Failure Analysis of Engineering Structures: Methodology and Case Histories
Foreword by V.S. Arunachalam
Why does a material fail? There can be only four reasons: the material is subject to an environment beyond its design envelope; it is an inappropriate choice for the design and operating conditions; the material, to start with, is defective; or the design itself is wrong. It is vital to know the reasons as component failures can lead to catastrophic accidents causing heavy loss of life and property. Such accidents can slow down or even temporarily stunt the development of new artifacts and systems that appeared so promising. An inappropriate gasket design, of all things, delayed the space shuttle program by many years.
Every failure leaves its own telltale signs in the macrostructure and microstructure of the failed component. It is not always easy to read those signs because the accident could have destroyed the evidence irreversibly, and the failed component itself could present conflicting evidence. In spite of these difficulties, failure analysis has grown to be an important tool in the design and manufacture of engineering parts.
Materials derive their properties from the structure they exhibit, and when they fail, the structure shows that as well. That is why microscopes have become essential tools in failure analysis. Increasing resolution, improved depth of focus, simultaneous chemical analysis at molecular levels, and imaging of imperfections have now become commonplace, thanks to advances in electron, x-ray, and laser optics. Some of the most recent work in hydrogen embrittlement has been made possible because of the availability of sophisticated analytical tools.
Can we simulate a failure in laboratory conditions? Interestingly, an early account of such a simulation where a failure was recreated came out of Nevil Shute’s novel, No Highway (Amereon Limited, 1988). Since then, the fiction was made real when the Comet aircraft crash was simulated in a specially built water tank. Nowadays, mechanical, physical, and chemical testing of materials and components, in addition to modeling of parts and simulation of components in service, have become commonplace. Thanks to the availability of powerful computers, large computer memory, and impressive processing speeds, computer simulations today provide the verisimilitude of components in service with realistic operating and environmental conditions—all without actually breaking the component. The ubiquitous computer has given us other tools as well, such as fault tree analysis, information, and data mining of past accidents.
Why is the past so important? Psychologists tell us we learn from experience, especially from failures. Every experience adds more information to memory so that our cognitive skills become less bound, and reasoning becomes more logical. That is why we have to document our experiences properly and derive lessons from them. In spite of such efforts, accidents will unfortunately continue to happen because of deliberate acts such as sabotage, or the lessons learned of the past instances have not diffused well, or even for reasons that are beyond our control and past learning. But their numbers will continue to reduce, making our lives safer and property more secure; look at the earthquake-proof structures or the pressure vessels that engineers have built today.
The Bangalore National Aerospace Laboratories (NAL) Failure Analysis Centre has grown to become India’s foremost group for this area of analysis. The scientists and engineers working in this group have built a rich repertoire of experiences in failure analysis. The procedures they follow, the techniques they use, and the inferences they draw from the observations make this book a very useful contribution to the study of failure analysis. They have not limited themselves to run-of-the-mill engineering failures, but share their rich and varied experiences in such areas as sabotage with explosives and also litigations that inevitably follow accidents. I have had the privilege of working with the authors of this book and have marveled often at their professional skills and the commitment they brought to their work. ASM International is to be congratulated for publishing this book and thus enabling the NAL group to share their experiences with the global engineering community.
Distinguished Service Professor
Carnegie Mellon University, Pittsburgh, PA, and
CSTEP, Bangalore, India
Foreword by V.S. Arunachalam, Failure Analysis of Engineering Structures: Methodology and Case Histories, By V. Ramachandran, A.C. Raghuram, R.V. Krishnan, S.K. Bhaumik, ASM International, 2005
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