Initial failure

The transverse (circumferential) fissures illustrated in Figs. 9.8 and 9.9 are similar to failures that had occurred in many tubes. All failures occurred near the tube sheet at the hot end of the exchanger (Fig. 9.10). The initial failure had occurred 3 years earlier. 

If an isotropic material is subjected to multi-axial stresses then the situation is slightly more complex but there are well established procedures for predicting failure. If a,i and Oy are applied it is not simply a question of ensuring that neither of these exceed ar- At values of and Oy below oj there can be a plane within the material where the stress reaches ot and this will initiate failure. 

The fragility analysis evaluates the conditional fraction of failure of plant structures and equipment as a function of ground motion. The seismically initiated failure of plant components is expressed in terms spectral acceleration at 5.0 Hz which is between the fundamental frequency of the... 

The demand-related exposure is the historical number of demands for change of state experienced by the equipment population. In theory, the evaluation of this demand exposure is rather simple. In practice, the number of demands on a piece of equipment can originate from four different sources testing, automatic and manual initiation, failure related maintenance, and interfacing maintenance. The contribution each of these categories makes to demand related exposures is summarized below ... 

Another aspect of epoxy resin mortar floorings which needs careful attention is that their coefficients of thermal expansion are approximately three times that of concrete. This, coupled with the relative low thermal conductivity of epoxy mortar, can cause stresses to be induced at the resin mortar/concrete interface under conditions of thermal shock (e.g. thermal cleaning), resulting in break-up of the flooring due to initial failure in the concrete. Two approaches have been tried to overcome this problem ... 

Poor mechanical properties of rubber products may also be due to matrix separation [257], Just as in other systems, separation gives rise to cavities and initiates failure. These processes prevail in systems with poor adhesion and become more probable with the increasing filler modulus. 

Drug treatment failures may result from a variety of factors. Initial failure to respond to a-adrenergic antagonists occurs in 20% to 70% of treated patients. It is likely in these patients that the static factor may predominate as the cause of symptoms in these patients. Initial failure to respond to 5a-reductase inhibitors occurs in 30% to 70% of treated patients. 

Creep leads ultimately to rupture, referred to as creep-rupture, stress-rupture or static fatigue. Creep-rupture of thermoplastics can take three different forms brittle failure at low temperatures and high strain rates ductile failure at intermediate loads and temperatures and slow, low energy brittle failure at long lifetimes. It is this transition back to brittle failure that is critical in the prediction of lifetime, and it is always prudent to assume that such a transition will occur [1], A notch or stress concentration will help to initiate failure. 

Moderate Wall tube External corrosion of wall tube on casing side. After initial failure, tube broke in two, allowing steam and water to enter furnace... 

The incident investigation team must look specifically for evidence that provides the point of initial failure, its progression path, and the preexisting conditions that led to the initiation. Having an understanding of a fundamental failure mode and the sequence of events, the investigator... 

Initial failures by Weitz and Scheffer to obtain epoxides from i-jrioemaldehyde or crotonaldehyde were presumably caused by excessive alkalinity in the reaction medium, and may be rectifiable by suitable pH control. 

For emergency cooling, it is critical that the temperature does not fall below the solidification point of the reaction mass. Otherwise a crust would form, resulting in reduced heat transfer, which again may favor a runaway situation. The remediation may then have worse effects than the initial failure. 

H.T. Hahn, S.W. Tsai On the behavior of composite laminates after initial failures. J. Comp. Matls. 8, 288-305 (1974)... 

ESC is mostly a surface-initiated failure of multiaxially stressed polymers in contact with surface-active substances. These surface-active substances do not cause chemical degradation of the polymer, but rather accelerate the process of macroscopic brittle-crack failure. Crazing and cracking may occur when a polymer under multiaxial stresses is in contact with a medium. A combination of external and/or internal stresses in a component may be involved. 

This intense and multifaceted goal-orientated search for the solution of a synthetic problem may have as an additional fringe benefit , an explosion-like accumulation of new information related to various areas of chemistry. In fact, the origin of many outstanding discoveries in organic chemistry can be traced to the initial failures of synthetic plans, to those misfires that prompted chemists to revise their current views. 

The other aspects of the definition state that if there is a fire and it is anticipated, the damage cannot be greater than the failure that was anticipated. If a pyrophoric fire is anticipated and safeguards are put in, but the fire bums down a unit, it was obviously not controlled since there was damage beyond the initial failure. The same is the case for injury to personnel as a direct result of the fire. (This does not include someone spraining an ankle while retrieving a fire extinguisher, for example). 

Figures 8.51 and 8.52 show differences between the behavior of polypropylene filled with glass beads at different temperatures. In both cases, the debonding between filler and the matrix requires the lowest level of energy and confirms that this is the most likely mode of failure. The volume fraction of filler has little effect on debonding, cavitation, and yielding at 0°C. At -6()°C, yielding is improved by increasing concentration of filler. Debonding is initiated at the poles and begins plastic yielding in the matrix which ultimately leads to failure. Strain required to initiate failure is reduced when the filler concentration is increased. ...

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