Asatellite component is in the shape of a cube with 10cm edges, has an evenly distributed mass of 2 kg and one bolt hole at each of four corners. if the maximum predicted random vibration environment is 10 grms, what bolt size would be a good choice for restraint? what other factors might drive bolt size besides force/stress?
We have the following data:
Mass = 2 kg
R.V = 10 Grms
g = 9.8 m/s^2
edge of cube = 10 cm = 0.1 m
Assume that the force is divided between the four bolts, the restraint force will be:
Total Restraint Force = 196.2
Force on each bolt:
Assume the bolt material as metric class 4.6 with:
Proof strength = 225 MPa
Tensile strength = 400 MPa
Yield strength = 240 MPa
The load can be either horizontal or vertical, thus we check for tension and shear.
Assume that the load is on the bolts.
Maximum and Minimum bolt load is =
(where stress concentration factor = 2.2)
The rotating beam fatigue strength is:
Assume machined thread, the surface condition factor will be:
Fatigue strength for infinite cycles:
Using modified Goodman relation with assumed factor of safety:
Axial load of the bolt is 49.05 N.
Principal stress are:
Using endurance strength values:
The bolt is safe in shear.
We will need to check:
1. Natural frequency of supporting system
2. Range of excitation frequencies