摘要 :
The gradual deployment of Electro Mechanical Actuators (EMAs) as primary flight controls actuators, driven by the "more electric" approach, must be paired up with a solid prognostic background in order to overcome the limited expe...
展开
The gradual deployment of Electro Mechanical Actuators (EMAs) as primary flight controls actuators, driven by the "more electric" approach, must be paired up with a solid prognostic background in order to overcome the limited experience and to support the system during his lifecycle. In fact, assessing EMAs actual states thanks to Prognostic and Health Monitoring (PHM) systems and detecting potential failures is crucial to guarantee the compliance to the relative safety requirements. The research activity described in this paper focuses on the development of a model-driven deterministic methodology based on Failure Modes Maps (FMMs). Thanks to data obtained through a Numerical Test Bench (NTB) and a Simplified Model (SM), the proposed prognostic algorithm is proved capable of detecting and identifying the source and magnitude of two different failures: rotor eccentricity and increased friction. After a short description of the implemented models and a general overview of typical EMA failure modes as well as FMMs development, the proposed algorithm is explained in detail. This is followed by a comprehensive study of the two simulated failures as well as the creation of the relative FMMs. Finally, the proposed prognostic algorithm is successfully applied on the obtained FMMs.
收起
摘要 :
Background: Early right ventricular failure (RVF) is common after left ventricular assist device (LVAD) implantation and often leads to increased morbidity and mortality. It is difficult to predict early RVF on the basis of clinic...
展开
Background: Early right ventricular failure (RVF) is common after left ventricular assist device (LVAD) implantation and often leads to increased morbidity and mortality. It is difficult to predict early RVF on the basis of clinical and hemodynamic parameters. We investigated the utility of mean arterial pressure (MAP) to central venous pressure (CVP) ratio in predicting early RVF.
收起
摘要 :
Sloping structures have gained increasing interests in recent years due to their capability of breaking the incoming level ice in a dominant bending failure mode. However, 'level ice' is a theoretical simplification. A typical ice...
展开
Sloping structures have gained increasing interests in recent years due to their capability of breaking the incoming level ice in a dominant bending failure mode. However, 'level ice' is a theoretical simplification. A typical ice field in the Arctic consists of discontinuous ice features, such as ice floes of varying sizes. This forms a naturally broken ice field. As Arctic exploration and exploitation advance into deeper waters, floating structures are usually employed with support from ice management operations to manually create a broken ice field. Therefore, a general approach towards ice-sloping structure interactions, in which the floe size is a major variable, is proposed in this paper. In this context, two failure modes have been frequently observed, i.e., the local out-of-plane flexural failure and the global in-plane splitting failure mode. Depending on the size of the floe ice, the out-of-plane flexural failure mode can further be categorised into: 1) direct rotation of a small ice floe, 2) radial/circumferential cracking of a finite size ice floe, and 3) circumferential crack formation within a semi-infinite ice floe. These categories together with the in-plane failure mode make a total of four possible failure scenarios for floe ice. One contribution of this paper is the search for analytical closed-form solutions to evaluate the aforementioned four failure scenarios. Substantial efforts have been directed towards transferring an existing closed-form solution based on the Symplectic Mechanics to estimate the critical force that causes the radial/circumferential cracking failure scenario. In addition, previously published analytical solutions were compiled to examine the critical force that causes the remaining three failure scenarios. With the available analytical solutions, we quantify different failure scenarios' competitions. Particularly, failure maps can be constructed according to the floe size, ice thickness and associated ice material properties. The compiled analytical solutions can be easily implemented within a multi-body dynamic simulator to examine the performance of sloping structures in an ice field covering a large temporal and spatial scale. (C) 2015 Elsevier B.V. All rights reserved.
收起
摘要 :
In this work, the failure mechanisms of GFRP/PVC foam core sandwich structures subjected to three-point bending are analysed. By varying the skin thickness (t) and the span length between supports (l), experimental tests were carr...
展开
In this work, the failure mechanisms of GFRP/PVC foam core sandwich structures subjected to three-point bending are analysed. By varying the skin thickness (t) and the span length between supports (l), experimental tests were carried out in order to find the relationship between the geometrical configuration of the sandwiches and the failure mechanism. By plotting failure mechanism on a graph of l against t, a failure map was created identifying the three typical failure mode regions of these sandwiches. The graph clearly shows the failure mode corresponding to each combination of l and t. To help optimise the use of these sandwich beams as structural elements, a theoretical failure mode map was constructed. The theoretical model results were consistent with the experimental ones, and so we can conclude that the theoretical model is a reliable predictor of failure mechanisms in sandwiches with defined geometry.
收起
摘要 :
Past few decades have seen an upsurge in failure analysis techniques capable of dealing with reliability issues up front in the early stages of the product development process. Most of these approaches are centered on component-sp...
展开
Past few decades have seen an upsurge in failure analysis techniques capable of dealing with reliability issues up front in the early stages of the product development process. Most of these approaches are centered on component-specific failures. However, with the advent of highly complex systems that derive functionalities from multiple physical phenomena domains, more emphasis is required on identifying failures arising due to various system interactions, which is largely absent in existing failure analysis approaches. Owing to the causal nature of system interaction failures, the use of cognitive maps in system modeling and simulation for failure analysis is highly suitable. This paper proposes a structured framework for the development and use of cognitive map-based system models capable of capturing all types of failure modes, including interaction failures. The applicability of the proposed framework is demonstrated with the example of an electric water heater.
收起
摘要 :
Competing failure modes are investigated for circular sandwich plates comprising quasi-isotropic E-glass/epoxy composite faceplates (with [-60/0/60]_(ns) configuration) and polyvinyl chloride (PVC) foam core under bending. Clamped...
展开
Competing failure modes are investigated for circular sandwich plates comprising quasi-isotropic E-glass/epoxy composite faceplates (with [-60/0/60]_(ns) configuration) and polyvinyl chloride (PVC) foam core under bending. Clamped sandwich plates are loaded using flat-ended punch at the center of the plate. Three competing failure modes, viz., core indentation, core shear and face failure/microbuckling, are considered. Analytical estimates for elastic response (stiffness) and initial failure load are proposed, and these are verified by experimental measurements and finite element (FE) predictions. Good agreement (with in ± 20%) is observed among analytical estimates, experimental measurements and FE predictions. Analytical estimates for the failure modes are used to plot the failure mode map in non-dimensional plate radius versus faceplate thickness plane for a given material system. The failure mode map thus constructed is assessed by considering a few sandwich plate geometries. Normalized sandwich mass and failure load contours are superimposed onto the failure mode map to identify the locus of minimum weight design by numerical search. Effect of geometrical parameters of the sandwich plate on failure load and mode is also investigated.
收起
摘要 :
The rapid evolution in technology is leading to complex engineering systems confounding the problems of failure analysis processes. Earlier efforts have concentrated on failure analysis of components but have proven insufficient f...
展开
The rapid evolution in technology is leading to complex engineering systems confounding the problems of failure analysis processes. Earlier efforts have concentrated on failure analysis of components but have proven insufficient for analysing the complex physical systems. In this paper, a cognitive map-based approach suggested by Augustine et al. (2012) for system interaction failure analysis is further improved to develop populated network structure considering structural variation. The numerical values to causal arcs are assigned considering qualitative linguistic variables to represent causal relationship between two nodes. The structural variability in cognitive maps due to input from experts or sources is addressed by effectively combining the cognitive map diagrams (networks) and related information received from several sources into single network diagram. A combined adjacency matrix is developed considering credibility weight assigned to each experts. The proposed approach is capable of capturing system interaction failures as well as component failures, which is useful at the early stage of design. A relatively complex physical engineering system of fuel injection is presented as an example to demonstrate the effectiveness of the proposed approach.
收起
摘要 :
With the development of different technologies, the use and importance of Enterprise Resource Planning (ERP) systems continue to increase daily. In parallel with this increasing use, a lot of research is being done to successfully...
展开
With the development of different technologies, the use and importance of Enterprise Resource Planning (ERP) systems continue to increase daily. In parallel with this increasing use, a lot of research is being done to successfully complete ERP implementation projects. However, despite these researches, reported case studies show that the success rates of ERP projects are meager.Based on the examples of experienced failure, researchers determine very different failure factors with varying perspectives for companies in different industry sectors, cultures, and sizes. It is becoming increasingly difficult for many practitioners and researchers to understand these failure factors correctly. Our objective is to investigate the state-of-the-art ERP Failure Factors that could benefit practitioners to utilize that information potentially.We review the body of knowledge related to ERP failure factors in the form of a systematic literature mapping (SLM). We pose four sets of research questions and systematically develop and refine a classification schema. The initial pool consisted of 353 articles. Systematic voting was conducted among the authors regarding the inclusion/exclusion criteria. As a result, there were 72 technical articles in our final pool.This SLM provides an overview of ERP critical failure factors (CFF) with different focused headings. These headings cover qualitative coding about CFF names, CFF rankings, the relation between CFF and ERP processes and failure modes, etc.The results of this study would benefit three groups of stakeholders: (i) Researchers who work on ERP Failure Factors, (ii) Solution implementers who provide consultancy services to companies that carry out ERP Implementation projects, and (iii) ERP project implementation managers. These stakeholders could utilize the results of this SLM to catch the trend of ERP implementation challenges.
收起
摘要 :
The mechanism of load transfer within the bolted joint of a laminate sheet made from ultra-high molecu-lar weight polyethylene (UHMWPE) plies is investigated both experimentally and by an analytical model. The nature of load trans...
展开
The mechanism of load transfer within the bolted joint of a laminate sheet made from ultra-high molecu-lar weight polyethylene (UHMWPE) plies is investigated both experimentally and by an analytical model. The nature of load transfer and the active failure mechanisms are obtained as a function of joint ge-ometry and of the lateral clamping force on the faces of the laminate (by pre-tensioning of the bolt). A combination of X-ray tomography and optical microscopy reveal that the dominant failure mechanism in the clamped joint is shear failure involving splits of the 0 ° plies and sliding at the interface between the 0 ° and 90 ° plies. A simple analytical model is developed for this shear failure mechanism and, upon not-ing the competing failure mechanisms of bearing failure, bolt shear and of tensile failure of the 0 ° plies, a failure mechanism map is constructed in terms of the geometry of the bolted joint, for the case of no pre-tension of the bolt. The analytical model for shear failure suggests that the enhancement in joint strength with increased pre-tensioning of bolt is due to the fact that the shear strength of the UHMWPE increases with increasing hydrostatic pressure.
收起
摘要 :
Background Myocardial extracellular volume (ECV) accumulation is one of the key pathophysiologic features of heart failure with preserved ejection fraction (1117pEF), Our aims were to (1) measure ECV by cardiac magnetic resonance ...
展开
Background Myocardial extracellular volume (ECV) accumulation is one of the key pathophysiologic features of heart failure with preserved ejection fraction (1117pEF), Our aims were to (1) measure ECV by cardiac magnetic resonance TI mapping using the modified Look-Locker inversion recovery (MOW) sequence, (2) validate MOLLI-ECV against histology, and (3) investigate the relationship between MOLLI-ECV and prognosis in IIEpEF.
收起
原文获取