Shear Limit of M5 Bolt
Shear Limit of M5 Bolt
(OP)
I am trying to calculate the amount of weight that a 4 bolt hole pattern (4" x 2") of M5 bolts can support without damage to the bolts and/or tapping pad they are mounted to.
The bolts are 10.9 class (grade 8, medium carbon steel) bolts with the following specs
Proof Load (MPa) = 830
Yield Strenth (MPa) = 940
Tensile Strength (Mpa) = 1040
If you assume that the bolts are 20 mm long and 10 mm is threaded into the tap pad, how much weight could the above bolt hole pattern support.
I would greatly appreciate some help on this matter.
Wes
The bolts are 10.9 class (grade 8, medium carbon steel) bolts with the following specs
Proof Load (MPa) = 830
Yield Strenth (MPa) = 940
Tensile Strength (Mpa) = 1040
If you assume that the bolts are 20 mm long and 10 mm is threaded into the tap pad, how much weight could the above bolt hole pattern support.
I would greatly appreciate some help on this matter.
Wes





RE: Shear Limit of M5 Bolt
If you don't consider pretension, and the force is shearing the bolts through the threaded region, then the mass that would cause bolt fracture is approximately:
m = F/A
where
m = mass
F = force due to mass
a = gravitational acceleration (assumed to be 9.8 m/s2)
F = 5 · τ · A
where
τ = bolt shear strength (assume to be 0.6 * 1040 MPa)
A = screw root diameter area = 12.69 mm2
m ~ 4000 kg
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Shear Limit of M5 Bolt
The bracket is mounted to 4 tap pads on a ballistic steel side wall that is angled at around 60 degrees to the horizontal.
If we disregard the pretension and tap pad, your calculations show that one M5 can hold 4000Kg before it will break!!! Does that mean the 4 bolt pattern could support 16000kg!!!
What is screw root diameter area?
What pretenstion do you recommend?
Does the amount of thread engagment change the max load?
What does Proof Load, Yeild Strength and Tensile Strength mean?
Hopefully you'll bare with me...I'm an electrical engineer!
Thanks alot,
Wes
RE: Shear Limit of M5 Bolt
Screw root diameter area is the area associated with the smallest diameter of the screw thread. For an M5 (which has a major diameter of 5 mm), the root diameter is ~ 4 mm.
Recommended pretension for general purpose joints is ~ 0.75 · yield strength.
Thread engagement can change max axial load, but won't affect allowable shear load much.
Proof load is defined as 0.9 · yield load. Yield load is equal to yield strength · stress area. Yield strength is the stress that produces 0.2% offset strain. Stress area is a little larger than the root diameter area. Tensile strength is the maximum stress that a material can resist.
4 N m is a low torque for these bolts. You probably are achieving only 0.5 · Fy, which is ~ 5 kN. Five bolts with 5 kN force gives 25 kN joint preload. If the friction coefficient between the coated steel and aluminium pieces is ~ 0.1 (conservative estimate), then the joint can resist 2500 N before it slips. This is ~ 255 kg.
If this is a critical structure, you should use the services of a qualified engineer. Good luck.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.