The effect of the environment on high temperature fatigue of cross-ply C/epoxy laminated composites

The present paper focuses on the effect of the environment on high temperature fatigue for C/epoxy cross-ply composites. [0(2)/90(2)](s) cross-ply carbon/epoxy HTS40/TACTIX 742 composite laminates are tested in traction-traction (R = 0.1) fatigue at 150 degrees C under three different environments (air, 2 bar N-2, 2 bar O-2). This type of specimens is affected by transverse cracks that onset on the lateral specimen edges starting by the early stages of fatigue. A long-distance microscope has been employed for transverse crack counting on the lateral sample edge, and the role of the environment on kinetics of crack multiplication has been assessed. Experimental results have been interpreted through the use of a model based on the calculation of the Energy Release Rate, G, employed for the identification of the critical values of G, G(c). The role of the environment has been elucidated through a correlation between Gc and Elastic Indentation Modulus (EIT) values measured on the sample external surface. The existence of such a correlation enables to define and setup environmental fatigue acceleration procedures.