A non-liner constitutive model of three typical biomass material pelletization for capturing particle mechanical behaviors during the elasto-visco-plastic deformation stage

The main objective of this work was to develop a non-liner constitutive model to reveal and predict the connection between the applied pressure and the evolution of particle mechanical behaviors for biomass pelletization. Three materials were selected: Pinus sylvestris var. mongolica Litv. sawdust as the relative standard material, Eucalyptus urophylla sawdust and residue of Flammulina velutipes as representatives of fast-grown forest and edible fungi cultivation residue, respectively. Pelletizing experiments were carried out using an uniaxial piston–cylinder densification apparatus in conditions of 8%–16% moisture mass content and 80–120 °C temperature with maximum applied pressure of 80 MPa. The model was established for the elasto-visco-plastic deformation stage on the basis of rheology concept according to the recorded data of applied force, displacement, and time. The model coefficients were calculated and found that elastic modulus E, plastic modulus R, and viscous coefficient η were closely related to pellet volume expansion rate, unit density, and Meyer hardness, respectively. Comparisons between the measured pressure values and the values predicted by the model illustrate that the constitutive model established in this investigation is reliable.