缝合复合材料层合板拉伸疲劳损伤及其机理

TENSILE FATIGUE DAMAGE AND ITS MECHANISM OF STITCHED COMPOSITE LAMINATES

对有、无缝合复合材料层合板的拉伸疲劳性能进行了试验研究,考察了0°缝合对复合材料光滑板拉伸疲劳损伤扩展规律的影响.通过有限元素法分析了有、无缝合复合材料层合板的应力状态分布情况,对缝合复合材料层合板的拉伸疲劳损伤及其扩展机理进行了分析.研究表明,缝合改变了复合材料层合板拉伸疲劳损伤起始与扩展的机理,针脚附近的面内正应力σ_x与层间剪应力的集中对层合板拉伸疲劳损伤的发生与扩展有着重要的作用,自由边界处的层间集中应力对缝合板的疲劳性能也有影响.自由边界处的层间集中应力是导致无缝合层合板疲劳损伤及其扩展的主要原因.

Stitched laminate is a new kind of composite structure to improve the interface strength of composite. But the in-plane properties of the laminate may reduce because there are local fiber bending in the laminate plane and in the thickness direction,and the damage induced by the stitching threads.A lot of researches have been carried out on the properties of laminates to push this material into engineering applications,such as in-plane tension and compression,compression after impact,hygrothermal properties,etc.But few studies have been performed on stitched composite fatigue properties.The aim of this paper is to comprehend the fatigue damage development and mechanism of stitched laminates under tensile loads.The material of the laminates was uni-weave T300/QY9512 stitched in 0°direction.Un-stitched laminates were studied for comparison with the stitched laminates. Experimental study was carried out on the fatigue performance of stitched and non-stitched composite laminate.The finite element models were established to obtain the stress or strain distributions in the laminates. The mechanism of tensile fatigue damage origination and propagation of stitched laminates was analyzed. The results show that the tensile fatigue damage origination and propagation mechanisms of laminates have been changed by stitching.The stress concentration of in-plane stressσ_x and interlaminar shear stress near the stitching node plays an important role in damage origination and propagation.Stress concentration of interlaminar stress at the free sides has effect on fatigue performance of stitched laminates.The stress concentration of interlaminar stress at the free sides is the main reason that causes fatigue damage and its propagation of non-stitched laminates.