How do environmental factors affect composite material properties?

Composites are sensitive to environmental exposure: Moisture: Matrix absorbs moisture (equilibrium 0.5-2%), Plasticizes matrix, reduces glass transition temperature (Tg), Decreases hot/wet properties (30-40% knockdown), Reversible with drying. Temperature: Elevated temperature reduces modulus and strength, Maximum service temperature limited by Tg, Cold temperature can increase brittleness. Combined effects: Hot/wet condition typically worst case for design, Matrix-dominated properties most affected (compression, shear). UV exposure: Surface degradation, embrittlement, Mitigated by paint. Testing: Condition specimens at elevated temperature and humidity, Test at temperature to capture degradation, Generate B-basis for environmental conditions. Design: Use hot/wet allowables for strength-critical structure, Protect from direct environmental exposure, Consider worst-case conditions over service life. Material selection: Different resins have different moisture sensitivity, BMI and PEEK better than standard epoxy at temperature.