Oedometric compression of a granular material: computation of energies involved during breakage with a discrete element modelling

A numerical model able to simulate the grain breakage with the discrete element method, using the “Non-Smooth Contact Dynamics” is presented. The model reproduces 3D grains having complex shapes and is tested in single grain and in oedometric compressions. Numerical simulations are then carried out to evaluate the different energies active during breakage (surface creation and redistribution energies). The surface creation energy is estimated. Results are closed to the ones found in the literature.

Quantification of grain breakage during creep based on X-ray microtomography

Delayed compression is among the leading causes of long-term deterioration in granular systems, especially when it is mediated by the action of pore fluids. This time-dependent process is often classified as ‘creep’, a term conveying time-dependence without specifying the causes of deformation. This paper presents a methodology based on X-ray synchrotron microtomography to track delayed microstructural changes in compacted sand. Experiments on materials characterized by different grain size and shape have been designed to measure macroscopic variables such as strain rate, as well as to visualize the topological and morphological alterations of the constituting particles. The results reveal that non-negligible inelastic processes such as grain breakage manifest during the first stages of loading, as well as during the ensuing constant-stress delayed compaction. A substantial role of the grain morphology was detected in both stages. Specifically, while samples made of angular grains displayed early breakage due to the exacerbated fragility of the particles, specimens made of rounded grains did not develop a markedly polydisperse structure prior to creep, which led to comparably more intense delayed fracturing. Furthermore, samples consisting of round grains were also found to exhibit more intense shape alterations, with morphological indicators that tended to converge over time towards those of initially angular grains. These results suggest that characterization and simulation of creep in granular media need to encompass a variety of microscopic processes controlled by grain-scale properties, thus requiring multi-scale testing and modelling techniques.

Structural parameters for X-ray micro-computed tomography (μCT) and their relationship with the breakage rate of maize varieties

Background High grain breakage rate is the main limiting factor encountered in the mechanical harvest of maize grain. X-ray micro-computed tomography (μCT) scanning technology could be used to obtain the three-dimensional structure of maize grain. Currently, the effect of maize grain structure on the grain breakage rate, determined using X-ray μCT scanning technology, has not been reported. Therefore, the objectives of this study are: (i) to obtain the shape, geometry, and structural parameters related to the breakage rate using X-ray μCT scanning technology; (ii) to explore relationships between these parameters and grain breakage rate. Result In this study, 28 parameters were determined using X-ray μCT scanning technology. The maize breakage rate was mainly influenced by the grain specific surface area, subcutaneous cavity volume, sphericity, and density. In particular, the breakage rate was directly affected by the subcutaneous cavity volume and density. The maize variety with high density and low subcutaneous cavity volume had a low breakage rate. The specific surface area (r = 0.758*), embryo specific surface area (r = 0.927**), subcutaneous cavity volume ratio (0.581*), and subcutaneous cavity volume (0.589*) of maize grain significantly and positively correlated with breakage rate. The cavity specific surface area (− 0.628*) and grain density (− 0.934**) of maize grain significantly and negatively correlated with grain breakage rates. Grain shape (length, width, thickness, and aspect ratio) positively correlated with grain breakage rate but the correlation did not reach statistical significance. The susceptibility of grain breakage increased when kernel weight decreased (− 0.371), but the effect was not significant. Conclusions The results indicate that X-ray μCT scanning technology could be effectively used to evaluate maize grain breakage rate. X-ray μCT scanning technology provided a more precise and comprehensive acquisition method to evaluate the shape, geometry, and structure of maize grain. Thus, data gained by X-ray μCT can be used as a guideline for breeding resistant breakage maize varieties. Grain density and subcutaneous cavity volume are two of the most important factors affecting grain breakage rate. Grain density, in particular, plays a vital role in grain breakage and this parameter can be used to predict the breakage rate of maize varieties.