Research And Application Of Cyclic Constitutive Models For Cold-formed Steel And Aluminum Alloy Materials

In recent decades,the field of space structure has been developing rapidly.More and more long-span structures with beautiful shape,comprehensive function and simple installation are constructed.Long-span spatial structures are dynamic load-sensitive structures because of their light weight and large flexibility.When they are subjected to cyclic loads such as earthquakes and strong winds,the structures are prone to large deformation,resulting in the destruction of the building envelopes and even the destruction of the whole structure.It is necessary to analyze the dynamic performance of structures,and the accurate and efficient constitutive model is of great significance for analysis of members and structures.The contents of this research are as follows:Firstly,cold-formed Q235 B steel specimens were tested for their monotonic tensile properties and hysteretic properties.The specimens were taken from different positions,such as the weld,adjacent weld,corner,and flat regions of cold-formed largesection square steel tubes.6061-T6 aluminum alloy specimens were tested for their monotonic tensile properties and hysteretic properties.The specimens were taken from the flange plate of the Temcor joint.The mechanical properties of cold-formed steel and 6061-T6 aluminium alloy under cyclic loading were analyzed by the test results.Then,based on the combined hardening constitutive model,the combined hardening parameters of cold-formed Q235 steel and 6061-T6 aluminum alloy were fitted,and the recommended values were given.In addition,the constitutive model of both cold-formed Q235 steel in different regions and 6061-T6 aluminum alloy was redeveloped by using the user material subroutine UMAT of ABAQUS.The developed constitutive model was divided into four parts: monotonic loading,loading along the skeleton curve,unloading and reloading.The proposed values in each stage of the constitutive model were given.In order to verify the accuracy of these two constitutive models,the simulation under the same loading pattern was completed by the finite element software ABAQUS.The simulation results conform well to experimental results.Finally,the proposed combined hardening constitutive model parameters were applied to the hysteretic test simulation of the Temcor joints made of 6061-T6 aluminum alloy.The results were compared with the test values and the simulated values under ordinary material properties.Besides,the proposed combined hardening constitutive model parameters were applied to the hysteretic simulation of the coldformed large-section square steel tubes made of cold-formed Q235 steel.The results were compared with the simulated values under ordinary material properties.The results showed that the combined hardening constitutive model can achieve the same ultimate strength as the isotropic hardening constitutive model,but the energy dissipation capacity of materials can be estimated more safely by using combined hardening constitutive model.Besides,the redeveloped cyclic constitutive model was applied to the wind-induced vibration analysis of single-layer latticed shells.The results show that the stress distribution of members and the variation trend of joint displacement are similar but slightly different.The main reason for the difference is that the reloading process of the material was optimized in the refining constitutive model of UMAT,which reflects the energy dissipation ability of the material more accurately.Therefore,the refining constitutive model is valuable in the dynamic performance analysis of the structure.