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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

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**Differences Between Metals and Composites**

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**Elevated temperature and moisture reduce the material operational limits.**

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**Degradation of S-Glass/Epoxy Tape**

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= 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

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

Fiber Direction 10

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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

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**Damage Tolerance Overview - Life Criteria**

Non-Detectable Damage Detectable Damage 12

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

Kt 13

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**Maximum Compression Fatigue Strength (Strain)**

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

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**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

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**Heat Absorption Lightning Strike and P-Static**

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

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**Composites must be protected against galvanic corrosion.**

BMS 5095 is Boeing Material Specification for sealant. Ref. Only. 17

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**Structural Composites Property Definition**

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**Mathematicians have “saved the day.”**

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**Materials Properties and Laminate Analysis Theory**

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

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

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**Classical Laminated Plate Theory**

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**Establishing Lamina (Ply) Properties**

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**Work in strain instead of stress.**

P P/S(E*A) e*Elamina 25

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**Work in strain instead of stress.**

Ei= ei*Elamina 26

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**Lamina Ply 1, 2, 3 Coordinate System**

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**Laminate Ply X, Y, Z Coordinate System**

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

transpose 29

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3-D Lamina Analysis 21 30

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Compliance 31

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**For An Isotropic Material (Homogeneous Metal)**

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**Stiffness Matrix (Inverted Compliance Matrix )**

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**Stiffness Matrix Applied to Isotropic Metals**

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

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

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**Transformation Matrix**

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**Stress Strain Relationship**

FOR EACH LAMINA 38

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**Laminate Properties from Lamina Properties**

[A]= Extensional Stiffness Matrix [B]= Bending Coupling Matrix [D]= Bending Stiffness Matrix 39

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**Composite Analysis Flow Diagram**

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

Laminate 41

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**Inplane Stiffness and Strength**

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**Laminate Bending Behavior**

STIFFER STIFF 43

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**So far, we have considered one class of laminates.**

Symmetric Balanced Laminate 44

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**Unbalanced and Nonsymmetric Laminates Result In Warping**

Unbalanced Laminates Unbalanced and Nonsymmetric Laminates Result In Warping 45

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**Unbalanced laminates shear when you pull on them.**

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**Unsymmetric laminates bend when you pull on them.**

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Bending 48

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Curvature 49

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Coupling 50

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**Laminate Average Tensile Modulus (Ex)**

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**Laminate Average Shear Modulus (Gxy)**

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**Thermal Expansion Coefficient**

TYPICAL RANGE USED 53

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

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

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**Absorption of Moisture With Time**

Saturation (Epoxy Matrix) F/G 3% by Wt. Gr 2% by Wt. K49 4% by Wt. 56

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

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