Papers by thierry chotard
Journal of Materials Science Letters
ABSTRACT
Journal of the European Ceramic Society, 2002
Early hydration (0-24 h) of Secar 71, a calcium aluminate cement, has been examined in-situ by ul... more Early hydration (0-24 h) of Secar 71, a calcium aluminate cement, has been examined in-situ by ultrasonic testing for pastes prepared at 20 C (W/C=0.33, 0.38 or 0.40) and at 5 C, 40 C and 60 C (W/C=0.33). The ultrasonic measurements consist of following the velocity of the longitudinal ultrasonic wave, V L (frequency=1 MHz), transmitted inside the specimen and also the reflection coefficient, R, at the interface between the cement and the container of the paste, which is a polymethylmethacrylate mould. The variations of V L as a function of setting time can be described by a dissolution-precipitation mechanism. Lastly, the changes in R can be linked with morphological changes occurring inside the cement paste, especially the progressive formation of crystallised hydrates.
Journal of the European Ceramic Society, 2003
In this paper, a new application of the acoustic emission (AE) technique is proposed. This non-de... more In this paper, a new application of the acoustic emission (AE) technique is proposed. This non-destructive and in situ method, widely used in damage characterisation, permits us to follow the cement hydration at the early age from a few minutes to a few hours after mixing. The acoustic emission (AE) signals concerning a pure aluminous cement paste, (water to cement
Journal of the European Ceramic Society, 2007
In this paper, some applications of acoustic emission (AE) technique to characterise the liquid t... more In this paper, some applications of acoustic emission (AE) technique to characterise the liquid transfer mechanisms during drying process of a porous ceramic are presented and discussed. Results are compared with the general theory of drying and a more recent approach dealing with thermodynamic modelling itself based on capillary stresses and hygromechanical coupling. The sensitivity of the acoustic emission technique
Journal of the European Ceramic Society, 2005
... Different types of analysis can also be done concerned with amplitude, duration, energy and .... more ... Different types of analysis can also be done concerned with amplitude, duration, energy and ...Acoustic emission was continuously monitored during cement early age (from 0 to 24 h ... are encountered in testing brittle materials in direct tension, indirect methods become attractive. ...
Composites Science and Technology, 2000
This article reports detailed results on the impact damage and residual mechanical behaviour of s... more This article reports detailed results on the impact damage and residual mechanical behaviour of some pultruded glass-fibre/polyester structures. The impact aspects studied include damage analysis and the impact behaviour of these shapes. The influences of test parameters such as impact velocity, impactor mass and impactor size were emphasised as well as the type of damage observed. Four-point flexural tests were
Composite Structures, 2001
This paper presents an experimental investigation on the residual mechanical behaviour of patch-r... more This paper presents an experimental investigation on the residual mechanical behaviour of patch-repaired composite pultruded structures initially submitted to low-velocity impact loading. It reports detailed results about static, fatigue and impact tests performed on dierent glass/polyester impact-damaged structures repaired by low-cost and manual techniques. All the tests were conducted at room temperature. It appears that, ®rstly, for all the studied structures, the initial static strength is completely recovered. Secondly, for two types of pultruded structures, the fatigue crack-growth life does not recover its initial values but compared with the damaged specimen, the lifetime is signi®cantly enhanced. Residual performances of both undamaged and repaired specimens seemed to be in¯uenced by the pro®le geometry (in fatigue bending tests) and especially by the open/closed characteristic of the structures. Carefully designed, external scarf patch repairs can recover more than 85% of the undamaged mechanical behaviour, depending on the type of residual applied loading.
Cement and Concrete Research, 2001
Nondestructive and in situ characterisation techniques, such as ultrasonic measurements, permit t... more Nondestructive and in situ characterisation techniques, such as ultrasonic measurements, permit to follow cement hydration at the early age from a few minutes to a few hours after mixing. The technique reported in this paper is based on measurements in reflection modes. Results concerning an aluminous cement, Secar71, are presented (water-to-cement weight ratio (W/C): 0.3 and 0.4; temperature of measurement: 20°C; duration: 0 ± 24 h). Information deduced from ultrasonic measurements (longitudinal wave velocity, reflection coefficient) associated with other data obtained from X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric (TG) measurements enable to propose a qualitative description of hydration's chronology. The sensitivity of these ultrasonic parameters to hydrates formation and structuring is underlined.
Ceramics, 2019
Mullite-Zirconia refractories are well known for their good resistance to corrosion and thermal s... more Mullite-Zirconia refractories are well known for their good resistance to corrosion and thermal shock. In this study, several mullite-zirconia composites were developed from andalusite, alumina and zircon sintered at 1600 °C for 10 hours. The samples were subjected to thermal shock carried out after heating at 1200 °C, in order to study the mechanical and thermomechanical behaviour as a function of the amount of zirconia dispersed in the mullite matrix. It appears that that the amorphous phase (SiO2), determined by X-ray diffraction, produced by the decomposition of andalusite, increases considerably with the amount of final zirconia in the composite and has a very important influence on the porosity. This amorphous phase seems also to have an important influence on the mechanical properties of the material. The characterisation of the thermomechanical behaviour (elastic properties and damage monitoring) was carried out thanks to ultrasonic techniques (US echography and Acoustic Emi...
Le Centre pour la Communication Scientifique Directe - HAL - memSIC, Jun 16, 2019
Le Centre pour la Communication Scientifique Directe - HAL - Université Paris Descartes, 2011
International audienc
Materials used in solar receivers are exposed to high stresses, i.e. high temperatures (up to 100... more Materials used in solar receivers are exposed to high stresses, i.e. high temperatures (up to 1000° C in current solar towers, 1400°C for next generations, resp. 350 and 700°C for linear concentrators); high spatial thermal gradients (mainly due to the non-uniform concentrated solar irradiation) and high dynamic thermal gradient (e.g. fast during cloud passing or slow due to the daily cycling from dawn till dusk). Due to these very severe conditions, the materials degrade over time, their properties change, leading to reduced performance and ultimately to the failure and the ruin of the associated structure, increasing the cost of operation. Accurate in-situ measurements are required in order to select the materials (development and qualification stages with SFERA-III Research Infrastructures) or improve their lifetime and the optimal operation of a solar plant (commercial stage). However, the health evaluation of solar receivers is typically observed subjectively during downtime at...
A promising route toward affordable and efficient solar energy conversion lies in the development... more A promising route toward affordable and efficient solar energy conversion lies in the development of the high temperature Concentrated Solar Power (CSP) tower. The extreme thermal stress conditions to which the tower receivers may be submitted raise the question of the ability of these components to efficiently perform over extended periods of time. Conventional methods commonly used to assess the mechanical stability and lifetime of these components involve laboratory testing, which suffers from the fundamental inability of these methods to effectively reproduce the real operating conditions. In this work, we suggest an original set-up based upon the use of acoustic emission for in-situ thermomechanical investigation of receiver materials exposed to concentrated solar irradiation, named IMPACT (In-situ thermo-Mechanical Probe by ACoustic Tracking). The ability of this set-up to precisely track the nature, the location and the dynamics of mechanical defects in the receiver material ...
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Papers by thierry chotard