Creep Strength of Aluminum Alloy Conductor

154 Pages·2014·14.86 MB·English

by  Gerard, Thomas John

CREEP STRENGTH OF ALUMINUM
ALLOY CONDUCTOR
by
Thomas John Gerard
A THESIS
submitted to
OREGON STATE COLLEGE
in partial fulfillment of
the requirements for the
de gree of
MASTER OF SC IENGE
May 1958
AHFBOIISDT
Redacted for Privacy
Amogt*tc Pruful*ur of il*ahralaal Sngln**rl*g
In Shmgp of lrJor
Redacted for Privacy
Ecad of Dryartucut af fmh*ntarl Eagfprmiag
Redacted for Privacy
Shntnnen of, Ssbsol ft,riluata Sounl,ttro
Redacted for Privacy
saarn of Sr*thntn Sohsel
tb.tlr lr
Detr pntrcnbail,,furthf /c ,/,?-t#­
by E;Lrn Evrnl
typcdl
ACKli'OWLEDGMENT
o.
The author is deeply indebted to G. l'aasohe,
Associate Professor ot Mechanical Engineering, Oregon
State College, for his extensive help in this project.
He is grateful to the members of the faoulty and
stu~
dent body who constructed and calibrated the apparatus.
He wishes to thank the Kaiser Aluminum and Ohemieal
Corporation tor making this investigation possible, and
in particular, Doctor Roger Olleman, Department of
Metallurgical Research, for his kind The
suggest1~ns.
author is grateful to Mr. Robert Leduc who kindly helped
him .in the preparation of graphs for this paper.
TABIE OF CONTENTS
Page
BACKGROUND...................................... 1
Introduction•••••••·••••••••••••• ; • ; •••·• • • • • l
Objectives••••••• 7
~•••••••••••••••••••••••••
Scope•••••• •••• •• •••••••·••••• ••• 8
~ ~ ~ ~ · .~.....
History•••••••••••••••••••• ••••••·••••••••• 8
~
Definition of Terms•••••••••••••••••••••••• 9
THEORY•••••••••••••••••••••••••••••••••••••••••• 10
Factors Affecting Creep•••••••••••••••••••• 10
Metallurgical $xplanations................. 17
Creep Correlations......................... 29
Summary•••••••••••••••••••••••••••••••••••• 36
CREEP TESTING••••••••••••• 37
~~.~••••••••••••••••••
ASTM Specifications........................ 37
Creep Testing ·or ·Aluminum ·AlloyConductor.. 39
Test Material•••••••••••••••••••••••••••••• 40
Creep Testing Machines ••• ••• • • • • • • • •• • • • • • • 44
Test Equipment ••••••••••••••••••••••••••••• 45
Calibration................................ 57
Load Calibration........................... 58
TEST CONDITIONS................................. 59
Specimens.................................. 60
Loads•••••••••••••••••••••••••••••••••••••• 61
Duration of Test••••••••••••••••••••••••••• 63
Observations••••••••••••••••••••••••••••••• 63
I
Ri SULTS•••••••• ~••••••••••••~••••••••••••••••~•• bh
64
General••••••••••••••••••••••••••••••••••••
Performance of Equipment ••••••••••••••••••• 65
INTERPRETATION OF RESULTS •• 68
~~.~•••••••••••••••••
General Correlations....................... 68
Preload•••••••••••••••••••••••••••••••••••• 71
Correlation of Prestressed Specimens....... 76
10,000 Hour Test••••••••••••••••••••••••••• 84
Conductor and Wire Correlations............ 87
Page
Manu1'actur1ng Lot Correlations•••••••••••••• 90
Residual Stresses........................... 95
Effect of Clamps,........................... 97
CONCLUSIONS •• •~•••••••••~•••••~•••~••••••••••••~• 98
Theory••••••••·. • •• ._•• • • •••••••••• ~ ~.. • • • ..• • • 98
Equipment ••• ". •.•·•• • ••••• ~ ............, • .,. • • • • • 98
Procedure.,. •••• •......•·•••·•..............._" • • • 99
Test Result .s••••••••••• ~ • ~, ~., ••••••• • • • • • • • • 99
••••••••••, ••••••• ••• 101
~EOOMENDATIONS ~ ~·•t•••••••••
BIBLIOGRAPm·••• •,• • ••••• , •· • • .............., •.....• • 103
APPENDIX•• : ••••••••••••••••••••• .... ~ ~ ~. ~ .~ , ~ ~ ~... ~-• 107
LIST OF FIGURES
Page
Figure 1. The Creep Curve•••••••••••••••••••••• 10
Figure 2. Effect of Tempe-rature on the Str·e-ngth
of ·Grain'S and Grain Boundari-es••••••• 16
Figure 3. Interior View of the Enclosure ••••••• 46
Figure 4• Loading and TakErtip Ends . of the Creep
48
Testing Machine••••••••••••••••••••••
Figure 5. Cutaway Sketch of' the Enclosure •••••• 49
Figure 6. External View of the Enclosure•••••••• 53
Figure 7. Schematic · or ·The .Air Conditioning
56
System••••••••·•••••••••••••••••••••••
Figure 8. Log...Log·o:ne Holir Preload Correlation
74
Curve•••••••••••••••••••••••••••••••••
Figure 9. Stress-strain·curve ·ror ·on.e ·Hour·
Preloads •••••••••••••••••••••••••••••• 75
Figure 10. Strain•Time Comparison Ourves of Pre­
stressed Specimens.................... 77
Figure 11. Log-Log Correlation ·ourves ·or ·p:re•
Stressed Specimens.................... 79
for
Figure 12. Stra1n-T1ma Curv$ the 10,000 Hour
Test Specimen......................... 85
Figure 13. Log-Log Strain-Time Curve for the
10,000 Hour Test Specimen............. 86
14.
Figure Creep Comparison Between Conductor
and Single Strand••••••••••••••••••••• 88
Page
Figure 15. Log-Log Correlation of Creep or ·
89
Conductor s.nd Single Strand.........
Figure 16. Manufacturing Lot Var1at1ons ·1n
Creep of Single Strands••••••••••••• 91
Figure 17. Log-L.og Creep Correlation of Manu­
facturing Lot Variations in -Single
Strands•• • • • ••••• • • • 92
e • •• ., • ·• • • ·•. • • ·•. •
Figure 18. Manufaet\U'ing Lot Variat1ons ·in·
Creep of Conductors................... 93
Figure 19. Log-Log Creep Correlation of Manu-.
raeturing Lot ·Vs.rlat1.ons in ·C on•
due tors.............................. 94
Figure 20. Effect of Creep Strain -upon Residual
Stresses in Conductors................. 96
LIST OF TABLES
Page
Table 1. Nominal Composition or ·the Test
Material................................ 1
Table 2. Test Cond1t16na ·or Series ·) and Series
4 Specimens. • • • • • • • • • • • • • • • • • • • •.• • • • • • • 62
Table .3. Table of Constants ·for the Creep
Equation••••••••••••••••••••••••••••••• 72
C~EP S~NMHOFALWDmM
ALLOY CONDUCTOR
BACKGROUND
IntrQd;setion
'!'he use of aluminum tor conduction of electricity
from the generating station to the user i.s now almost
standard throughout the electrical power indust17.
The change from the use of copper, formerly used, has
been brought about by the fortuitous combination of
good electrical conductivity, good corrosion resistance,
light weight, and relatively good strength by
pos~essed
aluminum. To decrease the cost of a transmission line it
a
is desirable to have as strong conductor as possible,
consistent with other factors. to enable the use of
fewer towers. Recently. efforts have been made to
increase the strength of aluminum by alloying and other
treatments.
In addition to the electrical load. a conductor is
required to withstand mechanically induced forces such
as tension. These cause the conductor to sag. This
sag has been found to increase over a period of time due
to plastic flow. It is the purpose of this thesis to
investigate the characteristics and extent of this
2
plastic flow as a step toward evaluation ot the new
aluminum alloy conductor as a transmission line material.
The elastic deformation of a metal specimen sub­
jected to a load within the proportional limit ot the
material may be predicted with a high degree of accuracy,
since the modulus ot elasticity remains essentially con­
stant tar the material. The limit of elastic strain and
the plastic strain exhibited by metals undergoing rel­
atively short time loads above the elastic limits is not
as easy to determine, since each new alloy may exhibit a
different plastic strain However, these rates may
rate~
be evaluated quickly by mean-s ot short time tests. This
plastic strain is generally of but indirect importance
to the designer who designs within the elastic limits;
he uses plastic strain as an added factor of safety.
Of direct concern to the design engine r is the
plastic deformation exhibited by metals subjected to
constant stress at loads well below the elastic limit
f.or long periods oi' time. Under ambient temperatures
this plastic strain is almost indeed, under
negl1g1bl~;
some conditions it might be undetectible without the aid
ot special equipment. However, in any part o! great
length this plastic deformation may become quite
noticeable. Should the part be loaded for any long