TENSILE STRENGTH AND RING TEST

Results of ring tests on a gympsum plaster, with and without limestone inclusions, are presented with the emphasis on small hole sizes. The tensile strength varies within the ring test between two constant values. One is the true tensile strength in this situation for large hole sizes when the elastic calculations adequately represent the physical situation. The other is a totally fictitious tensile strength for small hole sizes which have no effect on failure. Tensile strength variation within the ring test is thus explained by the gradual breakdown of elasticity theory as the hole size is reduced. Tensile strength variation between the ring test and Brazillian test, however, remains a paradox. It is shown that the latter variation is not caused by ignoring the compressive stress component in the Brazilian biaxial stress field. © 1969.