Reliability Engineering

7Life-Cycle Conditions

The actual loading conditions on a product are often assumed based on engineering specifications or conjecture. This approach can lead to costly overdesign or hazardous underdesign, and consequently, increased investment. Hence, a formal method is necessary to capture the life-cycle load conditions of a product.

This chapter discusses a systematic methodology for developing a life-cycle profile (LCP) for a product. The LCP can thus be used for design and test for reliability assurance. The life-cycle conditions should be collected on actual products if possible.

7.1 Defining the Life-Cycle Profile

The life cycle of a product includes manufacturing and assembly, testing, rework, storage, transportation and handling, operational modes, repair, and maintenance. The life-cycle loads include thermal (steady-state temperature, temperature ranges, temperature cycles, and temperature gradients), mechanical (pressure levels, pressure gradients, vibrations, shock loads, and acoustic levels), chemical (aggressive or inert environments, ozone, pollution humidity levels, contamination, and fuel spills), physical (radiation, electromagnetic interference, and altitude), and/or operational loading conditions (power, power surge, heat dissipation, current, and voltage spikes). The extent and rate of product degradation depend upon the nature, magnitude, and duration of exposure to loads.

Defining and characterizing the life-cycle conditions can be the most difficult part of ...