Failure Mechanisms Research Articles

Numerical Modeling of Engineering-Scale Jointed Coal Mass and Confining Pressure Effect

In coal masses, joints serve as crucial components influencing mechanical responses and failure mechanisms. The joint distribution complicates the acquisition of physical parameters for engineering-scale coal masses, and traditional laboratory or in situ tests often suffer from inaccuracies and high costs. Therefore, examination of the dynamic properties of engineering-scale coal mass is generally performed by numerical simulations. This paper proposes a model construction approach using two-dimension Particle Flow Code (PFC2D) software to study the mechanical properties of engineering-scale jointed coal mass, addressing the limitations of conventional models by integrating scale effects, accuracy, and computational efficiency. Firstly, the distribution characteristics and mechanical parameters of the joints in the coal mass were obtained based on field statistics and laboratory experiments. The parameters of the laboratory-scale model were calibrated by the numerical matching method. The discrete element model for the engineering-scale coal mass was constructed by the step-by-step matching method. The confining pressure effect on the coal mass under a biaxial loading condition was studied, while the strength change, fissure evolution, and failure mechanism under different confining pressures and fissure degrees were investigated. Based on the simulation results, a quantitative relationship was established between the mechanical parameters, fissure degree, and confining pressure under compression conditions. Ultimately, the failure zone ahead of the working face and the distribution of the abutment pressure were assessed using the mechanics parameters of coal masses with diverse joint distributions.

Brittle failure analysis and modeling of high-burnup PWR fuel cladding alloys

Abstract The aim of this research is the development of methods for predicting mechanical behavior and identification of limiting conditions to prevent brittle failure of high-burnup (HBU) pressure water reactor (PWR) fuel cladding alloys. A finite element (FE) model of the ring compression test (RCT) was created to analyze the failure behavior of zirconium-based alloys with radial hydrides during the RCT. An elastic-plastic material model describes the zirconium alloy. The stress-strain curve needed for the elastic-plastic material model was derived by inverse finite element analyses. Cohesive zone modeling is used to reproduce sudden load drops during RCT loading. Based on the failure mechanism in non-irradiated ZIRLO® claddings, a micro-mechanical model was developed that distinguishes between brittle failure along hydrides and ductile failure of the zirconium matrix. Two different cohesive laws representing these types of failure are present in the same cohesive interface. The key differences between these constitutive laws are the cohesive strength, the stress at which damage initiates, and the cohesive energy, which is the damage energy dissipated by the cohesive zone. Statistically generated matrix-hydride distributions were mapped onto the cohesive elements and simulations with focus on the first load drop were performed. Computational results are in good agreement with the RCT results conducted on high-burnup M5® samples. It could be shown that crack initiation and propagation strongly depend on the specific configuration of hydrides and matrix material in the fracture area.

Study on the Failure Mechanism and Movement Characteristics Prediction of Gongdang Landslide in Linzhi, China

Instability of landslide accumulation bodies is one of the common geological hazards under the influence of rainfall and water impoundment, especially under the transformation of rainfall patterns caused by global climate changes. Owing to the fact that determining the landslide potential failure mode is vital for preventing landslide disasters, this paper takes the Gongdang landslide as the research object to study the landslide deformation mechanism and predict movement characteristics. Firstly, the geological conditions of the study area and landslide were determined according to the field investigations; secondly, the physical and mechanical parameters of the sliding mass were clarified through laboratory tests. Moreover, the particle flow code (PFC) method was utilized to simulate the potential failure process of the landslide based on the three-dimensional numerical model according to the geological features and the micro-parameters. The results showed that the landslide deformation process lasted approximately 640 s with the stage characteristics of displacement and velocity and presented the evolutionary process with the local instability deformation. The simulation results are of practical significance and application value by effectively illustrating the potential deformation and failure process of the Gongdang landslide, which provides a reference for predicting and preventing the potential failure process of geological hazards in similar engineering through field investigations, laboratory tests, and numerical simulation.

Residual reliability of a composite material subjected to buckling and post-buckling tests: the case of reinforced concrete

This article examines the residual reliability of composite materials, focusing on reinforced concrete subjected to buckling and post-buckling tests, a crucial topic in civil engineering. The main aim of the study is to assess how these loads affect mechanical properties, including compressive strength and elongation at break, while identifying associated failure mechanisms. A rigorous methodology was adopted, involving experimental tests on reinforced concrete samples, followed by microscopic analysis and comparison with literature data. The results reveal a significant decrease in compressive strength and modulus of elasticity with increasing loads and loading cycles. In addition, the study highlights a reduction in elongation at break, indicating a loss of ductility and stiffness of the material. Failure mechanisms observed include cracking and delamination, suggesting that the residual reliability of reinforced concrete is inferior to that of advanced composites. These findings underline the importance of appropriate design to ensure the durability of reinforced concrete structures, taking into account the impact of extreme loads and environmental conditions. This research contributes to a better understanding of the behavior of composite materials under critical conditions, providing recommendations for improving design and construction practices in civil engineering.

Role of thermal and electric fields in the failure mechanism of metallized film capacitors: insights from molecular chain dynamics within polymer dielectrics

Abstract The seamless integration of modern power systems and renewable energy sources heavily relies on advanced power electronics technologies, with metallized film capacitors (MFCs) playing a pivotal role in this ecosystem. Ensuring the operational efficiency and safety of these systems necessitates a thorough understanding of MFC failure mechanisms. In this study, molecular dynamics and density functional theory are employed to analyze the microscopic parameters governing MFC failure characteristics across a temperature spectrum of 25 °C–105 °C. The investigation is geared toward theoretically assessing MFC failure mechanisms under varying voltage ramp rates. Our findings highlight temperature as the primary influencer of failure characteristics at slower ramp rates (50 and 75 V s−1), where the interplay between carrier transport and intermolecular interaction energy dictates the trend of capacitor failure voltage—a pattern of initial increase followed by decrease with temperature. Conversely, higher voltage ramp rates accentuate the significance of the electric field. At a rapid ramp rate of 900 V s−1, the dominance of the electric field mitigates the impact of temperature, resulting in minimal variation in failure voltage across temperatures. Moreover, under intense electric fields, the reduction in free volume within the polypropylene unit exhibits a rapid decline, significantly constraining the mobility of molecular chains. Consequently, certain segments of these molecular chains exhibit localized alignment and directional movement. The rise in molecular polarity and reduction in energy gap contribute to substantially lower failure voltages compared to slower ramp rates. This study offers robust theoretical insights into comprehending MFC failure characteristics, thereby ensuring their reliable operation in demanding environments.

Fundamental Insights into Copper-Epoxy Interfaces for High-Frequency Chip-to-Chip Interconnects.

Future processes and materials are needed to enable multichip packages with chip-to-chip (C2C) data rates of 50 GB/s or higher. This presents a fundamental challenge because of the skin effect, which exacerbates signal transmission losses at high frequencies. Our results indicate that smooth copper interconnects with relatively thin cuprous oxides (Cu2O, CuI) and amine-functional silane adhesion promoters improve interfacial adhesion with epoxy dielectrics by nearly an order of magnitude. For the first time, we present X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy evidence of Cu(I)-O-Si bond formation at silane-treated interfaces. Thus, relatively smooth interconnects can benefit from reduced skin losses while maintaining their mechanical integrity and reliability. Failure mechanisms of Cu interconnects with cuprous and cupric oxide (CuO, CuII) are explored using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). These results indicate that both cupric oxides and relatively thick cuprous oxide interfaces lead to relatively weaker interfaces compared with thin cuprous oxides with adhesion promoters.

Effects of pore water and pore air pressure on the slope failure mechanisms due to rainfall in centrifuge investigation

BackgroundThe slope failures triggered by heavy rainfall are challenging to predict. However, their severe impact and potential for extensive damage emphasize the urgent need for effective strategies to mitigate these risks. This study aimed to investigate the effects of pore water pressures (PWPs) and pore air pressures (PAPs) on slope failure during heavy rainfall under centrifuge condition. Three centrifuge rainfall model tests were conducted with varying rainfall intensities (I) and relative densities (Dr). In this experiment, the slope model was subjected to a centrifugal acceleration of 30 G.ResultsIn all cases, slope failures started at the slope toes when the PWPs became positive and phreatic surfaces appeared on the slope surface. In the Toyoura sand case, the PAPs increased slightly at the slope crest, hardly changed at the slope toe, and oscillated at the slope shoulder due to rainwater infiltration. The entire slope failure was observed in this case. In the Silica sand cases, only localized slope toe failures were observed. The PAPs slightly oscillated with small changes in the silica sand case with a relative density of Dr = 50%. However, in the case with a Dr = 25%, the PAPs at the slope toe significantly increased compared to the other parts, and the oscillations were comparatively large. After the first failure occurred at the slope toe in the silica sand case with a Dr = 25%, cracks and slip lines appeared at the slope crest.ConclusionsThe three cases illustrated the complex relationship between soil properties, rainfall intensity, and the dynamics of pore water and pore air pressure on slope stability during heavy rainfall. From the behaviour of PAPs and PWPs in all cases, it was found that the transition from air to water occurred smoothly, and the isolation of air was not observed even during heavy rainfall. Changes in PAPs were far smaller than those in PWPs, indicating a smaller impact on slope stability than PWPs.

Ring penetrometer for interface shear testing on sand under low-stress conditions

Accurate characterisation of near-surface soils is essential for the design of subsea cables, pipelines, and shallow foundations. Conventional laboratory testing equipment is not well adapted to these applications where the operative stress levels are typically <10 kPa. This paper presents and interprets a comprehensive test campaign using a novel flat ring penetrometer. This device measures interface friction at stress levels as low as 1 kPa. Drained friction parameters for a range of sands obtained from the ring penetrometer are compared to other friction measurements from centrifuge sled and interface shear box tests. The results demonstrate the repeatability of the ring penetrometer, and the benefit of the simple but rigorous interpretation approach. The residual friction measured in the ring and centrifuge sled tests shows no dependency on stress level, which contrasts with the interface shear box results. It is shown that the apparent stress-dependency could be an artefact of system friction in the shear box. A correlation between friction coefficient and device settlement rate is identified, with the maximum friction mobilised as the settlement rate approaches zero, consistent with the combined bearing-sliding failure mechanism. These findings highlight the value of the ring device for interface friction measurement.

Effect of print orientations, layer thicknesses, and weathering on the mechanical properties, failure mechanism, and service life of 3D‐printed photocured resin parts

AbstractThis study investigates the effects of print orientation, layer thickness, and weathering on the mechanical properties, failure mechanisms, and service life of stereolithography (SLA) 3D‐printed photocured resin parts. Samples were printed with various orientations (0°, 22.5°, 45°, 67.5°, and 90°) and layer thicknesses (0.025 mm, 0.05 mm, and 0.1 mm), then subjected to accelerated aging at 60°C, 0.7 W/m2 ultraviolet (UV) light, and 100% humidity for 500 and 1008 h. Mechanical properties were evaluated through tensile, flexural, and compression tests, with fractography conducted on failed surfaces. Service life was estimated by assessing strength retention under simulated environmental stressors. Results showed that a 0.025 mm layer thickness at a 0° orientation yielded high tensile and flexural strengths of 44.66 and 86.88 MPa, respectively. The highest compressive strength of 76.9 MPa was achieved at 90° orientation. After 500 and 1008 h of weathering, tensile, flexural, and compressive strengths declined by 19%, 26%, 25%, 37%, and 22%, 31%, respectively. Additionally, the weathering effect transformed the elongation at break from elastic to brittle, and fractography showed an increase in voids and failures. Service life predictions indicated that the 0.025 mm thickness had the longest durability. Future work can extend this research to other photocured resins and composites to evaluate their performance in real‐world environments.Highlights 3D printing and weathering parameters on the part quality were investigated. Tensile, flexural, and compression tests were used to assess parts strength. Fractography was conducted to ascertain the failure mechanism of the printed parts. Service life models were developed based on mechanical strength retention.

Strengthen of metal-polymer direct molding bonding via three-dimensional porous mechanical interlocking

This paper proposes a direct metal–polymer forming–bonding method using three-dimensional (3D) porous mechanical interlocking to achieve high-strength metal–polymer connections. In this method, porous copper is initially sintered onto copper plates, followed by the infusion of molten polymer into the pores, forming a robust copper–polymer bonded structure. Incorporating microneedle arrays into the copper plates further enhances the bond between the porous copper and the polymer. Characterization of the pore morphology and mechanical properties confirmed the formation of large-area 3D micro-interlocking. Tensile tests on samples with varying porosities showed connection strengths exceeding 30 MPa, with a maximum recorded strength of 37 MPa. Finite element analysis supported the high bonding strength and provided insights into failure mechanisms. This cost-effective technique offers superior copper–polymer bonding strengths, and introduces novel concepts for composite heat exchanger design and manufacturing.

Limit analysis of earthquake-induced landslides considering two strength envelopes

Abstract. Stability analysis of soil slopes undergoing earthquake remains an important research aspect. The earthquake may have some different effects on slope stabilities associated with nonlinear and linear criteria, which need to be further investigated. For homogeneous soil slopes undergoing earthquakes, this paper established the three-dimensional (3D) failure mechanisms with the power-law strength envelope. The quasi-static method was employed to derive the work rate done by the earthquake in limit analysis theory. The critical heights and critical slip surfaces associated with nonlinear and linear criteria were obtained for four slope examples undergoing different seismic loads. Comparisons of the nonlinear and linear results illustrated that two critical inclinations (resulting from the overlap of nonlinear and linear results) both decrease as the seismic force increases, but their difference is almost constant. For steep slopes, the use of linear strength envelope can lead to the non-negligible overestimation of slope critical height. This overestimation will become significant with the increase in seismic force, especially for the steeper slope with a narrow width. Since the seismic force has a positive influence on equivalent internal friction angle, the critical slip surface for the slope-obeying nonlinear envelope tends to be slightly deeper as the earthquake becomes stronger. For steep soil slopes undergoing the earthquake, the development of 3D stability analysis with a nonlinear yield criterion is necessary and significant. These findings can provide some references for the risk assessment and landslide disaster reduction of soil slopes.

Review and Perspectives on Direct Regeneration of Spent Ternary Cathode Materials Based on Failure Mechanisms

Review and Perspectives on Direct Regeneration of Spent Ternary Cathode Materials Based on Failure Mechanisms

Flexural Behavior and Failure Modes of Pultruded GFRP Tube Concrete-Filled Composite Beams: A Review of Experimental and Numerical Studies

Pultruded glass fiber-reinforced polymer (GFRP) materials are increasingly recognized in civil engineering for their exceptional properties, including a high strength-to-weight ratio, corrosion resistance, and ease of fabrication, making them ideal for composite structural applications. The use of concrete infill enhances the structural integrity of thin-walled GFRP sections and compensates for the low elastic modulus of hollow profiles. Despite the widespread adoption of concrete-filled pultruded GFRP tubes in composite beams, critical gaps remain in understanding their flexural behavior and failure mechanisms, particularly concerning design optimization and manufacturing strategies to mitigate failure modes. This paper provides a comprehensive review of experimental and numerical studies that investigate the impact of key parameters, such as concrete infill types, reinforcement strategies, bonding levels, and GFRP tube geometries, on the flexural performance and failure behavior of concrete-filled pultruded GFRP tubular members in composite beam applications. The analysis includes full-scale GFRP beam studies, offering a thorough comparison of documented flexural responses, failure modes, and structural performance outcomes. The findings are synthesized to highlight current trends, identify research gaps, and propose strategies to advance the understanding and application of these composite systems. The paper concludes with actionable recommendations for future research, emphasizing the development of innovative material combinations, optimization of structural designs, and refinement of numerical modeling techniques.

Bayesian-based multi-class damage identification on prestressed reinforced concrete bridges

Model-driven structural system identification techniques are effective for comprehensive damage assessment but relying on a single model for structural identification (St-Id) can lead to unreliable results due to the ill-posed nature of the inverse calibration problem. To address this issue, this work explores the potential of multi-class digital twins, derived from sets of competing model classes, each one characterised by a distinct failure mechanism. To accelerate the calibration process, Kriging metamodels are employed, facilitating the fusion of diverse data types, such as modal displacements, frequencies, and static rotations. The Bayesian Information Criterion (BIC) is utilised to identify the most suitable model class. This research specifically targets the damage assessment of prestressed reinforced concrete girder bridges, which represent a significant portion of the global bridge stock. To this end, a numerical model of a representative span is developed, followed by a parametric analysis to evaluate the proposed approach’s effectiveness. Various damage scenarios including stiffness reduction and tendon prestress losses are considered, demonstrating the method’s capability for quasi-real-time multi-class damage identification. The study emphasizes the combined use of modal features and static rotations within a Bayesian framework, underscoring the importance of data fusion in achieving effective damage identification for these structures.

Experimental and numerical investigations on the performance of screw micropiles under pull-out and lateral loads

ABSTRACT Screw micro-piles are becoming progressively popular for inherent advantages and installation convenience. Their load-transfer technique and failure mechanism are complex and they bear more loads compared to the conventional piles, due to soil-thread interactive shear and bearing stresses. Available knowledge on performance of such piles is limited. The authors conducted a series of small-scale model tests on pull-out and lateral load-displacement characteristics of screw micro-piles embedded in soft cohesive soil. A sophisticated test set-up is developed to carry out the experiments under controlled conditions. The tests are followed by three-dimensional finite-element modeling by ABAQUS. The numerical output data closely matched with experimental results. Utilizing the finite-element model, interface shear stress distributions, load-transfer mechanism and failure envelop development are studied. The pile capacities are found to be influenced by different pile parameters, like pitch, embedded length, diameter, thread angle, etc. A set of important conclusions are drawn from the entire study.

A Modified Bearing Capacity Model for Inclined Shallow Anchor Cable with Experimental Verification

Most theoretical models of shallow anchor cables do not take the effect of anchor inclination into consideration, which is an important factor influencing load distribution, stress concentration, and failure mechanisms. In this paper, a modified bearing capacity was developed for a single anchor cable, taking the anchor inclination into consideration, based on the principle of limit equilibrium. Then, a series of indoor pull-out tests of single anchors with different inclinations were performed, where the effects of the anchor inclination on the bearing capacity and failure mechanisms were carefully analyzed. The experimental bearing capacities were compared to the predicted data of the proposed modified model, as well as other existing experimental results, aiming to verify the applicability and accuracy. The results show that the bearing capacity increases with decreasing anchor inclination because the vertical component of the force acting on the anchor cable increases. The failure models of the anchor cables, pulled out at different angles, exhibit an asymmetric “inverted trumpet” shape, which is caused by the varying stress distributions around the anchor cable during pull-out. In addition, the bearing capacities of the theory differ very little from the experimental and previous results, with a max error of nearly 10%. This study confirms that the proposed model reliably captures the effects of anchor inclination, providing valuable insights for designing inclined anchors in engineering practice.

Influence of water saturation on mechanical characteristics and fracture evolution of coal rock assemblage with rough interfaces

To comprehensively investigate the influence of water content on the mechanical and crack propagation characteristics of coal rock assemblage (CRA) with a rough interface, uniaxial compression tests were conducted on specimens with varying water content. Nuclear magnetic resonance (NMR) and acoustic emission (AE) techniques were employed to monitor the water content and AE signals throughout the experiment. The physical and mechanical properties, as well as the extent of crack development and acoustic emission (AE) parameters, were comprehensively investigated under conditions of water erosion. The results demonstrate that a rough interface contributes to an enhancement in the compressive strength of the composite material. Moreover, the moisture content exerts a significant influence on various aspects of the composite specimen, including its compressive strength, time b value, crack development, and crack propagation. With the increase in water content, the initial single slope shear failure of the composite specimen gradually transitions into a multi-section shear failure mechanism. Under the influence of water-rock interaction, sandstone within the formation undergoes a metamorphosis from a densely cemented structure to an irregular honeycomb-like configuration. This transformative process engenders novel porosity and fractures, ultimately compromising the rock’s mechanical strength. The analysis focuses on the relationship between the AE parameter b and uniaxial stress and water content, with emphasis on its relevance to damage theory. A damage model based on water immersion rate was established to elucidate the correlation between damage variables and water content. This was achieved by considering the characteristics of water-rock coupling AE and constructing a structural model of the water absorption process in different pore throats, thereby providing valuable insights for stability design and evaluation of roadway rock masses.

Progress of material degradation: metals and polymers in deep-sea environments

Abstract Given the critical need for ocean exploration, improving the durability of materials in the deep-sea has become a paramount concern. The harshness of deep-sea, such as high pressure, variable seawater flow rates, and corrosive media, lead to premature aging and failure. This work examines the utilization of metals and polymer coatings in deep-sea applications, detailing the characteristics of the deep-sea and its influence on these materials. In particular, chloride ions in seawater pose significant hazards to metal corrosion, which is the main reason for metal failure. Then, the degradation process and the latest research advances of various materials in the deep-sea environment are summarized, and the failure mechanism of the metal/coating system in the deep-sea is analyzed. It was found that the failure of polymer coatings can be divided into three processes, and adding an appropriate amount of fillers to the coating (such as adding 0.2 % graphene to water-based polyurethane) can extend the service life of the coating. Finally, the development trend of the company in the future is predicted. It has guiding and reference significance for the study of the failure behavior of metals and polymers in the deep-sea environment.

Mechanical characterization of failure mechanisms during the cutting of <i>Caragana korshinskii</i> Kom. branches

Mechanical characterization of failure mechanisms during the cutting of <i>Caragana korshinskii</i> Kom. branches

A Study on the Influence of the Rotating Speed and Load on the Grain Structure and Wear Properties of Bearing Steel GCr15 During Bearing Service

In order to study the wear failure mechanism and structure evolution law of bearings under different speeds and contact loads, an elastoplastic model of a 7009AC bearing was established in this paper. The stress, temperature rise and grain size during dry friction and wear of the bearing inner ring were simulated with the finite element method. The effects of the inner ring speed, load pressure and other parameters on the wear rate were studied. The relationship between the grain size and yield strength of GCr15 bearing steel was obtained. The effects of the initial grain size, rotational speed and load pressure on the bearing wear failure were studied. The evolutions of the grain size during service were predicted by means of the dynamic grain recrystallization (DRX), static grain recrystallization (SRX) and grain growth (GG) subprogram. The results show that the contact stress has a more significant effect on the early failure wear than the bearing speed, and the increase in the contact stress will aggravate the wear rate of the bearing inner ring. Under the same working conditions, the smaller the grain size, the more significant the influence of the cycle times on wear was. The heat-affected zone produced a local high temperature in the contact area, temperature flashes of up to 580 °C could occur in the central contact area, and the temperature decreased gradually with the increase in the depth from the contact area. It is noteworthy that both the surface and the subsurface of the material produced grain refinement; the grain size was refined from 20 μm to 0.4–12 μm under different working conditions. And the degree of refinement of the subsurface was higher than that of the surface.