Diametral Compression of Short Cylinders with a Central Hole as a Method for Assessing the Tensile Strength of Brittle Materials

Abstract

The possibility of assessing the fracture resistance of brittle materials by testing short cylinders, solid and with a central hole, under diametral compression has been investigated. The computational analysis was performed using the finite element method with the ANSYS program. It was shown that the stress distribution in a disk with a hole is similar to that in a disk without a hole, but it has disturbances caused by the stress concentrator in the form of the hole. The normalized values of the maximum principal stresses for a disk with a hole are more than 5 times higher than those for a disk without a hole. Experimental analysis was carried out by testing short cylinders made of brittle materials—cast iron and graphite—both solid and with a central hole. It was found that the fracture resistance determined by the formula of the ASTM D3967-95a standard is practically the same for solid cast iron specimens, while for graphite specimens it differs by 1.5 times from the true fracture resistance of the materials. When testing specimens of cast iron and graphite with a central hole, the fracture resistance differs from the standard by 1.5 and almost 2.5 times, respectively. The different nature of specimen failure was also noted—slow controlled fracture for cast iron and dynamic fracture for graphite, according to their respective deformation diagrams. As an example, the results of testing real cylindrical specimens with a central hole—uranium dioxide fuel pellets—are presented. It is shown that the results of testing graphite ARV-1 specimens and fuel pellets are in good agreement. Thus, the possibility of testing small short cylinders using the diametral compression scheme for indirect assessment of tensile strength of brittle materials is confirmed. A calculation equation is proposed for the indirect assessment of the tensile strength of brittle materials based on the results of testing small short cylinders with and without a central hole under diametral compression.