Study On Low-speed Impact And Residual Strength Of Composite Laminate Multi-bolt Connection

Composite laminates are widely used in various fields due to their high specific strength,lightweight and designability.The mechanical connection of composite laminates has high bearing capacity,high reliability and convenient disassembly,which is one of the common connection methods at present.However,composite laminated panel components often suffer from impacts such as hail and bird strikes in the working environment,resulting in a decrease in connection strength.Under low-speed impact,the connecting part is more susceptible to damage than the laminated plate itself,leading to connection failure.Therefore,the research on the residual connection strength of composite laminates under low velocity impact can provide theoretical basis and technical support for the design of composite structures.Firstly,under quasi-static loading conditions,this article uses numerical simulation methods to create a quasi-static tensile simulation of multi nail connections based on the single nail connection of laminated plates.Explored the effects of various factors on the stress around the holes in laminated plates and the strength of the connector matrix,and conducted in-depth research on the distribution of multi nail load.Secondly,in terms of low-speed impact dynamics,based on different analysis modules of ANSYS and LS-DYNA,the mechanical properties of laminated plates after low-speed impact were studied.Based on the rectangular arrangement of four nail connectors,a comprehensive simulation study was conducted on the impact resistance and residual tensile strength of multi nail connections in laminated panels.Finally,low-speed drop hammer impact tests were carried out on laminated plate connectors to compare and verify the simulation results.At the same time,relevant impact test analysis was supplemented and improved for countersunk multi nail connectors that are difficult to model and analyze in numerical simulation.The specific research work is as follows:(1)Under quasi-static load,based on single nail connection,the reliability of model parameters and simulation methods is verified,and the general law of stress distribution around the holes in laminated plates is obtained.This lays the foundation for subsequent research on multi nail connection,and the ultimate tensile strength of single nail and multi nail connections is verified through experimental assistance.Analyze the various influencing factors of multi nail load distribution and compare the methods and structures that are conducive to improving the uniformity of nail load distribution.(2)In terms of dynamics,comparative analysis has determined a method that can simulate the entire process of composite laminated plate connectors.By combining LS-DYNA’s explicit and implicit analysis with low-speed impact dynamics and quasi-static tensile analysis,the lowspeed impact and residual tensile mechanical properties of laminated plate connectors were systematically studied.Based on the analysis of impact contact force and residual connection strength,the influence factors such as preload,ply structure,connection area,and layout mode are carefully studied.At the same time,damage failure modes were introduced to reasonably predict the damage and failure situation of laminated plates.(3)In the low-speed impact test,a detailed comparison was made between the strength changes of laminated plate multi nail connectors before and after impact,and the vulnerable areas of laminated plate connectors that are prone to failure after impact were identified,which is helpful for the improvement and strengthening of subsequent structural design.At the same time,the focus of the experiment was on the area of the connection area and the impact resistance of the countersunk connection,and numerical simulation analysis was supplemented for verification.