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Polymeric matrix composite materials are used when high characteristics are needed, good resistance under severe working conditions and low specific weight. Implementing polymeric matrix composite materials, specially, glass reinforced ones, resulted in the substituting of classical materials, whose quantities are more, and more, limited. Composite material products can be obtained to their final shape when manufacturing or, when necessary, can be submitted to further machining processes. Polymeric matrix composite materials can be conventionally machined (cutting, turning, drilling, milling or broaching) or / and non-conventionally machined (laser, ultrasound, etc.). Researches on milling machinability of glass fibers reinforced polymeric composites are at their very beginning, in our country, this paper pointing out some important aspects of research on cutting forces in cylindrical-face milling. There is also presented a data measuring, acquisition and processing system for the experimental model, as well as a real time control scheme designed to determine the measuring errors. Keywords: polymeric matrix, glass fibers, milling, cutting forces, automation system

Atomistic molecular modeling based on forcefield simulations, dissipative particle dynamics (DPD) mesoscale computational method and electrochemical techniques are here used to investigate the mechanical properties, structural morphology and electrochemical response of poly(pyrrole) (PPY )- poly(aniline) (PANI) conductive polymer composite. Computational bulk models of PPY-PANI were implemented at atomistic- and meso-scale and composite films were made available by electropolymerisation on platinum support. Further data concerning mechanical properties, structural morphology and electrochemical response of PPY-PANI composite films were collected by means of in silico investigations, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Both approaches showed that the new formed composite material behave as new material with enhanced characteristics when compared with single component. Concerning material morphology and mechanical properties, simulated bulk systems were homogeneous and their Young’s moduli ranged from 0.04 to 0.475 GPa depending on the material composition. Based on CV measurements, it is stated that the electrochemical activity, reversibility, electrical conductivity and cycle-life stability of the PANI-PPY composite is significantly higher than the pure conducting polymer. Keywords: PPY-PANI films, atomistic- and meso-scale modeling, mechanical testing, electrochemical properties

A series of bismaleimides were used to prepare polymers in an attempt to achieve materials with improved properties. Structurally different bismaleimide compounds were synthesized by the reaction between 3(4)-maleimidobenzoylchloride with various diphenols having or not substituents to the aromatic rings. Polymers based on these compounds were prepared by the Michael addition of diamine to bismaleimides. Fourier transform infrared (FTIR), proton nuclear resonance (1H-NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and atomic force microscopy (AFM) were used to characterize these materials. Keywords: bismaleimide monomers and polymers, thermal characterization

The multilayer structure consisting of alternative sheets of paper and ethylene-propylene elastomers was investigated for electrical applications. The changes in the main electrical characteristics, namely volume resistivity, dielectric loss, permittivity were determined for the evaluation of material stability under accelerated degradation promoted by g irradiation. The satisfactory response of this sandwich structure is illustrated by sample resistivity placed around 1015 W.m, permittivity less 2.025 and dielectric loss not higher than 0.04. The correlation between degradation effects and electrical properties is presented. Keywords: electrical insulation, synthetic rubber, cellulose, multilayer structure

The aim of this work is to obtain and characterize some collagen/hydroxyapatite composite materials obtained by collagen matrix immersion in SBF, for different immersion times. The obtained composite materials were characterize by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy detector (EDS) and complex thermal analysis. The main differences between the composites obtained by different immersion times can be visualized by SEM images. The increasing immersion time lead to a more compact composite material, with lower porosity as exhibited in the recorded SEM images. On the other hand, not only the morphology is changed but also the composition of the composites. At high immersion time, onto the composite materials, sodium chloride (NaCl) crystals can be observed. The presence of NaCl can be easily identified by XRD and, based on the relative characteristic peaks intensity can be quantified. Keywords: SBF immersion, collagen matrix mineralization, morphological changes versus immersion time

When making a denture, a removable partial prosthesis or a removable orthodontic appliance, long term preservation of structure and function require that potential irritating effects are kept at minimum. Polymer manufacturing technology with optimal properties and the material type are essential for a successful treatment. Increasing the biomechanical comportment of polymeric materials implies fiber reinforcing. The different fibers reinforcing products made very difficult the evaluation of their performances and biomechanical properties analysis. The aim of this study was to assess the quality of various polymeric materials used in dental technology and to validate the en face OCT defectoscopic evaluation of polymeric dental prostheses by using scanning electron microscopy (SEM). SEM investigations evidenced the nonlinear aspect of the interface between the polymeric material and the fiber reinforcement and materials defects in some samples. The advantages of the OCT method consist in non-invasiveness and high resolution. In addition, en face OCT investigations permit visualization of the more complex stratified structure at the interface between the polymeric material and the fiber reinforcement. Keywords: polymeric materials, defectoscopy, en face optical coherence tomography, scanning electron microscopy

This paper presents a failure model applicable for unidirectional fibers reinforced composites that point out the fiber-matrix interface role in the mechanics of the failure process. The model is applicable in any plane stress state case. The ABAQUS/Standard finite elements program is used to point out the applicability of failure model. The deformation of a square plate with the dimensions of 100x100 mm, having a hole with the diameter of 50 mm in the middle, was analyzed. The plate is realized from composite materials with unidirectional fibers oriented at an angle of 45o. The visualization and the interpretation of the simulation results have been made with the help of ABAQUS/Viewer module. The obtained diagrams reflect a very good concordance between the predictions of the failure model and the results provided by other models. This confirms the hypothesis on whose basis the unidirectional composite failure model was formulated. Keywords: composite materials, failure, unidirectional fiber glass, polyester resin

In this paper, we obtained experimentally the elasticity modulus and tensile strength, for four types of composite materials made of epoxy resin reinforced with wheat straw, with different spatial orientation for reinforced. Using experimental results, we have obtained the original formulas, for the calculus of tensile strength and elasticity modulus, for the types of specified materials. These relationships are dependent on the percentage of fibers oriented in the direction of request, and which have the length equal with the test sample. In the case in which the percentage is equal to unit, the relations coincide with the ones from unidirectional composite materials. We determined experimentally the coefficient of internal damping and eigen frequencies, for bars embedded at one end and free at the other, made from epoxy resin reinforced with wheat straw, targeted unidirectional, bidirectional and random. Keywords: composite materials, elasticity modulus, tensile strength, damping coefficient, wheat straw

Mesoporous silica was obtained by the acid attack of a serpentinite rock. This material was soaked with acrylonitrile (containing azobisisobutyronitrile as initiator) and the radical polymerization led to the obtaining of polymer inorganic-organic nanocomposites. The polymer nanocomposites were transformed in carbon-silica nanocomposites by the cyclization and graphitization of the carbon chain polymer. Heating the carbon-silica nanocomposite in nitrogen atmosphere allowed the synthesis of silicon nitride, a raw material for special ceramics. Keywords: radical polymerization, nanocomposite, silica, silicon nitride