11:30 AM - 11:45 AM
[PPS07-09] Influence of the hierarchical granular structure of planetesimals on the strengthening process: Experimental evaluation
Keywords:planetesimals, dust, hierarchical structure, compaction, tensile strength
The strength of planetesimals strongly affects the fate of these bodies. The configuration of constituent particles should affect the strength. Planetesimals formed in gravitational instability are thought to be a “hierarchical granular aggregate”, i.e., an aggregate of “pebbles” that are configurations of dust “grain”. Initially, such objects should behave as an aggregate of pebbles. However, deformation, fragmentation, and the coalescence of pebbles due to self-gravitational consolidation, etc. may eventually lead to similar physical properties as an aggregate of homogeneous grains. In this study, we focus on compaction and the resulting strength growth during this transition process. In this presentation, we compare the experimental results of "hierarchical" and "homogeneous” samples and then report the relationship between the compaction behavior and pebble strength, and the effect of pebble particles on the tensile strength of the sample after consolidation.
Our sample consists of glass beads with a diameter of 4.2 μm (Potters-Ballotini, EMB-10). We used agglomerates contained in the original or wet sample powder as pebbles. Experiments were performed using pebbles (agglomerates) with a diameter of 1-2 mm. We performed compaction experiments and tensile strength measurements of the hierarchical "pebble" sample and homogeneous "powder" sample, they are prepared by filling pebbles or sample powder into a cylindrical container, respectively. In the compaction experiments, the maximum pressure applied to the samples was varied on the order of 104 - 106 Pa. The tensile strength of samples after compaction was measured by the Brazilian test. Pebble strength was also measured for each sample because the strength of the Pebble varies depending on the conditions during preparation and storage. The interior of some compaction samples was observed by CT scan.
The relationship between the filling factor of the sample and the pressure applied to it (compaction curve) obtained from the compaction experiments showed that in the initial stage of compaction, the pressure required to compact a pebble sample was larger than that of a powder sample for the same filling factor. The pressure required for compaction increased with increasing pebble strength. The differences between samples are gradually lost as sample compaction progresses. This suggests that the effect of the physical properties of the pebble is lost after a certain degree of compaction. The pressure at which the difference between the pebble and powder samples disappears also increases with pebble strength. Comparison of the compaction curves of the pebble samples reveals that for pressures lower than approximately 10 times the pebble strength and filling factors smaller than ~0.5, the compaction curves normalized by the pebble strength collapsed into a single line. This suggests that compaction in this range progresses due to the fragmentation of the pebble. In the presentation, we also report the strength of the sample after compaction and the results of observations of the interior of the sample.
Our sample consists of glass beads with a diameter of 4.2 μm (Potters-Ballotini, EMB-10). We used agglomerates contained in the original or wet sample powder as pebbles. Experiments were performed using pebbles (agglomerates) with a diameter of 1-2 mm. We performed compaction experiments and tensile strength measurements of the hierarchical "pebble" sample and homogeneous "powder" sample, they are prepared by filling pebbles or sample powder into a cylindrical container, respectively. In the compaction experiments, the maximum pressure applied to the samples was varied on the order of 104 - 106 Pa. The tensile strength of samples after compaction was measured by the Brazilian test. Pebble strength was also measured for each sample because the strength of the Pebble varies depending on the conditions during preparation and storage. The interior of some compaction samples was observed by CT scan.
The relationship between the filling factor of the sample and the pressure applied to it (compaction curve) obtained from the compaction experiments showed that in the initial stage of compaction, the pressure required to compact a pebble sample was larger than that of a powder sample for the same filling factor. The pressure required for compaction increased with increasing pebble strength. The differences between samples are gradually lost as sample compaction progresses. This suggests that the effect of the physical properties of the pebble is lost after a certain degree of compaction. The pressure at which the difference between the pebble and powder samples disappears also increases with pebble strength. Comparison of the compaction curves of the pebble samples reveals that for pressures lower than approximately 10 times the pebble strength and filling factors smaller than ~0.5, the compaction curves normalized by the pebble strength collapsed into a single line. This suggests that compaction in this range progresses due to the fragmentation of the pebble. In the presentation, we also report the strength of the sample after compaction and the results of observations of the interior of the sample.