Investigating the testing procedure limits for measuring particle strength distribution

A new design of a compression tester and an investigation of the testing procedure are presented. The tester enables us to accurately measure the force versus displacement of single particles down to 0.1 mm. By a numerical evaluation of test accuracy the required number of particles is obtained. For most of the investigated materials only 50–70 tested particles are sufficient to fall below an error of ± 5%. This procedure allows a sufficient number of particles that accurately result in the reliable breakage force, strength and energy distribution and prevent unnecessary tests. Usually, a quasi-static experiment is required leading to small compression force rates. Increasing the compression force rate may significantly reduce the test time. Therefore, the effect of the compression force rate on the breakage force of salt and glass spheres is examined to check the limit of the quasi-static region. It is shown that for glass spheres the limit is about 7 N/s.

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► We examined the highest possible compression force rate for a quasi-static regime.
► Salt may be compressed with force rates as high as 10 N/s.
► Glass should not be compressed at force rates higher than about 7 N/s.
► We examined the number of measured particles required for strength distribution.
► For most of the materials 50–70 particles are sufficient.