Mohr-Coulomb failure criterion from unidirectional mechanical testing of sand cores after thermal exposure

Abstract

Sand core samples were subjected to thermal pre-conditioning profiles between 200 and 500 °C both in ambient air and under sealed conditions. These were customised similar to an industrial cast aluminium cylinder head. The samples were investigated via unconfined compression, splitting tensile, shear, and bending tests. The suitability of the data to parametrise a Mohr–Coulomb failure criterion model was evaluated.Four core types were examined more closely. The relative retained strength evolution was largely independent of the test type. Structural changes such as hardening or degradation were indicated by changes of the elastic bending modulus. In particular, polyurethane-coldbox-bonded sand cores after 400 °C pre-conditioning without air exchange retained 40% of the initial strength compared to 20% after treatment in air. Less atmospheric influence was revealed by furan warmbox-bonded cores, showing a decrease to 30% of the initial strength up to a 300 °C pre-conditioning temperature. Inorganic silicate-bonded cores using quartz sand exhibited a decrease in strength to 10% up to a 400 °C pre-conditioning temperature. In contrast using a silicate-bonded sintered mullite granulate, more than 50% of the initial strength was retained up to a 500 °C pre-conditioning temperature.Based on position-dependent temperature profiles, evolving during casting within the insulating sand cores, the mechanical behaviour until failure can be predicted and assigned, further allowing the evaluation of the mechanical core removal.