Study of the dimensions of double-torsion test specimens

Double-torsion tests were carried out to ascertain whether a thin test specimen would affect the results of tests involving two test specimen sizes, one with a thickness five-fold greater than the particle size of the material and the other with a three-fold greater thickness. The width of both test specimens was ten times that of their thickness and their length was double their width. The material used was an alumina-based refractory castable without cement. It is important to ascertain the influence of the thickness of double-torsion test specimens when materials with a coarse microstructure are involved. Otherwise, test specimens would have to be very large, rendering the experimental procedure difficult, in respect of the size of sintering furnaces and the size of accessories for the test. It was shown that test specimens with lower thicknesses were representative when the calibration curve of the compliance, the length of the crack at which the break occurred (critical crack length), and the shapes of the R-curve and of the load vs. displacement curves were analysed. However, an analysis of the mean values of R and of the total fracture energy showed that these values were dependent on the size of the test specimens. 43 refs.