27.1 STRAIN CAUSED BY AXIAL LOADS

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À  p

Under simple axial loads metals and other materials act like simple springs. This behavior is known as elastic

If the material becomes permanently deformed this is known as plastic deformation.

Consider a generic load-deflection curve,

This curve is produced by forcing the deformation, then measuring the holding force using a special tensile tester. The specimen pictured above is fastened into a hydraulic or screw based machine. The specimen is then stretched and the applied load measured. The curves can be directly drawn from using load and deflection.

Secondly, the graph above is often changed as shown to make it independent of geometry.

Note that Young's modulus is a spring constant for a unit volume of material. To get it into a traditional spring constant we must multiply it by area, and divide by lengh.