Delayed failure

An additional issue in fiber strength is that of fatigue (22), which can produce delayed failure of a fiber. Fatigue is thought to be caused by a surface reaction of fiber and OH causing the growth of subcritical flaws to the point where fracture occurs. 

System models assume the independent probabilities of basic event failures. Violators oithis assumed independence are called Systems Interactions, Dependencies, Common Modes, or Common Cause Failure (CCF) which is used here. CCF may cause deterministic, possibly delayed, failures of equipment, an increase in the random failure probability of affected equipment. The CCF may immediately affect redundant equipment with devastating effect because no lime is available for mitigation. If the effect of CCF is a delayed increase in the random failure probability and known, time is available for mitigation. 

Barth, C. F., Steigerwaid, E. A. and Troiano, A. R., Hydrogen Permeability and Delayed Failure of Polarised Martensitic Steels , Corrosion, 25, 353 (1969)... 

In the majority of cases, the tests are conducted using a dead-weight lever-arm stress-rupture rig with an electric timer to determine the moment of fracture, but a variety of test rigs similar to those shown in Fig. 8.89g are also used. The evaluation of embrittlement may be based on a delayed-failure diagram in which the applied nominal stress versus time to failure is plotted (Fig. 8.103) or the specimen may be stressed to a predetermined value (say 75% of the ultimate notched tensile strength) and is considered not to be embrittled if it shows no evidence of cracking within a predetermined time (say 500 h). Troiano considers that the nature of delayed fracture failure can be described by four parameters (see Fig. 8.103) ... 

Fig. 8.103 Schematic representation of delayed failure characteristics of a hydrogenated high-...

Delayed Failure see under Sustained Load Failure. 

The water-vapour action causing the delayed-failure reaction is an activated process similar to corrosion of silicates in an aquatic environment. Following the chemical reaction, an unstable compound is formed... 

Liquid metal-induced embrittlement (LMIE), particularly solid metal-induced failure result in accelerated brittle failure on normally ductile metals under applied or residual stresses when in contact with liquid or solid low-melting point metal. SMIE was first noted as the delayed failure of steels in solid Cd environments. 

Figure 7.93 Overall image of the fracture surface of nano-Ni after delayed failure in the presence of Hg...

P. F. Becher and T. N. Tiegs, Elevated-Temperature-Delayed Failure of Alumina Reinforced with 20 vol% Silicon Carbide Whiskers, J. Am. Ceram. Soc., 73[1], 91-96 (1990). 

It may be of interest to note here that the failure of glass exhibits a dependence on time. For example when a constant stress of the order of magnitude of K/c is applied, the time-to-failure varies inversely as the applied stress. On the contrary if the applied stress is continuously increased such as to keep a constant strain rate, stress-to-failure varies directly as strain rate. These are manifestations of delayed failure which is due to the phenomenon of fatigue. Observations made under constant stress measures the static fatigue while the observations under constant strain rate conditions measure dynamic fatigue. The difference in... 

Tressler, R.E., K.L. Rugg, S.W. Martz, and S.A. Newcomb. 1995. Delayed failure of ceramic fibers at elevated temperatures. Pp. 375-380 in High-temperature ceramic-malrix composites 11 manufacturing and materials development. Vol. 57 in Ceramic Transactions, A.G. Evans and R. Naslain (eds.). Westerville, Ohio American Ceramic Society. 

S Roy and J N Reddy, A finite element analysis of adhesively bonded composite joints with moisture diffusion and delayed failure , Computers Structures 1988 29(6) 1011-1031. 

Strength degradation with decreasing stress rate in brittle materials is known to occur by slow crack growth (delayed failure or fatigue) of an initial crack, and is expressed as ... 

Hydrogen embrittlement is brought about, when the material absorbs evolved hydrogen during some processes. Some examples are acid pickUng, electrolysis, and uses in various vaporized atmospheres. It sometimes leads to fractures. Usually, the phenomenmi nfight occur after a long time. Therefore, it is often called delayed fracture or delayed failure . 

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