Short Edge Margin

Your question is confusing.

However, I would not assume that bearing failure occurs before shear tear-out - it all depends on your geometry and materials. Note - you could argue that bearing failure is necessary in order to move the shear stress planes into 2 tangential lines, but that is for another topic.

If you don't need to meet an applicable code for edge spacing then I would suggest checking out both cases by calculation.

Bearing Stress: σ=F/(d x t)

Shear Tear-out: τ = F/(2 x a x t)

Where:

F = force

d = diameter of hole

t = thickness of plate

a = distance from close hole edge to plate edge

Hello :

thanks for ur reply.If u do not assume that bearing will always occur first then I have one more question.

In my case tear out allwable is more even with 1.3 d edge than bearing allowable so does that mean bearing will fail first than the tear out.And if we keep on increasing the load then tear out failure will also occur?

thanks

I can't give any numbers for your case because you haven't provided enough info, especially concerning the "three parts". I am not sure what you mean by that, if you mean three sheets, or three bolts, 2 bolts set back from the other .....?

But it may be easiest to look at an example (I completed it with rivets before I realized you said bolts and I didn't go back to change the numbers ):

NOTE: This is assuming that your rivets (bolts) aren't going to fail - it is only looking at two cases of the parent material.

Material: 6061-T4

Shear Strength: 9500 psi

Bearing Strength: 50,000 psi

3/16" rivets (0.191" hole)

0.063" Sheet

Maximum bearing Force = θ(d)(t) = 50,000(0.1875)(0.063) = 591 lbs

Maximum shearing Force = τ(2)(a)(t) = 9500(2)(0.161)(0.063) = 193 lbs

So, in this example (with only one rivet analyzed at your 1.63d distance) the system will fail in shearing at 193 lbs force before bearing failure occurs.

Does this help any?

Hi

I think it helped. Three parts in my case is , 3 pieces of material (plates)joined by bolt pattern.All of them aluminum and top and bottom are 0.1 inch thick and middle one is 1.25 inch thick which has edge margin less than 2d but top &bottom peiecs of material have 2d edge for all the bolts.bolt dia is 0.3inch.

As middle one is 1.25 inch thick I thought it must be having high bearing strength than other 2.Hence even though it has 1.36 edge margin its shear tear out allowable may be more than bearing allowable of other two, if this is true then may be i need not to worry about increasing the edge margin for middle one because top or the bottom one fails first before the middle one in bearing.

SO am i right?

Okay,

Things are becoming a little clearer now.

HOWEVER, you can not say one way or the other without doing the math (and I don't have time right now to do it). It also heavily depends on the orientation and loading of the three plates. For example, it could be the case that you have a force of 1000 lbs on the 1.25" plate, where the two 1" plates are equal and opposite and only see 500 lbs force each.

It that is the case then, even though the middle plate is thicker and would have a higher allowable shear load, it must resist twice the force - and consequently the middle plate may fail in shear BEFORE the two 1" plates fail in bearing.

In any case you must perform the calculations (once you know your loading).

I suspect that you will find that the limiting factor will be shear tear-out of the 1.25" middle plate

NOTE: I forgot a factor in my last calculations for the bearing shear stress, when you get under 2d edge distance (or 1.5d depending on who you listen to) there is an additional reduction factor that you need to add.

Damn!!!! I really have to start reading more carefully.

You said that the upper and lower plates are 0.1" , not 1"

I now suspect that you are right - that is, the upper and lower will fail first. And you do not need to worry about the edge distance of the middle 1.25" plate.

I would still run the numbers though.

I read your question again after answering - and realized that the example I gave probably doesn't answer your question so I hope this does:

If you know for certain that your tear-out allowable (even with 1.3d edge), is more than your bearing allowable than YES, it will fail in bearing first.

It is tough to answer your second part because bolting failures with bearing stresses get a little 'messy'. That is, the hole starts to crumple and the stresses are hard to analyze because there is almost a tearing/ripping effect of the steel. But yes, once bearing failure has occurred - if you add more load you will eventually experience "shear tear-out".

These conditions may interact. Hole deformations will occur before tea out and a poorly supported, out of round bearing will heat much faster than a well mounted bearing. Excessive heat build up being the usual cause of bearing failure.

FEA software like Algol would probably support a very thorough understanding of the stress in this structure.