Conical head fasteners under shear loads

[RocketCrazy]

I saw old posts about calculating stresses in flat head screws which are loaded in shear. Some comments said that the effect of the cone on the head should not affect the stresses and could be neglected. I want to share my disagreement with these comments. There is additional tension in the bolt due to the ramp angle being loaded normal to the conical surface. This is similar to a wedge being pushed under something and raising it. In addition to this additional tension there is increased bending in the bolt. This has two components, the first being the shear load applied at half the thickness of the head. The moment arm being from that point to the surface of the threaded interface. Because of the conical head this moment arm does not apply at the mid thickness of the hole but at the head of the bolt. The second bending effect is from the tension component of the normal load. This adds to the shear moment. All this said, if one does all the proper calculations and stress combinations you might find that the capacity of the fastener is decreased by nearly half. FEA can also verify this affect. Check it out. I have.

Rocket Crazy