Life Data

2 tools in the Reliability area.

Weibull Life Analysis

Life-data analysis of failure times with suspensions (units still running or removed unfailed): the two-parameter Weibull fitted by median-rank regression (Johnson's adjusted ranks, Bernard's or the exact median ranks, regression on Y with the X-on-Y alternative) and by maximum likelihood with the suspensions in the likelihood, Fisher-matrix confidence bounds on the shape and scale, on a B-life and on the reliability at a chosen time, the characteristic quantities of the fitted distribution (MTTF, median, B1 / B5 / B10, R(t), F(t), hazard rate, the time for a reliability target and the expected failures in a fleet), a lognormal and an exponential alternative compared by log-likelihood and AIC, the Kaplan-Meier nonparametric survival estimate with Greenwood standard errors, and three figures: the Weibull probability plot with the fitted lines, the hazard rate and the reliability curves of the three models over the Kaplan-Meier steps.

5 worked examples reproduced, listed on the tool page.

Accelerated Life

Accelerated life test data analysis: failure and suspension times pasted by stress level are fitted jointly by maximum likelihood to a life-stress model (Arrhenius with the activation energy in eV, inverse power law, Eyring, the temperature-humidity relationship and Peck's form) combined with a Weibull (common shape), lognormal (common slope) or exponential life distribution. The page reports the parameters with their standard errors from the observed information, the acceleration factor from every test level to the use condition, the life at use (median, mean, B1, B10 and a chosen B-life with normal-approximation confidence bounds), the reliability at an entered time at use, the likelihood-ratio tests of a common shape and of the life-stress relation against the separate fits of each level, the probability plot of every level with the common-slope lines, the life-stress plot and a stress table. The default case is the three-temperature Arrhenius-lognormal example of the NIST/SEMATECH e-Handbook (Sections 8.4.2.1 and 8.4.2.2), whose printed activation energy, slope, log-likelihood and likelihood-ratio statistic the page reproduces.

4 worked examples reproduced, listed on the tool page.

Other Reliability sections

System Models · Growth and Testing · Physics of Failure · Maintainability and Availability · Safety Analysis