Impact testing devices

[shorion]

As the subject says, I'm looking for a device which can measure the impact force for me of a load that is connected to a chain that falls.

I've seen a few out there and was wondering which one you guys recommend. The load will be in the rance of 5-20 tons.

I've been coming across impact loading more and more in my work and decided its time I back up theory with actual test results.

One that gives the load would be nice. Acceleration and impact time are good as well however not essential as if you have the impact load you can design to the load.

It should be able to connect to a chain.

Preferably its usb and has a install and leave kind of deal so I can leave it in places for a day to get the maximum and average number of peak stresses.

Regards

 

[GregLocock]

So you want to measure the tension in the chain as a function of time?

Any idea what frequency range you need? or the impact time if you like?

I think you are looking for a load cell, 20 kN or so

I've used these guys in the past, they aren't the most expensive around

https://www.pcb.com/Products.aspx?m=1204-02A

Cheers

Greg Locock


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[CoryPad]

Do you need the equipment to provide a frame and fixturing? Try Instron:

http://www.instron.com/en-us/testing-solutions/by-test-type/impact

 

[FennLane]

What do you mean by an impact?

Trying to test at impact rates with conventional testing machines is really difficult as to obtain high speeds is very expensive in terms of hydraulic systems and electromechanical machines will never be fast.

You need to consider Drop Weight machines fitted with suitable slack adapters and probably needing Piezzo Electric Load cells to obtain sufficient dynamic response to measure forces accurately at high rates.

20 Tonne machines would be huge and very, very costly

 

[1gibson]

Not sure how detailed you need to be, but the first thing I would do is get a spring scale with a needle that records max load, put it on the chain, and go from there. Check the reading daily or periodically (after each lift if you really want) manually record and re-set the needle.

Actually a quick image search for "20 ton spring scale" shows that digital models are available, and they probably have these features built in.

 

[GregLocock]

Yes simple might be better. Another way that can be useful is to use a hydraulic ram connected to a pressure gauge.

Cheers

Greg Locock


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[Ron]

Check with Keithley Instruments and MicroMeasurements. You can get instantaneous strain measurements, load and stress. Since these will give you a response spectrum you can also get the decay of each. You could also throw in an accelerometer for additional measurements.

You might have to put several pieces of equipment together and do a little programming of a data collection/analysis program, but both are relatively easy. I've used such for dynamic structural analysis of amusement rides and industrial equipment.

 

[gruntguru]

The spring balance may be a good starting point but it will change the response of the system (being much "softer" than the other components).

Strain gauging a link in the chain or a custom designed link with strain gauges are cheap solutions that will give good dynamic response.

je suis charlie

 

[IRstuff]

I would vote for the accelerometer approach; it's not going to change the dynamics of the problem, and it's going to have sufficient frequency bandwidth to accurately record the impact.

TTFN
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[GregLocock]

But with an accelerometer only you end up having interminable discussions about the dynamics, eg how much of the targets mass is involved,

Cheers

Greg Locock


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[IRstuff]

Given a choice, wouldn't you want the accurate raw data to be the acceleration, as opposed to the mass? You can always measure the mass after the fact, and only need to measure it once, since the mass won't change over time, unless gigantic chunks are breaking off. If your measured acceleration/force is inaccurate, what then, and how would you even know?

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[gruntguru]

That's fine if the mass is a nice solid chunk of something. If it is a multi-part structure or flexible in any way, the accelerometer results will be rubbish. (BTDT)

je suis charlie

 

[IRstuff]

If it's that flexible, the spring balance results would probably have all sorts of interesting oscillations as well. The OP mentions 5 to 20 tons, so, it doesn't sound like something that's going to be floppy.

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[GregLocock]

I meant the participation of whatever the known mass is striking is always a tricky one to decide, the more instrumentatin the better.

Otherwise on a force hammer for modal work we'd just use a hammer with an accelerometer, whereas the force gage is also essential.

Cheers

Greg Locock


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[IRstuff]

Sure, I get that. But, I would think that having the load hit a load cell would be a more representative measurement. I don't see how anything on the chain side could be used without drastically altering the impact conditions.

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[gruntguru]

If it's that flexible, the spring balance results would probably have all sorts of interesting oscillations as well. The OP mentions 5 to 20 tons, so, it doesn't sound like something that's going to be floppy.

Absolutely no comparison. Something that looks like a rigid structure - say a 1m x 1m x 0.05m steel plate with chain and accelerometer attached to the centre of a 1 x 1 face - will produce a peak acceleration way in excess of the peak force divided by the mass. The peak force under impact loading is not accelerating the entire mass uniformly. Only the section attached to the chain is experiencing the peak acceleration.

OTOH the spring balance will measure the peak force (and infer acceleration) accurately, but the system is much more compliant and the peak force much lower than the chain with no spring balance.

je suis charlie

 

[geesamand]

I recently designed (but did not build) a system to measure the impulse torque on a backstop device.

It became clear that a piezoelectric force sensor was the way to go. They are very fast and can capture the force v time for highly dynamic events. You can in most cases configure the data collection system to buffer a bit of time and trigger the saving of data to disk, if you want to capture an event automatically and ignore extraneous data.

This type of system isn't cheap but if you want the data free of inertial influences, probably one of the best.