Effect of Fluctuating Load..

Hello friends,
We all know that because of dynamic load the strength of a body or member decreases like in the case of bending and unbending the wire in order to break it instead of applying axial force on it. So in order to design a body having dynamic load acting on it, we consider endurance limit instead of U.T.S. . But i want to know that why the strength of material decreases because of dynamic load? what happens inside the material that the strength of material decreases only because of dynamic load not in static load?
Waiting..

Replies

  • Siddhant Mukherjee
    Siddhant Mukherjee
    @#-Link-Snipped-# : Fluctuating load leads to fatigue. When we stress a material, and the stress is somewhere around yield strength the dislocations in a material start to move and when these dislocations move to other place plastic deformations occur. In fatigue, since the stresses are fluctuating, the dislocations tend to move in to and fro manner like a vibration resulting in cracks. These cracks act as stress raisers and material fails at a much less stress than the UTS.

    Surf the internet about "Cottrell Atmospheres"

    Cottrell Atmosphere
  • Sekocan
    Sekocan
    As I know, fluctuating loads (which may be seen on a simple rotating shaft) also leads crack propogation. Micro cracks in the material may grow and cause sudden failure.
  • Ankush Sharma
    Ankush Sharma
    Sekocan
    As I know, fluctuating loads (which may be seen on a simple rotating shaft) also leads crack propogation. Micro cracks in the material may grow and cause sudden failure.
    But even micro cracks also present in materials which are loaded statically and in these materials crack propagate only when the value of yield strength of material is equal to critical stress (brittle materials) and we also loaded material upto yield strength and when the value of yield strength is less than critical stress( ductile materials) and again we loaded up to yield strength . So why don't the material fail before yield strength in this normal loading as in the case of fluctuating load.
  • Ankush Sharma
    Ankush Sharma
    S.mukherjee
    @#-Link-Snipped-# : These cracks act as stress raisers and material fails at a much less stress than the UTS.
    But even micro cracks also present in materials which are loaded statically and in these materials crack propagate only when the value of yield strength of material is equal to critical stress (brittle materials) and we also loaded material upto yield strength and when the value of yield strength is less than critical stress( ductile materials) and again we loaded up to yield strength . So why don't the material fail before yield strength in this normal loading as in the case of fluctuating load.

You are reading an archived discussion.

Related Posts

hello friends, I read this on various books and even on google that "Any motion which repeats itself after an interval of time is known as vibration". this simple line...
dear sir i am new to this crazy engineers i am unable to wer is the POST option to ask my questions . plz guide me thanks
can anyone plz tell me how to find an IEM project on THERMAL BAGGING CARRIER
Australian app developers from Factorial Products Ltd. has come up with an innovative way to help you hang out with your "bros" without having to worry about texting your girlfriend....
The Other Side, a book by Faraz Kazi and Vivek Banerjee is a wonderful read and delight for readers with interests in supernatural activity. This book is sure to satiate...