gauge length - proof stress (1 Viewer)

[chen yi]

Can anybody tell me what gauge length is with respect to proof stress? I read that the parallel line is drawn 0.2% to the gauge length... WHAT DOES THAT MEAN?? =|

 

[Templar]

For materials that do not have an inflexion point in the stress strain diagram (ie one where the line just turns into a curve), proof stress is found by drawing a line 0.2% to the right of the straight line section of the graph (Hooke's law), and the intersection of that line to the graph is the proof stress.

 

[MoNNiE]

Proof stress refers to those materials which do not have a defined yeilding point (such as aluminium, Plastic, etc) when it undergoes tensile forces. It is a line that is drawn parallel approximately to the modulus of Elasticity (Hookes Law) at a 0.2% offset or 0.002 micronunits in the strain axis.
the Yielding Point is the specific transition load where the material turns from being elastic (able to transform back into its orginal shape) to become partically permanantly deformed.

gauge length is just the orginal length of the specimen (being measured!!...).. in reference to the proof stress..

remember strain = extension/orginal gauge length

here's a picture to illustrate it better (dodgy colours sorry! )