[ckelloug]

From Materials Science and Engineering, an Introduction by William D. Callister Jr.

critical fiber length:

l_c=sigma_f*d/t_c

where:

l_c is the critical length: the length of fiber for which the fiber will carry it's maximum load,

sigma_f is the ultimate tensile strength of the fiber

d is the fiber diameter

and t_c is the shear yield strength of the matrix (or the shear strength of the bond between the fiber and the matrix)

This equation says that the length of the fiber necessary for the fiber to carry maximum load is proportional to the strength of the fiber and the diameter and inversely proportional to the bond strength with the matrix.

The modulus of the material will be

E_c=K*E_f*V_f + E_m*V_m

where

E_c is the elastic modulus,

K is an empirical parameter = 1/5 for randomly oriented milled fibers

E_f is the modulus of the fiber,

V_f is the volume percentage of the fiber

E_m is the modulus of the matrix and V_m is the volume percentage of the matrix.

A quick skim of Callister shows that the ultimate strength of a short fiber composite requires knowledge of the stress in the matrix when the composite fails which we do not have.

I can research this more at some point in the future but I figured I'd stop before anyone dozed off.

Regards all,

Cameron

[the4thseal]

how do cure the epoxy at elevated temperatures, how do you build the hot box? more importantly control temperature? what about temperature control switches and where do get them? i am trying to control the variables of the samples i am making. thoughts?

[jhudler]

Search eBay for "temperature Controller" in Business & Industrial

or Category:

Business & Industrial> Industrial Electrical & Test> Industrial Automation, Control> Temperature Controllers

Those PID Temperature Controller's look ok, they come with a thermocouple ready for use.

[Jay C]

PID controller for controlling the heat and maintaining a set temperature.

Jay

[the4thseal]

i hook up heating elements to it and it turns them on and off? right? that simple?

[jhudler]

how do you build the hot box?

I've not been using a heated chamber for my testing. Well I'll admit to using a toaster oven thats good at holding a constant 50 C.

But the Reichhold 37-137/37-606 epoxy we've chosen only needs room temperature to cure.

If your going to add heat, that allow it to harden for 24 hours (cure in 7 days), which allows the Exothermic reaction to subside.
Otherwise exothermic runaway will cook the epoxy.

If you have something you want to cure faster, then after the first 24 hours point some heat lamps at it.

[svenakela]

Even though you have an epoxy that cures in room temp, "top-heating" is always a recommendation. After 24 hours, raising the temperature always makes a better bonding as the last molecules hook up with each other.
Based on 30 years of epoxy experience and a workshop known worldwide to make the best carbon fibre racing masts, top-heating after cure is used even when working with the hand lay-up laminates. Everything from prepreg autoclav laminates to hand rolled test molds gets its boost. I would recommend it to everyone.

Regards,
Sven

[ckelloug]

Svenakela has way more experience than I do but from what I've read, curing temperature affects the number of molecular bonds in the cured mixture and thus the stiffness, especially at higher temperatures.

Most other slow curing epoxies for which I've read the datasheet have cure schedules that are something like room temperature till it hardens, 2 hours at 70C 4 hours at 150C. (Note that this is made up data from memory). GEnerally speaking, epoxies, especially slow curing ones won't achieve their best high temperature performance unless post cured at high temp.

The cure schedule given for 37-127 is 24 hours at 25C followed by 2 hours at 121C.

--Cameron

[jstransky]

Is anybody able to help me to find the author of the pictures on post#30 and #243on this thread.

Help me.

[ckelloug]

jstransky,

Welcome.

Those posts are from a German group that had built some epoxy/granite mill parts. I don't read german so I didn't ever really follow it. Apparently they commercialized it too much and the german forum took their work down as they didn't allow commerical traffic on the forum.

RotarySMP on this thread who reads German knows the most about these pictures as far as I know.

I'll PM him and see if he comments.

Regards all,

Cameron

[thomasz]

I'll PM him and see if he comments.

Hello!

I think you're looking for us? We are the german group you talk about.
I hope I can give you some answers for your question if you have one, but
my english is not so good - i'll give my very best

For further information look also at www.thomas-zietz.de.

Bye
Thomas

[harryn]

This should be self explanatory,from Crosslink Technology

Formulated Epoxies, Urethanes and Custom Cast Electrical Parts

"Our strength is in our Formulations"



Precautions:

Almost all formulated epoxy and urethane materials contain at least some volatile ingredients. These ingredients are an essential part of the product and will start flashing off under vacuum. This is evidenced by the fact that the mix being de-aired never seems to be totally free of bubbles no matter how long it is vacuumed. Care should be taken not to vacuum strip the material. In most cases vacuum at 29” Hg for 5-10 minutes will sufficiently de-gas the mixture.
Larry

Hi, I decided not to re-quote Larry's entire post, but his point is quite valid here. There are epoxy materials on the market with varying amounts of solvent content, down all the way to zero percent or nearly so.

The solvent plays a key part in the formulation of properites, but epoxies can be forumulated with almost no solvent / volatiles. Of course, this is almost starting again from ground zero on the mix properties.

The semiconductor and space related industries use very low outgassing and nearly solvent free epoxies. Cost for these can be significant.

[jhudler]

Ok it's been almost a month since we heard from Walter.

Anyone know if he's ok?

Jack

EDIT: Never mind he's alive and well posting in other groups!!!

[jhudler]

Still working on getting a proper setup that will allow be to cast test pieces for D790 tests.

Just got the vibrator in today and waiting on pure DGEBA, and hardener without Nonyl phenol, big vacuum gauge (not going to use my thermocouple anymore), some o-rings and a fresh tube of Dow Vacuum Grease.

Now I have to leave for a week to visit the family for Thanksgiving in Tennessee. Sigh... the holidays are upon us. Ba-Humbug

Jack

[walter]

Hi Jack,

Not much to report at the moment. I'm doing blueprints for the rest of machine parts (picture Wyllie E. Coyote blueprints to catch the roadrunner) and trying to incorporate some of the ideas that have come up over the past couple of weeks- e.g. Larry's surface plate tech, RotarySMP's Austrian link and your vibrating vacuum mixer.
No, I'm not building one :-), just doing away with vibrating the mold!

Ok, back to work..


Cheers!

[Steven.ji]

Helllo, everyone who will provide me the comparision between polymer concrete and grey iron?

[ckelloug]

Stevenji,

The article you want is this one:

http://machinedesign.com/ContentItem...eonmetals.aspx

Regards all,

Cameron

[jhudler]

I'm trying to find out if we should be looking Bisphenol F (DGEBPF) instead of Bisphenol A (DGEBPA). Perhaps cost? Need to look more.

http://www.hrsd.com/pdf/Coatings%20M...PENDIX%20C.pdf

Here's an intersting comparision at Hexion.
EPON Resins 826 and 828 are DGEBPA
EPON Resins 862 and 863 are DGEBPF

http://www.hexion.com/pds/D/DGE%20of...-%20DGEBPF.pdf

[walter]

Very interesting Jack, thanks for posting it. Any idea about the cost?

[MaX-MoD]

Hi, I've got some French litterature for you, about some industrial use of EG: molds, rectification, inserts etc.
if you don't understand French still you've got the pictures^^
nah, kidding, just ask me for precision

http://www.microplan-group.com/W/Dow...th_2005_fr.zip