Introduction Composites have found their place in aerospace and in the sporting goods industry, where they have displaced many metal applications. The replacement of metal by composite directly has major pitfalls. When an isotropic metal is replaced by an orthotropic system, care must be taken to include biased material to overcome the weakness (resin matrix) in the transverse direction thus adding more weight. This Achilles Heel (resin) is aggravated by the operating environment of moisture and temperature causing a major degradation in strength. 1

Differences Between Metals and Composites 2

Elevated temperature and moisture reduce the material operational limits. 3

Degradation of S-Glass/Epoxy Tape 4

= 50oF Ref. MIL. HNDBK. 17 5

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due to matrix contraction. In a multidirectional laminate, the stiff fibers in adjacent plies will not let much contraction or swelling take place. Therefore... due to matrix contraction. due to matrix expansion. 9

Any moisture absorbed into the resin causes each ply to try to swell in the 2-direction. Fiber Direction 10

At any temperature below the cure temperature, each ply in a laminate wants to contract in the 2-direction. Built-in thermal stresses resulting from post cure cool-down to room temperature must be considered in the structural analysis. Fiber Direction 11

Damage Tolerance Overview - Life Criteria Non-Detectable Damage Detectable Damage 12

Under static loading, composites have a higher notch sensitivity than metals. Kt 13

Maximum Compression Fatigue Strength (Strain) Under fatigue loading, composites have a lower notch sensitivity than metals. Maximum Compression Fatigue Strength (Strain) 14

Exposure to Fluids Abrasion and Rain Erosion Composites must be protected against service environment. Exposure to Fluids Effect is accommodated by reduced design allowables. Apply conventional (polyurethane) finishes. Abrasion and Rain Erosion 15

Heat Absorption Lightning Strike and P-Static Composites must be protected against service environment. Heat Absorption Lightning Strike and P-Static 16

Composites must be protected against galvanic corrosion. BMS 5095 is Boeing Material Specification for sealant. Ref. Only. 17

Structural Composites Property Definition 18

Mathematicians have “saved the day.” 19

Materials Properties and Laminate Analysis Theory 20

The analysis for continuous fiber-reinforced, laminated composites differs from that of metals because:- 21

Analyses of laminated composites utilize two types of mathematical models to define material behavior: 22

Classical Laminated Plate Theory 23

Establishing Lamina (Ply) Properties 24

Work in strain instead of stress. P P/S(E*A) e*Elamina 25

Work in strain instead of stress. Ei= ei*Elamina 26

Lamina Ply 1, 2, 3 Coordinate System 27

Laminate Ply X, Y, Z Coordinate System 28

Laminate Theory for An Orthotropic (Different) Properties in Material Lamina All Directions - 2-D transpose 29

3-D Lamina Analysis 21 30

Compliance 31

For An Isotropic Material (Homogeneous Metal) 32

Stiffness Matrix (Inverted Compliance Matrix ) 33

Stiffness Matrix Applied to Isotropic Metals 34

Laminate Analysis q = 45o q = 0o q = -45o 35

Laminate Analysis For each lamina in the laminate: THESE ARE THE BASIC BUILDING BLOCKS FOR THE CLASSICAL LAMINATE ANALYSIS. 36

Transformation Matrix 37

Stress Strain Relationship FOR EACH LAMINA 38

Laminate Properties from Lamina Properties [A]= Extensional Stiffness Matrix [B]= Bending Coupling Matrix [D]= Bending Stiffness Matrix 39

Composite Analysis Flow Diagram 40

Comparison Between Engineering Constants of Angle-Ply and Unidirectional Composite Lamina Laminate 41

Inplane Stiffness and Strength 42

Laminate Bending Behavior STIFFER STIFF 43

So far, we have considered one class of laminates. Symmetric Balanced Laminate 44

Unbalanced and Nonsymmetric Laminates Result In Warping Unbalanced Laminates Unbalanced and Nonsymmetric Laminates Result In Warping 45

Unbalanced laminates shear when you pull on them. 46

Unsymmetric laminates bend when you pull on them. 47

Bending 48

Curvature 49

Coupling 50

Laminate Average Tensile Modulus (Ex) 51

Laminate Average Shear Modulus (Gxy) 52

Thermal Expansion Coefficient TYPICAL RANGE USED 53

GENLAM “Composites Design”, by Stephen W. Tsai, published by Think Composites, P.O. Box 581, Dayton, Ohio 45419, Telephone: (513) 429-4594 54

The absorption of moisture by the matrix is the major environmental hazard to composite strength. 55

Absorption of Moisture With Time Saturation (Epoxy Matrix) F/G 3% by Wt. Gr 2% by Wt. K49 4% by Wt. 56

Equilibrium Moisture Content as a Function of Relative Humidity for AS/3501-6 57