Simplified approach for ductile fracture mechanics SSTT and its application to Eurofer97

The determination of fracture-mechanical properties is often very challenging, because the available standards like ASTM E1820 need specific size-requirements for the specimen dimensions to obtain valid fracture toughness. Especially in the ductile regime, where the presence of plasticity around the crack tip is affected by the multiaxial stress state and its triaxiality, the size-requirements are frequently not met. The fulfilment of the size-requirements needs the testing of big specimens, which is often not possible. If we now think of specimens, which are irradiated in test modules for future fusion reactors, their size cannot be as big as required, because the available volume for irradiation is restricted. This fact highlights the need of Small Specimens Test Techniques (SSTT) for the determination of fracture-mechanical properties in the ductile regime. The presented work focuses on an approach for the determination of fracture-mechanical properties in the ductile regime including stable crack growth and crack-resistance behavior. The authors have developed the initial approach some years ago and within this work the approach was simplified as much as possible. The basic idea of the approach is, that the crack growth can be simulated using Finite Element Method combined with a cohesive zone model. The cohesive zone model is a two parametric model, namely the cohesive stress σ$_{c}$ and the cohesive energy Γ$_{c}$, which are identified on small specimens only. The new simplified approach was now validated on ferritic-martensitic steel Eurofer97 at room temperature. In the past, the approach used complicated features like a CCD camera system and has now been simplified in a way that no CCD camera system is required. The main part of the approach is the identification of cohesive zone parameters (cohesive stress σ$_{c}$ and energy Γ$_{c}$) on small specimens. The cohesive stress σ$_{c}$ can be determined on notched round tensile specimens with different notch root radius to account for different stress states or stress triaxialities in the specimen. With dedicated Finite Element modelling a local fracture stress dependent on stress triaxiality can be identified. The cohesive energy Γ$_{c}$ can be carried out by simulating the small fracture-mechanical specimen using the Finite Element Method combined with the cohesive zone model and parameter fitting to experimental results. The cohesive energy Γ$_{c}$ is treated to be identified, if the simulated crack-resistance curve describes the experimental behavior. After identification of these parameters, a big fracture-mechanical specimen can be simulated using the cohesive zone parameters already determined on small specimens. Finally, the crack-resistance curve of a big specimen can be predicted and a valid fracture toughness can be identified if the size-requirements of the big specimens are met. In case the requirements are not fulfilled, a bigger specimen geometry can be simulated until all size criteria are met. With this method, the testing of big specimens can be avoided. For the future there is a Round Robin exercise planned including defined test matrices to demonstrate the general applicability of the approach

Tiempo lingüístico y aspecto. Aproximaciones conceptual y contrastiva: árabe, francés y español

Este artículo tiene como principal objetivo exponer las especificidades temporales y aspectuales del sistema verbal de la lengua árabe en contraste con el de las lenguas romances, en este caso, el español y el francés, como paso imprescindible previo a la realización de un estudio empírico sobre la adquisición de los pretéritos imperfecto e indefinido del español como L3 por aprendientes arabófonos tunecinos con L2 francés. Tal contraste sugiere que, a pesar de la disparidad entre las lenguas romances aquí examinadas y el árabe en lo que a expresión de tiempo pasado y aspecto se refiere, las combinaciones semánticas entre aspecto léxico y flexivo son ampliamente similares en las tres lenguas, por lo que se puede formular como hipótesis que la adquisición de los pretéritos imperfecto e indefinido del español, así como su semántica aspectual, no deberían plantear problemas para los arabófonos tunecinos con L2 francés

A mechanistic study of the formation of polymer nanoparticles by the emulsification-diffusion technique

The mechanism of formation of polymer nanoparticles prepared by the emulsification-diffusion method was evaluated under different preparation conditions and by turbidimetry measurements. Biodegradable poly (D,L-lactic acid) was used as the polymer model. The results show that each emulsion droplet will form several nanoparticles and that the interfacial phenomena during solvent diffusion determine the size properties of the resulting colloid particles. These phenomena cannot be entirely explained by the convection effects caused by interfacial turbulence. We suggest that nanoparticle formation is due to diffusion alone, and we propose a mechanism based on the "diffusion-stranding” mechanism for spontaneous emulsification. In this mechanism, the diffusion of solvent causes local supersaturation near the interface, and nanoparticles are formed, due to the phase transformation and polymer aggregation that occur in these regions. This interpretation is supported by the turbidity measurements made at different polymer concentrations and stirring rate

Comparison of Three Processes for Parenteral Nanoemulsion Production: Ultrasounds, Microfluidizer, and Premix Membrane Emulsification

International audienceNanoemulsions are of great interest for pharmaceutical applications, including parenteral dosage forms. However, their production is still limited and requires more efficient and adaptive technologies. The more common systems are high-shear homogenization like microfludizers (MF) at industrial scale and ultrasounds at research scale, both based on high energy limiting their application for sensitive drugs. Recently, a process based on premix membrane emulsification (PME) was developed to produce nanoemulsions. These three processes have been compared for the production of a model parenteral nanoemulsion containing all-trans-retinoic acid, a thermolabile molecule which is used in the treatment of acute promyelocytic leukemia in a parenteral form. Droplet size and active integrity were studied because of their major interest for efficacy and safety assessment. Regarding droplet size, PME produced monodispersed droplets of 335 nm compared to the other processes which produced nanoemulsions of around 150 nm but with the presence of micron size droplets detected by laser diffraction and optical microscopy. No real difference between the three processes was observed on active degradation during emulsifcation. However, regarding stability, especially at 40 o C nanoemulsions obtained with the microfluidizer showed a greater molecule degradation and unstable nanoemulsion with a 4 times droplet size increase under stress conditions

Redispersible lipidic nanoparticles obtained by Fluid Bed Drying

Abstract Formulation of aqueous dispersions of lipidic nanoparticles is an elegant way to enhance and control drug bioavailability, ameliorate stability, and mask bitterness of some drugs. They are interesting vectors for oral delivery of lipophilic and, to a certain extent, hydrophilic substances. Their production can be done without the use of organic solvents, this make this kind of formulation ideal for pediatric use. [1] Therfore, these systems can present some instability phenomena, in order to prevent eventual issues, lipidic nanoparticles are classicaly dryed by spray-drying or lyophilisation technics into reconstitutable powders, the commun of these technics is their highly cost witch limited their use at large scale in cosmetic and pharmaceutical industries. [2], A comparison between Fluid Bed Drying and classical drying methods (lyophilization and spray drying) was performed, the comparison took into consideration quality of the obtained powder and its redipersibility, drug stability during the process and the effect of the drying method on particle size, the benefit of each method was highlighted

Vitamin E encapsulation within pharmaceutical drug-carriers prepared using membrane contactors

Vitamin E encapsulation within pharmaceutical drug-carriers prepared using membrane contactor

Preparation of liposomes: a novel application of microengineered membranes

Liposomes with a mean size of 59–308 nm suitable for pulmonary drug delivery were prepared by the ethanol injection method using nickel microengineered flat disc membranes with a uniform pore size of 5–40 μm and a pore spacing of 80 or 200 μm. An ethanolic phase containing 20–50 mg ml−1 phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or Lipoid® E80), 5–12.5 mg ml−1 stabilizer (cholesterol, stearic acid or cocoa butter), and 0 or 5 mg ml−1 vitamin E was injected through the membrane into an agitated aqueous phase at a controlled flux of 142–355 l m−2 h−1 and a shear stress on the membrane surface of 0.80–16 Pa. The mean particle size obtained under optimal conditions was 84 and 59 nm for Lipoid E80 and POPC liposomes, respectively. The particle size of the prepared liposomes increased with an increase in the pore size of the membrane and decreased with an increase in the pore spacing. Lipoid E80 liposomes stabilized by cholesterol or stearic acid maintained their initial size within 3 months. A high entrapment efficiency of 99.87% was achieved when Lipoid E80 liposomes were loaded with vitamin E. Transmission electron microscopy images revealed spherical multi-lamellar structure of vesicles. The reproducibility of the developed fabrication method was high

Preparation of surfactant-free nanoparticles of methacrylic acid copolymers used for film coating

The aim of the present study was to prepare surfactant-free pseudolatexes of various methacrylic acid copolymers. These aqueous colloidal dispersions of polymeric materials for oral administration are intended for film coating of solid dosage forms or for direct manufacturing of manoparticles. Nanoparticulate dispersions were produced by an emulsification-diffusion method involving the use of partially water-miscible solvents and the mutual saturation of the aqueous and organic phases prior to the emulsification in order to reduce the initial thermodynamic instability of the emulsion. Because of the self-emulsifying properties of the methacrylic acid copolymers, it was possible to prepare aqueous dispersions of colloidal size containing up to 30% wt/vol of Eudragit RL, RS, and E using 2-butanone or methyl acetate as partially water-miscible solvents, but without any surfactant. However, in the case of the cationic Eudragit E, protonation of the tertiary amine groups by acidification of the aqueous phase was necessary to improve the emulsion stability in the absence of surfactant and subsequently to prevent droplet coalescence during evaporation. In addition, a pseudolatex of Eudragit E was used to validate the coating properties of the formulation for solid dosage forms. Film-coated tablets of quinidine sulfate showed a transparent glossy continuous film that was firmly attached to the tablet. The dissolution profile of quinidine sulfate from the tablets coated with the Eudragit E pseudolatex was comparable to that of tablets coated with an acetonic solution of Eudragit E. Furthermore, both types of coating ensured similar taste masking. The emulsification-evaporation method used was shown to be appropriate for the preparation of surfactant-free colloidal dispersions of the 3 types of preformed methacrylic acid copolymers; the dispersions can subsequently be used for film coating of solid dosage form