Secondary Bending Effect Of Composite Single-lap Bolted Joints

With the development of new materials and technology,the requirements on auto performance and safety are becoming higher and higher.CFRP is widely used in auto industry due to its excellent properties.The mechanical connection is adopted to achieve the connection between composites and other parts of the car body,and most of them are single-lap bolted joints.However,single-lap composite bolted joints will generate severe secondary bending phenomenon due to eccentric load path with respect to the asymmetric structures under tensile load.Moreover,the secondary bending effect can cause the fastener to tilt in the hole,which implies that the stress distribution in the vicinity of the holes is not uniform through the thickness direction and also has a great impact on the bearing strength of the structure.At present,the existing literatures mainly study the influence of secondary bending on bolted joints in terms of the structures and dimension.But there are few investigations about the defects caused during the manufacturing.Therefore,the effects of the perpendicularity error,clearance and delamination(such as the delamination position through the thickness direction and the delamination size)on the single-lap composite joints are analyzed in this paper.In addition,the effect of secondary bending on the mechanical behavior of composite bolted joints is also analyzed in this paper.Firstly,combining with several damage modes of composite materials,proper failure criterion was selected and UMAT subroutine was written,and the running process of UMAT in ABAQUS was introduced briefly.Then the 3D finite models of double-bolt single-lap bolted joints were established,and the mesh independent was discussed to achieve the exact calculation of the models.Finally,the models were validated to be available in comparison with the experimental data from dissertation.In addition,the damage process from initial damage to structural failure was analyzed.It was found that the numerical damage contour models on the surface of specimen was similar with experimental damage contour,which indicated that the progressive damage model could exactly predict the damage evolution of the joints.Secondly,single-bolted single-lap composite bolted joint was established and validated.Then the effects of perpendicularity error(tilt direction and inclination of bolt)and clearance on secondary bending were studied.Secondary bending curves,damage evolution and stress distribution around the hole boundary were obtained to analyze secondary bending effect.And the changing of out-of-plane deformation and the area between two laminates during loading process were also analyzed to further understanding secondary bending effect.Finally,for double-bolted single-lap bolted joints,the effects of pre-load and perpendicularity error(tilt direction and inclination of bolt)on the secondary bending effect were studied by means of parametric study respectively.In addition,for double-bolted singlelap bolted joints with delamination,the effect of delamination size and its position through thickness on the secondary bending was analyzed.