I need help with my composite coursework asap

General Composites Discussions Engineering Talk
#1

In the mechanical lab i made carbon composites and carried out the three point flexure test, in the report i have questions i need to write about in the discussion and thers 3 i cant get my head round as to what exactly they mean, im a civil engineering student so that mite explain why i find this subject hard :confused:.

the three questions are:

  1. Do the measured mechanical properties align with calculated values?

  2. How close are Vf, Vv, Ef, σ’ and ILSS between samples of similar configuration?

  3. Failure modes (using optical/electron microscopy?)(is this the single and multiple shear failure)

Any help would be great :smiley:

#2

Hey,
I’ve taken a class that covers this so I can help you out. Could you post your data and given information (strength results, layup schedule etc. and I can help you out.

Also I’ve moved this thread to Engineering Talk since it’s more appropriate for that forum.

Out of curiosity what university do you attend? I’m currently an undergraduate ME.

#3

All of the test results are on excel its impossible to fit them in the post and theres no attachment icon, im going to plymouth university england

#4

can i send it to u in an email

#5

Yea feel free to send it to me. Contact me through the contact us link up top and I’ll email you back. Sorry for the trouble but spammers love these boards and I have to run a tight ship otherwise they’ll overwhelm this place with junk.

#6

no problem iv the email sent through contact us, cheers

#7

I am curious, and I guess others are as well. Would there be a way to “look over your shoulder”

#8

So I got your data but I’m missing a few key things.

  1. To calculate the mechanical strength I need the modulus of the fiber and the modulus of the matrix. I also need the layup schedule. I might have missed them but double check that you sent them to me because I don’t see it.
    It looks like you used Sicomin SR8100 but verify since professors sometime have inaccuracies on their lab sheets.

  2. I don’t know the configuration of the samples so I can’t say which one matches what. I also have one question on your data. For Plates A-L did you make 5 similar samples to test?

3)Again without knowing the orientation of the fibers, or the loading for your two pictures I can’t comment much but here’s what I can speculatoe. For one of hte pictures you can see multiple cracks running at near 45 degree angles, heavily suggesting shear failure.
For the other you once again can see the crack running at a 5 with a a clear interlaminar failure between two plies. The very clean break and the fact that it occured in the middle of the laminate and not the edge suggests shear since the max normal load in bending is the top and bottom but the maximum shear load is near the center. The interlaminar shear stress depends on the number of plies and the orientation of those plies but like I said above judging from that super clean fracture right inbetween plies I’d put my money on ILSS.

I’m a student like you and I haven’t had a ton of experience with this but even if something I say is wrong hopefully it’ll help you spark the right idea.

@ Herman
I can’t post someone else’s data online but Tomgaa is more than welcome to attach the files here if he likes. I hope he does since this is really good stuff!

#9

Thanks for the quick reply,

  1. Ec is the modulus of the fibre and its in the flexture tables, il email you the lab schedule now.

  2. i only did plate F and there are 5 samples that were tested on each specimen, the other plate A-L (not including F) are other students plates and not mine we were just even there results, i only need to answer the questions on my plate F

  3. the alignment of the fibres are in the forms iv just sent you, as far as i know its [0/90] [0/90] : [90/0] [90/0]

p.s how do i attach the files for herman

#10

Click the little paper clip icon and attach each file that you want. I’ll look at these numbers tonight and try and get you a results. For sample F your results look pretty consistent. For failure modes one of them looks like multiple shear failure and the other one looks like ILSS failure that led to total failure of laminate.

Like I said though I’ll double check all of this and send you what I think. Hopefully it helps!

#11

AppendixA.doc (104 KB)

AppendixB (1).doc (190 KB)

Coursework_template_for_JS_report (2).doc (47.5 KB)

IMG_0213.jpg
IMG_0213.jpg2591×1935 603 KB

IMG_0227.jpg
IMG_0227.jpg2591×1935 574 KB

the excel files wont attach unfortunitly,

  1. Do the measured mechanical properties align with calculated values? this question is the only one iv left iv the second one done as i can compare from the tables, bu for this one do i make a list of the mechanical properties of a carbon composite, such as strength and what ever else is regarded as a mech property, can compare to the values iv gotten in the tables???
#12

Will take a look at it later. Put the excel files in a zip file, and I guess the uploader will accept that.

#13

ILSS_tests_2010 (5).pdf (175 KB)

iv attached the ILSS file but the flexure is too big il work on it

#14

Is your question which values you can compare? If so you can compare the modulus and the ultimate strength quite easily. Did you want me to run those numbers?

#15

well what are the mechanical properties of a carbon composite i know one is strength, so my taking on it would be (remember im a civil engineering student) is that u would list the mechanical properties of a carbon composite and compare the values you get for that property.

#16

You can compare the modulus and ultimate strength quite easily. You’ll find that the modulus data will probably be more accurate than the ultimate strength data. That was the case for my tensile tests of composite coupons and the variability required me to use a weibull modulus as well. Bending is more accurate for brittle materials though so the quality of your ultimate strength data is likely a better.

To compare modulus use the rule of mixtures. To compare ultimate stress try finding the failure strain of the fiber then using the slope of the modulus to find that failure stress.

#17

The modulus of carbon fiber is typically 20 msi (138 Gpa) and its ultimate tensile strength is typically 500 ksi (3.5 Gpa)can i use this as my comparison???

#18

You could but as I was asking before do you know what fiber you used?

For my project I used Toray T700 so I found the data sheet and used those numbers. I also used ACP EZ Lam resin and again got the datasheet and used those numbers. With both those sets of data I could calculate the ideal tensile strength and compare it to my real life values. For the failure data I assumed complete failure at the fiber failure strain and calculated the failure strength from there. Attached is the datasheet I used. From that you can see that the modulus is 230 gpa, a 60 to 70 percent increase in what you predicted.

I see that you know the resin you used but if you don’t have the fiber type used I guess you’re going to have to approximate one. However there are different types for fiber so your guess probably won’t be correct.

Since you’re a student like me I know you have a deadline sometime. If you’d need faster help I could help you over aim, skype, google talk, or yahoo. Just send me your ID and I’ll add you .

#19

i no we used the carbon fibre whether thers different kind of carbon fibres i dont know bu in the lab we only had 3 fibres carbon, glass and hybrid and i used carbon

#20

To accurately calculate the values you’re going to need the material strength. Maybe email your and ask? Or is it on the lab sheet?