Mircea Cristian Dudescu

Versatile self-assembled graphene oxide membranes obtained under ambient conditions by using a water–ethanol suspension

Nowadays there is a special interest in synthesising well-controlled self-generated graphene oxide (GO) membranes by scalable, cheap, mild and non-toxic synthesis pathways without negatively affecting their remarkable properties. Keeping this in mind, in this study we report a low cost and scalable pathway that can be used for preparing free-standing GO membranes by a self-assembly process under ambient conditions at an air–liquid interface of an isopycnic sorted GO water–ethanol fraction. The precursor GO suspension used for the preparation of this membrane-forming fraction is obtained by subjecting graphite to a more active-protected oxidative exfoliation, in which non-toxic and non-hazardous gases are generated. To improve the exfoliation and to obtain the isopycnic separation of well-defined GO fractions, ultrasonication and centrifugation are used. The prepared self-assembled GO membranes with controllable thickness are strong enough to be harvested in a simple way. The tunability of the morphological, structural and optical properties of the membranes is obtained by varying the self-assembly time. A structural model for the membrane formation via the self-assembly process is also proposed. Since during the self-assembly process mild conditions and non-toxic components are used, this method can be successfully applied in specific areas like the fabrication of biohybrid platforms or environmentally friendly devices.

Obtaining and Characterizing Alginate/k-Carrageenan Hydrogel Cross-Linked with Adipic Dihydrazide

The aim of this paper is obtaining and characterizing hydrogels based on different ratios of oxidized alginate (oA) and k-carrageenan (C), chemically cross-linked with adipic dihydrazide (adh). The alginate (A) was first oxidized with sodium metaperiodate in order to transform it into the dialdehyde derivative, a more reactive compound than alginate. A known procedure for oxidation of alginate with sodium metaperiodate in ethanol-water in order to improve alginate reactivity by transforming the hydroxyl end-groups into dialdehyde was used, preceded by a partially cleavage of the alginate chains. In the second stage, the mixture of dialdehydic derivative of oxidized alginate, k-carrageenan and glycerol subjected to reaction with adipic dihydrazide leads to a Semi-Interpenetrated Network covalently cross-linked alginate/k-carrageenan hydrogel (oACadh), based on the dihydrazone compound which is responsible for the chemical cross-linking. Pure alginate, k-carrageenan, oxidized alginate, adipic dihydrazide and the cross-linked hydrogel were characterized by: FTIR, XRD, and SEM.

V-Beam Thermal Actuator’s Performance Analysis Using Digital Image Correlation

This paper analyses the influence of the V-beam thermal actuator’s geometrical parameters on its mechanical behavior. Experimental measurements were performed using Digital Image Correlation (DIC), which is a gray scale value tracking algorithm that evaluates the position shift of a pixel between at least two images taken at different deformation stages. These results are compared to multi-physics simulation data obtained using Finite Element Analysis (FEA) as well as to analytical values based on the electro-thermal and thermo-mechanical presented models.

Research on Producing Complex Metal Parts with Lattice Structure by Selective Laser Melting

This study evaluates the manufacturability and performances of periodic cellular lattice structures designed by repeating a cubic unit cell and produced by SLM using titanium powder. The effects of unit cell size on the manufacturability, density, compression and bending properties of the manufactured cellular lattice structures were investigated. Lattice structures manufactured with various unit cell sizes ranging from 0.5 to 1.2 mm could be produced free of defects by the SLM process, with a novel type of supports. By the increasing of the cell size, a decrease of the applied load together with an enhancement of the flexure extension were observed. Specimens with a cell size higher than 1 mm manifested an excellent flexibility by flexure tests.

Calibration of a Shear Specimen

Different geometries of shear test specimens were experimentally and numerically investigated. They are used for calibration of a virtual model, to be used for sheet metal blanking. Different specimen configurations were simulated in order to determine the strain and stress fields and the potential of producing pure shear failure. Tensile and shear tests were performed using DC01 steel material. The experimental data are used later to calibrate a material with Johnson-Cook elastic-plastic model.

EVALUATION OF THE MECHANICAL PROPERTIES AND SURFACE TOPOGRAPHY OF AS-RECEIVED, IMERSSED AND AS-RETRIEVED ORTHODONTIC ARCHWIRES

Background and aims This experimental study mainly aims at comparing the most important mechanical properties of the new orthodontic archwires, those immersed in fluorinated solution, the as-retrieved ones and the intra-oral used ones. Methods A total of 270 arch wires were tested, using tensile testing and three-point bending tests. The tested archwires were made of Stainless Steel, Nickel Titanium, Beta-Titanium and physiognomic covered Nickel Titanium. The tested archwires were subjected to three types of treatments: immersion into fluorinated solution, immersion into carbonated drinks and intra-oral use. Results The immersion caused variations of the activation and deactivation forces of all arch wires. The most affected arch wires, in terms of bending characteristics, were the intra-oral used ones. Conclusions The alteration of mechanical properties of the orthodontic arch wires by their immersion into fluorinated solutions and soft drinks could not be statistically demonstrated.

Micro-tweezers Based on V-Beam Thermal Actuator

This paper presents some modeling aspects regarding an application of the V-beam thermal actuator in micro-manipulation. The influence of the Micro-tweezers’ geometrical parameters on the output gripping force is analyzed in order to provide the basis on the future design of some task oriented structures. Numerical simulations are performed on the complete V-beam thermal actuator - Micro-tweezers assembly in order to evaluate the proposed model. The results provided by the two approaches on this problem proved to be in good agreement. As referred to in the paper, the V-beam thermal actuator’s behavior as a separate entity has been previously investigated by both numerical and experimental methods.This paper presents some modeling aspects regarding an application of the V-beam thermal actuator in micro-manipulation. The influence of the Micro-tweezers’ geometrical parameters on the output gripping force is analyzed in order to provide the basis on the future design of some task oriented structures. Numerical simulations are performed on the complete V-beam thermal actuator - Micro-tweezers assembly in order to evaluate the proposed model. The results provided by the two approaches on this problem proved to be in good agreement. As referred to in the paper, the V-beam thermal actuator’s behavior as a separate entity has been previously investigated by both numerical and experimental methods.

Experimental Validation of a Finite Element Model of an Osteoporotic Human Femoral Bone Using Strain Gauge Measurement

The complications of fractures caused by osteoporosis have a mortality rate of 15-20 % in elderly people, leading to severe physical disability and long term home care [1]. Although currently, the technology that allows us to prevent osteoporosis and fractures caused by this disease exists, the statistics are concerning and can be considered basis for further research regarding this pathology of the bone tissue. This paper aims to address this issue form an engineering perspective by achieving experimental validation of a finite element model of an osteoporotic human femoral bone using strain gauge measurement for an in vitro analysis. A Computer Aided Design (CAD) model based on a CT of a human femoral bone was then used in a numerical analysis. The material constants used are taken from the literature and have been validated experimentally by strain gauge technique.