Flexural test ASTM D790

General Composites Discussions Composites Talk
#1

Hello everyone,

I am a new member, I am learning MS at Korea. In my work, I have tested carbon sheet (plain weave) 1mm thickness following ASTM D790 standards, dimension of the specimen was 50.8x12.7x1 mm and test on 25.4mm support span. The carbon sheet was T300 TORAYCA and flexural modulus they mention is 125 GPa. But in my result, I calculated the result always about 50~55 GPa, I don’t know the reason why the result unequal too much with data sheet from the manufacturer. The forcing at breaks was 33~38 Kgf.

Does anyone do this test? Please help me.

Thanks and best regards.

#2

Did the manufacturer use the same ATSM testing method?

Or maybe the result is because of process? What was your cure cycle like? Did you have proper ramp/soak? This is prepreg right? What resin system did you use vs manufacture? Where there voids in the laminate? Did you use autoclave? What was the ply schedule? How many specimens did you make?

There are a lot of factors that could give bad results. Could be a layup or cure process thing or maybe it was in the way the specimens were prepared? Or maybe the results the manufacture give aren’t realistic?

#3

125 GPa E modulus sounds like an UD fiber 0° Laminat.

in fiber direction, Often in the fibre technical data sheets you find UD values.

Your 55 Gpa for plain weave is reasonable.

#4

was it a bending test?

#5

was it a bending test?

#6

I made this test following ASTM D790. I tested more than 10 specimens. Yes, because I don’t know everything about the properties of this material. I checked carefully the process and calculated again. But the results still bad. I think the datasheet from manufacturer may be unrealistic.

#7

Could you explain more details? 125GP is only for UD?

#8

Do your results form specimen still vary? Are your values still 55 GPa for flexural modulus?
A flexural modulus for for plain weave is always lower compared to 0° UD laminate due to ondulation.

#9

yes. I was bending test

#10

I did not change specimens dimension. The result change a little from 50-55 GPa for all test. In datasheet they do not mention which was UD or something. I attach the datasheet below

#11

I believe Toray is using unidirectional, not woven. You would need to use their unidirectional, and their exact same resin to get similar results. Even then, you may get higher or lower results. Their results are likely the average, if not the maximum values from testing. A- and B- basis values will be quite a bit lower. Composites, by nature, are inconsistent in strength. The only reason they are used in structures is because even when accounting for possible low values in strength, they still outperform metals in many situations.

-Ben

#12

The composite property data posted by Toray is for uni prepreg (Toray Composites epoxy systems) and are meant to be nominal data. Note that the data was normalized to 60% FVF, so any difference in matrix, process, and FVF would lead to differences in flex strength values.

#13

Thanks, but this material I bought from company and I request them to provide datasheet. They gave me datasheet T300 Toray. I did not make material by myself

#14

What is FVF? tgundberg

#15

FVF is Fiber Volume Fraction

#16

Your test is good. Your results are good.

If you have Unidirectional fibre you have 60% fibre and 40%resin ratio.
The Toray test its made with unidirectional fibre.

If you use that fibre in plain wave, you have half fibre in the direction of effort.
Then the modulus and the strenght will be more or less the half. 125/2=67,5 GP.
As you have the ondulation of the fibre the modulus is less than the half, then your result is very good, 55 GP. :wink: