| The all-terrain crane is a kind of rotary arm of the engineering hoisting machinery.It has the advantages of mobile flexibility,high pass-ability,high lifting capacity and easy assembly and disassembly;therefore it is widely used in wind power equipment installation,bridge construction,petrochemical equipment installation,urban high-rise building construction and other engineering construction areas.The telescopic boom is the key bearing structure of the all-terrain crane.It is composed of multiple independent telescopic boom sections(TBS).Each TBS is a slender thin-wall box-type plate/shell structure,and it is made of high-strength steel plates with unequal thickness after bending and welding process.With the rapid development of engineering construction,large engineering modular construction has become the dominant construction method,and items can be hoisted heavier,higher,and farther.The demand and application for the large tonnage all-terrain crane equipped with large cross section TBS has increased,and the safety and reliability problems of the TBS have become much more prominent.The local buckling stability of the TBS is one of the key factors which affects the hoisting ability and safety of the crane,and its structural safety and reliability are of great concern.The difficulties in analyzing the local critical buckling load(CBL)of a large tonnage all-terrain crane are that the telescopic boom has a complex structure and is bearing the multidirectional combined load,the cross-sectional shape is irregular.The existing analytic formulas cannot accurately calculate the CBL.In this paper,the analysis method and influencing factors of the local buckling stability of the all-terrain crane's telescopic boom structure are studied based on the school-enterprise cooperation project “The local buckling of the large section telescopic boom analysis software development”.Finite element method is the most widely used numerical simulation method in the research and development of crane structure,which can establish complex structural models,analyze structural strength,stiffness and tip-over stability.In order to accurately and rapidly predict the CBL of the telescopic boom,the QAYX all-terrain crane's telescopic boom is taken as the research object,and the gantry experiments of the local bending buckling failure and local torsional buckling failure of the telescopic boom are designed.The strain and CBL during the above two local buckling failures are tested.A three-dimensional finite element model of the overall boom structure that can fully reflect the local stress of the telescopic boom and the contact relationship between the TBS is established.Eigenvalue methods,nonlinear implicit methods and nonlinear explicit methods are used to analyze the strain and CBL of the telescopic boom.The nonlinear method comprehensively considers the structural geometric nonlinearity,material nonlinearity and contact state nonlinearity.The results show that when the experimental structure is in the states of local bending buckling and local torsional buckling,the TBS material is in the elastic range.When the TBS is in the state of local bending buckling,the experimental CBL is 18.87 t,and the eigenvalue CBL is 26.68t;the nonlinear implicit method analysis CBL is 20.99t;the nonlinear explicit method analysis CBL is 20.29 t.When the TBS is in the state of local torsional buckling,the testing CBL is 21.05 t,the eigenvalue CBL is 30.31 t,the nonlinear implicit method analysis CBL is 23.10 t,and the nonlinear explicit method analysis CBL is 22.71 t.In the nonlinear implicit method and the explicit method results,the stress of the TBS in the adjacent buckling state changes from a continuous state to a wrinkle stress,and the wrinkle stress region coincides with the measured buckling failure region.The critical load of nonlinear explicit analysis is closest to the measured value.The deviation of eigenvalue method is the largest.According to the analysis time,nonlinear explicit analysis is the most time-consuming and eigenvalue analysis is the least time-consuming.The influences of element type,element size,calculation speed,analyzing and calculation method on the analysis result are studied.The results show that the element length of 20mm(1/23.3 of the arc radius of the lower cover,and 1/10 of the arc length of the lower cover),the 4 node shell element model of TBS,nonlinear implicit method,multi core parallel computing method can effectively predict the CBL of the telescopic boom,and the result is balanced with accuracy and calculation speed.The influence of structural defects on CBL is studied.The eigenvalue buckling mode,sinusoidal waveform,single point circle and weld geometry form are taken as a structural defect to improve the perfect structure fast calculation model,and to carry out buckling defect sensitivity analysis.The results show that the structural defects have a very significant effect on the CBL.The CBL is very sensitive to the initial defect of high order eigenvalue buckling mode,sinusoidal waveform and single point circular defect.When the amplitude of the defect reaches the same level as the thickness of the plate,the critical load of buckling is no higher than 75% of the critical load of the perfect structure.Compared with the torsional buckling,the TBS critical load is more sensitive to the defect under the flexural buckling condition.The influence of structural parameters on the CBL is studied.Based on the structural fast calculation model and the structural parameter range of 300 t to 1600 t all-terrain crane TBS provided by the cooperation plant,the influence of basic parameters and reinforcement parameters on the CBL are analyzed.The results show that the ratio of thickness to thickness of the lower cover plate,which represents the thickness of the telescopic boom,has the largest influence on critical load in the basic parameters of the section.In the reinforced structure,the lateral gluing is the most effective for increasing the CBL of the telescopic arm.The results show that the ratio of radius to thickness has the greatest influence on the CBL in the basic section parameters;in strengthening the structure,the lateral plate is most effective for increasing the TBS CBL.This paper combines the modeling and analysis of experience,using the feature parametric modeling technology,to develop a finite element calculation program which has the functions of automatic modeling,automatic calculation,automatic results extraction for large sections of the boom structure buckling,provides a convenient designing and analyzing tool for designing the frame structure of crane. |
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