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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
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