Failure-time ratio

Robert A, ChazouiEeres O. Prothrombin time in liver failure Time, ratio, activity percentage, or international normalized ratio Hepatology 1996 24 ... 

Figure 7.79 illustrates the influence of alloy composition on the potential dependence of the failure-time ratio of carbon steel in a carbonate-bicarbonate environment (Ref 116, 117). The failure-time ratio is... 

Survival and failure times often follow the exponential distribution. If such a model can be assumed, a more powerful alternative to the Log-Rank Test is the Likelihood Ratio Test. 

As we have already seen, there will be settings where the pattern of differences between treatment groups does not conform to proportional hazards, where the hazard ratio is not a constant, single value. Such situations are best handled by using an alternative model to incorporate baseline factors. The accelerated failure time model is an analysis of variance technique which models the survival time itself, but on the log scale ... 

Figure 3. Generalized design diagram used for structural ceramics showing minimum failure time os. applied structural load. Each curve represents a differed ratio of the proof test load to the service load.

Oven-aging of the 6-mil films was carried out at 140°C. The failure times are summarized in Table V. This table shows that at a DSTDP/ phenol ratio of 4/1, (Vile) gives better results than Phenol A. Vile gives the best results at high DSTDP/phenol ratios, whereas the opposite is observed for Phenol A. 

The reduction of degradation enhancement due to orientation is better seen when samples are stretched and then the time to fail, under UV radiation, is recorded. The results are shown in Fig. 6 where one should notice the break in scale for the reference (non-oxldlzed) sample. There is a drastic decrease in failure time (F.T.) for low draw ratios 1 < X < 1.7. This can be attributed to stored elastic energy which makes the chemical bonds more reactive toward UV, even at low stress levels. As X increases and the polymer structure becomes more and more oriented, F.T. Increases steeply before reaching a plateau once the orientation process is more or less completed. If we consider that photooxidation is oxygen diffusion controlled (1-5), the orientation effect is to decrease such diffusion by making the structure much more compact so that the degradation will be reduced. 

Figure 6. Failure time under UV exposure vs. uniaxial draw ratio of LDPE.

Table 1. The angles of critical failure surface (0 and 9 ), time ratio (t j T) and minimum value of...

The last time component, which should be estimated to assess the system availability ratio, is the expected failure time in a single renew cycle. The time depends on the failure probability in a given inspection period, assuming that at the moment of a previous inspection performance any defect has not been detected. It lays the foundation to define the following equation ... 

This paper deals with the PSA level-1 studies of a nuclear system with the possibility of recovery of some failed units during accident progressions. A scheme of PSA level-1 studies with the combination of partially dynamic repairable event tree and repairable fault tree is introduced. The quantification of repairable fault tree is performed based on the concept of up-time and down-time ratio for steady state system. A case study on the PSA of ASTRID DHR system with an initiating event is performed and found that repair of some units within the grace period during accident progression can reduce the CDF considerably. In future works, the proposed scheme would be implemented using dynamic reliability methods with the considerations of common cause failures and non-linear failure behaviors. 

Some trials [14] have measured the thermal expansion coefficients of some masonry parts (varying brick types) and studied the relationship between this ratio and the failure times for the same relation walls between thickness and slenderness. The results show that the structural performance of the walls significantly improved when reduces the coefficient of thermal expansion. 

In addition to the torque-rise behaviour the steepness of the curve may be expressed with the torque/time ratio, which is the stress/strain ratio, i.e., modulus. Between the two gum-rubbers in question, there is a significant difference in modulus. The gum rubber giving a steeper curve is stiffer than the other one. The peak may be interpreted as the failure point [4]. The stiffer rubber has a smaller strain to break and the softer rubber is more deformable. The former tends to fall in Region I of mill processability and the latter in Region II. The former may contain macrogel in a significant amount, if it is an emulsion-polymerised diene rubber. See Chapters 4 and 6 for additional information. 

In the present study we analyze the results of HDPE pipe sustain pressure test at elevated temperature and various hoop stress level (80 C 4.7 5.5 MPa). Some material properties are shown in Table 1. The failure time for each stress level is recorded, when the leak is observed. After the specimen failure, the fracture surface was inspected by optical and SEM microscopy to observe and characterize the fracture mechanism. All brittle fractures observed resulted from through cracks. A number of various size small cracks have also been developed at the time, when the largest crack(s) caused the le. In many cases, multiple through cracks were detected. It offers for analysis a set of cracks grown under the same controlled tenqierature and stress level. All the observed cracks have been originatod from inclusions. The size and location of an inclusion play an important role in failure time. A combination of random size and location of the inclusions results in a large scatter in failure time at the same applied stress, commonly reported for pipe failures [9]. A summary of plied stresses, failure time, inclusion size and location observed on the fracture surface is presented Table 2. The size of the inclusion is reported in wall thickness direction. The normalized apparent depth of inclusion location indicated in the Table 2, was measured as the ratio between the distance from the inclusion center to outer surface and... 

Practical probability is the limit of two ratios (Section 2.2). The numerator is the number of cases of failure of the type of interest (N) the denominator, the nonnalizing term is the time duration over which the failures occurred or the total number of challenges to the system. The former has the units of per time and may be larger than 1, hence it cannot be probability which must be less than 1. The latter is a dimensionless number that must be less than 1 and can be treated as probability. 

Results have been presented on one experiment. It involved a 5.659-m vessel containing 1000 kg of butane with a fill ratio of 39%. The vessel s contents were heated to 99°C, which is near but still below the supetheat-limit temperature, producing an internal pressure of 14.6 bar gauge. Vessel failure was then initiated. Measured pressure-time histories indicated that a number of separate pressure pulses occurred. They are plotted in Figure 6.6 as the overpressure-time relationship measured at 25 m from the vessel. 

Since most time-dependent failures have larger life dispersions, we must consider the maximum and minimum ratios of 4 1 and 40 1. Generally, relative life dispersion increases with the absolute value of MTBF. That is, wear items with a relatively short life expectancy such as rider rings on reciprocating compressors will have a comparatively smaller dispersion than components such as gear tooth flanks, which can be expected to remain serviceable for long periods of time. 

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