[martinw]

This assumes you have a press, screw, hydraulic or rack.

Take a piece of cold rolled steel. Support it on two pieces of round stock a known distance apart. The round stock will have to be blocked up a few inches because space is needed underneath the center of the cold rolled.

Now you have a simply supported beam for which you can easily determine I and can make a plot of beam deflection versus load.

Mount a dial gauge under the center of this beam; apply pressure from the press; again via a piece of round stock at the center. Now you can relate deflection of the beam to the force being applied by the press.

If it is a hydraulic press it should have a gauge; you can now calibrate the gauge in terms of force applied by the press. If it is a screw press you will need to use a torque wrench and if it is a rack driven press you just need a spring scale between you and the end of the lever.

You will need to choose the dimensions of the cold rold and the distance between the supports to get the calibration rig somewhere close to the range you want to measure. Just remember you have to be in the elastic region during calibration. If the dial gauge does not return to zero when the force is removed you have move into plastic deformation.

EDIT; Obviously I was reading Yugami's mind, or vice versa.

Dear Geof,

I will probably have completely misunderstood, in which case, apologies.

You are suggesting that this is a way to calibrate the force applied by the "force applier"?

If this is a calibration procedure, the "knowns" are the sectional dimensions of the "calibration" beam and its Young's modulus, and the dimensions and positions of the standard loading forces and reactions. Is that right? Simply supported point load at mid-span? Your idea is to use the steel beam as a force reference by measuring its deflection and using book values for material properties?

I'm being slow...

Best wishes

Martin

[walter]

Looking good Bruno! That should give you some good vibrations..

I went a step further and plugged it into a rheostat. All I need now is another motor with another rheostat, so I can work both sides of the mold. Crossing frequencies should be fun.


Cameron,
Did you get the test lab price quote? What are we looking for, tension/compression, density? Any other tests?


Larry,
Small particle theory sounds interesting. My size 40 fine quartz has average particle size of 2.8 micron. Could this be the ticket?

[ckelloug]

Walter,

I didn't get the test lab quote yet. I will have to use that obsolete communication system favored by Industry: the telephone and call them tomorrow. Ideally, tensile and compressive strength and tensile and compressive moduli are all things we want to know. If we know the moduli then we can predict the deflections in machines built with our composites. The ultimate strengths will let us know how much load parts will take before breaking. Since you guys doing the experimental work are making large samples, I'd say that a food scale and a ruler will do just fine for density measurements.

Precise measurements are only worth investing in if we think it is possible to repeat what was done and make more of the same material tested. Good notes on what has been done will be very helpful when the time comes to formally test recipes.

In a composite beam without reinforcement like rebar etc, we will ultimately be limited by the tensile strength of the material.

One interesting idea both to improve tensile strength and to null out static deflection due to the wight of a beams is post tensioning. If some small tubes are cast into the beams below the neutral axis, one could insert some high tensile strength bolts or perhaps some music wire with the appropriate fittings after the cure running through the tubes. One could then set the beam on parallel rails on a big epoxy surface flat sitting with the ends supported on parallel rails. Using a dial indicator and a dial indicator stand, one could carefully tighten the bolts/wires in the bottom of the slab and null out static deflections resulting in a beam that is perfectly straight under the normal load conditions. Since the tension wires would only contact the ends of the beam, they should not transmit vibration unlike embedded rebar. This may be a completely stupid idea as it's a touch complex but it is similar to what is done in certain types of engineered concrete bridge spans and it can be used to fully remove static deflections.

As for small particle dispersion reinforcement, I believe 2.8 micron sand falls into the large particle category. Callister, my materials textbook suggests between .1 and .01 microns for dispersion reinforcement candidates. That pretty much leaves carbon black and silica fume. Fortunately, Cabot makes silica fume as well so I'll call my newfound apps engineer friend over there and inquire. I have no real data on dispersion hardening as it appears to be mainly black magic in determining what works for given conditions. I'm going to see what I can dig up. The Cabot engineer did say that smaller particle sizes make it more difficult to disperse the pozzolan into the matrix e.g. mix the goo.

P.S. I am an expert in severely over-engineering things so let me know if and when I have flooded the thread with an overabundance of ideas. It should also be noted that I am on sabbatical from my real job right now (so I can finish building my shop) and I am having a blast here getting the brain exercise trying to make this E/G thing work well.

[martinw]

Walter,



In a composite beam without reinforcement like rebar etc, we will ultimately be limited by the tensile strength of the material.

One interesting idea both to improve tensile strength and to null out static deflection due to the wight of a beams is post tensioning. .

Dear Cameron,

1) Rebars will fix any tensile problems.

2) Who cares about static deflection under self-weight? It's the deflection under shifting and variable loads that matters, isn't it?

IMVVVVHO,

Best wishes,


Martin

[ckelloug]

Dear Cameron,

1) Rebars will fix any tensile problems.



2) Who cares about static deflection under self-weight? It's the deflection under shifting and variable loads that matters, isn't it?



Martin

On point 1 In strength terms you are absolutely right. I have a theory however that due to their continuous nature and their higher Q value that they may transmit more vibration. I have not worked out a way to do the analysis yet to determine anything so all I have is a conjecture. The effect is probably minimal anyway.

On point 2 I think you are largely right about static deflection as well. The only case where I think it could matter is in keeping a gantry beam _exactly_ parallel with the table. If you can dynamically adjust this deflection to zero by post tensioning, then I believe it might be possible to size gantry beams a bit smaller and also make the Z axis vary less with respect to the y-axis position of the milling head on the gantry.

In a 12.5 inch square 4 ft long E/G beam with no reinforcement, I calculate the deflection as being about .0004inches at the center with a 200 pound mill head and a 525 lb weight of the beam. If .0004 is an acceptable deflection on the gantry beam then static deflection can be safely ignored.


In short, I'm a metals guy and a theoretician at present so I think in terms of reducing all sources of error in the system for the most accurate possible parts. For a CNC wood router, the two concerns I mentioned here are probably nil.

[lgalla]

Sandi,WOW I have never heard of 400minute pot life.Take my previous sugestion and "Sweat it"Do a sample mix and let it sit for 200 minutes before adding aggregates.Check the temperature if it is getting hot add the aggregates.Your hardner choice needs post cure.296 would be a better choice,eg.25minute pot life.A 25 minute pot life will probably be hours with the aggregates.
Walter you have micron silica,sand,epoxy,carbon black,Zeeospheres,vibrator in the works,etc.Do you have a hammer???
Cabosil and other fumed silicas.01 micron are thixotrops which thicken the epoxy at very low ratios and the cost is high.A very low % will result in vasoline consistancy.It is designed to prevent saging on verticals.It would not allow heavy loadings of larger aggregates.Here is an example I coppied ;
Normally, Cabosil is added at a 1% to 7% proportion based on the weight of the liquid (resin, hardener, thinner) involved. Because resin and Cabosil have such different densities, weight proportions are awkward. For example, one gallon of polyester weighs 9 pounds; 7% of 9 lbs is 10 ounces, which for Cabosil is about 1.25 gallons by volume. For many situations, volumetric proportions are more convenient. A gallon of resin and a gallon of Cabosil is a 50/50 ratio by volume, but only 5% by weight. Incidentally, this 50/50 volume ratio results in a resin consistency about like vaseline. Lesser amounts yield a more liquid consistency, whereas greater amounts yield thicker pastes. The exact amount used is determined by the application. The addition of Cabosil has no effect on such properties as pot life, cure time , etc., and only affects strength to the degree that entrapped air reduced cross-sectional area.

Larry

[walter]

Walter you have micron silica,sand,epoxy,carbon black,Zeeospheres,vibrator in the works,etc.Do you have a hammer???

Broke the hammer crackin' walnuts. Ordering 2 new hammers!

[walter]

Did I say walnuts?!

I meant E/G !!

[lgalla]

John,allrocks are not created equal.We know from the machinery guys E/Q or E/G is the stuff machines are made of.We are having enough trouble with known rocks.Adding another is adding to the confusion.I am sure you will have good results,but I will stick with granite or quartz which is cheap filler.
Larry

[lgalla]

Cameron here is something to decifer,Its all Greek to me.Found info searching Google"filler particle size vs strength.
) State Research Institute of Structural Graphite Materials, Elektrodnaya ul. 2, Moscow, 111524, Russia

Abstract The effect of the grain size of the filler on the mechanical properties (compressive, bending, and tensile strength and modulus of elasticity) of synthetic graphite is analyzed using data for commercial structural graphites. As the mean particle size of the filler (deltaav) decreases from 3000 to 1 mgrm, the modulus of elasticity increases, on the average, from 10 to 15 GPa, and the compressive, bending, and tensile strength increases by about one order of magnitude. The Griffith equation is used to evaluate the size of defects that initiate fracture (c c) in different types of graphites. It is shown that the factors determining the critical defect size depend on the particle size of the filler. For deltaav > 150 mgrm, c c is comparable to deltaav or deltamaxthinsp. In the range 30 < deltaav < 150 mgrm, c c is equal to or greater than deltamaxthinsp. In graphites with deltaav < 30 mgrm, c c far exceeds deltamax and, presumably, corresponds to the particle size of the molding powder.
From a laymans point,looks like fine fillers offer better specs over rocks.Fine spheres arrest cracks as I assume the micro crack will circle the sphere and end.A large 1/2" aggregate would be a very large crack indeed.I am just trying to guess why micro particulate is better.I am refering to cracking as cast iron has damping qualities as it is full of micro cracks which gives it it's damping properties.
Larry

[lgalla]

Cameron I can't speak for the other members,but .0004 is what they would like,but a 500lb gantry is scary to them.I see posts where the guys are worried about a 100lb gantry and 50lb Z axis.For the wood guys deflection is not a big issue as the spoil board is surfaced to be level with the gantry.At .004 what is the deflection.I don't think anyone here is making opitical accuracy tables.
Thanks for all the input
Larry

[ckelloug]

Larry,

I worked out that a 4.25 inch square E/G beam 48 inches long, with the 16GPa strength from my last calculation, should have enough strength to be within .004 deflection at the midpoint and weight about 60 lbs along with 50 lbs of z axis load for 110 lbs total.

As for the Russian abstract, that was interesting. Maybe not $43.00 worth of interesting but. . . Putting this in closer to layman's terms: as particle size decreases in graphite from about 150 times the width of a hair to the width of 1/20th of a hair, deflection in a beam made from the material goes down 33% for the same load and the ultimate load carried by the beam before it breaks is 10 times what it was before.

The mechanism is this. Imagine a block of epoxy as a bunch of tinkertoys. Each round hub has spokes coming out in several directions and the pattern of a bunch of tinker toys put together at the same angles is repetitive but, like the work of a child, it contains mistakes. These mistakes are called dislocations. If the structure contained no dislocations, aka was a perfect crystal, it would be very strong. When the epoxy is bent, these mistakes in the tinkertoy structure try to move in order to allow the structure to flex. In the tinkertoys, imagine a few missing spokes and spokes that are just barely pushed into the hubs. The effect of adding the tiny particles is like placing the tinkertoy structure into a bucket of pingpong balls. Anywhere you grab the structure and try to bend it, the hubs and spokes hit pingpong balls before they move very far. This effect is called dislocation pinning generally and in this case dispersion hardening. If bowling balls were used instead of the pingpong balls, the sticks in the tinkertoys would be too short and you would get some regions filled with globs of tinkertoys and other regions filled with bowling balls but no regions where large portions of the structure of tinkertoys was connected to itself.

In short, small particles cause keep the molecules of material from sliding past each other on the atomic scale. I would suspect that once a crack decided to form in the material that it would probably just keep going unless it hit a larger aggregate particle which was strong enough to stop it. That's why high strength concrete with pozzolans also has aggregate. Both macro and micro reinforcement are beneficial.

I do expect that the micro reinforcement is probably not needed at the level required to make the stuff turn into vaseline. If it's truly thixotropic however, vibration at the right frequency should make it thin right out.


P.S. I've written the first version of my program for doing crude beam calculations. It's in java so it is portable but I am still figuring out a way that it can be run without a hassle since it is the wrong dialect of java to run from a web browser right now.

[lgalla]

Cameron quote:
"P.S. I learned some other interesting stuff in the library today about small particle reinforcement, but I'll leave everybody in suspense until I have some hard data in a day or two."
Mork from planet Ork says NA-NU Na-NU.
Nano particulate re-Inforce-Cement?
Cameron Thanks for all the reaserch
Larry

[VoxLimbo]

Can you provide a bibiography with source ranking so we can duplicate your research?

Cameron quote:
"P.S. I learned some other interesting stuff in the library today about small particle reinforcement, but I'll leave everybody in suspense until I have some hard data in a day or two."
Mork from planet Ork says NA-NU Na-NU.
Nano particulate re-Inforce-Cement?
Cameron Thanks for all the reaserch
Larry

[ckelloug]

Here is the info I alluded to yesterday but waited to disclose until I had the price and talked to the company along with the bibliography of sources I've used lately.

The information I found on small particles involved strengthening epoxy with particles much smaller than silica fume aka 20nm particles. The particles are so small that unlike carbon black or silica fume, they <B>DO NOT</B> cause an increase in viscosity!

Nanoparticles provide better fracture toughness, better compressive/tensile modulus by a factor of 100 in some cases, lower shrinkage, lower coefficient of thermal expansion, less heat distortion and better surface finish and abrasion resistance. These SiO2 nanoparticles come wetted in epoxy so there is no problem with mixing or agglomeration.

These SiO2 particles are made by Nanoresins, a spinoff of Hanse-Chemie in Germany. They cost 25$ to 35$ dollars a pound and are added in quantities of no more than 10% by weight. The URL of the company is www.nanoresins.com. I have attached to this post the datasheet sent to me by the leader of the U.S. operation, Dr. Oliver Pyrlik, Technical Sales Director Nanocomposites, hanse chemie USA inc. They have graciously offered me some samples which I may accept when I can deal with them.

I may have confused some people by saying hard data in my last post but what I meant is that I wanted to find the price and talk to the company before raising hopes here. I haven't done any lab work and can't until I stop sitting here posting and go finish building my shop

I am approaching this problem with the idea of working smarter, not harder. I'm thinking that if we design our epoxy mix to use safe additives and admixtures and the smallest practical aggregates for the strength needed then we will likely produce parts with a nicer finish than even the commercially built machines while requiring a minimum of work. Judging by Walter's results from the composite made with just sand, it sounds like it might be reasonably easy to come up with a viable composite without huge aggregates.

<h4>Bibliography of materials I have used in my posts:</h4>

Materials Science and Engineering An Introduction
Third Edition
William D. Callister Jr.
John Wiley & Sons, Inc.
Copyright 1994
ISBN 0-471-58128-3

This is the book whose chapter 17 got me thinking about small particle reinforcement. The technique is still so cutting edge that there is little data 13 years after this book was published.

Introduction to Mechanics of Solids
Egor P. Popov
Prentice Hall
Englewood Cliffs, NJ
Copyright 1968

This book is out of print but a xerox authorized by the publisher surved as the text for most of my engineering mechanics class some years ago. I found a used copy of the book at Powells books in Portland. I've been using chapter 13 to study the process of working out deflections with Lagrangian methods using techniques like Castigliano's Theorem.

ASTM Standard D695
Standard Test Method for Compressive Properties of Rigid Plastics
Annual Book of ASTM Standards 1985 edition

This is the ASTM standard for doing compressive tests of reinforced plastics. I have used it as guidance in my quest for an improvised testing machine to determine the properties of our materials.

Polymer Composites from Nano to Macro Scale
Frederich Klaus
Springer
Copyright 1995
ISBN 0-387-24176-0

This is the book that led me to the above discussion on 20nm sol-gel silica reinforced epoxy as mentioned above. Most of the book is about unrelated things but the 10 or so pages starting from pg 92 were fascinating and said such things like "100 fold increase in modulus" with the introduction of the nano-particles. They pointed out using cure temperatures of up to 200 C. They also listed the use of CAA, Cobalt Acetylacetonate from Sachem Chemicals, and N,N Dimethyl Benzamine as catalysts in addition to the epoxy's normal hardener in the 1% to 1.5% by weight range and indicated approximately 5% strength improvements for the CAA. CAA is even safe!

Marks Standard Handbook for Mechanical Engineers
1987 Edition
McGraw Hill Inc.

I've used this for looking up things like moments and Accepted young's moduli and other misc data for back of the envelope calculations.

[walter]

Thanks Cameron, much appreciated.

I'm working on my own Quartz Formula and I'd be happy to test your nanosand.

Now here's the thing .. I think I've got the "Sand" part covered. I'm all sand. Quartz is 7 on Mohs scale and I fully intend to utilize that.

Now what about the "Epoxy" part? Are we getting the max performance?

Zanite guys advertise their epoxy as "specially-formulated-high-strength-epoxy".

I wonder how high-strength is our epoxy...

Larry?

[ckelloug]

Hi Walter et. al

I called US Composites today and they told me that their low viscosity slow curing epoxy is Reichhold 37-606. Since this is the hardener and the specs are given for an epoxy on page 3 of the data sheet, one would assume that Reichhold 37-140 is the epoxy corresponding to US Composites 63556x series epoxy where I use the x to deisignate the part number changes due to different sized containers.

This epoxy doesn't look like anything special. Data sheet is attached.

[romihs]

Ckelloug,

Thanks for joining this thread. Your input and expertise are invaluable!

Really good information you posted there.

Thanks

Best Regards

Sandi

[walter]

I am approaching this problem with the idea of working smarter, not harder. I'm thinking that if we design our epoxy mix to use safe additives and admixtures and the smallest practical aggregates for the strength needed then we will likely produce parts with a nicer finish than even the commercially built machines while requiring a minimum of work.

In another words, a home brewed Quartz-Epoxy composite that can rival a commercial unit!

That would certainly push the envelope and introduce new dimensions of performance here on the Zone..

I see two separate solutions:

1. super-low-cost, easy to use E/G filler for weldments/machine bases; ( no problem- we already have that)

2. higher priced option for high performance E/Q machine tools!
(we can have it in 6 months)

I guess that was the original plan, look at the interest (and great feedback) it's getting...

But Are we up to the challenge?
_

[ckelloug]

Friends, (fyffe in particular),

I've finally gotten done a small java applet that solves the deflection at the center of a beam without shear for any of the parameters FL^3/48EI. It's just a nice gui on some trivial algebra. Given Fyffe's spreadsheet for the moment of inertia calculations, one can use this to do the calculations tweaking parameters and seeing what happens. I had planned to add automatic moment of inertia for common shapes and a table of young's modulus's to it but I haven't yet and wanted to see if anybody had feedback.

If you have the latest version of java installed in your web browser, it should work for you. Instructions are to download the zip file and unpack it on your harddrive. Then open Beamer.html in a web browser and barring unfortunate circumstances, the java applet should load and work. I've tested this on Suse Linux 10.2 with firefox 2.0.

Finally, feel free to PM me with comments about how badly I write Java or other comments. I think it's literally the 15th programming language I've had to use in the past year and as a result, I can't seem to find a good way to implement anything in any language now. Why I am learning another programming language while I am on sabbatical is beyond me. . .

:cheers: