Design for Reliability

Chapter 10

Stress Analysis During Design to Eliminate Failures

Louis J. Gullo

Principles of Stress Analysis

Stress analysis begins by identification of those values or parameters that stress a design during any particular user application, mission profile, or operational profile. Once the values or parameters are identified, they must be controlled in the design. Components and materials should be selected that have the strength to withstand the stress parameters in the nominal case as well as the worstcase operating conditions.

Failures during production and early life wearout mechanisms are precipitated by stress. When stress exceeds the strength of a design, parametric degradation and failures occur. Design for reliability is achieved by ensuring that the strength of the design has adequate margin to handle the stresses applied to an item over its lifetime. With adequate design margin on those parameters, the life of a product or system is extended through elimination of design weaknesses attributed to early life wearout failure mechanisms and avoidance of failures that are critical to mission success. Electrical and mechanical stress analyses are performed to determine the operating stresses to be experienced by each component, product, and system commensurate with the reliability prediction calculations and the engineering design information available. Thermal stress analysis may be carried out on components that are sensitive to high and low temperature extremes, rapid thermal ...