Failure Behavior Study Of Composite Bolted Joint

With the wide application of composite materials in aerospace structures, the joint of composite materials becomes indispensably important link. Because of the countersunk head bolt joint not only meets the connected structure surface is smooth but also can deliver larger load steadily which has gradually become the preferred mode of joint of aircraft structure fitting. Composite countersunk head bolt connection failure occurs mainly in the joint connection. So the connection joint failure of composite material countersunk head bolt is of great important.The software of ANSYS and Laminate Tools are combined. Based on study of the composite countersunk bolt connection failure, the new failure criteria and degradation criteria are defined while using experimental and finite element analysis methods. Via macroscopic scale of composite countersunk connection failure modes and microcosmic aspects about compare of SEM photos and layers failure of joint. Based on the appreciate algorithm,the analysis parameters of composite countersunk joint are studied.As while combining the characterization of composite joint failure behaviors in the macroscopic scale and microcosmic aspects, the accuracy of head bolted finite element method in the macro scale, it shows the same failure mode of FEM and experiments, and the displacement of the load curve shape of the two types of failure are similar. The error maximum carrying load is less than 20%; Based on using the macroscopic view, the scanning electron microscopy and finite element analysis layer failure consistent form are achieved, and addition demonstrates the accuracy of the algorithm. After verifying the accuracy of the finite element method, the composite material countersunk screw connection failure analysis parameters were studied. The effects of countersunk head(h/t), countersunk bolt diameter(d), the bolt preload between the surface and the base, friction impact factor(μ) on composites countersunk bolt connection strength are studied, the results show that with the increase of countersunk head screws countersunk head ratio, after the composite countersunk bolt connection strength first increases and then decreases, when the ratio was 0.55 countersunk head when the composite countersunk bolt connection owns maximum strength; With bolt diameter(d) increasing, the composite countersunk bolt connection strength decreases. When the value of the bolt diameter is 4mm, the composite material countersunk screw connection owns maximum strength; with the increase of composite countersunk bolting preload, when the failure of the laminate thickness direction does not occur, the composite countersunk bolt connection strength increases; as the contact surface between the friction factor(μ) of when increasing around composite laminates bore no failures occur along the stretched direction, the connection strength of the composite countersunk head bolts, with μ increases, increases.