Buckling and postbuckling of axially-loaded CNT-reinforced composite cylindrical shell surrounded by an elastic medium in thermal environment

Buckling and postbuckling behaviors of nanocomposite cylindrical shells reinforced by single walled carbon nanotubes (SWCNTs), surrounded by an elastic medium, exposed to a thermal environment and subjected to uniform axial compression are investigated in this paper. Material properties of carbon nanotubes (CNTs) and isotropic matrix are assumed to be temperature dependent, and effective properties of nanocomposite are estimated by extended rule of mixture. The CNTs are embedded into matrix via uniform distribution (UD) or functionally graded (FG) distribution along the thickness direction. Governing equations are based on Donnell’s classical shell theory taking into account von Karman-Donnell nonlinear terms and interaction between the shell and surrounding elastic medium. Three-term form of deflection and stress function are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain load-deflection relation from which buckling and postbuckling behaviors are analyzed. Numerical examples are carried out to analyze the effects of CNT volume fraction and distribution types, geometrical ratios, environment temperature and surrounding elastic foundation on the buckling loads and postbuckling strength of CNTRC cylindrical shells

PERCEPTIONS OF SCIENCE HIGH SCHOOL STUDENTS TOWARD BLENDED TEACHING

Under the impact of the COVID 19 pandemic, it is a must for education institutes all over the world to incorporate online teaching into their teaching program. In Vietnam, high school teachers and students are now familiar with blended teaching in which students will learn from at least 30% of their lessons online and 70% face-to-face. This research aims at investigating Vietnamese high school students’ perceptions toward the benefits and challenges of blended teaching. Two research questions will be answered (1) “What are high school students’ perceptions toward the benefits of blended teaching?” and (2) “What are high school students’ perceptions toward the challenges of blended teaching?”. There were 200 sciences students (72 participants majoring in Physics, 60 in Chemistry, and 68 in Biology) from 3 high schools for the gifted in Vietnam who participated in the study. The results of the research show that the majority of participants agreed on the benefits and challenges of blended teaching in the context of high school for the gifted in Vietnam. The current study suggests that teachers should have an effective lecture design to help their students acquire science knowledge better in blended classes.  Article visualizations

Testing and modelling of butt-welded connections in thin-walled aluminium structures

The present paper experimentally investigated the mechanical behaviour of butt-welded joints and evaluated suitable numerical approaches for modelling them in thin-walled structures with large shell-based models. Welded connections of both similar and dissimilar materials were first experimentally investigated. Two extruded plates in 6060 and 7003 in temper T6 were used as parent materials for Metal Inert Gas (MIG) welding. Three welded joints were made by combining the two parent materials. Extensive testing was carried out to investigate microstructure, hardness and mechanical stress–strain behaviour of the base materials, heat-affected zones (HAZ) and weld metals. Cross-weld tensile tests with two weld orientations (with respect to the loading direction) were performed to study the load–displacement and fracture behaviour of the welded joints. The experimental results were also used to provide inputs to calibrate and validate shell element-based models simulating the response of welded aluminium structures. Two modelling approaches were investigated. The first approach, which is a conventional “mechanical analysis”, used material model inputs from the experimental testing, assuming uniform HAZ strength. The second modelling approach, which is proposed in this study for engineering applications, relies on inverse modelling of the load–displacement behaviour of similar material cross-weld tension tests to optimize the HAZ and weld properties. The newly proposed modelling approach was further verified based on a set of verification tests of cross-weld tension, using shell-based models with different mesh sizes. A good agreement between numerical and experimental results both in terms of load–displacement and fracture behaviour was obtained, suggesting that the novel modelling approach could be a reliable and efficient method for designing butt-welded aluminium structures.publishedVersio

On-the-Fly Fusion of Large Language Models and Machine Translation

We propose the on-the-fly ensembling of a machine translation model with an LLM, prompted on the same task and input. We perform experiments on 4 language pairs (both directions) with varying data amounts. We find that a slightly weaker-at-translation LLM can improve translations of a NMT model, and ensembling with an LLM can produce better translations than ensembling two stronger MT models. We combine our method with various techniques from LLM prompting, such as in context learning and translation context

Approches d'homogénéisation numériques incrémentales pour le calcul des structures hétérogènes élasto-plastiques et élasto-visco-plastiques

In this work, computational homogenization methods for nonlinear materials with elasto-plastic and elasto-visco-plastic phases are developed, with application to the computation of heterogeneous structures made of these nonlinear materials under cyclic loading. The proposed techniques are based on incremental approaches. In a first part, we develop a methodology to determine the size of an RVE in the nonlinear case for the types of nonlinear behavior mentioned above. For this purpose, a convergence study of the parameters of a semi-analytical incremental constitutive law is carried out. This method allows reducing computational times related to the identification of these parameters and provides a better approximation of the effective constitutive relationship, which can then be used in a structure calculation once identified. In a second part, we propose an incremental computatioal homogenization method in which the originality is to compute directly the effective tangent tensor by superposition of numerical solutions computed by finite elements on an RVE, by taking advantage of the linearization of the problem at each increment. An alternative scheme to classical multilevel finite element techniques (FE2) is then developed, with the advantage of a reduced number of computations to perform on the RVE. The technique is applied to the computation of heterogeneous, nonlinear structures, for anisotropic microstructures or with complex morphologies and for phase with elastoplastic behavior with isotropic and kinematic hardeningCe travail porte sur le développement de méthodes d'homogénéisation numériques pour les matériaux non linéaires élastoplastiques et élasto-visco plastiques avec pour finalité le calcul de structures hétérogènes faite de ces matériaux sous chargements cycliques. Les techniques proposées se basent sur des approches incrémentales. Dans une première partie, nous développons une méthodologie pour déterminer la taille du VER dans le cas non linéaire pour les types de comportements cités précédemment. Pour cela, une étude de la convergence statistique de paramètres d'une loi semi-analytique incrémentale est menée. Cette méthode permet de diminuer les temps de calcul pour l'identification des paramètres et ainsi qu'une meilleure approximation de la loi de comportement effective, qui peut ensuite être utilisée dans un calcul de structure. Dans une deuxième partie, nous proposons une méthode d'homogénéisation numérique incrémentale dans laquelle l'originalité est de calculer le module tangent effectif par superposition de solutions numériques calculées par éléments finis sur le VER, en exploitant la linéarisation du problème à caque incrément. Un schéma alternatif aux techniques telles que la méthode Eléments finis multi niveaux (FE2) est ainsi développé, avec pour avantage un nombre réduit de calculs éléments finis à effectuer sur le VER. La technique est appliquée au calcul de structures hétérogènes non linéaires élastoplastiques, pour des microstructures anisotropes ou de morphologies complexes, et pour des lois de comportement locales élastoplastiques avec écrouissage isotrope et cinématiqu