Pull-through Characteristics Of Carbon Fiber Braided Composites In Hot And Humid Environment

The design of the connection mode of composite structure is very important to the overall structure.Among the connection modes of composite materials,bolt connection has obvious advantages in various connection modes,so it is of great significance to study the use of bolt connection in composite materials.Pull off failure is a key problem in connection design of composite structures.The pull-out failure of composite structure connection is a failure mode caused by the excessive load of bolt along the plate thickness direction,and its failure mechanism is complex.It is of great significance for the design and analysis of composite structures to study the pull-out failure process of composite laminates.In this paper,the in-plane pull-out mechanical properties of carbon fiber braided composite laminates with countersunk holes are studied by experimental method and numerical simulation method,The failure law of carbon fiber braided composite laminates in dry environment at room temperature was studied,and the failure process of composite laminates was verified by numerical simulation of finite element.The experimental results show that the pull-out failure process can be divided into two stages:in the first stage,the load and displacement increase linearly until the initial damage occurs;In the second stage,the load and displacement fluctuate until the ultimate failure of composite laminates.There are two main failure modes of laminates: obvious delamination in the thickness direction.On one side of the countersunk hole,there is a fiber fracture extending around the hole,and the extension direction is in a straight line;The effect of temperature and humidity on the pull-out behavior of composite laminates was studied through pull-out experiments under different temperature and humidity.The experimental results show that the damage load test values of dry environment test are higher than that of wet environment test,and the damage load test value of 180 ? is the most prominent,up to 7.1%,while that of room temperature and 120 ? is 2.7% and 2.5%respectively.The results show that the heat treatment has the most obvious effect on the high temperature resistance of the composite specimens.The results show that the matrix is brittle at low temperature and dry state,and the average pull-out stiffness of the specimens at low temperature and dry state is 5.74% higher than that at room temperature,but the elongation decreases,and the mechanical properties of the specimens become more unstable.