ORIGINAL ARTICLE CFD Modelling of Temperature Distribution and Material Flow Investigation During FSW of DH36 Shipbuilding Grade Steel Avinish Tiwari 1 • Pardeep Pankaj 1 • Saurav Suman 1 • Pankaj Biswas 1 Received: 26 March 2020 / Accepted: 21 June 2020 Ó The Indian Institute of Metals - IIM 2020 Abstract A modified heat transfer and material transfer model was investigated for friction stir welding of DH36 steel by considering the Eulerian framework in steady state. During this analysis, temperature-dependent properties of the workpiece and the tool material were used. The mate- rial viscosity was modelled as a non-Newtonian vis- coplastic fluid depending on the temperature and flow stress. The heat generation at the tool workpiece interface incorporated the partial sticking and partial sliding condi- tion. An asymmetric and skewed temperature distribution at the advancing trailing side was observed. Asymmetry of temperature distribution was increased with an increase in the tool traverse speed. It was observed that the tempera- ture was maximum at the interface between the shoulder and tool, and the peak temperatures decreased non-uni- formly along the thickness direction. The results of mate- rial flow analysis indicated that the hot plasticized material flew ahead the tool along the retreating side in counter- clockwise direction, passed the tool and got released behind the tool during the welding stage. There existed a swirl region on the advancing side which was highly prone to defect formation. The temperature field and plastic flow field of the computational model matched satisfacto- rily with the experiment results. Keywords CFD  DH36 steel  WC tool  Thermal history  Material flow  Mechanical properties 1 Introduction The friction stir welding (FSW) process is highly complex in nature due to its nonlinear coupled behavior of the physics involved. Complex physical interaction occurs si- multaneously during FSW process, including the thermal, mechanical and coupled interactions. Heat flow and material flow during FSW process depend on the thermo- physical properties of the workpiece material, the tool material, tool workpiece contact condition and the welding condition. The interactions between the materials, affect the weld thermal (heating and cooling) cycles, flow anal- ysis, and the quality characteristics of the friction stir welded joints. From the beginning, the FSW technique has been extensively investigated by numerical techniques and the experimental characterization to optimize the process window and weld quality [1–5]. Numerical simulations can ease the more in-depth understanding of the complex physics involved during the FSW process. Several attempts were made previously to establish numerical models based on the coupled nature of the process [6–9]. The previous attempts were focused mostly on the thermal analysis and unconcerned to the material transportation behavior [10–12]. Frigaard et al. [13] developed 3D thermal model for FSW of aluminium alloys. The numerical simulation was compared with the experimental recorded temperature readings and a good correlation was observed. Chao et al. [14] proposed a model for heat transfer analysis for FSW of & Avinish Tiwari avit252@gmail.com Pardeep Pankaj pankajpardeep22@gmail.com Saurav Suman sauravnitmz@gmail.com Pankaj Biswas pankaj.biswas@iitg.ac.in 1 Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India 123 Trans Indian Inst Met https://doi.org/10.1007/s12666-020-02030-7