Abstract
Design engineers are continually asked reliability questions such as: (1) how long is your newly designed device/product expected to last and (2) how can you make cost-effective design changes to improve the reliability robustness of the device? Often the designer will attempt to answer these questions by stating a safety factor χ which was used for a design.\( \xi_{\text{design}} = \xi_{\text{strength}} /\chi . \)The safety factor, however, is only a qualitative indicator of the reliability margin of the designed device. It states that the designer tried to stay below the expected material’s strength distribution by some safety factor χ. For example, the designer may have used a safety factor of χ = 2.
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Notes
- 1.
A REF = 2 means that the improved design should last 2 times longer than the original design, a REF = 3 means the improved design should last 3 times longer than the original design, etc.
- 2.
Recall that the stress-level σdesign must be greater than the yield-strength σyield for creep to occur.
- 3.
The value of n creep = 5 is used so often in creep analysis that it is generally referred to as the literature as the five-power-law for creep behavior.
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McPherson, J.W. (2013). Increasing the Reliability of Device/Product Designs. In: Reliability Physics and Engineering. Springer, Heidelberg. https://doi.org/10.1007/978-3-319-00122-7_14
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DOI: https://doi.org/10.1007/978-3-319-00122-7_14
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Online ISBN: 978-3-319-00122-7
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