Abualnassr,
Basically, MTBF and MTTF are aimed at quantifying life statistics for a given product or system. They are useful for identifying weak links in a design, or for looking at the effects of temperature or electrical stress. They sometimes are requested (required) by customers.
As mentioned, there are a number of online discussions of these, and other topics in Reliability Engineering. You have indicated an interest in getting in to reliability engineering. One of the software vendors who has a lot of good material is:
I work in a reliability engineering consulting group,
(We offer a number of training modules)
Go check out these sites.
Also, join ASQ.org . They have good materials, and you can get certified (e.g., CRE; discussed elsewhere in this forum.).
Also, go get a book on reliability engineering. Here are a couple of suggestions:
Practical Reliability Engineering
Patrick D. T. O'Connor
(a classic; bit expensive, but very good. Get at Amazon.com)
Halt, Hass, and Hasa Explained: Accelerated Reliability Techniques by Harry W. McLean
(Get at ASQ.com; cheaper there than Amazon )
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Contact me if you would like to discuss further.
John Cooper, CRE
johnc@opsalacarte.com
John Cooper, ASQ CRE
johnfcooper@comcast.net