MIL-DTL-3124E(SH)
The resulting stresses and deflections, when added to the maximum normal operating values, shall be not more than
the allowable stresses or deflections.
3.4.17.3 Allowable stresses. The combination of shock and operating stresses shall be not more than
0.2 percent offset yield strength at operating temperature. The unit loading for combined shock and operating loads
on babbitted bearings shall be limited to 22,000 lb/in2. The criteria for failure when plastic set is permissible shall
be the effective yield strengths in tension and shear of the material defined as follows:
σ = σy + F(σu σy)
γ = 0.6σ
Where:
σ = Effective yield strength in lb/in2.
γ = Effective shear strength in lb/in2.
σy = 0.2 percent offset yield, elastic limit, or other normal definition of material yield strength in lb/in2.
σu = Tensile strength or other normal definition of material failure strength in lb/in2.
F = Factor which takes into account the efficiency with which the material in the member is utilized, the
cross-section of the material, and the type of loading. The value of F is equal to the quantity (load
required to completely yield the member divided by that load required to initiate yielding) minus 1.
The following are examples of F:
F = 0.0 if element is in pure tension.
F = 0.0 for any brittle material, that is, one which has less than 10 percent elongation before
fracture in a tension test.
F = 0.5 if section is rectangular and loading is pure bending.
F = 0.7 if section is solid and circular and loading is pure bending.
F = A / (6 + 2A) if section is I beam.
A=
(Web width) x (Depth of section)
2 x (Flange width) x (Flange thickness)
3.4.18 Nil-ductility properties. When carbon steels with less than 1 percent of any one alloy are used in the
generator mounting feet or mounting brackets, bearing caps, bearing pedestals, and frames, nil-ductility transition
temperatures shall be not greater than 53.6 °F (see 4.6.19.2). This requirement shall not apply to plate thicknesses
less than 5/8 inch or greater than 4 inches.
3.4.19 Inclined operation. The generator shall operate in accordance with the performance requirements of this
specification, shall maintain satisfactory lubrication, and shall experience no loss of lubricating oil under the
following conditions. The momentary inclination cycle shall be as specified (see 6.2).
a. When the generator is permanently inclined from the normal horizontal position as much as 5 degrees
rotated on the normal horizontal axis through the center of the machine and 15 degrees rotation clockwise or
counterclockwise about the axis of rotation.
b. When the generator is momentarily inclined from the normal horizontal position as much as 10 degrees in
lieu of 5 degrees as specified in (a) and 45 degrees in lieu of 15 degrees as specified in (a).
3.4.20 Vibration resistance (environmental vibration). The generator shall withstand environmental vibration
conditions in accordance with Type I of MIL-STD-167-1.
3.4.21 Vibration (internally excited). The generator shall be balanced so that the reading of the vibration
indicator shall be in accordance with MIL-STD-167-1 (see 4.6.5).
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