Volume 60, Issue 3

Abstract: Since the invention of the first UAV’s, different industries realized it’s capabilities and potential uses. Drones and UAV’s are part of our everyday life and their development has seen an unprecedented speed due to their multiple applications, from scientific research to military applications. When we talk about UAV’s we also talk about composite materials. Today’s drones and UAV’s are using almost exclusively carbon fiber, glass fiber and 3D printed materials. This paper presents the development and testing of fiber carbon materials along with a future concept of an UAV. In the end of this paperthe results of testing the materials are presented.

Abstract: The present work studies the positive or negative effect of zeolite mineral on the tensile and flexural mechanical behavior of a wood-plastic composite. Eight different blends were developed, the components used were wood flour (WF), polypropylene (PP), zeolite (Z) and maleic anhydride modified polypropylene (MAPP) as coupling agent. The eight blends were made using a counter-rotating twin-screw extruder, while the specimens were produced on a plastic injection molding machine with a 60ton clamping capacity. The standards used to determine the tensile and flexural mechanical properties were ASTM 638 and ASTM 790, respectively. Ten repetitions of each mixture were carried out. In addition, a reference (100% polypropylene) was used to compare the results obtained to determine whether the effect of using the zeolite mineral generated positive or negative results in the compounds obtained. Both studies showed that as the proportion of zeolite increases in the blend, the tensile and flexural properties are affected. However, the mixture (M7) with proportions in its components of, 34.375% WF, 55.875% PP, 6.75 % Z and 3% MAPP, showed an increase in the tensile and flexural mechanical properties, indicating a strong relationship between the components that integrate the wood-plastic composite (WPC), mainly between wood and mineral.

Abstract: Personalizing prosthetic components based on individual anatomical landmarks can increase implant lifespan and it can reduce the postoperative complications due to prosthesis geometry that does not mold on the patient’s anatomy. This article aims to present a method of optimizing shoulder prostheses by conducting both medical and technological studies, based on which a personalized prototype was obtained, designed according to the patient`s landmarks. Thus, a computer-assisted methodology has been developed that targets the preoperative planning of shoulder arthroplasty starting from the traditional planning used by orthopedic surgeons, as well as the principles of determining the relevant humeral parameters. Initially, a set of DICOM CT (Digital Imaging and Communications in Medicine) patient scans with a presumed fracture at the glenohumeral joint requiring a shoulder arthroplasty was used. The acquired data were transferred to a medical image processing software, where was performed the bone segmentation, specifying the image processing algorithms used to reconstruct the geometry of the patient`s shoulder. The 3D model of the humerus obtained during this stage was imported into a CAD (Computer Aided Design) software application where the humeral anatomical landmarks were established and used to design a suitable prosthesis according to patient`s needs, which was manufactured through additive manufacturing using a biocompatible material.

Abstract: Positive airway pressure (PAP) is the standard treatment for patients with moderate to severe obstructive sleep apnea, especially when a correctable anatomic obstacle is not identified. The PAP efficiency strongly depends on the appropriate use during sleep. Despite the recent advancements in PAP interface designs, overall adherence to therapy remains low. The main sources of discomfort consist of air leakage and mask overtightening leading to skin problems. However, these disadvantages have been partially reduced by new interfaces like nasal pillows that have the capacity to reduce the contact of the silicone cushion with the skin, reducing the chances of skin irritation. At the same time, assuring a better seal prevents air leakage and is particularly useful in patients with internal valve insufficiency. We present a case of a 57-year-old patient with severe sleep apnea syndrome whose efficient treatment was delayed by an inadequate PAP mask prescription at diagnosis. Due to low treatment compliance secondary to the perceived adverse effects of the oronasal mask, the patient decided to discontinue treatment for two years with subsequent aggravation of sleep apnea symptoms. The patient’s sensitivity to the silicone mask cushion and treatment ineffectiveness due to internal valve collapse were the main causes of treatment failure. After changing of PAP interface, the patient achieved long-term compliance. Our case report reflects the importance of choosing the most suitable PAP interface in accordance with the patient’s particularities. In the absence of this approach, appropriate treatment might be delayed with detrimental consequences, especially in severe cases. Considering PAP adherence following therapy initiation usually predicts long-term compliance, finding the best mask design from the beginning can predict therapeutic success.

Abstract: The materials of the article are devoted to obtaining the material based on a mixture of natural rubber with the refractory cement filler in a certain proportion and the study of its physical and mechanical characteristics. The samples with different cement contents were formed to determine the optimal proportion of cement additives in the mixture. The resulting analysis showed that the material with a cement proportion of 15 (pphr) has the best characteristics, in which an increase in the values of the maximum tensile pressure (8.98 MPa) was achieved, a decrease in the values of elongation, while an increase in the value of hardness and wear resistance, and minimum level of absorption was observed when the samples were immersed in technical oil - by 1.29%.

Abstract: Nowadays, the increasing use of plastic materials in friction and wear applications, particularly in industrial robotic grippers, is a growing trend in modern industry. Plastics are replacing traditional materials like metals and composites due to their unique properties and significant advantages. Plastic materials used in industrial robotic grippers offer several advantages, such as their low friction coefficient, enabling smooth and precise movement of the gripper and minimizing the risk of damaging the objects being manipulated. This paper presents a comparative study and analysis of the friction coefficient between various plastic materials and the C45 alloy steel, a superior alloy used in industrial applications. The investigated materials include PETG, PLA, PLA with aluminum, ABS, two types of TPU, and two types of UV-sensitive resins. This study aims to evaluate the friction performance of these materials in order to identify the most suitable options for friction and wear applications, such as industrial robotic grippers. To achieve this, dry kinetic friction tests were conducted between 3D printed plastic material samples manufactured by using FDM and SLA technologies, and the C45 alloy steel on the CETR UMT-2 tribometer. The friction coefficient was measured by recording the force required for displacement in two horizontal directions.

Abstract: The plastic speed meter housing for automobiles requires accurate parts and assembly to inform the driver of their exact speed. For accurate assembly, the molded speed meter should have a minimize amount of deformation. In this study, to obtain injection molding conditions that minimize the deformation of the speed meter, the main molding conditions that cause the deformation of the speed meter were identified using the Taguchi method. By combining the confirmed molding conditions, 150 data sets were created, and machine learning was conducted using the data set. The model with the best accuracy learned through machine learning was the Linear Regression model. The results of this Linear Regression model were then validated with test data. The optimal injection molding conditions were derived by inputting 5000 molding conditions data into the learned Linear Regression model. Injection molding analysis was performed using the derived injection molding conditions, and the amount of deformation was reduced by about 6.4% compared to the case where current molding conditions were applied. The optimal molding conditions obtained by machine learning were applied to actcual molding. The amount of deformation of the mold amount of the molded speed meter housing was smaller than the amount of deformation predicted in the machine learning model.

Abstract: This study has proved the value of the bioplastics in replacing the classical polymers used for various applications by employing a new and original econometric model which underlines the interdependence between the bioplastics price and the following mechanical properties: Young modulus, Tensile strength and Elongation at break. The model was applied for 5 different bioplastics: polylactic acid (PLA), cellulose acetate (CA), poly (butylene succinate) (PBS), Bio-polyethylene (Bio-PE) and Bio-polyethylene terephthalate (Bio-PET). The biopolymers cover a large range of bioplastics both biodegradable and non-biodegradable. The developed model was run on Gretl software using the OLS (ordinary least squares) method. The residuals values are acceptable which means that the interdependence model fitted well the known data. Among all bioplastics studied, polylactic acid (PLA) exhibits the best constants in terms of reproducibility. All the regression equations obtained for the econometric study offer the possibility of forecasting the price for any other sort of bioplastic and it is a useful tool for assessment the financial impact of a bioplastic.

Abstract: The paper proposes the analysis of strain and stress state, through experimental and numerical means, of a circular hole type concentrator. The strain state is analyzed through the microscopic Digital Image Correlation technique, due to the small scale of the samples, whose calibrated region is 10x8 mm. The numerical analysis is conducted using the Finite Element Method, through a static structural analysis, using a linear-elastic material model. The results from the two procedures are compared by means of strain field distribution around the stress concentrator and stress variation at the concentrator peak cross section. For validation, the analytical gross stress concentrator of the problem is used as baseline, Ktg. The results show that accurate reading can be achieved on this small scale. Additionally, the experimental method has also successfully identified crack initiations and propagations on the tested samples, significantly smaller than 1 mm, which can reveal future fracture mechanics analysis and supply data to models adapted to microscopic scale phenomena.

Abstract: The main objective of the research was to study the influence of the abrasive water jet cutting (AWJC) parameters on the surface roughness parameters Rz1max and Rt, obtained when processing Kevlar fiber-reinforced polymers (KFRP). For this purpose, a full factorial experimental program was designed and roughness evaluations were carried out in two different zones of the cut slot. In this way, it was possible to test the statistical significance of the input parameters effects and characterize both these regions, by means of prediction models proposed for each roughness parameter. Finally, response surfaces and level curves were represented to facilitate the selection of proper factors combination to achieve surface finish requirements.

Abstract: A study was conducted on SEBS-based composites granules containing different volume fractions of carbon nanotubes (CNTs) using a twin extruder and hot pressing procedure to produce a SEBS/CNTs membrane. SEM was used to study the membrane`s morphology, revealing a 3-D network of CNTs. TGA was utilized to measure the degradation temperature of SEBS polymer and determine the actual volume fraction of CNTs. The mechanical properties, electrical conductivity, and cyclic strain sensing behavior of the SEBS/CNTs were investigated using a tensile testing machine and pico-ammeter. Mathematical models were used to fit the measured data, demonstrating the strain sensing potential of the composites. The composite membrane with 2 wt.% of CNTs exhibited superior electromagnetic wave absorption performance with a minimum reflection loss (RLmin) value. This study provides promising opportunities for the development of advanced materials.