1.8. SUMMARY 19
1.8 SUMMARY
Engineering design is a process in which a design idea is checked for its feasibility, rephrased by
engineering technical language, designed, and then manufactured into a product that will serve
the society. e engineering design is a process not only because it takes a period of times to be
completed, but also because the prototype of design must be built and fully tested before it can
be released to the society. One description of the engineering design process is the five-phase
engineering design process—Phase One: Needs Assessment; Phase Two: Design Specifications;
Phase ree: Conceptual Designs, Phase Four: Detailed Design; and Phase Five: Implementa-
tion. e contents of this book are the key techniques required to design components in Phase
Four: Detailed Design.
Reliability R is defined as the probability of a component, a device or a system performing
its intended functions without failure over a specified service life and under specified operation
environments and loading conditions. e reliability-based mechanical design is the main topic
of this book. It uses the reliability to replace the factor of safety to form a design governing
equation for linking all design parameters together. One dilemma for the traditional design
theory with the factor of safety in mechanical component design is that it cannot provide any
tool to assess the component failure, which is a reality in industries. e reliability-based me-
chanical design is an advanced design theory and can provide a tool to solve this dilemma. A
few highlights about the reliability-based mechanical design are follows.
• All main design parameters such as materials strengths, component dimensions, external
loadings, and the loading-induced component stresses are treated as random variables for
considering their uncertainties.
• e component is designed with required reliability. Its physical meaning is the percent-
age of components working properly under specified operation environments and loading
conditions over a specified service life.
• Probability of failure F of the component will be .1 R/ and indicates the percentage
of components which cannot work properly under specified operation environments and
loading conditions over a specified service life.
• e higher the reliability a component has, the safer it will be. However, the higher relia-
bility of a component also implies a higher cost of the component.
1.9 REFERENCES
[1] Voland, G., Engineering by Design, Pearson Prentice Hall, 2004. 2, 5
[2] Le, Xiaobin, Anthony, D., Roberts, R., and Moazed, A., Instructional methodology
for capstone senior mechanical design, ASEE International Conference, Vancouver, BC,
Canada, June 26–29, 2011. 2
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