Fatigue Behaviour of Multilayer Braided Fabric Reinforced Laminates

In this paper, the fatigue behaviour of the laminated composites made from an epoxy matrix and four layers of flat regular braided carbon fiber fabrics of different braiding angles was investigated experimentally. Three laminate lay-ups were used. They are: [10 ⁰ /10 ⁰ /10 ⁰ /10 ⁰ ], [28 ⁰ /10 ⁰ /10 ⁰ /28 ⁰ ], and [28 ⁰ /28 ⁰ /28 ⁰ /28 ⁰ ], where 10 ⁰ within the bracket indicates that the single layer braid lamina had a braiding angle of 10 ⁰ inclined with the longitudinal (loading) direction. The static tensile and tension-tension fatigue tests were conducted for those laminates, and detailed fatigue data are reported in the paper. Failure mechanisms of the tested laminates were also characterized. The stiffnesses and strengths (including static tensile and fatigue strengths) of the [10 ⁰ /10 ⁰ /10 ⁰ /10 ⁰ ], [28 ⁰ /10 ⁰ /10 ⁰ /28 ⁰ ], and [28 ⁰ /28 ⁰ /28 ⁰ /28 ⁰ ] laminates were the highest, intermediate, and the lowest respectively. However, different failure mechanisms were recognized. It was found that under the uniaxial tensile or a high-level fatigue load, the [28 ⁰ /28 ⁰ /28 ⁰ /28 ⁰ ] laminate failed catastrophically as a result of fiber breakage nearly across the cross section of the specimen. Delamination was seen only when a low-level fatigue load was applied to the laminate. In the case of the [10 ⁰ /10 ⁰ /10 ⁰ /10 ⁰ ] laminate, a laminate longitudinal splitting was the main failure mode. No delamination accompanied the laminate failure. For the [28 ⁰ /10 ⁰ /10 ⁰ /28 ⁰ ] laminate, significant delamination was found with any applied load (whether static or tensile fatigue of any load level). Splitting, both across the cross-sectional breakage and longitudinal, were involved in the failure of this combined laminate. These findings provide a useful insight into understanding the fatigue behaviour of braided fabric reinforced laminates.