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The forming interface is the weak link of thermoplastic composite complex structures. To explore the effect of polymer crosslinking on the failure behavior of thermoplastic composite remelting interface using "Preforming + Remelting bonding" process, the all‐atom models of different types of interfaces were established, and a molecular dynamics (MD) simulation was conducted on the uniaxial tensile failure process of the remelting interface. The failure behavior of the remelting interface with different preforming processes was tested to verify the correctness of MD simulation, and the influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified. The results showed that the yield stress of the uncrosslinked interface reaches 283.2 MPa and 16.0% and 50.6% higher than that of the unilateral and bilateral crosslinked interfaces respectively. The polymer crosslinking reaction during the preforming stage will reduce the interlaminar bonding performance. The interlaminar shear strength (ILSS) of the uncrosslinked interface is 87.46 MPa and 7.21% and 27.36% higher than that of the unilateral and bilateral crosslinked interface respectively, and only 3.95% lower than that of the non‐remelting sample formed by standard process. This research provides a new approach for predicting and analyzing the effect of polymer crosslinking on remelting interface properties of thermoplastic composite using "Preforming + Remelting bonding" process. Highlights: The failure behavior of different thermoplastic composite remelting interfaces was studied.MD simulation was conducted on the uniaxial tensile failure process of the remelting interface.The influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified.It is effective to explore the failure mechanism of thermoplastic remelting interface by MD simulation. [ABSTRACT FROM AUTHOR]

To optimize the assembly methods of honeycomb structures and enhance their design flexibility, this study investigated the impact mechanical responses of tandem honeycomb-core sandwich structures with varying misalignment assembly lengths. Impact tests were conducted across different energy levels on single-layer and tandem honeycomb-core sandwiches to observe their impact processes and failure behaviors. Our findings indicate that tandem honeycomb cores significantly enhance the impact resistance compared with single-layer configurations, even though a misaligned assembly can deteriorate this property. A finite element model was developed and validated experimentally; the model showed good agreement with the experiments, thereby allowing the simulation and evaluation of the impact responses. Herein, we reveal that specific misalignment lengths can either increase or decrease the impact resistance, providing insights into improving the resilience of tandem honeycomb-core structures. Our results not only contribute to enhancing the impact resistance of honeycomb-core sandwich structures but also offer a valuable basis for their practical applications in engineering. [ABSTRACT FROM AUTHOR]

In advanced nuclear power systems, structure materials have compatibility problems with lead-bismuth eutectic coolants such as liquid metal corrosion, and the corrosion failure behavior of the circulation pump is one of the main causes of nuclear safety accidents. Specifically, this paper reviews the failure behavior of the main pump in a flowing lead-bismuth environment for a prolonged period, alongside the prediction of the impeller blade's fatigue life. The development process and main structure of the nuclear reactor are introduced, and the failure behavior and influencing factors of the impeller blade of the main pump are discussed in detail. This paper also provides an in-depth analysis of material composition, oxygen content, temperature, corrosion time, relative velocity, and coating, to identify the failure reason and mechanism of the structural components featuring austenitic stainless steel as the main material. Finally, the fatigue life of the impeller and its prediction model are described from the perspective of fatigue failure, and the reliability analysis of fatigue life prediction is analyzed. [ABSTRACT FROM AUTHOR]

The exploration of material failure behavior not only involves defining its limits and underlying mechanisms but also entails devising strategies for improvement and protection in extreme conditions. We've pioneered an advanced multi-scale, high-speed ascending thermal shock testing platform capable of inducing unprecedented heat shocks at rates surpassing 105 °C/s. Through meticulous examination of the thermal shock responses of carbon nanotube (CNT) films, we've achieved remarkable breakthroughs. By employing an innovative macro-scale synchronous tightening and relaxing approach, we've attained a critical temperature differential in CNT films that exceeds an exceptional 2500 °C—surpassing any previously reported metric for high-performance, thermal-shock-resistant materials. Notably, these samples have demonstrated exceptional resilience, retaining virtually unchanged strength even after enduring 10,000 thermal shock cycles at temperatures exceeding 1000 °C. Furthermore, our research has revealed a novel thermal shock/fatigue failure mechanism that fundamentally diverges from conventional theories centered on thermal stress. [ABSTRACT FROM AUTHOR]

Sandstones exhibit a complex, stress-dependent behavior characterized by nonlinearity and inelasticity. This study delves into the mechanical properties of sandstone through two distinct triaxial compression experiments: monotonic and cyclic tests, under confining pressures ranging from 0 to 20 MPa. Based on plastic strain analysis, two stress-dilatancy models were developed to describe nonlinear plastic dilatation behaviors. The introduction of the "plastic dilatancy line" concept, derived from comparing plastic dilatancy stresses with crack damage strengths, marks a significant advancement in understanding sandstone's inelastic models. It was found that the plastic flow directions are not perpendicular to the yield surfaces marked by the characteristic strengths. This indicated that the non-associated flow rule is suitable to describe the macroscopic plastic deformations of sandstone. Furthermore, it was identified confining pressure as the dominant influence on sandstone failure, with cyclic loading modes playing a secondary role. An increase in confining pressure shifts the macroscopic failure modes from splitting-tension to mixed shear-tension, and ultimately to shear failure. Scanning Electron Microscope (SEM) analyses indicated that loading–unloading (L–U) cycles induce more significant mineral grain fragmentation compared to monotonic testing, thereby markedly decreasing sandstone's failure strength due to accumulated damage from grain-crushing. Additionally, the dip angles of dominant fractures in samples subjected to cyclic tests are typically smaller than that in monotonic tests. This investigation not only sheds light on the complex mechanical behaviors of sandstones but also provides a vital theoretical and practical framework for future research in this field. [ABSTRACT FROM AUTHOR]

The presence of horizontal layered rocks in tunnel engineering significantly impacts the stability and strength of the surrounding rock mass, leading to floor heave in the tunnel. This study focused on preparing layered specimens of rock-like material with varying thickness to investigate the failure behaviors of tunnel floors. The results indicate that thin-layered rock mass exhibits weak interlayer bonding, causing rock layers near the surface to buckle and break upwards when subjected to horizontal squeezing. With an increase in the layer thickness, a transition in failure mode occurs from upward buckling to shear failure along the plane, leading to a noticeable reduction in floor heave deformation. The primary cause of significant deformation in floor heave is upward buckling failure. To address this issue, the study proposes the installation of a partition wall in the middle of the floor to mitigate heave deformation of the rock layers. The results demonstrate that the partition wall has a considerable stabilizing effect on the floor, reducing the zone of buckling failure and minimizing floor heave deformation. It is crucial for the partition wall to be sufficiently high to prevent buckling failure and ensure stability. Through simulation calculations on an engineering example, it is confirmed that implementing a partition wall can effectively reduce floor heave and enhance the stability of tunnel floor. [ABSTRACT FROM AUTHOR]

Cryogenic medium pressure forming has been developed to form the complex-shaped tubular components, in which the needed shape and tube diameter directly determine the complex evolution of biaxial stress in bulging process. The superposition of biaxial stress and cryogenic temperature complicates the deformation behaviors, especially for the final fracture and bulging limit, which determine the forming quality of components. Therefore, the effects of tube geometry on failure orientation and fracture strain of Al-Mg-Si alloy tubes under cryogenic biaxial stress were elucidated, by utilizing cryogenic free bulging with different length-diameter ratios. The failure orientations and corresponding damage modes under different bulging geometric conditions were revealed. The influence mechanism of tube geometry and temperature on the failure mode was analyzed theoretically. A fracture model was established to predict the fracture strain in cryogenic bulging. The failure mode changes from circumferential cracking to axial cracking with the decreasing length-diameter ratio, owing to the stress sequence reversal induced by the significant nonlinearity of the stress path under a small length-diameter ratio. The failure mode can inverse under a larger length-diameter ratio of 1.0 at -196 °C because of the enhanced nonlinearity, which is promoted by the improved plasticity at cryogenic temperature. The established model based on the more accurate assessment of hardening ability during deformation can accurately predict the fracture strain with an average deviation of 10.6% at different temperatures. The study can guide deformation analysis and failure prediction in the cryogenic forming of aluminum alloy tubular parts. [ABSTRACT FROM AUTHOR]

A series of numerical true triaxial compression tests were carried out on rubber–sand mixtures (RSMs) by means of the 3D discrete element method to study the effect of the intermediate principal stress ratio b on the failure properties of RSMs with different rubber contents (RCs), and to explore the effect mechanism from a microscopic point of view. The numerical simulation results show that as the intermediate principal stress ratio b increases and the peak deviator stress q p e a k gradually increases, while the peak internal friction angle φ b first increases and then decreases. The numerical simulation results were compared with four common strength criteria, including the modified Lade–Duncan criterion, the SMP criterion, the FKZ criterion and the DP criterion. The comparative analysis showed that the existing common criteria cannot accurately predict the damage state of RSMs, suggesting the necessity for further research. At the micro level, the combined effects of the intermediate principal stress ratio b values and RC on the micro-parameters, such as the coordination number, average normal stress between particles, probability density and anisotropy, were investigated. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the mechanical characteristics of deep coalbed methane reservoir rocks (DCMRR) is crucial for the safe and efficient development of deep coalbed gas resources. In this study, the microstructural and mechanical features of the coal seam roof, floor, and the coal seam itself were analyzed through laboratory experiments. The impact mechanisms of drilling fluid and fracturing fluid hydration on the mechanical properties and failure behavior of coal seam rocks were investigated. The experimental results indicate that the main minerals in coal seams are clay and amorphous substances, with kaolinite being the predominant clay mineral component in coal seam rocks. The rock of the coal seam roof and floor exhibits strong elasticity and high compressive strength, while the rock in the coal seam section shows a lower compressive capacity with pronounced plastic deformation characteristics. The content of kaolinite shows a good correlation with the mechanical properties of DCMRR. As the kaolinite content increases, the strength of DCMRR gradually decreases, and deformability enhances. After immersion in drilling fluid and slickwater, the strength of coal seam rocks significantly decreases, leading to shear fracture zones and localized strong damage features after rock compression failure. The analysis of the mechanical properties of DCMRR suggests that the horizontal well trajectory should be close to the coal seam roof, and strong sealing agents should be added to drilling fluid to reduce the risk of wellbore collapse. Enhancing the hydration of slickwater is beneficial for the formation of a more complex fracture network in deep coalbed methane reservoir. [ABSTRACT FROM AUTHOR]

In this paper, the three-dimensional progressive damage finite element models of composite bolted connection and adhesive-bolt hybrid connection were constructed, and the accuracy of the model is verified by comparing with the experimental results. The energy-based B-K criterion was used to simulate the damage and evolution of the adhesive layer, and the effects of bolt hole diameter, pre-tightening force and layup sequence on the failure characteristics of composite mechanical connections were analyzed. The results show that, in the bolted connection model, the final failure mode is typically extrusion damage near the bolt hole, with matrix failure being the primary form of failure. Appropriately increasing the diameter of the bolt hole or applying an appropriate pre-tightening force can both enhance the connection strength. Maximal strength of the connection structure is achieved when the first layer in the connection area is oriented at 0°, whereas if the first layer is oriented at 90°, the connection's bearing capacity is minimally reduced. In the adhesive-bolt hybrid connection model, the fiber and matrix damage of the four plies closest to the adhesive layer mainly spread along the 45°direction, and the damage is mainly matrix tensile damage. [ABSTRACT FROM AUTHOR]

Concrete columns are used to support embankments built on soft soils. Use of three groups of centrifuge model tests, this study exhibited the global performance of embankments supported by plain concrete columns and reinforced concrete columns. The objective of the centrifuge tests was to reveal the failure mechanism and the contribution of the reinforced concrete columns to embankment stability. In comparison with plain concrete columns, use of reinforced concrete columns alleviated the release and transfer of stress in the ruptured concrete matrix, thereby avoiding continuous failure, which improved the overall stability of the embankment. Based on parametric analysis, Pareto multi-objective optimization method was proposed to determine the optimal column configuration design. The optimization results showed that placing reinforced concrete columns from the toe to the shoulder, combined with the installation of plain concrete columns near the embankment's centerline, not only satisfies the stability requirement of the embankment, but also minimizes construction costs and resource usage. Reinforced concrete columns which positioned of Rows 1–4 was suggested in this study. [ABSTRACT FROM AUTHOR]

Failure of resistance spot welds in computer-aided engineering models is based upon criteria that incorporate test data obtained in various loading conditions including different proportions of tensile, shear, and moment loads. The decomposition of the critical load into its respective shear, tensile, and bending moment components is influenced by the rigid body motion during their corresponding mechanical tests. Continuous tracking of the weld orientation and the deformed coupons is required for accurate determination of the load components at the onset of failure. A comprehensive experimental investigation was performed to characterize the critical failure load components in combined loading using various orientations of KS-II tests and a range of coach peel coupon geometries. Mechanical testing was coupled with digital image correlation (DIC) to systematically evaluate empirical force-based failure models for resistance spot welds of two third generation advanced high strength steels with optimal and suboptimal fusion zone diameters. New analysis methodologies using DIC were developed to account for rotation and deformation of the joint in the determination of the shear, normal, and bending moments acting on the spot-welded joints. The coach peel test results for both steels revealed a non-convex experimental fracture locus in bending-tension loading cases. The conventional assumption of a convex failure locus overestimated the critical bending moment strength between 7 and 66%. Results indicated that changes in the operative failure mechanism from pullout/partial-pullout to interfacial can expand the fracture loci within the shear-tensile loading mixities. Improved alternative functional forms for the weld failure models were proposed and contrasted with conventional models that assume convexity. [ABSTRACT FROM AUTHOR]

In this paper, the firing process and structural failure behavior of outdoor mechanical car parks are innovatively investigated under diverse conditions, leveraging fire experiments, FDS fire simulation, and finite element simulation. The fire experiments reveal the intricate interplay between flame spread and airflow, highlighting the enhanced risk of fire propagation among adjacent spaces. The temperature profile, mirroring the fire's lifecycle, is delineated into three distinct stages: initial growth, full development, and eventual decay. Notably, full-scale fire simulation in FDS validates the experimental outcomes, underscoring the scalability and reliability of our scaled-down experiments. Furthermore, finite element simulations offer a profound understanding of structural safety in various parking spaces during a fire. Critically, the susceptibility of columns to failure underscores the imperative need for enhanced fire prevention measures in column design, representing a significant advancement in fire protection engineering. [ABSTRACT FROM AUTHOR]

This paper discusses the mechanical failure analysis of Inconel 625 parts fabricated through the Wire and Arc Additive Manufacturing (WAAM) process. Three additive structures were manufactured with three inter-pass layer temperatures (IPT), such as 100, 200, and 300 °C. The tensile specimens were extracted from the additive structure in three principal orientations to evaluate the failure behavior concerning the deposition layer longitudinal (IN625-L), transversal (IN625-T), and diagonal orientations (IN625-D). Grain morphology and grain size varied with different inter-pass layer temperatures. An electromechanical tensile testing machine was used to conduct standardized testing to evaluate the tensile properties. The tensile curves were plotted to describe the tensile strength of the components in three orientations. The mechanical anisotropy and failure behavior of different orientations were defined with the grain boundaries and grain size. Compared to the other two orientations, IN625-D has a higher tensile strength. Because of their distinct orientations, the IN625-L and IN625-T specimens contain more elongated grains, and the IN625-D specimen has more grain boundaries. The strength obtained from grain boundaries is more significant than individual grains. [ABSTRACT FROM AUTHOR]

The main load-bearing structure of submarines is the pressure shell. Shell failures are usually caused by high hydrostatic pressure and its own potential geometric imperfections. This paper proposes a cylindrical shell with a strong corrugated stiffening structure. Two theoretically geometrically identical shells are fabricated using CNC machining to ensure the reproducibility and reasonableness of the results. Firstly, the point cloud data of all the geometric parameters of the corrugated pressure cylindrical shells were obtained using a 3D scanner. Geomagic Control X 3D inspection software was used to determine the geometric deviations of the shells. Geometric reconstruction was performed using Geomagic Design X reverse modeling software to capture potential imperfections of the shells. The aluminum shells were then welded and placed in the pressure chamber. Failure loads were obtained for all shells by constant water injection and pressurization. Considering the confined nature of the pressure chamber, a nonlinear finite element analysis of the corrugated pressure cylindrical shell was carried out using Abaqus/Riks, taking into account actual fabrication imperfections. Finally, the failure behavior of the shells under uniform external pressure was determined. The results show that both corrugated pressure cylindrical shells have high machining accuracy. The numerical simulation results of the critical buckling load of the corrugated pressure cylindrical shells were in good agreement with the test results. The corrugated structure has additional advantages in retarding the generation and expansion of shell surface defects. The equilibrium path of the corrugated pressure cylindrical shell can be maintained in a smooth and continuous state, showing stable buckling behavior. This study will provide new inspiration for the structural design and failure prediction of the submarine pressure shell. [ABSTRACT FROM AUTHOR]

Plated grillage with combined openings was susceptible to complex failure behaviors as the main load-bearing structure of the superstructure on passenger ships subjected to deck loads. Additionally, the deformation and stresses generated during the welding of the plated grillage complicated the prediction of its failure behavior. In this case, a new partitioned inherent strain method and nonlinear finite element method were used to simulate the welding and loading process, and experiments were designed and carried out to make comparisons, unveiling the influence regulations between the failure behavior of the structure and the loading condition, the initial welding state. This research on the failure mode analysis of plated grillages could provide references for the optimization of the structural form of plated grillages and the cargo loading scheme on the deck of a real ship. [ABSTRACT FROM AUTHOR]

Failure behavior is the key property needed to be characterized in asphalt concrete at low temperature, which is one of the major influence factors for service life of asphalt pavement. In this study, the reinforcing effect of glass fiber on failure process of asphalt concrete under indirect tension (IDT) test at − 10 ℃ was investigated using acoustic emission (AE) and digital image correlation (DIC) techniques. Control asphalt concrete (CAC) with no fibers was also carried out for comparison. The evolutions of AE parameters including amplitude, count, duration, rise time and corresponding cumulative ones were obtained and analyzed to characterize the failure processes of fiber reinforced asphalt concretes (FRACs) and control one, which were compared with the results from static displacement and strain data obtained through DIC. The effect of fiber length was also investigated to better understand the reinforcing mechanism and determine the proper reinforcing fibers. The test results revealed that low temperature failure processes of CAC and FRAC could be effectively classified according to the variations of AE parameters and corresponding cumulative ones. Three and five failure stages were identified for CAC and FRACs, respectively, which could clearly reflect the reinforcing effect of glass fiber. Cumulative AE parameters presented better identification effect on fiber reinforcement than displacement or strain, while stain data exhibited favorable performance for microcrack initiation. As for the fiber length effect on damage failure process of FRAC, evolutions of cumulative AE parameters before final failure of specimen became more stable with the increase of fiber length within 6–20 mm. AE technique presented great potential for failure behavior analysis and explanation of fiber reinforcing mechanism in asphalt concrete, which also provided promising method for real-time monitoring of cracking in asphalt pavement.

A variety of methods have emerged to tailor the mechanical properties of 3D-printed continuous fiber-reinforced thermoplastic composites (CFRTCs) through geometry design or manufacturing parameters. However, the potential to achieve customized failure behavior is not exploited. In this study, the effect of different layer orders on load bearing and failure of 3D-printed CFRTCs is investigated. Carbon fiber-reinforced polyamide composites with six layer orders were prepared and the mechanical response in 4-point bending was investigated. We show that the failure behavior ranges from catastrophic to pseudo-ductile, and we distinguished four typical stress-strain responses. We found that the location and the thickness of matrix-only layers strongly influence the failure. For the latter, we present a linear relationship to the ductility index which shows that toughness can be increased with thicker matrix layers. Our results facilitate the design of CFRTCs with customizable failure behavior, thus contributing to safer applications.

The continuous casting mould is the most crucial core component of the continuous casting production line, which undertakes the important tasks of cooling, heat conduction, abrasion resistance and high-precision forming of the billet surface during the high-speed vibration drawing process of the molten steel. Based on the engineering application practice of mould surface protective coatings in domestic steel plants, the advantages, disadvantages and developing trends of electroplated alloy coatings and thermal spray coatings on the surface of mould copper plate were summarized, as well as the main failure forms and formation mechanisms at different locations of mould surface after service under actual working conditions, providing the basis for optimizing the design of coating compositions and corresponding performance in different areas. Moreover, the service results and application advantages of the thermal spraying/vacuum diffusion composite technology developed by the project team in major domestic steel plants were introduced in detail. Finally, it was pointed out that thermal spraying technology will gradually replace electroplating technology and become the core technology of mold surface protection, and high entropy and medium entropy alloy coating has great application potential.

In the present study, the Ni coatings on the surface of carbon fibers (CFs) were purposely regulated to provide the enhanced interfacial microstructure evolution and mechanical properties of CF reinforced Al–Mg matrix (CF/Al–Mg) composites. With increasing the pH value and deposition time, the coating thickness increased with the formation of island-like agglomeration as the pH value was 4.5. Based on the stable electroless plating process, different thicknesses of interconnected coatings were applied in the CF/Al–Mg composites fabricated by a semi-solid rolling process in open space. With the optimal thickness of 2.15 μm, the relative density of the composites increased from 89.7 % to 98.1 %, compared with that of the composites with the thickness of 0.54 μm due to eliminated un-infiltration defects. Simultaneously, optimized fiber dispersion and interfacial behavior were obtained, leading to effective load transfer, more energy absorption and consequently significant enhanced mechanical properties. The ultimate tensile strength (UTS) of the composites was 183 MPa with the largest improvement, which was 96.8 % higher than that of the matrix.

To optimize the assembly methods of honeycomb structures and enhance their design flexibility, this study investigated the impact mechanical responses of tandem honeycomb-core sandwich structures with varying misalignment assembly lengths. Impact tests were conducted across different energy levels on single-layer and tandem honeycomb-core sandwiches to observe their impact processes and failure behaviors. Our findings indicate that tandem honeycomb cores significantly enhance the impact resistance compared with single-layer configurations, even though a misaligned assembly can deteriorate this property. A finite element model was developed and validated experimentally; the model showed good agreement with the experiments, thereby allowing the simulation and evaluation of the impact responses. Herein, we reveal that specific misalignment lengths can either increase or decrease the impact resistance, providing insights into improving the resilience of tandem honeycomb-core structures. Our results not only contribute to enhancing the impact resistance of honeycomb-core sandwich structures but also offer a valuable basis for their practical applications in engineering.

The deformation characteristics exhibited by the hierarchical structure in composites and their influence on compressive properties are investigated by controlling the deformation of carbon fiber multifilament under axial compressive loading. Our findings reveal that the deformation curve of carbon fiber composite materials under axial compression loads is nonlinear. Specifically, for 12 K high‐strength and medium‐modulus carbon fiber multifilament, when the compression load exceeds approximately 600 N, the buckling of individual fibers leads to shear deformation that damages the interface between the fiber and resin. Consequently, the compressive deformation of the multifilament composites transitions from elastic to plastic deformation. By enhancing the support force exerted by the resin on the multifilament composite and reducing the load span within the range of 2–4 mm, it is possible to effectively minimize or eliminate the overall buckling that may occur during the compression process of the multifilament composite. This results in a higher secant modulus under the same level of deformation. Additionally, it reduces the step difference between the compression and tension regions in the cross‐section of carbon fiber formed by the buckling, while the compression strength of the carbon fiber multifilament increases from 2.32 to 4.78 GPa. Highlights: Characteristics of compression deformation of carbon fiber multifilament.Regulation of the degree of buckling of carbon fiber multifilament.Cross‐section morphology under different compression failure mechanisms.Influence of the degree of buckling on compressive properties of carbon fiber. [ABSTRACT FROM AUTHOR]

In this study, a novel lattice structure with Y-shaped cores was designed. Specimens of the structure were fabricated using 3D printing technology for quasi-static compression tests. Numerical simulations were also performed to investigate the mechanical properties and failure behavior of the lattice structure. The numerical results are in good agreement with the experimental results. The numerical simulations are used to reveal the failure processes and failure mechanisms of structures with different relative densities. The results show that the relative density has significant effects on the mechanical properties of the lattice structure, and that different methods of changing the relative density lead to different results. [ABSTRACT FROM AUTHOR]

The growth stress induced by thermally grown oxide (TGO) is one of the main reasons for the failure of thermal barrier coatings (TBCs). In this study, the failure behavior of TBCs was examined based on different growth modes of TGO. A TBC thermo-mechanical model with a simplified sinusoidal interface morphology was established by the secondary development of a numerical simulation. The plasticity and creep behavior of materials were considered. Based on the subroutine development, the non-uniform growth of the TGO layer was realized. Cohesive elements were also applied to the TC/TGO interface. The stress distribution and evolution at the TC/TGO interface were investigated. Then, the cracking behavior near the interface was studied. The results show that lateral growth causes the off-valley site to replace the previous off-peak site as a vulnerable site. The non-uniform growth accelerates damage in the off-valley site, which leads to a change in the failure behavior. These results will provide significant guidance for understanding the TBC failure and the development of advanced TBCs. [ABSTRACT FROM AUTHOR]

The influence of water on rock deformation and failure behavior is a critical variable to consider when developing unconventional shale reservoirs. To better understand this effect, we conducted a series of triaxial compression tests on four mudstone lithofacies, namely siliceous calcareous mudstones, siliceous mudstones, calcareous mudstones, and carbonate-rich mudstones from the Naparima Hill Formation, under water-saturated conditions at confining pressures up to 130 MPa. Our results showed that the mudstones displayed brittle, brittle–ductile transition, and ductile failure behaviors as the confining pressure increased. Mudstones with low strength, high porosity, and high silica and clay contents exhibited a strong water-weakening effect, leading to a significant reduction in failure strength. Conversely, high strength, low porosity, and carbonate-rich mudstones showed minor water-weakening effects. We also developed a failure behavior model to predict the brittle, brittle–ductile transition, and ductile zones in the mudstones. The model showed that the transition from brittle to ductile behavior occurs over a wide range of confining pressures, and it occurs at a lower pressure threshold in saturated compared to dry conditions. Additionally, the model suggests that the presence of water results in a wider transition zone between brittle and ductile behavior, as well as a larger ductile zone. Overall, our findings suggest that the water-weakening effect can significantly decrease the depth at which the brittle–ductile transition occurs in mudstones, emphasizing the importance of considering water as a critical variable in rock deformation and failure behavior. Highlights: Triaxial compression test was conducted on mudstone specimens to investigate the impact of water content on failure behavior. An experimental model that predicts the brittle, brittle–ductile transition, and ductile failure behavior is developed for water-saturated mudstones. Low-strength, high-porosity mudstones with high levels of silica and clay are significantly weakened in the presence of water. Brittle–ductile transition behavior is influenced by the strength, porosity, and mineralogy of the mudstones. Brittle–ductile transition occurred over a wide range of confining pressures, with a lower threshold in saturated than dry conditions. [ABSTRACT FROM AUTHOR]

The non-persistent jointed rock mass is prone to compressive-shear and tensile-shear failures. Tensile-shear failure has been studied less than compressive-shear failure. This study develops a new shear test apparatus for cubic rock specimens to explore the tensile-shear failure of jointed rock mass under varying joint persistence and compare it to compressive-shear failure. The jointed rock specimens are sheared and monitored using acoustic emission (AE) equipment, an infrared thermal imager, and a high-speed camera to track stress, AE signal, temperature, and deformation. Based on the test results, RFPA2D numerical simulation is conducted to investigate the effect of joint persistence on the compressive- and tensile-shear strength of the rock bridge. Tensile- and compressive-shear stress curves differ greatly. The former may have several stress peaks and peak AE count time does not equal peak strength time. The rock specimen's compressive-shear strength is far higher than its tensile-shear strength, but tensile-shear tests accumulate more AE counts and energy. Tensile-shear failure has a large crack opening and rapid temperature progression. The rock specimen cools before peak strength, which is the opposite of compressive-shear failure. The two tests differ significantly regarding crack development and deformation evolution. The shear strength of the specimens in the compressive-shear and tensile-shear tests decreases approximately linearly as joint persistence increases, and the shear strength of the rock bridges increases and then decreases. Previous research showed that increasing joint persistence increases rock bridge cohesiveness. At relatively high joint persistence, however, the considerable cohesion weakening of the rock bridge caused by tensile cracks near the joint tip should be considered. The findings could contribute to a better understanding of the failure process of jointed rock mass under compressive-shear and tensile-shear stresses. Highlights: Compressive- and tensile-shear tests on cubic rock-like specimens were conducted on a novel test apparatus. Effect of joint persistence on compressive- and tensile-shear failure behavior was investigated. AE, thermal infrared imager, and DIC technologies were utilized to analyze the failure mechanism difference between compressive- and tensile-shear tests. The rock bridge's shear strength increases first and then decreases with joint persistence increasing in both compressive- and tensile-shear tests. [ABSTRACT FROM AUTHOR]

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Anchorage failure of a suction anchor is more likely to occur in low-strength muddy clay. This paper focuses on the failure behaviors of suction anchors and muddy clay stress responses. The centrifugal model test was used to study the loading processes of suction anchors with various pulling angles. Firstly, the multi-stage developing process of anchoring force was analyzed according to the test results. Numerical modeling was used to validate the test results. The displacement of the suction anchor and muddy clay soil were analyzed using the numerical results. Then, the numerical and testing results were compared to analyze the horizontal soil pressure responses around the suction anchors. It was found that the change in loading direction affected the distribution and development of soil stress. The horizontal soil resistance played a crucial role in improving the bearing capacity. The soil stress variation and anchor displacement revealed that the suction anchors exhibited multi-attitude coupling movement during the inclined pulling. The vertical pulling suction anchor showed shear–slip failure behaviors, while the inclined pulling suction anchors showed compression–shear–slip coupling failure behaviors. The results of this study provide insight into the interaction mechanism between suction anchors and muddy clay, serving as a reference for the design and application of suction anchors. [ABSTRACT FROM AUTHOR]

Continuous basalt fiber (CBF) is an outstanding inorganic fiber produced from nature, which has a wide range of applications in the field of armor protection of national defense military. However, the mechanical response and failure mechanism of 3D printed CBF reinforced components are still not well understood. Here, the 3D printing thermoplastic composites with high volume fraction CBF have been successfully prepared by fused deposition modelling (FDM) method. The effects of fiber printing direction and polymer matrix type on the tensile and flexural properties of the 3D printed composites have been explored, and the detailed failure morphology has been characterized using scanning electron microscopy and optical microscopy. It was found that under high fiber volume fraction, 3D printed CBF reinforced polyamides (PA) composites have the best ability to maintain material integrity of the composites, followed by acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). Besides, the results from rule of mixtures can accurately predict the longitudinal Young’s modulus of the 3D printed specimens, but there exists a large discrepancy for the prediction of the tensile strength. The microstructure analysis shows that the failure modes of 3D printed composites mainly include fiber debonding, fiber pull-out, stress whitening and matrix cracking.

A series of numerical true triaxial compression tests were carried out on rubber–sand mixtures (RSMs) by means of the 3D discrete element method to study the effect of the intermediate principal stress ratio b on the failure properties of RSMs with different rubber contents (RCs), and to explore the effect mechanism from a microscopic point of view. The numerical simulation results show that as the intermediate principal stress ratio b increases and the peak deviator stress qpeak gradually increases, while the peak internal friction angle φb first increases and then decreases. The numerical simulation results were compared with four common strength criteria, including the modified Lade–Duncan criterion, the SMP criterion, the FKZ criterion and the DP criterion. The comparative analysis showed that the existing common criteria cannot accurately predict the damage state of RSMs, suggesting the necessity for further research. At the micro level, the combined effects of the intermediate principal stress ratio b values and RC on the micro-parameters, such as the coordination number, average normal stress between particles, probability density and anisotropy, were investigated.

Bending failure modes in solid stem wood and solid culm bamboo varies depending on material and geometric properties. Solid culm cross-sections of Oxythenantera Abyssinica round bamboo resemble to wood, but are anatomically different in their mode of growth and tissue organization. The bending stress gradient and failure behavior has highly related with the culm internal voids termed as hollowness which depends on age of bamboo. Hollowness (k) refers the relative proportion of void volume to solid volume with in a culm. Full culm beam specimens with length of 3.5 m were subjected to bending under 4-point static loading according to ISO 22155. Pattern of vertical deflection varies depending on the maturity of the culm. A statistical and experimental results showed that, for K values between 12-15% a mixed mode of local buckling with a longitudinal shear splitting failure mode was resulted in 4-year age bamboo specimens with a slight (14 mm) shift from the shear center inducing large vertical deflection (142 mm) at midspan. A kink buckle and green stick modes were observed in 2-year and 3-year ages culms at failure point of 124 and 158mm at length ‘L’ (L/2.5 to L/4.5) from shear center with a k value 25-27% and 18-22% respectively.

This study presents the results of experimental research on the behavior and stretching of hollow cylindrical epoxy tubes made of glass, carbon, and kevlar fibers subjected to axial compression load. Hollow cylindrical tubes were fabricated by fiber winding method using glass, carbon, and kevlar fiberreinforced composite materials. In this study, hollow cylindrical composite tubes with constant outer (Ø17 millimeters), two different inner diameters (Ø12 and Ø13 millimeters; 2 ve 2,5 millimeters wall thickness), and 80 millimeters in height. Experimental research was carried out for two dissimilar wall thicknesses and four fiber orientation angles. The compressive strengths of all samples were investigated experimentally by applying loads in the axial direction. Twenty-four configurations of composite specimens were fabricated (three reinforcement materials, four winding angles, and two wall thicknesses) to research the impact of axial compression stress. Experimental results revealed that polymer reinforcement material, fiber winding angle, and wall thickness have a significant impact on the compressive stress of cylindrical composite tubes as a result of applied load in the axial direction. The conclusions show that the compressive stress of all reinforcement rises as the orientation angle and wall thickness increase under an axial compression load, and the compressive stress reaches a maximum when the orientation angle is 90° under an axial compression load. It was observed that the axial compressive stress was highest in glass/epoxy samples with 217 MPa, followed by carbon/epoxy samples with 173 MPa and kevlar/epoxy samples with 145 MPa, respectively. The axial compressive stress of all samples was highest at a 90° orientation angle and lowest at a 15° orientation angle. were found to have low values. It was observed that the axial compressive stress value increased in all reinforcement materials as the wall thickness increased. [ABSTRACT FROM AUTHOR]

In this paper, the firing process and structural failure behavior of outdoor mechanical car parks are innovatively investigated under diverse conditions, leveraging fire experiments, FDS fire simulation, and finite element simulation. The fire experiments reveal the intricate interplay between flame spread and airflow, highlighting the enhanced risk of fire propagation among adjacent spaces. The temperature profile, mirroring the fire’s lifecycle, is delineated into three distinct stages: initial growth, full development, and eventual decay. Notably, full-scale fire simulation in FDS validates the experimental outcomes, underscoring the scalability and reliability of our scaled-down experiments. Furthermore, finite element simulations offer a profound understanding of structural safety in various parking spaces during a fire. Critically, the susceptibility of columns to failure underscores the imperative need for enhanced fire prevention measures in column design, representing a significant advancement in fire protection engineering.

The main load-bearing structure of submarines is the pressure shell. Shell failures are usually caused by high hydrostatic pressure and its own potential geometric imperfections. This paper proposes a cylindrical shell with a strong corrugated stiffening structure. Two theoretically geometrically identical shells are fabricated using CNC machining to ensure the reproducibility and reasonableness of the results. Firstly, the point cloud data of all the geometric parameters of the corrugated pressure cylindrical shells were obtained using a 3D scanner. Geomagic Control X 3D inspection software was used to determine the geometric deviations of the shells. Geometric reconstruction was performed using Geomagic Design X reverse modeling software to capture potential imperfections of the shells. The aluminum shells were then welded and placed in the pressure chamber. Failure loads were obtained for all shells by constant water injection and pressurization. Considering the confined nature of the pressure chamber, a nonlinear finite element analysis of the corrugated pressure cylindrical shell was carried out using Abaqus/Riks, taking into account actual fabrication imperfections. Finally, the failure behavior of the shells under uniform external pressure was determined. The results show that both corrugated pressure cylindrical shells have high machining accuracy. The numerical simulation results of the critical buckling load of the corrugated pressure cylindrical shells were in good agreement with the test results. The corrugated structure has additional advantages in retarding the generation and expansion of shell surface defects. The equilibrium path of the corrugated pressure cylindrical shell can be maintained in a smooth and continuous state, showing stable buckling behavior. This study will provide new inspiration for the structural design and failure prediction of the submarine pressure shell.

Reinforced concrete and steel structures are commonly used in bridge construction; thus, researchers have conducted relatively comprehensive analyses of their dynamic responses and damage mechanisms under blast loads. However, for a new type of I-shaped steel‒concrete composite structure with various structural performance advantages, there remains a lack of effective experiments and analyses of damage modes. In this paper, three I-shaped steel‒concrete composite specimens are designed and fabricated, and explosion experiments under different explosion scenarios are performed. The experimental results show that under the support of an I-shaped steel plate, the structure has a strong ability to withstand the blast load. The concrete damage area on the rear blast surface is small, and the I-shaped steel plate does not yield under a small explosive equivalent. Based on the experimental results, the dynamic response and failure behavior of the I-shaped steel‒concrete composite structure are numerically evaluated using Autodyn explicit dynamic analysis software. By considering different working conditions and by taking the deformation and damaged areas of the structure as the damage index, the key explosion resistance factors of the structure under contact explosion are studied. Some important structural parameters greatly influence the explosion resistance of the structure, including the thickness of the I-shaped steel plate; however, increasing the strength of concrete does not significantly improve the explosion resistance of the composite structure. [ABSTRACT FROM AUTHOR]

Composite laminated bolted joints are increasingly used in the aerospace industry, and most researchers are involved in the study of the failure behavior of composite bolted joints' structures. Because of the complexity and stability of the structure, precisely predicting the damage evolution and failure behavior of the composite laminated bolted joint becomes rather difficult. In this paper, an asymptotic damage model is proposed to predict the failure behavior of the composite bolted joint structure. The model is based on the frame of mainstream criteria and some improvements are made to adapt to the particularity of composite laminated bolted joints. Combining the damage model with the finite element method, the failure behavior of single-lap and double-lap bolted joint structures are predicted and analyzed. In order to guarantee the reliability of the model, the corresponding experimental study is conducted, and the results show that the simulation curve and the experimental data are in good agreement. This damage model can further predict the failure behavior of various types of complex composite laminated bolted joints effectively. [ABSTRACT FROM AUTHOR]

The stress state in a rock mass is complex. Stress redistribution around underground excavation may lead to various failure modes, including compressive-shear, tensile-shear, and tensile failures. The ability to perform laboratory tests with these complex stress states is significant for establishing new strength criteria. The present paper introduces a new rock testing system with “tensile-compressive-shear” loading functions. The device includes bi-directional and double-range hydraulic cylinders, auxiliary loading equipment, and roller rows that can perform direct compressive-shear tests, direct tensile tests, and direct tensile-shear tests. The testing system provides maximum vertical and lateral loading forces of 2000 kN and allows testing cubical rock specimens with dimensions of 0.5 m × 0.5 m × 0.5 m. The performance of the testing machine was evaluated by testing a rock-like material based on cement mortar under compressive-shear, tensile, and tensile-shear stress states. The failure process and deformation characteristics were monitored during loading using acoustic emission (AE) transient recorder, piezoelectric AE sensors, a high-speed camera, and a thermal infrared camera. The failure mechanism was investigated by analyzing AE counts, AE amplitude, strain, and temperature changes on the rock specimen surface. The test results confirmed that the testing system could successfully simulate the abovementioned stress path. The AE counts and amplitude responses were influenced by different failure modes. The temperature response during the compressive-shear test indicated the development of a high-temperature band on the rock specimen surface. In contrast, a negligible temperature change was observed during the tensile and tensile-shear tests. The newly developed multifunctional rock testing system allows laboratory tests under various failure modes. The monitoring results of multiple variables during rock failure tests provide valuable information on failure characteristics.

Earthquake and rainfall may be coupled, which will lead to landslides easily, but the studies about this problem are at the initial stage. In this paper, the failure behavior and mechanism of a slope under the action of earthquake after rainfall were investigated with a shaking table test, based on similarity law. The experimental results showed that the failure process of the slope during earthquake after rainfall undergoes four characteristic stages. There exist velocity zoning in the slope during failure. The moisture content of soil in the slope has different growth rates at different positions during rainfall. Transient and cumulative pore water pressure occurs in the slope during earthquake after rainfall. However, due to the short period of earthquake action, the soil moisture content is not very sensitive to this action, but the pore water pressure changes sharply during earthquake. Under the combined action of rainfall and earthquake, there is a multi-physical field effect in the slope. Rainfall weakens the strength of the soil, mainly causes local instability of the slope. More extensive damage of the slope is caused under the combined action of seismic inertia force. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the forming mechanism and bearing behavior of single-lap composite riveted joints with different hole diameters (4.82 mm and 4.9 mm) and squeeze forces (15 KN, 18 KN, 20 KN, and 23 KN). Pressure riveting and tensile tests are conducted to composite riveted joints to obtain the joint interference, joint stiffness and bearing strength needed to quantitatively evaluate their deformation features and mechanical properties. Furthermore, microscopic studies on damaged areas using applying ultra-depth three-dimensional microscope to monitor damage evolution are conducted to comprehend the joint shear failure mechanism. Results show that the hole diameter and riveting force have a significant effect on the performance of the joint. The forming damage occurs mainly in the hole wall near the driven head and is dominated by fiber crushing and interfacial shear cracks. The radial expansion of the rivet shank is not uniform under the riveting force and the whole is drum shaped. But the hole expansion of the joint at 4.82 mm hole diameter is more uniform than 4.9 mm, which would lead to better joint stiffness and bearing strength. Moreover, high interference fit would cause the shear fracture of the rivet, while lower interference joints are dominated by compression-pull mixed failure. In general, the size of interference fit is an unneglectable factor in the composite riveted joints that should be thoroughly investigated. [ABSTRACT FROM AUTHOR]

Featured Application: Numerical simulation of I-shaped RC beams under combined blast and impact loads. The existing literature mainly focuses on the research of reinforced concrete (RC) beams under a single load such as blast or impact. In this paper, the slab–rib–slab RC beam, a new type of structure widely used in bridge structures, was taken as the research object. The explicit dynamic analysis software LS-DYNA was used to numerically analyze the dynamic response and failure behavior of I-shaped RC beams under combined blast and impact loads. For this reason, an effective numerical analysis model was obtained by carrying out experiments on I-shaped RC beams under contact explosion. The key factors affecting the dynamic response of the structure under combined loads were numerically analyzed. Numerical results showed that different load application sequences have important effects on the dynamic response of the structure. When the impact load was first applied to the structure, more severe concrete damage and deformation occured in the depth direction of the beam. However, when the blast load was first applied to the structure, the concrete at the lower flange was damaged in the span direction of the beam due to tension, and no large-scale concrete spallation occurred in the depth direction. This was mainly due to the different mechanisms of blast and impact loads. In addition, the vulnerability of the I-shaped RC beams varied with some structural parameters, including span, depth, and configuration of reinforcement. At the same time, the results showed that the structure is more sensitive to changes in structural parameters when it is first subjected to impact loads. [ABSTRACT FROM AUTHOR]

The knowledge of the influence of high dynamic loads on the electrical and mechanical behavior of lithium-ion cells is of high importance to ensure a safe use of batteries over the lifetime in electric vehicles. For the first time, the behavior of six commercial Li-Ion pouch cells after a constrained short-time acceleration (300 g over 6 ms) with a resulting cell surface pressure of 9.37 MPa was investigated. At this load, two out of six cells suffered from an internal short circuit, showing several damaged separator layers across the thickness in the area of the cell tabs. For the cells that remained intact, a range of measurement techniques (e.g., inner resistance measurement, electrochemical impedance spectroscopy (EIS), or thermal imaging) was used to reveal changes in the electrical property resulting from the load. The cells without short circuit show an increase of internal resistance (average of 0.89%) after the dynamic pre-load. The electric circuit model based on the EIS measurement indicates a decrease of the resistance R1 up to 30.8%. Additionally, mechanical properties of the cells in an abuse test subsequent to the dynamic pre-load were significantly influenced. The pre-loaded cell could sustain an 18% higher intrusion depth before electrical failure occurred as compared to a fresh cell in an indentation test. The results of this study revealed that a high acceleration pulse under realistic boundary conditions can lead to critical changes in a battery cell's properties and needs to be taken into account for future safety assessments. [ABSTRACT FROM AUTHOR]

A double-ceramic-layer (DCL) thermal barrier coating consisting of quasi-columnar structured (Gd0.9Yb0.1)2Zr2O7 (GYbZ) on top and yttria-stabilized zirconia (YSZ) beneath was deposited by plasma spray-physical vapor deposition (PS-PVD). The as-deposited GYbZ/YSZ coating is composed of a dense continuous layer at the bottom and a columnar layer growing on it. The columnar layer comprises taller coarse columns, shorter tapered columns, and particles filling in the gaps between the columns. The thermal shock behavior of the coating is evaluated in a burner rig at 1300 °C, during which the coating mainly fails in the form of delamination. The coating initially delaminates in the regions where the particles are embedded beneath the taller GYbZ columns tips. Subsequently, delamination occurs in the lower region of GYbZ coating and eventually fails at the TGO/YSZ interface. A finite element model tailored to the microstructural characteristics of the DCL coating was established. Stress distributions of the coating indicate that the discontinuities of the strain tolerance caused by abrupt microstructural or componential changes lead to multiple out-of-plane stress (σ22) concentration spots. The position and procedure of the delamination of GYbZ coating obtained based on the energy release rate of each σ22 concentration spot are consistent with experimental results.

The growth stress induced by thermally grown oxide (TGO) is one of the main reasons for the failure of thermal barrier coatings (TBCs). In this study, the failure behavior of TBCs was examined based on different growth modes of TGO. A TBC thermo-mechanical model with a simplified sinusoidal interface morphology was established by the secondary development of a numerical simulation. The plasticity and creep behavior of materials were considered. Based on the subroutine development, the non-uniform growth of the TGO layer was realized. Cohesive elements were also applied to the TC/TGO interface. The stress distribution and evolution at the TC/TGO interface were investigated. Then, the cracking behavior near the interface was studied. The results show that lateral growth causes the off-valley site to replace the previous off-peak site as a vulnerable site. The non-uniform growth accelerates damage in the off-valley site, which leads to a change in the failure behavior. These results will provide significant guidance for understanding the TBC failure and the development of advanced TBCs.

Anchorage failure of a suction anchor is more likely to occur in low-strength muddy clay. This paper focuses on the failure behaviors of suction anchors and muddy clay stress responses. The centrifugal model test was used to study the loading processes of suction anchors with various pulling angles. Firstly, the multi-stage developing process of anchoring force was analyzed according to the test results. Numerical modeling was used to validate the test results. The displacement of the suction anchor and muddy clay soil were analyzed using the numerical results. Then, the numerical and testing results were compared to analyze the horizontal soil pressure responses around the suction anchors. It was found that the change in loading direction affected the distribution and development of soil stress. The horizontal soil resistance played a crucial role in improving the bearing capacity. The soil stress variation and anchor displacement revealed that the suction anchors exhibited multi-attitude coupling movement during the inclined pulling. The vertical pulling suction anchor showed shear–slip failure behaviors, while the inclined pulling suction anchors showed compression–shear–slip coupling failure behaviors. The results of this study provide insight into the interaction mechanism between suction anchors and muddy clay, serving as a reference for the design and application of suction anchors.