Study On Damages In Bolted Joint And Drilling Process Of Composite

Bolted joint is an extensively used connection in composite structure. The connection strength is an essential factor to guarantee the safety and reliability of the structure. The design parameters and connecting hole quality of the composite dominate the structural connection strength. Therefore studying the effects in these two aspects through numerical simulation method helps greatly to improve designs of structure and drilling process for composite. This Master dissertation numerically investigates the influence factors to composite bolted joint strength and the damage introduced from drilling process based on finite element software ABAQUS. The specific works include:(1) A laminated block element containing multilayers is proposed and in which 3D Hashin damage criterion and a self-defined stiffness degradation model based on Camanho model are involved. In this element, the in-plane damage can take place for individual ply and the equivalent reduced element stiffness is obtained consequently. For the merits of decrease of total degree of freedom and contact nodes in FE model, significant reduction of computing time and elevation of convergence efficiency are achieved for this laminated block element. This element has been implemented based on ABAQUS via user's subroutine.(2) The progressive damage around connecting hole of single bolted joint in composite is simulated by using the laminated block element proposed in this dissertation. This element is validated with experimental data. Its computational efficiency has also been proved greatly improved via comparing with the conventional element model. Parameter study of single bolted joint strength is conducted and it is found that ply ratio has a great influence on the strength and failure mode. It also reveals that elevating the ratio of panel width to hole diameter(W/D) and the ratio of length of hole center to panel edge to hole diameter(E/D) can improve the connection strength, however this improvement will reduce when the ratios are over a certain degree.(3) This laminated block element is also used to study the drilling qualities made by twist drill and diamond bit respectively. It is found that diamond bit is better than twist drill in terms of orifice damage, orifice stress distribution and the stress concentration of bit itself. Though the diamond bit will cause a slightly more orifice burr, it is considered to have more advantage than twist drill in composite hole drilling with comprehensive comparisons.