FTM 112: The Wedge Tensile Test

Fastener Training Minute 112: The wedge tensile test

This edition of the Fastener Training Minute with Carmen Vertullo was originally published January 12, 2017 as “The Wedge Tensile Test” during episode 112 of Fully Threaded Radio.

Well, hello everyone, this is Carmen Vertullo with your Fastener Training Minute from the Fastener Training Institute and the Carver FACT Center here in El Cajon, California. Today I want to talk to you about a test that is peculiar to fasteners called the Wedge Tensile Test. This is one of the most common tests in all of fastenerdom, but it’s also one that is often done incorrectly because certain Labs, particularly those which are not familiar with fasteners sometimes get it wrong.

And when they get it wrong the results or the consequences can be quite severe for the supplier, especially if the fasteners are already on a job site being installed.
So when we return I’ll tell you more about the Wedge Tensile Test and this particular error that seems to occur from time to time. And while we’re on the break if you happen to have one, get out your IFI 9th Edition Fastener Handbook and turn to page 1145 and you’ll be in ASTM F606 where it tells us about the Wedge Tensile Test.

We’re talking about the Wedge Tensile Test. Many tests in fastening systems are pretty common to all materials, hardness test, tensile test, certain types of dimensional inspections, and so on, but this one is particular to the fastener world and that’s the Wedge Tensile Test.

For the Wedge Tensile Test we put the fastener in a standard Wedge Tensile Test machine, and tensile testing means we pull it until it breaks. We essentially put a load on the fastener and see how strong it is. With a Wedge Tensile Test we put a wedge under the head. It forces the head to bend during the test and the purpose of it is to test the head to body ductility at the fillet route radius. So this test ensures that we didn’t do anything detrimental to the material when the head was formed. Now, these wedges don’t have a very severe angle, somewhere between four degrees and 10 degrees depending upon the size of the bolt.

One of the things that happens often though is we will send our product out to a lab. Usually this happens with subsequent testing. For example on a job site where the building owner wishes to have the product tested at an independent lab. So we send our bolts out they do the Wedge Tensile Test and it fails. Almost all of the time when this occurs the reason is because they failed to read a very important footnote in table 2 of ASTM F606, and that footnote says the following exactly. If you have the IFI Fastener Handbook out you should read it with me.

It says heat-treated bolts that are threaded one diameter or closer to the underside of the head shall use a wedge angle of six degrees for sizes quarter through three quarter and four degrees for sizes over three-quarters of an inch.

So what this is basically saying is that bolts that are threaded closer to the Head use a smaller wedge and if they are not threaded closer to the head, the wedge angle is greater than that. Oftentimes the Labs just look at the table, they don’t look at the footnote and they test these short bolts and end up failing them.

So if you have a failed Wedge Tensile Test, before you accept it, look it up, ask whoever did the test what wedge they used. Also, oftentimes, the test lab will not put the wedge angle on the report. This is very bad practice. They should put it on the report so you will know.

So once again, there are some things that test Labs don’t always get right this and this is one of them,. If you ever run across this, please let me know because I like to collect these kinds of things because we can learn from them.

This has been Carmen Vertullo with the Fastener Training Minute. Thanks for listening.

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