# Triangular Position Multi-Bolt Layout Structure Optimization
###### Abstract  
Stress concentration often occurs around bolt holes in load-bearing joint structures of large complex equipment, ships, aerospace and other complex machinery fields, which is an important mechanical factor leading to the failure of joint structures. It is of great engineering significance to study the phenomenon of stress concentration on connected structures for the safety of large and complex equipment; meanwhile, the layout of bolts seriously affects the stress around holes. Many scholars have studied the layout optimization of multi-bolted structures through experiments and simulations, but few algorithms have been applied to the layout optimization of bolted structures. And most of the studied types of multi-bolt structures are symmetrical. Therefore, in this paper, the gray wolf algorithm is used to optimize the layout of nickel steel plate connectors with a bolt layout in triangular position, and the optimal objective function is found based on the hole circumferential stress of the nickel steel plate, maximum shear stress of the bolt and bending stress of the nickel steel plate. Comparing the optimal values obtained by the fruit fly optimization algorithm, particle swarm optimization algorithm, gray wolf optimization algorithm, multiverse optimization algorithm and wind driven optimization algorithm, the accuracy of selecting the gray wolf algorithm for optimization is verified. A multi-bolt connection structure model was established in ABAQUS, and the surface stress before and after optimization was compared to verify the correctness of the gray wolf algorithm applied to the structure layout optimization of the nickel steel flat bolt connection. The results show that under the force of 15 KN, compared with the original bolt structure layout, the optimized upper side nickel steel plate bore peripheral stress is reduced by 73.1 MPa, and the optimization rate is 24%; bolt stress is reduced by 47.7 MPa, and the optimization rate is 12.5%; when the load is less than 18 KN, the optimization effect of both the upper nickel steel plate and bolt group is more than 10%. When the load is greater than 18 KN, the optimization effect is reduced, and when the load is greater than 21 KN, the nickel steel plate has exceeded the yield limit. Due to the existence of fixed constraints, the optimization of the lower nickel steel plate is not obvious. The results of this study can provide data and theoretical support for the layout optimization of the nickel steel flat bolt connection structure, and help to improve reliability analysis and health monitoring in complex assembly fields such as large complex equipment and aerospace. b 2023  
nut diameter is small, the stability of the bolt-connected structure can be improved [4]. [PERSON] et al. [5] tested the mechanical properties of asymmetrical bolts and came to the conclusion that the performance of the copper gasket is stable and bearing capacity is higher than that of an aluminum gasket. Moreover, under the action of a copper gasket, the coefficient of friction imbalance is between 0.919 and 1.050, which can show good slip and energy dissipation under earthquake conditions. It takes time and effort to study the effect of bolt layout on the mechanical properties of the connected structure by experiment, so many researchers optimize and analyze the performance of the bolted structure by the simulation method. [PERSON] et al. [6] used a parametric model to adjust the layout of the bolt connection plate by changing the radius and angle of the bolt connection, and then analyzed its influence on the modal frequency. The results show that there are some order mode frequencies that affect the bolt layout, and these frequencies should be avoided. [PERSON] [7] optimized the shape of the starting point and root of the thread, and also optimized the bolt rod and thread, which reduced the stress by 34%, reduced the stiffness of the bolt, increased the stiffness of the bolt connection and greatly extended the fatigue life.