Analysis Of The Influence On The Stability Of Lattice Boom By Residual Stress And Geometric Defects

With the rapid development of social economy,especially driven by the demand for nuclear power engineering,wind power generation,petrochemical projects,municipal engineering,transportation construction,etc.,the market demand for crawler cranes with superior performance and large working space is also increasing.The lattice structure has the advantages of light weight,good rigidity,good bending performance,reasonable force,and small windward area.Therefore,it is widely used in the products of construction machinery,such as in the boom system of crawler cranes and tower cranes.The lattice boom is an important load-bearing structure of crawler cranes,but the initial defects of the structure will have a certain impact on its load-bearing capacity and it is inevitable.Among them,geometric defects and welding residual stress caused by welding cannot be ignored.In this paper,The84m(working range 68o)boom of 750 t crawler crane is as an example to simulate geometric defects and welding residual stress.The main research contents are as follows:(1)The boom structure is studied and analyzed,and the multi-scale finite element boom model of beam element and solid element is established,which is suitable for the numerical simulation of geometric defects and welding residual stress.The multi-point constraint technology(MPC)is studied,and the connection problem between different types of elements is solved.(2)The thermal analysis of the structure is researched and analyzed.The life and death unit technology is used to realize the heat source movement during the welding process;the thermal-structural indirect coupling analysis technology is used to realize the transformation process of the temperature field to the stress field during the welding process,and the process of the temperature field and stress field of the path are studied in detail.(3)The initial geometrical defects of the boom structure are statistically analyzed.According to the boom manufacturing and installation process,the initial geometrical defects of the boom are divided into two categories.Based on the research and analysis of the existing geometric defect simulation methods,a multi-order modal stochastic coupling method suitable for the simulation of geometric defects produced by boom manufacturing and an equivalent load method suitable for the simulation of geometric defects produced by boom installation are proposed.(4)The nonlinear stability of the ideal boom,the boom model with only geometric imperfections,only residual stresses and double imperfections are calculated.The results show that the existence of geometric defects weakens the overall stiffness matrix of the structure and reduces the critical bearing capacity of the structure obviously.However,the existence of residual stress causes the local stress concentration phenomenon at the intersecting position between the chord and the belly rod,which leads to the failure and instability of the boom in advance.The effect of welding residual stress on the critical bearing capacity of the boom structure is weaker than that of the most unfavorable geometric defects.This study provides an important reference for the simulation of the initial defects of the structure.