Dynamic response of ceramic shell for titanium investment casting under high strain-rate SHPB compression load

Abstract

The mechanical performances of ceramic mold are crucial for the quality of casts in investment casting. However, most of the previous researches were focused on the quasi-static performance which is not sufficient for the accurate failure analysis of shell mold under complex stress state. In this investigation, dynamic mechanical behaviors of Al2O3-SiO2 ceramic shell for investment casting have been studied using split Hopkinson pressure bar (SHPB) at high strain rates. Sand pack samples and pure slurry samples were considered for the testing in order to further understand the mechanism of fracture. Weibull approach was then applied to describe the strength distribution of ceramic shells. The dynamic increase factor (DIF) of compressive strength increased from 1.23 (863 s−1) to 2.03 (1959 s−1) indicating the high dependency of mechanical property to strain-rate. The cross-section and fracture surface were analyzed through scanning electron microscopy (SEM). The microstructural investigations showed that the crack propagation in the ceramic shell is mainly through the weak interface between sand particles and slurry region under quasi-static load. At high strain-rate, the crack propagation path is different which extends through the well sintered slurry region and even runs through the sand particles. The mechanism of crack propagation path is analyzed based on Griffith criterion. In addition, the feature of stress-strain curves indicates the layered structure which plays an important role in the process of fracture.