Damage Analysis of a Ferritic SiMo Ductile Cast Iron Submitted to Tension and Compression Loadings in Temperature

Tensile and compression tests were carried out on a ductile cast iron for temperatures up to 1073 K. The damage caused inside and around graphite nodules was evaluated as a function of the local equivalent plastic strain by using microstructural quantifications. The mechanical properties are strongly dependent on a temperature above 773 K. Concerning tensile behavior, an evolutional law issued from the Gurson model representing the void growth as a function of the deformation and temperature was successfully employed. It is demonstrated that the strain state and the temperature have a strong influence on the void growth function. In the case of compression tests, the temperature has a weak influence on the nodule deformation for temperatures lower than 773 K, and the mechanical behavior is driven by the viscoplastic properties of the ferrite. For higher temperatures, the mechanical properties in compression are progressively modified, since graphite nodules tend to remain spherical, and ferrite grains are severely deformed. A synthesis of the damage mechanisms is proposed in the studied range of temperature and plastic strain. It appears that the graphite nodule aspect ratio can be used as an indicator of the deformation under compression loading for temperatures ranging from room temperature to 673 K

Investigation of the internal structure of flax fibre cell walls by transmission electron microscopy

The development of the use of flax fibre as reinforcement of eco-friendly composite materials requires a good knowledge of its hydrothermal and mechanical behaviours. To this end the fibre internal structure must be finely investigated. Transmission electron microscopy was used to analyse the morphology of the fibre cell walls in terms of the arrangement of the layers and their thickness. Thus, an alternative eco-friendly staining method, based on oolong tea extract was successfully implemented. The results reveal an arrangement at the nanoscale slightly different from the classical four layer model encountered in the literature: the inner layer includes three to four sub-layers. The cell walls comprises two outer layers of relative thickness of about 10 %, a middle layer of about 70 % and a group of thinner layers (called sub-layers) that are contiguous to the lumen with relative thickness of about 20 %

Fracture toughness of glasses and hydroxyapatite: a comparative study of 7 methods by using Vickers indenter

Numerous methods have been proposed to estimate the indentation fracture toughness Kic for brittle materials. These methods generally uses formulæ established from empirical correlations between critical applied force, or average crack length, and classical fracture mechanics tests. This study compares several models of fracture toughness calculation obtained by using Vickers indenters. Two optical glasses (Crown and Flint), one vitroceramic (Zerodur) and one ceramic (hydroxyapatite) are tested. Fracture toughness and hardness are obtained by using instrumented Vickers indentation at micrometer scale. Young's moduli are obtained by instrumented Berkovich indentation at nanometer scale. Fracture toughness is calculated with models involving crack length measurements, and by models free of crack length measurements by considering critical force, chipping, pop-in. Finally, method based on the cracking energy, commonly employed for coated materials is also used. The aim of this work is to compare seven methods, which enable the facture toughness determination, on four brittle materials. To do so, it was necessary to determine some specific constant in the case of Vickers tip use. On the one hand, results show that methods using crack length, critical force, edge chipping or pop-in lead to comparable results, and the advantages and drawbacks are highlighted. On the other hand, the indentation energy method leads to underestimated results of about 20%

Mechanical properties of thermally sprayed porous alumina coating by Vickers and Knoop indentation

Depending on the thermal spraying conditions, coatings obtained can present different defects, like pores, cracks and/or unmelted particles, and different surface roughnesses, that can affect the determination of the hardness and elastic modulus. The present work investigates the mechanical properties, determined by means of Knoop and Vickers indentations, of a plasma as-sprayed alumina coating, obtained with a nano-agglomerated powder sprayed using a PTF4 torch, in order to highlight how the surface defects interfere into the indentation process. As a main result, Knoop indentation compared to Vickers one gives less dispersive results (15% and 33%, respectively), that are, in addition, more representative of the coating properties. The mean values obtained are 110 ± 40 GPa for the elastic modulus and 1.75 ± 0.42 GPa for the hardness. In addition, and for the two indenter types used, multicyclic indentation has been performed because it allows a more appropriate characterization of such heterogeneous coatings due to the representation of the mechanical properties as a function of the indentation load and/or the penetration depth, leading to more reliable results according to the depth-variability of the coating microstructure

Effect of microwave drying, calcination and aging of Pt/Al2O3 on platinum dispersion

The effect of heating method employed for drying and calcination during the synthesis of 1 wt% Pt/Al2O3 catalyst was investigated. Conventional heating (CH) in resistive oven and microwave heating (MW) in single mode were applied, and the Pt dispersion and Brunauer-Emmett-Teller (BET) surface area were measured to characterize the samples. It was evidenced that the fast and homogeneous heating offered by the microwave heating led to higher Pt dispersion. However, this benefit was only achieved when the subsequent calcination was performed in a conventional oven. The aging in microwave oven of conventionally prepared—as well as MW-prepared—catalysts demonstrated the great ability of microwave irradiation to accelerate platinum sintering. After 1 h at 800 °C under microwave, catalysts showed a dispersion of 5%. Therefore, microwave treatment should be considered for accelerated catalyst aging but should be avoided as a calcination technique for the synthesis of highly dispersed Pt/Al2O3

Effect of Microwave Drying, Calcination and Aging of Pt/Al2O3 on Platinum Dispersion

The effect of heating method employed for drying and calcination during the synthesis of 1 wt% Pt/Al2O3 catalyst was investigated. Conventional heating (CH) in resistive oven and microwave heating (MW) in single mode were applied, and the Pt dispersion and Brunauer-Emmett-Teller (BET) surface area were measured to characterize the samples. It was evidenced that the fast and homogeneous heating offered by the microwave heating led to higher Pt dispersion. However, this benefit was only achieved when the subsequent calcination was performed in a conventional oven. The aging in microwave oven of conventionally prepared—as well as MW-prepared—catalysts demonstrated the great ability of microwave irradiation to accelerate platinum sintering. After 1 h at 800 °C under microwave, catalysts showed a dispersion of 5%. Therefore, microwave treatment should be considered for accelerated catalyst aging but should be avoided as a calcination technique for the synthesis of highly dispersed Pt/Al2O3

Damage Analysis of a Ferritic SiMo Ductile Cast Iron Submitted to Tension and Compression Loadings in Temperature

Tensile and compression tests were carried out on a ductile cast iron for temperatures up to 1073 K. The damage caused inside and around graphite nodules was evaluated as a function of the local equivalent plastic strain by using microstructural quantifications. The mechanical properties are strongly dependent on a temperature above 773 K. Concerning tensile behavior, an evolutional law issued from the Gurson model representing the void growth as a function of the deformation and temperature was successfully employed. It is demonstrated that the strain state and the temperature have a strong influence on the void growth function. In the case of compression tests, the temperature has a weak influence on the nodule deformation for temperatures lower than 773 K, and the mechanical behavior is driven by the viscoplastic properties of the ferrite. For higher temperatures, the mechanical properties in compression are progressively modified, since graphite nodules tend to remain spherical, and ferrite grains are severely deformed. A synthesis of the damage mechanisms is proposed in the studied range of temperature and plastic strain. It appears that the graphite nodule aspect ratio can be used as an indicator of the deformation under compression loading for temperatures ranging from room temperature to 673 K

Approche multi-échelle de la structure et du comportement mécanique d'une fibre de lin

Ce travail de recherche porte sur la compréhension de la structure de la fibre de lin aux différentes échelles et sur l'étude de son comportement mécanique. En effet, dans le contexte de développement durable, le recours aux ressources végétales s'étend à de nombreux domaines d'applications industrielles dont celui des éco-composites structuraux. Dans un premier temps, sept variétés de fibres de lin sont comparées en terme morphologique (diamètre), de biocomposition et de propriétés mécaniques. Ensuite, l'étude structurale de la fibre de lin a porté sur les parois constitutives (nombre, épaisseur) et l'orientation des microfibrilles dans ces parois. L'analyse des courbes de contrainte-déformation obtenues par traction uniaxiale a permis d'évaluer les contributions élastique, viscoélastique et "plastique" au comportement globale de la fibre. L'orthotropie de son comportement mécanique a été mise en évidence par des essais de nanoindentation. Ces différentes données ont alors été utilisées pour identifier les paramètres majeurs qui gouvernent le comportement mécanique de la fibre de lin. Ainsi, des simulations du comportement mécanique de la fibre ont été entreprises dans le but de proposer une description phénoménologique.This PhD thesis deals with the understanding of the flax fibres structure at different scales and the studying of its mechanical behaviour. Indeed, in the context of sustainable development, using plant resources covers several fields of industrial applications including structural eco-composites. At first, seven varieties of flax fibres were compared in terms of morphology (diameter), biochemical composition and mechanical properties. Then, the structural study of the flax fibre dealt with the cell wall layers (number, thickness) and the microfibrils orientation in these layers. The analysis of the stress-strain curves obtained by uniaxial tensile test was used to estimate the elastic, viscoelastic and "plastic" contributions to the global behaviour of the fibre. The orthotropy of its mechanical behaviour has been demonstrated by nanoindentation testing. Finally, these data were used to identify the principal parameters that define the mechanical behaviour of the flax fibre. Thus, simulations of the mechanical behaviour of the fibre have been initiated to propose a phenomenological description.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Microwave sintering of large size pieces with complex shape

International audienceIn this study, large size pieces of kaolin with a complex shape were successfully sintered in a microwave multimode cavity. The challenge was to obtain a sample homogeneously sintered on a large surface. For this purpose, prior to sintering, a finite element modelling study was carried out to determine the optimal experimental set-up configuration permitting to have an electromagnetic field as homogenous as possible around the sample. In this case, it was pointed out that the hybrid heating configuration (use of susceptors) was the most suitable configuration.The samples experimentally obtained were structurally and mechanically characterized. Therefore, it was highlighted that the microwave sintered samples present a microstructure and mechanical properties similar to those of samples conventionally processed for a lower sintering temperature.Finally, the microwave sintering permit to significantly reduce the energy consumption required for the production of sintered ceramic pieces, which is crucial for sustainable development

Effects of the Susceptor Dielectric Properties on the Microwave Sintering of Alumina

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