تعیین تنش های جوش باقی مانده
Abstract
1-Introduction
2-Incremental hole-drilling method
3-Experimental test setup
4-Test results
5-Residual stress distribution from finite element analysis
6-Conclusions
Acknowledgements
References
Abstract
Tubular arch bridges are susceptible to fatigue problems due to stress concentrations, welding imperfections and tensile residual weld stresses. These bridges are composed of circular hollow section profiles welded together in tubular joints. This paper describes the determination of residual weld stresses in T-joints with the incremental hole-drilling method. The residual stress distribution can be used to determine fatigue crack behavior and fatigue lifetime more precisely. The incremental hole-drilling method is used to measure residual welding stresses on two similar T-joints. Experimental residual stress measurements were performed with the aid of the RS-200 milling guide. Strain gauge rosettes are attached to the test surface and with the milling guide, a small hole is drilled through the center of the strain gauge rosette. Strains at incremental depths are measured and the residual stresses are calculated according to ASTM E837-13a. A comparison is made between residual stress distributions obtained with finite element simulation and the experimental measurements. The distributions from finite element simulation show tensile yield stresses close to the weld while the experimental measurements indicate tensile yield stresses only in the axial direction of the primary tube. In all other cases, the residual stresses are tensile within 50% of yield stress or even compressional. However, more measurements on similar test specimens are necessary for a reliable residual stress distribution. Knowledge of the residual stress distribution is essential to accurately estimate the crack development under fatigue loads. In future research, the residual stresses can be used to study the influence of residual weld stresses on the fatigue lifetime and improve the design of steel tubular joints in arch bridges.
Introduction
Tubular steel arch bridges are highly appreciated for their aesthetic value. The use of hollow tubes with circular sections and the connections in the nodes where several tubes meet, ensures a smooth shape [1]. These structures are composed of several steel bridge joints where larger primary tubes are welded together with smaller secondary tubes. The fatigue strength is important because the numerous welded joints introduce high stresses near the weld toe of the joints. These high stresses are the result of the welding process and the influence of geometric discontinuities on the flow of the stresses, resulting in possible fatigue failure [2]. The welding process introduces residual welding stresses near the welded tubular joints. Residual stress distributions can have large stress gradients due to their non-uniform behavior [3]. These stress gradients make it necessary to perform residual stress measurements in order to estimate the influence on the fatigue strength of the welded joints in tubular arch bridges. The fatigue strength can be increased by the presence of compressive residual stresses [4]. Tensile yield stresses tend to open cracks and have a detrimental influence on the fatigue crack propagating under cyclic traffic loadings on the bridge. Residual stress can make the difference between a fatigue micro crack to grow or not. Moreover, residual stresses can also influence the rate of crack propagation, since the tensile residual stress field is often associated with a shorter fatigue life [5]. Therefore, accurate fatigue design of fatigue-sensitive bridge components requires knowledge of the distribution of the residual welding stresses.