L型复合材料机械连接接头承载能力与失效行为研究

L型复合材料连接结构已应用于运载火箭结构的端框设计,但目前对于该结构的承载能力和破坏模式缺乏研究。将典型的L型连接端框简化为无弧度的平直L型接头片段,通过单向对拉试验,对6 mm和8 mm两种厚度L型机械连接接头的承载能力和破坏模式进行了研究。由承载能力试验结果表明:L型接头在拉力作用下呈现出明显的A、B、C三个阶段,其中A阶段的拉力最大值可作为该类接头结构的极限承载能力。采用有限元方法分析接头的破坏模式,仿真与试验结果的误差为2.5%,取得了较好的一致性。由数值分析表明:拉力作用下L型接头的承载能力主要取决于螺栓压紧区附近和直角拐角区域的层间强度和基体强度;在原铺层信息基础上增加0°层数和降低90°层数,对接头承载能力提升效果不明显。研究结果可为L型复合材料连接结构的设计提供参考。

Carrying Capacity and Failure Behavior of Mechanically Fastened L-Joints in Fiber-Reinforced Composites

The composite L-type structures have been used in the design of launch vehicle end frame structures, but relevant researches on carrying capacity and failure behavior are still lacking. The representative end frame structures are simplified as L-joints without the arc in this paper. The tests on mechanically fastened composite L-joints with thicknesses of 6 mm and 8 mm under the uniaxial tensile loading are conducted. Carrying capacity and failure behavior of the L-joints in different thicknesses are analyzed. It is shown that there are three phases in load-displacement curves of the L-joints under tensile loads, and the peak load of A-phase can be taken as the limit carrying capacity. Numerical simulation is carried out, and simulation results accord well with experiment results. According to the simulation results, the damage zone focuses on the bolt pressing area and the corner, and the peak load value of A-phase depends on interlaminar strength and matrix strength in the damage zone. The carrying capacity of L-joints increases slowly when raising 0° lay count ratio or reducing 90° lay count ratio. The research results can be used as a reference for the design of composite L-joints.