With the increasing complexity of engineered systems (and their interactions with the environment in which they operate — not to mention the organizational and human factors which impact their operation), concepts for improving reliability are increasingly important. Designing for reliability also requires an understanding of the nature of complexity itself. Klaus Minzer, in ” Thinking in Complexity: The Complex Dynamics of Matter, Mind and Mankind” (a book I strongly recommend) defines complexity in terms of the resulting non-linear behavior of complex systems. He explains the non-linear dynamics of complex systems with fascinating examples, from the evolution of life and emergence of intelligence to complexity in cultural and economic systems. I find his thoughts to fit in very well with concepts of complexity in engineered systems, and especially with how they fail.
Failure in complex systems often comes about due to a non-linear response to a load or an input (wheteher the input is something expected during normal operation or is due to an external event, such as a weather phenomenon or an accident). Engineers study how these non-linear responses happen, and how techniques for robust design of systems or incoporation of sensors and automated response systems can detect and correct a process or mechanism “going off the rails” before disaster can strike. In many cases, the non-linearity is due to an unseen or unintended interaction between compoents or processes. A relatively small loss in elasticity in an o-ring due to cold weather can lead to a rapid escape of burning gases which in turn leads to a catastrophic failure of a space shuttle, for example. I feel that failure is, in a sense, a way of recognizign the true complexity of a system. Of course, it would be far better to understand the complexity, the accompanying interactions, and the potential for non-linear response in an engineered system before a failure occurs.
I am a co-author on two articles appearing in Mechanical Engineering, the magazine of ASME, which address complexity and failure. You can find the first at: http://memagazine.asme.org/Articles/2011/December/Complexity_Consequence.cfm
The second should be appearing in the March issue.
Both will help to explain some of the issues which make reliability of complex systems both a critical and difficult goal for engineers.