Papers by Keyword: Matrices

Abstract: Euler equation of column stability can be expressed by the finite differential form. According to the real requirements of column stability, coefficient matrices the differential equations are solved by the matrices calculation method. Then, the critical stress of column stability of constant section of the simply supported beams is obtained. The results are compared with the analytical results. The error analysis is also presented, which includes the error reasons and measures for diminishing the error. The proposed method has positive meaning for the variable section beams.

Abstract: Due to ecological and sustainability constraints, in late years we see great achievements in green technology in the field of materials science. The development of high-performance biocomposites (made from natural resources) is increasing worldwide. The challenge in working with natural fiber reinforced composites is the large spectrum of possibilities for making them.Biocomposites properties are influenced by a number of variables, including the fiber type, environmental conditions (where the plant fibers are sourced), processing methods, and any modification of the fiber. It is well known that recently exists a large interest in the industrial applications of composites containing biofibers reinforced with biopolymers. The characteristics of reinforcing fibers used in biocomposites, including source, type, structure, composition, as well as mechanical properties, will be reviewed. The variety of biocomposite processing techniques as well as the factors (moisture content, fiber type and content, coupling agents and their influence on composites properties) affecting these processes will be discussed.Techniques for processing the natural fiber reinforced composites will be discussed based on thermoplastic matrices (compression molding, extrusion, injection molding, and thermoforming), and thermosets (resin transfermolding, sheet molding compound). Their influence on mechanical performance (tensile, flexural and impact properties) will be evaluated. Finally, the work will conclude with recent developments and future trends of biocomposites.

Abstract: Introduction. The osteoconductive materials are very important in the bone regeneration procedures. The aim of this paper is to evaluate the interface between the old bone and the new regenerated one.Materials and methods. Ten rat femurs were used for this investigation. Under strict supervision, ten holes were drilled in the rat femurs and then filled with Bio-Oss® (Geistlich, Wolhusen, Switzerland). matrix. The samples were obtained after 3 month from the procedure and were investigated by MicroCT. A common Synchrotron Radiation X-Ray micro-CT experiment was performed at the SYRMEP Beamline of the ELETTRA Synchrotron Radiation Facility (Trieste, Italy). The 900 radiographic projections were acquired with a beam energy of 29 keV over 180° (0.2 degrees step) with a resolution of 9μm. A sample – detector distance of 16 cm was considered. The tomographic reconstruction was performed by means of the common filtered back-projection method. The 3D reconstructions were obtained at the University of Ancona using specific software, VGStudio Max.Results: The synchrotron offered 900 microCT files that were used to make the 3D reconstruction of the bone. After tomographic reconstruction, 3D renderings of obtained data may be made by electronically stacking up the slices. These 3D volumes may be also sectioned in arbitrary ways, zoomed and rotated in order to locate better the individual details. While the 2D slice images and 3D renderings are very useful for making qualitative observations of an internal concrete structure, the real benefit is the quantitative information that can be extracted from the 3D datasets.The reconstructions allow observing the normal rat bone, the new regenerated bone and also the rest of nonactivated matrix of Bio-Oss® (Geistlich, Wolhusen, Switzerland). The system permits to make measurements in order to quantify the volume of the new bone formation and also the status of the bone defect, in order to define the healing process.Conclusions: The MicroCT method proves to be an important imagistic tool for nondestructive evaluation of the interface between the new regenerated bone and the old one from the rat femurs. This method allows numerical quantification of the new regenerated bone and define the healing bone process.

Abstract: The performances of composite materials are influenced by the properties of the matrix used. The latter ensures the desired form and the protection of the reinforcements against the external attacks. This work comprises a comparative study between laminates developed with different matrices in epoxy resin. Their characterization has to choose the best matrix able to give best results in static and dynamic tests. The resins used are provided by Granitex Algéria and which are primary Médapoxy STR resins, Médapoxy inject 812 and Médapoxy Al resin. Hence, the results of tensile tests prove a fragility of the AL resin which influences the maximal constraint of traction compared to the STR primary resin. Furthermore, Inject 812 resin shows very limited mechanical properties due to the changes of the epoxy network with the addition of diluents which has significantly decreased its viscosity.

Abstract: Retracted article: The mode matching method is applied to analyze generalized ridged waveguides. The tangential fields in each region are expressed in terms of the product of several matrices, i.e., a functional matrix about x-F(x), a functional matrix about y-G(y) and a column vector of amplitudes. The boundary conditions are transformed into a set of linear equations by taking the inner products of each element of G(y) with weight functions. Two types of ridged waveguide are calculated to validate the theory. Several new modes not reported in previous analysis are presented.

Abstract: The mode matching method is applied to analyze generalized ridged waveguides. The tangential fields in each region are expressed in terms of the product of several matrices, i.e., a functional matrix about x-F(x), a functional matrix about y-G(y) and a column vector of amplitudes. The boundary conditions are transformed into a set of linear equations by taking the inner products of each element of G(y) with weight functions. Two types of ridged waveguide are calculated to validate the theory. Several new modes not reported in previous analysis are presented.

Abstract: The purpose of this paper is to discuss the stability of linear system with constant coefficients. A simple practical criterion for the stability of linear system with constant coefficients is obtained.

Abstract: Main applications for preceramic polymers (precursors) are ceramic fibres, ceramic matrices and coatings. The requirements for the polymer are determined by the intended application and differ from a cross-linkable liquid to meltable and curable or unmeltable but soluble solid. For applying these precursors on a larger scale, they must be processable by conventional polymer processing techniques. Furthermore, the starting material should be cheap and readily available, and the synthesis should be uncomplicated. Considering these criteria, specially tailored precursors in the system Si-C-N (silazanes) were synthesized in a laboratory scale by ammonolysis of different chlorosilanes. After investigating the properties suitable precursors were produced in a pilot plant (approx. 5 kg). Variation of both the functional groups of the chlorosilane educts and the synthesis conditions lead to precursors with tailored properties (liquid, solid, soluble) and a special cross-linking behaviour (catalyst, initiator, electron-beam). Selected applications with the special precursors were presented for producing ceramic SiCN-fibres via melt-spinning also with a precursor modified with multi-walled carbon nanotubes as well as for processing a new kind of metal-ceramic gradient compound by reaction of SiCN-precursors with Ti-powders during pyrolysis.