Effects of toughened interlaminar layers on fatigue damage progress in quasi-isotropic CFRP laminates

Damage progress in quasi-isotropic CFRP laminates under tensile fatigue loading is investigated microscopically. The onset and growth of transverse cracks and delaminations are observed by an optical microscope and soft X-ray radiography. To study the effects of toughened interlaminar layers on microscopic damage progress, two material systems are used. One is T800H/3631 CFRP without toughened interlaminar layers. The other is a newly developed CFRP, T800H/3900-2 with toughened interlaminar layers. The toughened interlaminar layers contain tough and fine polyamide particles dispersed in the base epoxy resin. By the edge observation, transverse crack density and delamination ratio are measured as a function of the number of stress cycles. By the X-ray radiography observation, delamination onset and growth in the width direction are detected. It is found that delamination onset and growth are suppressed by the toughened interlaminar layers. Paris law analysis is performed for quantitative characterization of transverse crack multiplication and delamination growth.