MOLA Bolt Analysis Results

Using UAI/NASTRAN

The table below gives the results of the bolt analysis performed using NASTRAN grid point forces and SPC forces. The values in the Load column were taken directly from NASTRAN results. The NASTRAN run used gravity loads of 20.6g in the X and Y directions; and 22.8g in the Z direction, which is the launch direction. The worst case loads for each area of interest were taken from the results and used in the calculations.

The ninth and tenth columns are the most important. They show the Margins of Safety. These numbers need only be positive to show that the bolt will hold. As can be seen, all margins here are positive. MS yield is the stress relative to the material's yield stress, i.e., the stress it takes to permanently deform the bolt. MS ultimate is the stress relative to the material's ultimate stress, i.e., the stress necessary to break the bolt.

To refresh yourself on what each of the components listed below are, jump to the FEM exploded view.

Bolt Margins of Safety	Size	Area (in²)	Load (lb)	F_y (psi)	F_u (psi)	Stress_y	Stress_u	MS_y	MS_u
Honeycomb panel to e-box	8-32 UNC	0.014	168.1	65000	80000	46504.46	56405.00	0.40	0.42
Honeycomb panel to Ti Support tube	10-32 UNF	0.02	315.4	65000	80000	48856.25	59039.00	0.33	0.36
Honeycomb panel to Feet	10-32 UNF	0.02	346.1	65000	80000	49815.63	60113.50	0.30	0.33
Interface plate to Ti Support tube	10-32 UNF	0.02	140.5	65000	80000	43390.63	52917.50	0.50	0.51
Interface plate to Detector	6-32 UNC	0.00909	17.2	65000	80000	40182.62	49324.53	0.62	0.62
Interface plate to Laser housing	1/4-28 UNF	0.0364	140.7	65000	80000	41415.87	50705.77	0.57	0.58
Interface plate to Primary mirror	10-32 UNF	0.02	16.7	65000	80000	39521.88	48584.50	0.64	0.65
Feet to Nadir panel	8-32 UNC	0.014	205.9	65000	80000	48191.96	58295.00	0.35	0.37

FS on yield = 1.25, FS on ultimate = 1.4

The equation used to calculate these stress values is:

Bolt Stress = (.6)(F) + [(.5)(Load)(FS) / (Area)]

The term (.6)(F), where F is the material yield or ultimate stress, is used to show that about 60% of the bolt's preload (how much the bolt is tightened) goes into the bolt.
The (.5) term assumes that about 50% of the actual load goes into the bolt while the other 50% goes into the frame that's being bolted together.
Load is taken from NASTRAN analysis results, in this case forces from SPCs or GRID Points.
FS is the Factor of Safety used, which is 1.25 on yield and 1.4 on ultimate in this case. These numbers just add a bit of conservatism so that we're extra safe.
Bolt area is given in the third column in the table. It's a standard number for a particular bolt.

The equation used to calculate the margin of safety for yield is:

MS = [(bolt material yield stress) / (actual bolt stress)] - 1

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This page is maintained by Ryan Simmons, at Ryan.Simmons@nasa.gov.
This page was last updated on April 30, 1996.