aluminum alloy, right).]]
Peening is the mechanical working of metals by means of hammer blows or by blasting with shot (shot peening). Peening is a cold work process. It tends to expand the surface of the cold metal, thereby relieving tensile stresses and/or inducing compressive stresses. Peening also encourages strain hardening of the surface metal.
Residual stress
Plasticdeformation induces a residual compressivestress in a peened surface, along with tensile stress in the interior. This stress state resembles the one seen in toughened glass, and is useful for similar reasons.
Surface compressive stresses confer resistance to metal fatigue and to some forms of corrosion. The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior.
Work hardening
Cold work also serves to harden the material's surface. This makes cracks less likely to form at the surface and provides resistance to abrasion. When a metal undergoes strain hardening its yield strength increases but its ductility decreases. Strain hardening actually increases the number of dislocations in the crystal lattice of the material. When a material has a great number of dislocations, plastic deformation is hindered, and the material will continue to behave in an elastic way well beyond the elastic yield stress of the non-strain hardened material.
Copper and other malleable metals that respond well to strain hardening. Some forms of copper, such as ductile wire, are easily deformed, yet beaten copper articles are quite stiff. Strain hardening may be reversed by annealing.
Hand peening may be performed using a peening hammer. It is still used today in the hand manufacture of high quality cutting blades.
Hand peening may also be performed after welding to help relieve the tensile stresses that develop in the weld metal and surrounding base metal on cooling.
Alabama State Capitol
The Alabama State Capitol is located on Goat Hill in Montgomery, Alabama. The structure was built in 1851.
History
The first Capitol in Montgomery was built in 1847, and was destroyed by fire in 1849. The current State Capitol was built on the previous Capitol's foundations, and was completed in Read More...
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Anna Manahan is an actor with a long history in movies, TV and stage productions. She won the Tony Award for Best Supporting Actress in a Drama for her role as the exasperating, doomed Irish mother in fighter aircraft for which the General Motors Corporation in September 1942 submitted a proposal to meet a U.S. Army Air Force requirement for a fighter possessing an extremely high rate of climb. The proposal was for an aircraft that used the most powerful liquid-cooled engine the
