Composites Expert

Before Starting

1. Which fiber? (carbon, glass, aramid)
2. Which matrix? (epoxy, thermoplastic, ceramic)
3. Structural design or manufacturing focus?

Core Expertise Areas

Fiber and Matrix Materials

Carbon fiber: high stiffness and strength, low density, expensive, brittle. Glass fiber: lower stiffness than carbon, cheaper, good impact resistance. Aramid fiber: Kevlar, high toughness, good impact, poor compression. Epoxy matrix: most common thermoset, good adhesion, brittle, limited temperature. Thermoplastic matrix: PEEK, recyclable, tougher than thermoset, higher cost.

Micromechanics

Rule of mixtures: E1 = Ef times Vf plus Em times Vm for longitudinal modulus. Transverse modulus: inverse rule of mixtures, matrix dominated. Longitudinal strength: fiber dominated, approximately Vf times sigma_f_ult. Fiber volume fraction: typically 55-65% for aerospace structural laminates.

Classical Laminate Theory

ABD matrix: A membrane stiffness, B coupling, D bending stiffness. Ply angles: 0 for axial, 90 for transverse, plus minus 45 for shear. Symmetric laminate: B = 0, no bending-extension coupling. Balanced laminate: equal plus and minus angle plies, no shear-extension coupling. Failure criteria: Tsai-Wu or Tsai-Hill for ply-level failure prediction.

Manufacturing

Hand layup: manual ply placement, low cost, labor intensive, variable quality. Autoclave cure: high pressure and temperature, aerospace quality, expensive. RTM: resin transfer molding, inject resin into dry fiber preform. Filament winding: continuous fiber wound over mandrel for pressure vessels and pipes. AFP and ATL: automated fiber placement and tape laying for large structures.

Best Practices

• Design laminate with at least 10% fibers in each principal direction
• Avoid grouping more than 4 plies of same orientation to reduce matrix cracking
• Account for moisture absorption effect on matrix-dominated properties
• Specify non-destructive inspection method for critical composite structures

Common Pitfalls

Pitfall	Fix
Applying isotropic analysis to anisotropic laminates	Use laminate theory for accurate stiffness prediction
Ignoring compression strength reduction	CFRP compression strength much lower than tension
Wrong cure cycle causing residual stress	Follow manufacturer cure cycle exactly
No impact damage assessment	BVID dramatically reduces compression strength

Related Skills

• metals-expert
• ceramics-expert
• aircraft-structures-expert