Failure Sequence Research Articles

Dynamic tensile behaviours of heterogeneous rocks: The grain scale fracturing characteristics on strength and fragmentation

The dynamic tension behaviours of granites are tested with the split Hopkinson pressure bar and the quasi-static responses including the compression and Brazilian splitting are carried out with a material testing system. The experimental results show the tensile strengths behave significant strain rate effect. In order to characterize the realistic fracturing process from the viewpoint of grain scale failure, a multiple scale discrete element model considering the micro heterogeneity is proposed using the digital image processing of mineral scanning for rocks. Comparison of the experimental and numerical tension stress as well as the ultimate fragment state indicates the grain-based model is reasonable in simulation of dynamic tension test on granites. Then the three-wave superposition, crack propagation sequences, end forces and the stress distribution are discussed to confirm the stress equilibrium in the specimen. Using the microheterogeneous model, the micro fracturing process and fragmentation in association with energy dissipation at different strain rates are discussed. It is found that the failure sequence can be divided into five stages as crack initiation, propagation, coalesce, branching and indentation crush on the stress curve in dynamic loading. The intrinsic mechanism of the strain rate effect is believed to be the transitions of the micro fracturing type, orientation and the damage degree in the specimen and in turn exhibiting more energy dissipation as well as fragmentation transition from sparse fracture to pervasive pulverization. Finally, the scaling model of the dynamic increase factor for granite is derived and the characteristic strain rate, increase rate factor values are discussed.

Probability and Frequency Derivation Using Dynamic Fault Trees

Dynamic Fault Tree (DFT) is suitable to capture functional and dynamic dependencies among events leading to system failure. There exist several approaches for analyzing DFTs, each of them suffers from drawbacks that limit its practical use. This paper presents a comprehensive methodology based on the structure function determination. It consists in performing both qualitative and quantitative analysis to establish failure sequences and to calculate the likelihood (probability and frequency) of dynamic systems failure. Failure sequences are extracted from the minimal canonical form of the top event and allow getting disjunctive failure sequences. From the quantitative point of view, the probability and frequency of any DFT top event are developed to make the proposed model able to quantify the failure probability and frequency of dynamic systems and the frequency of accident scenarios. The proposed procedure is applied on two benchmark examples: the first one is a safety‐related system while the second one is an accident scenario with dependent protection layers. In order to check the validity of the proposed method, the derived numerical results are compared with those obtained from Markov Chains models. © 2018 American Institute of Chemical Engineers Process Saf Prog 37: 535–552, 2018

The Effect of High-Frequency, Structured Expert Feedback on the Learning Curves of Basic Interventional Ultrasound Skills Applied to Regional Anesthesia.

Proficiency in needle-to-ultrasound beam alignment and accurate approach to structures are pivotal for ultrasound-guided regional anesthesia. This study evaluated the effects of high-frequency, structured expert feedback on simulation training of such abilities. Forty-two subjects randomly allocated as controls or intervention participated in two 25-trial experiments. Experiment 1 consisted of inserting a needle into a bovine muscular phantom parallel to the ultrasound beam while maintaining full imaging of the needle. In experiment 2, the needle aimed to contact a target inside the phantom. Intervention subjects received structured feedback between trials. Controls received a global critique after completing the trials. The slopes of the learning curves derived from the sequences of successes and failures were compared. Change-point analyses identified the start and the end of learning in trial sequences. The number of trials associated with learning, the number of technical errors, and the duration of training sessions were compared between intervention and controls. In experiment 1, learning curves departed from 73% (controls) and 76% (intervention) success rates; slopes (standard error) were 0.79% (0.02%) and 0.71% (0.04), respectively, with mean absolute difference of 0.18% (95% confidence interval [CI], 0.17%-0.19%; P = 0). Intervention subjects' learning curves were shorter and steeper than those of controls. In experiment 2, the learning curves departed from 43% (controls) and 80% (intervention) success rates; slopes (standard error) were 1.06% (0.02%) and 0.42% (0.03%), respectively, with a mean difference of 0.65% (95% CI, 0.64%-0.66%; P = 0). Feedback was associated with a greater number of trials associated with learning in both experiment 1 (mean difference, 1.55 trials; 95% CI, 0.15-3 trials; P = 0) and experiment 2 (mean difference, 4.25 trials; 95% CI, 1.47-7.03 trials; P = 0) and a lower number of technical errors per trial in experiments 1 (mean difference, 0.19; 95% CI, 0.07-0.30; P = .02) and 2 (mean difference, 0.58; 95% CI, 0.45-0.70; P = 0), but longer training sessions in both experiments 1 (mean difference, 9.2 minutes; 95% CI, 4.15-14.24 minutes; P = .01) and 2 (mean difference, 7.4 minutes; 95% CI, 1.17-13.59 minutes; P = .02). High-frequency, structured expert feedback compared favorably to self-directed learning, being associated with shorter learning curves, smaller number of technical errors, and longer duration of in-training improvement, but increased duration of the training sessions.

FRAM for Systemic Accident Analysis: A Matrix Representation of Functional Resonance

Due to the inherent complexity of nowadays Air Traffic Management (ATM) system, standard methods looking at an event as a linear sequence of failures might become inappropriate. For this purpose, adopting a systemic perspective, the Functional Resonance Analysis Method (FRAM) originally developed by Hollnagel, helps in identifying nonlinear combinations of events and interrelationships. This paper aims to enhance the strength of FRAM-based accident analyses, discussing the Resilience Analysis Matrix (RAM), a user-friendly tool that supports the analyst during the analysis, in order to reduce the complexity of representation of FRAM. The RAM offers a two-dimensional representation which systematically highlights the connections among couplings, and thus even the highly connected group of couplings. As an illustrative case study, this paper develops a systemic accident analysis for the runway incursion happened in February 1991 at LAX airport, involving SkyWest Flight 5569 and USAir Flight 1493. FRAM confirms itself a powerful method to characterize the variability of the operational scenario, identifying the dynamic couplings with a critical role during the event and helping in discussing the systemic effects of variability at different level of analysis.

Crashworthiness assessment of double-hull tanker structures under ship grounding actions

Ship grounding is considered as a serious maritime accident which highly contributes to environmental pollution. This impact phenomenon attracts audiences to be studied and assessed since in an instantaneous moment, oil or waste from the damaged bottom tank can spill and contaminate wide water territory. In this study, grounding scenario is modelled as hard grounding where a rock geometry is chosen as representative of oceanic obstruction. The contribution of several main parameters, such as target component and oceanic obstruction are evaluated. The method is to apply a virtual experiment by nonlinear finite element (FE) method to conduct a simulation. A chemical tanker is taken as representative of a marine structure which is subjected to impact load on its bottom structure during interaction with the obstruction. The results indicate that the space between girders provides less resistance in the crushing process. The internal energy in this work is presented to estimate the strength capability of the impacted component, which is followed by the deformation pattern on the lower part of the bottom structure. Finally, the effect of the obstruction on failure sequences in grounding is summarised.

Remembering Financial Crises: The Risk Implications of the Rise of Institutional Investors in Project Finance

Barely a decade ago, a cascading sequence of market failures threatened to topple the global financial system. Public responses to the recent Financial Crisis were immediate and drastic to resuscitate the global economy while attempting to make the markets safer. Many financial services sectors have since recovered to pre-crisis levels. One such industry is project finance, which comprises various financing arrangements often used to fund long-term infrastructure or industrial projects. Curiously, significant post-crisis banking regulations and other global credit enhancement initiatives are pushing banks out of project finance and giving rise to institutional investors. This Comment argues that animated institutional activity in project finance may increase both financial and, more notably, governance risks. Further, increased institutional investment in project finance shifts the risk intended to be captured under new banking regulations to unregulated markets and makes the financial system more complex and interconnected. Ultimately, public responses to the Financial Crisis may have the unintended consequence of increasing project-level risks and injecting seemingly regulated systemic risk back into the global financial system.

Connection behaviour and the robustness of steel-framed structures in fire

The full-scale fire tests at Cardington in the 1990s, and the collapse of at least one of the WTC buildings in 2001, illustrated that connections are potentially the most vulnerable parts of a structure in fire. Fracture of connections causes structural discontinuities and reduces the robustness provided by alternative load paths. An understanding of connection performance is essential to the assessment of structural robustness, and so to structural design against progressive collapse. The forces and deformations to which connectionscan be subjected during a fire differ significantly from those assumed in general design. The internal forces i generally start with moment and shear at ambient temperature, then superposing compression in the initial stages of a fire, which finally changes to catenary tension at high temperatures. If a connection does not have sufficient resistance or ductility to accommodate simultaneous large rotations and normal forces, then connections may fracture, leading to extensive damage or progressive collapse of the structure. Practical assessment of the robustness of steel connections in fire will inevitably rely largely on numerical modelling, but this is unlikely to include general-purpose finite element modelling, because of the complexity of such models. The most promising alternative is the component method, a practical approach which can be included within global three-dimensional frame analysis. The connection is represented by an assembly of individual components with known mechanical properties. Component characterization must include high-deflection elevated-temperature behaviour, and represent it up to fracture.In reality a connection may either be able to regain its stability after the initial fracture of one (or a few) components, or the first failure may trigger a cascade of failures of other components, leading to complete detachment of the supported member. Numerical modelling must be capable of predicting the sequence of failures of components, rather than considering the first loss of stability as signifying building failure. It is necessary to use a dynamic analysis, so that loss of stability and re-stabilization can be tracked, includingthe movements of disengaging members and the loadsharing mechanisms which maintain integrity and stability within the remaining structure, until total collapse occurs.

Connection behaviour and the robustness of steel-framed structures in fire

The full-scale fire tests at Cardington in the 1990s, and the collapse of at least one of the WTC buildings in 2001, illustrated that connections are potentially the most vulnerable parts of a structure in fire. Fracture of connections causes structural discontinuities and reduces the robustness provided by alternative load paths. An understanding of connection performance is essential to the assessment of structural robustness, and so to structural design against progressive collapse. The forces and deformations to which connectionscan be subjected during a fire differ significantly from those assumed in general design. The internal forces i generally start with moment and shear at ambient temperature, then superposing compression in the initial stages of a fire, which finally changes to catenary tension at high temperatures. If a connection does not have sufficient resistance or ductility to accommodate simultaneous large rotations and normal forces, then connections may fracture, leading to extensive damage or progressive collapse of the structure. Practical assessment of the robustness of steel connections in fire will inevitably rely largely on numerical modelling, but this is unlikely to include general-purpose finite element modelling, because of the complexity of such models. The most promising alternative is the component method, a practical approach which can be included within global three-dimensional frame analysis. The connection is represented by an assembly of individual components with known mechanical properties. Component characterization must include high-deflection elevated-temperature behaviour, and represent it up to fracture.In reality a connection may either be able to regain its stability after the initial fracture of one (or a few) components, or the first failure may trigger a cascade of failures of other components, leading to complete detachment of the supported member. Numerical modelling must be capable of predicting the sequence of failures of components, rather than considering the first loss of stability as signifying building failure. It is necessary to use a dynamic analysis, so that loss of stability and re-stabilization can be tracked, includingthe movements of disengaging members and the loadsharing mechanisms which maintain integrity and stability within the remaining structure, until total collapse occurs.

Reliability Model of Consecutive $(2, k)$ -Out-of-( $2, n$ ) :F Systems With Local Load-Sharing

Most previous reliability models of consecutive k-out-of-n system assume that the components are independent or their reliabilities are equal. The system reliability can be obtained according to the configuration of $k$ consecutive failed components. However, for consecutive $(2,k)$ -out-of- $(2,n)$ systems with local load-sharing, workloads on failed components will be equally shared by both vertically and horizontally adjacent components. Consequently, the component failure probability density function (FPDF) may be unequal and dependent on the actual load (both original and sharing load), which is determined by the states of adjacent components. Furthermore, the component FPDF may be time-varying with the failure sequences of adjacent components. Therefore, reliability modeling must consider the component dynamic process determined by the failure sequences of adjacent components, instead of the static configuration determined by failure states of adjacent components in the traditional models. To solve the above issues, this paper develops a new reliability model for consecutive $(2,k)$ -out-of- $(2,n)$ systems with local load-sharing. The system and component dynamic processes are automatically searched and combined into a set of state transition paths. In each path, the component load-varying process can be confirmed, by considering the influence of adjacent failures on its shared load. Based on the state transition paths, the component and system reliability models are further derived, according to the confirmed load processes of each component. Finally, we present graphical illustrations of the reliability evaluation of cable-strut systems in long-span suspension bridges.

Estimation for Expected Energy Not Served of Power Systems Using the Screening Methodology of Cascading Outages in South Korea

The uncertainty of complex power systems increases the possibility of large blackouts due to the expectations of physical events, such as equipment failures, protection failures, control actions failure, operator error, and cyber-attacks. Cascading outage is a sequence of dependent failures of individual components that successively weaken the power system. A procedure to identify and evaluate the initiating events and perform sequential cascading analysis is needed. In this paper, we propose a new screening methodology based on sequential contingency simulation of cascading outages, including probabilistic analysis and visualization model. Performance of a detail cascading analysis using practical power systems is suggested and discussed. The proposed screening methodology will play a key role in identifying the uncontrolled successive loss of system elements.

A compact nonlinear dynamic analysis technique for transmission line cascades

Progressive failures, or cascades, have played a major role in numerous transmission system collapses around the globe during severe wind and ice storms. The failure of a line component overloads the system and initiates a failure sequence that can cause the collapse of many towers. This article describes the development of a special-purpose nonlinear dynamic analysis technique for the modelling of multi-span line sections under progressive failure scenarios. This method performs time-domain analysis based on a central finite difference scheme, adapted for a non-constant time increment. All the main line components are incorporated in the analysis. In particular, a special beam-column element is employed to describe geometric and material nonlinearities of angle members in steel lattice towers. The method is validated using full-scale test results for a single lattice tower and a line section containing seven towers.

3D geomechanical model tests on asymmetric reinforcement and overall stability relating to the Jinping I super-high arch dam

The deformation and failure of deep soft rock roadways become more prominent. In this paper, two true triaxial model tests were carried out to investigate the deformation and failure law of deep soft rock roadway excavation and the stability characteristics of the surrounding rock after the support. The surrounding rock stress and roadway deformation characteristics can be divided into three stages: advance influence, rapid change and stability. The deformation and failure sequence during the excavation process of the model roadway is “vault → sidewalls → arch springing → roof collapse”. Roof stability is the top priority. After the supporting structure is applied, the surrounding rock stress increases obviously and the roadway deformation decreases. The model test results are verified through field monitoring, and the key deformation parts of the deep soft rock roadway and the characteristics of the supporting structure force are clarified, which can provide reference for later research.

Thermal barrier coatings with interface modified by 3D mesh patterns: Failure analysis and design optimization

AbstractSurface patterning of the bond coat using a three‐dimensional mesh offers a promising approach to improve the durability of the thermal barrier coatings (TBCs), in which the geometry parameters of the mesh play a vital role. The objective of this work is to investigate the failure behavior of the air‐plasma sprayedTBCs with mesh, and to identify the optimal mesh design. The study revealed that the failure sequence of theTBCs with mesh patterns consisted of (I) initiation of the interfacial and ridge cracks (around the top of the mesh); (II) cracks propagation and buckling of theYSZlayer; (III) interfacial cracks deflection and coalescence with ridge cracks, leading to final spallation. The critical parameters governing each step of the failure sequence were discussed and proposed. For a typicalTBCs withYSZthickness about 200 μm, the critical mesh heighthand spacing lengthLis about 110 μm and 7 mm, respectively, when the mesh widthwis fixed at about 480 μm.

Engine to wing structural design under critical loads caused by a propeller blade loss

To support the propeller blade loss loads in a turboprop aircraft the engine mounting system has to be carefully designed. The joints have to withstand the flight loads, however, during the blade loss event they have to fail before the wing gets damaged. Using a FEM model and Monte Carlo simulation techniques the possible failure sequences for a broad spectrum of flight conditions have been obtained, including different propeller frequencies, blade loss sizes, angular positions where the blade is lost and also material properties. The structural model includes non-linear behavior, damages, and several types of failure together with stochastic variables which can incorporate parameter uncertainties. Finally, the pylon to wing support is designed to guarantee, with high level of confidence, no major hazard on the aircraft due to this dynamical phenomenon.

Experimental study to identify premonitory factors of landslide dam failures

Identifying premonitory factors before final failure for long-existing landslide dams is of high importance in disaster prevention and risk reduction. In this study, a series of large-scale (outdoor) experiments were designed and conducted to identify premonitory factors that may be used in failure prediction for actual landslide dams. Surface deformation, especially dam-crest settlement, dam seepage-water turbidity and self-potential across the dam crest were selected as the target parameters. Changes in these parameters showed apparent correlations between each other. Based on the monitoring data obtained and the observation performed during the tests, the deformation and failure sequence of the dam model can be separated into four time-sequential periods: 1) Emergence of seepage water and front wetting. In this period, the monitoring parameters did not show any obvious changes. However, wetting was observed in the downstream face. 2) Hyperconcentrated flow discharge. In this period, water flowed out of the drainage channel, and the vertical deformation of the dam body became obvious, while the turbidity of the seepage water increased. 3) Emergence and development of cracks on the dam crest. In this period, the dam-crest settlement also increased. 4) Sudden collapse and final failure. In this period, self-potential across the dam crest decreased rapidly, and the dam-crest settlement reached a peak value. Therefore, dam-crest settlement, seepage-water turbidity and self-potential changes can be regarded as premonitory factors of landslide dam failure.

Failure Prognosis of High Voltage Circuit Breakers with Temporal Latent Dirichlet Allocation

The continual accumulation of power grid failure logs provides a valuable but rarely used source for data mining. Sequential analysis, aiming at exploiting the temporal evolution and exploring the future trend in power grid failures, is an increasingly promising alternative for predictive scheduling and decision-making. In this paper, a temporal Latent Dirichlet Allocation (TLDA) framework is proposed to proactively reduce the cardinality of the event categories and estimate the future failure distributions by automatically uncovering the hidden patterns. The aim was to model the failure sequence as a mixture of several failure patterns, each of which was characterized by an infinite mixture of failures with certain probabilities. This state space dependency was captured by a hierarchical Bayesian framework. The model was temporally extended by establishing the long-term dependency with new co-occurrence patterns. Evaluation of the high voltage circuit breakers (HVCBs) demonstrated that the TLDA model had higher fidelities of 51.13%, 73.86%, and 92.93% in the Top-1, Top-5, and Top-10 failure prediction tasks over the baselines, respectively. In addition to the quantitative results, we showed that the TLDA can be successfully used for extracting the time-varying failure patterns and capture the failure association with a cluster coalition method.

Sublinear-Time Maintenance of Breadth-First Spanning Trees in Partially Dynamic Networks

We study the problem of maintaining a breadth-first spanning tree (BFS tree) in partially dynamic distributed networks modeling a sequence of either failures or additions of communication links (but not both). We present deterministic (1+ϵ)-approximation algorithms whose amortized time (over some number of link changes) is sublinear in D , the maximum diameter of the network. Our technique also leads to a deterministic (1+ϵ)-approximate incremental algorithm for single-source shortest paths in the sequential (usual RAM) model. Prior to our work, the state of the art was the classic exact algorithm of Even and Shiloach (1981), which is optimal under some assumptions (Roditty and Zwick 2011; Henzinger et al. 2015). Our result is the first to show that, in the incremental setting, this bound can be beaten in certain cases if some approximation is allowed.

11.34: Cross‐aisle seismic behaviour of drive‐in rack systems

ABSTRACTThis paper presents the results obtained from a comprehensive series of earthquake tests carried out on fully loaded drive‐in steel storage racks. The earthquake waveforms used are actual ground motion records obtained from various locations around the world. The ground motions were applied in the cross‐aisle direction, in which the frames are made of a series of couples of uprights interconnected by diagonal braces to form upright frames. The upright frames were fully braced from top to bottom, and presented the most commonly used system configuration in the industry. In the tests, the 3D structural response was recorded to understand the global behaviour of drive‐in rack systems. The paper also presents the sequence of failures of different components that occurred during the tests, and the impact of these on the system behaviour.

Bending overload and thermal fatigue fractures in a cast exhaust manifold

Abstract The left exhaust manifold of a Ford Y-Block engine failed at two different locations after nearly fifty years of service. A study was conducted in order to determine if the main causes and the sequence of failure of this component were related to its operation. A detailed analysis comprising materials characterization, fractography and a thorough finite element modeling was carried out. The results showed that the normal operation of the engine induced several thermal fatigue cracks, which were primarily located in the outermost runners of the component. One of these cracks propagated unstably during the operation, producing one of the fractures. The other one was generated during an overhaul, when a bending load and an improper assembly condition propagated a preexisting crack. In addition, the presence of a mixed graphite distribution comprising A, B and D flake graphite compromised the mechanical properties of the exhaust manifold, and aided in the process of crack propagation.

The Use of LOM, SEM, FIB and APT to Clarify the Sequences of Failure of a Hot Dip Galvanized Structural Steel Section

Journal Article The Use of LOM, SEM, FIB and APT to Clarify the Sequences of Failure of a Hot Dip Galvanized Structural Steel Section Get access Michael Panzenbóck, Michael Panzenbóck Department of Physical Metallurgy and Materials Testing, Montanuniversitát Leoben, Austria Search for other works by this author on: Oxford Academic Google Scholar Caroline Freitag Caroline Freitag Department of Physical Metallurgy and Materials Testing, Montanuniversitát Leoben, Austria Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 326–327, https://doi.org/10.1017/S1431927617002318 Published: 04 August 2017