Beam Breaking Energy

[beneb]

Hello, I'm hoping to find some assistance with a project I'm working on.

So, we have a bend press--a 3 point or 4 point setup which we use to test welds. For simplicity's sake, lets just say a generic beam with a weld in the center of the span between the supports with a load that presses down from the top.

Quite often, the sample will break during testing down the centerline of the weld. This results in the 2 halves of the sample slamming down into a steel plate that is a few inches below. During testing, we take load and deflection data so I have a fair amount of that to work with.

What I'm trying to do is estimate the energy of the 2 halves either at the moment it breaks or a fraction of a second later when they impact the plate. The eventual goal is to add a little bit of "cushion" to this setup to soften the blow a bit.

Am I over simplifying it by thinking it would be the area under the force/displacement curve of our data? Or is there another method to calculate/estimate this?

Many thanks.

 

[DrZoidberWoop]

I may be missing the mark, but couldn't you simply put a piece of wood or hard rubber surfaced plate where you want to mitigate the impact?

 

[XR250]

I would assume area under the F-d curve. W = Integral (F(x)dx)

 

[Agent666]

I'm kind of with the DrZ, just keep putting a bigger 'widget' under the impact point until it performs as expected and has the desired effect.

Seems like the effort to get some exact answer far outweighs the $5 for a piece of wood or something else that could cushion the blow and protect the apparatus. Unless you've already tried that and it didn't work for some reason?

https://engineervsheep.com

 

[phamENG]

And while integrating your force/deflection curve would give you the work done to the beam by the press, that's not related to the impact of the pieces on the steel plate. I would expect you'll get this for the force of impact:

F= W_b + sqrt(W_b²+KW_bV²/g)

where

W_b=weight of falling body
K=spring constant of supporting member
g=gravitational acceleration

(Credit to Blodgett)

 

[SwinnyGG]

You know how much force the press is applying to the beam, correct? And you know the mass of the beam?

F=MA is going to get you pretty close...

If it were me I'd probably start with simple solutions. I.e weld a simple sheet metal tray and fill it with 5 or 6 inches of fluffy sand.

 

[rb1957]

put a comfy cushion on the plate !

Put a loop of duct tape on the specimen, stuck to either side of the weld.

another day in paradise, or is paradise one day closer ?

 

[beneb]

Thanks for the replies, all.
I do favor the simple solutions--we actually have some big blocks of cardboard we slide under the specimens now that kind of help, but we go through a lot of them. We were brainstorming some possible improvements and that got me wondering about the physics. I suppose part of the reason I posed the question is "academic pursuit" or curiosity, but I'd also like to do a little figuring to maybe eliminate some of the trial & error.
Again, I appreciate all the feedback!