| This thesis investigates the multiscale fatigue damage evolution in rib-to-deck joints of orthotropic steel deck(OSD)of a steel arch bridge under traffic loading.A multiscale model is established to describe the fatigue damage evolution throughout the bridge lifecycle.The polycrystal microstructure together with the crystal plasticity constitutive model are used to simulated the micro short crack nucleation and growth.After the micro short crack in the microstructure grows up to an initial long crack length,macro long crack propagation is simulated in the substructure.As a case study,the multiscale fatigue damage evolution in the rib-to-deck joints of the OSD of the steel arch bridge under moving vehicles is simulated using the proposed method.The main research contents and conclusions of this thesis are as follows:(1)A framework with consideration of micro short crack nucleation and growth as well as macro long crack propagation for multiscale fatigue damage evolution of steel bridge deck is proposed.Based on phase transformation,the relationship between the change of Gibbs free energy and the number of fatigue cycles can be obtained.Nucleation occurs when the number of grain cycles reaches the critical value.The propagation life of micro short crack is assumed to be the sum of the nucleation life except the initial nucleation life.The proposed micro short crack nucleation and growth model can well describe the process of fatigue microcrack initiation,propagation and coalescence.(2)The polycrystal microstructure is modeled by the Poisson-Voronoi tessellation method.The crystal plasticity constitutive model is implemented by using the user-defined subroutine UMAT in the finite element software Abaqus.The material parameters which are applied to the mechanical properties of welded joints of orthotropic steel deck are adopted.To validate the crystal plasticity constitutive model,the fatigue test is carried out.After the micro short crack in the microstructure grows up to an initial long crack length,macro long crack propagation is simulated in the substructure by linear fracture mechanics.According to the microscopic image technique and beach mark technique,the applicability and accuracy of the multiscale fatigue damage evolution model are validated to some extent.(3)As a case study,the multiscale fatigue damage evolution of the steel arch bridge is simulated using the proposed method.Multiscale finite element modelling and substructure techniques are jointly used to model a steel arch bridge and multiscale fatigue damage evolution in rib-to-deck joints under moving vehicles is well simulated.Compared with the traditionally numerical method of fatigue damage simulation,the multiscale damage evolution model proposed in this thesis has made some meaningful improvements.It’s a new method to analyze the damage evolution of rib-to-deck joints of orthotropic steel deck throughout the bridge lifecycle and it provides an effective approach to accurately predict the fatigue life of steel bridges. |
