Carbon Fibre Tensile and Structural Testing
topic
Carbon fibre tensile property testing uses impregnated strand (ISO 10618) or single-fibre (ISO 11566) methods to characterise tensile modulus, tensile strength, and failure strain of PAN-based and pitch-based carbon fibres for aerospace composite design allowables and industrial quality control. Impregnated strand test (ISO 10618): 500–1,000 mm strand length, epoxy-impregnated (Vf 55–65%), tabbed ends, gauge length 150 mm, crosshead speed 2 mm/min, strain by extensometer (0.5% strain full scale, ±0.1% accuracy) — reports composite tensile modulus E₁ (GPa) and composite tensile strength σ₁ (MPa), converted to fibre properties using rule of mixtures. Single-fibre test (ISO 11566, Textechno Favimat+, gauge length 25 mm, 1 mm/min): measures individual filament diameter (Dₐ by resonance vibration, 5–7 µm for T300 PAN-based), breaking force (50–200 mN), tenacity (MPa = N / (π/4 × D² × ρ), where ρ = 1.78 g/cm³ PAN-based). Weibull statistics applied to single-fibre tensile data (minimum 100 fibres): shape parameter m (scatter indicator, m > 5 = low scatter, aerospace standard; m < 3 = high scatter, industrial grade) and characteristic strength σ₀. Surface properties (XPS — X-ray photoelectron spectroscopy: O/C ratio 0.10–0.20 for surface-treated fibre indicates adequate oxidative surface treatment for epoxy adhesion — untreated fibre O/C < 0.05 gives ILSS interlaminar shear strength 25–35 MPa versus treated 55–70 MPa). Fibre areal weight (FAW, g/m² of UD tape or woven prepreg, ±2% tolerance) by gravimetric measurement on 10 × 10 cm specimens — FAW uniformity determines void content in composite laminate.
Role
Carbon fibre testing generates the mechanical property design allowables and quality certification data that aerospace composite manufacturers require for aircraft structural certification — tensile strength Weibull statistics, surface treatment O/C ratio, and FAW uniformity data from incoming fibre testing directly determine whether composite parts meet the structural design margins mandated by FAA and EASA airworthiness certification.