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A bottom–up multi-scale performance transfer chain is developed to ascertain the gradual change in the law of vibration characteristics in spatial steel truss structures under fatigue loading. This chain derives the interrelationship between vibration characteristics and the performance of each structural component. Based on the evolution characteristics of the performance model of the member scale in the transfer chain, a new analytical model of the shape function is established. Building on these foundations, a refined model was formulated to depict the gradual change of vibration characteristics in spatial steel truss systems under fatigue loading. This model integrates the cumulative damage rule, the structural residual performance rule, the finite element method and other pertinent theories. The gradual change in vibration characteristics of a steel truss girder bridge subjected to train loads was analyzed using a self-developed three-dimensional finite element analysis framework tailored explicitly for assessing gradual change issues in spatial steel truss structures. The analysis results indicate that the effective residual cross-sectional area and the structural frequency continuously decline as the service time increases. This comprehensive study advances the understanding of fatigue-induced changes in spatial steel truss structures. It offers analytical perspectives for predicting and mitigating the long-term impacts of dynamic loads on large-scale infrastructural components.

The wind-induced fatigue damage is an important reason for the structural deterioration of transmission tower-line systems. The study of the fatigue damage of transmission towers is a basic requirement to ensure their normal service. To simulate the fatigue damage evolution occurring in the joints of the tower, a verified hybrid multiscale finite element (FE) model is first developed by concurrent modeling and substructuring techniques. Second, a fatigue damage model based on continuum damage mechanics is calibrated by conducting a fatigue crack initiation experiment and integrated into the FE material model by subroutines technique. Third, an improved Bayesian updated probability density evolution method (BUPDEM) with higher efficiency is proposed based on the Kriging method. Finally, based on the multiscale FE model and the damaged material model, the strategies for stochastic analysis of fatigue damage of transmission tower-line systems are proposed together with a numerical example for illustration. The results of the example show a good accuracy of the proposed BUPDEM.

The wind field environment in mountainous zones is complex. If the wind field characteristics are regarded as stationary and Gaussian, the inaccurate response results of the structure will be obtained. In this paper, a fatigue evaluation method of steel truss suspension bridge members under non-stationary and non-Gaussian buffeting is proposed. This approach can solve the fatigue evaluation problem of steel truss suspension bridge members under mountain wind. Firstly, the normal wind speed (stationary and Gaussian) is obtained by the harmonic wave synthesis method. The wind speed considering non-stationary characteristics is obtained by adopting time-varying power spectrum. Secondly, through non-linear translation, the wind speed considering non-stationary characteristics is transformed into wind speed considering both non-Gaussian and non-stationary characteristics. Finally, combined with the Palmgren–Miner rule, the effects of three different buffeting responses on fatigue damage of suspension bridge members are studied. They are traditional buffeting response, buffeting response considering non-stationary characteristics and buffeting response considering both non-stationary and non-Gaussian characteristics. The results indicate that the fatigue damage of the main cable of the suspension bridge is the biggest at the mid-span. Under the same wind speed, considering two characteristics, the component fatigue damage will further increase.

Damage to composite structures can accumulate over time and lead to fatigue failure in their actual use environment. Therefore, it is critical to establish a suitable fatigue life prediction model. This work developed an improved fatigue life prediction model based on the effects of equivalent damage and load interactions. Validation and comparison of the improved fatigue life prediction model were carried out using test data of composites subjected to secondary and tertiary loading. The analysis indicates that the accuracy of fatigue life prediction for composites under variable amplitude load is improved by the damage equivalence prediction model, which accounts for the influence of load application sequence and load interaction. Furthermore, a comparison with existing fatigue life prediction models reveals that the proposed model predicts fatigue life more accurately under different amplitude loads.

Purpose- This paper describes finite element fatigue damage modeling.

Design/Methodology/Approach- Fatigue life prediction and damage progressive evaluation are analytically studied. We present a numerical implementation of the studied models into the home made finite element code MPEF. Numerical simulations are performed on composite and metallic material. We carried out a parametric study to investigate the influence of model's parameters on the damage accumulation and their sensitivity on its kinetics. Simulations are conducted for two different loading levels to characterize cumulative damage and to study loading sequence effect. A comparative study is performed to characterize the efficiency of the two models to describe the damage evolution for the two different materials.

Findings- Numerical examples are presented to illustrate its performance.

Originality/value- This paper intends to present a comparative study of the damage evolution for metallic and composite material under uniaxial loading. The effect of the loading sequence will be investigated.

In this paper is presented and discussed the damage tolerance and fracture characteristics of three rapidly solidification processed magnesium alloys. Test specimens of the magnesium alloy were deformed under both quasi-static and fully reversed total strain amplitude controlled cyclic loading. The quasi-static and cyclic stress response characteristics are discussed in light of the competing and synergistic influences of nature of loading, response stress, intrinsic microstructural effects, dislocation-microstructural feature interactions and macroscopic fracture.

Permeability testing technology is an evaluation method which based on the electromagnetic induction principle which states that induced voltage is proportional to the change in rate of flux in the closed magnetic circuit of probe to test the permeability change of specimen. It can detect various changes related to the permeability in a certain area of the component with high precision such as stress concentration, fatigue damage, aging and decay, etc. Taking Q235 and 45 # steel as examples, the relationships between the detection signal and the tensile stress, residual stress and fatigue damage were studied from experiments. The results show that permeability testing technology can effectively measure the stress state of rod material specimen and the maximum stress of rod material specimen which had been suffered before. We can calculate the maximum stress by measuring the residual stress after stress was applied to the rod material specimen. The detection sensitivity of the fatigue damage was lower than the stress concentration. The detection sensitivity of fatigue damage of the low carbon steel Q235 was greater than the medium carbon steel 45 # steel. The research indicated that the permeability testing technology has a broad application prospects.