Fatigue performance improvement of patch-plate welding via PWHT with induction heating

Significance 

Steel bridges are susceptible to damages and degradation as a result of the corrosion and fatigue effects. While both preventive and reactive maintenance and repair measures have been adopted in restoring the stiffness and strength of deteriorated bridge members, numerous challenges are faced. For instance, in the widely used patch-plate joining method, both welding and bolting joining methods are used depending on the situations and conditions of the members. Despite being reliable, bolting is disadvantageous in many ways: decrease in the sectional area, increase in weight and poor adhesive property. On the other hand, welding which has been seen as a promising alternative joining method is no fully effective. Welding and welding processes may lead to defects, fatigue cracks and residual stress. As such, these concerns should be thoroughly examined in welding to patch-plate joining to produce high-performance joints.

To this note, Professor Mikihito Hirohata from Osaka University together with May Phyo Aung and Hirohito Katsuda from Nagoya University examined the basic features of residual stress generated by patch-plate welding for the repair of steel structural members through numerical and experimental simulations. Specifically, they proposed a fatigue performance improvement method comprising of post-weld heat treatment and induction heating. Their work is published in the Journal of Constructional Steel Research.

The research team observed that welding residual stresses in the patch and base plates comprised of tension and compression respectively. This was attributed to the differences in the rise of temperature during welding due to the difference in the size of the base plate and patch plate. Additionally, high tensile residual stress almost similar to yield stress of the materials was generated along the weld line direction. Thermal elastic-plastic analysis taking into account the creep properties was used to simulate the welding and post-weld heat treatment processes. The welding residual stress and corresponding reduction by annealing were reproduced at high accuracy.

For the four-point bending fatigue experiment performed on the as-welded specimens using different loading patterns, the fatigue life of the specimens was significantly improved. For instance, the fatigue life nearly doubled when the tensile stress due to bending load was applied to the weld toe. The same trend was reported when compressive stress due to bending load was applied. However, the improvement in fatigue life affected by the residual stress was limited to the magnitude and stress pattern.

A close comparison was conducted to determine the possible difference between the experimental specimen and its simulation model with actual structural members. Even though the simulation is a promising one for investigating the post-weld heat treatment in actual structural members, the following needs to be taken into consideration: size differences between the experimental specimen and actual members, and the differences and effects of the boundary conditions which forms the basis of the future work.

Using the post-weld heat treatment in combination with induction heating, an improvement of the fatigue life of the patch-plate joints was reported. Interestingly, this approach is not only applicable to patch-plate welded joints but also other types of joints involving stress conditions. It is these good results that made Professor Mikihito Hirohata, the lead author, express his confidence in the role of the study in ensuring good health, functionality, and reliability of future steel bridges.

About the author

Mikihito Hirohata

2018.4-now Associate Professor, Division of Civil Engineering, Department of Global Architecture, Graduate School of Engineering, Osaka University, Japan

2015.9-2018.3 Associate Professor, Department of Civil and Environmental Engineering, Graduate School of Engineering, Nagoya University, Japan

2011.2-2015.8 Assistant Professor, Department of Civil and Environmental Engineering, Graduate School of Engineering, Nagoya University, Japan

2008.4-2011.1 Specially Appointed Assistant Professor, Joining and Welding Research Institute, Osaka University, Japan

2008.3 got doctor’s degree in Civil Engineering, Division of Civil Engineering, Department of Global Architecture, Graduate School of Engineering, Osaka University, Japan

2005.3 got master’s degree in Civil Engineering, Division of Civil Engineering, Department of Global Architecture, Graduate School of Engineering, Osaka University, Japan

2003.3 got bachelor’s degree in Civil Engineering, Division of Civil Engineering, Department of Global Architecture, School of Engineering, Osaka University, Japan

Research fields: Civil Engineering, Structural Mechanics, Steel Structures, Welding and thermal technologies

Reference

Aung, M., Katsuda, H., & Hirohata, M. (2019). Fatigue-performance improvement of patch-plate welding via PWHT with induction heating. Journal of Constructional Steel Research, 160, 280-288.

Go To Journal of Constructional Steel Research

Check Also

Improving the prediction of fluid flow and geochemical reactions by accounting for cm-scale variations in rock properties in reservoir models