Research On Bearing Strength Of Thick Composite Laminates With Multiple Bolted Joints

Composite material is now widely used because of its great mechanical properties.Joint design is indispensable and important in the aircraft structure design.Composite material are now gradually used in the main force-bearing components which make the laminate thicker and the bolt diameter become bigger and the strength in connecting area is much more complex.Because of the load non-uniformity existed in the thickness direction lead to the occurrence of the bending of bolt and non-uniformity of hole-edge stress distribution in thickness direction,which result in some deviations in the analysis for thick laminates based on theoretical analysis for the original thin laminates.Therefore,researches on the joint strength of bolted joints between thick composite laminate and metal have theoretical significance and practical value.Based on the experimental study and numerical simulation,this paper has studied the strength of the double-bolt,single-lap thick composite laminate specimens and multiple-bolt,single-lap thick composite laminate specimens.The main contents are as follows:(1)T800S/BA9918 composite double bolts single lap composite joint has been chosen to do the experiment.Failure mode of joint specimen were investigated and bearing loads were finally obtained.The 3D finite element model for predicting joint strength of the structure based on the incremental damage analysis method was established.The reasonability and effectiveness of the model were validated by the comparison between numerical simulation and experimental data.The load distribution and evolution of different damages were studied based on this model.The impact on calculating result of mesh density has been studied.The effects to the damage mode and load distribution of thickness have been studied.The effect that thickness?w/d?friction coefficient and hole pitch have on the structure strength have also been studied.(2)The 3D finite element model of multiple bolts single with the bolts distributed symmetrically was established.The load distribution and evolution of different damages were studied based on this model.The impacts that thickness has on the load distribution?damage modes have been analyzed.The effects horizontal hole pitch and vertical hole pitch have on the structure have also been studied.(3)The 3D finite element model of multiple bolts single with the bolts distributed staggered was established.The load distribution and evolution of different damages were studied based on this model.The impacts that thickness has on the load distribution?damage modes have been analyzed.The difference between the structure strength of the multiple bolts single with the bolts distributed symmetrically and the staggered is also analyzed.