On validity of the value of tensile strength of dry moulding and core mixtures

The tensile strength in the cured state of molding and core sands is one of the important characteristics of molding materials. However, there is a significant spread of values at determining the tensile strength, which indicates the deficiencies of the existing methodology. The standard sample for tensile strength is a “figure-of-eight” shape. When it is tested for tension, the stresses in the holdsite points under central loading are 2–2.5 times greater than in the neck; therefore 8–12 % of the samples are destroyed in the holdsite points, and not along the neck. In this article, it is proposed to change the design of the standard “figure-of-eight” sample – to make a recess on one side of the neck, while creating an eccentric loading of the sample. The conducted studies and modeling show that using eccentric loading of the sample, due to the manufacture of a one-sided recess in the neck of the sample with a depth of 2–3 mm and a radius of at least 4 mm, the spread of strength indicators on the samples is 2–3 times less than on the standard one, and therefore the validity of the indicators is much higher.