Flex Test on the Cheap

I'd hardly think you need a hydraulic press to flex some expanded polystyrene!

What are the dimensions of the piece you are testing?

It sounds like a V simple rig should be able to do it...

Tape a rule alongside it and use a spring balance to pull it, note deflection and poundage until the break point.

Or am I over simplifying? (as usual!)

PS. I've used the above method to plot draw weight vs deflection of longbows upto 70lb.

Del

I need to be able to show that I am producing a piece of foam of adequate strength. The standard is ASTM C203. I can cut a sample piece from a produced part, say 2" x 2" x 12". I want to convince an auditor that this is a decent replication of the ASTM test. the desired psi is 35 minimum.

That sounds more like compression than flex?

I would think the spec would give a clear indication of test method or what exactly is required.

It should be simple enough to make a board with say four feet each 1" square section...load up the board with bricks until you get the foam to fail or permanently deform.

I just searched for ASTM C203...

It says it is a 'Test Method'

You need to get the spec'... then you can work out how to do it.

The spec' may cost...but it will doubtless be cheaper than a test rig!

It does say flexural test...as a simple cantilever beam....

So it should be very easy, once you know the dimensions needed for the test piece.

It's probably just a test piece supported at either end and loaded at the centre...this is easilly done with some weights.

Del

If you use a low striction air cylinder with minimal instrumentation, you should be able to build it for a few K's.

Blimey...give me $500 and the spec' I'd do it in half an hour, with stuff lying around in the garage.

The problem is not knowing the spec' .

How to do 'it' is probably V easy.

I'll see your $500 and do it for $50 with whats on my desk.

Ok you got it .

That psi figure is meaningless unless we know what it refers to, but I'm fed up with asking that same question.

It could mean

35lb per squ" of cross sectional area supported over 1 foot or all sorts of other possible configurations.

As an asside...I object to having to pay for spec's which we are obliged to conform to. What do the rest of you guys think about that?

Del

You can do a simple production run GO-NO GO test. Machine test specimen, support between two fixed points, apply fixed load at center point, measure deflection. You will need the standard to know test span. The formulas the ASTM standard uses for strength calculations will probably be simple beam formulas for strength. A specified load and deflection will give you a strength in psi. Determine the exact load and deflection to meet your minimum strength target if when that load is applied it deflects < = that minimum it is a GO.

The need is to test foam for a minimum flex of 35 psi. The three point rig is doable. The issue is how to conduct the test. We can cut a sample of up to 2" x 2" x 12". I guess we need to push down on center of the part until we have reached the breakpoint and then record the weight. What is the formula that we would use to calculate the result?

GOOGLE Beam loading

http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_display.cfm?case=simple_centerload

http://www.engineersedge.com/beam_bending/beam_bending2.htm

Is it possible that the manufacturer of the plastic has done the test you require, or are you the manufacturer?

The manufacturer of the raw material has done all of the tests, etc. to demonstrate the capability of the raw material. We need to prove on a regular basis that we are performing our molding operation properly by doing a flex test (among others).