MSCI 301  -  Homework #5        PJL  2/11/04

From the book:  problems  4.44,  4.51,  4.60  .

Plus two extra problems, E1 and E2 below:

E1)  A mechanical engineer ran three sets of journal bearing tests 
     to evaluate a new solid lubricant and needs to know the median 
     time to failure (MTTF) for each set of tests.

     a) Five samples were tested, all failed.  The fail times in hours 
        are:  .36,  1.00,  2.71,  7.38,  7.89 .  What is MTTF?

     b) Four samples were tested, all failed.  The fail times in hours 
        are:  .13,  .36,  1.00,  2.81 .  What is MTTF?

     c) Six samples were tested.  Two of them failed, at 2.72 and 7.39 
        hours.  The other four samples had not failed at quitting time 
        that day.  What is the best estimate of MTTF?

E2)  A materials engineer ran accelerated life tests on a new batch 
     of magnet material.  It appears this material looses its 
     magnetization too easily.

                at 150 deg. C, MTTF was 10.1 hours
                at 100 deg. C, MTTF was 103. hours

     a) Calculate the activation energy for this de-magnetization process.
        Hint: It's roughly an electron volt, give or take a factor of 2.

     b) Estimate MTTF for this material at room temperature, 25 deg. C
        Hint: It's roughly a year, give or take a factor of 2.