Carbon Fiber Laminate Design & Testing

Composite Manufacturing • Classical Laminate Theory • Mechanical Testing

Designed, fabricated, and tested symmetric 4-ply carbon fiber laminates to evaluate how inner ply orientation affects flexural modulus using both experimental testing and theoretical modeling.

Project Summary

This project investigated the relationship between ply orientation and mechanical performance in wet-layup carbon fiber composites. Using Classical Laminate Theory (CLT) alongside experimental testing, we evaluated how internal fiber directionality influences stiffness and failure behavior.

Key Variables Studied
  • Inner ply orientation ([45/0]s, [45/90]s, [45/-45]s, [45/45]s)
  • Fiber volume fraction (~35%)
  • Manufacturing variability (alignment, curing, voids)
  • Weave efficiency and material properties

Fabrication Process

1. Wet Layup

Hand-laid 2×2 twill carbon fiber with epoxy system (mass ratio 55:50:16) to form symmetric 4-ply laminates.

2. Vacuum Bagging & Cure

Vacuum bagged for ~8 hours at room temperature to consolidate plies and reduce void formation.

3. Specimen Preparation

Panels cut into ASTM D790 coupons (12.7 × 50.8 mm) using waterjet cutting for high precision and minimal fiber distortion.

4. Quality Considerations

Controlled fiber alignment, resin distribution, and curing conditions, though variability remained due to hand fabrication.

Testing & Characterization

Performed 3-point bend testing using an Instron universal testing machine to determine flexural modulus and failure behavior.

Key Figures of Merit
  • Flexural Modulus (Eflex)
  • Yield Strength
  • Stress–Strain Behavior
  • Failure Modes (fiber vs matrix dominated)

Results & Insights

Gallery

Full project presentation — detailed methodology, modeling, and results

SEM fractography of carbon fiber/epoxy laminate failure showing matrix-dominated cracking with brittle epoxy fracture, fiber–matrix interfacial debonding, and fiber pull-out, indicative of limited interfacial shear strength and non-uniform load transfer across the fiber network.
Abrasive waterjet machining of cured laminates for ASTM D790 specimens, providing ±0.025 mm dimensional accuracy while preserving fiber alignment and minimizing edge-induced defects such as fraying, delamination, and resin-rich boundary regions.
Three-point bending test performed on an Instron 68TM-50 using ASTM D790 thin-sheet geometry (12.7 × 50.8 mm coupons, 25.4 mm span) to extract flexural modulus from load–displacement data under controlled displacement loading.

Future Improvements