Unitspecific timedependent stress profiles

[Geoff Lee]

Very pleased to see the addition of time-dependent stress profiles to ALTA's capabilities.

In practice, we find many constraints which lead to each unit having been through differing stress profiles. i.e. units experiencing differing amounts of time at differing stress levels.

My reading of your ALTA 6 release info. suggests to me that all units must have been operated over the same stress profile. Is this the case?

Thanks
Geoff

[RS Support]

Geoff

No, as a matter of fact the results are more "accurate" if more than one profile is present.

I guess we need to add additional case studies ( http://www.reliasoft.com/alta6/a6examples.htm ) to illustrate this. Until we do that an example of multiple profiles that can be easily solved using ALTA-PRO is the classic oil breakdown (Nelson, Accel. Life Testing, pp.495).

[RS Support]

Continuing on the previous note, I should point out that this example is a good indication of the problem type.
If you attempt to recompute the example as given in the textbook using ALTA-PRO you will get different results from the author. (There is an error in the data set given and the answers as given by the author in the textbook. The author is aware of that.)

[Geoff Lee]

Thanks very much for the response.

I have reviewed Nelson's example which you quoted. I note that, in that case, time on each step varies for each unit. However the stress levels are consistent across all units. Could you just please confirm whether ALTA also allows the units to use differing stress levels.

Thanks
Geoff

[RS Support]

Yes, i.e. given 12 units, 6 can be subjected to a step stress profile while the other 6 can be subjected to a monotonically increasing stress profile.