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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 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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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Differences Between Metals and Composites 2

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Elevated temperature and moisture reduce the material operational limits. 3

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Degradation of S-Glass/Epoxy Tape 4

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses = 50 o F Ref. MIL. HNDBK. 17 5

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 6

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 7

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 8

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 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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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Any moisture absorbed into the resin causes each ply to try to swell in the 2-direction. Fiber Direction 10

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 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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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Damage Tolerance Overview - Life Criteria Non-Detectable DamageDetectable Damage 12

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Under static loading, composites have a higher notch sensitivity than metals. KtKt 13

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Maximum Compression Fatigue Strength (Strain) Under fatigue loading, composites have a lower notch sensitivity than metals. 14

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

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Composites must be protected against service environment. Heat Absorption Lightning Strike and P-Static 16

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Composites must be protected against galvanic corrosion. BMS 5095 is Boeing Material Specification for sealant. Ref. Only. 17

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Structural Composites Property Definition 18

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Mathematicians have saved the day. 19

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Materials Properties and Laminate Analysis Theory 20

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses The analysis for continuous fiber-reinforced, laminated composites differs from that of metals because:- 21

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Analyses of laminated composites utilize two types of mathematical models to define material behavior: 22

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Classical Laminated Plate Theory 23

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Establishing Lamina (Ply) Properties 24

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Work in strain instead of stress. Strain Stress e *E lamina P/S(E*A) P 25

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Work in strain instead of stress. Strain Stress e i *E lamina E i= 26

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Lamina Ply 1, 2, 3 Coordinate System 27

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Ply X, Y, Z Coordinate System 28

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses transpose 29 Laminate Theory for An Orthotropic (Different) Properties in Material Lamina All Directions - 2-D

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 0 0 0 0 00 21 3-D Lamina Analysis 30

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Compliance 31

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses For An Isotropic Material (Homogeneous Metal) 32

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Stiffness Matrix (Inverted Compliance Matrix ) 33

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Stiffness Matrix Applied to Isotropic Metals 34

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Analysis q = 45 o q = 0 o q = -45 o 35

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Analysis For each lamina in the laminate: 36

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Transformation Matrix 37

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Stress Strain Relationship FOR EACH LAMINA 38

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses [A]= Extensional Stiffness Matrix [B]= Bending Coupling Matrix [D]= Bending Stiffness Matrix Laminate Properties from Lamina Properties 39

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Composite Analysis Flow Diagram 40

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Lamina Laminate 41 Comparison Between Engineering Constants of Angle-Ply and Unidirectional Composite Lamina

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Inplane Stiffness and Strength 42

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Bending Behavior 43 STIFFER STIFF

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses 44 Symmetric Balanced Laminate So far, we have considered one class of laminates.

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Unbalanced Laminates Unbalanced and Nonsymmetric Laminates Result In Warping 45

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Unbalanced laminates shear when you pull on them. 46

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Unsymmetric laminates bend when you pull on them. 47

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Bending 48

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Curvature 49

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Coupling 50

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Average Tensile Modulus (E x ) 51

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Laminate Average Shear Modulus (G xy ) 52

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Thermal Expansion Coefficient TYPICAL RANGE USED 53

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses GENLAM Composites Design, by Stephen W. Tsai, published by Think Composites, P.O. Box 581, Dayton, Ohio 45419, Telephone: (513) 429-4594 54

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses The absorption of moisture by the matrix is the major environmental hazard to composite strength. 55

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Absorption of Moisture With Time Saturation (Epoxy Matrix) F/G 3% by Wt. Gr 2% by Wt. K 49 4% by Wt. 56

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Application of Advanced Composites to Helicopter Structures Strengths and Weaknesses Equilibrium Moisture Content as a Function of Relative Humidity for AS/3501-6 57

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