Current Progress on the Design and Analysis of the JWST ISIM Bonded Joints for Survivability at Cryogenic Temperatures

1
Current Progress on the Design and Analysis of
the JWST ISIM Bonded Joints for Survivability at
Cryogenic Temperatures

• Andrew Bartoszyk, Swales Aerospace
• FEMCI 2005 Workshop
• May 5, 2005

2
JWST/ISIM Stress Team

• Andrew Bartoszyk, Swales Aerospace Stress
  Analysis
• John Johnston, NASA GSFC Analysis Lead
• Charles Kaprielian, Swales Aerospace Stress
  Analysis
• Cengiz Kunt, Swales Aerospace Stress Analysis
  Lead
• Joel Proebstle, Swales Aerospace Stress
  Analysis
• Benjamin Rodini, Swales Aerospace Composite
  Materials
• Daniel Young, Swales Aerospace Stress Analysis

3
Design and Analysis Challenges

• Design Requirements
• Metal/composite bonded joints required at a
  number of nodal locations on the JWST/ISIM
  composite truss structure to accommodate bolted
  instrument interfaces and flexures.
• Survival temperature at 22K ( 400oF) 271K
  total DT from RT.
• Composite truss tube with high axial stiffness
  (23 msi) and low axial CTE ( 0 ppm/K).
• Multiple thermal cycles throughout design life of
  structure. In order to survive launch loads,
  joints cannot degrade more than an acceptable
  amount.
• Design/Analysis Challenges
• Large thermal mismatch stresses between metal
  fitting and composite tube at cryogenic
  temperature (22K).
• Analysis and design experience is very limited
  for metal/composite bonded joints at temperatures
  below liquid nitrogen (80K).
• Thermo-elastic material properties and strengths
  for composites and adhesives at 22K are not
  available and difficult to test for.

4
ISIM Basic Joint Assemblies
Plug
Saddle
T-Joint (Gusset Clips)
5
Basic Plug Joint Details
Metal Fitting (Invar 36) E 18.8 msi a 1.5
ppm/K

• Adhesive Bond (EA9309)
• E 1.1 msi
• G 0.4 msi
• 47.8 ppm/K
• Fsu 11.6 ksi (80 MPa)

Hybrid Composite Tube Eaxial 23 msi Ehoop
6.7 msi aaxial -0.13 ppm/K ahoop 3.7
ppm/K Szz 2.9 ksi (20 MPa) Szx Syz 5.8 ksi
(40 MPa)
75 mm square composite tube w/ nominal 4.6 mm
wall thickness
interlaminar strengths

• Stiffness and strength properties are given for
  22K.
• Thermal expansion properties are secant CTE from
  RT to 22K.

6
Composite Modeling and Mesh Size

• Mesh size 2.5 mm square in-plane
• Surface plies at bonded interfaces modeled
  individually
• Aspect ratio ? 2.5/0.071 ? 35
• Laminate core modeled with thicker elements
• Adhesive modeled with one element through the
  thickness
• Same mesh size used in all joint FEMs including
  development test FEMs
• Stress recovery Element centroid for
  interlaminar, corner for others

Symmetry Constraint
Ply 1 Ply 2 Ply 3
Invar Fitting
Adhesive (0.3 mm thick)
Symmetry Constraint
x
Ply 1 Explicit Props (T300/954-6 Uni Ply) Ply 2
Tube Smeared Props (T300/954-6 Uni Ply) Ply 3
Tube Smeared Props (M55J/954-6 Uni Ply)
y
View A-A
7
Lamina Failure Criteria Bonded Joints
33
s33
Under thermal loads, metal/composite bonded
joints typically fail in composite interlaminar
stresses.
11
F33
22
F23
Design Space
?13 / ?23 1.5
t23
F13
F13 gt FRSS gt F23
FRSS
t13
8
Interlaminar Failure Prediction
An empirical Interlaminar Failure Criterion is
used for critical lamina where s33 is peel
stress, trss is resultant transverse shear
stress, and F terms are material constants
dependent on interlaminar strengths, which are
being determined by testing.
s33
F33
Margin Calculations Stress State 1 Stress
State 2
State 1 (peel-shear interaction)
tRSS
FRSS
State 2 (compressive normal and shear)
9
Bonded Joint Design Sizing Flow
Material Characterization
START
Preliminary Design Tube Layout, Cross Section,
Laminate, Joint CAD Concepts
Phase 1B Double Strap Design
Identify Basic Joint Elements Plug, Saddle,
T-Joint Concepts
Phase 1B Double Strap Testing
Estimate Cryo Properties
Correlate Cryo Properties Revise Analysis
no
Good SFc
Preliminary Basic Design Thermal Survivability
SFc gt 1.0 (gt 1.5 Goal)
yes
Preliminary Basic Design Launch Loads MS gt 0
Calculate Envelope Joint Launch Loads
Optimize Basic Design MS gt 0
FS Factor of Safety (Requirement) SFc
Calculated Safety Factor MS Margin of
Safety SFc Allowable/Stress MS SFc/FS - 1
Verify Under GHT Loads
Phase 1C Strength Degradation Testing
Phase 2 Breadboard Joint Testing
Flight Joint Detailed Design Analysis
FINISH
10
Bonded Joint Analysis Correlation - Procedure

• Coupon Analysis
• Design
• (Match Flight Joint
• Critical Stresses)

5. Flight Joint Analysis
Design Limit Load (Mech Thermal)
3. Test Coupon Analysis
2. Coupon Testing
4. Failure Curve
Test Failure Load (Mech Thermal)
11
Basic Plug Joint Detailed Stress Analysis
Phase 2 Plug Joint
1/16 Slice
ISIM Plug Joint
Node Count 5,570 DOFs 16,710
12
Basic Plug Joint - FEM
Adhesive (0.3 mm thick)
x
z
y
Ply 1 Ply 2 Ply 3
Symmetry Constraint
A
Symmetry Constraint
A
Symmetry Constraint
x
Ply 1 Explicit Props (T300/954-6 Uni Ply) Ply 2
Tube Smeared Props (T300/954-6 Uni Ply) Ply 3
Tube Smeared Props (M55J/954-6 Uni Ply)
y
View A-A
13
Basic Plug Joint - Applied Loads
Load Case Type ? T (K) Fz (N) Remarks
1 Thermal -271 0 RT to cold survival temperature (22K)
2 Thermal I/F 1g -271 4513 Thermal plus worst case tension (I/F 1g) and worst case compression (I/F 1g)
3 Thermal I/F 1g -271 -9096 Thermal plus worst case tension (I/F 1g) and worst case compression (I/F 1g)
4 Launch 0 83200 Absolute max axial load from ISIM beam element model loads run (includes additional effective axial load due to moment load)
Symmetry Constraint
Fz (applied as pressure load on face)
x
z
14
Basic Plug Joint - Margin Summary
Load Case Failure Mode Failure Mode Allowable (MPa) Abs Max (MPa) MS Comments
Thermal Mechanical (-271K I/F 1g) Ply-1 (T300) s-t interlaminar   0.40  
Thermal Mechanical (-271K I/F 1g) Ply-3 (M55J) s-t interlaminar     0.32  
Thermal Mechanical (-271K I/F 1g) Invar (Blade) VM yield 275 115 0.91 assume strength properties at cryo to equal properties at room temperature
Thermal Mechanical (-271K I/F 1g) Invar (Blade) VM ultimate 414 115 1.57 assume strength properties at cryo to equal properties at room temperature
Launch Ply-1 (T300) s-t interlaminar   0.92  
Launch Ply-1 (T300) s11 1380 162 3.73 max corner stress. allowables are based on explicit props.
Launch Ply-1 (T300) s22 81 12.4 2.63 max corner stress. allowables are based on explicit props.
Launch Ply-3 (M55J) s-t interlaminar     0.38  
Launch Tube s11 439 157 0.55 max corner stress. allowables are based on tube smeared props.
Launch Tube s22 241 42 2.19 max corner stress. allowables are based on tube smeared props.
Launch Invar (Blade) VM yield 275 167 0.32 max corner stress in blade, localize stress raisers at blade/hub interface not included
Launch Invar (Blade) VM ultimate 414 167 0.77 max corner stress in blade, localize stress raisers at blade/hub interface not included

• Margins presented at PDR, Jan 2005.

15
Basic Plug JointPly 3 Interlaminar Stress Plots
Thermal I/F
y
z
Invar fitting
sxx (MPa)
MS 0.32 (shear dominated failure)
tRSS (MPa)
Invar fitting
16
SF and Failure Curve Basic Joint Assemblies
25.0


ISIM Basic Joints


Assumed Failure Curve (RSS shear)
20.0
15.0
Clip
SF 1.54
10.0
Saddle
SF 1.84
5.0
Interlaminar Normal (MPa)
Gusset
SF 1.52
0.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
-5.0
Plug
SF 1.99
-10.0
-15.0
Interlaminar RSS Shear (MPa)
17
DSJ Test Data and Estimated Failure Curve
25.0
20.0
FWT
Clip Peel Shear D/S
15.0
Double-Strap Peel 900
10.0
Interlaminar Normal (MPa)
5.0
FRMS
F23
F13
F23
F13
FRSS
0.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
-5.0
Clip Shear D/S
B-Basis Data
Double-Strap Shear 900
ISIM Basic Joints
-10.0
2,3 Failure Curve (90deg shear)
1,3 Failure Curve (0deg shear)
RSS Shear Failure Curve
-15.0
Interlaminar Shear (MPa)
18
Remarks and Conclusions

• Material characterization testing and joint
  development testing are in progress. Test
  results will be critical for analysis correlation
  and the final design/analysis of the ISIM
  metal/composite bonded joints.
• A Phase-2 test program is underway and will
  include thermal survivability testing of basic
  joints including a plug joint.
• An evaluation of strength degradation due to
  multiple thermal cycles will also be included in
  the joint development test program.
• The ISIM Structure successfully passed PDR
  (Preliminary Design Review) in January 2005,
  design requirements have been met. Critical
  Design Review is scheduled for December 2005.