Bruce Sommer,

1
Helium Tank Strength Assessment

• Trent Martin
• Lockheed Martin Space Operations
• AMS-02 Superconducting Magnet Group Meeting
• July 24-25, 2003

2
Introduction

• Overview of Analysis
• Finite Element Model Description
• Component Stresses
• Margin of Safety Summary Table
• Preliminary Buckling Analysis
• Outstanding Issues on Helium Tank

3
Overview

• The Helium Tank is analyzed for the following
  load conditions
• Launch-Cold with 3 bar Internal Pressure
• Landing-Cold with 3 bar Internal Pressure
• Landing-Warm with 1 bar External Pressure
• Material Strength allowables are adjusted to
  account for both the warm and cryogenic
  conditions of the Helium Tank.
• The cold material allowables are determined by
  coupon tests at cryogenic temperatures. (2 sigma
  values from test samples)
• The warm material allowables are taken from the
  Military Handbook 5H and the ASTM Standards.

4
Finite Element Model Description

• Helium Tank Finite Element Model (FEM) is a fine
  meshed model composed of 119867 Elements and
  111881 Nodes.
• The same model is used for both strength and
  stability analysis.
• A local model is used for more detailed analysis
  of the Central Ring.
• All Major components are modeled with discrete
  elements.
• Mass representation elements are used for smaller
  nonstructural components such as the cryo.
  valves, TMPs, tubing, etc

5
Helium Tank FEM Model
6
Detailed Central Ring Model
This model is inserted in the high stress region
of the Central Ring of the full Helium Tank Model.
7
Mass Representation of Cryo. Valves
Cryo. Valve Mass Elements
8
Component Stresses

• The critical stresses for the Helium Tank are
  driven by the low yield strength of 5083
  aluminum.
• All contour stress plots of the Helium Tank
  Components are for von Mises stresses only.
• All Margins of Safety for ultimate stresses are
  higher than the those for yield.

9
Component Stresses Central Ring

• Parent Material

Governing Load Launch 3 bar Internal
Pressure Max Von-Mises Stress 28.22 ksi ( 194.6
N/mm2)
Max Stress Location
10
Component Stresses Central Ring

• Weld Area

Governing Load Launch 3 bar Internal
Pressure Max Von-Mises Stress 11.69 ksi ( 80.6
N/mm2)
Max Stress
11
Component Stresses Thro Tubes

• Parent Material

Critical Stress Region
Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 32.01 ksi ( 220.7
N/mm2)
Max Stress
12
Component Stresses Thro Tubes
Critical Stress Region

• Weld Area

Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 23.38 ksi ( 161.2
N/mm2)
Max Weld Stress
13
Component Stresses Inner Rings
Critical Stress Region
Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 20.29 ksi (139.9
N/mm2)
Max Stress
14
Component Stresses Outer Rings
Critical Stress Region
Governing Load Launch 3 bar Internal
Pressure Max Von-Mises Stress 17.65 ksi (121.7
N/mm2)
Max Stress
15
Component Stresses End Dishes
Critical Stress Region
Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 13.95 ksi (96.2
N/mm2)
Max Stress
16
Component Stresses Porous Plug
Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 27.0 ksi (186.2
N/mm2)
Max Stress
17
Component Stresses Burst Disk
Max Stress
Governing Load Landing Full 3 bar Internal
Pressure Max Von-Mises Stress 7.32 ksi (50.5
N/mm2)
18
Margin of Safety Summary Table
Notes 1. Parent material property at cryo
temperature 2. Weld material property
at cryo temperature 3. Safety Factor
for yield 1.10 4. Weld material
properties are used conservatively for inner and
outer rings.
19
Stability Analysis of Helium Tank

• Stability analysis for the Helium Tank is done by
  Lockheed Martin Michoud.
• Current analysis results reflect the following
  loading conditions
• Internal pressure of 3 bar
• External pressure of 1 bar
• Inertial loads will be combined with the
  corresponding pressure loads for future analysis.

20
1 bar External Pressure Linear Eigenvalue
Solution

• Helium Tank - Outer Rings - ( 1-bar external
  pressure)
• pcl 30.40 psi (0.21 N/mm2), pcr 12.75 psi
  (0.09 N/mm2)

21
3 bar Internal Pressure Linear Eigenvalue Solution

• Helium Tank - Inner Rings - ( 3 bar internal
  pressure)
• pcl 112.4 psi (0.78 N/mm2), pcr 60.7 psi
  (0.42 N/mm2)

22
Helium Tank Preliminary Stability Analysis Summary
Notes 1 ) Knock Down Factor (KDF) from
asymptotic theory _at_ imperfection 0.06 in (
1.50 mm) 2 ) pcl classical pressure 3 ) pcr
critical pressure (pclKDF) 4 ) SF Safety
Factor 5 ) MS Margin of Safety 6 ) Lateral
pressure Not imperfection sensitive for ZL (
Batdorf's parameter ) gt 300. 7 ) Inner Ring ZL
11.985 8 ) Outer Ring ZL 6.178
23
Helium Tank Preliminary Stability Analysis
Imperfection Sensitivity
Helium Tank Outer Rings
Note Helium Tank design is in the lower region
of the curve where test values are lower than the
theoretical curve. Thus the knock down factor is
higher.
24
Helium Tank Preliminary Stability Analysis
Imperfection Sensitivity (cont.)
Helium Tank Outer Ring
25
Proposed Buckling Solutions

• Assumption
• Geometric imperfections cannot be reduced.
• Proposed Solutions
• Outer Rings Add an additional circumferential
  rib between the existing ribs (5 total) and
  increase the rib height from 14 mm to 19 mm.
  Total weight increase for Outer Rings is
  estimated to be 17.6 lbs (8.1 kg) .
• Inner Rings Increase skin thickness in middle
  region of Inner Rings between Thro Tubes from 4.7
  mm to 5.4 mm. Total weight increase for Inner
  Rings is estimated to be 12.45 lbs (5.6 kg).

26
Margins of Safety for Combinations of
Imperfection/Thickness
27
Outstanding Issues

• Leak-Before-Burst (LBB) analysis for fracture
  control and report.
• Test data to determine the strength of the
  Through Tube flange material, as per
  recommendation of LMSO materials group.
• Perform NASTRAN non-linear buckling analysis.
  This will include both the effects of
  internal/external pressure combined with inertial
  loads.

28
Outstanding Issues (cont.)

• All weld allowables approved by the materials
  group are only for single pass welding.
  Additional data will be required from HBE to
  qualify and accept any multiple pass welding in 4
  mm and 6 mm thick welds.
• Stress analysis report will be written after
  completion of the analysis pending results of
  material tests.