Failure and Deformation of Metal Deformation The amount

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Failure and Deformation of Metal

Failure and Deformation of Metal

Deformation • The amount that a material increases or decreases in length when a

Deformation • The amount that a material increases or decreases in length when a load is applied to it • Things that are very brittle (cast iron) deform very little before they break-things that are ductile (aluminum, rubber) deform before breaking

Ductility vs. Brittleness • Ductility is the ability of a material to withstand tensile

Ductility vs. Brittleness • Ductility is the ability of a material to withstand tensile force when it is applied upon it as it undergoes plastic deformation • Brittleness is the opposite of ductility as it refers to the ability of materials to break into pieces upon application of tensile force without any elongation or plastic deformation • Glasses and ceramics are considered brittle where as gold and silver are ductile materials.

Cleavage-Brittle Failure • Typical example is a breakage in cast iron. Atoms simply break

Cleavage-Brittle Failure • Typical example is a breakage in cast iron. Atoms simply break apart from each other and separate. • This type of failure appears bright, rough, and granular

Shear-Ductile Failure • When under load, the atoms in the material start to slide

Shear-Ductile Failure • When under load, the atoms in the material start to slide past each other within the crystals (grains) • Shear will sometimes cause materials to “neck down” before breaking • Two forms-slip failure and twinning failures

Slip Failure • When a ductile material is stretched and fails it is called

Slip Failure • When a ductile material is stretched and fails it is called a slip failure • Slip plane-rows of atoms start to slide past other rows-not just single atoms

Twinning • A zone instead of lines of atoms are deformed • The crystal

Twinning • A zone instead of lines of atoms are deformed • The crystal structure on either side of the twinning zone stays the same

Work Hardening • When a material is subjected to a load then relaxes and

Work Hardening • When a material is subjected to a load then relaxes and this process repeats over and over again the material eventually becomes harder than it started out as