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Poly(methyl methacrylate) (PMMA) has a broad spectrum of uses, especially in medical applications. The role of fine-grained alumina particles of PMMA composites was investigated in this study. The composites were based on PMMA modified with dimethyl itaconate (DMI) as a matrix and alumina particles (Al2O3) and alumina doped with iron (Al2O3-Fe) modified with 3-aminopropyl-trimethoxysilane (AM) and flax oil fatty acid methyl esters (biodiesel) as reinforcements. Three particle sizes were measured (~0.4, ~0.6 and ~1.2 μm). The highest thermal conductivity values were measured for the composite 5 wt.% Al2O3-Fe-AM. With the addition of 3 wt.% Al2O3-AM to the PMMA/DMI matrix, mechanical properties were improved (tensile strength, strain, and modulus of elasticity). An artificial neural network model based on the Broyden-Fletcher-Goldfarb-Shanno iterative algorithm was investigated for prediction of thermal conductivity and mechanical properties of the composites showing satisfactory results. This is relevant for applications for optimization of dental materials to produce dentures, which were exposed to variations in temperature during the application.

Thermal properties of acrylate-based composite combined with alumina-based particles were investigated. The composites were made of poly (methyl methacrylate) (PMMA) modified with dimethyl itaconate (DMI) as a matrix. Neat alumina particles (Al2O3) and alumina doped with iron oxide (Al2O3-Fe) modified with 3-aminopropyl-trimethoxylane (AM) and flax oil fatty acid methyl esters (biodiesel - BD) were used as reinforcement. Thermal conductivity measurements showed that composite with alumina particles with the highest alpha phase content had the highest thermal conductivity values. Mechanical properties (tensile strength, modulus of elasticity and elongation at break) were improved by the addition of modified alumina particles to PMMA/DMI matrix. The thermal properties are the most improved for composite with 3 wt.% Al2O3-Fe-AM particles that had the lowest temperature in a crack zone was noticed (10.28 %) compared to PMMA added due to the better stiffness and highest thermal conductivity.

High strength, high toughness, and low weight make fiber-reinforced composite materials important as an alternative to traditional materials. Due to their application in different fields, such as construction, aviation, marine, automotive technologies and biomedicine, their production has increased leading to the increasement of composite wastes. New technologies for managing fiber-reinforced composite wastes have been developed to solve the issue of end-of-life of these materials. The aim of this paper is to emphasize recycling technologies used for fiber reinforced composites, and their potential reusage.

The paper presents static and dynamic tests of carbon/epoxy composite materials with fiber orientation at 0°/90° and ±45°. The main tensile properties were determined as a basis for subsequent dynamic tests, in which permanent dynamic strength, crack growth, and crack growth rate in the material due to the action of fatigue load were assessed. Comparisons were made regarding the structure of the tested specimens. Samples were obtained from prepregs with a specific density of 1600 kg/m3. The tests were performed at room temperature. Scanning electron microscopy (SEM) was used to analyze the damage in the material during these tests, the mechanisms of their further damage progression and, the impact on the growth and growth rate of the initial crack in the material. The analysis of numerical results and micromechanical analysis confirmed the dominant role of the reinforcing structural element in the material in all performed tests. The obtained results are of great importance in the application of composite materials of such structures under different operating conditions and load regimes. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 451-03-68/2020-14/200135]

The effect of one step-and a new (short) two-step aging on the resistance to stress corrosion cracking of an aluminum alloy 7000 series was investigated, using slow strain rate test and fracture mechanics method. Aging level in the tested alloy was evaluated by means of scanning electron microscopy and measurements of electrical resistivity. It was shown that the alloy after the new two-step aging is significantly more resistant to stress corrosion cracking. Values of tensile properties and fracture toughness are similar for both thermal states. Processes that take place at the crack tip have been considered. The effect of the testing solution temperature on the crack growth rate on the plateau was determined. Two values of the apparent activation energy were obtained. These values correspond to different processes that control crack growth rate on the plateau at higher and lower temperatures. [Projekat Ministarstva nauke Republike Srbije, br. TR 34028 i br. TR 34016]

Metallic biomaterials, which are mainly used for the damaged hard tissue replacements, are materials with high strength, excellent toughness and good wear resistance. The disadvantages of metals as implant materials are their susceptibility to corrosion, the elastic modulus mismatch between metals and human hard tissues, relatively high density and metallic ion release which can cause serious health problems. The aim of this study was to examine metallic ion release from Co-Cr-Mo alloy in artificial saliva. In that purpose, alloy samples were immersed into artificial saliva with different pH values (4.0, 5.5 and 7.5). After a certain immersion period (1, 3 and 6 weeks) the concentrations of released ions were determined using Inductively Coupled Plasma - Mass Spectrophotometer (ICP-MS). The research findings were used in order to define the dependence between the concentration of released metallic ions, artificial saliva pH values and immersion time. The determined released metallic ions concentrations were compared with literature data in order to describe and better understand the phenomenon of metallic ion release from the biocompatible cobalt-based alloy. [Projekat Ministarstva nauke Republike Srbije, br. III 46010 i br. ON 174004]

Due to their excellent characteristics, such as chemical inertness, mechanical resistance, low Young’s modulus, high corrosion resistance, and outstanding biocompatibility, titanium and its alloys are the most used metallic materials for biomedical applications. In dental practice, these materials have demonstrated success as biomedical devices which are used for repairing and replacing failed hard tissue. However, the oral cavity is constantly subjected to the changes in the pH value changes and such an environment is strongly corrosive for titanium dental implants. The objective of this study was to examine ion release from commercially pure titanium (cpTi) in artificial saliva with different pH values (4.0, 5.5 and 7.5). The concentrations of released titanium ions were determined after 1, 3 and 6 weeks using Inductively Coupled Plasma - Mass Spectrometry. The results indicate that the ion release from commercially pure titanium in the artificial saliva is dependent both on the pH of artificial saliva and duration of immersion. [Projekat Ministarstva nauke Republike Srbije, br. III46010 i br. ON 174004]

The main objective of the research presented in this paper was to carry out a statistical-mechanical analysis concerning the tensile test of glass-epoxy composite materials in order to calculate their relevant tension properties and micromechanical structure destruction process. The analysis was done at room temperature, and its results were derived based on the structure of the glass woven 280 g/m², ”twill texture” with the width value of 100 cm, type - Interglass 92125, and epoxy resin type MGS L 135. Samples were shaped by hands with 35% of fabric volume part. The consumed portion of resin was 220 g/m², the thickness of the laminate was 0.308 mm, and the mass of the laminate was 500 g/m2. There were a total of eight layers built in the panel. The micromechanical analysis was derived from the crack surfaces data collected on a scanning electronic microscope, and it showed the mechanisms of damage, and development of cracks until the occurrence of the final break under the tension load.

The significance of composite materials and their applications are mainly due to their good properties. This imposes the need for their recycling, thus extending their lifetime. Once used composite material will be disposed as a waste at the end of it service life. After recycling, this kind of waste can be used as raw materials for the production of same material, which raises their applicability. This indicates a great importance of recycling as a method of the renowal of composite materials. This study represents a contribution to the field of mechanical properties of the recycled composite materials. The tension mechanical properties (tensile strength and modulus of elasticity) of once used and disposed glass-epoxy composite material were compared before and after the recycling. The obtained results from mechanical tests confirmed that the applied recycling method was suitable for glass-epoxy composite materials. In respect to the tensile strength and modulus of elasticity it can be further assessed the possibility of use of recycled glass-epoxy composite materials.

Construction materials, traditionally used in process equipment, are today successfully replaced by composite materials. Hence, many pipes are made of these materials. The subject of this study was the influence of liquids on the state of stresses and tensile strengths in the longitudinal and circumferential direction of glass-polyester pipes of a definite structure and known fabrication process. These analyses are of great importance for the use of glass-polyester pipes in the chemical industry. The tensile properties (the ultimate tensile strength and the modulus of elasticity) were tested and determined for specimens cut out of the pipes; flat specimens for the tensile properties in the longitudinal direction and ring specimens for the tensile properties in the circumferential direction. First, the tension test was performed on virgin samples (without the influence of any liquid), to obtain knowledge about the original tensile properties of the material composite studied. Subsequently, the specimens were soaked in alkaline solutions: sodium hydroxide (strong alkali) and ammonium hydroxide (weak alkali). These solutions were selected because of their considerable difference in pH values. The specimens and rings were left for 3, 10, 30 and 60 days in each liquid at room temperature. Then, the samples were tested on tension by the standard testing procedure. A comparison of the obtained results was made based on the pH values of the aggressive media in which the examined material had been soaked, as well as based on the original tensile properties and the number of days of treatment. Micromechanical analyses of sample breakage helped in the elucidation of the influence of the liquids on the structure of the composite pipe and enabled models and mechanisms that produced the change of strength to be proposed.

Polymer composite pipes with glass fiber reinforcement have today a wide usage in the chemical and process industries. The basic subject of this paper is the determination and distribution of stresses and strains in longitudinal and circumferentional directions of glass-polyester pipes under tension test. Also, the tension strengths in both directions are determined out. Tension test was performed on an electro-mechanical test machine on flat samples and rings obtained by cutting of pipes produced by the method 'Filament winding' with glass fibers reinforcement ±55°. Also, the micromechanical analysis on fracture surfaces was done by SEM, which provided the knowledge about models and mechanisms of fracture on applyed loading.

The subject of this paper is micromechanical analyses of the crack on glass wovenepoxy composites subjected to in-plane compression load. Identification and understanding of the first damages as micro-cracks and micro-mechanisms and their further spreading during compression loading of construction of composite material are of great importance for every special usage and life prediction. Five different structures of glass epoxy composites were tested with orientation of reinforcement 0º/90º and ±45º. The specific weights of reinforcement were 125, 170, 210, 550 and 880 g/m². The analysis of compression test results was performed on the basis of the structure. Micromechanical analyses of surface cracks of the samples was carried out by scanning electron microscopy, and the established models and mechanisms of initiation and propagation of cracks are very valuable in predicting the behavior of the real constructions subjected to compression load.

Mechanical properties of composite materials are conditioned by their structure and depend on the characteristics of structural components. In this paper is presented a numerical model by which the bending properties can be predicted on the basis of known mechanical properties of tension and pressure. Determining the relationship between these properties is justified having in mind the mechanics of fracture during bending, where the fracture takes place on the outer layer which is subjected to bending while the break ends on the layer subjected to pressure. The paper gives the values of tension, pressure and bending properties obtained by the corresponding mechanical test. A comparison of the numerical results of bending properties obtained on the basis of the model with the experimental ones, shows their satisfactory agreement. Therefore, this model can be used for some future research to predict bending properties without experiments.

Pipes made of composites glass fiber/epoxy resin are predominantly used in the chemical industry, construction, infrastructure and war technique. The pipes made for this purpose are in their use exposed to static and dynamic loading. Depending on the purpose, the pipes, especially those in complex structures, can be loaded by torsion. In that case, exceeding allowed tensions can cause damages such as cracking the fibers and matrix delamination. These damages can lead to the appearance of cracks on the pipes and in many cases to complete breakage of the pipe. Because of this, it is very important to evaluate composite pipes exposed to torsion and find out in which way the construction is weakened, what actually is the main goal of this paper.

The aim of this paper was to present the determination of tensile strength Rm and modulus of elasticity Et of glass-epoxy composites at two different temperatures (at room temperature t=20°C, and at t =—50°C). Standard mechanical testing was carried out on glass woven-epoxy composite material with different structures (two specific weights of reinforcement, 210 g/m2 and 550 g/m2) and orientations (0°/90° and ±45°). Micromechanical analysis of failure was performed on a stereo microscope and SEM in order to determine real models and mechanisms of crack.

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