Volume 61, Issue 1

Abstract: Carbon fiber-reinforced polymer composites are widely used materials in the aircraft industry, automotive sector, marine applications, civil engineering, and daily consumer goods, due to their superior mechanical properties at a relatively low density compared to metallic materials. The studied composites are composed of an epoxy resin matrix in which three layers of carbon fiber fabric are embedded, oriented at 0 and 90 degrees. Carbon fiber-reinforced polymer composites were manufactured using the Vacuum Assisted Resin Transfer Molding technique. The tensile failure mechanism in carbon fiber-reinforced polymer composites is an extremely complex phenomenon influenced by numerous factors. This study aims to evaluate the mechanical behavior of carbon fiber-reinforced composites through tensile testing and to compare experimentally obtained results with those calculated using the mixture rule. Additionally, the behavior of the materials under tensile stress was analyzed using the digital image correlation method. Estimating mechanical properties based on the mixture rule is a common practice in the design phase of polymer composites. This study`s novelty and originality lie in its anticipation of the tensile strength and modulus of elasticity of the studied composites. This anticipation was achieved using a virtual instrument developed in the LabVIEW graphical programming environment. The experimentally obtained results for the tensile characteristics of the studied materials are suitable for this type of composite. These results were compared with estimates derived from the mixture rule, and the absolute error was determined.

Abstract: Acrylonitrile-butadiene-styrene (ABS) material is widely used as a protective rigid shell and impact absorber in bike helmets, providing vital protection against head injuries under specific working conditions. However, ABS aging in helmets could affect the safety factor of helmets and shorten the service life. Exploring the transformation during aging process for real assembled helmets made of ABS out shells is crucial for the investigation and fabrication of high performance helmets. Herein, the effect of long-term aging on the physical properties of practical helmets made of ABS outer shells has been discussed systematically. Four different types of helmets were subjected to different aging conditions, i.e., outdoor environment, ultraviolet exposure, hot air, and humid-heat conditions. The impact property and stiffness tests were carried out as a function of aging time and aging conditions. The measured helmets were capable of meeting engineering tolerances when aged under outdoor, ultraviolet, and hot air conditions, and could deliver competitive mechanical performance to their pristine helmets. Yet, after aging under humid-heat for 800 h, the helmets showed an obvious decrease in impact strength, gloss, and stiffness. The influence of different aging conditions was further investigated by thermal and spectral characterizations. The study might provide some valuable advice for helmet performance evaluation.

Abstract: This study investigated the effects of different solutions (artificial saliva, Listerine Cool Mint-alcohol containing and Colgate Plax-alcohol free) on the nanohardness, elastic modulus and surface roughness of enamel surface and composite materials (Admira Fusion, Clearfil Majesty Esthetic and Mosaic Universal). Specimens of 2 mm depth and 5 mm diameter were stored in solutions for 12 h at 37°C. Baseline and final measurements were obtained using a HYSITRON TI 950 TriboIndenter testing machine. The applied force to each specimen increased from 0 to 1000 µN. For SEM images, one sample in each group was covered with a thin layer of mix of gold and palladium using a sputter coater (Quorum Q150R ES, UK). Scanning electron microscopy (SEM) images were taken at 5000× magnifications to evaluate the surface morphology. Statistical analysis for hardness, elastic modulus and roughness was performed by Two-way ANOVA, Benferroni and Tukey HSD at a significance level 0.05. The results of this study showed that the highest value of surface roughness and lowest hardness and elastic modulus were presented by Admira (p[0.001). Listerine caused significantly increased surface roughness (p[0.001) and decreased hardness and elastic modulus parameters (p[0.001). The mouthrinse containing alcohol caused more significant changes in the nanohardness, elastic modulus, surface roughness values of enamel and composite surfaces.

Abstract: Anterior skull base reconstruction is a complex surgical procedure that requires careful evaluation of the patient`s condition and the expertise of a skilled surgical team. Skull base reconstruction objectives focus on providing water-tight separation between the intracranial and extracranial contents, closing dead space, and returning reasonable form and function. Regarding the reconstruction options, the main categories are non-vascular grafts, loco-regional flaps, free tissue transfer or bony-free flaps. The major challenge in reconstructive surgery is the effective sealing of the defect due to its uneven edges and the conformation of the anterior skull base. Given this challenge, we are considering the possibility of designing a prosthetic for anterior skull base defects using the 3D printer.

Abstract: Part dimensional inaccuracies serve as a barrier from adopting Additive Manufacturing (AM) processes in mass production. Fused Deposition Modeling (FDM) is a thermoplastic based low cost AM process which can create conceptual models, prototypes and end user industrial parts. The current study involves predicting the optimal parameter settings and significant parameter for reduced geometric deviations in printed part using Nylon filament reinforced with 20% carbon fiber. Five input factors such as build orientation, layer thickness, infill density, raster angle and infill pattern have been considered for preparing the experimental layout through taguchi’s mixed fractional factorial design. The changes in length, width and thickness of the printed part from CAD value have been evaluated individually through ANOVA and Signal to Noise Ratio method (Smaller the better). Layer thickness is significant only for variations in length, but build orientation affects both width and thickness dimensions. The geometric deviations are further analyzed using combined multi criteria decision making (MCDM) approaches such as Entropy-CoCoSo and PCA-TOPSIS. The optimal parameter settings obtained for reduced geometric deviations is found to be Flat orientation, 0.1mm layer thickness, 50% infill density, 0° raster angle and cubic infill pattern. Layer thickness is found to be highly significant parameter influencing the geometric deviations subsequently followed by build orientation from both the MCDM methods. The multi response performance index values obtained from Entropy-CoCoSo has been trained using classification algorithms such as decision tree, random forest and Naive Bayes. Naive Bayes algorithm outperformed other methods with highest classification accuracy of 99.4% in a training-testing split ratio of 75:25.

Abstract: In this paper, new epoxy resin/rubber powder/hollow beads three-phase composites were prepared by designing the incorporation of fly ash hollow beads with different mass fractions (5%, 10%, 15%, and 20%) as new reinforcing phases into epoxy resin/rubber powder two-phase composites with 5% mass fraction of carbon black rubber powder. Quasi-static compression tests were conducted at room temperature to test the compressive properties of the oxygen resin/rubber powder/hollow beads composites. Calculate the energy absorption properties and energy absorption efficiency of the composites from the compression curves. Fracture characteristics of compressed material specimens with microscopic morphology were observed by scanning electron microscopy. By systematically analyzing the effect of fly ash hollow beads content on the mechanical properties of epoxy resin/rubber powder/hollow beads three-phase composites, it was found that fly ash hollow beads as reinforcing materials can effectively improve the brittleness and yield strength of epoxy resin/rubber powder as well as the energy-absorbing properties and efficiency of the composites. The energy absorption properties of the epoxy resin/rubber powder/hollow beads composites increased and then decreased with the increase in the mass fraction of fly ash hollow beads. In the epoxy resin/rubber powder/hollow beads composites, the most significant performance was observed when the mass fraction of fly ash was 10%.

Abstract: Additive technologies are continually evolving and are crucial in numerous industries, including medical, aerospace, and automotive, but they can also play an important role in the prototyping phase. Due to additive manufacturing, amateurs and enthusiasts can construct simple projects as well as large projects with specialized usage in specific applications. When it comes to complex pieces, traditional manufacturing technologies such as milling, chipping, drilling, and so on have specific constraints, often need even additional production processes to complete the item. All of these constraints can be solved with additive technologies. This work investigates Fused Deposit Modeling (FDM) printing of many specimens with varying properties in order to analyze PLA (Poly Lactic Acid) material behavior following tensile testing. The collected findings will be analyzed in order to determine the specimens with the most significant behavior according on the modified parameters.

Abstract: Polymers are commonly utilized sophisticated materials that may be found in nearly every item we use daily. Polymers` relevance has recently been highlighted due to their applications in several fields of science, technology, and industry, ranging from fundamental usage to biopolymers and medicinal polymers. The research aims to study the effect of annealing with irradiation on the optical properties of PMMA films used in many industrial and medical applications. Where UV-Vis spectroscopy was used to study the absorption and emission spectra in calculating the optical parameters, it was found that the optical energy gap of the indirect transmission type decreases with the increase in the thickness of the thin films. Also, the optical parameters such as the absorption coefficient, refractive index, attenuation coefficient, and dielectric constants increase with increasing thickness. The character of FTIR spectra and the locations of the bands have been demonstrated to change with different time annealing temperatures with irradiation. Irradiation has been demonstrated to change the shape of FTIR Spectra and the placement of the peaks.

Abstract: The aim of the study was to experimentally verify the enhancement of certain mechanical properties of a composite material consisting of unsaturated polyester matrix reinforced with fiberglass, by incorporating specific proportions of sodium aluminosilicate (SAS) powders and talc as fillers for the fabrication of large wind turbine blades. Samples composed of these materials, with varying combinations of the added components, underwent testing for tensile and bending strength, and experiments were conducted to determine their modulus of elasticity. The findings indicate that the inclusion of SAS in the matrix material resulted in increased values of tensile strength and modulus of elasticity up to certain proportions. Solely adding talc to the matrix material led to a rise in bending strength. Increasing the talc percentage in the matrix material reinforced with 20% fiberglass resulted in decreased tensile strength and elastic modulus of the samples, while incorporating a blend of SAS and talc into the matrix material reinforced with 20% fiberglass significantly boosted the elastic modulus and tensile strength of the samples under tensile conditions.

Abstract: Polypropylene is a material recognized for its tensile properties, as well as for the stability of its chemical structure, an important element that has allowed the use of this material on a large scale, in a wide range of fields of activity, especially in the medical field. This study aims to highlight the structural properties of polypropylene, which contribute to improving the prognosis of vascular microsutures, through the comparative analysis of the results obtained after performing lymphatico-venous anastomosis in lymphedema patients. The research was focused on analyzing the importance of the diameter of the polypropylene thread and its tensile properties on the patency of the lymphatic anastomosis, through the comparative analysis of two groups of patients who benefited from micro-vascular sutures. The database was made up of a group of 82 patients divided into two groups who benefited from supermicrosurgical interventions by using polypropylene thread 11.0 (37 cases involving 148 anastomoses), respectively 12.0 (45 cases involving 180 anastomoses). The results of the research revealed that the group of patients who benefited from microvascular anastomoses using 12.0 poly-propylene thread recorded both better anastomosis patency rates and a significantly reduced rate of complications due to the rejection reaction of the suture material, under the conditions a significantly reduced tensile strength.

Abstract: Polyurethane foam as an important sound absorption material is limited by the poor flame resistances in building field, but the modifications of flame resistances tend to have adverse effects on the sound absorption performance. Herein, dibutyltin dilaurate and triethylenediamine are used simultaneously as catalysts, and four new types of flame retardant polyether polyols (FPMPO) are synthesized and combined with modified expanded graphite (PEG) to prepare the flame resistance flexible polyurethane foam (FFPUF) by one-step method. The results show that the combination of the two catalysts can control the cell structure of FFPUF availably for sound absorption. The FPMPO have little negative influence on the cell morphology and the sound absorption performance of FFPUF, but the increase of flame resistances is finite due to the limited amount of FPMPO. In order to improve the flame retardant properties further, the FPMPO and the PEG are combined in the modification. Benefitting by the effective control structure and the modification with composite flame retardant, the FFPUF shows excellent sound absorption and flame retardant properties. The LOI value of FFPUF is 33.4 and the vertical burning level reaches V-0, and the average sound absorption coefficient maintains 0.68 in the 800-6300 Hz range.

Abstract: This paper describes the development of new types of dynamically cross-linked thermoplastic elastomers based on ethylene-propylene-terpolymer rubber and low-density polyethylene, reinforced with plasticized starch and montmorillonite with a chemically modified surface. An octylphenol-formaldehyde resin in the presence of stannous chloride dihydrate was used as a vulcanizing agent. The samples were obtained on a Brabender Plasti-Corder mixer, at appropriate temperatures and rotation speeds, using the dynamic vulcanization method and the melt intercalation technique. The mixtures obtained were modeled in the form of plates with standard dimensions using specific molds and a laboratory-scale electrical press. The obtained samples were analyzed from the point of view of the physical-mechanical properties, the melt flow index, as well as from the structural and morphological point of view. It was observed that the characteristics of the samples are influenced by both the composition and the methods of obtaining used. According to the obtained characteristics, the new elasto-plastic materials can be used in fields such as the footwear industry (for the production of: soles, heels, protective boots), in the rubber and plastics industry, the automobile industry, agriculture or construction (when making gaskets, technical items, hoses, etc.). They can be easily processed into different finished products by methods specific to plastics.

Abstract: The basic idea of this study is based on the hypothesis that it is possible to obtain nanostructures by stimulating local chemical reactions. Starting with this hypothesis we assumed that it is possible to disperse some inorganic agent into the epoxy resin and stimulating the mixtures we could get some nano-structures what are changing the basic electric behaviour of the polymer matrix. We dissolved some metallic chlorides in DMF (dimethylformamide) and we mixed together the solution with the epoxy resin (the main component). Applying various external stimuli we get materials showing various properties, different from the epoxy resin properties. The electric photoconductivity is increased (in some cases) but the mechanical properties are damaged due the solvent presence into the polymer matrix.

Abstract: To overcome PLLA’s poor crystallization capability, using nucleating agent as crystallization improvement strategy was performed in this study. PPAPH as PLLA’s an organic nucleating agent was firstly synthesized, and then PLLA was blended with different PPAPH loading through melting blend method, the resulting influences of PPAPH on PLLA’s performances were investigated using the relevant testing instruments. Melt-crystallization revealed that PPAPH played important role in promoting PLLA’s crystallization through providing effective sites of heterogeneous nucleation, and effect of PPAPH loading on PLLA’s melt-crystallization was very poor, indicating that low PPAPH loading could cause PLLA to possess powerful crystallization capacity. In addition, the relative low final melting temperature was beneficial for PLLA/PPAPH’s crystallization. However, an increase of cooling rate during cooling stage weakened PLLA/PPAPH’s crystallization capacity. PLLA/PPAPH’s cold-crystallization suggested that PPAPH had an inhibition effect on cold-crystallization process to some extent. Melting behaviors depended on heating rate and previous crystallization including melt-crystallization at various cooling rates and isothermal crystallization at various crystallization temperatures. PPAPH enhanced PLLA’s fluidity, tensile modulus and tensile strength. Unfortunately, PLLA’s transmittance was seriously weakened as PPAPH loading increased, as well as the elongation at break continuously decreased.

Abstract: This paper describes the use of video and digital image processing in investigation of the impact between a rigid hemispherical shape impactor and Hybrid Polyurea-Polyurethane-MWCNTs Nanocomposite Coatings. An experimental study was performed for six sample configurations: single aluminum plates (reference test), multilayer plates with 4 types of coatings and double aluminum plates. The impact phenomenon was recorded with a high-speed video camera and the variation of the projectile`s velocity during the impact was obtained through digital analysis. Additionally, the test was instrumented using a force sensor specially designed and mounted on the impactor. The video processing was used to draw the velocity curves and to estimate the evolution of the contact forces between the impactor and the multilayer structures, the results obtained being compared with the force sensor data. Some differences between these two types of measurements are observed, so in order to analyze the configurations behavior, a numerical study of the phenomena was performed in LS-DYNA software using a 2D axial symmetric model. The simulations showed that the profile of the force evolution measured with the sensor is affected by the chosen constructive solution and the data obtained based on the video images are more accurate. The deformations were analyzed, the maximum deformation based on image processing and the residual deformation based on 3D Scan post-test. The video technique combined with 3D Scan are precise enough to study the impact at low velocities and the numerical simulations provide results according to reality. The hyperelastic coatings contribute to a better resistance of the aluminum plates.

Abstract: The biomaterials applicable in dental implantology, or implantology generally, are subject to specific requirements, namely biocompatibility, osseointegration, resistance to fracture/ oxidative degradation/ long-term compressive stress/ hydrolisis in boiling water, suitable morphology, suitable physical properties (including mechanical properties), aesthetics, etc. When selecting a suitable material for dental implants, it is also necessary to consider the patient`s current health condition and possible complications when placing titanium implants and alloys. If there is a risk of an allergic reaction or hypersensitivity to any of the components of the metal prosthesis, the placement of a semi-crystalline thermoplastic implant - called polyetheretherketone, abbreviated PEEK - is a possible option. Such a wide range of stiffness means that PEEK formulations can be produced with modulus values similar to cortical bone. PEEK is classified as a High Performance Polymer of polymer pyramide (such as Polysulfones polybutylene terephthalate). PEEK can be applied for dental abutment and dental body. This article summarises basic information on the structure and properties of PEEK polymer, advantages/ disadvantages (compared to metal - titanium restorations), application and general information from the examined field.