Residual stress

Residual stress

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.

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 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.

ee also

* Shot peening
* Autofrettage
* Tempered glass
* Prince Rupert's Drop
* Prestressed concrete

References

*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

* [http://www.msm.cam.ac.uk/phase-trans/residual.html Residual stress information at Cambridge University]
* [http://www.twi.co.uk/j32k/protected/band_3/ksrhl001.html Residual stresses at The Welding Institute]
* [http://www.protoxrd.com/residualstressinfo.htm Residual Stress Information at PROTO Manufacturing]


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Residual stress — Residual stress. См. Остаточные напряжения. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • residual stress — noun : a stress that exists within a solid body though no external stress producing forces are acting and that is due to some inequality of previous treatment of adjacent parts poorly annealed glass may be highly unstable because of residual… …   Useful english dictionary

  • residual stress — Metall. a stress in a metal, on a microscopic scale and resulting from nonuniform thermal changes, plastic deformation, or other causes aside from temporary external forces or applications of heat. [1930 35] * * * …   Universalium

  • residual stress — stresses that remain within a body as the result of plastic deformation, casting or rapid temperature change. Stress expressed in force per unit area (pounds per square inch) …   Mechanics glossary

  • residual stress — noun Physics the stress present in an object in the absence of any external load or force …   English new terms dictionary

  • KOWARI - Residual-Stress Diffractometer — KOWARI is the name of the new neutron Residual Stress Diffractometer at Australia s new research reactor OPAL, ANSTO. Strain scanning using thermal neutrons is a powder diffraction technique in a polycrystalline block of material probing the… …   Wikipedia

  • Stress corrosion cracking — (SCC) is the unexpected sudden failure of normally ductile metals or tough thermoplastics subjected to a tensile stress in a corrosive environment, especially at elevated temperature (in the case of metals). SCC is highly chemically specific in… …   Wikipedia

  • Stress (physics) — Stress is a measure of the average amount of force exerted per unit area. It is a measure of the intensity of the total internal forces acting within a body across imaginary internal surfaces, as a reaction to external applied forces and body… …   Wikipedia

  • Stress (mechanics) — Continuum mechanics …   Wikipedia

  • stress — the intensity of internal force acting at a point in an object. Stress is measured in units of force per area. Examples of a stress include a tension, a thrust, and a shearing force applied stress critical resolved shear stress maximum stress… …   Mechanics glossary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”