Mechanics of Composite Materials Lesson 3 Metal Matrix

Mechanics of Composite Materials Lesson 3

Metal Matrix Composites ■ What are metal-matrix composites? Metal matrix composites have a metal matrix. Examples include silicon carbide fibers in aluminum, graphite fibers in aluminum.

Advantages of MMCs ■ ■ ■ Higher specific strength and modulus over metals. Lower coefficients of thermal expansion than metals by reinforcing with graphite. Maintenance of high strength properties at high temperatures.

Degrading properties in MMCs ■ Are there any properties which degrade when metals are reinforced with fibers? Yes, they may have reduced ductility and fracture toughness.

Typical mechanical properties of metal matrix composites

Step 0: Cutting the shape

Step 1: Apply Aluminum File

Step 3: Lay Up Desired Plies

Step 4: Vacuum the specimen

Step 5: Heat to Fabrication Temperature

Step 6: Apply Pressure and Hold for Consolidation Cycle

Step 7: Cool, Remove and Clean Part

Schematic of Diffusion Bonding

Ceramic Matrix Composites ■ What are ceramic matrix composites? ■ Ceramic matrix composites have matrices of alumina, calcium alumino silicate (CAS), lithium alumino silicate (LAS). Examples include Silicon Carbide/CAS and Carbon/LAS.

Advantages of CMCs High strength, hardness and high service temperatures ■ Chemical inertness ■ Low Density ■

Table 1. 13 Typical mechanical properties of some ceramic matrix composites

Manufacturing of Ceramic Matrix Composites Slurry Infiltration

Application of CMCs

Carbon-Carbon Compoistes ■ What are carbon-carbon composites? Carbon - Carbon composites have carbon fibers in carbon matrix.

Advantages of Carbon-Carbon Composites ■ ■ ■ Gradual failure Withstand high temperatures Low creep at high temperatures Low density High thermal conductivity Low and tailorable coefficient of thermal expansion

Advantages of Carbon-Carbon Composites ■ ■ ■ Great strength to weight ratio High modulus, thermal conductivity, and electrical conductivity Good thermal shock resistance, abrasion resistance, and fracture toughness Excellent high temperature durability in inert or vacuum environment Good corrosion resistance

Table 1. 14 Typical mechanical properties of carbon-carbon matrix composites

Applications of C-C Composites ■ Space Shuttle Nose Cones �Re-entry temperature of 3092 K ■ Aircraft Brakes �Saves 450 kgs of mass � 2 -4 times durability vs. steel � 2. 5 times specific heat of steel

Schematic of Analysis of Laminated Composites