Abstract: Under fatigue cycle loads with different stress ratios, digital image correlation (DIC) is used to investigate the damage modes and processes of carbon fiber laminates. Using Instron8803 electro-hydraulic servo fatigue machine to perform fatigue tests on composite laminates, and DIC technology to collect information during the damage process, combined with micro failure morphology, the fatigue failure modes of composite materials were analyzed. The fatigue life of composite laminate was affected by the stress ratio under the condition of tensile-tension fatigue loading. The smaller the stress ratio, the shorter the fatigue life, and the fatigue life of the sample decreased from 6×10⁵ to 6×10³ when the stress ratio decreased from 0.6 to 0. The DIC technique was used to analyze the layered damage of the laminate in the thickness (Z) direction, and a width (Y) strain contour was obtained. Comparing the micro-morphology of fatigue failure and tensile failure, it was found that the delamination damage appeared on the fatigue fracture obviously, the resin matrix between layers failed, and the fiber in the layer was pulled out.

Key words: CFPR, digital image correlation, stress ratio, tension-tension fatigue, micro-morphology