experimental measure of permanent deformation 1

[shingouz]

Hello,
At first sorry for my bad english
Is there any experimenal technique that allow permanent deformation measure at several points into a body ( I want to measure plastic deformation of a bolt axis).
Thank you

 

[rb1957]

a micrometer ? measure the bolt before and after test (to determine permanent set)

 

[shingouz]

Thank you for your reply, in the attached picture you can see the numerical results that i want to validate using an experimental approach, so can we measure the plastic strain at those points (1 to 7)?

 

[metengr]

Most likely strain gages would be necessary.

 

[btrueblood]

Are you trying to determine the deformation of the bolt due to rolling/cold working? You may want to use strain gages and residual stress methods (e.g. cut the surface and look for the elastic springback due to residual stress).

 

[chicopee]

I don't know if this will help but back in the late '60's I scribed rectangular patterns, of known dimensions, on blank copper pieces before they were punched thru a die to form round caps.

 

[TVP]

Here are two links to papers by Dr. Tekkaya that describe methods for linking plastic strain during deformation to hardness measurement and finite element simulation methods:

http://www.technet-alliance.com/uploads/tx_caeworld/Paper_hardness.pdf

http://ajse.kfupm.edu.sa/articles/301C_08p.pdf

You can find other English-language information by performing a Google keyword search using the following terms:

visioplasticity (not viscoplasticity)
"plastic strain" extrusion DEFORM flownet

 

[rb1957]

do you want to measure when the bolt is installed in a hole ?

 

[dhengr]

You could just measure btwn. to gage points, before, during and after testing, just as they do on a typical tensile test specimen. On a whole bolt, this should give you good average values, then repeat the test to get an average of specimens. This is a symmetrical enough problem so that you might take a center line slice of the material and do a tension test on it. Now you can see gage points on the surface of this slice, maybe at discrete points in length or dia., to start to see any variations over length or distance from bolt center line. Then with some clever Theory of Elasticity and Mathematical manipulations rotate this slice 180° to get the solid bolt. Compare this with some non-linear FEA results and see what you get. Your sketch seems to indicate that you want to measure, strain or permanent deformation at some discrete internal point, maybe at different dia’s. or at different length locations. But, you have not defined the loading conditions or what you are really trying to measure so we are kinda in the dark on this, and just guessing at what you are trying to do.

 

[shingouz]

Thank you all for your answers, I think that linking plastic deformation to work hardness measurment is a good idea but we should cut the bolt into two parts to perform this measure. Is there any non destructive technique to perform this measurment (perhaps 3D Digital imaging correlation or ultrasonics..)
rb1957: No i want to measure the plastic deformation after completing the test.
dhengr: It is a double lap bolted joint and the we measure after the joint failure

 

[rb1957]

then how about an earlier suggestion of marking the bolt. maybe add a circumference mark thru pt4 as a datum for the others. mind you, if its a double shear joint it should be hard to remove the bolts, maybe you'll have to cut up the flanges to access the bolt ? since its a double shear joint, are you looking at plastic strain along the load or across it (bending it out of true) ?