Research On Mechanical Behavior Of Truss Structure Failure Process Based On Large Deflection Theory

Overloading and local cracks in members are the main reasons for the failure of truss structures.Overload will lead to the instability of the compression members in the truss structure,which will lead to the continuous failure of the truss structure from local to whole.When a crack appears in the compression member,its critical load will be greatly reduced,and the truss structure is more likely to be damaged.Quantitative analysis of the mechanical behavior of the truss structure failure process provides the necessary theoretical basis for analyzing the remaining life of the truss structure,preventing the damage of the truss structure,preventing and reducing disasters and strengthening the structure.The compression member in the truss can be regarded as the compression member with elastic constraint and initial deflection,and the relationship between the axial pressure and the displacement of the rod end is the key to the analysis of the mechanical behavior of the truss structure in the failure process.In this paper,the elastic-plastic compression rod is taken as the research object first,and the large deflection deformation theory and the direct method are used to analyze the initial deflection,restraint stiffness and the mechanical behavior of the compression rod after the compression rod is unstable when the two act together,that is,the relationship between the axial pressure and the displacement of the compression rod.Influence.When the compression member in the truss has cracks,it becomes very complicated to analyze the relationship between the axial pressure and the rod end displacement by the direct method.In this paper,the energy method is used to calculate the relationship between the axial pressure and the end displacement of the elastic compression rod with cracks.The method uses the weight function method to solve the crack stress intensity factor,and uses the relationship between the crack stress intensity factor and the energy release rate to obtain the crack surface free energy.Therefore,it lays a foundation for the research on the mechanical behavior of the failure process of the truss structure.After obtaining the relationship between the axial pressure of the compression rod and the displacement of the rod end,this paper takes the steel truss of the rectangular section rod as the research object,and uses the ANSYS finite element analysis software to study the mechanical behavior of the statically indeterminate truss structure and the statically indeterminate truss structure in the failure process.,the mechanical behavior of the truss structure failure process under overload and compression bars with cracks was analyzed respectively.The compression members in the truss structure are replaced by nonlinear spring elements in ANSYS.The calculation results show that: 1)Compared with the calculation results of the small deflection theory,the nodal displacement under the same load is smaller when the structure is damaged by the large deflection theory.For example,the statically indeterminate truss structure:based on the small deflection theory,when F=18100 N,the key node position is 9.59 mm;based on the large deflection theory,the key node displacement under the same load is 9.46 mm;therefore,the truss using the large deflection theory The structure has a higher load-carrying capacity.2)Local cracks appear in the compression member,and the structural bearing capacity is reduced and it is more likely to be damaged.Taking the statically indeterminate truss without cracks as a reference,when the crack length reaches 20% of the plate thickness and F=16600 N,the displacement value of the key nodes in the structure increases from 4057.66 mm to4614.70 mm,an increase of 13.73%.Therefore,the existence of cracks reduces the bearing capacity of the structure and accelerates the failure process of the truss structure.