Harsha Badarinarayan

Crystal Plasticity and Grain‐Orientation‐Dependent hkl‐Lattice Strain in Polycrystalline SUS316

Non-uniform deformation at the micro-structural level is considered as critically important because it contributes a lot to study the early stage failure process in engineering components. To understand the deformation micro-mechanisms of stainless steels under complex stress states, we start with the heterogeneous deformation examination at the grain level under uniaxial loading condition and try to correlate the micro-deformation with the intergranular damage existing in many industrial processes. Due to the popularity, stainless steel 316 polycrystal is chosen in this study. The crystal plasticity finite element method (CPFEM) based on the crystalline slip theory is employed to establish a fundamental framework to predict the lattice strain evolution. Single-crystal elastic constants as part of the input information for CPFEM are obtained through the least square fitting to the neutron diffraction lattice strain data. Yielding behavior and the load carrying responsibility onset of the plastic deformation are discussed among several crystallographic planes, leading to the insight discussion between the lattice strain evolution and intergranular damage.

Load Partitioning Mechanisms in Stainless Steel 440C by Crystal Plasticity Based Micromechanical Modeling Approach

Stainless steel 440C with high content of C and Cr is the desired candidate in many engineering component for bearing purpose due to the extremely high yield strength and resistance to corrosion and erosion. However, high content of C and Cr usually results in carbides precipitates during cooling process. In this work, deformation mechanisms and the interplay between martensitic matrix and carbides precipices are explored using crystal plasticity finite element method (CPFEM). Two deformation stages are clearly revealed correlated to the yielding of matrix and precipitate respectively. When the “softer” phase, matrix is approaching the yielding point, lattice strains of matrix cease increasing and experience the stable stage, while precipitates carry more stresses. When sample is further deformed and precipitates are yielding, lattice strains in matrix exhibit elastic relaxation.

Acoustic Sound Source Identification in a Gasoline DI Pump for High Pressure Fuel Flows

The passenger class automobiles operating with gasoline direct injection (DI) pump have a better fuel economy than the automobiles operating with gasoline port fuel injection (PFI) pump. The fuel economy is higher because DI pump injects fuel directly into combustion chamber at pressures over 150 bar compared to a PFI pump which injects fuel into combustion chamber through inlet port at pressures over 50 bar. By injecting fuel directly into the combustion chamber, DI system prevents condensation of fuel, pressure leakage and improves atomization of fuel for internal combustion process. However, the disadvantage of high pressure operation is that the DI pump is noisier than a PFI pump. The loud sound in a DI pump is generated due to phenomenon such as high pressure pulsations, liquid jet impact and high velocity flows. To investigate the sound production in a DI pump, High fidelity hybrid numerical simulations were developed using CFD and Acoustic tools to simulate the operational effects and identify the behavior of internal components of DI pump. The fidelity of the numerical simulations depends on the transient boundary conditions and the fluid structure interactions in the DI pump. The CFD simulation model of DI pump has 8 million mesh elements and the simulation model is computed using 256 cores of super computer operating at a rate of 2 TFLOPS. The results derived from the CFD simulations were processed using a commercial acoustics tool for computing sound pressure level in liquid domain. Sound pressure level in liquid domain is used as a relative parameter for distinguishing the behavior of liquid-acoustic sources. The results from the numerical simulations provide a good account of the behavior of internal components in DI pump and the simulation results are in good agreement with the experiments performed on DI pump.© 2014 ASME

Friction Stir Welding of Magnesium Oil Pan

In this research, the feasibility of FSW dissimilar magnesium alloys was investigated. Specifically, die cast magnesium MRI-153M and AZ31 (plate) were butt-welded using the FSW technique. The effects of weld parameters (tool rotation (rpm) and weld speed) on the weld quality have been quantified in terms of hardness profile across the weld as well as tensile strength. Weld surface and cross section were also analyzed. Tensile testing showed that the welded material failed in the base material (MRI-153M) and not in the weld region. Weld cross section analysis showed void free welds were achieved at weld speeds up to 500 mm/min. Furthermore, a smooth and glossy surface ripple appeared on the weld beads and only a small amount of burr was observed. The Mg alloys were then welded together in an experimental oil pan cast in the USCAR-Magnesium Powertrain Cast Component Project. Finally, the oil pan assembly was successfully water bath-leak tested in water bath at 82.7KPa (12 psi) pressure for 3 minutes to validate the applicability of FSW.

Analysis of temperature and plastic flow during friction stir spot welding using particle method with elastic-plastic model

Friction stir spot welding (FSSW) is a new metal-joining process, and a numerical simulation code to calculate optimal welding conditions is desired. In this paper, we analyzed temperature distribution and plastic flow during FSSW process by solving the elastic-plastic deformation equations using the particle method. Calculation results indicate that, temperature distribution is circler patterns and the temperature below the rotation tool is 300 °C at 0.7 s when the diameter of the tool is 8 mm and the rotation speed is 2500 rpm. The material of the metal plate near the outside of the tool protrudes to cause the burr. The calculation result is similar to our experimental result. Plastic flow pattern of material in the metal plate is obtained. The obtained complex flow pattern is important to mix metal material and the weld strength of FSSW. The length of the pin of the tool, the tool diameter, the tool rotation speed, and the tool plunge speed are important parameters for mixing of metal material. The mixing of metal material below the concave shoulder is strong.Copyright

Defect prediction in copper motor rotor die casting using numerical simulation

Copper die-casting is still a relatively new casting process and the numerical formulation of this process is still in its developmental stages. A casting simulation software - ADSTEFAN was used to numerically determine the porosity in edge-gated copper rotor die-casting. The results obtained from simulation were then compared to the real die-cast copper rotors that were produced. Shot profiles are shown to be very instrumental in controlling porosity. Profiles designed to pre-fill a portion of the gate end ring at the slow shot speed prior to accelerating to the fast velocity to fill the conductor bars and ejector end ring are shown to be very effective in minimizing and controlling porosity. Since the electrical conductivity of copper is nearly 60% higher than that of aluminum, substituting copper for aluminum in the rotor would markedly increase the electrical efficiency of the motor.