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UD Fibre Strength vs Angle Orientation

http://www.talkcomposites.com/Topic14920.aspx

By sts - 2/3/2015 9:58:47 AM

Hi,

I am trying to understand behaviour of UD composite as I increase an angle from 0° . Is this changing the same way for all types of fibres or has to be determined experimentally?

I thought it is related to transformation matrix formula  for strength qx= q1*cos^2 (angle) + q2*sin^2(angle) + 2Tau*sin(angle)*cos(angle)  

but compare with strength vs angle plots I found online it does not change quite the same way.

Thanks,

Stan 
By ChrisR - 2/3/2015 3:01:47 PM

OK, you need to decide which way you are looking at it i.e. 

1) If I apply N force at A angle what will the X and y forces be in the laminate OR
2) If I have a laminate with max stress of X, Y and T what is the maximum force I can apply as I vary the angle A

You should get two very different graphs, 1) will probably be a Mohr's stress circle and 2) will likely be an elongated sine wave going top to bottom (assuming X=max and A=0)

You must remember though that this is a LAMINATE not a fibre so you need to work out the properties for the LAMINATE i.e. x direction is UD with xx fibre ratio, y direction is pure matrix at xx fibre ratio and the go on to calc T - but for all this you need to decide what fibre, matrix and fibre/matrix ratio you intend to use