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Long Fiber Laminates

Mechanical characterization of a composite structure is more complex than that of a non-composite material.. Single layer of laminate is not isotropic?requires 9 stiffness and strength constants:Longitudal Young's Modulus, E1Transverse Young's Modulus, E2Poisson's Ratio, v12In-plane Shear Modu

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Long Fiber Laminates

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    1. Long Fiber Laminates Jim LaRowe Tim Spinner

    2. Mechanical characterization of a composite structure is more complex than that of a non-composite material. Single layer of laminate is not isotropic requires 9 stiffness and strength constants: Longitudal Youngs Modulus, E1 Transverse Youngs Modulus, E2 Poissons Ratio, v12 In-plane Shear Modulus, G12 Longitudal Tensile Strength, (s1T)ult Longitudal Compressive Strength, (s1C)ult Transverse Tensile Strength, (s2T)ult Transverse Compressive Strength, (s2C)ult In-plane Shear Strength, (t12)ult A monolithic (and isotropic) material requires only 4 such constants (ex. steel)

    3. Fiber reinforcements typically have small diameters Reasons for using thin fibers include: A reduction in the number of inherent material flaws increasing material strength

    4. Fiber reinforcements typically have small diameters Reasons for using thin fibers include: Small diameters allow a larger fiber-matrix interface area per same volume.

    5. Fiber reinforcements typically have small diameters Reasons for using thin fibers include: 3. Small diameter increases fiber ability to bend without breaking.

    6. Laminate structures are constructed from multiple layers (laminas) A laminate can have all laminas stacked in the same direction or plies can be angled Orientation of lamina:

    7. Laminate Code

    8. Unidirectional Laminates Unidirectional fibers are used for carrying simple loads such as uniaxial tension. The composite strength along the fiber direction is easier to estimate for a unidirectional composite. Stiffness and strength are higher for a unidirectional composite, for the same volume of fibers per unit volume composite Reinforcement efficiency of multidirectional composites are 1/5 of that of unidirectional fibers

    9. Quasi-isotropic Laminates Quasi-isotropic laminates behave similar to an isotropic material, with elastic properties the same in all directions For N (N = 3) lamina of same material and thickness, a quasi-isotropic layering will require each lamina oriented at an angle of 180o/N between each other. Examples: [0/60] [0/45/90]S [0/36/72/-18/-54]

    13. Long vs. Short Fibers Long Fibers Easier to process and orient Impact resistant, low shrinkage, improved surface finish, and dimensional stable Short Fibers Low cost, easier to work with, fast cycle time fabrication procedures Fewer flaws therefore higher strength

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