Creep Prevention – Creep Resistance - Definition

Creep prevention is based on the proper choice of material is also crucial. Creep resistance of materials can be influenced by many factors such as diffusivity, precipitate and grain size.

Creep, known also as cold flow, is the permanent deformation that increases with time under constant load or stress. It results due to long time exposure to large external mechanical stress with in limit of yielding and is more severe in material that are subjected to heat for long time. The rate of deformation is a function of the material’s properties, exposure time, exposure temperature and the applied structural load. Creep is a very important phenomenon if we are using materials at high temperature. Creep is very important in power industry and it is of the highest importance in designing of jet engines. For many relatively short-life creep situations (e.g. turbine blades in military aircraft), time to rupture is the dominant design consideration. Of course, for its determination, creep tests must be conducted to the point of failure; these are termed creep rupture tests.

Creep Prevention – Creep Resistance

Creep prevention is based on the proper choice of material is also crucial. Creep resistance of materials can be influenced by many factors such as diffusivity, precipitate and grain size. In general, there are three general ways to prevent creep in metal. One way is to use higher melting point metals, the second way is to use materials with greater grain size and the third way is to use alloying. Body-centered cubic (BCC) metals are less creep resistant in high temperatures. Therefore, superalloys (typically face-centered cubic austenitic alloys) based on Co, Ni, and Fe are capable of being engineered to be highly resistant to creep, and have thus arisen as an ideal material in high-temperature environments.

For device of selected material, it is of the highest importance to operate the device within limits, which are especially maximum service temperature and stress. The rate of creep is highly dependent on both stress and temperature. With most of the engineering alloys used in construction at room temperature or lower, creep strain is so small at working loads that it can safely be ignored. However, as temperature rises creep becomes progressively more important and eventually supersedes fatigue as the likely criterion for failure. The temperature at which creep becomes important will vary with the material. For safe operation, the total deformation due to creep must be well below the strain at which failure occurs.

References:

Materials Science:

U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
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Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

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Creep

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