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The life comparison and stress-strength tools include the Target Reliability Parameter Estimator, which allows you to explore how you could attempt to change one of the parameters in order to meet a specified target reliability. The plot and reliability estimate will be based on the altered distributions, and therefore may be appropriate only within the context of your specific "what-if” analysis.
To open the Target Reliability Parameter Estimator window, choose [Life Comparison/Stress-Strength] > Analysis > Parameter Estimator or click the icon on the control panel.
You can use the Target Reliability Parameter Estimator with any combination of distributions. The Weibull++ and ALTA versions of the tool are similar, except for one setting:
The Solve Parameters based on Coefficient of Variation (CV) check box is available only in the Weibull++ version of the tool and when the distributions are either both normal or both lognormal. Select the parameters to estimate and then enter the CV value. The tool will then estimate the parameters that would result in the target reliability.
The example shown next displays the Weibull++ version of the tool. In this example, the first data set shows the parameters of a Weibull distribution, while the second data set shows the parameters of a lognormal distribution. If we are trying to achieve a target reliability of 90% and select to estimate the beta of the first data set, then the tool will hold the rest of the parameters constant and estimate a beta value that would result in the 90% target reliability. For this example, the result is a beta estimate of 1.5200.
To see how the change in the parameter value affects the plot, click Update. The Target Reliability Parameter Estimator window will close and the plot will refresh. The control panel will display the new probability value or reliability estimate, as well as a status that indicates that the parameters have been altered.
For a practical example on how you might use the Target Reliability Parameter Estimator tool, see: http://www.ReliaWiki.org/index.php/Stress-Strength Analysis in Design for Reliability
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