Deniz Uzunsoy

Sandwich composites are preferred in many sectors such as aerospace, automotive, and construction due to their lightweight nature and high tensile and flexural strength. In this study, the flexural strength properties of glass fiber reinforced sandwich composites were investigated. The core materials were used as extruded polystyrene (XPS) and polyethylene terephthalate (PET); the matrix material was epoxy. The sandwich composites were produced by resin infusion under flexible tool method by bonding them with glass fibers on the outer surfaces. Surface laminates consisting of glass fiber reinforced epoxy material were arranged according to two stacking orders: 0°/-45°/+45°/90° (Type I) and 90°/-45°/+45°/0° (Type II). Three-point bending tests were used for mechanical performance evaluations. Stereo microscope analysis was applied to examine the surface images. According to the test results, it was observed that Type I samples had higher maximum loads than Type II samples; XPS Type I reached 355 N (±5 N) and PET Type I reached 1375 N (±25 N). In addition, layer separation and cohesive matrix fractures were observed.

The environmental risks caused by accumulated rubber wastes have increased the need of recovering these wastes rather than disposing of them. Pyrolysis of waste rubber is recognized as a promising technique. While pyrolysis products oil and gas have previously found industrial applications, there is currently a shortage of viable applications for the solid pyrolysis residue, recovered carbon black (RCB). This study examines the potential use of the RCB as a substitute for virgin carbon black (VCB) in Ethylene Propylene Diene (EPDM) rubber formulation. The goal of this research is to expand technical understanding about the use of the RCB as a green raw material in the rubber industry. In order to characterize the VCB and RCB, Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDX), Fourier Transform Infrared (FTIR) analyses, and standard test methods were used. The compounds were produced by replacing the VCB with RCB in the EPDM matrix at various loadings. The influence of the RCB addition on the rheological, physical, mechanical and thermal properties of the EPDM composites was evaluated and compared to those formed with the only VCB. The RCB filled compounds usually show detectably inferior properties compared to the only VCB filled compound due to more impurity content, less active surface area, and limited surface functionality of the RCB filler. Although, the VCB can’t be completely replaced by the RCB, the results showed that overall performance of the 75-25 compound is better than the reference compound with 100% VCB filler. Moreover, the more RCB may be utilized in combination with the VCB depending on the permissible deviations from the properties of the end products.

CuCrZr alloy is a widely preferred material in the space, defense, and electronics industries with its high thermal and electrical conductivity properties. There are limited publications on the investigation of the tribological properties of CuCrZr alloys produced via the selective laser melting (SLM) method. In this study, it was aimed to optimize the process parameters and examine the effect of process parameters on density, hardness, microstructure, and tribological properties of domestically produced CuCrZr powder to be produced by the SLM method, which allows the production of complex structured parts. The optimum process parameters of the CuCrZr alloy were determined as laser power of 435 W, scanning speed of 350 mm/s, layer thickness of 0.02 mm, laser diameter of 0.1 mm, hatch distance of 0.1 mm, and energy density of 621.42 J/mm3. The relative density, hardness, COF, and wear values of the samples produced with the optimized SLM process parameters were obtained as 99% and 96 HV, 0.5520 ±0.1648, and 1.17x 10-4 (mm3/N.m), respectively.

Polyaniline boronic acid, a conducting polymer with unique properties, has gained attention for its potential applications in batteries, sensors, drug delivery systems, and electrochemical devices. Understanding the redox behavior of this polymer in the presence of sugars is of particular interest due to the potential implications for its functionality in various applications. Cyclic voltammetry is employed to analyze the redox behavior of the polymer in aqueous solutions with glucose and table sugar. Preliminary results suggest that the presence of glucose improves, and table sugar declines the peak values. The diffusion coefficient of the polymer is found as 2.6x10-9 cm2/s. The choice of supporting electrolyte, exemplified by potassium carbonate and potassium chloride, also exhibited an influence on redox behavior of polyaniline boronic acid, and peak potential and peak values are higher in potassium chloride solutions.

In this study, mechanical properties of continuously cooled low carbon steels were predicted via Artificial Neural Network (ANN) and Multiple Linear Regression (MLR) models. Unlike the previous studies, laboratory scaled self-generated data that consists of chemical compositions and cooling rates were used as input while yield strength (YS), ultimate tensile strength (UTS) and total elongation (TE) were served as target data. The prediction performances of the models were compared by applying new data set extracted from external sources like previously studied research papers, thesis or dissertations. A better agreement between predicted and actual data was achieved with ANN model. Additionally, the response of ANN model to new external data resulted in lower prediction errors even the data has one or more input value that is not included in the range of training data set. Unlike ANN model, MLR model shows a significant decrease in prediction accuracy when input data has non-uniform distribution or target data takes place in relatively narrow range. In general, it was shown that ANN model trained with self-generated data can be used as an efficient tool to estimate mechanical properties of continuously cooled low carbon steels that are produced with various conditions, even for the phenomena between input and output is complex and data distribution is non-uniform.

This study is concerned with the optimisation of the processing parameters for the selective laser melting (SLM) of pure copper. The influence of these parameters on the microstructure, density and mechanical properties of copper samples produced by SLM is investigated in detail. Taguchi analysis is used to assess the importance of key building parameters including layer thickness, laser spot size and hatch distance on density. In addition, ANOVA is used to describe the contribution of each parameter to the density. The results reveal that layer thickness is the most effective parameter on density with an impact rate of 88.86%. Contrary to this situation, it appears that the effect of laser spot size and hatch distance on the density is quite limited, with an impact rate of 2.57% and 0.10%, respectively. Optimum results, including a relative density of 95.4% and a hardness of 63 HV, are achieved under specific parameters: a layer thickness of 0.03 mm, a hatch distance of 110 mm and a laser spot size of 70 ?m. This study provides a valuable insight into SLM processing of pure copper and offers practical recommendations for optimising the parameters used.

This study aimed to determine the effects of varying Aluminum oxide (Al₂O₃) and Graphene Nanoplatelets (GNP) concentrations on epoxy-based polymer composites’ mechanical and tribological characteristics. Al₂O₃ (1 to 5 wt.%) and GNP (0 to 1 wt.%) reinforced epoxy matrix composites were produced with sonication and stirring magnetic route. Mechanical, microstructural and tribological properties of composites were investigated via X-ray diffraction (XRD), Archimedes’ Method, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Raman spectroscopy, hardness, impact, tensile, compressive and wear tests. The highest ultimate tensile strength and compressive strength were found at 62.83 and 137 MPa for 3 wt.% reinforced Al₂O₃ epoxy matrix composites, and it was observed that there was a 38% and 17% increase compared to neat epoxy, respectively. The highest impact strength was found for 3 wt.% Al₂O₃ and 1 wt.% GNP-reinforced composites and increased by 19% compared to neat epoxy. The best hardness was found for 3 wt.% reinforced Al₂O₃ and 0.25 wt.% GNP-reinforced composite, and there was a 22% increase in hardness compared to neat epoxy. Also, the highest wear resistance (1.686x10⁻⁶ mm³/Nm) and lowest Coefficient of Friction (COF, 0.13755) were determined for the same specimen.