Numerical Analysis And Strength Prediction Of Composite Bolted Joint

Fiber reinforced composite has been extensivelly used in aeronautical structures instead of metals because it has the excellent characteristics of high specific strength,high specific modulus and strong designability.With the limit of integral forming technology for composites,there will be connected problem in large structure.The mechanical joint is often chosen for the large bearing structure.Due to the inherent anisotropy of composites and discontinous fiber after punching on laminates,the initiation and growth of damage in the bolted joints is very complicated.Therefore,it has great engineering significance to do research on the failure of joints and emplore how to improve composite joints efficiency.The glass fiber/vinyl resin is the reaearch object of this paper.The specimens are made by using vacuum assisted molding process.The basic parameters are measured according to the national standard,these parameters are prepared for the finite element simulation.The displacement-load curves of the bolted joints under different bolted-torque and layers are measured through the tensile test of the single-lap composite joints,and the effects of these two factors on the failure mode has been researched.The progressive damage analysis for composite bolted joints is carried out by using Shokrieh failure criterion and modified Tserpes stiffness degradation model.The jointed model is based on a three-dimensional finite element model,and each layer of the laminate is established by using Orthogonal anisotropy solid element.The influence of contact friction between the joints components has been considered.The effect of bolted-torque and interference fit on the initiation and progression of the damage in single bolted joints has been studied by using this model.The method of homogenizing the load distribute in multi-bolt laminate joints has also been researched.Combining the experimental result and finite element simulated result,we find that:(1)Applying appropriate bolted-torque(2kN in this paper)can increase the failure load and initial stiffness of the bolted joints,it also can reduce the damage area surrounding the bolted hole.But excessive bolted-torque will make the bolted joints failing in advance so that the failure load of the bolted joints will be decreased.(2)The strength of composite bolted joint is the largest by stacking the 0~??90~?and?45~?uniformly,and the failure mode is the bearing failure which is the safest failure mode;the strength of composite bolted joint is lower by using orthogonal stacking whose failure mode is shear damage;the jointed strength of laminate stacking with?45~?is the smallest,and the failure mode is tensile failure.(3)The initial damage will be generated on the bolted joints after applying interference fit;but appropriate magnitude of interference(1.5%in this paper)can delay the axpansion of the damage and make the damage around the hole distribute uniformly,also it can increase the failure strength of the bolted joints.A large number of element around the hole will be damaged when the magnitude of interference is too large,which will cause the reduction of the bolted joints strength.(4)Compared with spring element model,the load distribution calculated by using finite element model is more accurate.The gap fit and interference fit can all reduce the load ratio of maximum bolted load.When stiffness of the two lap plates differ considerably,the load distribution will be even by using the gap fit and interference fit at the same time.