Flexure/Shear test data processing
Flexure/Shear test data processing
(OP)
Hello everyone,
I was wondering if anyone has a formula for deriving the flexural and shear strength of the composite from data obtained from a plain flexure/shear stress test using a 3 point flexure/shear test fixture (e.g. http://www.wyomingtestfixtures.com/Products/page37...)
Thanks,
M
I was wondering if anyone has a formula for deriving the flexural and shear strength of the composite from data obtained from a plain flexure/shear stress test using a 3 point flexure/shear test fixture (e.g. http://www.wyomingtestfixtures.com/Products/page37...)
Thanks,
M





RE: Flexure/Shear test data processing
Tom S.
RE: Flexure/Shear test data processing
I am trying to correlate computed values myself. I don't use Nastran so I'm out of luck from that standpoint, therefore I am relying on "The Laminator". Perhaps there is a better program (cheap)
I understand that engineers routinely predict flexural and shear strength from multipoint (3 minimum) flexural test results. I suspect there is some formula behind all this... I would like to get that information and I hope someone would help me out
I can live with a 10% variance as long as the computed values are below the actual ones!
RE: Flexure/Shear test data processing
Stress (flexure) = (0.75*L*P)/(b*d*d)
Stress (shear) = (0.75*P)/(b*d)
where P is the load of the 3-point test.
Regards
sgdon
RE: Flexure/Shear test data processing
>
>Stress (flexure) = (0.75*L*P)/(b*d*d)
>
>Stress (shear) = (0.75*P)/(b*d)
>
>where P is the load of the 3-point test.
To make sure I understand the values are for the test specimen and are:
L - length
b - width
d - thickness ... right?
Now what would the formula look like for a 4 point test?
Also, I have recently come accross a similar formula for the (flexure stress):
F = 3*P*L/2*b*d*d ... Any comments on this one?
RE: Flexure/Shear test data processing
Apologise for the mistake here. Yes, you were right, the flexure stress factor should be 1.5.
For 4-pt test, you can similarly derive from 1st priciple, i.e. obtain moment from the triangular stress block and equate to the moment obtained from the free body diagram.
Thanks
RE: Flexure/Shear test data processing
>Apologise for the mistake here. Yes, you were right, the
>flexure stress factor should be 1.5.
No problem... Just beginner's luck on my end
>For 4-pt test, you can similarly derive from 1st priciple,
>i.e. obtain moment from the triangular stress block and
>equate to the moment obtained from the free body diagram.
This is really testing the limits of my current understanding :-(...So the formula for a 4 point test would be written how?
F = ?
RE: Flexure/Shear test data processing
For 4 pt and still assuming elastic, one can work out to be
Stress=Moment/Elastic modulus (For rectangular section, elastic modulus=bd^2/6)
Moment = (P/2)*l/3 (assume total load on the beam is P)
i.e. Stress=Pl/(b*d*d)
Having, i did come across people quoting 0.75Pl/(b*d*d). Now, this time round, you tell me why is that so?! I hope someone else may also be able to answer that..
sgdon