Tensile and compressive strengths of fine magnesia, alumina and silica powder beds were measured. Although the direct tensile test has been commonly used for powder beds with sufficiently high tensile strength, the radial compression test was employed in the present study because of its simplicity and easiness. The size effect of test pieces and the distribution of its strength were discussed using the specimens with different diameter (D) and thickness (W). The results are as follows.
(1) The tensile strength (St) of the specimens with W/D=1/2 slightly decreased with increasing diameter of powder beds as shown in Fig. 3.
(2) For the powder beds having the same diameter but different thickness, the tensile strength had a peak at W/D=1/2, beyond which it decreased gradually and below which it decreased rapidly as shown in Fig. 4.
(3) The distribution of strength for powder beds with W/D=1/2 and D=20mm could be approximated by a Gaussian's distribution or Weibull's distribution with the high coefficient of uniformity (m>20) as shown in Fig. 5.
The compressive strength (Sc) of the specimens with W/D=2 was measured by the conventional uni-axial compression test. As shown in Fig. 7, Sc Was related to St by the equation, Sc≈7 St. On the other hand, the Griffith's theory with the assumption of random crack distributions gave Sc=8St. From this relationship and the above (3), it is suggested that powder beds are highly uniform brittle materials.
