LUG STRENGTH, SKEWED FASTENER
LUG STRENGTH, SKEWED FASTENER
(OP)
Fellow stress engineers:
I am a concessions engineer faced with a fastener 2.2 deg off perpendicular. Because of geometrical constraints, the proposed solution is to fit spot-faced support washers on either face of the joint. Does anyone know of a method/approximation for assessing lug strength in such a case?
Louis
I am a concessions engineer faced with a fastener 2.2 deg off perpendicular. Because of geometrical constraints, the proposed solution is to fit spot-faced support washers on either face of the joint. Does anyone know of a method/approximation for assessing lug strength in such a case?
Louis





RE: LUG STRENGTH, SKEWED FASTENER
Is the hole off perpendicular, or is the fastener tipped in the hole?
Any bushings in the hole?
RE: LUG STRENGTH, SKEWED FASTENER
RE: LUG STRENGTH, SKEWED FASTENER
Otherwise, it is difficult to assess the impact of a single misdrilled hole. For the most part, if it is a single fastener in a sufficient quantity, I would assess the joint strength without the suspect fastener. If good, then I would not worry about it. Additionally, I believe misalignements of 2 deg. are allowed with Hi-Loks per spec. Since you are slightly over that number, I would use self-aligning washers to allow the bolt proper clamp-up.
From a fatigue issue, the misalignment will cause a slight decrease in fatigue capability.
jetmaker
RE: LUG STRENGTH, SKEWED FASTENER
RE: LUG STRENGTH, SKEWED FASTENER
Oversizing the hole would result in a horrendously low edge distance and we have a skewed hole, rather than a skewed bolt in a perpendicular clearance fit hole...
Louis
RE: LUG STRENGTH, SKEWED FASTENER
The only strength effect would be due to the spotface.
RE: LUG STRENGTH, SKEWED FASTENER
Thanks for your response, but the hole was drilled skew at short edge distance. It is clearance fit, so there is a bit of play in the hole, but I am interested in assessing the slightly elliptical hole at low edge distance.
Louis
RE: LUG STRENGTH, SKEWED FASTENER
short eD is critical for loading towards the edge, if the majority of the loading is parallel with the edge, it might be acceptable.
i'd worry more about the head of the fastener; being perpendicular with the fastener diameter, it's now not parallel with the outside face. there is a small amount of misalignment allowed with most fasteners, if you're in this range you probably don't have a prolem with the hole. if you're outside this, as well as thinking of the effect of the hole, i think you'll need tapered washers.
RE: LUG STRENGTH, SKEWED FASTENER
Thanks for your contribution. Our proposal is to fit spot-faced support washers which will allow good seating of nut and bolt-head, but I am still left with assessing the static strength and F & DT with skew and short-edge distance; hence my original question, namely does anyone know of methods/approximations for considering lug strength where the hole is skewed.
Louis
RE: LUG STRENGTH, SKEWED FASTENER
RE: LUG STRENGTH, SKEWED FASTENER
Analytically, using a larger diameter encompassing the tangent points at the top and bottom surfaces will give you adequate conservatism both as a static lug (if it really is) and for damage tolerance. For damage tolerance, the input stress levels and stress intensity factor solutions are nowhere close to 0.99926 accuracy.
From a damage tolerance perspective, you are probably going backwards by spotfacing, unless it is well blended.
RE: LUG STRENGTH, SKEWED FASTENER
Your comment about the short eD is correct for ultimate loading, but not accurate for fatigue as a load parallel to the edge would present a big fatigue concern.
jetmaker
RE: LUG STRENGTH, SKEWED FASTENER
Thanks for your contributions. The subject fastener is one of a structural joint, not a pivot pin.
The hole was drilled at shorter-than-design edge distance as well as skewed and the proposed spot-faces are in additional support washers and therefore do not contribute to fatigue sensitivity in load-carrying components. I probably will treat the hole as perpendicular and of a diameter slightly larger than nominal to account for the skew.
Louis
RE: LUG STRENGTH, SKEWED FASTENER
RE: LUG STRENGTH, SKEWED FASTENER
For two degrees we wouldn't have bothered to take the angle of the pin into account for the pin forces. (Nominally as the pin is canted over it will wind up taking a bit of tension as well as shear.)
Since this is part of a group and will be torqued up, there's usually a bit in hand.