1. 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

2. Differences Between Metals and Composites2

3. Elevated temperature and moisture reduce the material operational limits.3

4. Degradation of S-Glass/Epoxy Tape4

5. = 50oF
Ref. MIL. HNDBK. 17 5

6. 6

7. 7

8. 8

9. 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

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

11. 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

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

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

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

15. 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

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

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

18. Structural Composites Property Definition18

19. Mathematicians have “saved the day.”19

20. Materials Properties and Laminate Analysis Theory20

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

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

23. Classical Laminated Plate Theory23

24. Establishing Lamina (Ply) Properties24

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

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

27. Lamina Ply 1, 2, 3 Coordinate System27

28. Laminate Ply X, Y, Z Coordinate System28

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

30. 3-D Lamina Analysis 21 30

31. Compliance 31

32. For An Isotropic Material (Homogeneous Metal)32

33. Stiffness Matrix (Inverted Compliance Matrix )33

34. Stiffness Matrix Applied to Isotropic Metals34

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

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

37. Transformation Matrix37

38. Stress Strain Relationship
FOR EACH LAMINA 38

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

40. Composite Analysis Flow Diagram40

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

42. Inplane Stiffness and Strength42

43. Laminate Bending Behavior
STIFFER
STIFF 43

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

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

46. Unbalanced laminates shear when you pull on them.46

47. Unsymmetric laminates bend when you pull on them.47

48. Bending 48

49. Curvature 49

50. Coupling 50

51. Laminate Average Tensile Modulus (Ex)51

52. Laminate Average Shear Modulus (Gxy)52

53. Thermal Expansion Coefficient
TYPICAL RANGE USED 53

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

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

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

57. Equilibrium Moisture Content as a Function of Relative Humidity for AS/3501-657