Determination of Fundamental Mechanical Properties of Biomass using the Cubical Triaxial Tester to Model Biomass Flow

Abstract. The flowability of biomass is an indicator of the relative easiness with which biomass will flow and handle. Unfortunately, this term of flowability is not defined with first-principle based theories. The measurements of flowability are often conducted based on empirical or tertiary experiments. This status quo impedes advancing the design and operation of biomass handling systems by employing engineering principles. It is imperative to establish an experimental protocol that minimizes empirical aspects of flowability characterization to account for the variability of biomass properties. Cubical triaxial tester (CTT) is a true triaxial tester with a flexible pressure application membrane that is capable of determining fundamental mechanical properties of bulk biomass with minimal confounding effects of the test device. This study demonstrates the operational principles of the cubical triaxial tester and the procedure of triaxial tests. Parameters of Mohr-Coulomb, Modified Drucker-Prager, and Cam-Clay model parameters are determined for milled Corn stover and Douglas fir with two sets of triaxial tests, i.e., hydrostatic compression triaxial test and conventional compression triaxial test. The determination of bulk mechanical properties pertains to the flow characteristics of biomass can be performed unambiguously owing to the operational principle of CTT that is applying stresses in principal directions and measuring strains in corresponding principal directions. This paper will highlight the advantages of a CTT in the characterization of mechanical properties of bulk biomass, which is a steppingstone for engineering a reliable biomass handling.