Residual Stress Relaxation of DRWDs in OSDs under Constant/Variable Amplitude Cyclic Loading

Abstract

An orthotropic steel deck (OSD) has a complicated structure, and its fatigue life is mainly determined by various welding details. Fatigue assessment of deck-to-rib welding details (DRWDs) under long-term train loads is an important concern for engineers. Properly assessing the initial residual stress and the mechanism of stress relaxation in DRWDs under long-term external loading is a prerequisite for predicting the fatigue damage and service life of OSDs. In this paper, a finite element analysis method is proposed to calculate the residual stress relaxation in DRWDs of OSDs under constant/variable amplitude cyclic loading. First, experiments on full-size OSD specimens were carried out using the hole drilling strain-gauge method, and the multi-axial distribution characteristics of residual stress on the sub-surface of the deck were obtained. On this basis, a refined residual stress analysis model of DRWDs using thermal-structural sequence coupling analysis and life and death unit technology is established, and the accuracy of the model is verified by the test data. Second, a coupling stress analysis model that considers the welding residual stress and mechanical stress using cyclic plastic constitutive model is established. The combined influence of number of cycles, stress amplitude, and stress ratio on multi-axial residual stress relaxation effect under constant/variable amplitude cyclic loading is investigated. Finally, a release formula of welding residual stress relaxation coefficient is proposed based on the external loading stress amplitude, stress ratio, and material yield stress. The results show that (1) with the increase in the number of loading cycles, the stress decreases until it is stabilized, while the global distribution of welding residual stress remains unchanged. Most of the welding residual stress release (about 95%) occurs in the first cycle; (2) the residual stress relaxation decreases with the increase in stress amplitude and increases linearly with the stress ratio; (3) the residual stress release is controlled by the maximum amplitude stress in the variable amplitude cyclic loading. After the residual stress is released, the stress will not continue to be released if the DRWDs have the same or smaller amplitude loading.

The study of redistribution in residual stresses during fatigue crack growth

“…This is because the stress magnitude at the crack front exceeds the yield strength as the load amplitude increases and the residual stresses are relaxed after the unloading. These results are in good agreement with the results obtained in [24] and [25].…”

“…The result presented in Figure 9 is in agreement with [39]. Zhong et al [24] observed the similar results.…”

“…Yonezawa et al [23] investigated the effects of cyclic loading on the residual stress relaxation, and estimated the fatigue life of steel joints considering residual stresses. Zhong et al [24] studied the relaxation of welding residual stresses under constant and variable amplitudes cyclic loading, considering effects of stress ratio and material yield stress on residual stress relaxation. Ghaderi and coworkers [25] carried out a numerical and experimental investigation to study the effective parameters on residual stress relaxation in welded aluminum plates under cyclic loading.…”

Experimental Investigation on Residual Stress Distribution and Relaxation Effect at Double-Side Welded Rib-to-Deck Joints of Orthotropic Steel Decks

“…The amounts of relaxation are almost up to 30% or more, except the measuring point at the outside weld on the U-rib. It is noted that the amount of WRS relaxation does not increase with the stress amplitude increases as expected [12][13] [14], although it also depends on the initial WRS at the same time [15]. Principally, the reasons behind this phenomenon are that the test data are limited, and the microstructure of each test specimen after welding is discrepant.…”

“…Of the limited WRS measurement on OSDs reported in the literatures, only a few have been conducted in an innovative double-side welded RTD joints, especially for the magnitude and distribution of transverse WRS. Moreover, WRS of RTD joints will release under cyclic loading [12][13] [14]. WRS relaxation may occur when dislocation movements engender induced by additional applied loads or thermal energy, which change the local plastic constraints and results in residual stress redistribution [15] [16].…”