Calculating Force Transmitted by Rubber Mountings to Failed Bracket

[reza_9216]

I'm having difficulties in finding an answer to the issue show in the attached pic. Fracture surface on the failed bracket! I have the properties of the mild steel, the properties of the rubber mountings, and the number of the cycles per minute. What i can't figure out is the load or the force that is being transmitted from the rubber mountings to the bracket that has caused the bracket to fail. what force?

The rubber mounting is to damp the movement of the other bracket (on the left hand side of the rubber mounting, which is connected to the engine fan).This only happens when the vibrator inside the machine turns on and off.

when the engine starts off ,the fan and the bracket (2) vibrate and the vibration goes through the rubber mounting and then through the bracket 1 until it is damped.

What I'm trying to do is to calculate the bending moment and based on the number of cycles i have, find the alternative and ultimate tensile strength from the S-N curve in order to make sure that i have the right material (mild steel) for the bracket.

My question is how to calculate the force from the bracket 2 to rubber mounting and the net force transmitted to bracket 1.

 

[pantaz]

Just my $0.02 -- From what I can see in the photo, the failure occurred at the point where the bracket transitions from a curve to straight. If that transition is too abrupt, you have what we colloquially call a "stress riser" -- the forces are concentrated at a small point. I believe that may complicate the calculations a bit (I don't understand the math enough to help you, unfortunately.)

 

[reza_9216]

pantaz, thank you for your reply...but my only problem now is how to calculate the force that is exerted through the rubber mounting, just behind the bracket number 1...