Reliability HotWire: eMagazine for the Reliability Professional
Reliability HotWire

Issue 26, April 2003

Tool Tips

*When conducting analysis using the General Log-Linear life-stress relationship in ALTA 6, how do I specify the stress relation for each selected stress column?

You can specify the type of stress in each stress column using the Stress Relation window. Once you have entered your data and selected the General Log-Linear life-stress relationship, the Stress Relation icon will become enabled, as shown in Figure 1. Note: this functionality is available only in ALTA 6 PRO.

Figure 1: Enabled Stress Relation icon.

Click the icon or select Stress Relations from the Data menu to open the Stress Relation window. For each stress column selected to be used in the calculations, you will be able to specify the type of transformation to be applied. The Stress Relation window and the available stress relations are shown in Figure 2.

Available stress relations

Figure 2: Stress Relation window and available stress relations.

As you can see from Figure 2, there are three stress relations from which to select. 

  • None (V=X): is an exponential type transformation and is the default stress relation. This type of relation is commonly used for thermal type stresses. It is also used for indicator variables, such as 0 (switch off) and 1 (switch on). Selecting this type of relation is also equivalent to using the Proportional Hazards model.

  • Reciprocal (V=1/X): is an exponential type transformation. This is most commonly used for thermal type stresses.

  • Logarithmic (V=ln(X)): is a power type transformation. This is typically used for non-thermal type stresses.

Once you have selected the stress relations to be applied, click OK. The Data Folio Control Panel will display an indication that stress relations have been specified, as shown in Figure 3.

Figure 3: Stress relations indicated.

A Yes indicates that stress relations have been specified for the selected stress columns. If no stress relations have been selected, then None will be displayed. When you estimate the parameters, the specified stress relation for each stress column will be taken into account.

 

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