Crack due to thermal fatigue

[WZN322]

I have an assembly part with a primary torque tube and a failsafe tube. This failsafe tube has 2 tiny cracks near each other on a same fastener hole whilst the common hole on the primary tube does not crack. im trying to find out what caused the crack and only thing that came to my mind is the thermal fatigue.

1. Anyone has any reference about understanding the crack pattern for different scenarios like fit up, tensile, shear, bending, thermal etc...
2. Does the cracking due to thermal fatigue has a particular pattern by looking at the SEM pic of the cross section of the crack on the part (attached)?

Thanks.

 

[metengr]

There is not much information to provide any meaningful help. Why would you believe thermal fatigue? What is the source of thermal stress? Mechanical fatigue could be a possibility. I would send this to a metallurgical lab for proper evaluation.

 

[EdStainless]

material, size, temperature swings?
How about some info.
Thermal fatigue is difficult to analyze, because it is a fatigue crack.
You have to find a way to eliminate mechanical stress as the driver.

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P.E. Metallurgy, Plymouth Tube

 

[Chumpes]

hello
Your picture does not have very good resolution and looks a bit blurry : as said by metengr, send the cracked sample to metallurical lab for evaluation.
Thermal fatigue is mechanical fatigue for which stress variations are induced by temperature changes, the morphology of the cracks will remain the same for both.
I don't have a reference for understanding difference between crack patterns, this comes with experience...

 

[Puneet Bobel]

Dear sir,

after see your report, when you assembe this fitting. a extra ordinary pressure is applied.