Mechanical and physical properties of isothermally aged carbon fiber‐epoxy composites

Isothermal aging of continuous carbon fiber‐epoxy resin composites containing epoxy resin derived from diglycidyl ether of bisphenol‐A (DGEBA) and methylene dianiline (MDA) and 64 vol% of carbon fibers with orientation angles of 0°, 45°, 90° and crossply fibers was performed in vacuum, air and nitrogen atmosphere. The impact strength of the 45° ply composites increased from 149 kJ/m 2 to 15.5 × 10 2 kJ/m 2 after isothermal aging in vacuum at 200°C for 13 h. The interlaminar shear strength (ILSS) of the 90° ply composites increased from 3 to 4 MPa after isothermal aging at 184°C for 336 h in nitrogen atmosphere. The flexural strength of the 90° ply composites, however, remained unchanged (∼80 MPa) after isothermal aging in nitrogen at 184°C for 336 h. The impact strength of the 90 degree ply composites decreased by 20% (∼15 kJ/m 2 to 12 kJ/m 2 ) and 80% (∼15 kJ/m 2 to 3 kJ/m 2 ) after isothermal aging in nitrogen atmosphere at 184°C for 336 h and in air at 200°C for 336 h, respectively.