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  1. driveline

    Sharp Hardness Variation

    metengr, I double checked the microhardness readings by asking for a direct Rockwell reading. I know that they can be suspect, case in point I had two labs and our in-house QC check this and all three were different. But the average was off by 10pts. One lab actually measured 16pts low. Can...
  2. driveline

    Sharp Hardness Variation

    metengr, The ductile failure was due to a sudden overload which would probably have failed the part anyway, I know this because a second part failed that was made to spec. The metallurgist said the grain structure was fine bainite throughout. You say "detailed metallurgical analysis" could...
  3. driveline

    Sharp Hardness Variation

    davefitz, How can the furnace process be monitored to prevent this? Our QC guy has been pushing the use of cpk for some time. Carburize, (1) This part was not surface hardened. I believe they use an austemper process, they claim it's proprietary as the parts are commonly 1/2 thick or...
  4. driveline

    Sharp Hardness Variation

    What causes hardness to fall off rapidly? I have a heat treated hot rolled steel part that failed in service which was examined and revealed a hardness drop of 10pts within 1/2 inch of the failed zone. A metallurgist examined the grain structure and concluded fine grain throughout. Does this...
  5. driveline

    Surface Wear Effects on Shot Peening

    Diamondjim, The material is AISI 5160, heat treated to 38 HRC.
  6. driveline

    Surface Wear Effects on Shot Peening

    The peen media is cut wire which I am told forms the best shape for peening. The life improvement is 30x to 50x, not 30 to 50%. I have been told this is an extreme example, usually 10x life improvement at best. I am not familiar with the flame spray prcocess. Is this the same as flame...
  7. driveline

    Surface Wear Effects on Shot Peening

    Carburize, The wear occurs at contact from a loose joint (can't change this) and from abrasion along the surface of the part (can't change this either). Lubricant would work at the first wear area for a while, but it would not last long in the second area. It would have to be a permanent...
  8. driveline

    Surface Wear Effects on Shot Peening

    I have an application that has seen significant fatigue life improvement in a lab test by adding shot peening to the process. 30x to 50x life improvement. The problem is, the lab test does not simulate all of the service conditions. The part can undergo significant surface wear, beyond the max...
  9. driveline

    Impact Strength and Fatigue Relations?

    davefitz, This new european fatigue analysis technique is similar to what I was assuming. I was trying to make a connection between a material's susceptibilty to quench cracks and inclusions and fatigue life. But now I see that the Charpy sample would have to contain the specific stress riser...
  10. driveline

    Impact Strength and Fatigue Relations?

    I have been trying to find some good data that relates Charpy impact values to fatigue resistance. I know that the Charpy test is rarely used in a design sense, but the stubborn engineer in me keeps finding hypothetical connections between the two. If two materials have the same hardness and...
  11. driveline

    securing lexan

    ornerynorsk, My intial research led me to try using grommets on the first prototype. After a weathering test, the lexan was removed and there were small cracks forming at the edges of the drilled holes. I summised that the grommets didn't allow enough movement for normal thermal expansion. I...
  12. driveline

    securing lexan

    I have an application where lexan sheets are mounted with bolts through drilled holes. The sheets are used as protective screens for machine operators so they are subjected to severe impacts on occasion. And occasionally the sheets crack after impact along the drilled holes. I can't assure...

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