THEORETICAL AND EXPERIMENTAL STRESS ANALYSES OF COMMON MECHANISMS IN FARMMACHINERY

118 Pages·5.727 MB·English

by  ALI, SYED AEJAZ

THEORETICAL AND EXPERIMENTAL STRESS ANALYSES OP
COMMON MECHANISMS IN FARM MACHINERY
By
SYED AEJAZ ALI
A THESIS
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Agricultural Engineering
1952
ACKNOWLEDGMENTS
The author wishes to express his thanks and sincere
appreciation for the helpful suggestions and timely guidance
and encouragement from the following persons who brought this
project into existence.
Dr. W. M. Carleton, professor in charge of major work.
Professor A. W. Farrall, Head of Agricultural Engineering
Department.
Professor H. F. McColly, Agricultural Engineering De­
partment .
The writer is also grateful to Dr. R. T. Hinkle, and
Professor Paul DeKoning both of the Mechanical Engineering
Department for their cooperation and assistance in making
possible the use of electronic instruments. The author also
expresses his thanks for the help received from other staff
members and persons in charge of the research laboratory in
the Agricultural Engineering Department.
THEORETICAL AND EXPERIMENTAL STRESS ANALYSES OP
COMMON MECHANISMS IN FARM MACHINERY
By
Syed Aejaz All
AN ABSTRACT
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of
DOCTOR OP PHILOSOPHY
Depart of Agricultural Engineering
Year 1952
I/ ) / ) f
a
Approved_
'
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SYED AEJAZ ALI ABSTRACT
In the development and manufacturing of the farm im­
plements and machinery, a common practice that had been
followed very extensively, and still is followed to a certain
extent is to design a machine or its part basing the know­
ledge on the rigorous mathematical theory or derived and
empirical formulas plus the previous experience in the ex­
perimental trial and error methods* These analytical solutions
were frequently aided by many safety factors assuring the de­
signer that his designed mechanisms were devised with a suf­
ficient margin of safety.
These practices which are very much refined and improved
in the industrial design by the exhaustive theoretical in­
vestigations supported by the highly developed experimental
techniques, have begun to influence the realm of farm equip­
ment design. Experimental methods developed and introduced
during the past decade for the amelioration of design and
developmental procedures in the industrial work are at present
being utilized by a farm machinery design engineer. The photo­
elasticity, X-ray analysis, brittle lacquer method and the
electric strain gauges are among the many experimental means
made available for the determination and analysis of stresses
and strains which form the basis of any design.
With these constantly improving trends in the field of
machinery design, an attempt was made by the author to use one
of the available means, namely the electric strain gauges as
- V -
SYED AEJAZ ALI - ABSTRACT
an aid for the experimental stress analysis. The goal set
for the utilization of this experimental technique was to
evaluate analytically, the stresses in some of the commonly
used mechanisms in farm machinery, to determine the stresses
from the experimental work and to compare or correlate the
two. For this purpose, an experimental laboratory machine
was constructed representing the common mechanisms such as
the plunger assembly, the mower assembly, and the belt and
gear drives.
It was apparent from the experimental results that the
magnitudes of stresses in the above mechanisms was in almost
every case higher than the theoretically determined values.
Moreover, the stress patterns as revealed by the experimental
work not only point out the form and types of stresses in the
assembly, but also serve as a tremendous aid as a valuable
tool for the design engineer in the field of farm machinery.
Such factors as the effects of centrifugal forces, the re­
peated stresses, and the variable power requirements influ­
enced the stress pattern in each of the above assemblies.
TABLE OP CONTENTS
Page
INTRODUCTION................... 1
REVIEW OP LITERATURE................................ 4
Progress of Stress Analysis....................... 5
Description of Experimental Methods............... 9
Analogies.............................. ......... 9
Membrane Analogy.............................. 10
Electric Analogy.............................. 15
Hydrodynamical Analogies...................... 15
Photoelasticity................................. 16
Mechanical Strain Gauges and Testing Machines... 25
X-ray Techniques for Stress Analysis........... 27
Brittle Lacquer Method.......................... 51
Electric Strain Gauges and Their
Instrumentation................................. 57
PURPOSE OP THE INVESTIGATION........................ 56
Instrumentation of the Project.................... 58
The Brush Analyzer.............................. 59
The Mercury Torquemeter......................... 59
The Stroboscope................................. 64
The Simpson Meter Model 260................... 64
The Electric Dynamometer........................ 65
Experimental............................ 67
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Page
The Analysis of the Centre-Crank Mechanism..... 70
Flywheel....................................... 70
Connecting Rod................................ 72
Crankshaft.................... 74
The Analysis of the Side Crank Mechanism........ 75
The Gear Drives.............................. 80
The V-belt Drives............................. 8l
CONCLUSIONS................................ 84
SUGGESTIONS FOR FURTHER STUDY....................... 86
APPENDIX............................................. 87
SELECTED BIBLIOGRAPHY.................................. 106
LIST OF FIGURES
Figure Page
1 Model Under Study in a Plane Polarlscope 20
2 Localized Stresses in the Fillets of a
Gear Tooth................................... 22
3 Stresscoat Lacquer Selection Chart . . 3^-
4 Stresscoat Pattern on Crankshaft Loaded
in Bending.................................... 36
5 Three Basic Circuits of Wire Resistance
Gauge s........................................ 4-3
6 Strain Gauge Drawbar Dynamometer............. 47
7 Bonded Wire Gauge Torquemeter................ 48
8 Small Magnetic-coupled Torquemeter........... 50
9 General-purpose Economy Oscillograph
Type S 14-C.................................. 55
10 Wiring Diagram Brush Analyzer Model BL 310... 60
11 Detail Drawing of the Mercury Torquemeter.... 62
12 Mercury Torquemeter Mounted on the Main
Shaft......................... 63
13 Instruments Used in the Project.............. 66
14 Side View of the Experimental Machine 68
15 Rear Right Side View of the Experimental
Machine....................................... 69
16 Graph of Effects of Load Variation on
Crankshaft Stresses.......................... 76
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Figure Page
17 Strain Recordings of 1/2 inch Gauge at the
Pitman Mid-section for Variation Speeds..... 78
18 Dynamic and Static Wiring Circuit for
Electric Strain Gauges....................... 102
19 Top View of the Assembly..................... 10j5
20 Side View of the Assembly..................... 104
21 Front View of the Gear Assembly.............. 105
LIST OP TABLES
Table Page
I Thickness Radiographed with Different
Voltages........................................ 29
II Characteristics of Stresscoat Brittle
Coatings............................. 35