Rennes, France
Rennes, France
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Brammer P.,LGCGM | Brammer P.,University of Rennes 1 | Brammer P.,Renault S.A. | Bartier O.,LGCGM | And 6 more authors.
Materials and Design | Year: 2012

In instrumented indentation testing, especially in the nano and micro scales, low scale artefacts such as sensor sensitivity, surface roughness, imperfect indenter tip geometry and material heterogeneity can create significant deviations of the measured indentation load-depth curve from the ideal curve corresponding to the bulk material. This study assesses the influence of an offset of the measured penetration depth on the identified bulk mechanical parameter values when using a reverse analysis model based on spherical indentation. It is shown through numerical examples that significant errors arise if the identification procedure is based on the load values recorded at penetration depth values. In over to overcome this effect, an alternative exploitation of the reverse analysis model is proposed, which is based on the use of the slope of the indentation curve at indentation load values. In addition, it is proposed to neglect the data at low load values in order to avoid the effect of low scale artefacts on the shape of the indentation curve at low load values. The proposed approach is applied to the numerical examples, and then an experimental case of a blunted indenter tip is presented. In all cases, the proposed approach provides accurate identification results which are not affected by low scale artefacts. The proposed approach can be significantly useful when analysing indentation curves obtained in the nano and micro scales, as well as indentation curves obtained in industrial conditions. © 2012 Elsevier Ltd.

Glouannec P.,University of Southern Brittany | Collet F.,LGCGM | Lanos C.,LGCGM | Mounanga P.,French National Center for Scientific Research | And 5 more authors.
Materiaux et Techniques | Year: 2011

Hempcrete is a lightweight composite bio-material obtained by mixing lime, hemp fibres and water. Used in building construction, hempcrete is not used as load-bearing wall but mainly as filling material associated to a wooden structure. Several hempcrete formulations have been tested and three processes of hempcrete fabrication are also studied here. Power-law relation appears considering the compressive strength versus the effective density. Thermal conductivity measurements as functions of the density and the water content allow the determination of the material insulation capacity. Lying on material storage capacity and humidity transfer, hydric characterization is realized thanks to the estimation of the isothermal sorption-desorption curves and of the water vapor permeability. © 2011 EDP Sciences.

Chamoin J.,LGCGM | Collet F.,LGCGM | Pretot S.,LGCGM | Lanos C.,LGCGM
Materiaux et Techniques | Year: 2011

Hempcrete is a non loadbearing material that is use to infill a wooden framework. This material is obtained by mixing lime binder, hemp and water. In order to reach an easy implementation, the required quantity of water is higher than the quantity needed for a classic concrete mixture. This quantity also depends on the used manufacturing process. The aims of this paper are to show why hemp shiv increases the quantity of water during manufacturing and to find a treatment to reduce the absorption capacity of hemp shiv, while preserving initial properties like vapour permeability, insulation properties. An experimental bench for wetting test is set up and treatment protocols with a waterproof polymer by immersion are performed in the laboratory. © 2011 EDP Sciences.

Brammer P.,LGCGM | Brammer P.,Renault S.A. | Hernot X.,LGCGM | Mauvoisin G.,LGCGM | And 2 more authors.
Materials and Design | Year: 2013

Perfect indenter geometry is quite difficult to manufacture, especially in the nano and macro scales. Indentation curves obtained with imperfect indenter geometry can show strong differences with those obtained with assumed perfect indenter geometry, thereby leading to erroneous data exploitation results. This numerical study brings out the effect of imperfect spherical indenter geometry on indentation load-penetration depth curves, and on the mechanical properties identified by a reverse analysis model based on ideal spherical geometry. It is shown that a method to take account of geometrical imperfections is essential. Two correction methods based on geometrical and physical considerations are assessed, as well as the relevance of the use of the penetration data or the contact data. A method based on the equality of mean contact pressures and indenter volumes under the contact surface is found to be most relevant, as confirmed by the quality results obtained after application of a reverse analysis model. The proposed method is of particular interest in the case of the use of an imperfect indenter whose profile is accurately known. © 2013 Elsevier Ltd.

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