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Old July 21st 16, 03:43 PM posted to rec.aviation.soaring
Dan Marotta
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Posts: 4,601
Default Al-Ko Trailer Tongue failure

A question for the mechanical engineers on this group:

Isn't it true that the load rating of a bolt is an indication of the
tensile strength of the bolt and not its shear strength? Is there any
indication of the shear strength of a bolt? Can anything be inferred
about shear strength from tensile strength?

On 7/20/2016 8:31 PM, Dave Springford wrote:
Hi Tom,

Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).

After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.

I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.


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Dan, 5J