Papers by Keyword: Confinement

Abstract: We investigate the possibility to use silicon, titanium and tungsten as bonding materials between a SiC substrate and a SiC layer, a novel substrate for application in high-power electronics. By using transmission electron microscopy, scanning transmission electron microscopy and X-ray scattering techniques, we address the high temperature-induced phase and morphology changes in thin layers composed of these materials and at their interfaces with SiC. For all three materials, we show that the homogenous continuous film created after low temperature deposition transforms into a discontinuous structure following high temperature annealing. All layer’s structures tend to reach an epitaxial relation with the SiC substrates. In contrast to Si layer which preserves its composition, both Ti and W layers are transformed into new phases which were identified. We evidence that these peculiar structural and compositional changes in the layers, which were studied as a function of annealing temperature and time, are related to mechanisms of SiC dissolution and transport of C, Si, Ti, W atoms at the interface. Potential chemical and structural reactions during interface reconstructions are discussed in relation to the experimental findings.

Abstract: This work investigated green fluorescence Organic Light Emitting Diode (OLED) with four hole blocking materials HBMs. Aims to enhance color performance in QD-OLED panels to produces a set of light with red, green, and blue sub-pixels. The HBM examined in this scenario consist of: (4,7-diphenyl-1,10-phenanthroline)Bphen, Tris(8-hydroxyquinoline aluminium)Alq₃, (2,2′,2″-(1, 3,5-benzinetriyl)-tris(1-phényl-1-H-benzimidazole)TPBi, (3-phényl-4(10-naphtyl)-5-phényl-1,2,4-triazole)TAZ. These holes blockings materials have different electron mobility and different hole-blocking barriers. A numerical model based on the drift-diffusion formalism was created to study electron and hole transport in OLEDs. The model includes continuity equations, conduction diffusion current, and the Poisson equation. The simulation showed the performance of each device was affected by these properties of each HBM. The width of the emission zone depends on the HBMs employed, and when the electron mobility increases the recombination zone is wide in the HBL. It was found that the device with Bphen, Alq3, TPBi, and TAZ have electrical and optical characteristics that are respectively: Langevin recombination rate (2.25 x10²⁵ cm^-3s^-1, 1.74 x10²⁵ cm^-3s^-1, 1.04x10²⁵ cm^-3s^-1,1.79x10²⁴ cm^-3s^-1), singlet exciton density (2.87x10¹⁴ cm^-3, 2.2x10¹⁴ cm^-3, 1.31x10¹⁴ cm^-3, 0.22x10¹⁴ cm^-3), luminance (4700 cd/m², 4500 cd/m², 4400 cd/m², 3200 cd/m²). Our study provides a model system to examine the role of hole blocking materials on OLED optoelectronic properties.

Abstract: The electromechanical performances of dielectric elastomers were investigated after the incorporation of the confined permittivity enhancing fillers in bacteria cellulose (BC) into polydimethylsiloxane (PDMS) films. The purpose of this study is to investigate the capability of BC as a confinement matrix for the permittivity enhancing fillers to overcome the low relative permittivity and at the same time to increase the softness of the PDMS films. The metal oxide and silicone oil were confined in BC before being physically mixed with PDMS at different percentages. The results showed that the confined TiO2-BC increased the relative permittivity and at the same time maintained the softness of the PDMS films to some extent. In addition to that, by adding confined silicone oil-BC into the PDMS films, this PDMS based dielectric elastomer (DE) becomes even softer.

Abstract: This paper presents a critical review of the most established analytical models for the prediction of the compressive strength of FRP and FRCM-confined masonry columns. In particular, two types of fibres are analysed, i.e. glass and basalt. A wide dataset available in the literature is used for the application of the analytical models and for the development of parametric analyses useful for the critical comparison of FRP vs. FRCM confinement technique and glass vs. basalt fibres to be adopted as reinforcement of masonry substrate. The effects of stiffness and strength of the reinforcement, the number of reinforcing layers, the compressive strength of masonry and the cross-section shape are investigated.

Abstract: The paper presents compression tests of stocky and slender masonry pillars strengthened in bed joints with PBO fibres and an inorganic matrix. Five stocky pillars and four slender pillars were tested under static loading. Physical models were prepared using lime mortar similar to that used in historical structures. Fibres were applied in the grooves that were made after the mortar setting period in order to recreate real-world conditions. One of the models was subjected to preloading before the strengthening was applied. The failure modes, load-bearing capacity, cracking stresses, stiffness and deformations (longitudinal and transverse) were all determined through experimental testing. Strengthening effectiveness in terms of the increase in load-bearing capacity and stiffness, as well as anti-cracking was determined on the basis of the experimental results. The results obtained for the stocky and slender pillars were also compared, indicating the influence of slenderness on strengthening effectiveness. Special attention was also paid to failure modes and the interaction of the PBO fibres with the bed joint. Methods that strengthen pillars in their bed joints using PBO fibres increase their load-bearing capacity, stiffness and cracking resistance, while maintaining a satisfactory visual appearance which is especially important in heritage structures.

Abstract: This research investigates the efficiency of using Flax Fibers reinforced bio-sourced polymer by comparison to traditional system based on Carbone Fiber Reinforced Epoxy Polymer in order to confine recycled aggregates concrete. Four concrete formulations have been formulated by incorporating recycled aggregates from demolition waste (0%, 30%, 50% and 100%). An air-entraining agent was added to the formulations to achieve the level of 4% occluded air. The main objective is to discuss and to evaluate the effectiveness of confining them using bio-sourced composite by comparison to traditional ones. To hit this target, the developed approaches are both experimental and analytical. The first part is experimental and aimed to characterize the mechanical behavior of the materials: the composites used in the confining process the unconfined concrete (effect of incorporating recycled aggregates on the overall mechanical characteristics). We establish that bio-sourced composites are efficient in strengthening recycled aggregates concrete especially if they are air-entrained. The second part of this work is dedicated to analytical modeling of mechanical behavior of confined concrete with composite under compression based on Mander’s model. The input parameters of the model were modified to consider the rate of recycled aggregates incorporation. Comparison between experimental results and the modified Mandel’s Model is satisfactory.

Abstract: The models are predicting and analyzing on compressive and flexural testing by considering fiber reinforcement embedded in confinement concrete. In this work, steel 4340 fiber with high aspect ratio was developed in unique random spline shape and randomly disperse in confinement concrete. Fibers designed in 15.5mm of average length and amount were varied in range of 50 to 200 and 250 to 1000 for compressive and flexural testing, respectively. Both varied orientation and random dispersion of fiber were developed using MATLAB before embedded and analyzed in Ansys Workbench. The finite element model was validated in initial results on plain concrete prior study in influence of confining and fibers to structure. The model proposed showed that confining reinforcement increasing ductility and large deflections in structure testing. In addition, fibers as reinforcement slightly increases in strength for both compressive and flexural in certain number. These method reinforcement was help warning of failure prior to complete failure that use in construction material.

Abstract: Existing masonry columns are often susceptible to cracking due to overloading. Moreover, their fragility under earthquakes’ forces is of particular concern in seismic-prone regions. In order to mitigate these structural deficiencies, Fiber Reinforced Polymers (FRPs) are commonly used for external confinement. Full-jacketing, by means of FRP-wrapping is recognized to be very effective in improving the load bearing capacity and the ductility of masonry columns. Unfortunately, long-term effects seem to be detrimental for the masonry core, since its breathability is obstructed by the polymeric resin. Thus, a discontinuous application of the FRP-confinement appears to be more indicated in stone-masonry columns, allowing the humidity cycles to recur. On the other hand, the discontinuous wrapping negatively affects the confinement effectiveness, since both confined and unconfined masonry regions participate in the bearing capacity. In this sense, the present research is aimed to study the discontinuous confinement of half-scale masonry columns by means of Carbon-FRP strips. Unconfined and confined specimens were tested under uniaxial compression. The CFRP-confinement was studied by investigating the lateral strain in the confined and unconfined portions of the specimens. The results are reported and discussed in the paper in terms of failure modes, axial stress-strain and axial stress versus lateral strain relationships. The outcomes are reasonably convenient for a proper analytical interpretation of the phenomenon.

Abstract: A new generation of composite materials in the form of Fiber Reinforced Cementitious Matrix (FRCM) was recently used to strengthen the masonry structures. Six small scale masonry columns were tested under monotonic concentric load until collapse; three columns were confined with PBO (short of polyparafenilenbenzobisoxazole)-FRCM jackets, two with basalt–FRCM jackets while an unconfined column was used as a control specimen. The masonry columns investigated have a rectangular cross section 250x250 mm among the overall length equal to 770 mm, and the corners were rounded to a radius of 20 mm. The analysis was conducted varying the confinement ratio i.e. the number of fabric layers for each FRCM system. Obtained results allow evidencing the effectiveness of the confinement and the effect n-layer on the structural response of the masonry columns.

Abstract: The Fabric Reinforced Cementitious Matrices (FRCMs) are promising strengthening solution for existing masonry since the inorganic matrix is considerably compatible with historical substrates. Nevertheless, the matrix is responsible for the stress-transfer in composites so, in case of poor-quality mortar, the effectiveness of the strengthening can be limited or even compromised. For this reason, a few studies have been targeted to this aspect in the recent past, while numerical investigations are still limited. The present paper refers to a Finite Element (FE) analysis of masonry columns confined with FRCM composites developed by Abaqus-code and based on the macro-model approach. At this scope, available experimental results were used for the calibration regarding different types of the matrix (lime and cement based) for FRCM-confinement. The model was performed by using the Plastic (P) and the Concrete Damage Plasticity (CDP) material constitutive laws. The FRCM-strengthened system was preliminary modeled as a homogenous elastic material until failure. Typical failures of FRCM-systems are the detachment of the matrix from the substrate, slippage of the fibers within the embedding matrix, detachment of the composite strip at the fabric-matrix interface and fiber rupture. In this study, a perfect bond was considered for the interaction between the masonry column and the external reinforcement according to the experimental observations (calibration specimens). The parametric analysis allowed to evidence the influence of the mechanical and geometrical parameters on the structural performances of the FRCM-system in confining column.