Reliability Engineering

11Probabilistic Design for Reliability and the Factor of Safety

To ensure the production of a reliable product, reliability activities must start early in the product development cycle. In order to analyze the reliability of a product, we have to first understand how to analyze the reliability of its components. In order to achieve the desirable reliability level, various reliability methodologies and tools can be used throughout the life cycle of the product—from the early planning stages through design, development, production, field testing, and customer use.

This chapter covers basic models and principles to quantify and evaluate reliability during the design stage. It presents the probabilistic design approach and relationships between reliability and safety factor. The relationship between tolerances on the characteristics of the parts and reliability is also discussed. Probabilistic design requires analysis of the functions of random variables.

11.1 Design for Reliability

Reliability is a design parameter and must be incorporated into a product at the design stage. One way to quantify reliability during design and to design for reliability is the probabilistic approach to design (Haugen 1968; Kececioglu 1991; Kececioglu and Cormier 1968). The design variables and parameters are random variables, and hence the design methodology must consider them as random variables.

The basic premise in reliability analysis from the viewpoint of probabilistic design methodology is that a ...