Some studies in simultaneous failure in equipment items

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Virginia Tech

This study can be classified under the subject of equipment item replacement analysis. Simultaneous failure, SF, of the components of an equipment item, EI, is the topic of this thesis. Examination of the possibility of designing components of an EI for SF is one objective of the study. The motive for this objective is the belief that SF designs of EI minimize the total cost of acquiring and operating the EI.

Examination of the strength of materials reveals that design life of components is not sufficiently flexible to realize SF, and design requirements can predetermine design life. This is true for mechanical components such as links, gears, and bearings. Hence it was concluded that SF of the mechanical components of an EI, cannot be easily achieved.

The second objective of the study was to formulate a model for optimizing the design of the components of an EI with life considerations. A mechanical reliability model was first modified by the inclusion of fatigue stress-strength relationships, and the theory of Cumulative Damage. By mathematical manipulation to suit the principles of Lagrange's Method of Undetermined Multipliers, an optimization model has been developed. This model enables system and component design constraints and requirements to be included in the optimization process.