Fatigue analysis of Hammer

[sriram2hi]

I am currently investigating fatigue failure of a Hammer using ANSYS.

The hammer is used for size reduction of clinker. It has a groove(hole) on the top and is mounted on a rotating shaft(355 rpm) without any bearing. The impact force is developed during free fall of the hammer (weight is about 50kgs).
Kindly help me out in the following areas:

1. How to define cyclic loading of the hammer?
2. Which element i should use for solid modeling?
3. Hammer material is Cast tool steel (D2 type) and fatigue data is not available?

Being new to ANSYS, your help would be much appreciated.

 

[rb1957]

i guess it was no surprise that a cast hammer, loaded by impact, failed in fatigue.

most of the impact force is reacted by deceleration of the center of mass of the hammer. "most" cause some is going to be reacted at the shaft, the absense of a bearing implies to me that the hammer is fixed to the shaft (welded or keyed) ... as always draw a free body diagram.

i suggest a dynamic model. let the hammer accelerate (by gravity, or maybe it is driven by the shaft?) from the rest so that it has a velocity (and momentum) when it hits the target. the hard part is modelling the impact, the time profile of the impact force. do you have an data, or "just" guesses ? remember impulse is the time rate of change of momentum.

 

[sriram2hi]

Thanks for the reply.
Yes, you are right about the contact. The hammer is keyed to the shaft and not welded. The clearance can also be neglected.

All data that i have is the speed of shaft rotation and weight of the hammer. Besides, I can say for sure that the hammer under free fall is under gravity only and no angular momentum is acting due to shaft rotation.

Could you further clarify me what other data is required in this instance??