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The paper presents an algorithm to assess damages in composite structures, based on how natural frequencies of weak-axes bending vibration modes change due to damage. The authors have contrived a correlation between the strain energy stored in a segment of a beam-like structure and the frequency change for that mode if damage occurs on that segment. Finding that the dynamic behavior of composite structures can be best modeled using the share model, which consider the bending moment together with lateral displacement and share deformation, we worked out a relation which gives the frequency shift of all bending modes, involving one coefficient depending on the support type. To evaluate damages, we determine analytically the relative frequency shift as ratio between the frequency change and the natural frequency of the undamaged beam, for the more vibration modes, considering a large number of damage scenarios. Comparing these results with that obtained by measurements on the real structure, it is possible to detect and locate damages with high precision. The method was validated by numerous experiments. Keywords: composite materials, fiber reinforcement, damage detection, natural frequency

The paper presents results on friction and wear, obtained from testing polybutylene terephthalate (PBT) against steel in a block-on-ring tribotester, for dry sliding. There were identified particular processes characterizing the friction couple and the test conditions. Tests were done for three sliding speeds: 0.25 m/s, 0.50 m/s and 0.75 m/s and for five normally applied loads: 1.0 N, 2.5 N, 5.0 N, 10.0 N and 20.0 N. The sliding distance was 7500 m. For comparing reason, there were also done tests for blocks made of PTFE. For PBT-steel couple, the friction coefficient remains in an acceptable range for forces above 2.5 N but it has higher value at the lowest tested values of the force (F=1.0...2.5 N). For evaluating the wear of PBT blocks, there was plotted a wear map using as wear parameter the linear wear intensity as a function of sliding speed and normal force. On this map, there were identified two zones with low values. There were indentified particular processes taking place on the PBT blocks and the steel rings that explain the good tribological behavior of this friction couple. The results of these tests recommend PBT for tribological applications that would function under similar dry regimes. Keywords: friction coefficient, wear, PBT, dry sliding, block-on-ring

The main objective of this paper is to develop a complex experimental investigation and, by this way, to describe and analyze the influence of pulsed Nd: YAG laser cutting main parameters on the process energy consumption. The tested material was a Glass fiber/epoxy composite. The experimental program was performed by two approaches, factorial and classic. The design of experiments allowed the research results presentation as regression polynomial equation, Pareto effects diagram, response surfaces diagrams and single-factorial classic diagrams. A pertinent final discussion gave a global image and proved the validity of developed research. Keywords: design of experiments, pulsed Nd: YAG laser cutting, Glass fiber/epoxy composite, energy consumption ratio

Silk fibroin, from Bombyx mori solutions were electrospun into nanofibers with circular and ribbon like morphology. Diameters of the electrospun fibers were ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation of nanofibers and their morphology were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers morphology depends on the electrospinning parameters and became flattened with ribbon like shape with increasing the electrospinning temperature. The nanofiber diameter increased with the increase in the concentration of silk solution at all electrospinning temperature. Electric field showed different effects on the nanofiber morphology at 25oC. Referring to the literature the probable mechanism responsible for the change of morphology was pointed out. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and its distribution. It was shown that concentration of silk fibroin solution and electrospinning temperature had a significant effect on the fiber diameter. Keywords: biopolymers, scanning electron microscope, morphology, proteins, nanofibers, statistical analysis

This article presents the study of the opportunities and limits of employing nano-ZnO as additive to Paraloid B72 solutions used for consolidation of degraded, frail wood. The experiments were carried out on degraded spruce samples (Picea abies) in different conservation levels that were extracted from a frail wooden element of a massive gateway from the historic centre of Brasov (Romania) during its restoration. In this respect the samples were dimensioned at (20x20x30) mm and divided into three batches according to their initial conservation state: level I, very degraded samples with obvious loss of resistance and cohesion; level II, samples highly degraded but with structural cohesion and level III, samples with little degradation. Two consolidant formulations based on Paraloid B72 were used: a solution of 10% in ethanol and acetone mixture 1/1 (coded C4) and a similar solution modified with nano-ZnO additive in proportion of 2.5 % (coded C4-ZnO-2.5). All the samples were treated by total immersion for 1 hour in the prepared consolidants. The application treatment efficiency was evaluated by determining the consolidant uptake Csp [Kg/m3] and retention WPG [%], while the actual effects of the consolidation procedure were evaluated by determining the compression strength parallel to the grain tc// [MPa] and the water absorption in a total immersion test, WA [%]. Keywords: wood consolidation, Paraloid B72, nano-ZnO, compressive strength, FTIR spectroscopy

This paper analyses the influence of processing temperatures of acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6) and polyoxymethylene (POM) on some mechanical properties when injecting items used in the automotive industry. The ABS specimens were made at the following injection temperatures: 220, 230, 240 and 250°C. The PA 6.6 specimens were made at the following injection temperatures: 280, 290, 300, 310 and 320°C. The POM specimens were made at the following injection temperatures: 180, 190, 200, and 210°C. The mechanical properties were measured using tensile tests, the Izod impact test and the Shore Durometer hardness test. It was observed that for these three polymers, the increase in processing temperature leads to insignificant changes in hardness. The Izod impact strengths of PA 6.6 and POM decrease to a minimum with an increase in processing temperature, while the further increase in processing temperatures leads to an increase in impact strength. Where ABS is concerned, the increase in processing temperature results in an increase in Izod impact strength. The tensile strength at break is influenced by the processing temperature. The highest tensile strength at break for ABS was recorded at 220°C, for PA 6.6 at 310°C and for POM at 200°C. The lowest values were recorded at the lowest and highest processing temperatures. Keywords: acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6), polyoxymethylene (POM), tensile tests, Izod impact test, Shore Durometer hardness test

This work presents a study on the possibility of hydroxyapatite thin layers deposition on porous polyurethane support using biomimetic method, and pyridoxine (vitamin B6) incorporation in this layer. To achieve the formation of hydroxyapatite deposition on the surface of polyurethane and to incorporate the pyridoxine in the apatite layer, two types of biomimetic solutions, i.e. a supersaturated calcification solution (denoted SCS) and a modified SCS solution (denoted M-SCS) were used. The M-SCS solution was prepared by adding in the original SCS solution appropriate quantities of pyridoxine. The hydroxyapatite deposits are investigated by scanning electron microscopy (SEM) and Fourier-transform infrared transmission spectroscopy (FT-IR). The results obtained from SEM images and FT-IR spectra have shown that porous polyurethane/hydroxyapatite scaffolds with an interconnected network were produced, and pyridoxine is incorporated in the apatite layer. Keywords: Hydroxyapatite, polyurethane, pyridoxine, scaffold

The use of polymeric materials to replace metal or wood has become increasingly popular lately in most fields of activity. Specific amounts of reinforcement materials have been included in the structure of these polymeric materials in order to improve their mechanical properties. The increasing popularity of these types of materials was accompanied by the development of different machinery and technologies designed to process them, so as to make them as productive as possible and to achieve inexpensive high performance parts. Natural polyamide 6.6 is a polymeric material noted for its high rigidity, hardness, impact resistance, etc. The reinforcement materials added improve the mechanical properties of this type of material. Our research consisted of a comparative study of the behavior of polyamide reinforced with glass fibers and glass microspheres when subject to different mechanical stresses. The test specimens were processed by injection and relied on an experimental Taguchi plan with six input parameters each of them with two levels. The materials employed to carry out the comparisons designed to determine the mechanical and tribological properties were natural polyamide 6.6 reinforced with 30% glass fibers and 1% furnace black, and natural polyamide 6.6 reinforced with 30% glass microspheres and 1% furnace black used to prevent microsphere agglomerations. Considering all these issues, the actual research was focused on tensile stress vs. tensile strain comparisons at 23oC and 60oC, and on determining the friction coefficient using disc rotation and oscillation, XRD analysis, Scanning Electron Microscopy (SEM) and EDAX analysis. As concerns tensile stresses, high values were recorded both on the 23°C and 60°C tests when polyamide was reinforced with glass fiber. This is also supported by the SEM structure for the two composite materials under survey. The mean value of the disc rotation friction coefficient was lower when glass fiber was used as reinforcement material. This was also the case with the disc oscillation friction coefficient. The diffraction study conducted on the two materials revealed that polyamide 6.6 reinforced with 30% glass fiber did not have an amorphous structure, given the high number of peaks resulted further to diffraction, whereas polyamide 6.6 reinforced with glass microspheres exhibited an amorphous structure and a structure-specific diffraction. The chemical elements spectrum (EDAX analysis) reveals high mass and atomic percentages of C, O, Ca for both composite materials under survey. Keywords: fibers, microspheres, glass, mechanical properties, tribology, spectrum

Waste rubber cause both health and environmental problems and this has forced governments to develop laws for recycling. Using particles of recycled rubber in the domain of soundproofing materials is of major importance from a technical, economical and ecological point of view. In this paper we determine the ability of sound absorption of each obtained material by measuring the sound absorption coefficient depending on frequency, using the impedance tubes. Materials, as composite materials prototype, were made from particles of recycled rubber and a polyurethane binder, in combination with other materials existent on the market (cork of fabric). Keywords: recycled rubber particles, acoustical materials, sound absorption coefficient

It was evaluated, in vitro, the effect of different artificial saliva on the mechanical properties of elastomeric ligatures. A total number of 160 elastomeric ligatures were divided in four groups (n=40 in each group). Three groups were exposed to three types of artificial saliva, (unmodified artificial saliva, with coca cola and with topical fluoride agent), for a period of 28 days. The fourth group (control group) remained unexposed. Tensile load at failure was determined by stretching the ligatures using an Instron Universal Testing Machine, until they fractured. The obtained data was statistically analyzed at a level of significance (p < 0.05). The two-way ANOVA showed significant statistical differences within groups (p < 0.001) and between time intervals (p < 0.005). There were a statistical significant interaction between groups and time on tensile load at failure (p < 0.005). Artificial saliva, Coke and Topical Fluoride seem to cause an increase in force decay of elastomeric ligatures, with a decrease in tensile load at failure over time. Keywords: elastomeric, orthodontics, tensile load