Revisions: (last rev date 8/4/99)
1)Added first ten buckling modes for determination of critical buckling pressure.
2) Corrected maximum bending stress equation for cap
3) Added von Mises calculation and corrected buckling calculation
4) Corrected von Mises equation
5) Added O-ring groove diameter for diametral clearance and tab bending calculations.
6) Corrected index problem with radial moment equations
The following calculations are for determining the margin of safety
The format for this analysis package will be as follows:
A) Input of design parameters including dimensions, material properties, and design depth
B) Calculations for deformation and stresses in cylinders (check for thin wall or thick wall condition)
C) Buckling calculations for cylinders
D) Calculations for deformations and stresses in end plates,
E) Weight calculation
F) Summary of input and list of results including diametral gap, stresses, margins of safety and weight.
Note: The minimum margin of safety will be determined based upon the lowest margin calculated in the sections above. Thus, for a give pressure vessel, the maximum working pressure may be limited by the end plate thickness while for another it may be limited by the length of the cylindrical section. Therefor, if a desired allowable working depth is not reached, the limiting factor needs to be determined in order to effectively iterate the design to meet the requirements. Also, the diametral gap must be checked for the different pressures to assure that it falls within the maximum allowable from the o-ring vendor.
(pp02)
(pp18)
1) Dimensional input:
Is it thin wall (1=yes)?
Meridional (axial) stress:
Change in height:
Inside Diameter :
Outside Diameter:
O-ring surface diameter:
Case Length:
Cylinder Base
Thickness:
Wall thickness:
Radial displacement
of circumference:
Circumferential (hoop) stress:
Plug Diameter:
Groove Width:
Groove Diameter:
Axial Stress:
Change in OD (radius):
End Cap OD:
End Cap Thickness:
Tab Thickness:
Connector Diameter:
Hoop Stress:
Change in ID (radius):
Radial Stress:
Change in Length:
2) Material properties:
Shear Stress:
Von Mises Stress:
NiBrAl Alloy C95510 / AMS4880
Modulus of elasticity:
Material density:
Poisson's ratio:
Yield Stress:
Shear stress:
Water density:
3) Design depth and resulting pressure:
Number of pressure steps:
Pressure:
For the expressions in the case to be valid, the following condition must be true (i.e., condition = 1):
for buckling:
for stress:
(pp19)
MARGIN OF SAFETY:
Mean radius:
Cylinder Height:
For the expressions in the case to be valid, the following condition must be true (i.e., condition = 1):
Meridional (axial) stress:
Circumferential (hoop) stress:
MARGIN OF SAFETY:
Von Mises Stress calculation:
CASE VOLUME CHANGE
Corresponding margins of safety:
for yield strength:
(pp19)
Radial displacement
of circumference:
Change in height:
EndCap Flange/Case Bearing Stress
Diametral clearance (extrusion gap):
Bearing Area:
Pressure step:
End Cap Force:
Extrusion gap (radial):
Bearing Stress:
Margin of safey:
EndCap Flange Shear Thru Stress
Flange Shear Area:
End Cap Force:
Shear Stress:
Margin of Safety:
Outer radius:
Inner radius:
Length:
radius range variable
for yield strength:
for shear strength:
Pressure step:
Extrusion gap (radial):
Tube dimensions:
radius:
length:
For the expressions in the case to be valid, the following condition must be true (i.e., condition = 1):
The critical pressure for the initial buckling of a cylinder
number of lobes:
critical pressure:
Margin of safety on buckling:
Where experimental values of pcritical are +/- 20% of pmin !!!
Solid circular plate
Uniformly distributed pressure from r o to a
(Roark Table 24, Case 10a:
Cylinder Base Thickness:
If assumed simply supported:
Check stress in bottom:
Plate Constant:
Margin:
check small deflection assumption
(deflection < t/2)
Table 24
This file corresponds to Cases 2a - 2d in Roark's Formulas for Stress and Strain.
Annular plate with a uniformly distributed pressure q over the portion from r o to a
Outer edge simply supported, inner edge free
Plate dimensions:
thickness:
outer radius:
inner radius:
Shear modulus:
check small deflection assumption
(deflection < t/2)
Should be < 1 ???
Margin:
For a conservative approach, assume the outer edge of the tabs are free and the inner edge fixed
Case 1l:
Loading on tab:
Margin:
Case 1l:
For o-ring tab:
Loading on tab:
Margin:
1. Case Weight Calc.:
Cylinder:
cross sectional area:
internal volume:
external volume:
weight:
End Cap:
volume:
Tab:
Plug:
Cap:
Weight:
Total Weight:
2. Volume Change of Case at Depth:
Radius change due to press:
Length chane due to press:
Dished End Cap Spherical Segment Vol.:
external volume of cyl. (at depth):
external volume of cyl.
Pressure Case Volume Change
Assume Bulk Modulus of CH2O = 325,000 psi.
Compressed water vol. at depth:
Wet weight at depth: