750C tensile test furnace for optical strain measurement of Inconel

[14years]

Hello,

I'm not sure if this is better suited to the mechanical or materials forums, but I'm way out of my league on the materials end and hope someone here has some experience with high-temp tensile testing of metal specimens (Inconel in this case.) I have to design a small furnace that can maintain the air temperature around a tensile dogbone (3mmx5mm cross-section, 50mm gage length) at 750C. The main reason for starting from scratch is that I have to allow a 74mm working distance (high-mag focal plane distance) for optical strain measurement of the dogbone surface. The grippers have to extend into the hot section of the furnace. Does anyone have any general suggestions for thermal isolation to stem the heat loss through the gripper pull rods? I am looking at zirconia ceramics for couplers, pull rods, or maybe even clevis pins, but without any FEA facilities I am not comfortable with diverting away from tried-and-true overdesigned steel components. Can anyone point me to any useful resources or provide any general wisdom? Thank you very much for any assistance you can provide.

David

 

[Compositepro]

There are a number of approaches to your problem. If you need fast heat-up and don't need to maintain the temperature for long then it would probably be best to use a hot-air torch (electrically heated compressed air) to heat the gage length of the specimen and not heat the grips. You can modify the specimen to keep the grips out of the hot zone. Hot grips will be very expensive and difficult to operate.

A air torch is a once through type of heating so you don't need good insulation.

 

[EdStainless]

There are commercially available systems from Instron and Satec.
As I recall the ones that I used had rods that were insulated near the sample, and then cooled once they were out further.

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http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[gthelen]

14 Years,

MTS has a very nice induction system, small cols that wrap around the sample and not touch it. Usually used for higher heat ranges but can be used for this application.

Good luck with the vision system and the heat, the people I know that used that threw it away and started over with clamp on LVDT and Strain Gage Extensometers.

Vision systems have a tough time getting the required resolution at the micro strains for offset yield and modulus readings. Despite what the glossy literature says.