Arnaud Perrot

A novel settling and structural build-up measurement method

A new device, consisting of a rough plate immersed in the fluid sample, was developed to enable a simpler measurement of the sedimentation and yield stress increase of non-Newtonian suspensions. Due to the deformation of the material at rest or due to changes in the solid volume concentration by sedimentation along the vertical axis, the plate apparent mass varies with time. The apparent yield stress value of a fluid and the sedimentation rate could be calculated from this measurement.

Study of tribological behaviour of fresh mortar against a rigid plane wall

The interaction between a fresh cement-based material and a solid wall represents a considerable consumption of energy during an extrusion proces. In this article, the tribological behaviour of extrudible mortar and rigid wall friction is studied using a tribometer especially developed in the laboratory. Dynamic friction coefficient is highlighted. For fixed wall roughness, the friction velocity effect is analysed. Then, for fixed friction velocity, the roughness effect is analysed. Finally, the material structure evolution near the wall and the material erosion are analysed. L,interaction de matériaux à base cimentaire frais et une paroi solide représente une consommation énergétique importante dans les procédés d,extrusion. Dans cet article, le comportement tribologique d,un mortier extrudable et d,une paroi rigide est étudié au moyen d,un tribomètre développé et mis au point au laboratoire. Dans les travaux, le coefficient de frottement dynamique est tout d,abord mis en évidence. Pour une paroi de rugosité fixée, l,effet de la vitesse de frottement est ensuite analysé. Dans une partie suivante, à vitesse de frottement fixée, l,effet de la rugosité de la paroi est analysé. Enfin, l,évolution de la structure du matériau au voisinage de la paroi est présentée et discutée ainsi que l,érosion.

Tensile Characteristics of Coconut Fibers Reinforced Mortar Composites

Natural fibers such as coconut fibers are numerous in Indonesia. The tensile strength of coconut fibers produced in this country is among the highest of natural fibers ones. This paper is to determine the tensile strength of coconut fibers with or without special treatment (water washing dry) and assessment the ability of coconut fiber for reinforcement in mortar composites. Experimental observations on coconut fibers and mortars carried out. There were tensile tests and scanning electron microscopy (SEM) providing microstructural properties of coconut fibers. The results showed that the coconut fibers treatment increases tensile strength and provides higher failure strain values. It showed that coconut fibers largely improved tensile strength behavior of mortar composites. To a conclusion, the coconut fibers are able to be used as reinforcement for ductile mortar composites.

Couette Rheometry from Differential Approach: Comparative Study and Experimental Application

This paper presents a recent procedure for recovering the shear flow curve in Couette rheometer from torque‐rotational velocity data. It is the purpose here to extend the previous works and to compare our predictions in shear flow curve recovery with previous solutions in shear rate determination. With this goal, synthetic and experimental data of yield stress materials in Couette system are presently investigated.

A study on the limitations of a vane rheometer for mineral suspensions using image processing

This study presents the results from the rheological measurement of clay suspensions using vane geometry in a wide gap configuration. It focuses on how measurement of viscosity cannot be effective for two reasons: the limits of the vane geometry itself and the limits of the material depending on its content of solid particles. Image analysis of the flow while shearing the material is carried out to relate the flow behavior. Several approaches to compute the shear flow curve from torque-rotational velocity data are used. The results demonstrate that the applied setpoint while applying a logarithmic shear rate ramp can be very different from the calculated shear rate from existing theories. Depending on the solid volume fraction of the particles in the mixture, we relate the macroscopic behavior using image analysis and the shear flow curves to the rheophysical regime of the flow of the suspensions. Therefore, this paper has two simultaneous goals: the first one is to describe the physical phenomena which control macroscopic behavior and the second one is to highlight the limits of the vane geometry for viscosity measurement of mineral suspensions like kaolinite pastes.

Effect of Fibers Content on the Tensile Properties of Coconut Fibers Reinforced Cement Mortar Composites

The coconut fiber presents higher ductile properties than other natural fibers. In previous studies, it demonstrated than Indonesian coconut fibers presents an improved tensile strength and failure strain after washed with water and dried. The coconut fibers have the potential to reinforce material for construction, especially in earthquake areas such as tropical countries. The purpose of this research is to assess the benefit brought by coconut fibers content on the tensile behavior of mortar composite. Splitting tensile strengths were measured and microstructure observed using scanning electron microscopy (SEM). The influence of fiber content (expressed by a mass ratio fiber/cement) is investigated. The results show that a fiber content of 5% allows a 10 times higher deflection and presents a 1.5 times higher tensile strength than mortar without fiber. Further studies will focus on the bond strength between the fiber and the cement mortar matrix.

Extrusion Flow Modelling of Concentrated Mineral Suspensions

This study deals with the stability of the flow of cement-based materials induced by the extrusion forming process. Recently, such process has gained much interest because of its involvement in 3D printing process. The occurrence of the relative filtration of the fluid through the solid part of the material is governed by a competition between the permeability of the granular skeleton and the velocity of the extrusion process. Based on extrusion tests, two types of plastic behavior are proposed to describe the extrusion properties. The extrusion flow are tested under different conditions, such as sand proportion, ram velocity, die diameter, etc. The moisture contents on extrudates are calculated to describe the fluid filtration and the development of solid volume fraction. The experimental results are to be compared with the model prediction of the extrusion tests.

A localization analysis of a non-uniform damage lattice in presence of strength gradient

The failure of a non-uniform axial damage chain under uniform tension is studied both with discrete damage mechanics (DDM) and continuum damage mechanics (CDM). It is shown that a micomechanics-based nonlocal CDM model may be built from a DDM formulation, that may include material heterogeneities. DDM is based on a microstructured model consisting in multiples elastic-damage springs, whose elastic yield threshold is variable and depends on the position along the chain. We aim to develop a nonlocal CDM model as a relevant continuous formulation of the lattice DDM system. To do this, we rely upon a continualisation procedure applied to the difference formulation of the lattice problem, which gives us a nonlocal propagating damage model. The boundary conditions of the nonlocal CDM problem are equivalent to a finite length damage cohesive law. Analytical and numerical results show a strong proximity of the discrete and enriched continuous approaches for this heterogeneous bar problem, as well as the effectiveness of the nonlocal damage model to capture the softening localization phenomenon in heterogeneous quasi-brittle fields.

Scale effects in the static response of a one-dimensional quasi-brittle damage lattice

In this paper, we investigate the failure of a discrete elastic-damage axial system using both a discrete and an equivalent continuum approach. The microstructured damage chain consists of a one-dimensional damage lattice with direct nearest–neighbour interactions, which is composed of a series of periodic elastic-damage springs (axial lattice system treated in terms of discrete damage mechanics). We show that the damage lattice equations are equivalent to the centred finite difference formulation of a continuum damage mechanics (CDM) evolution problem. Such a discrete damage system reveals some scale effects on both the structural strength and stiffness. The nonlocal CDM in the hardening branch and cohesive damage model in the softening branch considered here are built using a continualisation procedure applied to the nonlinear difference equations of the lattice system. With this procedure, the difference equations to be solved are approximated by higher order differential equations. Using a rational asymptotic method, the continualised model appears to be equivalent to a nonlocal CDM model in the damage propagation zone. A finite length cohesive model is obtained in the softening range. A comparison of the discrete and the continuous problems for damage chains brings out the effectiveness of the new micromechanics-based nonlocal and cohesive continuum damage model, especially for capturing scale effects.

Nonlocal Continuum Damage Mechanics Approach of a Discrete Axial Chain under Non-Uniform Axial Load

The failure of a discrete elastic-damage axial system is investigated using both a discrete and anequivalent continuum approach. The discrete damage mechanics (DDM) approach is based on amicrostructured model composed of a series of periodic elastic-damage springs (axial DDM latticesystem). Such a damage discrete system can be associated with the finite difference formulation of aContinuum Damage Mechanics (CDM) evolution problem.The nonlocal CDM models considered in this paper are mainly built from a continualizationprocedure applied to centered finite difference schemes. A comparison of the discrete and thecontinuous problems for the chains shows the effectiveness of the new micromechanics-basednonlocal Continuum Damage modeling, especially for capturing scale effects.