Failure-in-time

To plan the tests correctly and economically requires knowledge of the performance of the material at the start. It is easy to select temperatures which lead to failure in times either too short to satisfy the standard, or too long to wait for. Adding a contingency for this adds considerably to the cost of testing. 

Failure in time (FIT) A rating equal to the number of failures in one billion (lO ) h. 

Failure in time (FIT) A unit value that indicates the reliability of a component or device. One failure in time corresponds to a failure rate of 10 per hour. 

Some standards hke the IS026262 [6] use the concept of failures in time (FIT) rather than MTBF and there are other important safety measures, e.g. mean... 

The objective of a service-life prediction (SLP) protocol is to provide the tools for estimating the functional life of a product without having to wait to measure time to failure in time-consuming, natural weathering tests. SLP can also be employed to... 

To elucidate the mechanism of failure in timing belts, measurements of the displacement in the cord and its vicinity were made and fatigue tests were carried out on the cord. The timing belt was of the rounded tooth STPD type. The study investigated which of the components of cyclic deformation belt interior in the belt interior initiate and promote cord failure. In particular, the curvature... 

The top failure metrics officially called PMHF (Probabilistic Metric for random Hardware Failures) in ISO 26262. It represents a comparable metric such as PFH (Probabilistic Failure per Hour) of lEC 61508. The top failure metrics of ISO 26262 focuses on failure probabilities, with which a safety goal could be violated, whereas PFH according to lEC 61508 is all about the probability of a danger through the system. Both target values of the metrics are specified in failure per hour (failure in time, FIT = lOE-9 h). Also in this case we assume an exponential distribution of the basis failure rate. The key difference between PFH and PMHF is that the PMHF is per safety goal and PFH for a safety-related system. The PFH considers mainly the probability that the system reaches in case of failure a de-energized safe state. 

Standard procedures that are used for testing of construction materials are based on square pulse actions or their various combinations. For example, small cyclic loads are used for forecast of durability and failure of materials. It is possible to apply analytical description of various types of loads as IN actions in time and frequency domains and use them as analytical deterministic models. Noise N(t) action as a rule is represented by stochastic model. 

It is easy to notice, that the protection against a short-circuit failure in the X-ray tube circuit implements due to the "soft" outer characteristic of the apparatus main circuit. The overvoltage protection at emergencies in the control system happens due to the redistribution of the magnetie flow, created by power winding I, between the 3,6 control yokes. Therefore the voltage on the X-ray apparatus anode drops approximately two times. 

Insufficient information about the properties, layout pattern of small defects, potential for their growth in time, usually leads either to an unjustified rejection (repair) or to underestimation of the importance of the defect and, as aconsequence, construction failure. Use of automated computerised means of control allows safe service of the old constructions, periodically repeating the UT and monitoring the development of discontinuities in the metal. The main idea of such policy is periodical UT of development of discontinuities or, in a more general form, monitoring of the metal condition. 

Depending on the length of time the interference processes are active, a distinction is made between short-term and long-term interference. Short-term interference is a rare occurrence resulting from a failure in a high-voltage installation... 

Depending upon the stress load, time, and temperature, the extension of a metal associated with creep finally ends in failure. Creep-rupture or stress-rupture are the terms used to indicate the stress level to produce failure in a material at a given temperature for a particular period of time. For example, the stress to produce rupture for carbon steel in 10,000 hours (1.14 years) at a temperature of900°F is substantially less than the ultimate tensile strength of the steel at the corresponding temperature. The tensile strength of carbon steel at 900°F is 54,000 psi, whereas the stress to cause rupture in 10,000 hours is only 11,500psi. 

When the utility can realistically be classed as "Normally Reliable" (fewer than one failure in 2 years) then its failure may be classed as a Remote Contingency event and the "1.5 Times Design Pressure Rule" may be applied. 

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. 

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