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Implementation of composite materials, especially of glass fibers reinforced ones, lead to replacement of classic materials, whose supplies are more and more limited. The machinability, as well as the machining procedures, of polymeric composites depend on various factors, such as matrix and reinforcing element types; the orientation of reinforcing elements, manufacturing method, etc. Thermal phenomena, occurring while machining, are very important, because the temperature into the cutting zone must not exceed certain value corresponding to vitrifying temperature. So, this paper presents the most important aspects required in order to obtain a mathematical model of temperature, as function of machining parameters, in cylindrical – face milling of glass fibers reinforced polymeric composites. Keywords: polymeric composite, glass fibres, milling, regression function

This paper presents the influence of the processing temperatures on the physico – mechanical properties of PC used in injection molding of high performance sport products. The samples (test-pieces) were obtained by processing PC at the following temperatures: 280°C, 295°C, 310°C, 325°C and 340°C. It was established that the pressure in the mold decreases as the processing temperature rises. Further, thermal analyses were performed (TG, DSC, and DMA) and it was noticed that the processing temperature had an influence on the thermal stability of the polymer and on the activation energy (Ea) of the glass transition phase, but the glass transition temperatures Tg were slightly influenced by the processing temperature. Keywords: polycarbonate, injection molding, TG, DSC, DMA

The paper shows a series of data concerning the formation and lignin nature of polymeric deposits built up at the beechwood pre-hydrolysis. By means of elemental compostion, data limit formulas (empiric) of deposits have been calculated also emphasizing the special influence of hidromodule over the structure of deposits. The second part of the paper shows aspects related to the recovery of lignin polymeric deposits in order to synthetize a lignin-phenol-formladehyde resin, useful to the wood processing sector as well as the energy sector. Keywords: pre-hydrolysis, beech, limit formulas (empiric), lignin-phenol-formaldehyde resins

Functional polyamides with hydroxyl pendant groups were prepared by the direct polycondensation of 5,5`-methylene-bissalicylic acid, with various diamines (p-phenylenediamine, 4,4’-oxydianiline and 4,4’-methylenedianiline) in N-methyl-2-pyrrolidone, using triphenyl phosphite and pyridine as condensing agents. The resulting polymers were chemically modified with 4-maleimidobenzoyl chloride, resulting in polyamides with maleimide pendant groups. The polymer structures were confirmed by elemental analysis data and spectroscopic (IR, 1H-NMR) characterizations. Their inherent viscosities were in the range of 0.22 to 0.34 dlg-1. The polymers were soluble in dipolar aprotic solvents such as dimethylsulfoxide, dimethylformamide, and were thermally stable up to 314 °C. The chemically modified polyamides exhibited better solubility and thermal stability than their unmodified counterparts. Keywords: polyamide, maleimide, Yamazaki-Higashi polycondensation, reactive polymers

The aim of the present work is to investigate the effect of different stress levels on the creep and recovery behaviour of polymer-matrix composites. Four hours creep followed by two hours recovery tests were performed to woven GFRP specimens at five different stress levels corresponding to five different percentages of ultimate static strength. Since the behaviour was linear viscoelastic, a four element viscoelastic model was applied. In addition, the viscoelastic behaviour observed was correlated with the degree of damage generated due to creep and its variation with the applied stress levels. Keywords: creep, recovery, linear viscoelastic behaviour, four parameter model

Both the theoretic elements of an interferometric method for the refractive index determination based on a Fabry-Perot etalon and the procedure of the Fabry-Perot cell obtaining are described in this paper. The results obtained by this method for PVA isotropic foils and for PVA foils including small amounts of potassium iodide are given here. Keywords: PVA, FPE, refractive index, isotropic materials

Full denture casting currently represents a technological alternative. The casting system we tested usually uses reversible hydrocolloids for investing wax patterns. Besides the system’s own advantages, the authors also noticed certain errors consecutive to casting, materialized in lack of substance and the development of porosities on the mucosal facets of the complete denture bases. Keywords: casting, full dentures, errors

The aim of the experimental study described in this paper was Lamb wave method evaluation for damage/defects detection of epoxi/glass composites. Can be used piezoelectric transducers - actuator/sensor - glued on the surface of investigated composite, using transmission mode. The chosen control parameter was the sensor signal attenuation because of defects that exists in examinated samples. The proposed monitoring system was efficiently in the detection of damage/defects such as holes, allowing for damage/defect size estimation. Keywords: composites damages detection, Lamb wave

Ultrasonic waveform is one of the parameters that characterize a material.Thus, in this paper, the authors aim to visualize and characterize different waveforms of a POLYPROPENE FOIL F-401. The experiment is made with non contact transducers (the resonance frequency is 50 MHz) by applying the method through transmission. There are determined the acoustical and spectral parameters such as the propagation velocity, the time of the flight of the ultrasound, the pulse width, the bandwidth, the peak frequency and its amplitude. The waveform without the sample beeing placed between the transducers (transmitter-receiver) is considered to be the reference. Then, the sample is placed between the transducers at different distances from the transmitter. These waveforms are compared and analysed relative to the reference. Keywords:ultrasounds, non-contact transducers, polymers, ultrasounds waveforms

The objective of this study is to compare the results obtained while determining the amount of residual monomer in three samples of acrylic resin in the first 24 hours after getting done the prostheses in the dental lab with the results of patch-tests performed on three subjects, after they have worn dentures for three months. Keywords: patch-test, acrylic resin, residual monomer, allergenic potential