Mechanical Components Example: Difference between revisions

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[[Image:new_arrhexample.gif|thumb|center|200px|Eta and Mean Life vs. Stress.]]
[[Image:new_arrhexample.gif|thumb|center|500px|Eta and Mean Life vs. Stress.]]
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It can be seen that life ( <math>\eta </math> , and the mean life) is almost invariant with stress.
It can be seen that life ( <math>\eta </math> , and the mean life) is almost invariant with stress.

Revision as of 13:08, 25 June 2012

Mechanical Components Example

A mechanical component was put into an accelerated test with temperature as the accelerated stress. The following times-to-failure 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


1) Determine the parameters of the Arrhenius-Weibull model.

2) What is your observation?



Solution

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


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


A small value for [math]\displaystyle{ B }[/math] was estimated. The following observations can then be made:


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


A small value for [math]\displaystyle{ 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]\displaystyle{ \eta }[/math] , and the mean life are plotted next.

Eta and Mean Life vs. Stress.


It can be seen that life ( [math]\displaystyle{ \eta }[/math] , and the mean life) is almost invariant with stress.