Track 1 Session 4
2:40 to 3:50 p.m. Wednesday June 14, 2006

Weibull Analysis of Failures with Different Stress Histories

A Weibull analysis provides good results when all failures have the same stress history. However, this analysis becomes less representative of real component life when the failures have different stress histories. Pressure, temperature, voltage, and load are examples of stresses to which a component could be exposed. This presentation describes a method for converting failures with different stress histories back to a single equivalent stress condition. The method uses matrix manipulations of the failure data and genetic algorithms to relate failures with different stress histories back to a single equivalent stress condition. Failures based on this single equivalent stress condition can then be used to conduct a conventional Weibull analysis. The application of this technique will be demonstrated with failure data from valves in positive displacement pumps. The stress variables for this analysis are the operating pressure and flow rate across the valves. In this application, the valves are exposed to different pressures and flow rates on a daily basis.

Key Words: Weibull, Equivalency, Time Varying Stresses, Reliability Calculation