Often when visiting customer sites, our service engineers find machines that have basic setup problems that can have a large effect on the accuracy of test results. A very common problem is testing with poorly preloaded grip locknuts. Placing a specimen under tension also places all items in the load string – grips, grip adapters, load cell, and so on – under tension as well.
Grips Supplied with Locknuts
If the locknut is insufficiently tight, the forces experienced during a test, particularly a cyclic test, can cause backlash in the load string leading to errors in the test data. Before testing, make sure that you preload the load string, using a load greater than the expected maximum load, and tighten the grip locknuts while the load is applied.
Grips Supplied with Locknuts
If the locknut is insufficiently tight, the forces experienced during a test, particularly a cyclic test, can cause backlash in the load string leading to errors in the test data. Before testing, make sure that you preload the load string, using a load greater than the expected maximum load, and tighten the grip locknuts while the load is applied.
2 comments:
I am confused by this, could you please clarify it again? This sounds like I should be putting in a preload above what I expect the specimen to take.
Hello and Happy New Year!
You will want to tighten the lock nuts while applying a tension greater than the maximum force you expect to see when testing. This will require a piece of material stronger than the material or specimen being tested.
The terminology may be causing some confusion, as the term “preload” is often used to mean a force applied prior to or at the beginning of a test. This “preload” is small relative to the expected max load achieved when testing the specimen.
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