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Material Forms

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Material Forms

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  1. Composite reinforcements come in many styles. Fibers can be continuous, or short. Continuous fibers can be collected to form a tow or thread which might consist of one thousand (1K), three thousand (3K), twelve thousand (12K), etc. filaments. The tow can be laid side by side to form a unidirectional tape or woven into fabric. The type of weave determines its drapeability and conformance to compound curvature. The resins can be applied directly to the fabric during lay-up or pre-impregnate the reinforcement prior to lay-up. Cure temperatures for prepregs range from 180 degrees F to higher than 400 degrees F. Material Forms 1

  2. For primary critical aircraft structures, we use pre-impregnated continuous fiber that is either collimated into uni-directional tape or woven into fabric. Tape is used where maximum stiffness is required in a particular direction, however, it is more difficult to drape over compound surfaces than fabric and tape needs additional transverse reinforcement to overcome the weaknesses of the resin matrix. Secondary structures are usually made from pre-preg fabrics or mat of short fibers. The examples to be passed out among the audience are typical forms. Introduction 2

  3. Laminae are single layers, and laminates are combinations of laminae. Transverse (90o) Unidirectional (0o) Bias (+ 45o) Detail I: Ply lamina state subscripts (1,2,3 system) Detail II: Laminate state subscripts (x,y,z system) 3

  4. A number of conventions for coding fiber direction, ply sequences, and fiber orientation percentages are used within the industry. Ply Sequence Coding and Layup Percentage Coding Example:- Superscripts: Subscripts: # of layers s = symmetrical s1 = S-glass tape f2 = graphite fabric [ +45f2 1/Os12/+45f21 ]S = [ +45f2 /Os1/ Os1/+45f2 ] + [ +45f2 /Os1/ Os1/+45f2 ] 4

  5. Tape and Fabric 5

  6. Fabric Weave Patterns 6

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