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Determining the dynamic properties in the frequency domain of aircraft structural elements is a very important aspect taken into account nowadays by aircraft manufacturers. One of the helicopters most exposed element to structural vibrations is the rotor blade, thus making its construction and the material choice a very important decision. Finite element methods can be used to assess the vibrational properties of such elements, in order to prove their airworthiness. The main objective of the article is to study how the use of different materials affects the structural behavior of the helicopter tail rotor blade, with regard to the frequencies at which these structures are prone to vibrate. The blade profile is the NACA0012 symmetric airfoil used on the IAR330 helicopter tail rotor blade and the main objective is to identify the best inner core material, while highlighting the importance of polymeric materials.

The low velocity impact response of hybrid epoxy composites reinforced with plain weave fabrics, ply orientation at various angles and filled stratified matrix was analyzed in this study. The hybrid epoxy composites were subjected to impact tests at 45J and 90J of energy levels with drop weight impact machine. The damaged areas were investigated by visual inspection of impacted and non-impacted surfaces and by tomographic images. It was found that the replacement of certain carbon inner plies with glass ones and the modification of fiber orientation improved the damage resistance of the hybrid composites with aramid outer layers subjected to impact loading at 45J of energy level.

The amniotic membrane is a readily available biomaterial with an important potential for tissue regeneration in dermatology and ophtalmology, with anti-inflammatory and anti-microbial properties. The extracellular matrix of the amniotic membrane is composed mainly of collagen, fibronectin and laminin. The purpose of our study was to investigate the structural modifications of collagen extracellular matrix of amniotic membrane upon interaction with two different antibiotics, frequently used in surgical and post- surgical procedure, respectively ciprofloxacin and gentamicin. SEM micrographs evidenced the ultrastructure features of dried amniotic membrane, with laminar structure, flexible, transparent, with no blood vesels or nerves. FTIR spectroscopy combined with deconvolution techniques was applied with the aim to determine the extent of denaturation upon treatment with different antibiotics. By spectral analysis, we concluded that gentamicin treatment is more favorable compared to ciprofloxacin, as the denaturation process is reflected by the lower sheet/turns ratio of the secondary structure composition.

Expanded polystyrene (EPS) is used in a variety of applications due to its characteristics, light weight, good thermal insulation and durability. Expanded polystyrene, when used to insulate buildings, undergoes various mechanical stresses, such as: compression stresses, bending stresses, dynamic stresses or shock stresses. This paper presents the results of three-point compression and bending tests for four types of polystyrene (EPS-50, EPS-80, EPS-100 and EPS-120) at different speeds. Based on the data resulting from the compression tests, the theoretical mathematical model was determined, which can be used both for determining the theoretical mechanical characteristics and for modelling the EPS properties in numerical simulations.

The paper deals with destructive testing of “new” group of material - Wood Plastic Composite (in short WPC). WPC emerging from a fusion of two different kinds of components - thermoplastics matrix and natural reinforcement (fibres or flour). Natural fibres offer several advantages - they are renewable, inexpensive, low-density, good isolate a sound and low cost. These components are mixed under the influence of high temperature and then pressed to make various shapes. This material contains cracks localized on the interface between the wood and plastic. These cracks occurred due to inhomogeneity of WPC and affected mechanical properties of final WPC product. The testing of mechanical properties (tensile test and bending test) were determinate in VUHZ Dobra (Ostrava) - following the ISO standards. Significant differences between mechanical properties after testing were caused by non-perfect encapsulation between components and non-homogeneity of materials.

The additive manufacturing technology has made its debut in the industrial field about 30 years ago, when prototyped parts were usually used at the 3D printing stage during fabrication, to give the end customer a truthful concept of how a part will looks when conventional manufacturing techniques were used for final part fabrication. Because of the increasing demand for non-toxic, biodegradable materials and products, human society is always searching for new materials with specific applications, which are able to fulfill the above-mentioned requirements. Consequently, it is essential to identify the qualities of these materials and their behavior when subjected to various external factors, in order to find their optimal solutions for application in various domains. Manufacturing parts from biodegradable materials by 3D printing represents a major concern of industry specialists. The 3D printing process involves several parameters whose influence on the sample functional characteristics is a topical issue. In this paper are determined influences of certain technological parameters (thickness of the layer, filling speed, and part orientation on the printing bed) on some mechanical properties (tensile strength, structure, thermal analysis by DSC, and friction coefficient). Experiments were performed on specimens made of three materials: PLA, HD PLA Green, and Impact PLA Gray. A complete factorial experimental plan was used with three input parameters on two levels. Each experiment was repeated three times following the process stability. The obtained mean values of the tensile test were used in the analysis. The analysis was performed with the MiniTab application, which allowed the parameters hierarchy by influencing each mechanical characteristic studied, model development, and optimum values setting.

The paper aimed to reveal, qualitatively and quantitatively, the modifications suffered by the PLA during the complex heating cycle specific to the 3D printing followed by laser marking. The obtained results showed that the melting point of the PLA decreases from 162.2oC (which is specific to PLA filament) to 153.1oC after the 3D printing process and to 149.7oC after the laser heating. The glass transition suffered the same lowering after the printing process but an important increasing after the laser heating. The elastic modulus evolution proved a decreasing of the plasticity and that is hapenning when the material suffers an increasing of its rigidity. The elongation viscosity was analyzed and its values were decreasing with the increasing of the temperature that happened on the material. The decreasing was produced by the reduction of the elasticity, when the chain branches are decreasing their length. The decreasing is more pronounced with the increasing of the temperature. The ratio between the loss modulus to the storage modulus and quantifies the way in which the PLA absorbs and disperses energy moves its peak from 65oC (curve specific to the PLA filament) to 45oC (curve specific to the last layer deposited by 3D printing process and re-heated by laser beam for marking). The peak means the lowest storage modulus, which is a measure of elastic response of a material, so the transition from glass to high elasticity moves to the lower temperatures.

Bisphenol-A (BPA) is widely spread among the endocrine-disrupting chemicals (EDCs). Different hormone derivates or various organochlorinated pesticides are industrial human-made “plastics.” EDCs are ubiquitary used in the modern world, and their impact on human health has been intensively studied in the last decades. BPA is used as a representative model for endocrine disruption mechanisms; it represents a critical element of producing polycarbonate plastics and epoxy resins, necessary for the manufacture of beverage or food containers, various personal-care products or dental industry products. Environmental exposure to BPA or other EDCs has resulted in functional or morphological drastically alterations of the genital tract or mammary gland that lead to earlier onset of different diseases, reduce fertility, or inducing prostate cancer. All the above have been observed via multiple in vitro analyses on human cells or in vitro analyses on animal models, especially rats. BPA causes prostate cancer through a sum o mechanisms. It increases the activation of various signaling pathways (Erk or Akt kinase), steroidal receptors recruiting chromatin, derived activity of different histone-modifying enzymes, transcription of various androgen receptor mutants detected in prostate cancer or acting via a pro-inflammatory mechanism that leads to prostate cancer progression once installed. Other EDCs such as different dioxins, cadmium, or inorganic arsenic are also incriminating in the neoplastic transformation of the prostate. This review aims to evaluate the current knowledge on this topic. Most of the authors agree on the carcinogenetic effects of these compounds. Extensive in vivo research on humans is imperative for a better and more accurate understanding of “plastics” impact.

In this paper it is presented a comparative theoretical study - performed by finite element analysis (FEA), of the tension state that appears at the level of the spine, as well as in the areas adjacent to it, under the following conditions: a) the existence of a comminutive fracture at the level of the vertebra T11; b) of the external immobilization of the body through a Lombax orthesis (LO) or of the internal immobilization of the column by means of a spinal fixator (SF); c) of performing some basic flexion or extension movements. In this study, both flexural force and extension force varied on three levels. The results of the comparative theoretical study were supplemented with the clinical observations obtained from a number of 52 patients who had suffered comminutive fractures in the T11 vertebra and who were treated - by external immobilization, in the Lombax orthesis or were surgically treated - by applying a trapped spinal fixator on the T10-T12 vertebrae. The study had demonstrated that, by immobilizing the body in the Lombax orthesis, following the application of the flexion or extension movement, the mobility of the body is low, the bone fragments move less distances by about 12% against to their displacement under the condition of immobilizing the column by a spinal fixator. Although, in the latter case, the displacements of the bone fragments are greater, the elastic behaviour of the spinal fixator determines the returning of the fragments and of the spine to the initial position as well as the distance between the vertebrae. Clinical investigations on patients treated by external immobilization of the body in the Lombax orthesis show that the values of the local kyphosis angle (LKA) are about 30% lower than the values of the same parameter obtained under the surgical treatment.

The concept of ballistic protection is a subject of great importance and is defined as representing all the capabilities of the military vehicle to withstand attacks, in order to ensure protection of the crew during the missions. The projectile-plate impact research must answer a series of questions on designer or fighter behalf, among which the most important would be whether the bullet penetrates or perforates and whether the velocity after the perforation ensures a lethal effect on the personnel. The current paper presents the numerical evaluation of the working together of aluminum layers with plastic materials in a multilayer structure with honeycomb core, on impact with a rigid projectile. Plastic materials have revolutionized many industries and they are increasingly used due to their main properties, low mass and high strength. The research included the use of plastics, the positioning within the panel and the study of the two constructive versions of the structure, with coupled and uncoupled layers. Post-processing model and interpretation of the results are offered and these could be enriched and customized for other situations, similar or less similar, implicitly, the method is provided, finding a quick answer to certain questions.