Critical Failure Mechanism Research Articles

Failure analysis in pyrolysis furnaces: Impact of carburization and thermal cycles on tube properties

The dominant failure mechanism in radiation coil tubes in pyrolysis furnaces is the detrimental interaction between carburization and reduced material ductility. This combination results in localized deformations, significant ovalization, and cracking in the tubes. At the same time, a second critical failure mechanism emerges during emergency furnace shutdowns, characterized by brittle fractures that can generate extensive longitudinal cracks in multiple tubes. This work presents a case study on the occurrence of failures that resulted in brittle fracture rupture of several tubes in a pyrolysis furnace that accumulated 43,720 h of operation. This highlights the practical importance of monitoring and managing the integrity of coil tubes. The tube samples were analyzed using optical and scanning electron microscopy, evaluation of carburization through magnetic permeability and NACE Test TM498, identification of carbides by X-ray diffraction (XRD), and dilatometry. Additionally, thermal stress analyses were performed using the finite element method, along with tensile tests at different temperatures. It was found that the tubes of the coil that operated at lower temperatures in their operational cycle did not rupture during the emergency shutdown, unlike other coils whose tubes experienced significant failures. An important contribution from this study is the demonstration of optimized operational cycle management and thermal control are essential in preserving protective oxide layers, minimizing coke formation and the effects of carburization and creep. This can reduce shutdown frequency and maintenance costs, improving the cost-effectiveness of the cracking process.

Multi-fidelity deep neural network with Monte Carlo dropout technique for uncertainty-aware risk recognition of backward erosion piping in dikes

Backward erosion piping (BEP) is an increasingly critical failure mechanism in dike systems, often triggered by floods resulting from extreme rainfall events, which are exacerbated by the ongoing shifts in climate patterns. This study embarks on a nuanced examination of BEP, a phenomenon that substantially undermines flood control and emergency management endeavors. Addressing the complexities of BEP incidents and the consequential variable impact on dike infrastructure, we have incorporated Monte Carlo dropout techniques within a multi-fidelity deep learning framework to enhance predictive accuracy and provide an uncertainty-aware assessment of BEP risk. Drawing on 16 sets of physical model experiments emulating dike structures from the lower Yangtze River basin in China, we conducted a detailed study of the BEP evolution mechanism under various hydrological scenarios intensified by climate change. These experiments allowed us to observe the initiation and progression of BEP in different conditions. The development of a structural equation model quantifies the effects of several critical factors—including those exacerbated by climatic variability—on BEP dynamics. Seven key factors were identified as influential to BEP risk levels, integrating distinct BEP traits, hydrological attributes, and dike engineering conditions. A Monte Carlo dropout-enhanced multi-fidelity deep neural network (MFDNN) was crafted, synthesizing low-fidelity experimental data with high-fidelity field case studies, to construct an advanced model for BEP risk level identification. Compared against four sophisticated machine learning models, our MFDNN demonstrated superior performance, effectively blending experimental insights with real-world occurrences. The proposed model emerges as a scientifically robust and pragmatic tool for delineating BEP risk levels in dike systems, providing vital guidance for categorizing BEP incidents and forging targeted, climate-informed emergency response strategies.

Classification of damage modes in scaled open-hole composite laminates under combined tension-shear loading using acoustic emission technique

The damage initiation and evolution of carbon fiber-reinforced polymer (CFRP) composite under multi-axial loading is of fundamental interest. This study investigates intra- and interlaminar damage modes induced in open-hole quasi-isotropic (QI) carbon/epoxy composite laminate under combined tension-shear loading using the acoustic emission (AE) technique. The effect of layer thickness is studied using three types of laminates with stacking sequences PL-1: [−452/452/902/02]s, PL-2: [−453/453/903/03]s (ply blocked), and SL-1: [−45/45/90/0]2s (a sub-laminate blocked or distributed). Clustering of acquired AE signals is carried out using hierarchical methods. Damage modes evolution for the open hole QI CFRP is captured using the clustered AE signal data. It is observed that the thickness scaling significantly affects the open-hole strength and the critical failure mechanisms. Dominant damage mechanisms are identified based on AE cumulative energy. Ply-level blocked (PL-1 and PL-2) laminates exhibit lower strength than the SL-1 blocked laminate. The findings from this experimental investigation indicate that the AE technique in conjunction with the clustering approach is a prospective tool for the structural health monitoring of composite structures under combined loading.

Unconventional fatigue failure of densified wood

Fatigue is a critical failure mechanism in various materials, often leading to catastrophic consequences. Designing materials with non-catastrophic fatigue failure is desirable yet challenging. This work presents the remarkable fatigue behavior of densified wood, exhibiting both a higher fatigue strength and non-catastrophic failure compared to natural wood. The improved bonding between wood fibers, primarily through hydrogen bonds, enables robust structural integrity even after fatigue failure. This mechanistic understanding offers insights for achieving non-catastrophic fatigue failure in diverse materials, presenting a fundamental principle for material design with broad implications.

Complex reaction mechanisms of electrolyte decomposition at large-scale Ni-rich Li-ion battery cells including electrode crosstalk effect

Ni-rich cathodes are essential for the advancement of high-energy lithium-ion batteries but encounter significant challenges at elevated voltages, including oxygen liberation and enhanced surface reactivity, which precipitate electrolyte decomposition. This study explores the intricate reaction mechanisms of electrolyte decomposition linked to the pronounced release of oxygen from the cathode lattice in large-scale 18650 cylindrical cells employing Ni-rich LiNi0.90Mn0.05Co0.05O2(NMC90)//graphite configurations, focusing on electrode crosstalk effects at high voltages. Notably, acetals such as methoxy methanol (49.93 %) and methane diol (50.07 %) were identified at 4.7 V, with their presence escalating at 4.9 V. Formaldehyde, present at 7.21 %, along with methanol (22.77 %), methane diol (36.35 %), and methoxy methanol (33.67 %), begins to manifest at 4.9 V. The dissolution of transition metals was analyzed using Inductively Coupled Plasma Atomic Emission Spectrometry, and changes in the double-layer capacitance were assessed through electrochemical impedance spectroscopy, further validating the link between these decomposition products and cathode failure associated with oxygen release. These insights reveal the complex relationship between electrolyte decomposition and cathode degradation due to oxygen release, highlighting a critical failure mechanism in large-scale cylindrical lithium-ion batteries.

Experimental and Numerical Analysis of the Three-Point Bending Behavior of Hybrid Adhesive-Bonded Aluminum–Wood Plates

Hybrid components of wood-based materials offer a high potential for automotive lightweight applications. To investigate the bending behavior of hybrid aluminum-wood plates, commercial 1-mm-thick sheets of EN AW-6016-T4 aluminum alloy were adhesive-bonded with 4.2-mm-thick plates of birch wood. Orientations of the wood fibers parallel (longitudinal) as well as perpendicular (transverse) to the rolling direction of the aluminum alloy sheet and three different moisture contents of the wood plate were considered. The hybrid aluminum-wood plates were subjected to three-point bending at room temperature. Simple wood plates without aluminum alloy sheets were also tested. The bending force-bending angle curves monitored during bending, the bending angles at maximum bending force and the surface strains were evaluated. Moreover, a finite element model of the testing setup was created using the LS-Dyna software. The different moisture contents did not significantly influence the bending angle; however, moisture decreased the maximum bending force. Debonding was identified as critical failure mechanism. The FE model that considered the experimentally determined material properties was able to predict the bending behavior for different moisture conditions.

Investigation of the stability of a fly ash pond facility using 2D and 3D slope stability analysis

A numerical investigation of the effect of pore pressure regime on the safety factor and the critical failure mechanism is presented for fly ash storage facility. Pore pressures’ measurements from standpipe piezometers and pore pressure estimated from seepage analysis are used to compare the factor of safety for a fly ash slope. This was applied for considering static and seismic scenarios. A probabilistic approach was applied to account for the uncertainties resulting from the limited data available and support a qualitative risk assessment evaluation. Slope stability analysis is conducted in two and three dimensions, adopting the limit equilibrium analysis approach, and also a finite element seepage analysis, to assess the stability of the slope. The two-dimensional cross-sections were extruded to three-dimensional models to estimate the factor of safety and associated shear failure. The results from the performed analysis suggest an increase in safety factor values of 5%.

Investigation of shear band strengthening by using different strengthening criteria

To prevent a critical failure mechanism, it is possible to simply strengthen the potential shear bands, which is a patented idea. The localization of potential shear bands that are most likely to form shear can be calculated. Before these shear bands can appear, they can be strengthened by injecting a cement suspension or using jet grouting at the locations where the most likely shear bands would occur. As a result, it is possible to increase the bearing capacity of the geotechnical system by focusing solely on the shear bands that are moste likely to form, minimizing the use of materials. Numerical modeling is employed to analyze the increase in bearing capacity. Four criteria for strengthening the shear bands are applied by incorporating them into a hypoplastic soil model, taking into consideration the material transition from soil to cement, as well as intermediate materials that can arise from jet grouting, which are mixtures of soil and cement. Two fundamental geotechnical systems, namely a shallow foundation and a retaining wall, are analyzed using ABAQUS/Standard for finite element analysis. The results demonstrate the potential of numerical modeling to identify the most critical localized areas in the soil that require strengthening, as well as the substantial increase in bearing capacity achieved after reinforcing the identified areas.

Energy release rate for steady-state fiber debonding in structural battery composites

Structural battery composites are multifunctional materials intended to provide energy storage capacity while maintaining their strength and load bearing capacity under significant mechanical loads. In this study, we investigate the mechanics of carbon fiber debonding, a critical failure mechanism in structural battery composites. The carbon fibers are intended to serve both as an electrochemically active material and to bear mechanical load in the composite system. We derive an analytical solution to the energy release rate for steady-state fiber debonding for different electrochemical and mechanical loading cases with the aid of the classical solution for the Eshelby inclusion problem. The analytical solutions are validated with finite element simulations. We find a higher energy release rate and thus a greater driving force for fiber debonding is caused either by a lower lithium concentration in the fiber and/or by greater transverse mechanical loads such as biaxial tension or shear applied at the far field in the matrix. We find that the model is predictive even for transversely isotropic fibers despite the assumption that the fiber is elastically isotropic in the model. This work can provide guidance for the design of mechanically robust structural batteries.

Three-dimensional discretization-based kinematic analyses of prestressed anchor cables reinforced rotational slopes subjected to earthquakes

Prestressed anchor cables are commonly utilized to reinforce slopes in earthquake-prone zones. The existing upper bound limit analyses of seismic slopes reinforced with prestressed anchor cables have the following limitations: (1) neglecting variable seismic excitations; (2) ignoring the three-dimensional spatial layout of cables because of using the plane-strain analysis. In this study, the time-space effects of seismic waves are analytically described by sin-cos functions incorporating wave amplification or soil damping. Based on the upper bound of plastic theory and a three-dimensional discretized failure mechanism, internal energy dissipation rate and work rates contributed by gravitational forces, variable seismic excitations, and prestressed anchor cables are computed. An energy-based function of dynamic factors of safety (DFS) is established, followed by a global optimization to identify the critical harmonic pattern of DFS. The accuracy is checked by numerical simulations where the seismic stability of an engineering slope adjacent to Yu-Huai railway is evaluated. Comparisons also show that the conventional simplified method not only cannot reflect the spatial layout of cables but also overestimate the mechanical contribution of cables. Finally, the dominant effects of the layout of cables, soil properties as well as physical parameters of seismic waves on the DFS and the critical failure mechanism are discussed.

Numerical modelling and experimental testing of vibration-based debonding quantification on tile panels

Interfacial debonding is recognized as the most critical failure mechanism in adhesively bonded tiling systems which may cause potential falling of tile panels. Several techniques have been well developed in this field to assess the tiling systems in terms of the existence of debonding. However, limited research has been found to be capable of quantifying the debonding. In addition, previous studies typically employed a one-excitation, one-detection approach with a large amount of testing points, and often targeted large debonding sizes. This research aims to fill the gaps by investigating the vibration responses of tile panels and identifying appropriate approaches for debonding quantification. It introduces a more efficient standardised one-excitation, multiple-detection method, reducing testing points required and extending the capability to smaller debonding sizes. Numerical simulation and experimental studies were conducted, and responses were collected and analysed in the frequency domain. Both benchmark-based and benchmark-free approaches were proposed with relevant quantification indicators correlated to debonding size. It was found that the natural frequency and energy within the lower frequency band are effective indicators of the debonding size when a benchmark is available for comparison. In the absence of benchmark, the correlation coefficient between different quadrants of the tile panels is capable of quantifying the debonding size. Additionally, the quadrant where the defect is most likely located can also be identified.

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

AbstractOxide scales play a pivotal role in obstructing surface chemical and electrochemical reactions, hence hindering chemo‐mechanical effects such as liquid metal embrittlement of steels. Therefore, the critical conditions and failure mechanism of the oxide film are of major interest in the safe service of steels. Though in situ microscopic methods may directly visualize the failure mechanism, they are often challenged by the lack of statistically reliable evaluation of the critical conditions. Here, by combining in situ scanning electron microscopy with a tapered specimen tensile test in a single experiment, we uniquely achieve a mechanistic study with statistically reliable quantification of the critical strains for each step of the dynamic process of film rupture. This is demonstrated with the oxide films formed on a ferrite–martensite steel in liquid lead–bismuth eutectic alloy at elevated temperatures, with in situ results falling right into the predictions of the statistical analysis. Explicitly, the integrated experimental methodology may facilitate the materials genome engineering of steels with superior service performance.

Experimental determination for interlaminar tensile strength of reinforced epoxy composites with flax fibers for L-angle specimens

The growing demand of laminated composite materials made of natural fibers and resins with a lower environmental impact in different applications requires a more detailed understanding about the performance during its service considering the delamination in curved parts are one of the most critical failure mechanisms. The present study focuses on an experimental investigation and calculation of the interlaminar tensile strength of unidirectional flax/epoxy laminated curved beams featuring varying thicknesses. The assessment is conducted through a four-point-bending test, in accordance with the ASTM D6415 standard, and the outcomes are subsequently correlated with the employed formulae. The study also involves an examination of the formulation and methodology applicability for the ILTS calculation of unidirectional flax/epoxy laminated curved beams. The analysis includes the impact on maximum interlaminar tensile stress and the evolution of delamination in the flax/epoxy laminated curved beams post-failure behavior. These findings have significant implications for accurately predicting the interlaminar tensile strength and post-failure behavior of such laminated curved beams.

Face stability analysis of tunnels in saturated soil considering soil-fluid coupling effect via material point method

The stability of the tunnel face has been an important issue investigated by many scholars. To fully study the failure evolution of tunnel face and the hydro-mechanical behavior of surrounding soils in saturated stratum, a two-phase single-point material point method (MPM) considering the fluid–solid coupling effect is adopted to investigate this issue. Firstly, this proposed method is validated by comparing with the results obtained from the existing literatures. Secondly a series of MPM simulations are carried out to study the critical support pressure and failure mechanism of tunnel face in saturated soils. The arching effect range and inclination angle of failure soil in front of tunnel face are analyzed and determined. Finally, the post-failure mechanism of tunnel face is investigated. The run-out distance and the flow-in mass of failed soil in tunnel are calculated through the parametric analysis. The results show that MPM can well predict the whole failure process of tunnel face. The proposed method can provide useful guidance for practical tunnel designs.

Improved Performance of Lithium-Ion Batteries using a Multilayer Cathode of LiFePO4 and LiNi0.8Co0.1Mn0.1O2

<p>In Li-ion batteries, a thick electrode is advantageous for lowering the inactive current collector portion and obtaining a high energy density. One of the critical failure mechanisms of thick electrodes is inhomogeneous lithiation and delithiation owing to the axial location of the electrode. In this study, it was confirmed that the top layer of the composite electrode contributes more to the charging step owing to the high ionic transport from the electrolyte. A high-loading multilayered electrode containing LiFePO<sub>4</sub> (LFP) and LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub> (NCM811) was developed to overcome the inhomogeneous electrochemical reactions in the electrode. The electrode laminated with LFP on the top and NCM811 on the bottom showed superior cyclability compared to the electrode having the reverse stacking order or thoroughly mixed. This improvement is attributed to the structural and interfacial stability of LFP on top of the thick electrode in an electrochemically harsh environment.</p>

Centrifuge and theoretical study of the seismic response of anchored steel sheet pile walls in dry sand

Displacement-based approaches have been proven to be effective for the seismic design of gravity retaining structures. However, application of these methods to embedded flexible walls, such as anchored steel sheet pile (ASSP) walls, is still an open issue, as the factors affecting the accumulation of permanent displacements of these systems are not fully understood. This paper presents the results of four dynamic centrifuge tests on small-scale models of ASSP walls in uniform dry sand. The experimental results showed that ASSP walls can experience different failure mechanisms depending on their geometry and on the magnitude of accumulated displacements. During the earthquake, the system exhibits an overall increase of its seismic capacity, caused by: (a) progressive mobilisation of the soil passive strength; (b) sand densification; (c) rotation of the walls; and (d) reduction of the retained height. Accounting for these effects in pseudo-static limit equilibrium solutions improved the predictions of both the critical failure mechanism and the maximum internal forces in the structural members. Moreover, it allowed development of an efficient analytical tool for the prediction of the seismic permanent displacements of these systems, based on Newmark's sliding block approach.

Lateral ultimate bearing capacity of modified suction caisson in uniform and linearly increasing strength undrained clays

AbstractThe modified suction caissons (MSCs) have a cylindrical external skirt surrounding the top of the traditional suction caisson to increase the horizontal bearing capacity. MSCs will be subjected to inclined lateral loadings for anchoring offshore floating facilities, and the maximum lateral bearing capacity will be reached when the loading direction passes through the rotation center of the MSCs to generate horizontal translation in the seabed. This paper proposed an analytical model consisting of a meniscus failure wedge near the mudline and a purely lateral flow‐around mechanism in deeper soil for MSCs moving laterally in clays. The upper‐bound analysis is conducted to obtain the ultimate bearing capacity of MSCs by optimizing only one parameter to approach the critical failure mechanism that offers the minimum energy dissipation. The influences of the external skirt length (L) and radius (R) and adhesion factor (λ) at the caisson‐soil interface on the bearing capacity of MSCs are investigated. The finite element limit analysis (FELA) results are used to verify the rationality of the presented failure mechanisms and upper‐bound predictions. It is proved that the presented upper‐bound analyses can well predict the lateral ultimate bearing capacity of the MSCs with a horizontal translation failure.

Energy absorption and collapse behavior of PP‐based pin‐reinforced composite sandwich panels under quasi‐static flatwise compression loading

AbstractThis article investigates the energy absorption and failure behavior of thermoplastic composite sandwich panels made entirely of polypropylene (PP) and pin‐reinforced core under quasi‐static compressive loading. The pins are manufactured by thermoforming and assembled with face sheets. The specimens were subjected to flatwise compressive loading to examine energy absorption capabilities. Moreover, the finite element method (FEM) is used to analyze core sandwich panels reinforced with cubic, cylindrical, beam, and cross‐beam pins. Furthermore, a closed‐form analytical model is adopted and developed to predict the critical load of these structures. The performed experiments were utilized to validate the damage mechanisms and critical displacements of the simulations and the analytically calculated maximum collapse loads. The results demonstrate that the predictions accurately capture both the critical failure load and failure mechanisms. Since the numerical results have a reasonable correlation with the experimental results and their output difference is <15%, FEM is used to investigate the collapse behavior of the pin‐reinforced foam‐filled panels. A comparison of the load–displacement, specific energy absorption (SEA), and maximum collapse loads of the samples shows that the cubic reinforced foam‐core sandwich panel has the maximum peak load and SEA. The FE model of pin‐reinforced foam‐filled panels reveals that the buckling of the reinforcements is postponed to a point beyond the critical one. Hence, PP foam can act as lateral support and delay the ultimate failure in panels, especially pin‐reinforced cylindrical sandwich panels, up to 40%.

Mechanical performance and failure behavior of screw-bonded joints of aluminum sheets and cross-laminated birch veneer plates

Integrating wood-based lightweight components into advanced multi-material car bodies requires capable and reliable technologies for joining or bonding of dissimilar materials. Therefore, the present experimental study investigates hybrid lap joints of 1.5 mm-thick sheets of EN AW-6016-T4 aluminum alloy and 9 mm- or 13 mm-thick plates of cross-laminated 1 mm-thick birch veneers. Two self-cutting screws and single-component polyurethane-based adhesive were used for each joint. The mechanical performance and the fracture behavior were tested under both quasi-static and cyclic shear-tensile loadings. At each load condition fracture of the joint occurred, but neither fracture of the aluminum alloy sheet nor fracture of the veneer plate were observed. Debonding of the aluminum alloy sheet from the birch veneer plate was identified as critical failure mechanism. The adhesive provided the main contribution to both the static strength and the fatigue performance of the joints. However, the energy absorption of the joint was mainly determined by the pull-out resistance of the screws, which was dependent on the thickness of the veneer plate. To optimize the strength-to-weight ratio of the joint and to exploit the load-bearing potential of the materials, the focus should be placed on the improvement of the bonding conditions or on the adaptation of the sheet/plate thicknesses.

Data-driven subsurface modelling using a Markov random field model

ABSTRACT This paper presents a method of subsurface modelling based on a Markov random field (MRF) model called Potts model. Potts model is an undirected graphical model and has been applied in image processing such as image denoising, restoration and inpainting. The proposed method is simple and requires only a few borehole data on soil types in both training and inference stages. Current implementations of the Potts model require substantial data for training, and they are not suitable for subsurface modelling. The proposed method was demonstrated through numerical examples for 2D and 3D virtual grounds and a real case history. In the numerical examples, the effect of the number of training datasets on the estimation results was also investigated. The proposed method can provide not only the most probable inference of subsurface model but also the spatial distribution of geological uncertainty and is compatible with reliability-based analysis in geotechnical engineering. The spatial distribution of uncertainty is informative in its own right. It directs the engineer to focus on mechanically important zones where the critical failure mechanism passes through if they coincide with the low-accuracy zones.