Composites are made of two main components: fibers and a matrix. Fibers carry load and can be made of materials like glass, carbon, and Kevlar. Fibers come in various forms like strands, woven meshes, and chopped fibers. The matrix is a fluid that hardens and holds the fibers in place. It can be made of materials like plastic. Examples of composites include carbon fiber and plastic skis, Kevlar and fiberglass boats, and concrete reinforced with steel. The document then discusses stresses in beams including bending stresses, maximum bending stress, and shear stress.

1. Composites

2. Learning Objectives: What are composites made of? How are composites fabricated? Composite Material Properties

11. Examples of Composite Members: Concrete slab reinforced with steel Carbon fiber and plastic snow skis Kevlar and fiberglass boats Concrete slab on a metal deck . Introduction concrete corrugated metal deck

12. Introduction Composite materials consist of two components: the fiber and the matrix Fiber – the load carrying material Matrix - the fluid binder that hold the fibers in place when it solidifies.

13. Fibers Materials: Glass fiber (hence, fiberglass) Aramid fiber (Kevlar) Graphite fiber (carbon) Metal fiber (concrete, ceramics) Boron fiber Wood fiber

14. Fibers Forms: Strands (roving) – typically used with mandrel . Direction and spacing controlled Woven mesh in sheets. Direction controlled Chopped fiber (approx 1” long) – random direction

16. Back to airplane wing

17. Stresses in Beams A.) Bending Stresses 1.) Introduction When a beam is subjected to positive bending moment, the top shortens and the bottom lengthens.

18. The bending strains are zero at the neutral axis. The bending strains increase proportionately with the distance from the neutral axis. The maximum strains occur at the top and bottom of the beam (outer fibers)

19. Since stress is directly related to strain  =  E), bending stress is also zero at the neutral axis and increases with the distance from the neutral axis. The maximum bending stresses occur at the top and bottom of the beam (outer fibers)

20. 2.) Maximum Bending Stress  b,max = Mc I  b,max = Maximum bending stress at a given cross-section (ksi). c = Distance from N.A. to the outer fibers of cross-section (in) M, I = as defined before. N.A. c top c bot y

21. 3.) Strong Axis vs. Weak Axis Strong Axis N.A. Weak Axis

22. B.) Shear Stress - Average Web Shear  v = V_ dt w d t w d t w d t w