Individual Failure Modes Research Articles

Study of Risk Evaluation System of High Arch Dam Based on Failure Mechanism

In view of the randomness in terms of high arch dam load, resistance and failure calamity loss as well as the fuzziness in terms of evaluation conclusion, a high arch dam risk evaluation system is established by means of risk analysis method. Natural factors, structural factors and human factors that lead to high arch dam failure are summed up on the basis of statistics. Through qualitative analysis coupled with quantitative estimation, it is determined that high arch dams generally involve five major failure modes: abutment rock mass destabilization, excess cracking, arch dam & dam foundation entire destabilization, extreme dam-overflow and destabilization of dam body along base plane. The state functions of individual major failure modes are established. An approach is made to the correlativity among the major failure modes and among the random variables within individual failure modes, and it is suggested that risk rate, economic loss risk value and life loss risk value should be used to assess the risk of high arch dams. A certain high arch dam abutment instability risk evaluation has been provided.

An acoustic emission study on the fracture behavior of continuous glass fiber/polypropylene composites based on commingled yarn

AbstractThe fracture behavior of continuous glass fiber reinforced polypropylene composites made of commingled yarn in the form of biaxial (±±45°) noncrimp warp‐knitted fabric, twill woven fabric, and swirl mat, respectively, was investigated by virtue of single edge notched tensile (SEN‐T) specimens. These composite laminates were manufactured by compression molding and cooled at two different rates (1°C/min and 10°C/min) during the last processing phase of the laminates. The failure mechanisms were studied by acoustic emission (AE) analysis. AE amplitude ranges corresponding to the individual failure modes have been identified. For biaxial noncrimp fabric reinforced materials, the failure mechanisms involved in the fracture procedure are governed by the interface related failure events. Higher cooling rate, which is accompanied by better fiber/matrix adhesion, results in not only the increase in the relative proportion of high‐amplitude failure events, but also the occurrence of a large quantity of fiber fracture events. For woven fabric and mat reinforced composites, fiber‐dominated failure mechanisms result in the higher fracture toughness when compared with biaxial noncrimp fabric composites. Under this circumstance, the change in cooling rate only results in the difference in the relative frequency of the individual failure modes. In addition, it is found out that the initiation fracture toughness of SEN‐T specimens can be easily assessed by marking the load value which corresponds to the first point of AE signals emitted stably in AE events‐displacement curves. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Component and system reliability analysis of nonlinear reinforced concrete grids with multiple failure modes

The bending moment redistribution is an inherent behavior in reinforced concrete grids, which increases the number of possible critical cross-sections susceptible to reach a limit state. Despite the fact that its influence could be important, the high number of failure cross-sections is not often considered in reinforced concrete reliability analyses. In this paper, a local approach of reliability analysis applied to grid structures is developed by taking into account the dominant failure modes. This approach is based on random sampling coupled with finite element analysis, through the use of a localized response surface technique. A mode selection strategy has been developed to capture the individual failure modes in order to classify their importance in the global system reliability. For large-scale systems, this procedure intends to reduce the global computational time in the reliability analysis. Numerical applications aim to show the effect of internal force redistribution, as well as the efficiency of the proposed approach and the interest of considering multiple failure modes.

Adaptive Optimal Sampling Methodology for Reliability Prediction of Series Systems

Simulation-based system reliability prediction may require significant computations, particularly when the expected value of the system failure probability is relatively low. A methodology is presented for variance reduction of sampling-based series system reliability predictions based on optimal allocation of Monte Carlo samples to the individual failure modes. An algorithm is presented for adaptively allocating samples to member failure modes based on initial estimates of the member failure probabilities pi. The methodology is demonstrated for a simple series system and a gas-turbine engine disk modeled using a zone-based series system approach. For the example considered, it is shown that the computational accuracy of the method does not appear to depend on the initial pi estimate. However, the computational efficiency is highly dependent on the initial pi estimate. The results can be applied to improve the efficiency of sampling-based series system reliability predictions.

Risk Based Acceptance Criteria for Joints Subject to Fatigue Deterioration

Different approaches to determine the acceptance criteria for fatigue induced failure of structural systems and components are discussed and compared. The considered approaches take basis in either optimization (societal cost-benefit analysis) or are derived from past and actual practice or codes (revealed preferences). The system acceptance criteria are expressed in terms of the maximal acceptable annual probability of collapse due to fatigue failure. Acceptance criteria for the individual fatigue failure modes are then derived using a simplified system reliability model. The consequence of fatigue failure of the individual joints is related to the overall system by evaluating the change in system reliability given fatigue failure. This is facilitated by the use of a simple indicator, the Residual Influence Factor. The acceptance criteria is thus formulated as a function of the system redundancy and complexity. In addition, the effect of dependencies in the structure on the acceptance criteria are investigated. Finally an example is presented where the optimal allocation of the risk to different welded joints in a jacket structure is performed by consideration of the necessary maintenance efforts.

Wear of rocks by water flow

The paper summarises recent results obtained from wear and erosion tests performed on rocks and cementitious composites. A definition of relevant wear types is given. Experimental facilities, failure modes, threshold conditions, parameter influence, and resistance parameters are discussed for jet fluid erosion, hydro-abrasive erosion, drop impact erosion, and cavitation erosion. No single failure mode determines the response of the materials to any of the investigated wear types. The individual failure mode depends on certain process parameters, on material structure, and in some cases on the testing facilities. Threshold conditions for failure introduction are discussed. All wear types are characterised by selective material removal. It seems that non-linear fracture effects (such as tension-softening) play a notable role in certain impact situations.

Reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation

AbstractThis paper presents an extension of reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation. The probability that a product fails on a specific mode is derived. Using this probability, the dominant failure mode on the product can be predicted. A practical example is presented to analyze an electronic device with two kinds of major failure modes–solder/Cu pad interface fracture (a catastrophic failure) and light intensity degradation (a degradation failure). Reliability modeling of an individual failure mode and device reliability analysis is presented and results are discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Improved nuclear power plant operations and safety through performance-based safety regulation

This paper illustrates some of the promise and needed future work for risk-informed, performance-based regulation (RIPBR). RIPBR is an evolving alternative to the current prescriptive method of nuclear safety regulation. Prescriptive regulation effectively constitutes a long, fragmented checklist of requirements that safety-related systems in a plant must satisfy. RIPBR, instead, concentrates upon satisfying negotiated performance goals and incentives for judging and rewarding licensee behavior to improve safety and reduce costs. In a project reported here, a case study was conducted concerning a pressurized water reactor (PWR) emergency diesel generator (EDG). Overall, this work has shown that the methods of RIPBR are feasible to use, and capable of justifying simultaneous safety and economic nuclear power improvements. However, it also reveals several areas where the framework of RIPBR should be strengthened. First, researchers need better data and understanding regarding individual component-failure modes that may cause components to fail. Not only are more data needed on failure rates, but more data and understanding are needed to enable analysts to evaluate whether these failures become more likely as the interval between tests is increased. This is because the current state of failure data is not sufficiently finely detailed to define the failure rates of individual component failure modes; such knowledge is needed when changing component-specific regulatory requirements. Second, the role of component testing, given that a component has failed, needs to be strengthened within the context of RIPBR. This includes formulating requirements for updating the prior probability distribution of a component failure rate and conducting additional or more frequent testing. Finally, as a means of compensating for unavoidable uncertainty as an obstacle to regulatory decision-making, limits to knowledge must be treated explicitly and formally. This treatment includes the formulation of probabilities through expert solicitation and the review of risk-informed, performance-based and engineering analyses used to evaluate proposed changes to existing technical specifications.

Failure cost design of structural systems

A systematic design approach based on applying weights to modes of failure is proposed. Representative individual failure modes are identified on the limit state surface using a nonlinear structural analysis program. Modal failure probabilities are computed in load space (in which randomness in structural resistance is included), and linearized around mean plastic moment capacities. Single- and multi-objective formulations with objectives of failure cost and initial cost, and with mean plastic moment capacities of structural members as decision variables are used. An iterative procedure with successively tighter bounds on the decision variables is employed. The procedure is applied to a simple frame for which optimum plastic moment capacities (single-objective case) and a trade-off curve between future (failure) cost and initial cost (multi-objective case) are found.

Multiparametric Limit Analysis of Frames: Part II—Computations

A systematic computational approach is developed for the generation of n‐dimensional global‐polyhedral‐limit hypersurfaces for frames. The maximal facets of the polyhedra are shown to correspond to unique failure modes. Algorithmic procedures are described for the identification of limit hypersurfaces and the individual failure modes. Bending‐moment distributions at collapse for each failure mode, load combinations leading to a given mode, and modal correlations can be obtained. Other structural properties of polyhedra are explored and illustrated with examples.

First order vs. second order reliability analysis of series structures

The paper presents an extension of the first order reliability method for computation of failure probabilities. The improvement is achieved by a better approximation to the limit state surface. The analysis is demonstrated for individual failure modes and for series structures. The results obtained are very close to ‘exact’ results obtained by simulation. The method is seen as a supplement to first order reliability methods for special cases. It is not meant to completely replace these methods.

Reliability analysis techniques for the design engineer

This paper describes a fault tree analysis package that eliminates most of the housekeeping tasks involved in proceeding from the initial construction of a fault tree to the final stage of presenting a reliability analysis in a safety report. It is suitable for designers with relatively little training in reliability analysis and computer operation. Users can rapidly investigate the reliability implications of various options at the design stage and evolve a system which meets specified reliability objectives. Later independent review is thus unlikely to reveal major shortcomings necessitating modification and project delays. The package operates interactively, allowing the user to concentrate on the creative task of developing the system fault tree, which may be modified and displayed graphically. For preliminary analysis, system data can be derived automatically from a generic data bank. As the analysis proceeds, improved estimates of critical failure rates and test and maintenance schedules can be inserted. The computations are standard—identification of minimal cut-sets, estimation of reliability parameters and ranking of the effect of the individual component failure modes and system failure modes on these parameters. The user can vary the fault trees and data on-line and print selected data for preferred systems in a form suitable for inclusion in safety reports. The programs, which are written in FORTRAN for an IBM 370, can accommodate up to 500 basic faults and 500 gates. Their application to a system with 355 basic faults and 285 gates is described.

Reliability-based optimization under random vibration environment

A methodology of formulating the optimum design problem for structural systems with random parameters and subjected to random vibration as a mathematical programming problem is presented. The proposed method is applied to the optimum design of a cantilever beam with a tip mass and a truss structure supporting a water tank. The excitations are assumed to be Gaussian processes and the geometric and material properties are taken to be normally distributed random variables. The probabilistic constraints are specified for individual failure modes since it is easier to specify the reliability level for each failure mode keeping in view the consequences of failure in that particular mode. The time parameter appearing in the random vibration based constraints is eliminated by replacing the probabilities of failure by suitable upper bounds. The numerical results demonstrate the feasibility and effectiveness of applying the reliability-based design concepts to structures with random parameters and operating in random vibration environment.

Optimum design of structures with random parameters

A general formulation of the minimum-weight optimization problem for indeterminate structures with random parameters is presented. The formulation enables the designer to specify maximum allowable probability of system failure and maximum allowable probabilities of occurrence of individual failure modes. All random parameters are characterized by their mean values and coefficients of variation, with the latter assumed to be amenable to realistic estimation at the outset. The standard deviations of response quantities are then obtained in a straightforward manner for use in the constraint equations, which generally resemble those for deterministic optimization problems. Several examples of truss and frame designs illustrate applications of the formulation.