arXiv subjects

Robert Peyroux

Publications and source records attributed to Robert Peyroux.

6 recordsLinked to original sources

arXiv2023

Experimental investigation of alkaline treatment processes (NaOH, KOH and ash) on tensile strength of the bamboo fiber bundle

The aim of this experimental research is to investigate the effect of different alkali solutions, their different concentration, and the soaking time on tensile strength of bamboo fiber bundles. The results of this research will suggest the method to extract bamboo fiber in order to develop biodegradable composite materials in the future. Bamboo strips were mechanically separated from Rough Giant Bamboos, and they were soaked in three different alkali solutions based on NaOH, KOH, and ash with three individual concentrations (5%, 10%, 20% w/w) for eleven different soaking times. The bamboo strips were then washed and naturally air-dried before separating bamboo fibers bundles (cross-section area between 0.06-0.27mm 2) by hand pull off. The tensile strengths of bamboo fiber bundles were determined according to ASTM D3039 standard whereas paper grips technique was applied to prevent damage from the machine clamps. The results suggest that the optimal time for soaking bamboo strips is 48 hours for all solution and concentration. Moreover, soaking bamboo strips in KOH, and NaOH with more than 5% (10%, 20%) concentration, bamboo fiber bundles were destroyed. On the other hand, soaking bamboo strips in all concentrations of ash solution, and 5% concentration of KOH, and NaOH provides the same tensile strength value as the one with the soaking bamboo strips in distilled water. Additionally, the alkali solutions have proven to be able to protect bamboo fibers from fungus growth in contrast to distilled water.

physics.app-ph↗

arXiv2021

Very weak carbonaceous asteroid simulants I: mechanical properties and response to hypervelocity impacts

The two on-going sample return space missions, Hayabusa2 and OSIRIS-REx are going to return to Earth asteroid regolith from the carbonaceous near-Earth asteroids Ryugu and Bennu. The two main processes that lead to regolith production are the micrometeorite bombardment and the thermal cracking. Here we report the production of a weak simulant material, analogue to carbonaceous meteorites with a CM-like composition, following the preliminary compositional results for Bennu and Ryugu. This asteroid simulant has compressive and flexural strength 1.8+/-0.17 and 0.7+/-0.07 MPa, respectively. The thermal conductivity (in air) of the simulant at room temperature is between 0.43 and 0.47 W/m/K. In order to distinguish the type of regolith that is produced by each of these processes, we present and discuss the results of the experimental campaign focused on laboratory hypervelocity impacts, using the 2-stage light-gas gun of the University of Kent, that mimic the micrometeorite bombardment. We find that this process produces both monomineralic and multimineralic fragments, resulting in a difficulty to distinguish the two processes, at least on these weak materials.

astro-ph.EP↗

arXiv2007

Short-time dynamics of a packing of polyhedral grains under horizontal vibrations

We analyze the dynamics of a 3D granular packing composed of particles of irregular polyhedral shape confined inside a rectangular box with a retaining wall sub jected to horizontal harmonic forcing. The simulations are performed by means of the contact dynamics method for a broad set of loading parameters. We explore the vibrational dynamics of the packing, the evolution of solid fraction and the scaling of dy- namics with the loading parameters. We show that the motion of the retaining wall is strongly anharmonic as a result of jamming and grain rearrangements. It is found that the mean particle displacement scales with inverse square of frequency, the inverse of the force amplitude and the square of gravity. The short- time compaction rate grows in proportion to frequency up to a characteristic frequency, corresponding to collective particle rearrangements between equilibrium states, and then it declines in inverse proportion to frequency.

physics.class-ph↗

arXiv2007

Influence of particle shape on shear stress in granular media

We analyze the contact and force networks in a dense confined packing of pentagonal particles simulated by means of the contact dynamics method. The particle shape effect is evidenced by comparing the data from pentagon packing and from a packing with identical characteristics except for the circular shape of the particles. A surprising observation is that the pentagon packing develops a lower structural anisotropy than the disk packing. We show in this work that this weakness is compensated by a higher force anisotropy that leads to enhanced shear strength of the pentagon packing. With the polygonal shape of the particles, the strong force chains are mostly composed of edge-to-edge contacts with a marked zig-zag aspect.

physics.class-ph↗

arXiv2007

Force transmission in a packing of pentagonal particles

We perform a detailed analysis of the contact force network in a dense confined packing of pentagonal particles simulated by means of the contact dynamics method. The effect of particle shape is evidenced by comparing the data from pentagon packing and from a packing with identical characteristics except for the circular shape of the particles. A counterintuitive finding of this work is that, under steady shearing, the pentagon packing develops a lower structural anisotropy than the disk packing. We show that this weakness is compensated by a higher force anisotropy, leading to enhanced shear strength of the pentagon packing. We revisit "strong" and "weak" force networks in the pentagon packing, but our simulation data provide also evidence for a large class of "very weak" forces carried mainly by vertex-to-edge contacts. The strong force chains are mostly composed of edge-to-edge contacts with a marked zig-zag aspect and a decreasing exponential probability distribution as in a disk packing.

physics.class-ph↗

arXiv2006

Vibrational dynamics of confined granular material

By means of two-dimensional contact dynamics simulations, we analyze the vibrational dynamics of a confined granular layer in response to harmonic forcing. We use irregular polygonal grains allowing for strong variability of solid fraction. The system involves a jammed state separating passive (loading) and active (unloading) states. We show that an approximate expression of the packing resistance force as a function of the displacement of the free retaining wall from the jamming position provides a good description of the dynamics. We study in detail the scaling of displacements and velocities with loading parameters. In particular, we find that, for a wide range of frequencies, the data collapse by scaling the displacements with the inverse square of frequency, the inverse of the force amplitude and the square of gravity. Interestingly, compaction occurs during the extension of the packing, followed by decompaction in the contraction phase. We show that the mean compaction rate increases linearly with frequency up to a characteristic frequency and then it declines in inverse proportion to frequency. The characteristic frequency is interpreted in terms of the time required for the relaxation of the packing through collective grain rearrangements between two equilibrium states.

physics.class-ph↗