development of design allowables data for adhesives for attaching

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DEVELOPMENT OF DESIGN ALLOWABLES DATA
FOR ADHESIVES FOR
ATTACHING REUSABLE SURFACE INSULATION
FINAL TECHNICAL REPORT
October 1972
HOR U.S. GOVERNMENT AGENCIES AND IHblR CONTRACTORS ONLY
Prepared Under Contract No. MAS 9-12392
GENERAL DYNAMICS
Convair Aerospace Division
Fort Worth, Texas
for
NATIONAL AERONAUTICS AND SPACE ADMINISTATION
MANNED SPACECRAFT CENTER
Houston, Texas
Page Intentionally Left Blank
DEVELOPMENT OF DESIGN ALLOWABLES DATA
FOR ADHESIVES FOR ATTACHING
REUSABLE SURFACE INSULATION
H. P. Owen
' M. T. Carroll • .-:
Convair Aerospace Division of General Dynamics
Fort Worth Operation
FINAL TECHNICAL REPORT
CONTRACT NO. NAS9-12392
October 1972
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
MANNED SPACECRAFT CENTER
HOUSTON, TEXAS
F O R E W O RD
This final report was prepared by General Dynamics' Convair
Aerospace Division at Fort Worth for National Aeronautics and
Space Administration, Manned Spacecraft Center (NASA,MSC) under
contract NAS9-12392 including CCA No. 1, "Development of Design
Allowables Data for Adhesives for Attaching Reusable Surface In-
sulation." Work reported herein was performed under the direction
of the Materials Technology Branch of the Structures and Mechanics
Division with I. K. Spiker as the Contracting Officer's technical
monitor. Development work reported herein was conducted between
17 January 1972 and 30 September 1972.
The authors wish to acknowledge the contributions of the
following individuals who were directly responsible for perform-
ing the program tasks and preparing this final report: J. E.
Halkias, E. W. Turns, J. D. Reynolds, and H. J. Weltman (Engineer-
ing Test Laboratories), R. V. Wolff and M. S. Howeth (Structures
and Materials) and E. W. Gomez (Stress Analysis).
T A B LE OF C O N T E N TS
Section Page
1 INTRODUCTION AND SUMMARY 1
2 TEST MATERIALS AND METHODS 5
2.1 Specified Adhesives ' 6
2.2 Selection of Adherends and Primers 6
2.2.1 Adherends (Substrates) 11
2.2.2 Primers 12
2.3 Processing 13
2.3.1 Mixing .and Handling Character-
istics 13
2.3.2 Uniformity of Lots 15
2.4 Vendor Quality Control Certificates 16
2.4.1 Selection of RTV Silicone for
Modification 16
2.4.2 Selection of Microballoon Fillers 16
2.4.3 Selection of Closed-Cell Silicone
Rubber Sponge 18
3 DEVELOPMENT OF REDUCED MODULUS AND LOWER
DENSITY ADHESIVE SYSTEM 19
3.1 Modification of Dow Coming's 77-137
RTV Silicone Material 20
3.2 Modification of GE RTV-560 Using
Microballoons as Fillers 21
3.3 Raybestos-Manhattan's Closed-Cell Sili-
cone Rubber Sponge, RL-1973, Bonded
Between GE RTV-560 25
3.3.1 Effect of Reduced Pressure on
RL-1973 Sponge 28
3.3.2 Selection of RL-1973/GE RTV-560
as the Fourth Adhesive System in
the Program 28
3.4 Density of Adhesives 30
iii
TABLE OF CONTENTS (Continued)
Section Page
4 MECHANICAL PROPERTIES 33
4.1 Adhesion in Tension 34
4.1.1 Test Method 34
4.1.2 Results and Discussion 35
4.1.3 Data Analysis 36
4.2 Adhesion in Shear 55
4.2.1 Test Method 55
4.2.2 Results and Discussion 55
4.2.3 Data Analysis 58
4.3 Tensile Modulus and Poisson's Ratio 70
4.3.1 Test Method 70
4.3.2 Results and Discussion 74
4.4 Shear Modulus 85
4.4.1 Test Method 85
4.4.2 Results and Discussion 86
4.5 Compression Modulus 102
4.5.1 Test Method 102
4.5.2 Results and Discussion 104
4.6 Poisson's Ratio 112
4.6.1 Results 112
4.6.2 Discussion 112
4.7 Constant Strain-Stress Relaxation 122
4.7.1 Test Method 123
4.7.2 Results and Discussion 127
iv
TABLE OF CONTENTS (Continued)
Section Page
5 THERMAL PROPERTIES 131
5.1 Thermal Expansion 132
5.1.1 Test Method 132
5.1.2 Results and Discussion 134
5.2 Thermal Conductivity 146
5.2.1 Test Method 146
5.2.2 Results and Discussion 148
5.3 Specific Heat 153
-5.3.1 Test Method 153
5.3.2 Results and Discussion 156
5.4 Thermal Cycling 157
5.4.1 Band-Shaped Specimens 157
5.4.2 Torsional Shear Specimens 159
5.4.3 Shear Strength at Failure 161
5.4.4 Tensile (Spool) Specimens 163
6 BEHAVIOR OF SILICONE RUBBER ADHESIVES AT
AND BELOW THEIR GLASS TRANSITION TEMPERA-
TURES 165
6.1 Observation of Specimens at and Below
Glass-Transition Temperature 166
6.2 Literature Survey Regarding Low Tem-
perature Properties of Silicone Rubber 167
6.3 Stress Relaxation of Polymers at Low
Temperature 168
7 CONCLUSIONS AND RECOMMENDATIONS 171
7.1 Conclusions 172
7.2 Recommendations 173
TABLE OF CONTENTS (Continued
Section Page
APPENDIX I Quality Control Documents Received for
Test Candidate Materials 177
APPENDIX II Summary of Regression Analysis and
i
Tolerance Limit Techniques Used in
189
Data Reduction
APPENDIX III Compilation of Stress-Strain Calcula-
195
tions
APPENDIX IV Summary of Strain Confidence Limits for
Best Fitting Regression Equation to
Stress-Strain Data 215
APPENDIX V Summary of Strength Confidence Limits
for Best Fitting Regression Equation
to Strength-Temperature Data 233
APPENDIX VI Tensile Modulus, Poission's Ratio
Least Square Computations 237
REFERENCES 241
vi
L I ST OF I L L U S T R A T I O NS
Figure Page
1 Program Overview 7
2 Tensile Specimen 8
3 Shear Specimen 8
4 Tensile Modulus Specimen 8
5 Shear Modulus Specimen 8
6 Compression Specimen 9
7 Density and Specific Heat Specimen 9
8 Thermal Expansion Specimen ' 9
9 Thermal Conductivity Specimen 9
10 Band-Shaped Specimen 10
11 Constant Strain Tension Adhesive Specimen IQ
12 Tensile Stress-Strain of Aluminum to Alumi-
num Bonded Butt Joints 0.064" Glue Lines
(approx.) Tests at 75°F 27
13 Shear Stress-Strain of Aluminum to Aluminum
Bonded Single Overlap Joints 0.064" Glue
Lines (approx.) Tests at 75°F 27
14 Volume Change Vs. Time at Vacuum and Pressure:
RM RL-1973 Sponge 29
15 Cylinder Adhesion Test Setup 35
16 Tensile Strength Vs. Temperature 38
17 Ultimate Elongation Vs. Temperature 38
18 Average Flatwise Tensile Strength of
Adhesive Materials 45
vii
LIST OF ILLUSTRATIONS (Continued)
Figure Page
19 Tensile Strength Vs. Temperature -
RTV-560 Material 46
20 Tensile Strength Vs. Temperature -
SLA-561 Material 46
21 Tensile Strength Vs. Temperature DC 93-046
Material 46
22 Tensile Strength Vs. Temperature RTV 560/
RL-1973 46
23 Tensile Stress-Strain RTV-560 (-270°F) 47
24 Tensile Stress-Strain RTV-560 (-200°F) 47
25 Tensile Stress-Strain RTV-560 (-175°F) 47
26 Tensile Stress-Strain RTV-560 (-150°F) 47
27 Tensile Stress-Strain RTV-560 (-65°F) 48
28 Tensile Stress-Strain RTV-560 (80°F) 48
29 - Tensile Stress-Strain RTV-560 (300°F) 48
30 Tensile Stress-Strain RTV-560 (350°F) 48
31 Tensile Stress-Strain SLA-561 (-150°F) 49
32 Tensile Stress-Strain SLA-561 (-65°F) 49
33 Tensile Stress-Strain SLA-561 (80°F) 49
34 Tensile Stress-Strain SLA-561 (300°F) 49
35 Tensile Stress-Strain SLA-561 (350°F) 50
36 Tensile Stress-Strain DC-93-046 (-270°F) 50
37 Tensile Stress-Strain DC-93-046 (-200°F) 50
viii