Life test

Safe fatigue life testing for crack resistance. 

Example 4. A particular microprocessor (MPU) is assigned for a fuel-injection system. The failure rate must be estimated, and 100 MPUs are tested. The test is terrninated when the fifth failure occurs. Failed items are not replaced. This type of testing, where n is the number placed on test and ris the number of failures specified, is termed a Type II censored life test. 

The testing situation where the duration is specified (ie, time-tmncated) is termed Type I censored life testing. 

Confidence-Interval Estimates. Confidence-interval estimates for the expected hfe or rehabihty can be obtained easily in the case of the exponential. Here only the limits for failure-censored (Type II) and time-censored (Type I) life testing are given. It is possible to specify a test as either time- or failure-tmncated, whichever occurs first. The theory for such tests is explained in References 16 and 17. 

Time-Censored Life Tests. In this case the total test time T is specified. From the test, r failures are observed. The 100(1 — a)% two-sided confidence interval for the expected life is... 

Point Estima.tlon, This is a Type II censored life-testing situation where n items ate placed on test and the test is terrninated at the time of the th failure. The life test produces the ordered failure times. .. /. The estimator for 9 is... 

Success Testing. Acceptance life tests ate sometimes planned with no failures allowed. This gives the smallest sample size necessary to demonstrate a rehabiUty at a given confidence level The rehabiUty is demonstrated relative to the test employed and the testing period. 

Tool life tests are used to evaluate the effects of changes in tool materials, cutting variables, processing history, workpiece composition, or workpiece microstmcture. Tool life, T, and cutting speed, can be related by the following equation ... 

Guide for the statistical analysis of Thermal Life Test data Motor and generators ratings, construction, testing and performance... 

The GIDEP Reliability-maintainability Data Bank (RMDB) has failure rates, failure modes, replacement rates, mean time between failure (MTBF) and mean time to repair (MTTR) on components, equipment, subsystems and systems. The RMDB includes field experience data, laboratory accelerated life test data, reliability and maintainability demonstration test results. The... 

Shinha, S. K. and B. K. Kale Life Testing and Reliability Estimation. John Wiley Sons (Halsted), New York, 1980. 

When all units have failed, the result is complete data. Singly-censored data result in life testing when testing is terminated before all units fail. And multiply-censored data result from ... 

In some life-testing work, units are put on test at various times but are all taken off together this is done to terminate testing by some chosen time to meet a schedule. 

The battery system has reached more than 1700 cycles in life cycle tests. The calendar life of the /zebra battery has been proven to be close to five years in a continuing life test. In practical operation in cars the ZEBRA battery exceeded 110000 km within a three year period. This excellent result proves the ZEBRA battery to be a reliable system. 

For a criterion of failure, life tests should measure the time required for a material to deteriorate to a condition where it is no longer capable of performing its intended function. Careful analysis and testing are required to determine the most important condition or property at the time of failure or the point when a material becomes inadequate to its intended function. 

The second case concerns the results, published by du Pont, of actual service life tests... 

After obtaining the prototypes, tests must be made to determine the utility. Generally these include a short time destructive test to determine the strength and to check out the basic design. Another test that is done is to use the product in the projected environment with stress levels increased in a rational manner to make for an accelerated life test. Other tests may include consumer acceptance tests to determine what instructions in proper use are required, tests for potential safety hazards, electrical tests, self-extinguishing tests, and any others that the product requires. In the case of high risk products, the test program is continued even after the product enters service. 

IGT selected Harshaw Ni-0104T nickel-on-kieselghur catalyst formed in 4 X y in. cylindrical pellets for the initial catalyst charge to the methanation section of the HYGAS pilot plant. This selection was based on high activity over a range of temperatures (274°-516°C) and space velocities. Catalyst activity life tests were conducted for 1420 hrs without deterioration (Table I) consequently, we felt that suitable longevity could be obtained in the pilot-plant methanation reactors. 

Fig.2. HBr conversion during catalyst life testing in single full-scale reactor tube showing high conversion throughout the test. The brief time at lower conversion was due to a unit upset.

It is necessary to determine r) 9) under reaction conditions, and a life test should be included in any catalyst development effort. The data from this test will... 

Situation A cream that contains two active compounds was investigated over 24 months (incomplete program if today s ICH standards are applied, which require testing at 0, 3, 6, 9, 12, 18, and 24 months). The assays resulted in the data given in file CREAM.dat. Program SHELFLIFE performs a linear regression on the data and plots the (lower) 90% confidence limit for the regression line. For each full time unit, here months, it is determined whether this CL drops below levels of y = 90% resp. y = 95% of nominal. Health authorities today require adherence to the 90% standard for the end-of-shelf-life test, but it is to be expected that at least for some products the 95% standard will be introduced. 

Wearable Devices and Wireless Networks Tools for Pervasive Health Care In-Life Testing... 

Calibration and maintenance programs [45], challenge tests [2], accelerated shelf life tests [53], auditing [2], sensory tests [46], microbial tests [47]... 

The methodology described In this paper has evolved over the past ten years but still remains very elementary It was developed to minimize the exceptional hazards associated with the design and Implementation of accelerated life tests Many accelerated life tests can be characterized as expensive failures, due to the use of poor experimental designs. Inadequate scientific and statistical expertise, and Insufficient peer review prior to Implementation The methodology outlined below Is Intended to reduce such failures ... 

Bain, L. J. Statistlcal Analysis of Reliability and Life-Testing Models Marcel Dekker New York, 1978. 

Vertical media with very high coercivities can be produced by plating into alumina pores [112], Some of these media are too hard to be easily written with present heads. Tailoring of the pore size can be used to obtain structures with the desired Hc [115, 116], however. Recording characteristics of disks have been determined [112-114, 116] such media show excellent promise as vertical recording media. In addition, structures with electrodeposited Fe in the pores were tested in life-tests at elevated temperatures and humidity and in corrosive atmospheres. They were found to perform satisfactorily. 

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