The Causes of Failure

Leaving aside abuse and gross faults that result in immediate failure, the cause of failure can be ascribed to one or more of a number of degradation agents covering both environmental and mechanical factors as listed in Table 1. 

Whilst many properties will change because of the environment, they will change at different rates and hence to different degrees. For example, fatigue life often deteriorates more rapidly than tensile strength with many synthetic mbbers hardness and modulus can rise appreciably whilst tensile strength remains virtually 

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Most fractography can be conducted with simple instmments such as a pocket magnifying eyepiece or an optical microscope. As with any detective work, it is important to maintain careful records and to pay close attention to details in the reconstmctions of the conditions under which fabrication and failure occurred. Seemingly unimportant details of fabrication, service, and/or the conditions under which failure occurred can frequently be the key to determining the cause of failure. 

Failure Mode and Ejfect Analysis (FMEA) This is a systematic study of the causes of failures and their effects. All causes or modes of failure are considered for each element of a system, and then all possible outcomes or effects are recorded. This method is usually used in combination with fault tree analysis, a quantitative technique. FMEA is a comphcated procedure, usually carried out by experienced risk analysts. 

The closer one is to the failure, the more its direct effects are apparent. The cumulative effects of failure are often overlooked in the rush to fix the immediate problem. Too often, the cause of failure is ignored or forgotten because of time constraints or indifference. The failure or corrosion is considered just a cost of doing business. Inevitably, such problems become chronic associated costs, tribulations, and delays become ingrained. Problems persist until cost or concern overwhelm corporate inertia. A temporary solution is no longer acceptable the correct solution is to identify and eliminate the failure. Preventative costs are almost always a small fraction of those associated with neglect. 

This represents the locus of all the combinations of Ca and Om which cause fatigue failure in a particular number of cycles, N. For plastics the picture is slightly different from that observed in metals. Over the region WX the behaviour is similar in that as the mean stress increases, the stress amplitude must be decreased to cause failure in the same number of cycles. Over the region YZ, however, the mean stress is so large that creep rupture failures are dominant. Point Z may be obtained from creep rupture data at a time equal to that necessary to give (V cycles at the test frequency. It should be realised that, depending on the level of mean stress, different phenomena may be the cause of failure. 

The pressure and temperature of a container s contents at the time of failure will depend on the cause of failure. In fire simations, direct flame impingement will weaken container walls. The pressure at which the container fails will usually be about the pressure at which the safety valve operates. This pressure may be as much as 20 percent above the valve s setting. The temperature of the container s contents will usually be considerably higher than the ambient temperature. 

When a coupling failure occurs, it is important to determine the cause of failure. Failure may result from a coupling defect, an external condition, or workmanship during installation. 

General corrosion damage was the cause of failure of an A1 alloy welded pipe assembly in an aircraft bowser which was attacked by a deicing-fluid — water mixture at small weld defects . Selective attack has been reported in welded cupro-nickel subjected to estuarine and seawater environments . It was the consequence of the combination of alloy element segregation in the weld metal and the action of sulphate reducing bacteria (SRB). Sulphide-coated Cu-enriched areas were cathodic relative to the adjacent Ni-rich areas where, in the latter, the sulphides were being continuously removed by the turbulence. Sulphite ions seemed to act as a mild inhibitor. 

A thorough study (cf. Ref. [40]) of failure modes in practice has shown that with this form of separation also the cause of failure has not been the separator the usual failure modes for leaf-type separators, as they have been described for sintered PVC separators, apply here as well. 

A time-and-motion modeling mind-set can easily blinker analysis of how best to improve the value created by research. Truly useful simulations of drug discovery must go beyond simplistic assumptions about yields at stage gates and address the causes of failure, starting to quantify the common concept of pipeline quality. ... 

These are not critical to lifetime unless misused and are not the cause of failure (or obsolescence) of the equipment. 

F.M. Gel fand V.S. Alipchenko, Ibid 1967, (63/20), 209-12 CA 69, 11865m (1968) [Reasons for a fail are and break in detonations in flooded coal mines were investigated, Expis Ammonit PZhV-20 and Uglenit E-6, coated with water-resistant material, were used in testing. (Compns are not given in CA). It was decided that the excess pressure of CH4 in flooded coal faces was the cause of failure and break of detonation]... 

To describe fully all the difficulties which beset the tyro in the manipulation of the various collodion processes, and to point out the causes of failure and the means of remedying them, would occupy too much space to be attempted In this work. In fact, each separate process, to be thoroughly explained arid discussed, would occupy a volume. There is, however, a strong analogy between them all, and a theory which appears to include them all. This the Editor will now proceed to discuss. 

There are several ways that actual joints can be tested. For quality control purposes, a proof test is commonly used, as described above. This test imposes a stress on the specimen but limits it to a point well below where any destruction of the joint can occur. This type of test only looks for serious flaws in the bonding processes such as interface contamination, air entrapment in the joint, or undercured adhesive. The prototype joints can also be tested to destruction by using similar test methods described above for standardized testing. This, however, is generally not done at great frequency because of the cost. Generally, most actual joint tests are performed to ascertain the cause of failure (i.e., forensic analysis of the failed joint) or for nondestructive determination of the adequacy of the bond. 

In the case of failure of a pipe made of polymeric material, the determination of Tg and 7m by thermochemical methods to ascertain the effects of thermal effects, determination of molecular weight and molecular weight distribution of the polymer, morphology of the sample or structure such as crystallinity and amorphous nature help to establish the cause of failure. 

What are the lessons learned from the failure of PAFC to become a commercial success and how do these lessons apply to other stationary fuel cell systems in development and demonstration Was the cause of failure only the high cost relative to the other DG systems The PAFC systems appeared to perform well. The federal government had spent more than 411 million on PAFC. Should it have continued... 

Drug disposition and metabolism are of essential significance in pharmaceutical research because of the interdependence of pharmacokinetic and pharmacodynamic processes. Limited intestinal absorption, inadequate distribution, fast metabolism, and toxic metabolites are some of the causes of failure of drug candidates during development. To reduce the rate of attrition resulting from such pharmacokinetic defects, disposition and metabolic studies should be initiated as early as possible in the screening of lead candidates. 

Another commonly used component is the capacitor. A capacitor is used to store electrical charge. Typically used in power suppHes and in timing circuits, these items are rarely the cause of failure in a system because all they do is store a charge and release it. Capacitors in a computer can be easily identified because they usually look like small metal cans or small disks with two connectors (Figure 1.5). 

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