Mechanical Engineering Calculators: Flange Coupling Bolt Bearing and Edge Shear-Out Calculator

Flange bearing and edge shear-out equations

The calculator begins with the same equal-radius torque model as Calculator #029. A concentric design torque creates total tangential force at the bolt-circle radius, then ideal equal load sharing assigns force to each bolt:

Projected bearing area and nominal bearing stress for one flange plate are:

For a free edge in the direction of bolt load, the actual finished hole establishes clear ligament. The conservative straight two-plane shear-out check is:

NASA TM-106943 presents projected bearing area and a conservative two-plane shear tear-out model. AISC uses the same directional clear-distance concept when separating bearing from tear-out, but this calculator does not implement AISC resistance factors or claim that a structural-steel specification governs a machine coupling.

Input interpretation

For a circular flange, tangential bolt force does not generally point radially toward the outside diameter. Determine the real free-edge path in the direction of each bolt’s local force rather than entering a convenient radial dimension automatically.

Worked example

Use the default inputs: 1,000 N·m, six bolts, 120 mm bolt circle, 10 mm bolt diameter, 11 mm hole, 12 mm flange thickness, 20 mm directional edge distance, 120 MPa bearing allowable, and 60 MPa shear-out allowable.

1. F_t,total = 16,666.666667 N and F_b = 2,777.777778 N.
2. Projected bearing area is 10 × 12 = 120 mm².
3. Nominal bearing stress is 23.148148 MPa, giving 0.192901× utilization.
4. Clear edge ligament is 20 - 11/2 = 14.5 mm.
5. Two-plane shear-out area is 2 × 14.5 × 12 = 348 mm².
6. Nominal edge shear-out stress is 7.98212 MPa, giving 0.133035× utilization.
7. Bearing governs. Nominal governing torque capacity is 5,184 N·m and continuous required thickness is 2.314815 mm.

The required thickness is a mathematical screening result, not a selectable flange geometry. Replace it with a realizable geometry and repeat every applicable strength, stiffness, fatigue, tolerance, and manufacturing check.

Geometry warnings and load sharing

The hole must leave positive material to the directional free edge and must remain smaller than adjacent bolt-center spacing. The calculator reports hole clearance, clear edge ligament, adjacent-hole ligament, and e/d_b for review.

NASA guidance describes 2D as common nominal edge-distance practice and cautions against an edge distance below 1.5D. The calculator therefore emits an engineering warning below e/d_b = 1.5; it does not turn that guidance into a universal coupling acceptance rule.

Equal force per bolt is an idealization. NASA RP-1228 notes that clearance and hole-position variation can cause one bolt to carry load before the rest of the group engages. Use a reviewed load-distribution method when fit, deformation, or tolerance makes equal sharing unreliable.

Engineering scope and limitations

This is a first-pass nominal stress screen. It excludes:

• local nonlinear contact pressure, hole ovalization, plastic redistribution, and bushing behavior;
• net-section tension, block shear, curved or interacting tear-out paths, flange bending, rim failure, and hub stress;
• bolt shear, tension, bending, preload, slip resistance, tightening, prying, and combined loading;
• shaft, key, spline, weld, casting, material defect, and balance checks;
• fatigue, fracture, fretting, corrosion, temperature, wear, impact, and misalignment;
• automatic material allowable, safety factor, code coefficient, bolt, hole class, fit, tolerance, or coupling selection;
• manufacturing feasibility, inspection acceptance, guards, standards compliance, or engineering approval.

Use the current standards and validated material data governing the real assembly. If utilization is marginal, geometry is below the cited range, or loads are not concentric pure torque, use a more rigorous connection analysis.