It seems a big misconception in different industries between those two terms “Reliability” and “Durability”. So, first thing first, I apply google research to find out what is definitions:
Reliability is defined as the probability that a product, system, or service will perform its intended function adequately for a specified period of time or will operate in a defined environment without failure. (Source American Society for Quality (ASQ))
Durability is the ability of a physical product to remain functional, without requiring excessive maintenance or repair, when faced with the challenges of normal operation over its design lifetime. (Source Wikipedia)
Reading those two definitions, the only difference is portion, that durability refers to be durable without service or/and maintenance. In other words, after replacing of all serviceable parts, and doing proper maintenance how long the product will be functional?
In other words, looking into the product, what is the reliability of my critical component/subsystem, that repair or maintain will cost so much, that it will be easier replace with new one.
As for example from automotive industry, if the Crankshaft of internal combustion engine will fatigue, you probably will require replace the entire engine. And just for the sake of this example we assume, that all other components can be served/replaced/maintain.
Meaning, if I will define the reliability of the crankshaft – this ultimately will define the durability of engine.
Having this all-in mind, the conclusion is as follow: Durability of the product is reliability of the critical (one, that cannot be replaced) component/subsystem in the product.
Durability of the product is private case of the total reliability.
We can’t say “this engine will be durable for 10,000 hrs”.
What need to be added is next “this engine will be functional at range of 8,000 to 12,000 hrs with RxxCxx”. The range of the time (8,000-12,000) indicate different end customer usage mode, Reliability and Confidence indicate from entire engine population, how many will pass this time range.
Want to know more? Please comment what is your organization definition.
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