedding light on potential improvements in submarine pipeline design and deployment.

Influence of fissure distribution characteristics on the dynamic response of fissured Rock: Quantity and spacing

The impact test of red sandstone with different fissure distribution was carried out by Split Hopkinson Pressure Bar (SHPB). The failure process of the specimen in the time dimension was captured by high-speed camera and digital image correlation (DIC). The crushing characteristics of the specimen were discussed from the fractal dimension. Furthermore, the influence of fissure distribution characteristics (quantity and spacing of fissures) on the mechanical properties and fracture behavior of fissured red sandstone was analyzed. The experimental results show that the fissure spacing is negatively correlated with the dynamic compressive strength and peak strain of specimen, while the fissure quantity is negatively correlated with the dynamic compressive strength and positively correlated with the peak strain. Cracks are categorized into five types based on the manner of their initiation and expansion. The crack initiation and propagation are jointly affected by tensile stress and shear stress, but the tensile stress is dominant. With the increase of the fissure quantity, the failure mode changes from tensile failure to tensile-shear mixed failure. The increase of fissure spacing does not change its failure mode, but the formation mode of the main crack changes. The fractal dimension increases with the increase of the fissure quantity, and decreases with the increase of the fissure spacing, i.e., the larger the fissure quantity is, the higher the degree of fragmentation is, and the larger the fissure spacing is, the lower the degree of fragmentation is. The research results can provide a theoretical reference for the study of dynamic failure mechanism of rock mass with non-persistent discontinuities.

Enhanced strength and toughness of carbon fiber reinforced aluminum matrix composite prepared via novel indirect extrusion method

The fabrication of large-sized, high-performance CF/Al composites presents significant challenges for the aerospace industry. This study introduces a novel indirect extrusion (IE) method for the high-quality production of CF/Al composites. The study investigates the infiltration mechanism of the alloy liquid during the IE process, highlights the technique's advantages, and systematically analyzes the mechanical properties and failure mechanisms of CF/Al composites. Results show that the aluminum liquid initially fills the interlayers and subsequently penetrates the fiber bundles, effectively shortening the infiltration distance. At a casting temperature of 800°C and an infiltration pressure of 40 MPa, the composite exhibits excellent forming quality and microstructural integrity. Compared to direct extrusion (DE) CF/Al composites, IE-CF/Al composites show significant improvements in compressive strength (16.72 %), flexural strength (16.87 %), fracture toughness (43.18 %), and work of fracture (90.61 %). The interlayer alloy and increased fiber spacing in IE-CF/Al composites enhance energy absorption capacity and reduce the risk of brittle fracture. This process lays a solid foundation for the high-quality production and application of CF/Al composites.

A comparative study on mechanical-electrical-thermal characteristics and failure mechanism of LFP/NMC/LTO batteries under mechanical abuse

Understanding the failure behaviors and failure mechanisms of lithium-ion batteries under mechanical abuse is essential for numerical reconstruction of abuse scenarios for different types of cells. This study investigates the mechanical-electrical-thermal characteristics, components tensile properties and failure mechanisms of LiFePO4 (LFP), Li(Ni0.5Mn0.3Co0.2)O2 (NMC), and Li2TiO3 (LTO) cells through indentation experiments, including ball intrusion, cylindrical intrusion, and out-of-plane compression modes at quasi-static loading rates. Additional ball intrusion experiments were conducted at varying loading rates. This study compares the effects of different material systems on battery performance under standardized mechanical abuse conditions. Post-test examinations analyze surface damage and internal component fracture morphology. Two distinct fracture modes were observed: ductile fracture and brittle fracture. The findings suggest that, under the same loading mode, LTO cells exhibit distinct failure behavior compared to NMC and LFP cells, attributed to differing material properties and resulting fracture modes during intrusion. Based on the analysis of the tensile results of the battery components, the cell fracture mode may be related to the tensile strength of the separator. The loading rate significantly impacts the mechanical-electrical-thermal performance of pouch cells, resulting in increased cell stiffness and shorter internal short circuit duration at higher loading speeds. However, the effect of loading rate is consistent across cells with different material systems.

Joint load-bearing behaviors and interface failure mechanism of encased coal samples under uniaxial compression

Concrete-encased coal pillars that serve as an effective support structure in coal mines have attracted increasing attention. This paper aims to explore the coupling bearing behaviors and the properties of interface force transfer between the interior coal and the encasing concrete. Laboratory uniaxial compression experiments were conducted on encased coal samples. Additionally, an interface force formula was derived based on deformation coordination and equilibrium conditions, and a mathematical formula was developed to estimate the load-bearing capacities of both the interior coal and the encased concrete. The research indicates that the stress–strain curve of the concrete-encased coal samples exhibits a distinct “double-peaked” phenomenon, and the load is transferred from the interior coal to the external concrete during the failure process. In the early stages of failure, the interface force enhances the strength of the coal pillar, while the lateral strain of the interior coal column exacerbates the damage to the encasing concrete. Moreover, the force at the concrete-coal interface is proportional to the axial loads and the mechanical properties of both materials. The strength of the coal pillar is significantly enhanced by lateral confinement. This study provides an experimental basis and theoretical analysis support for reducing the disaster of coal pillar instability.

Iodine-induced self-depassivation strategy to improve reversible kinetics in Na-Cl2 battery

Rechargeable sodium-chlorine (Na-Cl2) batteries show high theoretical specific energy density and excellent adaptability for extreme environmental applications. However, the reported cycle life is mostly less than 500 cycles, and the understanding of battery failure mechanisms is quite limited. In this work, we demonstrate that the substantially increased voltage polarization plays a critical role in the battery failure. Typically, the passivation on the porous cathode caused by the deposition of insulated sodium chloride (NaCl) is a crucial factor, significantly influencing the three-phase chlorine (NaCl/Na+, Cl-/Cl2) conversion kinetics. Here, a self-depassivation strategy enabled by iodine anion (I-)-tuned NaCl deposition was implemented to enhance the chlorine reversibility. The nucleation and growth of NaCl crystals are well balanced through strong coordination of the NaI deposition-dissolution process, achieving depassivation on the cathode and improving the reoxidation efficiency of solid NaCl. Consequently, the resultant Na-Cl2 battery delivers a super-long cycle life up to 2000 cycles.