Ok, news. Yes, as suspected, their quoted modulus is compressive only (though they do not state this). I independently corroborated the test values by updating an FE model. EG is just naff in flexure. Here ends the investigation.
Ok, news. Yes, as suspected, their quoted modulus is compressive only (though they do not state this). I independently corroborated the test values by updating an FE model. EG is just naff in flexure. Here ends the investigation.
Designing parts made using epoxy where stiffness is the key factor is what I do for a living. Your understanding of the properties of resin and what effects them is off.
Particularly on the importance of using resin as part of a composite and the effect of temperature on cured and curing resin.
Just because a resin is designed to do it's initial cure at room temp does not mean it achieves maximum stiffness from a room temp cure.
There is a reason why we post cure parts at high temperatures even if the initial cure was at room temp. Resin cured at room temp is far less temperature stable. That is universally true.
In other words, even the best room temp resin will start to soften in a warm room. Fully cured resin can become flexible if you leave it in a car on a sunny day (or around heat generating machinery).
Curing or post curing at higher temperatures increases the stiffness of the part and also raises the temperature that the resin would start to lose stability (I.e. soften and become flexible).
Someone expecting to build pro grade epoxy granite machines for a living should be capable of building a simple curing oven.
Aside from following an optimal curing schedule, the best method of compensating for undesirable properties of resin (I.e. that it's soft, brittle and expensive) is using it as part of a composite.
Adding stones makes it cheaper and harder. I can say from personal experience that epoxy granite marries extremely well to a steel tube skeleton too.
Steel square tubes are strong, stiff and hold screw threads well but they have horrible acoustics. Epoxy granite has exceptional acoustics but is potentially brittle and poor at holding screws. Together you have the best of both.
If you look at the various online epoxy granite how to vids and tutorials, you'll see that most cast epoxy granite machine bases around a steel or aluminum skeleton. It's just easier for attaching rails and ball-screws (without cracking the epoxy granite when you tighten screws).
Hi Geomon - I have no issue with the fact that post cured epoxy is better then ambient cured. This is like saying a stress relived steel frame is better then one that is not SR. These are relative conditions.
Also epoxy is a great adhesive and it sticks to metals really well so using metal inserts makes sense for machining purposes. But DIY Makers need a simpler path then what the "pros" use. My current view is that there is not enough consistent "proper" engineering data out there on EG that makes sense (which agrees with one of your statements). Another OP has posted this article and its good as the researchers have tested in tensile, flexure and compression. Unfortunately they did not publish the compression stiffness. But the key point is that the tensile and flexural modulus are very different. If they published compression stiffness this would be a good indicator of the non-isotropic behavior if this is the case (or poor testing for the purpose). This could be a testing bias in that the tests measure the strain over different intervals. This is why I am testing my own material to determine if its worthwhile using EG or UHPC or another composite. My current stance is that although fibreglass is low modulus (30GPa) at least I have decades of correlated data that shows the laminates I design have the same flexural, tensile and compressive stiffness so I can assume they are isotropic making design a reliable process. That's all that I want - a reliable design process or reliable data so good decisions can be made. Peter
But giving BLATANTLY WRONG data is not going to help them. It is called STRAIN RELIEVED not stress relieved, and your analogy makes no sense. It is compressive strength or resistance not stiffness and they can't publish it because there are THOUSANDS of different varieties and you are asking what food tastes like.
Much of what you post sounds like it was dreamt up by some 12 year old. That is why I told you months ago that you should stop making things up and now he has done the same.There is nothing wrong with not knowing something but there is a HUGE problem with spreading WRONG information.
Not all Epoxy or Resin stick well to metals. Epoxy and Resin are different things. They are used as a mixture in this case. Fiberglass is NOT low modulus 30GPa may be lower than steel but is not low. By the way I would like to know WHICH modulus you are refering to? When you say "low modulus". You are just throwing random words out to try and sound smart without knowing WHAT THE HELL you are talking about.
The dreamt up numbers you posted in the other thread were way off, by OVER 50% to be exact compared to the lowest ratio of aggregate to Epoxy resin that ANY other recipe lists. You need between 13% UP TO 20% by VOLUME of Epoxy which is why the few examples you see on youtube (where I assume you took your fantasy numbers from) look like dried turds full of holes (They are measuring by weight and using as low as 9% by weight) while the proffessional ones are smooth and even their marketing shows a free flowing slurry during casting. The only half decent amateur projects shown on youtube and the web show much higher quantities of resin used and this is also confirmed by those companies selling epoxy granite kits.
Bulk modulus, a measure of compression resistance
Elastic modulus, a measure of stiffness
Shear modulus, a measure of elastic stiffness
Young's modulus, a specific elastic modulus
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But giving BLATANTLY WRONG data is not going to help them. It is called STRAIN RELIEVED not stress relieved, and your analogy makes no sense. It is compressive strength or resistance not stiffness and they can't publish it because there are THOUSANDS of different varieties and you are asking what food tastes like.
Much of what you post sounds like it was dreamt up by some 12 year old. That is why I told you months ago that you should stop making things up and now he has done the same.There is nothing wrong with not knowing something but there is a HUGE problem with spreading WRONG information.
Not all Epoxy or Resin stick well to metals. Epoxy and Resin are different things. They are used as a mixture in this case. Fiberglass is NOT low modulus 30GPa may be lower than steel but is not low. By the way I would like to know WHICH modulus you are refering to? When you say "low modulus". You are just throwing random words out to try and sound smart without knowing WHAT THE HELL you are talking about.
The dreamt up numbers you posted in the other thread were way off, by OVER 50% to be exact compared to the lowest ratio of aggregate to Epoxy resin that ANY other recipe lists. You need between 13% UP TO 20% by VOLUME of Epoxy which is why the few examples you see on youtube (where I assume you took your fantasy numbers from) look like dried turds full of holes (They are measuring by weight and using as low as 9% by weight) while the proffessional ones are smooth and even their marketing shows a free flowing slurry during casting. The only half decent amateur projects shown on youtube and the web show much higher quantities of resin used and this is also confirmed by those companies selling epoxy granite kits.
Bulk modulus, a measure of compression resistance
Elastic modulus, a measure of stiffness
Shear modulus, a measure of elastic stiffness
Young's modulus, a specific elastic modulus
Hi Excited - I'll answer the things I can and I'm 16 not 12 thank you.
https://en.wikipedia.org/wiki/Bulk_modulus
These are the definitions of modulus I am familiar with, your definitions need expanding a bit. Happy to discuss the numbers but you will have to be more specific in your statements. If something is wrong then please correct it with what you think is the correct data that is the only way past opinion vs facts. 30GPa is low linear modulus in the stuff I do. E=200GPa is steel, 100-110GPa is cast iron, 110GPa titanium, 70GPa is aluminium, 89-100GPa is carbon fibre. So 30GPa is at the low end for me. For structural design purposes "modulus" is usually young's modulus or the linear modulus of the material. Bulk modulus is usually used for liquids as linear tensile modulus does not exist for liquids.
If I go to my heat treaters and ask for a frame to be strain relieved he will ask for an explanation. Maybe its a local thing.
Here's a link to a heat treaters that discusses stress relief as an example. Just picked one random seems to be OK.
https://www.industrialheating.com/ar...C%20turning%2C
13-29% epoxy by volume implies 87-71% solids ratio with no voids. From the tests I've done 70% Vs solids is doable but 87% Vs not likely would have voids.
Resin and Epoxy are loosely used where I come from to mean the same thing, Again in your area they maybe different. Sure there are 1000s of Epoxies and I expect people to pick the right one for the job. Always good to have a referee around.. Peter
I saw a guy [1] who tested a bunch of different epoxy-granite recipes, and compared the deflection against a piece of pure epoxy.
My takeaway is that fine particles dramatically improves the stiffness. These fine particles can be found in aluminum oxide powder used for sand-blasting. There are a lot of grades of particle sizes, but I can't find the table at the moment. Please do use protection while handing this stuff, while it is inert, it will never leave your lungs after you breathe it in.
[1] Epoxy granite stiffness - test and results
https://youtu.be/gjw5juGG1g8?t=1062