| dc.description.abstract | Cereal maize continues to be one of the most important crops in the world both for
human and livestock use. Bulk harvesting, transportation, handling and processing of
cereal maize is therefore important if the increasing global demand is to be met. In
Kenya, maize is the staple food-crop for the majority of the population. This calls for
the adoption of modern scientific methods in its production, storage and processing.
The use of 'existing constitutive models for granular engineering materials would
greatly help in accurate prediction of the behaviour of shelled maize en masse.
This research project investigated the engineering properties of three varieties of
shelled bulk maize pertinent to grain handling, storage and processing. In particular, it
investigated the stress-strain properties of bu~ maize in relation to Lade's
elastoplastic constitutive model for cohesionless sand and Maxwell-Weichert polymer
viscoelastic model, respectively. The Mohr-Coulomb failure criterion was also applied
to shelled maize en masse.
Stress--S--t-r-ain characteristics of the three varieties of bulk maize (Kitale 614 (V1)
Katumani A (V2) and Katumani B (V3)) were determined at 12% moisture content (wet
basis), using the triaxial equipment and the Senstar Universal Testing (SUT) machine.
Three different initial bulk densities (IBD) of 730 kg/m3 768 kg/m3 and 800 kg/m3
under three levels of confining stresses of 100 kPa, 200 kPa and 300 kPa were used
with the triaxial tests while two different initial bulk densities of 730 kg/m3 and 800
kg/m3 were used with the Senstar testing machine under cyclic uniaxial isotropic
loading. Both sets of tests were conducted at an axial strain rate (ASR) of 1.3
mm/min and data recorded after every 30 seconds for the SUT and after every 60
seconds for triaxial loading. The triaxial loading tests were continued until failure or
until 20% deformation (whichever came first) while the SUT tests were conducted until
20% deformation. Stress relaxation tests were conducted using the SUT machine for
the determination of the stress relaxation moduli and exponents.
The fourteen elastoplastic parameters under Lade's model were determined for maize
en masse. The results were verified and validated using data obtained from twenty
seven (27) different tests of the three maize varieties. Good agreements were found
between the predicted and measured values. The comparison between the measured
and the calculated values under Lade's model gave coefficient of determination (R2)
values of 0.95, 0.94 and 0.93 for the three maize varieties (V1, V2 and V3,
respectively) indicating that en masse maize can be considered as being elastoplastic
under this model. Maxwell-Weichert model gave R2 values of 0.87, 0.84 and 0.90 for
V1, V2 and V3 respectively. The stress relaxation moduli E1and E2and the relaxation
exponents k1.and k2 were determined under the viscoelastic model. Moreover, the
Mohr-Coulomb failure envelope for shelled bulk maize was developed with successful
determination of the angle of internal friction and the cohesion factor for the three
maize varieties. The low cohesion factors obtained under the Mohr-Coulomb criterion
justified the description of en masse shelled maize as being cohesionless.
These findings agree with other results from similar studies on wheat, rice and other
engineering materials and are expected to be useful in the design of bulk shelled
maize handling and storage facilities. The results may also provide important data for
future use in Finite Element Method (FEM), Finite Difference Method (FDM) or
Boundary Element Method (BEM) analysis of the behaviour of shelled bulk maize. | en |
