SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Munal
Date posted: Fri Aug 1 2:27:52 US/Eastern 2003
Subject: Reliabiltiy Vs Durability Vs Life
Can you please help me out regarding this.
In TS16949 - It is given that the company has to establish targets for these. So What is the difference between these three. And for bearing, How can we put the target for these three?
Subject: Reliability Definitions
Reply Posted by: B.W.Dudley
Date Posted: Wed Aug 6 13:48:26 US/Eastern 2003
Reliability - (1) The duration or probability of failure free performance under stated conditions. (2) The probability that an item can perform its intended function for a specified interval under stated conditions. For non-redundant items this is equivalent to definition 1. For redundant items this is equivalent to mission reliability which is the probability that the system will not fail to complete the mission considering all possible redundant modes of operation.
Durability - A measure of an itemís useful life (special case of reliability). Durability is usually defined by the length of the failure free or maintenance free operating period.
Useful life - The number of life units from manufacture to when the item has a non-repairable failure or unacceptable failure rate. Also, the period of time before the failure rate increases due to wear-out.
Operational service life - The number of life units an item has during actual operation of the item before a non-repairable failure or unacceptable failure rate.
A target for each considering a roller bearing would be:
MTBF - 360,000 (NPRD)used for reliability
MTTF - 40,000 (M-HDBK-217) used for durability and service life
Life - 88,000 (10 year logistic suportability)