Binder Fatigue

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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

plotted asvariables.

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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.

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.

Instruction Manual

WP 140 Fatigue TestingApparatus

Test instructions

Publication No.: 912. 000 00A 140 12 07/93

WP 140 Fatigue Testing Apparatus

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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

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Binder Fatigue