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INTRODUFatigue ofcan be cadirection) and respe A fatigue fthe
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Figure 1(ageometricafracture su
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-
intensify to the point where separation occurs within one of the
slip bands and a crack is formed.
Once started, the crack will develop at a point of discontinuity
in the material, such as a change in cross section, a key way, or a
hole. Less obvious points at which fatigue failure is likely to
begin are internal cracks, or even irregularities caused by
machining. In other words, when a load below the yield strength of
a material is applied repeatedly to a metallic specimen, Localized
Hardening occurs. Then a small crack appears, this crack is a Line
of Stress Concentration, which causes it to grow. As the crack
grows, the cross sectional area of the metal gets smaller until it
can no longer support the load. When fracture takes place, the
loading is called Fatigue Loading and the fracture is called
Fatigue Failure. Cracks generally starts at the surface of the
metallic material. As the crack grows, the two surfaces rub against
each other, polishing both faces to a dull metallic finish, whereas
the fractured surface show signs of plastic deformation and a
crystalline finish. TEST METHODS Fatigue failures occur most often
in moving machinery parts such as shafts, connecting rods, valves,
springs, etc. However, the wings and fuselage of an airplane or the
hull of a submarine are also susceptible to fatigue failures
because in service they are subjected to variations of stress. As
it is not always possible to predict where fatigue failures will
occur in service and because it is essential to avoid premature
fractures in articles as aircraft components, it is common to do
full-scale testing on aircraft wings, fuselage, engine pods, etc.
This involves supporting the particular airplane section in jigs
and applying cycling varying stresses using hydraulic cylinders
with specially controlled valves. Laboratory tests are also carried
out on particular materials to establish their fatigue
characteristics and to study factors such as their susceptibility
to stress concentrations. Fatigue can be generated in direct stress
due to axial loading or bending or shear stress due to cyclic
torsion or any combination of these. To determine the strength of
materials under the action of fatigue loads, specimens are
subjected to repeated or varying forces of specified magnitudes
while the cycles of stress reversals are counted to destruction. To
establish the fatigue strength of a material, quite number of tests
are necessary. For the rotating test, a constant bending load is
applied, and the number of revolutions (Stress Reversals) of the
beam required for failure is recorded. The first test is made at a
stress which is somewhat under the ultimate strength of the
material. The second test is made with a stress which is less than
that used in the first. This process is continued, and the
results
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plotted asvariables.
The ordinastress abonumber ofby a statem In the casfailure
willcorrespon Processortabulationswhich orddependinghave an e5(108)
cyc
Figure 3: A
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ate of the ove enduraf cycles) ament of the
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An S-N diagr
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he fatigueikely to ocust always h it corresp
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y based on
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ue test.
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Approximation of the S-N curve For many situations, in
preliminary design work, it is necessary to approximate the S-N
curve without actually running a fatigue test. For Steel it has
been found that a good approximation of the S-N curve can be drawn
if the following rules are used:
1. Obtain of the specimen (from a simple tension test, or from
tables). 2. On a log-log diagram, plot S against N as follows: at
zero reversals. 0.9 at N = 103 reversals. 0.5 at N = 106 reversals.
3. Join these points together to form an S-N curve.
Fatigue and Design Fatigue must be considered in the design of
all structural and machine components which are subjected to
repeated or fluctuating loads:
1. Usage of endurance limit: The value of the endurance limit is
usually obtained using a specimen prepared very carefully and
tested under closely controlled conditions. It is unrealistic to
expect the endurance limit of a mechanical or structural member to
match values obtained in the laboratory; there are several factors
that modifies the endurance limit (Table 1). To account for the
most important of these conditions a variety of modifying factors
are employed. Using this fact:
Se = Ka Kb Kc Kd Ke Kf Se Where Se : endurance limit of
mechanical element.
Se : endurance limit of rotating beam specimen. Ka : surface
factor. Kb : size factor. Kc : reliability factor. Kd : temperature
factor. Ke : modifying factor for stress concentration. Kf :
miscellaneous-effect factor.
With a material like mild steel, the actual stress range could
be kept below the endurance limit.
TABLE 1: CONDITIONS AFFECTING THE ENDURANCE LIMIT
Material: Chemical composition, basis of failure, variability.
Manufacturing: Method of manufacturing, heat treatment, surface
condition, stress concentration. Environment: Corrosion,
temperature, stress state, relaxation
times. Design: Size, shape, life, stress state, stress
concentration, speed.
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2. Usage of number of reversals, N: Alternatively, one can
design for a specified number of stress variations (magnitude and
direction) on condition that the element will be replaced at that
stage.
3. Increasing fatigue life of parts: Cracks occur usually under
the action of tensile stresses. Therefore, reduction of tensile
stresses will prevent fatigue and thus make the part life longer.
Tensile stress reduction can be achieved through creating a
constant compressive stress (compressive stresses closes cracks).
Two methods for creating constant compressive stresses are known:
Cutting-slots method. Shot-peening method.
Factors affecting fatigue life of materials Fatigue behavior of
engineering materials is highly sensitive to a number of variables.
Some of these factors include:
1. Mean Stress: It is half the algebraic sum of the maximum
stress and the minimum stress. Usually the dependence of fatigue
life on stress amplitude is studied at a constant mean stress m,
often for the reverses cycle situation (m = 0). As may be noted,
increasing the mean stress level leads to a decrease in fatigue
life.
2. Surface condition of material: It is known that highly
polished elements withstand fatigue much better than normally
machined ones.
3. Influence of the shape of specimen on stress flow: The shape
of the specimen is very important, since at corners ant notches the
local stress can be several times more than the calculated average
value.
4. Imperfections inside the material and at the surface: In
certain
materials, failure as a result of repeatedly cycled stress
generates localized slip pattern. Each slip segment work so that
very small cracks form in the material. The notch effect causes the
cracks to multiply until a network develops to cause fracture. If
these cracks are reversible (sealed) with the cycle, the material
is said to be ductile. If not, it will fracture. It is, therefore,
important that when a structure is to be cycled, sharp corners,
surface scratches, or notches must be avoided by the designer.
5. Environmental effects: such as thermal fatigue and Corrosion
fatigue.
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Instruction Manual
WP 140 Fatigue TestingApparatus
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Test instructions
Publication No.: 912. 000 00A 140 12 07/93
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Table of contents1 Introduction. . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 1
2 Function and layout . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 2
3 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 4
3.1 Alternating cyclic stress . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . 5
3.2 Loading of the sample . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 5
3.3 Fatigue strength under complete stress reversal. . . . . . .
. . . . . . . . . 6
3.4 Fatigue limit . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 6
3.5 Endurance . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 7
3.6 Stress-number diagram . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 7
4 Experiments . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 8
4.1 Commissioning and test run . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 8
4.2 Performing the experiment. . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 104.2.1 Insert the test bar . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 104.2.2 Start
the experiment . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 114.2.3 Terminate the experiment . . . . . . . . . . . . .
. . . . . . . . . . . . . 12
4.3 Evaluation of the experiment . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 124.3.1 The influence of various
curvature radii and
surface qualities . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 124.3.2 Producing a stress-number diagram. . .
. . . . . . . . . . . . . . . 13
5. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 15
5.1 Work sheet, stress-number diagram . . . . . . . . . . . . .
. . . . . . . . . . . 15
5.2 Technical specifications . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 16
5.3 Test bars . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 17
5.4 Index . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 18
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1 Introduction
With this machine, it is possible to demonstrate thebasic
principles of fatigue strength testing, in-cluding the production
of a stress-number dia-gram. The sample is subjected to a
purereversed bending stress in the machine. Via different sample
shapes, it is possible to showthe influence of the notch effect and
the influenceof surface quality on fatigue strength. The amplitude
of the reversed stress is infinitelyadjustable.The machine switches
off automatically if the sam-ple ruptures. The number of load
cycles is display-ed via a digital counter.
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2 Function and layout
In the revolving fatigue testing machine, a rotatingsample which
is clamped on one side is loaded witha concentrated force. As a
result, an alternatingbending stress is created in the cylindrical
sample.Following a certain number of load cycles, the sam-ple will
rupture as a result of material fatigue.The revolving fatigue
testing machine essentiallyconsists of - Spindle with sample
receptacle (1)- Drive motor (2)- Load device (3)- Switch box with
the electrical control and
counter (4)- Protective hood (8)
The spindle is mounted on two amply dimensionedrolling-contact
bearings. The spindle is driven by a smooth running a.c.motor with
a speed of approximately 2880 RPM.
4 2 8
1 7 3
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The test bar (7) is clamped in the spindle on oneside by a
collet chuck (5) and guided on the otherside in a floating bearing
(6).
Loading of the sample is performed using a springbalance (9) and
the floating bearing (6). Pre-stressing of the spring balance and
henceadjustment of the load is performed via a threadedspindle with
a hand wheel (10). The set load can be read from a scale on the
springbalance.
A digital, 8-digit counter (11) records the numberof load
cycles. The counter may also be switchedto rotational speed
measurement. The rotationalspeed is then displayed in
revolutions/minute.
The pulses for the counter are supplied by aninductive proximity
sensor (12) on the motorcoupling.
If the sample ruptures, the motor and the counterare halted
automatically via the stop switch (16).
The master switch (13), emergency off switch (14),motor control
switch (15) and counter (11) arehoused in the switch box (4).
13 14
15 11
12
10
9
Scale6
16
Collet Test bar (7) Floating chuck (5) bearing (6)
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3 Theory
Oscillating stresses are far more dangerous forstructural parts
and components than a static forceapplied once.In the event of
frequent repetition of a static loadwhich is in itself permissible,
a machine part mayrupture as a result of material fatigue. As
thenumber of load cycles increases, the permissiblestress level
declines. Even stresses which are below the yield point ofthe
material in the elastic range may lead to minorplastic deformations
as a result of local peak stres-ses inside the part. This effect
gradually destroysthe material due to the constant repetition
andeventually results in rupture. The absolute num-ber of load
cycles is a more decisive factor forfailure than the frequency.
With the WP140 revolving fatigue testing machine,it is possible to
monitor fatigue strength underreversed bending stresses. Via
various curvature radii and degrees of surfa-ce roughness of the
sample used, it is also pos-sible to examine the influence of the
notch effecton fatigue strength.
Residual fracturesurface: rough
Fatigue fracturesurface: smoothwith lines of rest
Appearance of the fracture surface of a sample
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3.1 Alternating cyclic stress
The cyclic stress is composed of a constant part,the mean stress
m caused by an initial load, anda superimposed cyclic part with the
alternatingstress amplitude a .
The largest stress occurring is termed maximumstress o m a, and
the smallest stress istermed minimum stress u m a .
Three ranges are distinguished in alternating cy-clic
stress:
- Range of pulsating stresses (tensile force)Mean stress larger
than the alternating stressamplitude m a
- Range of alternating stressesMean stress is smaller in total
than the alterna-ting stress amplitude |m| a
- Range of pulsating stresses (compression)Mean stress is
smaller than the negative alter-nating stress amplitude m a
3.2 Loading of the sample
Loading of the sample corresponds to a clampedbending bar under
a concentrated force F. Thisinduces a triangular bending moment Mb
in thesample. As the bending moment is fixed but the sample
isrotating, it is loaded by an alternating, sine-shapedbending
stress. The highest bending stress oc-curs on the shoulder of the
sample.
t
o a
u a
m
t
t
t
F
Mb
a
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This is a pure reversed bending stress withoutmean stress. For
this reason, it is only possible todetermine fatigue strength under
complete stressreversal W with a revolving fatigue testing
machine.It represents a special case of fatigue strength D.The
bending moment is calculated with the loadand the lever arm as
follows:
Mb F a
By using the section modulus of the sample
Wb d 3
32 it is possible to calculate the alterna-
ting stress amplitude.
a MbWb
32 a d 3 F
32 100.5 mm 8 3mm 3
F
a 2.0 1/mm 2 F
3.3 Fatigue strength under complete stress reversal
Fatigue strength under complete stress reversalW is the strength
at which the material does notfail even after N 10 106 load cycles
(steel). Itcan be assumed that failure as a result of
materialfatigue will no longer occur, and the endurance
isinfinite.
3.4 Fatigue limit
Stresses at which the material fails below the loadcycle limit
of 10 106 are termed fatigue limit.The corresponding number of load
cycles N untilrupture should be given in brackets, e.g.
W 5105 220 N/mm2.
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3.5 Endurance
Endurance refers to the number N of load cyclesuntil rupture at
a certain load. The magnitude ofthe load according to mean stress
and alternatingstress amplitude is given in brackets, e.g.
N 50 100 2.6 105
3.6 Stress-number diagram
The stress-number diagram (S-N diagram) por-trays the
correlation between the number of loadcycles until rupture and the
corresponding loadstress in graph form. This clearly shows that
asthe number of load cycles increases, the permis-sible load
asymptotically approaches the fatiguestrength w . When plotting a
stress-number curve, it is impor-tant that with alternating stress,
the mean stress,or with pulsating stress, the ratio of maximum
orminimum stress to mean stress, is kept constantfor the various
loads. As the mean stress is zero in the revolving fatiguetesting
machine, this condition is automaticallyfulfilled.
Alte
rnat
ing
stre
ss a
mpl
itude
102 103 104 105 106 107
Number of load cycles N (logarithmic)
Stress-number diagram for two different materials
a
w
0
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4 Experiments
4.1 Commissioning and test run
The following checks should be performed beforecarrying out
experiments- Erect the revolving fatigue testing machine and
connect to the power supply
- Remove the protective hood (unlock the faste-ners by rotating
the knobs to the left)
- Relieve the load device using the hand wheel(move the floating
bearing down to the bottom)
- Remove any samples which may be in position- Lightly tighten
the union nut on the collet chuck
- Mount the protective hood and lock with all fourknobs
DANGER!Never operate the revolving fatigue testing machi-ne
without the protective guard! Parts of the sam-ple could fly off
when it ruptures. Rotating machineparts must be protected against
accidental con-tact.
Knobs
DANGER!
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- Check whether the EMERGENCY OFF switch(14) is released (pull
out)
- Switch on the machine using the master switch(13)
- Reset the counter (11) using the RST button.The counter must
display zero
- Start up the motor using the motor controlswitch (15)
- Check whether the spindle is running smoothlyand true
- Check whether the counter is counting correct-ly
(approximately 2800 load cycles per minute).It is possible to
display the revolutionary speedin RPM by switching over with the
SEL button.
- Check whether the automatic stop device isfunctioning. To do
so, raise the floating bearing on the loaddevice by rotating the
hand wheel. The motor should then be stopped by the stopswitch
(16)
Once safe functioning of all components has beenestablished, the
experiments can begin.
15 11
13 14
Stop-switch(16)
Twist floatingbearing upwards
Reset here
Switch over to rev.speed display here
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4.2 Performing the experiment
4.2.1 Insert the test bar
- Relieve the load device using the hand wheel(the floating
bearing must be at the height ofthe spindle)
- First insert the test bar in the floating bearingof the load
device
- Then insert the test bar in the collet chuck andpush in as far
as the end stop
- Carefully tighten the collet chuck using awrenchSW30: Union
nutSW21: Steady spindle
- Check concentricity of the sample by rotatingthe spindle by
hand (correctly seated in thecollet chuck, sample not deformed)
IMPORTANT!Ensure that the sample is firmly seated in the
colletchuck. The sample receptacle must be clean
IMPORTANT
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- Mount the protective hood and lock with theknobs
DANGER!Never operate the revolving fatigue testing machi-ne
without the protective guard. Parts of the sample could fly off and
cause injurieswhen it ruptures. Rotating machine parts must
beprotected against accidental contact.
4.2.2 Start the experiment
- Switch on the motor
- Swiftly apply the required load by rotating thehand wheel.
Read off the load from the scaleon the spring balance
IMPORTANT!Never apply the load when the machine is idle,since
there is a risk of plastic deformation anduntrue running. Bring the
load to the final level as quickly aspossible, because the sample
is already under analternating load but the load cycles cannot yet
becounted because the load is too small.
- Reset the counter using the RST button inorder to begin
counting
Scale
IMPORTANT
DANGER!
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4.2.3 Terminate the experiment
- The motor halts automatically when the sampleruptures. Read
off the number of load cyclesfrom the counter and make a note of
the num-ber
- or manually stop the experiment after the re-quired number of
load cycles (no rupture) byswitching off the motor
- Remove the sample. Proceed in the samemanner as when inserting
the test bar.
DANGER!Risk of burns! The sample may be very hot imme-diately
after the experiment.
4.3 Evaluation of the experiment
4.3.1 The influence of various curvature radii and surface
qualities
Test bars 1 to 3 are examined
In all cases, the load F = 200N corresponding toa 400 N/mm2. 3
samples of each type are exa-mined.
Test bars, material Ck 35Type Curvature
radius r in mmSurface rough-ness Rt in m
Notes
1 0.5 4 Small radius, smooth2 2.0 4 Large radius, smooth3 2.0 25
Large radius, rough
DANGER!
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The following numbers of load cycles are achieveduntil the
sample ruptures:
As a result of the increased notch effect and theassociated
increase in local stress in the groove,the endurance with a small
curvature radius (testbar 1) is considerably lower than with test
bar 2.With an identical curvature radius, the sample withthe
smoother surface (test bar 2) has a higherendurance than the one
with the rougher surface(test bar 3). For this reason, components
subject to alternatingstress, such as crank shafts, have broadly
roundedgrooves with polished surfaces as far as possible.
4.3.2 Producing a stress-number diagram
This experiment was performed with test bar 3.The load was
gradually reduced from one experi-ment to the next from the maximum
value F = 200N corresponding to a 400 N/mm2. It should benoted that
the increments selected in the region ofthe expected fatigue
strength under reversed ben-ding stresses should not be too large,
becauseotherwise the experiment will last a long time or norupture
will occur.If the counter display is utilised to its full
capacity(max. 9.99 x 107 load cycles), the experiment maylast up to
593 h or 24.5 days!
Number of load cycles N 200 to rupture
Type Sample1 Sample 2 Sample 3 Average1 11300 11300 11700 114332
17150 17300 23700 193833 14030 12800 16300 14376
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The stress is entered over the endurance in thesemi-logarithmic
diagram (work sheet, stress-number diagram 5.1 ).
Apparently, the fatigue strength under completestress reversal
has not yet been reached at 240N/mm2. It will be around 200 N/mm2.
This is lowwhen one considers that the material of the testbars Ck
35 has a tensile strength Rm = 560 N/mm2.
Number of load cycles for test bar 3 under different loadsNo.
Load
in NStress a in N/mm2
Endurance N Duration wheren=2800 1/min
1 200 400 14030 5 min2 170 340 48800 17 min3 150 300 167000 60
min4 130 260 455000 2 h 42 min5 120 240 1280800 7 h 37 min
Alte
rnat
ing
stre
ss a
mpl
itude
in N/
mm
2
104 105 106 107 Number of load cyclesl N
100
200
300
400
a 500
0
Stress-number diagram for test bar 3 made of Ck 35
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5. Appendix
5.1 Work sheet, stress-number diagramAl
tern
atin
g st
ress
am
plitu
de N
/mm
2
104 105 106 107 Number of load cycles N
100
200
300
400
a 500
0
Stress-number diagram
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5.2 Technical specifications
Dimensions : Length x width x height : 920 x 415 x 560 mm
Weight: 38 kg
Electrical power supply: 230 V, 50HzAlternatives optional, see
type plate
Motor Speed: 2800 RPM Capacity: 370 W
Load device Force: 0 .... 300 N Reversed bending stress in the
sample: 0.... 600 N/mm2
Load cycle counter 8-digit, electronic, may be switched over to
revolutionary speed display
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5.3 Test bars
Test bars are made of tempering steel Ck 35,mechanical strength
properties:Rm = 560 N/mm2, Rp0.2 = 420 N/mm2
Test bar 1
Test bar 2
Test bar 3
Bezel 1 x 45
Bezel 1 x 45
Bezel 1 x 45
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5.4 Index
AAdjusting the load . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 11Alternating cyclic stress. . . . . . . . . . . .
. . . . . . . . . . . . . . . 5Alternating stress amplitude . . . .
. . . . . . . . . . . . . . . . . . . 5
BBending moment . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 5
CCollet chuck. . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 3Counter . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 9Curvature radius . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 13
DDrive . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 2
EElectrical power supply . . . . . . . . . . . . . . . . . . . .
. . . . . . 16Emergency off switch . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 3Endurance. . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 7
FFatigue limit . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 6Fatigue strength under complete stress
reversal . . . . . . . 6Fatigue strength under reversed bending
stresses . . . . . 4Floating bearing . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 3
IInserting the test bar . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 10
LLoad cycle counter . . . . . . . . . . . . . . . . . . . . . .
. . . . . 3, 16Load device. . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 16
MMaster switch . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 3Material fatigue . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 4Maximum stress . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 5Mean stress. . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5Minimum stress . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 5Motor control switch . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 3
NNotch effect . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 4, 13
PProtective hood . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 8Pulse generator. . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 3
RRange of alternating stresses . . . . . . . . . . . . . . . . .
. . . . . 5Range of pulsating stresses . . . . . . . . . . . . . .
. . . . . . . . . 5
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SSection modulus . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 6Spring balance . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 3Stop switch . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 3, 9Stress-number
diagram. . . . . . . . . . . . . . . . . . . . . . . . 7, 13Surface
roughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 4Switch box. . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 3
TTechnical specifications . . . . . . . . . . . . . . . . . . .
. . . . . . 16Theory . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 4
WWork sheet, stress-number diagram. . . . . . . . . . . . . . .
. 15
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Fatigue_theory.pdfFatigue.pdfwp1401e.pdfTable of contents1
Introduction 12 Function and layout 23 Theory 43.1 Alternating
cyclic stress 53.2 Loading of the sample 53.3 Fatigue strength
under complete stress reversal 63.4 Fatigue limit 63.5 Endurance
73.6 Stress-number diagram 7
4 Experiments 84.1 Commissioning and test run 84.2 Performing
the experiment 104.2.1 Insert the test bar 104.2.2 Start the
experiment 114.2.3 Terminate the experiment 12
4.3 Evaluation of the experiment 124.3.1 The influence of
various curvature radii and surface qualities 124.3.2 Producing a
stress-number diagram 13
5. Appendix 155.1 Work sheet, stress-number diagram 155.2
Technical specifications 165.3 Test bars 175.4 Index 18
wp1405e.pdfAAdjusting the load 11 Alternating cyclic stress 5
Alternating stress amplitude 5
BBending moment 5
CCollet chuck 3 Counter 9 Curvature radius 13
DDrive 2
EElectrical power supply 16 Emergency off switch 3 Endurance
7
FFatigue limit 6 Fatigue strength under complete stress reversal
6 Fatigue strength under reversed bending stresses 4 Floating
bearing 3
IInserting the test bar 10
LLoad cycle counter 3, 16 Load device 16
MMaster switch 3 Material fatigue 4 Maximum stress 5 Mean stress
5 Minimum stress 5 Motor control switch 3
NNotch effect 4, 13
PProtective hood 8 Pulse generator 3
RRange of alternating stresses 5 Range of pulsating stresses
5
SSection modulus 6 Spring balance 3 Stop switch 3, 9
Stress-number diagram 7, 13 Surface roughness 4 Switch box 3
TTechnical specifications 16 Theory 4
WWork sheet, stress-number diagram 15