Study On Mechanical Properties Of Composite Pre-tightened Tooth Connection Under Bending-tension Coupling

As a new type of composite connection technology,the composite pre-tightening force tooth connection shows good mechanical properties in practical applications.At present,the mechanical properties of composite pre-tightening force tooth joints under axial force have been systematically studied.In the actual structure,the joints will not only be affected by axial force,but also by bending moment.However,the mechanical properties of joints under the coupling of bending moment and axial force have not been studied.Therefore,this thesis first designed a test loading method suitable for composite pre-tightening force tooth connection structure,and carried out axial tension and bending-tension coupling tests of single-tooth and double-tooth joints through this method.Then,a three-dimensional progressive damage model based on the USDFLD subroutine and the Tsai-Wu damage criterion was established according to the test conditions.The progressive damage process of the joint under bending-tension coupling was analyzed under the condition of verifying the correctness of the model.Finally,taking the 92 m composite material-metal composite truss bridge as the research background,a three-dimensional progressive damage model of the key joint nodes of the truss bridge is established.The ultimate tensile bearing capacity of the key joint nodes under the maximum bending moment is predicted,and the safety of the key joint node design is verified.The main research contents of this thesis are as follows :(1)Firstly,based on the structure and mechanical characteristics of the composite preload tooth connection,a new bending and tensile test loading method for the composite preload tooth connection is designed.The bending and tensile coupling loading of the joint is realized by using the MTS test machine,the jack and the distribution beam.Then,the axial tension and bending-tension coupling failure loading tests were carried out on the composite pre-tightening force tooth joints.The failure modes,load distribution and the influence of different bending moments on the ultimate tensile bearing capacity of the joints under different loads were studied.The results show that the ultimate tensile bearing capacity decreases with the increase of bending moment,and the greater the bending moment,the more significant the influence on the ultimate tensile bearing capacity.Through strain analysis,it is found that the load distribution law of the two-tooth joint is similar under the coupling of axial tension and bending tension.That is,when the load is small,the load is mainly borne by the first tooth.As the load increases,the load distribution ratio of the first tooth gradually decreases and the distribution ratio of the second tooth gradually increases.(2)Based on ABAQUS subroutine USDFLD and Tsai-Wu tensor criterion,a three-dimensional progressive damage model of composite pre-tightening force tooth joint is established.Firstly,the strain value,load displacement curve and ultimate bearing capacity obtained by the model are compared with the experimental values.The two are in good agreement,which verifies the correctness of the model.Then,the progressive damage failure process,strain relationship and the influence of different bending moments on the ultimate tensile and compressive bearing capacity of the joints under different loads are compared and analyzed by using the model.The results show that the effect of the joint under bending-tension coupling can be approximately regarded as the linear superposition of the corresponding load in axial tension and pure bending.By comparing the progressive damage failure process of the joint under different loads,it is found that under the axial tensile load,the initial damage occurs at the root of the joint,and the ring is evenly distributed.With the increase of load,the damage expands uniformly along the axial and ring directions.Under the bending-tensile coupling load,the initial damage always appears on the lower surface of the joint,and the uniformity of damage propagation is affected by the bending moment.The larger the initial bending moment,the more uneven the damage propagation.(3)Based on the 92 m composite-metal composite truss bridge,the progressive damage model of the three key joint nodes of the lower rotating bar,the inclined web member and the inclined vertical bar of the truss bridge is established,and the ultimate tensile bearing capacity of the three types of joint nodes under the maximum bending moment is analyzed.The results show that the ultimate tensile bearing capacity of the three types of joints under the maximum bending moment is greater than the maximum axial force of the structure in the stress analysis,which verifies the safety of the joint design.