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Laminate Cross Pin Bearing Strength

Laminate Cross Pin Bearing Strength

Laminate Cross Pin Bearing Strength

(OP)
Hello, I am looking to cross pin (using a 10.9 grade stud) a laminate joint loaded in double shear to increase the strength in the joint beyond that given by the adhesive between laminate sections.

Questions I have is related to bearing strength and stress. How is bearing strength of a material typically defined in structural engineering? I have seen comments stating its higher than yield and some saying lower? Is there a standard that defines the bearing strength in regards to yield or UTS.

Also, in terms of stress, for a 10mm stud in a 12mm hole, can the bearing stress be calculated using the simple P/d*t (d being the bolt diameter).

I used the max stress equation for a cylinder in a cylindrical socket (attached) and it gives me crazy high stresses. Much higher than the simplified one above.

RE: Laminate Cross Pin Bearing Strength

Be aware that, for the pin to do anything useful, there already needs to be a significant force that has deformed the materials enough to transfer the load onto the pin, and possible already has sheared the adhesives.
For this reason, welded + bolted joints are not recommended. Safe to say your combination has the same downsides.

RE: Laminate Cross Pin Bearing Strength

(OP)
Thanks for this input kingnero. The pins are a last resort mechanical reinforcement if the adhesive fails between the composite sections. Hope this clears up the application.

RE: Laminate Cross Pin Bearing Strength

OK, that makes it clear.
A schematic view could make your question more clear.
You'll need shear strength of the pin (~ 540 MPa), bending resistance of the pin, and bearing resistance of laminate and pin, to be complete.
According to Eurocodes, bearing strength for pins can be up to 2.5 x fy. For (engineered) wood (= laminate?) I'd go lower, but I can't give you a reference.
Your table is for Hertzian contact stresses, mostly (exclusively?) used for steel/steel contact. I'd assume a rectangular contact area, instead of a line contact, for wood/steel contact.

RE: Laminate Cross Pin Bearing Strength

(OP)
Hi kingnero. I should of specified - the laminate is a GFRP composite which complicates things further. Is that Eurocode 2(or 3?) you are referring too? Thanks for the info about the Hertzian contact stresses - I wasn't aware it was exclusive to steel on steel but I knew due to the crazy large stresses I was seeing it was not applicable to this GFRP issue.

RE: Laminate Cross Pin Bearing Strength

The pin connection is described in Eurocode 3-1-8, ( = EN 1993-1-8 ) § 3.13.

I have no experience with composites whatsoever, so I can't help you with the bearing strength there. I'd check tear-out, because you say it's more of an emergency / safety system in case the adhesives fail. So you don't care if you exceed the bearing strength of the composite, as long as it doesn't tear out. You'll have to replace the connection and/or members anyway. Correct?

RE: Laminate Cross Pin Bearing Strength

(OP)
I used this standard for the pin design. Yes - tear out strength is more critical. I am unsure how to calculate tear out strength of the material however. I don't know how this relates to the materials tensile/compressive strength.

RE: Laminate Cross Pin Bearing Strength

(OP)
Thanks for all the help so far. I used Eurocode 3-1-8 for the pin design. You are correct - tear out strength is the important factor - how to find this for a composite however - I am unsure.

RE: Laminate Cross Pin Bearing Strength

In my experience in order to get anywhere near the theoretical values the holes must be very tight (very little motion before the pin is upset) and the assembly must be very snug side to side.
Any gaps and you are in bending and not shear.
And when you have a bearing material that is so much softer than the pin tearing will be the result.
Your large diameter mismatch would drive very high contact stresses likely crushing the composite before the pin deformed enough to carry much load.
You likely want to use the softest pin that you can get away with

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Laminate Cross Pin Bearing Strength

If you are using fasteners in a bonded joint the fasteners will see zero load until the bond fails.

And please don’t double/triple post.

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