Residual stress: Difference between revisions
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==External links== |
==External links== |
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*[http://www.minetek.donetsk.ua - Energy-saving technology and computerized equipment for vibration stabilization of residual stress (the only CIS 35-year-old Scientific School, who presented in 1988, the world's first installation of computer diagnostics) are intended to stabilize the residual stresses in welds, castings and other non-rigid dynamic metal ] |
*[http://www.minetek.donetsk.ua - Energy-saving technology and computerized equipment for vibration stabilization of residual stress (the only CIS 35-year-old Scientific School, who presented in 1988, the world's first installation of computer diagnostics) are intended to stabilize the residual stresses in welds, castings and other non-rigid dynamic metal ] |
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*[http://www.twi.co.uk/ |
*[http://www.twi.co.uk/technologies/structural-integrity/numerical-modelling/residual-stress-measurement/ Residual stress at TWI (The Welding Institute)] |
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*[http://www.msm.cam.ac.uk/phase-trans/residual.html Comprehensive resources on Residual stresses at Cambridge University] |
*[http://www.msm.cam.ac.uk/phase-trans/residual.html Comprehensive resources on Residual stresses at Cambridge University] |
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[[Category:Civil engineering]] |
[[Category:Civil engineering]] |
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Revision as of 14:25, 25 July 2012
Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. They remain along a cross section of the component, even without the external cause. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Another example occurs during semiconductor fabrication and microsystem fabrication when thin film materials with different thermal and crystalline properties are deposited sequentially under different process conditions. The stress variation through a stack of thin film materials can be very complex and can vary between compressive and tensile stresses from layer to layer.
Premature failure
Castings may also have large residual stresses due to uneven cooling. Residual stress is often a cause of premature failure of critical components, and was one factor in the collapse of the suspension bridge at Silver Bridge in West Virginia, United States in December 1967. The eyebar links were castings which showed high levels of residual stress, which in one eyebar, encouraged crack growth. When the crack reached a critical size, it grew catastrophically, and from that moment, the whole structure started to fail in a chain reaction. Because the structure failed in less than a minute, 46 drivers and passengers in cars on the bridge at the time were killed as the suspended roadway fell into the river below.
Controlled residual stress
While uncontrolled residual stresses are undesirable, some designs rely on them. For example, toughened glass and pre-stressed concrete depend on residual stress to prevent brittle failure. A demonstration of the effect is shown by Prince Rupert's Drop, where a molten glass globule is quenched to produce a toughened outer layer.
Bolted joints use residual stress to avoid subjecting bolts to fatigue. A gradient in martensite formation leaves residual stress in some swords with particularly hard edges (notably the katana), which can prevent the opening of edge cracks.
In certain types of gun barrels made with two tubes forced together, the inner tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. Parts are often heated or dropped into liquid nitrogen to aid assembly...
Press fits
Press fits are the most common intentional use of residual stress. Automotive wheel studs, for example are pressed into holes on the wheel hub. The holes are smaller than the studs, requiring force to drive the studs into place. The residual stresses fasten the parts together. Nails are another example where the stress created by penetration of wood then helps to keep the nail in place.
Compressive residual stress (metal alloy)
See shot peening
Measurement techniques
There are several techniques that are used to measure the residual stress. They can be classified as destructive and non-destructive methods. Mechanical methods or dissection uses the release of stress and its associated strain after doing a cut, hole or crack. Nonlinear elastic methods as ultrasonic or magnetic techniques requires a reference sample. X-ray diffraction is a non-destructive method which allows the measurement of residual stress in isolated spots spaced distances as small as 100 micrometres.[1][2][3] Neutron diffraction is an alternative non-destructive method which allows measurement of residual stress in isolated spots. The choice between these two techniques depends on the design of the mechanical part to be tested.
See also
References
- ^ Khan, Z.; et al. (2005). "Ceramic rolling elements with ring crack defects—A residual stress approach". Materials Science and Engineering: A. 404: 221. doi:10.1016/j.msea.2005.05.087.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Khan, Z.; et al. (2006). "Residual stress variations during rolling contact fatigue of refrigerant lubricated silicon nitride bearing elements". Ceramics International. 32: 751. doi:10.1016/j.ceramint.2005.05.012.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Khan, Z.; et al. (2007). "Manufacturing induced residual stress influence on the rolling contact fatigue life performance of lubricated silicon nitride bearing materials". Materials & Design. 28: 2688. doi:10.1016/j.matdes.2006.10.003.
{{cite journal}}: Explicit use of et al. in:|author=(help)
Further reading
- Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
External links
- - Energy-saving technology and computerized equipment for vibration stabilization of residual stress (the only CIS 35-year-old Scientific School, who presented in 1988, the world's first installation of computer diagnostics) are intended to stabilize the residual stresses in welds, castings and other non-rigid dynamic metal
- Residual stress at TWI (The Welding Institute)
- Comprehensive resources on Residual stresses at Cambridge University