Volume 59, Issue 3

Abstract: The paper generalizes the Timoshenko model for thick bars, using a new model that is applied to the vibration study of multilayer composite bars. In the proposed mathematical model, three coefficients are introduced that take into account the non-uniformities of the tangential and normal stresses in the bar section. The vibrations of some composite bars with a polypropylene honeycomb core with a thickness of 10 mm, 15 mm and 20 mm are experimentally studied, on the faces of which one or two layers of carbon fiber, respectively glass fiber was poured. For each analysed bar, the stiffness and the equivalent modulus of elasticity are determined and the variation of the damping coefficient according to the length of the bar is studied.

Abstract: The paper presents the results obtained after the tribology of composite materials with organic components intended for the manufacturing of brake shoes for motor and towed rolling stock. We analyzed the tribological behaviour of the samples of experimental composite material in comparison to the phosphorous cast iron frequently used for manufacturing brake shoes.

Abstract: The purpose of experiment was the highlight of the creep of ring from polyethylene pipe subjected to internal pressure. To create the internal pressure in the HDPE pipe ring, a weight of 4.5 kg was superimposed on it, in the form of a cylindrical plate. In order to evaluate the strains of the elastic element subjected to the tensile stress, respectively compression, tensometric marks 1 and 2 are placed on the outside, in the case of the circular section. The internal pressure test was performed to evaluate the strains of the material of a PE 100 polyethylene ring in two directions: one axial (longitudinal) and the other transverse (circumferential) in order to highlight the creep of the pipe material due to its structure. In a polyethylene pipe stressed at internal pressure, due to the symmetry the tangential stresses are zero. The axial strain initially showed a positive increase, followed by a decrease, reaching negative values towards the end of the experiment, while the circumferential strain recorded positive values, about 300 times higher than the initial ones. The principal stress changed approximately linearly. The circumferential stress recorded the maximum value of σ1=0.33 MPa (3.3 bar) after two and a half hours of experiment. Based on such this test could be calculate Poisson`s ratio ν.

Abstract: The use of fiber-reinforced polymer (FRP) composites in compressive members is advantageous to reinforced concrete structures in order to alleviate the problem of corrosion of steel reinforcement and to produce a lightweight and efficient structural element. This investigation aims to propose the theoretical models for capturing the axial loading capacity (ALC) of hollow concrete columns (HCCs) having main FRP rebars and transverse FRP spirals. All the glass-FRP-reinforced HCCs portray two-peak load performance. The first peak is due to the gross cross-sectional area of concrete while the second peak is due to the core material laterally wrapped with FRP spirals. For the prediction of the first peak load of HCCs which is equal to the maximum capacity of solid concrete columns, a database of 279 FRP-reinforced columns was produced from the previous research and the ALC models were suggested; one for capturing the first peak and the other for estimating the second peak ALC of HCCs. The predictions of proposed models were compared with the test results from the literature. A close relationship was perceived between the theoretical and experimental results.

Abstract: As part of this work, research was carried out on the effect of the addition of expanded perlite (PR) on the mechanical and thermomechanical properties of high-density polyethylene (PE) composites. Composites containing from 1 to 10 wt% of the inorganic filler were produced. Polyethylene-based composites manufactured by twin-screw extrusion and formed in the compression molding process were subjected to mechanical, thermomechanical, and structural analyses. The structure of polymer composites and filler was analyzed using scanning electron microscopy (SEM). It has been correlated with the static tensile tests and results of dynamic thermomechanical analysis (DMA). As part of the work, several thermomechanical parameters were calculated, and the obtained results were discussed with the evaluation of interfacial adhesion based on microscopic analysis. The research showed that despite introducing a 10 wt% of particle-shaped filler, the composites show increased stiffness without noticeable deterioration in tensile strength, simultaneously reducing toughness and brittleness. The analysis of the thermomechanical properties showed the lack of significant effects of the filler influence on the polymer matrix.

Abstract: This work was developed to analyze the adoption of paclitaxel-loaded silk fibroin nanoparticles (SFNPs) in subcutaneous transplanted tumor model of mouse hepatoma to explore its anti-tumor effect. Twenty-five specific pathogen-free (SPF) mice were selected to construct a subcutaneous tumor model of liver cancer, and they were randomly rolled into control group, group A, group B, group C, and group D, with five mice in each group. The silk fibroin was mixed with an organic solvent to prepare a suspension, and the SFNPs were prepared through centrifugation, ultrasound, and other methods. The paclitaxel-loaded SFNPs were prepared by mixing paclitaxel and silk fibroin aqueous solution, centrifuging, washing, and dispersing. Then, the five groups of mice were intervened by different dosage regimens to analyze the changes of various indicators. As a result, the prepared nanoparticles had uniform particle size, uniform distribution, no adhesion, and the average particle size was less than 500 nm. The tumor volume of mice in groups C and D on the 7th, 9th, and 13th days of administration were dramatically smaller than those in the control group, group A, and group B (P < 0.05). And the tumor volume (154.49 ± 9.65 mm3) of mice in group D on the 13th day of administration was dramatically smaller than that in group C (167.79 ± 9.72 mm3) (P < 0.05). The tumor mass (0.89 ± 0.14 g, 0.54 ± 0.13 g, and 0.46 ± 0.11 g) of mice in groups B, C, and D was dramatically smaller than that in the control group and group A (1.23 ± 0.12 g, 1.24 ± 0.11 g) (P < 0.05), and that of group D was dramatically smaller than groups B and C (P < 0.05). The apoptosis rates of tumor cells in groups C and D (46.38%, 48.23%) were greatly superior to those in the control group (16.7%), group A (21.33%), and group B (35.6%) (P < 0.05), and that of group D was greatly superior to that in group C (P < 0.05). In summary, paclitaxel-loaded SFNPs can effectively improve the targeting effect and bioavailability of drugs in the treatment of liver cancer, thereby improving the efficacy, and had a good application prospect.

Abstract: The purpose of this paper is to evaluate the behaviour of 3D printed honeycomb structures under low velocity impact loading for their use in energy absorption applications. Additive manufacturing technologies are part of a growing field that represents high interest for industries such as aerospace, automotive and naval. This paper aims to determine the mechanical properties of a 3D printed polymer - Polylactic Acid (PLA) manufactured by FDM (Fused Deposition Modelling) technology. In this regard, first the material is characterized by low velocity impact dynamic experimental tests. A finite Element Analysis (FEA) is performed in LS-Dyna software in order to validate the results. The samples were manufactured by varying the infill percent to investigate the influence of different parameters on a batch of samples for every configuration. The 3D CAD modelling for impact tests samples were performed in Catia V5. Among wide range of cellular structures, honeycomb non-auxetic hexagonal cell pattern was selected in this study, assuring high strength/weight ratio. The amount of energy absorbed during the impact, the failure and degradation of the impacted specimens were monitored, following the analysis of experimental and numerical data. A fair agreement was obtained between experimental and numerical results, showing that honeycomb developed lightweight structures exhibits a proper energy absorption capacity, with a mechanism of release similar to metal or composite materials honeycombs.

Abstract: Plastic pipes are being more widely used in various industries, as they combine both a rather light weight and quite high physical mechanical performance characteristics. The present article materials are devoted to the researches, relating to the determination of the various hydrocarbon compounds effect on some mechanical properties reduction degree of samples cut from HDPE pipes, represented by characteristic values of curves (strength - tensile strain) as an absorption result. In the course of the research, the gasoline presence in material structure of the pipe samples was noted to make the process unstable, and the curves representing a change in the characteristic values under study, depending on the immersion time in diesel fuel, tended to decrease throughout the entire immersion period. The experiments have shown that in the study of samples absorbing capacity a full saturation was obtained when immersed in diesel fuel and, despite large difference in absorbance values, the volume of absorbed hydrocarbons caused decline close to the studied characteristic values. Motor oils produced the most significant effect on the HDPE samples studied characteristics at the relatively low absorption values.

Abstract: Due to the extreme health concerns associated with asbestos-based brake linings, researchers are looking at using ecologically friendly bio-based biomaterials as reinforcing agents in composite materials used to make brake pad linings. The goal of this study is to see whether using sea shell (SS) powder in the production of asbestos-free brake lining materials is feasible. The powders were combined with the necessary fillers to make the brake lining. The reinforcing powders` compositions were varied between 20% and 35%, the resin binder`s composition was changed between 58 and 43 percent, and the filler metal and curing agents` compositions were kept constant. These ingredients were weighed, prepared, combined, cured, and moulded. The composite materials were tested for water and oil absorption, compressive strength, hardness, and wear. According to the findings, increasing the quantity of reinforcing components increases the water and oil absorption of the samples. With the addition of up to 35% content, the composite`s compressive strength increased proportionally. The tested coefficient of friction was found to be within acceptable limits. Furthermore, when mixed with other fillers and restricted, SS powder has showed tremendous promise in the production of brake linings.

Abstract: Fused deposition modeling (FDM) is becoming the most promised additive manufacturing (AM) process in recent years due to the evident benefits, such as high design flexibility, low cost, friendly and economically use. The current study considers an optimization of four different FDM parameters varied in three levels, as layer thickness (0.17 mm, 0.25 mm and 0.33 mm), infill density (25, 50 and 75%), shell thickness (0.8 mm, 1.2 mm and 1.6 mm) and raster angle (0º, 30º and 60º) with an objective to reduce printing time, part weight and to enhance flexural modulus using Polyethylene Terepthalate - glycol modified (PET-G) material. Mono optimization of FDM input parameters has been done using signal to noise ratio method obtained from Taguchi’s L9Orthogonal Array (OA) and multi response optimization is applied through Grey Relational Analysis (GRA) and technique of order preference similar to ideal solution (TOPSIS) techniques. The response or its criteria weightages are calculated using Shanon’s entropy and CRITIC method which gives different weightages for the considered responses. Printing time ranks top with 37% from entropy method followed by flexural modulus with 36% and part weight ranks last with 28%. Flexural modulus ranks tops with 43% followed by part weight with 29% and printing time takes last position with 28% weightage.The ranking of alternatives from GRA- entropy and GRA- CRITIC methods are similar by recommending A1B1C1D1 (0.17 mm layer thickness, 25% infill density, 0.8 mm shell thickness and 0° raster angle) but TOPSIS-entropy and TOPSIS – CRITIC methods suggested different parameter combination A2B3C1D2 (0.25 mm layer thickness,75% infill density, 0.8 mm shell thickness and 30° raster angle). From all the four different methods adopted for optimization, the parameter setting obtained from level total suggests A2B1C1D2 (0.25 mm layer thickness, 25% infill density, 0.8mm shell thickness and 30° raster angle) and completely opposite to the ranking of alternatives. The carried - out confirmation trials carried out validated the optimized settings resulted from different methods. Infill density is found to be the most significant factor as compared to other input factors over the output assessed parameters.

Abstract: Lensknob is a component that transmits light to users. It is essential to minimize the deformation to transmit the light uniformly. As a method of finding injection molding parameters capable of minimizing the deformation, the amount of deformation of the Lensknob was predicted in advance by numerical analysis of the injection molding. However, because it takes a considerable amount of time to analyze, we used the Decision tree as a Machine Learning model. As the injection molding parameters, we set the melting temperature, cooling time, holding time, holding pressure, and ram speed. We set the injection molding parameters based on the range recommended by Moldflow. A full factor method of factor 5 level 3 was applied in the experiment. We predicted the parameters for minimizing the deformation through the Decision tree learned with 243 experimental data. We set the criteria to evaluate the performance of the Decision tree. The parameters predicted by the Decision tree improved the deformation by about 10.37%.

Abstract: Metal-containing ionic liquids with general formula [Rmim]+MX3- (R=n-butyl or n-lauryl; M=Zn, Cd; X=Cl, Br) were synthesised and then characterized by nuclear magnetic resonance spectroscopy and infrared spectroscopy. The catalytic activity was tested in glycolysis of poly(ethylene terephthalate) (PET) with ethylene glycol (EG) with the main product being bis-2-hydroxyethyl terephthalate (BHET). The following parameters were varied: the catalyst type, the catalyst loading and the molar ratio between PET and EG. For every reaction conversion and selectivity were calculated. All these reactions arose with high selectivity in the desired product, the conversion of PET being quasi-total.

Abstract: Fused Filament Fabrication (FFF) is the most popular and widely used additive manufacturing process for printing polymer and composite products. Various production factors influenced the strength and stiffness of the part manufactured by 3D printing. A comprehensive experimental analysis was conducted in this study to examine the effect of FFF process parameters (infill density, pattern, and layer thickness) on mechanical properties and failure mechanism. The tensile, flexural, and impact test specimens were printed using ABS and carbon fibre reinforced ABS filaments in accordance with ASTM standards. Furthermore, dynamic properties are studied using dynamic mechanical analysis to estimate the loss factor and glass transition temperature under the impact of temperature and frequency in addition to static properties. Further, the results showed the addition of carbon fiber in ABS increases the mechanical properties. The failure modes are studied using optical microscopy and Scanning Electron Microscopy images and it has been visualized that due to improper layer deposition, poor bonding between the previous layer and low infill density creates a void in the specimen which results in poor mechanical properties. The Dynamic Mechanical Analysis showed that at higher frequency the molecular movement decreases which in turn stabilizes the composite behavior and reduces the loss factor.

Abstract: Epoxy based hybrid composites are extremely wide used materials in the polymer engineering field and always have a demand for their versatile applications. Nano clay is yet another trending substance handled by many researchers due to their enhanced abrasion characteristics. This research was performed to investigate the effect of dispersing nanoclay into epoxy matrix and further coupled with pineapple fibers to fabricate a hybrid composite of excellent mechanical property. 4 layers of Pineapple fiber mats were compression moulded with epoxy nanoclay blend to obtain composite specimens of 4mm thickness. Nanoclay was added into epoxy resin at four different weight ratios (2%, 4%, 6%, and 8%) to form four different combinations of matrix materials into which pineapple fiber mats were reinforced individually at a constant weight ratio of 25%. The enhancement of mechanical and abrasion rate of the hybrid composites were matched with those of the neat Epoxy/Pineapple fiber composites that are currently being developed as alternatives for brake pads. Moisture absorption rate of the composites were analysed to ASTM D570 and Morphology was inspected using Field Emission Scanning Electron Microscope (FESEM). The results depicted optimum mechanical performance at 4 wt% nanoclay infused epoxy/pineapple fiber composite that had a tensile strength of 166.75 MPa, flexural strength of 801.15 MPa and impact strength of 148.76 kg/sq. m. The least abrasion rate was detected in the composite with 8 wt% nanoclay content, resulting in an abrasion rate of 0.1064 g/m.

Abstract: To give full play to the advantages of perforated plate backed by porous materials in low and medium frequency noise absorption, this study uses Johnson-Champoux-Allard method with the finite element model to describe the acoustic characteristics of this composite structure. The effects of structural parameters of perforated plate and characteristic parameters of melamine foam on sound absorption coefficient were systematically investigated by numerical simulation. Practical composite were prepared to verify the reliability of the numerical simulation method. The simulation and experimental data in this study are helpful to promote the design of porous material-perforated plate structure for noise control in life.

Abstract: Fiber reinforced polymer composites (FRPCs) are considered as core structure in Multi layered armour systems (MAS) to take advantage of maximum energy absorption, mobility and cost criteria design. In this article, based on the problem defining attribute’s optimal material selection in FRPCs determined by Multiple criteria decisions making (MCDM) approach for considered alternative materials from polymer resin, synthetic and natural fiber. Attribute’s weightage and alternatives priority rank were determined through Fussy-Analytical hierarchy process (F-AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method. Obtained rank was compared with Preference selection index (PSI) an another MCDM method, for better computational conformity. Selected materials from MCDM approach, simulated for energy absorption ability and damage after impact were studied by considering Cowper-Symonds constitutive materials model using 3D macro shell analysis. Various impact velocities were considered from 3 to 50 m/s for rigid steel impactor directed towards the deformable plate. Parameter like Residual kinetic energy, Residual velocity, Energy absorption ratio after impact were studied numerically. Simulation results in terms of specific energy absorption were compared with the rank obtained in MCDM approach. Among the polymers considered epoxy, polyurethane and polyester found better choice. In fibers hemp and basalt found better materials choice for heterogenous FRPCs design in ballistic armour.

Abstract: Improving the crystallization performance of poly(L-lactide) (PLLA) is necessary to adapt for various applications. In the current work, N, N`-bis(isonicotinic acid) 1, 4-naphthalenedicarboxylic acid dihydrazide (NAIAH) was synthesized to be firstly aimed at promoting the crystallization of PLLA, and the NAIAH-nucleated PLLA materials were prepared using PLLA as a matrix material and NAIAH as a nucleating agent, and the crystalline nucleation, melting behavior, thermal decomposition and mechanical properties of PLLA/NAIAH samples were investigated by the relevant testing instruments. The results from the non-isothermal melt-crystallization from the melt of 190ºC indicated that the NAIHA could significantly accelerate PLLA’s crystallization, and played an efficient heterogeneous nucleation in PLLA’s crystallization. The effect of different final melting temperatures on PLLA’s melt-crystallization behavior showed that a relatively low final melting temperature was beneficial for the crystallization of PLLA, and the 170ºC was the optimum final melting temperature in this study. An increase of cooling rate could weaken PLLA/NAIAH’s crystallization ability, but the NAIAH was still able to promote PLLA’s crystallization upon the fast cooling at 50ºC/min, showing a powerful crystallization accelerating effect of NAIAH. PLLA/NAIAH’s melting behaviors after different crystallization conditions were affected by heating rate and crystallization temperature, and the double melting peaks appeared in melting DSC curves were assigned to melting-recrystallization. Thermal decomposition processes in air showed that the NAIAH decreased PLLA’s thermal stability, but the interaction of PLLA with NAIAH had an inhibition for a drop in onset decomposition temperature. Additionally, the introduction of NAIAH dramatically reduced PLLA’s tensile modulus and elongation at break.

Abstract: The scope of this paper is to determine the evolution of the dimensional value of the part and to study if there is gas and particle emission produced by the plant-based resin in the 3D printing process with mask stereolithography. For dimensional measurement, a solution with digital calliper is used. For the measurement of emission, two devices are used for indoor air quality. In the vertical direction of part body printed, it is possible to observe a descending linear type of direction with a minimum value at the highest element 3D printed. The data taken into account in this study are mathematically studied using the EXCEL regression equation for dimension. The gases emitted are measured with the booth devices in parallel for formaldehyde and volatile organic compound gases. For CO2 and particles, one of these devices is used. The air quality index was determined in relation to CO2 and, respectively, particle emitted. In the printing process, an increase in CO2 emission of 500 ppm can be observed in the initial phase of the process and a lower value in the body area. It is possible to consider that the quality air in 3D printing with plant-based clear resin is in the good to medium level from all types of emission. These data were put in ac-cordance with the level value offered by the manufacturer of the measuring devices. In this study the dimensional aspects are evaluated in parallel for two types of part bodies and the dimensional equations are the same after three mount times.

Abstract: Nowadays, the use of agricultural wastes is a high impact research area, due the fact that this kind of materials can provide some interesting properties to a polymer matrix. Among these materials, the seed shell are materials with no industrial applications, so it is necessary to find a use in the aim to avoid the pollution. The Styrene-butadiene copolymer (SBS) is a wide used material due it thermoplastic behavior. In present work, the inclusion of two different species of seed shell particles: (jatropha curcas seed particles (JCSP) and pistachio (PSP)) into a Styrene-butadiene copolymer (SBS) and their effect on the thermal behavior of the resulting composites have been studied. The composites were prepared by melting fussion process at different concentrations ranging from 2 to 10 phr (parts per hounded of resin). The obtained composites were characterized by means of Thermogravimetric analysis (TGA), Dynamic Mechanical Analysis (DMA) and infrared Spectroscopy (FTIR).