T.M.F.T: Thermal Mechanical Fatigue Testing Wale Adewole Siyé Baker Heriberto Cortes Wesley Hawk Ashley McKnight

Outline Project Scope Background Research Design Ideas Design Selection Future Plans

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.

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 strains…which 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.

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.

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.

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.

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.

Design Matrix

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.

Pro-E Drawing Aluminum Specimen Load Cell Holding Clamps

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. Raised Edge Thermocouple wire hole Load cell threaded attachment point

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

Initial FEM Analysis Displacement and reaction forces of constrained aluminum sample.

Initial FEM Analysis Initial stresses in the clamp from thermal expansion. Initial displacement in the clamp from thermal expansion.

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

Calculations Continued Water flow rate 60 gal/hr Laminar flow rate over the clamp. Water convection coefficient over clamp E+3 W/(m^2*K) Calculated energy loss through clamp at max temperature. 180 Watts

Revised FEM Analysis Using new values for convection coefficient. Temperature distribution not as dramatic with combined convection and water flow. Max=450°F Min=81°F

Estimated Cost

Testing Procedure Sample is place in tester. Water flow over clamps is initialized. The sample is heated to 150°F 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.

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.

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

Questions?