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: Dominique Roy
Date posted: Mon Aug 14 13:24:34 US/Eastern 2000
Subject: Environment factor conversion for NPRD-95
Some of our suppliers have to provide reliability calculations for mechanical parts. Our spec. is calling the use of NPRD-95, Gm environment for mechanical parts reliability predictions. Some of the parts failure rates found are available only in a Gf ou Gb environment. Are there conversion factors that can be applied to the base failure rate to reflect the Gm environment for mechanical parts?
From Gb, Gf, N, Ai, Au, ARW, CL to Gm.
Subject: Environmental Conversion Factors
Reply Posted by: Bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Tue Aug 22 10:43:00 US/Eastern 2000
The Reliability Toolkit;Commercial Practices Edition has some environmental conversion factors for different conditions. These factors are based on computer combination of a number of military systems that are primarily made up of electronic part types. Some electromechanical parts are included such as inductors, transformers, motors, relays, switches and connectors. If your component is one of these, then the following conversion factor could be considered to change the environment:
Ground Benign to Ground Mobile - MTBF(Gb) x 0.2
Ground Fixed to Ground Mobile - MTBF(Gf) x 0.4
Naval Sheltered to Ground Mobile - MTBF(Ns) x 0.7
Airborne Inhabited to Ground Mobile - MTBF(Ai) x 0.7
Airborne Uninhabited to Ground Mobile - MTBF(Au) x 1.8
Airborne Rotary Wing to Ground Mobile - MTBF(Arw) x 2.2
Cannon Launch - no information
If the part that you are considering does not fit the general electromechanical type, then you must consult the "Handbook of Reliability Prediction Procedures for Mechanical Equipment" NSWC-94/07 to compute a conversion factor based on the expected changes in the stresses that impact the particular component.