Hydraulic grips clamping force

[robmit]

Hello there,
I've got a problem regarding the clamping force on hydraulic grips on a universal testing machine.
For aluminium alloys works fine, but when i try on steel, it fails maintaining the clamping force on the grips.
The question: are there specifications regarding clamping forces for specimens?
Thank you in advance, and excuse the bad english.

 

[unclesyd]

Please post about how it is failing, like the sample is slipping out of the jaws. A picture of the holder would be a great help.
Also check the limits on sample size.

Get the manual for your testing machine and checkout it's capabilities as some are not intended for Steel. We have machines that are only good for polymers, composites, etc. A lot of machines that are capable of testing different materials require one to change the jaws are grips for different materials.

 

[tr1ntx]

Yes, sounds like it is not set to squeeze the aluminum very hard, then when you put the steel sample in, because it weighs so much more, it slips out. (guessing without more information)

 

[robmit]

Back with more info:
The machine it's a hydraulic 300kN testing machine.
All sample can and are fixed within grips, but, after test
is started, at different load(10-15kN) values, for steel samples
the test stops, claiming that a break was detected.
The sample did not break.
Bellow are some pictures with the grips and the sample.
The sample is deformed after retrieval.

 

[desertfox]

please load it up as a pdf and not a rar file

 

[unclesyd]

If your sample slips in your machine then it will sense a break due to changing load. If the grip is holding then you have a problem in the machine recording mechanism. Check the setting on the limit switch, whether it is loose, check and it for proper operation. On most machines there is peak picker that recods the highest value obtained. On some machines this is incoperated with the limit system.

Are the jaw teth sharp and clean>

Are the jaws harder than your steel sample?

Does this happean at the same load each time?

 

[robmit]

The cause was a faulty electrovalve in the gripping mechanism,
at least so it seems.
Thank you all for the sugestions.

 

[unclesyd]

Appreciated the feed back.

Hope you have it under control.