A methodology for integrating materials science with system engineering

The performance of a system is determined by variables of different kinds: some related to the micro/nanostructure of materials, others to the shape and architecture of the components of the system that are constructed from these materials, and yet others to the thermal, mechanical and chemical loading on the components. Design and optimization of the system requires evaluating the trade-offs between these variables. The example of tungsten filament for incandescent lamps is used to illustrate a new methodology for evaluating these trade-offs. We demonstrate how the 'system' can be partitioned into subsystems, one relating predominantly to geometry and the other to the microstructure. The subsystems interact through linking variables that permit superimposition of the design constraints imposed by filament geometry, and those imposed by the microstructure. The overlay defines a 'design regime' within which the filament would have the expected life. A possible application of the methodology is to find the bounds on manufacturing process parameters in order to achieve lifetimes that lie within given limits. The present analysis may be further generalized to include materials processing variables to aid in process control for the purpose of improving product reliability. (C) 1999 Elsevier Science Ltd. All rights reserved.