The Effect Of Connecting Hole Perpendicularity Error On The Performance Of Composite Bolted Joints

Carbon fiber reinforced epoxy composites are wildly used in automobile manufacturing, construction, national defense, aerospace and other fields due to their high specific strength, high stiffness, corrosion resistance and strong designability. There are two kinds of defects in the composites drilling process because of their strong anisotropy and organization dispersion: one is the shape and position error same as the metal materials processing, such as perpendicularity error, roundness error, surface roughness, etc.; Another is the processing defects of the carbon fiber composite materials, such as burr, tearing, delamination, micro cracks of hole wall, etc. These errors and defects may make big difference to the strength, stiffness, damage tolerance and fatigue life of composite structure. Scholars at home and abroad has carried out many studies about the effects of connecting hole defects on the performance of composite materials mechanical joints. However, there are little f, numerical simulation or experimental research about the effects of hole perpendicularity error on the performance of the composite materials mechanical joints.In terms of these problems, theoretical research about the effect of hole perpendicularity error on the mechanical properties of the carbon fiber reinforced epoxy composite bolted joints are conducted, which is supported by the national 973 project related research content, d plates as analysis object, to provide theoretical reference for evaluating the effect of hole perpendicularity error on the performance of large carbon fiber composite components in aviation. The main research work and achievements in this paper are as follows:(1) A stiffness degradation law for material damage is proposed based on the three-dimensional Hashin-type failure criteria and progressive damage theory. Numerical analysis about open-hole tensile test of carbon fiber composite are carried out using the UMAT subroutine. And the numerical results were compared with the experimental results. It is found that ultimate load and failure process of the numerical prediction results are in agreement with the corresponding experimental results, which verifies the reliability of the numerical analysis method.(2) The mechanical behavior and failure modes of single-bolt composite joints with hole perpendicularity error subjected to tensile loading are obtained by the single-lap single-shear tests and finite element mothed. The effects of hole perpendicularity error on the mechanical properties of single-bolt single-shear composite joints were analyzed by comparing the load-displacement curves and damages distribution for different hole perpendicularity errors.(3) The effect laws of tilt direction, tilt angle of hole as well as preload on the joint stiffness and bolt load distribution were obtained by both theoretical analysis and numerical simulation in terms of double-bolt single-shear composite joints.The research work and achievements provides a feasible technology reference for connection performance analysis of large composite components in aerospace.