UD Fibre Strength vs Angle Orientation

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UD Fibre Strength vs Angle Orientation

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sts	sts posted 10 Years Ago HOT Topic Details
Group: Awaiting Activation Posts: 3, Visits: 11	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= q1cos^2 (angle) + q2sin^2(angle) + 2Tausin(angle)cos(angle) but compare with strength vs angle plots I found online it does not change quite the same way. Thanks, Stan
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Warren (Staff)	Warren (Staff) posted 10 Years Ago HOT Post Details
Group: Administrators Posts: 2.5K, Visits: 8.5K	Different UD fibre types and different layups are going to perform differently compared to each other as you change the angle of load. Obviously the fibre itself is likely to be weakest at 90 degrees, however most UD's also have a fine supporting net fabric that will almost certainly have some influence on the data. Also resin matrix will again play an important part. Hence why on paper the formula may look ok but in practice there are quite a few variables that will influence the result Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
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sts	sts posted 10 Years Ago HOT Post Details
Group: Awaiting Activation Posts: 3, Visits: 11	Thanks for reply. So is it the theory still valid for angle change ?? Of course I would use ROM to calculate composite strength in all principle directions. Does this mean the formula I mentioned is the best case scenario but still is correct approach ??? many thanks
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ChrisR	ChrisR posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 363, Visits: 3K	It all depends on your application to which analsyis/design process you use, I personally like boggo standard laminate theory These books explain reasonably simply Engineering Design with polymers and composites, Gerdeen, Lord & Rorrer - CRC Press ISBN 0-8247-2379-1 Composite Materials design and applications, Gay & Hoa - CRC Press ISBN 1-4200-4519-9 Also try and get an extract of "Swanson" this has a step by step. Essentially: If you were to look at a single ply then you calc it the way you already have (but allowing an addition for the tension/compression value of the resin, you also need to allow for resin/fibre ratio in that calc. Say if you had a 7 ply laminate of UD, 0,45,-45,90,-45,45,0 you need to work out the allowable stress / stress capacity of each layer, then using laminate theory you can transform these into comparable distinct and equivalent layers expressed in terms of strength/stiffness to calc it in a single equation. It also allows you to build through section stress and strain diagrams to check the interlamina shear. All of this is purely theoretical without comparable test data from the fibre and the matrix. My advice when learning how to actually do the engineering side is to (if you can!) Calc a basic laminate (eg 2 ply with a core) BY HAND and in full, then build said laminate and test it then compare what you have vs what you calc'd NOTE: if you are using an FE approach then you need to know how to do this side of it anyway so you can check by hand that the values you are getting out are approximately right. - as the saying goes : dog poo in, dog poo out. ONLY once you are happy with the main data on simple structures can you then progress into more complex forms with more confidence. Edited 10 Years Ago by ChrisR
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sts	sts posted 10 Years Ago HOT Post Details
Group: Awaiting Activation Posts: 3, Visits: 11	ChrisR (03/02/2015) It all depends on your application to which analsyis/design process you use, I personally like boggo standard laminate theory These books explain reasonably simply Engineering Design with polymers and composites, Gerdeen, Lord & Rorrer - CRC Press ISBN 0-8247-2379-1 Composite Materials design and applications, Gay & Hoa - CRC Press ISBN 1-4200-4519-9 Also try and get an extract of "Swanson" this has a step by step. Essentially: If you were to look at a single ply then you calc it the way you already have (but allowing an addition for the tension/compression value of the resin, you also need to allow for resin/fibre ratio in that calc. Say if you had a 7 ply laminate of UD, 0,45,-45,90,-45,45,0 you need to work out the allowable stress / stress capacity of each layer, then using laminate theory you can transform these into comparable distinct and equivalent layers expressed in terms of strength/stiffness to calc it in a single equation. It also allows you to build through section stress and strain diagrams to check the interlamina shear. All of this is purely theoretical without comparable test data from the fibre and the matrix. My advice when learning how to actually do the engineering side is to (if you can!) Calc a basic laminate (eg 2 ply with a core) BY HAND and in full, then build said laminate and test it then compare what you have vs what you calc'd NOTE: if you are using an FE approach then you need to know how to do this side of it anyway so you can check by hand that the values you are getting out are approximately right. - as the saying goes : dog poo in, dog poo out. ONLY once you are happy with the main data on simple structures can you then progress into more complex forms with more confidence. Thanks Chris for response. I understand the approach you are suggesting but my case is much simpler. I just want to know if I have UD 0° composite lets say 1 layer only and I want to know if my theoretical approach is correct (according to transformation matrix formula above) i.e. when I lay my layer at certain angle off 0° axis what would be predicted strength. And does this strength vary the same way for all fibres (in theory should have if I am using same formula)?? Many thanks
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ChrisR	ChrisR posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 363, Visits: 3K	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
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