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Residual Stresses - Definition, Properties and Effects

By: Haseeb Jamal / On: Jul 08, 2017 / Definition, Material Properties
 
 

They have more surface exposure per unit volume, the flange tips tend to cool faster than flange-to-web junctures. Tension members response to load is much similar to that of tensile-test coupon . Member behavior may differ from coupon behavior because of:

  • Slip in bolted & riveted connections
  • Non-linear behavior of connections
  • Residual stresses in member
  • Residual stresses result principally from non-uniform cooling of hot rolled or welded shapes and from cold straightening of bent members.
  • They have more surface exposure per unit volume, the flange tips tend to cool faster than flange-to-web junctures.
  • Similarly, Central portion of web tends to cool faster than junctures
  • As a result, metal at junctures continues to contract as it cools after flange tips and web interior have cooled to temperature of surroundings.
  • This contraction is partially restrained by cooler metal.
  • Developing tensile stresses in regions of junctures & compressive stresses in remainder.
  • These are called residual Stresses
  • Magnitude and distribution of thermal residual stresses are influenced to considerable degree by geometry of x-section
  • 20 W's were investigated
  • An investigation on W's Revealed that flange tip stress varied from 4.1 to 18.7 Ksi
  • Residual stresses in web varied from 41Ksi comp; to 18.2Ksi tension.
  • Showing some W's develop residual tension over entire web, instead the pattern shown.
  • Only one out of 20 sections was thicker than 1 in.
  • Residual stresses tend to increase in magnitude with increase in thickness
  • Because of high concentration of heat, tensile residual stresses at the weld in welded members usually equal the yield strength of the weld metal itself.
  • Residual stresses in welded shapes are determined by section geometry and method of preparation of components.
  • Example H may be fabricated from Universal-mill plates or from plates flame-cut to width.
  • Because they are quenched and tempered, A514 rolled steel shapes are partially stress-relieved, so residual stresses are small
  • Quenching is the act of rapidly cooling the hot steel to harden the steel.
  • Quenched steel is hard and brittle. Often it is just too brittle and must be made more malleable, This is achieved by a process known as tempering.
  • The quenched steel is heated again but this time to a temperature between 200 °C and 300 °C.
  • When the metal reaches the tempering temperature, it is quenched again in cold water or oil. The result is a steel that is still hard but is more malleable and ductile
  • Fabricating operations such as cambering and straightening by cold bending also induce residual stresses.
  • These stresses are superimposed on the thermal residual stresses.
  • If member is straightened by rotorizing, which is a continuous procedure, the residual stress distribution will be changed along entire length of member.

Effect on Behavior of tension Members

 

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