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Fatigue Test
Practical Course Materials Science

Procedure

Following steps are necessary:

  • Preparing the specimen
    • Screwing and locking of two nuts on the first side of the specimen's thread
    • Applying grease to one pair of the washers
    • Placing the complementary ball joint washer into a wrap nut
    • Inserting the specimen with the locked nuts into the prepared wrap nut
    • Pulling the second wrap nut over the specimen's thread
    • Applying grease to the second pair of the washers
    • Screwing and locking of two nuts on the other side of the thread
  • Preparing the testing machine
    • Switching on the main oil pump
    • Activating the supply of the servo hydraulic testing cylinder
  • Mounting the specimen
    • Greasing a washer set
    • Putting it to the clamping device of the machine
    • Clamping the prepared specimen in between the clamping devices
    • Screwing the first wrap nut on by hand
    • Sticking the second washer combination to the clamping device
    • Activating "Probenschutz"
    • Moving the specimen into the washer combination by manual path control panel
    • Screwing the second wrap nut on by hand
    • Adjusting the force to -1.5kN pressure
    • Tightly screwing of the wrap nuts
  • Performing the test
    • Switching the control panel from "Weg" to "Kraft" and "Betriebsumschaltung" to "sofort"
    • Activating the secure condition of the test
    • Resetting the force to 0
    • Defining the dynamically applied load (Amplitude, Signalform, Frequenz, Blendzeiten)
    • Resetting the two displays (cycles)
    • Starting the test
  • Finishing the test
    • Saving the informations about the test details on the record sheet
    • Resetting the predefined path boundaries
    • Activating the specimen protection
    • Moving away the hydraulic cylinder by manual path control panel
    • Loosening the wrapping nuts
    • Removing of the broken specimen's parts form the warpping nuts
    • Conserving the fracture surface with synthetic varnish

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Result of Measurement

Result of measurement

Based on experimental results along with the calculations of the finite life and fatigue strength the Wöhler line can be determined.

In this practical course you have to determine

  • Fatigue Strength
  • Fatigue Life
  • Wöhler Line

Wöhler Line

Organization of Experimental Data

After determination of survival probabilities for finite life fatigue strength the data has to be plotted in a Wöhler line.

Practice

Checklist The steps

1. Preparing the specimen

Preparing the specimen

1. Measure the thinnest diameter of the specimen.
2. Screw two of the nuts on the one side of the specimen’ thread.

Caution  Make sure the nuts are thoroughly tightened and there stands not more than 1 round of the thread proud.

3. Apply some grease with a paper towel on the ball joint socket washer and attach the ball joint washer on it.
4. Attach the combination of both in the wrapping nut.

Caution  Make sure the ball joint washer is facing the bigger opening of the wrapping nut.

5. Repeat it for the other side of the specimen.

2. Preparing the testing machine

Preparations

1. Switch on the main oil pump (green light flashes up)
2. Activate the supply of the servo hydraulic testing cylinder (press stage II, then stage III)
3. Activate the path control ("Weg")
4. Activate the specimen prorection ("Probenschutz")

3. Mounting the specimen

Mounting the specimen

1. Attach grease on the remaining ball joint socket washers.
2. Put the specimen in between the clamping device of the machine. The wrapping nuts can be screwed on by hand.
3. Apply some pressure on the specimen by turning the wheel of the manual control.

Caution  The wheel is highly sensitive.

4. Increase the pressure to ~1.5kN and lock the wrapping nuts with the adequate open end wrenches.

4. Performing the test

Performing the test

1. Change the mode in the top right corner from “Weg” to “Kraft” by clicking on “Kraft” and “Betriebsumschaltung” “sofort”.
2. Activate the path boundaries in the middle of the screen.
3. Reset the force to zero.
4. In the lower left hand corner of the display, type into the box underneath "Ziel" zero and continue your input by pressing the enter key.
5. Execute the parameters by pressing the "start" button. Immediately changes the force value to the defined value.
6. Reset the amount of cycles by clicking right on it. Choose “Reset” “Diese Anzeige”.
7. In the box "Amplitude" the force amplitude has to be defined. The value has to be typed in and continued by pressing the enter key.
8. Start the test by clicking the yellow arrow (“Start”) on the left.

5. Finishing the test

Finishing the test

1. When the specimen is broken save the information about the test details on the record sheet.
2. Deactivate the path boundaries by pressing "Primäre Grenzwerte dieser Gruppe deaktivieren" and activate the specimen protection “Probenschutz”.
3. Make sure the mode “Weg” is activated.
4. Demount the specimen.
5. Cover the fracture surfaces with synthetic varnish.