T.M.F.T: Thermal Mechanical Fatigue Testing

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T.M.F.T Thermal Mechanical Fatigue Testing

• Wale Adewole
• Siyé Baker
• Heriberto Cortes
• Wesley Hawk
• Ashley McKnight

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Outline

• Project Scope
• Background Research
• Design Ideas
• Design Selection
• Future Plans

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Project Scope

• Locate and identify standards for thermal
  mechanical fatigue failure.
• Create a testing rig and a sample.
• Test the aluminum specimens and accurately
  identify the necessary properties.
• Use these results to create a program that can
  accurately predict if one aluminum sample will be
  better suited for a thermal mechanical fatigue
  application based on its mechanical properties.

4
Research

• American Society for testing and materials
  definition of fatigue.
• The process of progressive localized permanent
  structure change, occurring in a material
  subjected to fluctuating stresses and
  strainswhich may culminate in cracks or complete
  fracture after sufficient number of
  fluctuations.
• Constrained thermal fatigue is the result of a
  material not being able to expand under rising
  temperature.
• This constraint places the material under
  compressive forces with rising temperature and
  tensile forces during cooling.

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Design Ideas

• Manual Heating and Cooling
• Heating is done by placing specimen in a furnace.
• Cooling is done by placing the specimen in a
  water bath.
• Specimen is manually moved from the heat to the
  cooling chamber.
• Pros.
• Inexpensive.
• Simple design.
• Cons.
• Specimen holder is affected by temperature
  change.
• Long, and tedious process.

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Design Ideas Continued

• Resistance Heating and Convective Cooling
• Heating of the sample is done by a resistance
  heater placed near the sample.
• Cooling is done by convection with the
  surrounding air.
• Heating and cooling are toggled via electrical
  controls.
• Pros.
• Electrical control of heating and cooling cycles.
• Cons.
• Specimen holder not isolated from thermal
  effects.
• Long heating and cooling periods.

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Design Ideas Continued

• Hot Oil Bath
• Heating is done through placement in a hot oil
  bath.
• Cooling is done through dipping in a cooling
  bath.
• Specimen is mechanically moved from one bath to
  the other.
• Pros.
• Fast heating a cooling rates.
• Low amount of input from user.
• Cons.
• Testing rig is exposed to thermal fluctuation.
• Danger caused by splattering oil.

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Design Ideas Continued

• Thermal Isolation Rig
• Heating is done by electrical resistance heating
  coil placed around a small section of the center
  of the sample.
• Cooling is done by convection.
• Heating is turn off when sample reaches desired
  temperature.
• Pros.
• Thermal isolation of testing rig.
• Ability to measure sample temperature and load.
• Electronic control requires minimum user input.
• Cons.
• Larger cost.

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Design Matrix
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Final Design

• Thermal Isolation Rig
• Has the ability to test tension and compression
  of the specimen during heating and cooling
  cycles.
• Testing rig is isolated from the thermal
  fluctuation due to the cooling of the specimen
  holder clamps.
• Simple stationary design requires on moving
  parts.

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Pro-E Drawing
Load Cell
Aluminum Specimen
Holding Clamps
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Clamp Design

• Clamp 1(left)
• Designed to connect load cell to aluminum
  specimen.
• Raised edges to direct cooling water flow.
• Clamp 2(right)
• Stationary clamp attaches specimen to base.
• Hole for thermocouple wire to pass through.
• Raised edges to direct water flow.

Thermocouple wire hole
Load cell threaded attachment point
Raised Edge
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Calculations

• Energy transfer through Conduction.
• 130 Watts
• Energy loss due to natural convection.
• 8 Watts
• Time required to cool sample.
• 37 seconds

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Initial FEM Analysis

• Displacement and reaction forces of constrained
  aluminum sample.

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Initial FEM Analysis

• Initial stresses in the clamp from thermal
  expansion.

• Initial displacement in the clamp from thermal
  expansion.

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Initial FEM Analysis

• The initial temperature distribution on the clamp
  without cooling of the clamp.
• Entire clamp reaches over 400F.
• Unacceptable amount of heat from sample.

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Calculations Continued

• Water flow rate
• 60 gal/hr
• Laminar flow rate over the clamp.
• Water convection coefficient over clamp.
• 4.777E3 W/(m2K)
• Calculated energy loss through clamp at max
  temperature.
• 180 Watts

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Revised FEM Analysis

• Using new values for convection coefficient.
• Temperature distribution not as dramatic with
  combined convection and water flow.
• Max450F
• Min81F

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Estimated Cost
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Testing Procedure

• Sample is place in tester.
• Water flow over clamps is initialized.
• The sample is heated to 150F and the load cell
  is zeroed.
• Sample will be cycled between maximum temperature
  and minimum temperature until failure occurs.
• Data is collected from the sample at even
  increments.

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Data Acquisition

• The loads created by the thermal tension and
  compression of the specimen will be acquired by
  using a load cell that will be connected to a
  computer with lab view or a similar program.
• This data will be correlated with the temperature
  data obtained from the thermocouple throughout
  the experiment.
• This acquired data will be used to analyze the
  effect of thermal fatigue on different materials.
• It will also be used to obtain a relationship
  between material properties and thermal fatigue
  failure.

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Future Plans

• Order Parts
• Review design with sponsor.
• Begin machining of testing rig.
• Material analysis before and after testing.
• Create Operations Manual

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Questions?