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Degradation Analysis Folio

User-Defined Degradation Models

The Weibull++ nondestructive degradation analysis folio includes the option to predict failure times based on a user-defined degradation model. To use this option, you must provide the equation that defines the model, as well as specify ranges and initial guesses for the software to use when fitting the model.

Entering User-Defined Equations

To define a new degradation model, choose User-Defined from the drop-down list in the Degradation Model area. Then enter the model's Name and a Formula that represents the degradation over time. The formula can include parameters with any name (e.g., b or beta), but it should include x as the random variable for time.

As an example, the linear degradation model is defined next.

To save the equation in the project for later use, click the Add to Templates link.

To select an equation that was previously saved, click the Select from Templates icon . This opens the Existing Equation Templates window, which shows a list of all the saved templates. The buttons at the lower left side of the window allow you to add, edit or delete templates.

Entering Ranges and Guesses for Parameter Estimation

After specifying the user-defined degradation model, click the Function Parameters icon to provide a starting point for estimating the parameters. The following example shows the parameter estimates for each unit ID in a particular data set.

For each Unit ID, enter the following values:

To reset all your inputs in this window to the defaults, click the Initialize Parameters icon .

 

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