Impact damage 1

[athomas236]

Does anyone know how to calculate the depth and diameter of an indentation caused by a steel ball blown at a steel plate in a jet of air.

Thanks in anticipation.

athomas236

 

[peglor]

That sounds like a strain energy type problem. I've no idea how to actually go about solving it though.

 

[Hush]

I'm thinking you could treat it like a brinell hardness test. Figure out the force at impact. Plug in your hardness values for the ball and plate and derive the diameter of the impact crater from the formula in ASTM E10. Your ball would have to be far harder than the plate and it wouldn't be a true value but it should be close.

Another approach might be to treat the impact as a Leeb hardness test, determine your energy loss and some how relate that to the deformation caused. Sounds pretty complicated though.

 

[IRstuff]

Seems like a slight oversimplification, since the contact time and average force is dependent on surface yielding.

TTFN

 

[vtl]

Consider you have a dynamic loading on a plate overtime.

 

[Biggadike]

I think to get an accurate calculation of an impact crater you would need such a complex model of both ball and surface, the whole thing would be unworkable.
What would be far better would be to take your surface and your ball, impact them at a series of known or measured speeds, measure the crater and find the empirical relationship.
This will have the advantage of being accurate.
Gravity drops are favorite as the maths is easy. Another way would be a pendulum (like used in an impact test), basically anything which allows the kinetic energy at impact to be calculated.

 

[zzy]

This is a problem involving meterial's permanent deformation (indentation). It has to be solved as such. There are a few FEA (finite element analysis) softwares available to handle this problem.
The initial kinetic energy due to impact speed will be converted into strain energy less the loss. It is not so easy to express the strain energy in terms of the indentation because of material's nonlinearity by hand. But with the software, it can be done without problem.

 

[Biggadike]

FEA should work well if the complete system is modelled. The temptation would be to model the impacted surface as a giant block which may or may not reflect reality. Also, in order to get a fine mesh at the impact area, you might reduce the working size too far and miss larger flexing in the impacted part (depending on the real geometry, which we don't know)
Also, I do wonder how consistent the indent sizes of real balls fired at a real surface would be. Would they always be the same? Or would microstructural differences in material mean that there would be a band of sizes?
It all depends on how accurate you want the answer and how consistent your ball sizes, air flow etc. really are.

 

[athomas236]

Thanks guys for all your suggestions. I am not looking for absolute accuracy but trying to compare the sizes on indentations on brass with those on carbon steel.

athomas236

 

[Biggadike]

I still say the best way is to do some experiments. I'd be tempted to compare the data from the experiments with the calculations for harness tests (as Hush suggested) to see if there is a correlation. If you've got access to FEA then all the better but I'd always go for some real data to back up any calculations.