Template:Alta al stat prop sum: Difference between revisions

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===Arrhenius-Lognormal Statistical Properties Summary===
#REDIRECT [[Arrhenius_Relationship#Arrhenius-Lognormal_Statistical_Properties_Summary]]
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====Arrhenius-Lognormal Failure Rate====
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The Arrhenius-lognormal failure rate is given by:
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::<math>\lambda (T,V)=\frac{f(T,V)}{R(T,V)}=\frac{\tfrac{1}{T\text{ }{{\sigma }_{{{T}'}}}\sqrt{2\pi }}{{e}^{-\tfrac{1}{2}{{\left( \tfrac{{T}'-\ln (C)-\tfrac{B}{V}}{{{\sigma }_{{{T}'}}}} \right)}^{2}}}}}{\mathop{}_{{{T}'}}^{\infty }\tfrac{1}{{{\sigma }_{{{T}'}}}\sqrt{2\pi }}{{e}^{-\tfrac{1}{2}{{\left( \tfrac{{T}'-\ln (C)-\tfrac{B}{V}}{{{\sigma }_{{{T}'}}}} \right)}^{2}}}}dt}</math>
 
====When Using the Lognormal Distribution in ALTA====
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The parameters returned for the Arrhenius-lognormal distribution are always  <math>{{\sigma }_{{{T}'}}},</math>  <math>C,</math>  and  <math>B.</math>  The returned  <math>{{\sigma }_{{{T}'}}}</math>  is always the square root of the variance of the natural logarithms to failure. Also, if the "Show Scale Parameter" option is checked (on the Data Sheet tab in the User Setup), the returned mean value is always the mean of the natural logarithms of the times-to-failure, given by Eqn. (arrh-logn-mean). Even though the application denotes these values as mean and standard deviation, the user is reminded that these are given as parameters of the distribution, and are thus the mean (a function of stress as it can be seen in Eqn. (arrh-logn-mean)) and standard deviation of the natural logarithms of the data. The mean life value of the times-to-failure, as well as the standard deviation of times-to-failure (not the parameter) can be obtained through the Function Wizard in ALTA.
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Latest revision as of 05:30, 16 August 2012

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