Volume 60, Issue 2

Abstract: Using the experimental determinations obtained on the basis of compressive stress, some mechanical properties were studied for composite materials with the matrix of three types of resin, epoxy, unsaturated polyester and hybrid based on Dammar natural resin, which was reinforced with isophthalic resin granules NPG (Neopentyl Glycol) Chromat Kayan / Javari / Payette type. The stress-strain diagrams, compressive yield strength, compressive strength and modulus of elasticity in uniaxial compression were obtained. With the EDS analysis, the graphical distribution of the atomic spectra of the elements identified in the hybrid resin was determined and the image of the fracture surface of a hybrid resin specimen was presented based on the stereomicroscopic analysis (SEM).

Abstract: Acoustic protection is an important aspect in various industrial, commercial and residential applications. In order to reduce the transmission of noise, perforated panels are frequently used as a barrier. The present study aims to conduct a numerical analysis of plastic perforated panels for acoustic protection. The study employed a finite element method (FEM) approach and focused on the propagation of acoustic waves through perforations of varying diameters (30 mm, 40 mm, 50 mm, 60 mm, 70 mm and 90 mm) and at different frequencies (250 Hz, 500 Hz, 1000 Hz and 1500 Hz). The numerical analysis was conducted using the finite element software ANSYS. This work offers numerical analysis models of acoustic wave propagation, which can be used by those interested in similar problems, for different environments, in closed or open spaces. The results showed that the perforation diameter and frequency play a crucial role in the performance of the plastic perforated panels as an acoustic barrier. The results of the author’s research pointed out that the plastic materials can be used successfully in the construction of acoustic barriers. Next to it, the findings of this study can provide valuable insights for engineers and designers in the selection and optimization of plastic perforated panels for acoustic protection applications.

Abstract: To attain good geometric shape and size, machining of high-strength metal Fiber laminate becomes inevitable in the field of automotive industries. In this research, aluminum foam sandwiched with glass fiber reinforced polymer (GFRP) composites fabricated using a hand layup process. The glass Fiber composite was fabricated using aluminum foam with a thickness of 1 mm. The effect of abrasive water jet parameters such as pressure (P), stand-off distance (L), and nozzle diameter (D) on material removal rate (MRR) and Kerf angle (Ka) and Surface roughness were investigated. The results were compared without aluminum foam composites. Glass fiber composites with aluminum foam reduced the kerf angle by 44.18 %, and surface roughness (Ra) by 41.77 % as compared with glass fiber composites without aluminum foam. From the investigation, it was noticed that maximum pressure (220 Bar) and minimum stand-off distance (1mm) were optimum parameters for reducing the kerf angle and surface roughness. Also, Optical images of the hole were analyzed for surface quality.

Abstract: This paper aims to investigate the mechanical properties of polyurethane cement (different ratios) at different ambient temperatures. The temperature and proportion which affect the constitutive relation of the material were analyzed by axial tensile test. The microstructure and failure mode of polyurethane cement were studied using scanning electron microscope technology. At -40oC ~40oC, the stress-strain curves of polyurethane cement with different proportions were roughly similar. When the temperature was higher than 40oC, with the rise of temperature, the ultimate tensile strength of polyurethane cement specimens would decrease but the ultimate strain would increase. When the temperature was lower than -40oC, with the decline of temperature, the ultimate strain and tensile strength of polyurethane cement specimens would decrease. The ultimate stress of polyurethane cement with different ratios was different. With the rise of the proportion of polyurethane components, the ultimate stress would increase but the elastic modulus would decrease. Macroscopically, the failure modes of polyurethane specimens were different with the change of temperature. Brittle fracture occurred at low temperatures. At high temperatures, the specimen did not fracture, but a large number of “V”shaped cracks appeared at the edge. The higher the temperature, the more obvious this phenomenon was. At the microscopic level, the fibers didn`t break at high temperatures, and there were obvious cracks and more stubble on the surface of cracks at room temperature.

Abstract: The present paper considers the use of the results of the evaluations carried out by applying the `Six Sigma` statistical method to improve the vulcanization times of elastomeric composites on the external manufacturing cycle of several size types of car tires. This statistical approach aims to verify the distribution of the measured values of the external vulcanization times between the normal specification limits to optimize them and improve the performance, efficiency, and quality of the automotive tire vulcanization processes. Through the analysis carried out, the operations that caused delays and defects were identified, a program of corrective measures was carried out and after its execution, the fulfillment of the purpose was verified, namely the optimization of external vulcanization times and reducing the number of faulty tires. The new measured values of the vulcanization times were within the normal limits of the imposed specifications (LSS = 2.5). This situation corresponds to achieving a maximum level of performance and represents the successful completion of the quality improvement project.

Abstract: Melt processing poly(L-lactide) (PLLA) with a nucleating agent has been thought to be one of the most effective route to enhance PLLA`s crystallization and heat resistance. In the current work, a newly-developed organic nucleating agent named N, N`-bis(2-picolinyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NCAPH) was synthesized to investigate its effects on PLLA’s crystallization and melting behaviors. It is proved that NCAPH as an organic crystallization nucleating agent could provide large number of crystallization nucleation sites to improve PLLA’s crystallization, as observed from DSC and POM measurements. The result from melt-crystallization processes further showed that the final melting temperature and cooling rate were two important factors for affecting PLLA’s melt-crystallization behaviors in cooling, and the theoretical calculation result of frontier orbital energy indicated there existed probable intermolecular interaction between N-H of NCAPH and C=O of PLLA, which was proposed as nucleation mechanism of NCAPH for promoting PLLA’s crystallization. The melting behaviors of PLLA/NCAPH after non-isothermal crystallization or isothermal crystallization further confirmed the positive effects of NCAPH and NCAPH’s loading for the crystallization of PLLA, meantime, the melting behaviors depended on the heating rate, crystallization temperature, crystallization time, etc.

Abstract: This study evaluated surface durability use of manufacture 3D printed gears. Polymer gears were 3D printed using PLA, Tough-PLA, and TPU materials, Through different combinations of materials,three gears of the same size were manufactured: the PLA gear, the PLA plus TUP gear and the Tought PLA plus TPU gear. The surface wear test of the 3d-printed gears were on a self-designed test bench. The differences in mechanical performance between the polymer filaments were attributed to differences in crystallinity and the uniqueness of the fused deposition modeling (FDM) process, but by combining two materials with different features, it is possible to change the mechanical properties of 3D printed gears.In this study , from the changes of torque data during the whole experiment also showed the difference of transmission efficiency of three different gears.Scanning electron microscopy (SEM) revealed the different surface wear of three different gears under the same test conditions. During the gear surface wear test, a thermal camera was used to recorded the surface temperature changes of the gears, and SEM was used to analyze the wear of the gear surface. The test results showed Tough-PLA Plus TPU gear showed the best wear performance among the three different 3D printing gears tested.

Abstract: This study aimed to investigate the water sorption levels of 3 different condensable bulk fill composites, two flowable bulk fill composites, two microhybrid composites, one nanofilled composite, and one nanohybrid composite material polymerized with the same beam device on the 14th and 30th days.We evaluated nine different composite materials. The materials were prepared as cylindrical blocks (n=7) with a diameter of 7 mm and a thickness of 2 mm and polymerized. Each sample was kept in distilled water for specified times and measured by the ISO 4049 method.We used The Kruskal-Wallis test to compare more than two independent groups where numerical variables had no normal distribution. The Dwass-Steel-Critchlow-Fligner test evaluated differences between the groups if the non-parametric tests were applied. We used The Wilcoxon test to compare the numerical variables without normal distribution (water sorption values in the 14th and 30th-day measurements for each cement material).For water sorption, there was no statistically significant difference between the water sorption values of the resin composite materials on the 14th and 30th days. No statistically significant difference was found in comparing water sorption values between the 14th and 30th measurements for each resin composite material. There is a need for more extended studies by keeping the conditions constant for the evaluated composites and for bulk fill composites to be evaluated with 4mm samples.

Abstract: The flexural response of externally strengthened RC beams with GFRP and HFRP (hybrid FRP) sheets under monotonic and cyclic loading conditions are investigated. Fourteen beams in two series (Series1and 2) were cast for this study. Each series consisted of seven beams. A total number of 14 beams were cast, out of which 2 beams considered as control specimen. The 12 beams were externally strengthened with GFRP sheets (4 beams) and HFRP sheets (8 beams). Series 1 and Series 2 beams were tested for two-point static and cyclic loads. The experimental for ultimate strength, deformation, stiffness, ductility, energy absorption and modes of failures are conversed for all the tested beams. The peak load for the RC beams tested specimens under static loads were computed using ACI 440.2R-08 guidelines. An optimum increase of 171.43 % in ultimate load carrying capacity was found for the beam strengthened with HFRP sheets than the control beam. Also, the predicted ultimate loads exhibited the good convergence with the test results.

Abstract: In this research some composite materials built in sandwich type style are studied. The lower and upper layers, that reinforce the samples, are made from poplar strips. The core is made from crushed corn cob and the adhesion of all parts (layers and core) is made by using hybrid resins based on a combination from dammar resin and the synthetic acrylic one (with its hardener). The static and dynamic mechanical behaviour by testing the samples to tensile and bending were studied. Two types of hybrid resins were used: one abbreviated as type B with the percentage of 60% dammar and 40% acrylic resin with hardener and one abbreviated as type C with the percentage of 65% dammar and 35% acrylic resin with hardener. A general conclusion from this study it was: the mechanical properties decrase with the dammar percentage increase. This fact can be explained by the decreased mechanical properties of the natural dammar resin compared to the synthetic acylic on

Abstract: The structure of polyurethane and the physico-chemical properties of its components are considered. The most promising modifiers have been selected: TiO2, CaCO3. The features of the preparation of the studied polyurethane mixture, its composition, manufacturing technology and equipment are described in detail. The geometric properties, manufacturing processes and testing methods of samples are presented. The graphical dependencies of the influence of the parameters of sample preparation on their mechanical properties such as hardness, tensile stress at break, Jung`s modulus are given. The rational parameters of the technology for the production of samples modified with fillers to give them stable mechanical properties have been set. The maximum proportions of these fillers in polyurethane rubber are limited to 30-35%. It is proved that the addition of TiО2 and CaCО3 to the composition of polyurethane rubbers gives them special properties that allow them to expand the range of their industrial usage.

Abstract: In this paper, the authors propose to carry out a case study, on a visual part made of thermoplastic material from the automotive industry. Using the most up-to-date CAE systems, we will try to highlight the main appearance problems in long parts, namely the appearance of weld lines at the meeting of the flow fronts. The part will be processed using sequential, as well as non-sequential injection systems, respectively, in order to highlight the difference between the two, respectively to compare these two tests with the results of rheological simulation (CAE).