Corrected endurance limit at the constant strength σ e of the bolted connection is determined for the selected type, design, material, and joint loading from the formula:
σ e = σ' e k e k f [MPa, psi]
where:
|
σ' e |
basic endurance limit of a test bar from the selected material [MPa, psi] |
|
|
k e |
modified factor of stress concentration [-] |
|
|
k f |
factor of miscellaneous effects [-] |
1. Basic endurance limit σ' e
If you do not have available results of material tests of the selected bolted connection material and do not know the exact value of basic endurance limit, its value can be estimated by the program. In this case, the calculation designs the basic endurance limit according to the reversed traction - pressure formula:
σ' e ≈ 0.4 S U - for reversed traction - pressure
|
S u |
ultimate tensile strength [MPa, psi] |
2. Modified factor of stress concentration k e
High local stress concentrations originate in a joint when the bolted connection is fatigue loaded because of bolted connection notch effect. These concentrations considerably reduce the joint fatigue strength. Modified factor of stress concentration is determined from the ke = 1/K formula, where the fatigue-strength reduction factor K depends on the bolted connection type, shape, design, bolted connection quality, and the bolted connection loading.
3. Factor of miscellaneous effects k f
All other effects that can reduce or increase the fatigue strength of bolted connection (the influence of corrosion, for example) are included in this factor.