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===Mechanical Components Example===
<noinclude>{{Banner ALTA Examples}}</noinclude>
A mechanical component was put into an accelerated test with temperature as the accelerated stress. The following times-to-failure were observed.
A mechanical component was put into an accelerated life test with temperature as the stress type. The objective is to fit the Arrhenius-Weibull model to the observed data and analyze the result of the test. The following times-to-failure data were observed.




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<br>
1) Determine the parameters of the Arrhenius-Weibull model.
<br>


2) What is your observation?
The parameters of the Arrhenius-Weibull model were estimated using the ALTA standard folio. The results are:


<br>
====Solution====


::<math>\begin{align}
\beta =1.771460,\text{  }B=86.183591,\text{  }C=1170.423770.
\end{align}</math>


The parameters of the Arrhenius Weibull model were estimated using ALTA with the following results:


The estimate shows a small value for  <math>\beta</math>. The following observations can then be made:


<math>\beta =1.771460,\text{  }B=86.183591,\text{  }C=1170.423770.</math>
:* Life is not accelerated with temperature, or


:* The stress increments were not sufficient, or


A small value for <math>B</math>  was estimated. The following observations can then be made:
:* The stress values used in the test were well within the "specification limits" for the product (see discussion [[Introduction to Accelerated Life Testing#Stresses & Stress Levels|here]]).


<br>
• Life is not accelerated with temperature, or
<br>
• the stress increments were not sufficient, or
<br>
• the test stresses were well within the "specification limits" for the product (see discussion [[Introduction to Accelerated Life Testing#Stresses & Stress Levels|here]]).


<br>
The value of <math>\beta</math>  is not the only indicator for the observed behavior. As you can see from the data obtained from the test, the times-to-failure at all three stress levels fall within the same ranges. Another way to observe this is by looking at the Life vs. Stress plot. The following plot shows the scale parameter,  <math>\eta </math>, and the mean life. As you can see, the life ( <math>\eta </math> and the mean life) are almost invariant with stress.
A small value for  <math>B</math>  is not the only indication for this behavior. One can also observe from the data that at all three stress levels, the times-to-failure are within the same range. Another way to observe this is by looking at the Arrhenius plot. The scale parameter,  <math>\eta </math> , and the mean life are plotted next.
 
<br>
[[Image:new_arrhexample.gif|center|550px|Eta and Mean Life vs. Stress.]]
<br>
[[Image:new_arrhexample.gif|thumb|center|200px|Eta and Mean Life vs. Stress.]]
<br>
It can be seen that life ( <math>\eta </math> , and the mean life) is almost invariant with stress.

Latest revision as of 02:56, 16 August 2012

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A mechanical component was put into an accelerated life test with temperature as the stress type. The objective is to fit the Arrhenius-Weibull model to the observed data and analyze the result of the test. The following times-to-failure data were observed.


343 K 363 K 383 K
266.66 618.54 351.12
430.09 666.72 355.1
570.45 724.4 672.69
890.42 950.89 923.35
1046.65 1148.4 948.22
1158.14 1202.94 1277.04
1396.01 1492.56 1538.81
1918.38 1619.59 2020.34
2028.86 2592.29 2099.03
2785.58 3596.85 2173.04


The parameters of the Arrhenius-Weibull model were estimated using the ALTA standard folio. The results are:


[math]\displaystyle{ \begin{align} \beta =1.771460,\text{ }B=86.183591,\text{ }C=1170.423770. \end{align} }[/math]


The estimate shows a small value for [math]\displaystyle{ \beta }[/math]. The following observations can then be made:

  • Life is not accelerated with temperature, or
  • The stress increments were not sufficient, or
  • The stress values used in the test were well within the "specification limits" for the product (see discussion here).


The value of [math]\displaystyle{ \beta }[/math] is not the only indicator for the observed behavior. As you can see from the data obtained from the test, the times-to-failure at all three stress levels fall within the same ranges. Another way to observe this is by looking at the Life vs. Stress plot. The following plot shows the scale parameter, [math]\displaystyle{ \eta }[/math], and the mean life. As you can see, the life ( [math]\displaystyle{ \eta }[/math] and the mean life) are almost invariant with stress.

Eta and Mean Life vs. Stress.