Relevant Failure Mechanisms Research Articles

Progressive failure analysis of laminates with an open hole subjected to compressive loading (OHC) using the enhanced semi-discrete modeling framework

The Open-hole compressive (OHC) strength of a fiber reinforced laminate is one of the most critical allowables for design of aerostructures. In this paper, results for predicting the OHC strength using the semi-discrete damage modeling framework are presented. The predictions are seen to capture experimentally observed failure mechanisms and measured failure loads. The constitutive model includes local axial compressive failure (and subsequent load bearing at a reduced plateau stress) while maintaining numerical robustness. Standard stacking sequences (quasi-isotropic, “hard” and “soft”) have been analyzed and compared to publicly available databases. Additionally, the model is challenged to predict delamination-dominated failure due to ply-scaling. Overall, the model is able to capture relevant failure mechanisms, while the ultimate loads are predicted with good accuracy. Therefore, this framework can be used with confidence in predicting OHC strengths of laminates.

Full field crack solutions in anti-plane flexoelectricity

In flexoelectric materials, strain gradients can induce electrical polarization. However, internal defects such as cracks profoundly affect the electromechanical coupling properties of flexoelectric solids. In particular, anti-plane cracks involve less physical fields, which are easier to study. In this study, we present a comprehensive and innovative investigation of the anti-plane crack problems in flexoelectric materials, including semi-infinite and finite-length anti-plane cracks. For the first time, we formulate a full-field solution for semi-infinite anti-plane cracks in flexoelectric media by applying the Wiener–Hopf technique. Furthermore, the collocation method and the Chebyshev polynomial expansion are used for the first time to derive the full-field hypersingular integral equation solution for finite-length anti-plane cracks in flexoelectric solids. In addition, a comparative analysis between the full-field and asymptotic solutions for semi-infinite cracks is performed, shedding light on the discrepancies in the representation of the electromechanical coupling behavior near the crack tip. The mixed finite element method is used to compare with the full-field solutions of finite-length cracks. The agreement between the numerical results and the full-field solutions demonstrates the rigor of our study. This research advances the knowledge of defects in flexoelectricity and provides significant insight into relevant failure mechanisms.

Disentangled representation learning with physics-informed variational autoencoder for structural health monitoring

The maintenance and replacement of aging infrastructure is becoming increasingly costly, as a large number of structures is approaching the end of its design lifetime. Labor intensive manual inspection and assessment on a large scale is often infeasible, while data-driven machine learning techniques can fail to identify relevant failure mechanisms and suffer from poor generalization to previously unseen conditions, particularly when data is sparse. We propose a multi-task learning approach based on a physics-informed variational autoencoder that leverages a dictionary of physics-based models to improve the predictive performance when limited data is available. The latent space of the autoencoder is augmented with a set of physics-based latent variables that are interpretable and allow for prior knowledge on the latent variables to be included in the autoencoder formulation. To prevent the data-driven components of the encoder and decoder from overriding the known physics, a regularization method is used to impose physical constraints on the latent space and the generative model prediction. The feasibility of the proposed approach is evaluated on a case study of quay walls in Amsterdam, demonstrating improved performance over purely data-driven methods.

Bearing capacity of perforated surface foundations on sand

ABSTRACT Perforated foundations find widespread use in supporting offshore structures. However, there is a limited exploration of the bearing capacity of both single and multiple perforated foundations under combined loading. The finite element method is used to calculate the effect of perforations on the bearing capacity of strip surface foundations on sand subjected to combined loading in this study. The normalized bearing capacity ratio and yield surface are used to present the variation of bearing capacity, and the variation is explained by the relevant failure mechanism. The outcome indicates that the critical perforation ratio is around 0.07, and the value depends on the perforation number and loading conditions. When the perforation ratio is less than the critical perforation ratio, the combined bearing capacity of the perforated foundation will not be reduced. The bearing capacity decreases with the perforation ratio, where the number and ratio of perforation determine the decline rate and the shapes of the yield surface.

Pragmatic seismic collapse meso‐scale analysis of old Dutch masonry churches

AbstractThe demand for advanced nonlinear time‐history and seismic collapse simulations of old unreinforced masonry (URM) constructions to support informed risk evaluation and mitigation plans is rapidly increasing in the structural engineering profession. On one hand, offering cutting‐edge solutions based on the latest advances is challenging for practitioners, given the reduced timeframe usually available for projects and the specialized knowledge required. On the other hand, researchers frequently face difficulties in accessing old buildings and gathering key data required in complex numerical collapse analysis strategies. In this work, a pragmatic approach for evaluation of the earthquake collapse response of vulnerable old URM churches typical of the Northern Netherlands, now exposed to low‐magnitude induced seismicity due to gas extraction, is presented. To bridge the gap between academic and industry applications, an integrated framework is proposed that combines archival and onsite research, code‐based prescriptions, geometrical characterization and simplified discrete element modeling. Main outcomes include the identification of recurrent damage patterns for five old URM churches erected during the 11th, 13th, 14th, and 19th centuries, representative of key traditional multi‐leaf and cavity‐wall structural types, as well as relevant failure mechanisms and collapsed debris distributions for seismic signals of varying intensities. Produced results constitute a solid foundation of data on which to base the design of ad‐hoc retrofits and development of tailored risk assessment models. This study opens a new line of inquiry while discussing practical challenges and research questions which arose, to be of interest to both applied researchers and structural engineering professionals.

A Review on Ceramic Matrix Composites and Environmental Barrier Coatings for Aero-Engine: Material Development and Failure Analysis

Ceramic matrix composites with environmental barrier coatings (CMC/EBCs) are the most promising material solution for hot section components of aero-engines. It is necessary to access relevant information and knowledge of the physical properties of various CMC and EBCs, the characteristics of defects and damages, and relevant failure mechanisms. Then, effective failure prediction models can be established. Individually assessing the failure of CMC and EBCs is not a simple task. Models considering the synergetic effect of coating properties and substrate fibrous architecture are more reasonable and more challenging. This paper offers a review and a detailed description of the materials features, failure mechanism, and failure modeling for both CMC substrate and EBC coatings. The various methods for failure analyses and their pros and cons are discussed. General remarks on technical development for failure modeling are summarized subsequently.

Asset management for blue-green infrastructures: a scoping review

Abstract Urban drainage systems have developed way beyond the traditional piped combined or separate sewer systems. Many ‘new’ systems are being introduced, ranging from stormwater infiltration facilities to green roofs. However, the widely advocated blue-green infrastructures are typically overlooked by asset managers, which will very likely have detrimental effects on their performance, service life, and wider adoption. In this paper, the working group on Urban Drainage Asset Management (UDAM – https://udam.home.blog/) of the IWA and IAHR Joint Committee on Urban Drainage discusses whether the state-of-the-art knowledge based on conventional sewer asset management is sufficient to develop asset management for blue-green infrastructures (BGIs). The discussion is structured around the five preconditions for effective control and asset management. Results show that asset management for BGIs is still underdeveloped due to a lack of monitoring techniques covering the broad range of BGI benefits and performance indicators, inspection techniques covering relevant failure mechanisms and models describing these mechanisms, maintenance and rehabilitation options, and sufficient support tools to aid inhabitants in the operation and maintenance of their individual BGIs such as green roofs or vegetated swales.

Predictive System Reconfiguration for Fulfillment of Future Mission Requirements

Equipment failures can cause major disruptions to system operations. Although this is the case for engineered systems in general, it is especially applicable to autonomous systems as an operation or maintenance crew may not be available to remediate the situation during operation. Autonomous vehicles, for instance, may be performing critical missions miles away from the nearest manned support personnel when a failure occurs. In this work we propose and test an approach for automated predictive reconfiguration of an autonomous vehicle with the goal of delaying the occurrence of failures that would otherwise compromise mission accomplishment. The proposed approach is based on the Monte Carlo Tree Search (MCTS) method and assumes the availability of models describing relevant failure mechanisms and the relation between degradation and performance for each failure mode. Our solution introduces novel means for taking into account the uncertainty resulting from estimation of relevant parameters and states , with benefits in terms of reduction of computational cost compared to existing solutions. The proposed approach is successfully tested in a simulation environment.

Mechanisms of rock slope failures triggered by the 2016 Mw 7.8 Kaikōura earthquake and implications for landslide susceptibility

Landslide failure mechanisms are influenced by topography, lithology, structure and rock mass damage – factors that also control landslide susceptibility. Failure mechanisms, however, are rarely considered in regional-scale coseismic landslide susceptibility analyses. In this study, we use 3D pixel tracking in pre- and post-earthquake aerial imagery, geomorphic mapping, rock mass characterisation, and geophysical ground investigations to develop conceptual models for three earthquake-induced landslides triggered by the 2016 Mw 7.8 Kaikōura earthquake on New Zealand's South Island. Analysis of two incipient landslides in Cretaceous greywacke illustrates the failure stages of a rock mass comprising multiple sets of closely-spaced and low persistence discontinuities. Conversely, analysis of a landslide in Neogene massive siltstones illustrates the role of high-persistence bedding planes in generating large translational rockslides. These two distinct mechanisms typify failures in highly deformed basement and overlying massive sedimentary rocks respectively, and highlight the link between rock mass damage, failure mechanism, and initiation. In greywacke failures, the rupture plane initiated close to the ridgetop and propagated as a joint-step-path failure along pre-existing, but low-persistence joints whereas the landslide in Neogene siltstone initiated by sliding along weak, high persistence, bedding planes near the base of the slope where topographic stresses are highest. Analysis of landslide displacements furthermore points out that the evolution of landslides is closely related to rock mass characteristics. In highly jointed Cretaceous greywacke, relatively little displacement is needed for rock mass disintegration and avalanching to occur whereas in Neogene siltstone, the landslide displaces as a coherent body - even at large displacements.Our results suggest that (1) failure mechanisms and, as a result, coseismic landslide susceptibility factors, may vary fundamentally in different geological settings; (2) characteristic spatial landslide displacement patterns may be used to remotely identify relevant failure mechanisms; and (3) the amount of displacement that can be accommodated before a failure transitions from sliding to avalanching, is highly dependent on material characteristics and topographic constraints.

Ductile fracture modeling using the modified Mohr–Coulomb model coupled with a softening law for an ASTM A285 steel

Ductile fracture is one relevant failure mechanism in pressurized metallic components such as pressure vessels and pipelines. This work describes a framework to model ductile fracture based on phenomenological critical local strain criterion coupled with softening law rule to predict the onset of ductile fracture and tearing response in typical geometries extracted from an ASTM A285 steel. Overall, the numerical predicted load vs. displacement curves are in good agreement with measured data for all samples. Detailed numerical analyses are also performed to investigate the strain capacity of defected pipes under internal pressure and axial loading.

Modeling approach to estimate the bending strength and failure mechanisms of glued laminated timber beams

The numerical simulation of four-point bending tests on glued laminated timber (GLT) beams requires an adequate description of the material behavior and of relevant failure mechanisms. The wooden lamellas, building up the GLT element, include knots, as a result of the natural tree growth process, which significantly affect the mechanical behavior. The variability of the morphology and arrangement of these knots lead to a large fluctuation, especially of strength properties, along the wooden lamellas. This leads to complex and, in general, quite brittle structural failure mechanisms of the GLT element. Such failure mechanisms can numerically be described with discrete cracks, using the framework of the extended finite element method (XFEM) for cracks without predefined positions or cohesive surfaces for cracks with predefined positions. In this work, a modeling approach to reliably estimate the bending strength and failure mechanisms of GLT beams subjected to four-point bending tests is proposed. Herein, the approach is validated by simulating replications of experimentally tested GLT beams of two beam sizes and strength classes, where each knot group is considered as a section with reduced individual stiffness and strength in exactly the same position as in the real beam. The results show that the application of quasi-brittle material failure may still result in a brittle global failure of GLT beams. The present study exemplarily shows how valuable insight into progressive failure processes can be gained by allowing the formation of continuous crack patterns. Moreover, a refined consideration of the knot geometries with such sophisticated realizations of discrete cracks may be able to simulate the actual failure mechanisms even more precisely.

Loss Estimation for Typical Adobe Façades of Cuenca (Ecuador) Due to Earthquake Scenarios

ABSTRACT A relevant percentage of the world population lives in constructions made of sun-dried earth, which are built according to several techniques such as rammed earth, bahareque or adobe. This work specifically focuses on the adobe buildings located in the Historic Centre of Cuenca (Ecuador), recognized as a World Heritage Site since 1999. Although these buildings are characterized by different geometrical and material configurations, all of them have load-bearing façade walls made of adobe. This paper illustrates an analysis of the seismic vulnerability of these adobe façade walls according to different geometrical configurations and considering an out-of-plane loading. This study is based on original in-situ collected data about 45 one and multi-storey buildings. The seismic behaviour of the case studies is investigated through a demand versus capacity analysis based on 5 different failure mechanisms and considering a variable intensity of the seismic action. This procedure has allowed to classify the case studies according to their seismic vulnerability and to identify the most relevant failure mechanisms in such adobe façades. As a main result, some continued fragility curves have been produced to allow replicating this procedure to buildings with similar features. Finally, a repair cost estimation after seismic scenarios is estimated.

Theoretical prediction model and failure mechanism map of human skull porous structures with quasi-static bending performance

A theoretical model has been developed to predict the bending properties and failure mechanism of the human skull. The structure of the skull bone, which is naturally a porous material, was obtained via non-destructive 3D micro-computed tomography. By considering the combined influence of curvature and porosity of the skull, the mid-span deflection of the skull bone loaded in three-point bending was calculated using theoretical prediction. The cranial bending peak load corresponding to several possible failure modes was also analyzed, and the relevant failure mechanism map was generated. The models also showed that the curvature is a critical consideration for accurate precisions to be achieved. To verify the reliability of the theoretical results, as well as to gain a good understanding of the intrinsic connections between internal geometric features and mechanical properties of the cranium, 3D finite element (FE) models, based on posteriorly reconstructed by 2D cranial scanning images, were developed. The bending properties of various reconstructed sections were studied in detail using the FE simulation models, leading to an understanding of the bending failure mechanism and crack propagation path. The numerical results of deflection and peak loads agree well with the theoretical results. In addition, the failure modes of the numerical models have been verified using published experimental results. This work has overall demonstrated that the theoretical and numerical models would provide a reliable basis for predicting cranial bending performance.

Midterm Survivorship of an Uncemented Hydroxyapatite-Coated Titanium Femoral Component and Clinically Meaningful Outcomes in Patients Older Than 75 Years.

Purpose: It remains controversial whether cementless femoral components are safe in elderly patients. The aim of this study was (1) to determine the stem survival rate in patients >75 years of age who were treated with an uncemented femoral component and (2) to report clinically significant results on a mid-term follow-up. Methods: 107 total hip arthroplasties (THA) were retrospectively evaluated in 97 patients over 75 years of age (mean age 78 years, range 75–87) treated with an uncemented femoral stem. The minimum follow-up was five years (mean 6.4 years, range 5–8). Stem survival rates, clinically meaningful outcomes, and incidence of complications were evaluated. Results: Kaplan-Meier survival analysis, with the endpoint revision for any reason, showed a 6.4-year survival rate of 98% (95% CI, 95–99%; 63 hips at risk). The survival rates were comparable for male and female patients (log-rank test, p = 0.58). The modified Harris Hip Score (mHHS) improved from 42.2 (12 to 85) points to 81.1 (22 to 97) points (p < 0.0001). Mid-term minimal clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptomatic state (PASS) were 25, 84, and 70, respectively. Conclusion: An uncemented stem is a viable option in patients over 75 years with good clinical outcomes and survivorship. Periprosthetic fractures were not a relevant failure mechanism with the stem used.

Low-velocity impact damage research on 2-dimentional UHMWPE/CF hybrid woven laminates under preloading

This paper provides a comprehensive understanding of the influence mechanism of preloading on low-velocity impact resistance of Carbon Fiber Reinforced Polymer Composite (CFRP) Laminates toughened with Ultra-high Molecular Weight Polyethylene (UHMWPE) fiber in the form of two-dimensional hybrid woven. An innovative preloading apparatus with patent number CN110426278A was developed to apply two kinds of preloading: uniaxial tension and uniaxial compression. Three-dimensional distribution of internal damage and failure patterns obtained by high-resolution optical imaging and X-ray computed tomography, together with Scanning Electron Microscope (SEM) were employed to explain the experimental findings and relevant failure mechanisms.

Seismic failure analysis of concrete bridges exposed to scour

Scouring has been known as one of the most frequent cause of failure observed in bridge infrastructures. Not to mention, the evaluation of scour mechanism sheds light on pile foundation design and helps to prevent scour induced structural deficiencies. Thus, the scouring mechanism around bridge pile foundations should be extensively evaluated in order to predict the bridge safety under critical multi-hazard environment. In this study, the local scour mechanism around bridge piles was appraised considering discrete element methods (p-y curves) in order to reflect the nonlinear nature of soil structure interaction (SSI). Following that, bridge seismic behavior and relevant failure mechanism was evaluated with regard to nonlinear time history analyses (THA). In the conducted research, river crossing 7 – span Boğaçay Bridge located in Antalya, Turkey was selected as the case study. After SAP2000 finite element modeling (FEM), the bridge was exposed to twelve incremental scour depths up to six meters at all piers and was subject to subsequent seismic effects as concordant to the site that mimics a probable earthquake occurs after scouring regarding the Turkish Earthquake Code (TEC-2018). The modal responses indicated a simultaneous increase in natural periods with augmenting scour depth. In the analyses, the influence of scouring on pier displacement demands, pier accelerations and the internal forces at piers and piles were investigated. The analysis results indicated a significant increase in pier displacement demands with increasing scour depth especially in the transverse direction of the bridge. Further, due to the migration and spreading of plastic hinging from piers to piles due to scouring, the internal forces that were resisted by the strong axis of the pier columns decreased significantly. This fact led to the increase in pile bending moments and rotations in both orthogonal directions of the bridge. Thus, it was concluded that the probable multi-hazard effects of scouring and earthquake in river crossing bridges should be considered in bridge substructure design.

Nested Newmark model to estimate permanent displacement of seismic slopes with tensile strength cut-off

Nested Newmark model(NNM) is a conceptual framework to assessing post-earthquake movements including dispersed shear movements. The original NNM omits that the tensile stresses would be encountered in slopes induced by earthquakes. The purpose of this study is to introduce the tensile strength cut-off and the relevant failure mechanism into NNM and conduct the limit analysis to determine the seismic displacement. Parametric studies are carried out to further investigate the influence of the tensile strength and input ground motions on permanent displacement. Neglecting the tensile strength can underestimate the permanent displacements of slopes. As the peak acceleration increases, the underestimation becomes more significant. With the reduction of tensile strength, much larger deformation occurs next to the slope crest. Although the present results are limited to an example, the method is of value in practice to predict the post-earthquake profile of slope.

Investigation of Active Power Cycling Combined With Passive Thermal Cycles on Discrete Power Electronic Devices

Active power cycling (APC) is a standardized and well-established method for reliability assessment and product qualification in power electronics (PEs) technologies. Repetitive pulses of load current are applied to cause cyclic thermal swings in the p–n junction and in the whole semiconductor device. They induce thermo-mechanical stresses, which ultimately leads to the typical interconnect failure in the “devices under test.” However, these tests are insensitive with respect to new automotive system architectures, in which PEs devices are exposed to additional loads besides the intrinsic thermal swings. The trends in PEs toward miniaturization, higher power density, heterogeneous system integration, and the deployment of PEs in harsher environments combined with longer lifetime and higher uptime requirements strongly increase the reliability demands in general and the need for more improved reliability assessment methodologies in particular. The new testing methods shall be more comprehensive and more efficient, i.e., they shall simultaneously cover the real service conditions better and reduce testing time. One promising approach is the combination of loading factors—such as the superposition of active power cycling by passive thermal cycles (TC). Both loading factors are well known to cause most relevant failure mechanisms in PEs. In reality, the PE devices are exposed to both factors simultaneously. Hence, this load case should also be replicated in the test. The paper will report a systematic investigation of such superimposed test schemes, which cover the case of self-heating and passive heating (from neighboring elements) of the PEs devices under real service conditions. Typical discrete PEs components in TO-200 packages are selected as test vehicles as they are likewise relevant for the domains of consumer or automotive electronics. The paper details the test concept and discusses the quantitative and qualitative test results.

Re-evaluating safety risks of multifunctional dikes with a probabilistic risk framework

Abstract. It is not uncommon for a flood defence to be combined with other societal uses as a multifunctional flood defence, from housing in urban areas to nature conservation in rural areas. The assessment of the safety of multifunctional flood defences is often done using conservative estimates. This study synthesizes new probabilistic approaches to evaluate the safety of multifunctional flood defences employed in the Netherlands and explores the results of these approaches. In this paper a case representing a typical Dutch river dike combining a flood safety function with a nature and housing function is assessed by its probability of failure for multiple reinforcement strategies considering multiple relevant failure mechanisms. Results show how the conservative estimates of multifunctional flood defences lead to a systematic underestimation of the reliability of these dikes. Furthermore, in a probabilistic assessment uncertainties introduced by multifunctional elements affect the level of safety of the dike proportional to the reliability of the dike itself. Hence, dikes with higher protection levels are more suitable to be combined with potentially harmful uses for safety, whereas dikes with low protection levels can benefit most from uses that contribute to safety.

Hardness matching of rail/wheel steels for high-speed-train based on wear rate and rolling contact fatigue performance

Hardness matching between rail and wheel is important for the safe and economic operation of high speed train. In this work, various hardness of 39.5, 36.8, 33.4, 30.5, 28.1 HRC were achieved in the wheel steels tempered at 748, 773, 793, 813, 833 K, respectively. Then the twin-disc fatigue test under 1000 MPa of Hertzian contact stress, 1676 r min−1 of rotating speed (i.e., 300 km h−1) and 0.7% of creepage was conducted using these tempered wheel steels and U71MnK rail steel with the hardness of about 32 HRC. Thus various hardness ratio of Hr/Hw (Hr is the hardness of rail and Hw is the hardness of wheel) including 0.81, 0.89, 0.96, 1.07 and 1.17 were achieved. Finally, wear resistance and rolling contact fatigue performance of the wheels as the function of Hr/Hw were evaluated and the relevant failure mechanism was discussed basing on the worn morphology and mechanical properties. The results indicated that wear rate of wheels increased with Hr/Hw. Furthermore, the wheel/rail couple presented the longest fatigue lifespan of 150 000 cycles when Hr/Hw was 0.96. Thus it can be concluded that the optimal hardness ratio of Hr/Hw was 0.96 basing on the less wear rate and the longest fatigue lifespan of the wheel/rail couples under high speed of 300 km h−1 due to the reasonable strength, ductility, toughness and hardness of the wheel steel tempered at 793 K.