High load & low load transfer joints 1

[mateng1979]

Dear all,

I am a materials scientist/engineer working in the area of spot welding development for aircraft structures. As new tasks I have to analyse the joints mechanics (quasi-static strength, fatigue life). As a starting point we would like to base our experiments and analysis understanding on the riveted joints.
At the moment, I am trying to understand the concept of high load transfer (HLT) and low load transfer (LLT) joints (what are the differences and the specimen shapes). I have received a document mentioned two different specimens: one a rectangular specimen with 2 or 3 rivets and is called HLT and the other one dog-bone shaped and is called LLT specimen.
I would be very glad if you could briefly explain he differences of these two specimen types and why one is HLT and the other LLT. In addition it would be great if you could introduce me some sources to study the fundamentals of riveted joints analysis and experiments.

 

[rb1957]

i think it has less to do with specimen shape and more to do with the number of fasteners ... you'll get higher load transfer with fewer rivets.

you'll get most load transfer if you have a double lap splice specimen, so that all the load leaves one side into the splices and out again (and this configuration is symmetric so you'll limit (or control) the amount of bending in the specimen

 

[SWComposites]

high load transfer joint - means there is high loads in each fastener; hence the typical test specimen on has 2 or 3 fasteners to transfer the load
low load transfer joint - means there is relatively low loads in each fastener; hence the typical test specimen has a long column of fasteners, and the straps are tapered to achieve a relatively uniform, low load per fastener
static tests are typically only done with high load transfer specimens
fatigue tests are typically done with both types, to cover the range of joint designs

I suspect most joint fatigue data is proprietary.

hopefully you are not thinking of using spot welding for primary structure!

 

[mateng1979]

Thanks guys for the posts. I am wondering if you could suggest some sources (text books, paper,...) discussing the fundamentals of load transfer in such joints under static and fatigue experiments.

And of course we are not assuming to use spot welds in primary structures, otherwise I won't use such an aircraft to fly with!