Numerical and experimental study on thermal stress in grey iron castings

Abstract

Research on thermal stress analysis using the hybrid finite difference/finite element (FDM/FEM) computational method is still in its early stages, as the brevity of the bibliography attests. Inhomogeneous temperature distributions during the casting process lead to the generation of various thermal stresses during cooling from the pouring temperature to room temperature and from surface to core. It is impossible to measure residual stress experimentally during casting because the casting is covered by the moulds and its temperature is too high. Thus, the final thermal stress state and deformation must be inferred from measurements made at room temperature. Four moderately complex specimens, designed to be sensitive to residual thermal stress, were cast from grey cast iron. Residual stress levels were measured at various positions by the centre hole method using transducer strain gauges. These values, and cooling curves derived from thermocouple measurements, show reasonable agreement with the results of FDM/FEM simulations using a hybrid numerical model developed by the authors. Whole stage simulations suggest that section width has a stronger influence on residual stress than section length. The discrepancies between measured and calculated temperatures are attributed to the fact that the model does not incorporate the air gap or mould porosity effects.