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2124 AL + SiC COMPOSITE - Virginia Tech ... 10 Typical stress-strain curve for 2124+SiCw at 300 F. . . . 107 11 Typical room temperature stress-strain curve for unreinforced 2124

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Text of 2124 AL + SiC COMPOSITE - Virginia Tech ... 10 Typical stress-strain curve for 2124+SiCw at 300 F. ....

  • Keywords: Creep, Discontinuously Reinforced, Metal Matrix Composite, Aluminum, Parametric Models, Manson-Haferd Parameter

    ANALYSIS OF CREEP BEHAVIOR AND

    PARAMETRIC MODELS FOR 2124 AL

    AND 2124 AL + SiCW COMPOSITE

    Karen M. B. Taminger

    Thesis submitted to the Faculty of the

    Virginia Polytechnic Institute and State University

    in partial fulfillment of the requirements for the degree of

    MASTER OFSCIENCE

    IN

    MATERIALS SCIENCE AND ENGINEERING

    Robert W. Hendricks, Chair William D. Brewer

    Alex O. Aning Michael Hyer

    February 11, 1999

    Blacksburg, Virginia

  • ANALYSIS OF CREEP BEHAVIOR AND PARAMETRIC MODELS FOR 2124 AL

    AND 2124 AL + SiCW COMPOSITE

    Karen M. B. Taminger

    (ABSTRACT)

    The creep behavior of unreinforced 2124 aluminum and 2124 aluminum reinforced with

    15 wt% silicon carbide whiskers was studied at temperatures from 250°F to 500°F.

    Tensile tests were conducted to determine the basic mechanical properties, and

    microstructural and chemical analyses were performed to characterize the starting

    materials. The creep, tensile, and microstructural data for the 2124+SiCw composite were

    compared with a similarly processed unreinforced 2124 aluminum alloy. Applying the

    basic theories for power law creep developed for common metals and alloys, the creep

    stress exponents and activation energies for creep were determined from the experimental

    data. These results were used to identify creep deformation mechanisms and compared

    to predicted values based on a parametric approach for creep analysis. The results

    demonstrate the applicability of traditional creep analyses on non-traditional materials.

  • iii

    ACKNOWLEDGEMENTS

    There are numerous people who were instrumental in assisting me to finally complete

    this degree. First, I would like to thank my committee chairman, Dr. Robert W.

    Hendricks for his guidance and enthusiasm for my research. I would like to thank my

    committee, Dr. Robert W. Hendricks, Dr. Michael W. Hyer, Dr. Alex O. Aning, and Mr.

    William D. Brewer for having faith in my abilities, for being willing to tackle a graduate

    student from 300 miles away, and for exercising infinite patience with my timetable. I

    would also like to thank Mr. William D. Brewer of NASA Langley Research Center for

    serving as a mentor as well as an adjunct advisor for this degree, (even though he

    preferred a root canal to my defense). This degree would never have materialized (no

    pun intended) without the help of Ms. Jan Doran in the Materials Engineering Department

    at VPI&SU, who rescued my student file from certain oblivion on several occasions. My

    gratitude is also extended to Mr. George Allison of NASA Langley Research Center for

    his assistance with the tuition side of this degree. Finally, I would be remiss in failing

    to mention my husband, Brian, for all of his love and support, for picking up more than

    his share of the slack so that I could work on this thesis, and for always helping me to

    see the hope of a rainbow through a little black rain cloud.

  • iv

    CONTENTS

    ABSTRACT . . . . . . . . . ii

    ACKNOWLEDGEMENTS . . . . . . . . iii

    1 INTRODUCTION . . . . . . . . . 1 1.1 Development of Airframe Applications . . . . . 2 1.2 Materials and Properties . . . . . . . 7 1.3 Creep Degradation Mechanisms and Parametric Models . . . 17

    2 THESIS JUSTIFICATION . . . . . . . . 26

    3 PROCEDURES . . . . . . . . . 27 3.1 Experimental Design . . . . . . . 27 3.2 Material and Processing History . . . . . . 28 3.3 Microstructural Analysis . . . . . . . 31 3.4 Phase Identification . . . . . . . . 33 3.5 Tensile Tests . . . . . . . . 35 3.6 Creep Tests . . . . . . . . . 38

    4 DISCUSSION OF RESULTS . . . . . . . 44 4.1 Microstructural Analysis . . . . . . . 44 4.2 Tensile Data . . . . . . . . . 46 4.3 Creep . . . . . . . . . 48 4.4 Predictive Creep Models . . . . . . . 58

    5 CONCLUSIONS . . . . . . . . . 66

    REFERENCES . . . . . . . . . 67

    TABLES . . . . . . . . . . 74

    FIGURES . . . . . . . . . . 94

    A DEFINITION OF SYMBOLS . . . . . . . 145

    B TENSILE DATA . . . . . . . . . 146

    C CREEP DATA . . . . . . . . . 159

    VITA . . . . . . . . . . 202

  • v

    TABLE OF CONTENTS

    L IST OF TABLES

    1 Alloy compositions for 2024 and 2124. . . . . . 76

    2 Test matrix. . . . . . . . . . 77

    3 Tensile data for unreinforced 2124. . . . . . 81

    4 Tensile data for 2124+SiCw. . . . . . . 83

    5 Creep data for unreinforced 2124. . . . . . . 86

    6 Creep data for 2124+SiCw. . . . . . . . 87

    7 Creep stress exponents for unreinforced 2124 and 2124+SiCw. . . 89

    8 Activation energies for creep for unreinforced 2124 and 2124+SiCw. . 90

    9 Manson-Haferd parameter values for unreinforced 2124 and 2124+SiCw. . . . . . . . . 91

    10 Manson-Haferd predictions of creep stress exponents for unreinforced 2124 and 2124+SiCw. . . . . . 92

    11 Manson-Haferd predictions of activation energies for creep for unreinforced 2124 and 2124+SiCw. . . . . . 93

  • vi

    TABLE OF CONTENTS

    L IST OF FIGURES

    1 Skin temperature of a supersonic aircraft as a function of airspeed. . 98

    2 Thermal flight profile for a standard mission on the Concorde. . . 99

    3 Creep deformation-mechanism map for pure aluminum. . . . 100

    4 Optical micrographs of unreinforced 2124 and 2124+SiCw. . . 101

    5 SEM micrograph of polished cross-section of 2124+SiCw. . . 102

    6 TEM micrographs of 2124+SiCw after 143 hrs at 350°F/35 ksi. . . 103

    7 X-ray diffraction scans of as-received unreinforced 2124 and 2124+SiCw. . . . . . . . . . 104

    8 Al-Si binary phase diagram. . . . . . . 105

    9 X-ray diffraction scan of 2124+SiCw as-received and after 142 hours at 350°F with 0 and 35 ksi. . . . . . . 106

    10 Typical stress-strain curve for 2124+SiCw at 300°F. . . . 107

    11 Typical room temperature stress-strain curve for unreinforced 2124. . 108

    12 Effect of temperature on ultimate tensile strength. . . . 109

    13 Effect of temperature on proportional limit. . . . . 110

    14 Effect of temperature on 0.02% offset yield strength. . . . 111

    15 Effect of temperature on modulus. . . . . . . 112

    16 Strain gage information sheet. . . . . . . 113

    17 Creep of unreinforced 2124 and 2124+SiCw at 250°F and 37 ksi. . 114

    18 Creep of unreinforced 2124 and 2124+SiCw at 350°F and 25 ksi. . 115

    19 Creep of unreinforced 2124 and 2124+SiCw at 500°F and 17 ksi. . 116

    20 Creep of unreinforced 2124 and 2124+SiCw at 350°F and a stress ratio of 0.5. . . . . . . . . . 117

    21 Creep of 2124+SiCw at 350°F and 17, 25, and 35 ksi. . . . 118

    22 Creep of unreinforced 2124 at 350°F and 17, 25, and 35 ksi. . . 119

  • vii

    23 Creep of 2124+SiCw at 17 ksi and 350°F and 400°F. . . . 120

    24 Creep of unreinforced 2124 at 17 ksi and 350°F and 400°F. . . 121

    25 SEM fractographs of 2124+SiCw tensile specimens tested at 300°F and 500°F. . . . . . . . . 122

    26 Determination of creep stress exponents for 2124+SiCw. . . . 123

    27 Determination of creep stress exponents for unreinforced 2124. . . 124

    28 Effect of temperature on stress exponents for 2124+SiCw. . . 125

    29 Effect of temperature on stress exponents for unreinforced 2124. . 126

    30 Determination of creep threshold stress for 2124+SiCw. . . . 127

    31 Determination of creep threshold stress for unreinforced 2124. . . 128

    32 Determination of apparent activation energy for creep for 2124+SiCw. . 129

    33 Determination of apparent activation energy for creep for unreinforced 2124. . . . . . . . . 130

    34 Determination of Larson-Miller constant based on minimum creep rate for 2124+SiCw. . . . . . . . 131

    35 Determination of Larson-Miller constant based on minimum creep rate for unreinforced 2124. . . . . . . 132

    36 Determination of Manson-Haferd constants based on time to 0.05% strain for 2124+SiCw. . . . . . . 133

    37 Determination of Manson-Haferd constants based on time to 0.05% strain for unreinforced 2124. . . . . . 134

    38 Determination of Manson-Haferd constants based on minimum creep rate for 2124+SiCw. . . . . . . . 135

    39 Determination of Manson-Haferd constants based on minimum creep rate for unreinforced 2124. . . . . . . 136

    40 Manson-Haferd master curves for time to 0.05% creep strain. . . 137

    41 Manson-Haferd master curves for minimum creep rate. . . . 138

    42 Manson-Haferd predictions of creep stress exponents for 2124+SiCw. . 139

    43 Manson-Haferd predictions of creep stress exponents for unreinforced 2124. . . . . . . . . 140

  • viii

    44 Effect of temperature on predicted creep stress exponents for 2124+SiCw. . . . . . . . . . 141

    45 Effect of temperature on predicted creep stress exponents for unreinforced 2124. . . . . . . . . 142

    46 Manson-Haferd predictions of creep activation energies for 2124+SiCw. . . . . . . . . . 143

    47 Manson-Haferd predictions of creep activation energies for unreinforced 2124. . . . . . . . . 144

  • ix

    TABLE OF CONTENTS

    L IST OF EQUATIONS 1 Standard equation for simple power law creep. . . . . 21

    2 Basic equation for Larson-Miller parametric approach

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