Wedge Tensile Test -MTS 1

[ChrroberBT]

My Problem: I cannot collect an accurate modulus of elasticity for a round (.357" DIA - 1018 Steel). Using built in MTS TestWorks software to calculate Stress/Strain curves and built in functions to estimate the modulus of elasticity, the numbers that I am reading are Modulus of elasticity = 17.34 GPA(2515 ksi) for 1018 steel. 1018 steel should have a modulus of elasticity that is about 200 GPA.

I have some round tensile test specimens that have been machined to certain ASTM specs that have two flat gripping surfaces. I am using an MTS tensile test machine with hydraulic wedge grip style heads. My first test on the machine I compressed the clamping surface into a pancake and it skewed all of my data. Since the grips are knurled, I clamped the specimen so that there is no plastic deformation; however, the surface has knurl marks. The test is being conducted at .026 in/min (Determined by ASTM).

I have checked all of the functions in the software to make sure there was nothing silly throwing my E value off by a factor of 10. Is there any thing I am doing wrong that I might be doing?

Thanks,
Chris

 

[redroab]

Have you conducted tests successfully on a universal testing machine before? Knowing your experience level might go a long way in determining what's going on.

First things I'd check for is that you're not having any slipping of the specimen with respect to the jaw faces, and that all grips/accessories/etc. are adequately preloaded. You could also try testing some other specimens on this frame (preferably more compliant specimens) to determine if it's application specific or if you have a systemic problem.

 

[Compositepro]

Are you using a strain gage or extensometer to measure strain? You cannot use cross-head movement for modulus calculation.

 

[ChrroberBT]

Redroab,

This is my 3rd internship; however, this is the first internship that I have worked with materials testing. The specimen is not slipping with respect to the face, because I can see the knurl marks very clearly on the surface. I will work on posting a picture. I will investigate the preload on the hardware, It is in calibration. I am working on trying to get some flat specimens as well to test.



Compositepro,

Extensometer

 

[Compositepro]

Are you using the extensometer gage length and not the specimen length in your strain calculation?
Have you checked the extensometer calibration against a calibrator (it like a large screw micrometer)? There are many settings to adjust on an extensometer.