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By: Micah Bowen Experimental results for two thin plates being welded together using a laser beam weld were provided The temperature, residual stress and strain, and displacement of the workpiece will be replicated using finite element analysis 2 Reference [1] provided thermal, stress, and displacement data to compare against. Thermocouple Locations m m 9 mm 7 mm 4 mm 0 The experimental and FEA results from [1] will be used. 15 Laser Path 5 mm 10 mm 15 mm HAZ 1.5 mm FEA Temperatrure Locations Jig Clamps 200 mm (1) Chukkan, Jazeel Rahman, M. Vasudevan, S. Muthukumaran, R. Ravi Kumar, and N. Chandrasekhar. "Simulation of Laser Butt Welding of AISI 316L Stainless Steel Sheet Using Various Heat Sources and Experimental Validation." Journal of Materials Processing Technology 219 (2015): 48-59. Web. 3 The laser beam will be represented using a conical heat source with a Gaussian distribution shown below along with the equation 6 ∗ 𝜂 ∗ 𝑃 ∗ exp(3) − 𝑄 𝑥, 𝑦, 𝑧 = ∗𝑒 𝜋 ∗ (exp(3) − 1) 𝑥 2 +𝑦 2 𝑟𝑜 𝑧 2 4 The material being analyzed in this project 316L stainless steel The workpiece temperatures are as high as 1,450.0°C during welding. The melting temperature for 316L is 1,3751,400°C; therefore, the workpiece becomes molten around the weld This change to molten is accounted for in the 316L stainless steel properties Kou, Sindo. Welding Metallurgy. Hoboken, NJ: Wiley-Interscience, 2003. Print. 5 As the material heats up the yield stress decreased When the workpiece heats up to molten temperatures, the material begins to yield and goes from elastic to plastic. Plasticity occurs when a material is stressed beyond its elastic limit and yields resulting in large permanent deformations. As the material stress goes into the plastic region up to point A and is unloaded it returns to point B. The distance between the beginning of the curve and point B represents the permanent deformation. Digital image. Iron-Iron Carbide Phase Diagram Example., Web. 31 Oct. 2015. <http://www.cyberphysics.co.uk/graphics/graphs/stress_strain2.gif> 6 Finite element analysis will be used to represent the laser beam experiment Three steps to finite element analysis ◦ Pre-processing – The geometry of the system in modeled in a computer automated design program ◦ Solution – The program derives the governing matrix equations and solves for the displacement, strains, and stresses ◦ Post-processing – The analyst obtains the desired results of the analysis as well as checks the solution for possible warnings and/or errors 7 A 2D analysis of one of plates with symmetry was modeled The mesh density increased around the heat affected zone (HAZ) A transient thermal and structural run were made Applied Heat Source Symmetry Edge Increasing Mesh Density HAZ with Denser Mesh 8 A transient thermal analysis was selected and the thermal boundaries conditions were applied to the model: Symmetry Plane and Perfectly Insulated Conduction on Bottom Surface Convection and Radiation The heat source was applied to the top of the model Heat was applied gradually to allow the model to converge Thermal probes were added to track the temperature of the workpiece at specified locations 9 A transient structural analysis was selected and the thermal time history was imported into the structural run A compression only support was added to the bottom of the workpiece representing the jib Three elastic supports representing the jig clamps Elastic Supports Symmetry Compression Only Support 10 The FEA matched the HAZ from the experimental results Since the temperature was applied more gradually, the overall workpiece temperature was greater The peaks of the temperature matched the experimental data 1.2 mm 1,600 Temperature (°C) 1,400 1,200 1,000 0.3 mm 800 FEA [1] 0 mm 600 FEA 0 mm 400 200 0 0 25 50 75 100 125 150 175 200 225 250 Time (s) 11 In the FEA, the residual stress and strain are located at the interface between the two plates and does not span the entire workpiece There are multiple reasons this FEA did not capture the full residual stress and strain across the entire workpiece including: ◦ Using elastic supports at the end of the workpiece over a clamped constraint allowed the model to converge; however, these allowed for more lateral displacement compared to a fixed support ◦ By applying the heat slowly, the steep gradient of a weld is lost and the model does not plastically deform nearly as much as experiment in [1] does 12 The vertical displacement follows the experimental trend but is lower in magnitude This is due to the fact the heat was applied more slowly compared to the actual experiment 13 The FEA developed in this project could be converted into three dimensional to capture the structural affects along the length of the weld This model could also adapt different types of laser properties including different laser beam shapes, continuous verse pulsed laser and different laser welding patterns Another addition to this project would be to track the material phase as a function of heating and cooling rates for materials such as AISI 1010 carbon steel 14 When modeling a welding process using FEA, the following aspects are important: ◦ Ensuring there the mesh around the HAZ area is fine enough to properly predict the temperature distribution to the surround material ◦ Inclusion of temperature dependent material properties as well as thermal and structural boundary conditions representing the actual welding application 15