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Polypropylene fiber is widely used as a reinforcing material in composite materials of various engineering projects, because it has high strength and corrosion resistance. In this study, with the purpose of examine the impact of discrete polypropylene fiber on frost resistance of cemented soil, cemented soil treated with polypropylene fiber is used as the research sample. Firstly, the impact of curing time, fiber content and length on the strength of cemented soil has been considered. And then, the frost resistance characteristics of cemented soil reinforced by polypropylene fiber with the content of 0.5% have been investigated. The results show that with the development of curing time, the strength of cemented soil increases logarithmically. By adding an appropriate amount of polypropylene fiber, the strength of the specimen may be improved. In this study, cemented soil reinforced by polypropylene fiber 0.1% in content and 3 mm in length has the best reinforcement effect. After 21 cycles of freezing and thawing processes, a sharp decline in strength of cemented soil without fiber, and the strength loss ratio is up to 45%. There are cracks in the specimens, and some of the specimens have broken off. Differently, after 21 freeze-thaw cycles, the strength of the cemented soil with fiber decreased less, and the strength loss ratios are between 1 and 13%, and there are only small cracks on the surface of specimens. The results show that adding discrete polypropylene fiber is a suitable method to prevent the generation and development of internal cracks in the cemented soil during freezing and thawing, thereby improving the frost resistance. These results can be used as a reference for the application of cemented soil reinforced with fiber in seasonal frozen regions.

By using molecular dynamics, this study evaluates and compares the diffusion coefficients of CH4, CO2, H2, N2 and O2 gas molecules through a polysulfone / carbon nanotube, polysulfone / graphene and polysulfone / carbon nanotube-graphene composite membranes. Mechanical properties of the composites were assessed by performing virtual traction tests and the Young’s moduli exhibits values between 2.59 GPa for polysulfone membrane and 3.87 GPa for polysulfone / carbon nanotube-graphene composite membrane. The latter is found to exhibit superior permeability and mechanical properties, making it a promising device for gas separation.

Two different polyimide structures were synthesized by two-step polycondensation reaction in solution, in the first step using equimolar amounts of one of two aromatic diamine (DDM or MMDA) and one dianhydride (6HDA) in N,N-dimethylacetamide (DMAc) to obtain the poly(amic acids), followed in the second step by thermal imidization. In order to obtain novel polyimide/metal nano hybrid materials, conductive Ni/Cu nanoparticles were embedded on polyimide substrates, using laser ablation technique. The morphology of the resulted thin metal layers was investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results highlighted different surface characteristics of the auto-organized metallic/polymer nanoparticles, depending on the chemical structure of the polyimide substrate, the parameters of the laser ablation setup, the deposition time, the type of the metallic target. The obtained features of these polyimide/metal nano hybrid materials can be employed as an indicator of the possibility of using them for potential applications as conductive circuits or substrates for adhesion control.

Over the time, numerous studies have been reported describing successful pulmonary valve replacement, either with xenografts or allografts, performed in sheep model. In contrast, comparable results have not been achieved yet for aortic valve replacement in orthotopic position, which involves a more difficult surgical technique, high hemodynamic demands for the implanted valve and poor survival of animals undergoing this kind of surgery. To our knowledge, in Romania, these were the first orthotopic allogeneic aortic root implantations using the subcoronary technique, carried out by our team. We established feasible perioperative, anesthetic and surgical protocols, which will be used in future studies to evaluate the in vivo functional performances of decellularized valves compared with autologous adipose derived stem cells seeded valves. Therefore, a unique research core was created, which is currently the only center of this kind in our country, by joining a multidisciplinary team consisting of biomedical engineers, cardiovascular surgeons, anesthesiologists, cardiologists, pathologists, microbiologists and veterinarians, who will continue the research activity in the field of tissue engineering and translate experimental results into clinical activity.

In the last decades as the need for high economical and technical efficiency items/applications became acute, lightweight, high strength and low-cost materials development and investigation emerged as a logical and promising course of action. With high potential for both military and civil sector, the ultra-high molecular weight polyethylene (UHMWPE) is considered a new class of material. Among this class, the Dyneema® HB26 composite is of most interest for the present study. The present paper focuses on the static and dynamic investigation of the HB26 mechanical behavior experiencing an out of plane compressive load. For experimental purposes, using a 15 mm thickness panel two types of samples (cylindrical and cubic samples) were processed. For compression test Instron Testing Machine and the Split Hopkinson Pressure Bar (SHPB) were used. The experimental tests were then compared against the numerical findings highlighting a good consistency.

Because hyaluronic acid (HA) cosmetic gels are the most commonly used gels in the cosmetic industry, the purpose of this study was to develop a new gel formulation of HA in carboxymethyl cellulose sodium (Carmellose, CMC Na), prepared in three different ways and to characterize the gel obtained in terms of texture, pH, thixotropy and decide which preparation method is optimal for obtaining a cosmetic gel. The gel formulations were prepared by dispersing CMC Na in water and glycerol and mixing it in three different ways with HA (at the same time, after gelling and 24 h after gel preparation). The pH, rheological properties and texture of hydrogels were evaluated. The study demonstrated that the formulation prepared with CMC Na has higher viscosity and stability at a pH = 6-9. The viscosity depends on the preparation method of hydrogels, the highest values of the mechanical parameters were recorded in the formulation in which CMC Na and HA were added at the same time. The present study showed that the difference on the texture was realised by the used preparation method. In conclusion the preparation method of a hydrogel with CMC Na 4% and 1% HA has a significant influence on the texture profile and the viscosity characteristics.

Although autologous bone graft is the gold standard in bone reconstruction, the limited volume, the morbidity associated with the donor site, the dificult modelling of complex forms and the unpredictable rate of resorption fuel the researches towards the development of alloplastic materials as bone substitutes.A new fiber reinforced composite (FRC) was developed using 35% combination of monomers bisphenol A glycidylmethacrylate [bis-GMA], urethane dimethacrylate [UDMA], triethylene glycol dimethacrylate [TEGDMA], ) and 65% E-glass fibers (300 g/mp). Sixteen (n=16) male Wistar rats were used for the study. The experimental group (n=12) received intrafemoral implants of FRC. The control group (n=4) received intrafemoral titanium implants. After one month and three months respectively, tissues adjacent to implants were histologically evaluated. The intensity of the bone tissue inflammatory reaction, as well as the presence of the osteoblasts and the newly formed bone on the implant surface were the main criteria assessed. The FRC material determined a similar tissue reaction to Ti specimens, at one- and three-months follow-up. Both materials, inserted in the medullary canal, were surrounded by a fibrous connective tissue capsule, which, as time passed, underwent intramembranous ossification process. Fiber reinforced composite may be considered a promising alternative to titanium implants in critical size defects reconstruction.

The paper presents a numerical study regarding the mechanical response of the body of a freight wagon to the usual loads encountered during service. The main goal of the present research is to investigate the possibility to replace the steel walls of the wagon with walls made of laminated composites. In this way, the total mass of the wagon can be decreased, leaving room for supplementary load of goods. Finite element analyses of the wagon with steel walls is presented first, in order to show that most of the load is taken by the structure of the wagon, while the stresses in the walls are low. Further, composite plates with different thickness are studied to find the minimum value of thickness for which the displacements have values below a certain range. These thicknesses are further considered in the finite element analyses of the entire wagon with composite walls to investigate if the new walls significantly change the stresses in the vehicle structure. It was concluded that the replacement does not alter the stress state in the structure, and, consequently, it is a good solution for diminution of the total mass of the vehicle.

Although a standardized hip joint prosthesis is a quick and easy solution to repair most diseases related to the hip joint, it never satisfies the patient`s personal needs due to the uniqueness of the human anatomy. Femoral hip stem geometry is one of the factors that have an important impact on prosthesis lifespan or the revision surgery frequency that occurs due to postoperative complications, such as impingement or dislocation after THR (Total Hip Replacement). In this sense, the development of a custom hip stem prosthesis starting from a standardized femoral stem can bring benefits to the patient in time, being able to reduce the failure percentage of THR. The purpose of this article is the development of a custom prosthesis based on patient`s CT (Computer Tomographic) scans in order to be 3D printed with biocompatible materials, being able to serve as a study model in both engineering and medicine. Also this study represents a first step in understanding how to apply the unique distribution of mechanical properties in human bone, in order to manufacture a hip prothesis that can mimic them.

Specific heat and thermal linear expansion coefficient of epoxy composites reinforced with carbon, aramid, glass and hybrid fabrics with unfilled and filled stratified matrices were studied. The thermal measurements of specific heat were performed with Differential Scanning Calorimeter (DSC instrument) and those of thermal coefficient of linear expansion were realized with Thermomechanical Analyzer (TMA instrument). It was analyzed the influence of fiber orientation at various angles (±15°, ±30° and ±45°) and the effects of two types of filler mixtures added into polymeric matrix on the thermal behavior of composite materials. It was found that in case of epoxy matrix the added filler mixtures reduced its thermal coefficient of linear expansion and had an insignificant influence on specific heat. In case of epoxy composites reinforced with fabrics, the fiber orientation and fillers addition showed different effects on the investigated thermal parameters in dependence of the used reinforcement types.