To study failure

Visual inspection techniques are stressed as the most important tools used to study failures. This text is not a substitute for rigorous failure analysis conducted by experts, but it will help the reader identify and eliminate many cooling water system problems. Still, on occasion, the experienced, skilled, failure analyst using sophisticated analytical techniques and specialized equipment may be required to solve complex or unusual problems. Common sense, appropriate experience, and systematic investigation are, however, often superior to the more elaborate, but less effective, techniques used by some. 

XPS is used to evaluate surfaces prior to bonding yielding information which may relate to bond performance, as well as to study failure surfaces. The added advantage in XPS is that more sample types can be analyzed, such as nonconductive adhesive surfaces without the problems of charging found with other techniques such as AES, SIMS, and ISS. For this reason XPS is often the method of choice in post-fracture analysis. 

Initially, reliability studies in the rail industry focused on vehicles. Already in 1979 the need to study failures of traction motors in electric vehicles has been indicated (Plewako 1979). 

In this paper, the failure criterion developed in [1] was employed to study failure in a number of matrix-dominated laminates, such as [ 0]2s [i0/9O]s and some fiber-dominated 7t/4 laminates. For some 7t/4 laminates, test results showed that open-mode delamination could occur along interfaces adjacent to the 90° layer. Such failure of delamination depends on the stacking sequence of the laminate. Results indicated that the present method can also be used to predict the onset of open-mode delamination. 

A variety of experimental techniques have been employed to research the material of this chapter, many of which we shall not even mention. For example, pressure as well as temperature has been used as an experimental variable to study volume effects. Dielectric constants, indices of refraction, and nuclear magnetic resonsance (NMR) spectra are used, as well as mechanical relaxations, to monitor the onset of the glassy state. X-ray, electron, and neutron diffraction are used to elucidate structure along with electron microscopy. It would take us too far afield to trace all these different techniques and the results obtained from each, so we restrict ourselves to discussing only a few types of experimental data. Our failure to mention all sources of data does not imply that these other techniques have not been employed to good advantage in the study of the topics contained herein. 

Both friction and wear measurements have been used to study boundary lubrication of fuel because sticking fuel controls and pump failures are primary field problems in gas turbine operation. An extensive research program of the Coordinating Research Council has produced a baH-on-cylinder lubricity test (BOCLE), standardized as ASTM D5001, which is used to qualify additives, to investigate fuels, and to assist pump manufacturers (21). 

The most promising approach to laboratory techniques for predicting performance is to understand the mechanism of failure and then use iastmmental methods to study the susceptibiUty of a coating to failure. The most powerful tool available now is the use of esr spectrometry to monitor the rate of free-radical appearance and disappearance (117—119) (see Magnetic spin resonance). 

The accuracy of absolute risk results depends on (1) whether all the significant contributors to risk have been analyzed, (2) the realism of the mathematical models used to predict failure characteristics and accident phenomena, and (3) the statistical uncertainty associated with the various input data. The achievable accuracy of absolute risk results is very dependent on the type of hazard being analyzed. In studies where the dominant risk contributors can be calibrated with ample historical data (e.g., the risk of an engine failure causing an airplane crash), the uncertainty can be reduced to a few percent. However, many authors of published studies and other expert practitioners have recognized that uncertainties can be greater than 1 to 2 orders of magnitude in studies whose major contributors are rare, catastrophic events. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

The primary drawback to the application of XPS in adhesion science is associated with the limited spatial resolution of the technique. This can make it difficult to study processes that are highly localized, such as corrosion, or to accurately characterize certain types of failure surfaces where, for example, the locus of failure may pass back and forth between two phases. 

A significant development of the study was the use of event trees to link the system fault trees to (lie accident initiators and the core damage states as described in Chapter 3. This was a response to the ditficulties encountered in performing the in-plant analysis by fault trees alone. Nathan Villalva and Winston Little proposed the application of decision trees, which was recognized by Saul Levine a.s providing the structure needed to link accident sequences to equipment failure. 

Its unique design suggests several accident scenarios that could not occur at other reactors. For example, failure to supply ECC to 1/16 of the core due to the failure of an ECC inlet valve. On the other hand, some phenomena of concern to other types of reactors seem impossible (e.g., core-concrete interactions). The list of phenomena for consideration came from previous studies, comments of an external review group and from literature review. From this, came the issues selected for the accident progression event tree (APET) according to uncertainty and point estimates. 

The aim of the tests was to study tank-wall performance. Nevertheless, a few data on BLEVE effects are presented by Schulz-Forberg et al. (1984). An overpressure of 130 mbar was measured at 80 m from the tank position in one of the tests, and was attributed to combustion. Temperatures and pressures at the moment of tank failure were beyond the superheat limit 345-357 K and 24-39 bar, respectively (see propane data in Table 6.1). Fireball development from one test is presented in a series of photographs. The maximum diameter was approximately 50 m, and duration was approximately 4 seconds. Fragmentation data, to the extent published, are given in Section 6.3. 

Failure rates are computed by dividing the total number of failures for the equipment population under study by the equipment s total exposure hours (for time-related rates) or by the total demands upon the equipment (for demand-related rates). In plant operations, there are a large number of unmeasured and varying influences on both numerator and denominator throughout the study period or during data processing. Accordingly, a statistical approach is necessary to develop failure rates that represent the true values. 

Repair and maintenance records were analyzed to determine failure rates and distribution of failure modes. Preliminary findings are reported which include the Weibull distribution characteristics. Failure mode distributions are approximate. Overall mean-time-between-failure is given for the kiln, leach tank, screwfeeder, tank pump, tank gearbox, and kiln gearbox. The study was confined to an analysis of unscheduled repairs and failures. 

In medical follow-up studies on the length of survival of patients after treatment, contact with some patients may be lost or some may die from causes unrelated to the disease treated. Similarly, in engineering studies, units may be lost or fail for some reason unrelated to the failure mode of interest for example, a unit on test may be removed from a test or destroyed accidentally. 

Care must be taken to ensure that the criteria or methods used closely match the site-specific conditions under study. Failure to do so may result in early elimination of at-risk buildings from the analysis pool. Further, when standard criteria are being applied, care must be taken to ensure that the objective of the standard matches the intent of the study. A standard developed for equipment protection or loss prevention may not be appropriate for personnel protection. 

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