Integration of cast simulated mechanical properties into FEA for improved tensile strength evaluation of ductile iron gate valve bodies

Abstract

Valve production is one of the most cost competitive industries worldwide, and South African valve manufacturers face strong competition, predominantly from China. Simulation software can be used to engineering lighter, more cost effective products to stay ahead of competitors. The casting process affects the properties of the material resulting in a component with local variations in material properties and possibly discontinuities that are not accounted for in a stress analysis. This dissertation aims to investigate how the use of casting process simulation coupled with FEA can improve the accuracy of the stress analysis and identify the FEA input parameters that are most critical to the coupled simulation. This dissertation met these research aims through an extensive study of literature regarding the casting process and casting process simulation and the implementation an experimental investigation. The experimental investigation was carried out on SG42 Ductile Iron test samples and was used to evaluate the accuracy of the coupled simulation approach. It was determined that four casting simulation results (yield strength, young's modulus, residual stress and porosity) are important to integrate from the casting simulation into the stress analysis to more accurately predict the Factor of Safety of the component. An 18% increase in the accuracy of the stress analysis was observed after integrating the aforementioned properties over a stress analyis swith a single material definition, although the increase was mostly due to the integration of yield strength and porosity data. The main conclusion drawn from the research was that integrating casting simulation results into the stress analysis increased the accuracy of the stress analysis. The increase in accuracy significantly reduced the uncertainty regarding the materials strength, and the effect of the discontinuities present and can result in worthwhile cost savings for manufacturers through the reduction of section sizes that compensate for uncertainties in the material. Further research is however required on actual valve bodies to confirm these findings and determine the specific cost reductions achievable.