Ten items are put on the test, until all have failed. The first faliure occures

Question

Ten items are put on the test, until all have failed. The first faliure occures at 35 000 operating cycles. Regression analysis of the times to faliure shows a good fit to a two-parameter Weibull distribution, and the distribution parameters are derived. The specification states that the item should have a B10 life of 30 000 cycles. Discuss the practical implications assuming that the test shows complience with the specification.

In a previous problem, how might your judgment be influenced if the items is;

a) a seek bolt subject to fatigue loading

b) a plastic component in a child s toy

c) a lighting unit

d) a bearing in a gerbox

e) a light-emitting diode

Explanation / Answer

in the above example =

mean=30,000

x=35000

standard error for this example=5000

let take we have to be 99% confitent in manufactured items

t value at 99% at 9 degrees of freedom = 3.250

3.250= 35000-30000/se/n    ;where se is standard erroror standard deviation of sample

3.250= 35000-30000/se/10

3.250*se/10 =5000

5000/3.250*10=se

se=4865.043

as standard error calculated at 99% confidence interval is less than in the given example we can say that completing 35000 cycles is a good for an item.

a) the bolt should be able to load 35000 units of load to give it a yes to sell

b) the child's toy should work 35000 that will use plastic component to give it a yes to sell

c) it should light for 35000 units of time to give it a yes to sell

d) the bearing should revolve 35000 times to give it a yes to sell

e) it should light for 35000 units of time to give it a yes to sell

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