Deniz Uzunsoy

Contribution of MoS2 additives to the Microstructure and Properties of PM Copper Based Brake Material

Abstract The effect of a MoS2 additive on the microstructural evolution and properties of copper based brake linings has been investigated in this study. It was found that the quantity of additive as well as sintering cycle has significant effect on the density and hardness values of the produced material. The microstructure of designed brake lining materials showed that copper based matrix was surrounded by MoS2 particles. The microstructural investigation also proved that the lower boiling point elements such as Pb in the as-supplied powder vaporise during sintering from the structure, and this result in an increase in the porosity amount by lowering the overall density of brake linings. The Vickers hardness of brake linings decreased with the addition of molybdenum disulphide particles. MoS2 addition reduces wear rate of samples due to the solid lubrication effect.

Synthesis and characterization of graphene-epoxy nanocomposites

Abstract Graphene, a monolayer of carbon atoms arranged in a two dimensional lattice, has attracted great attention in recent years due to its extra ordinary properties and potential applications. One obvious application of graphene is in the field of nano-composites. In this work, graphene platelets (GPL) reinforced with epoxy nano-composites were fabricated by using soft molding technique in two different ratios with two different solvents. Raman spectroscopy and scanning electron microscopy (SEM) were used to investigate the structure of graphene and graphene reinforced composites. Tensile and dynamic mechanical analysis (DMA) in three point bending mode were used to investigate the mechanical properties of the composites. The tensile strength and strain to failure of nanocomposites of GPL reinforced epoxy nanocomposite were enhanced by 9.31 % and 34.78 %, respectively, while small improvement is observed in the elasticity modulus. Dynamic mechanical analysis has shown that with the addition of 0.1 and 0.5 wt.-% graphene nanoplatelets, storage modulus has increased by 20 and 46 % on the glassy region, respectively. The glass transition temperature is not affected with addition of graphene.

Non-Linear Modelling of PM Brake Lining Wear Behaviour

Abstract The brake friction materials in automotive brake systems play an important role in the overall braking performance of a vehicle. Wear test results have previously been presented for a 1040 steel disc interacting with a PM copper-based brake lining material without and with MoS2 additive at constant applied load and sliding velocity. In this paper, a non-linear model has been developed and compared with a previously developed linear model and experimental results. Nonlinear ARX model structure with sigmoid network having one hidden layer was used to find the best possible results. Linear and non-linear approaches have been applied to simulate the wear behaviour of the brake lining material. Comparative results showed that the nonlinear model provides results closer to the experimental study. Therefore, non-linear process modelling can be used as an effective tool for the prediction of brake lining material properties instead of time-consuming experimental processes.

Linear Model for PM Brake Lining Material Wear Behaviour

Abstract This paper presents a linear model for the dry sliding wear behaviour of a PM copper based brake lining material with the addition of MoS2. The model was based on experimental results related to standard pin-on-disk wear tests of the brake material with various MoS2 contents at constant applied load and sliding velocity. The wear load was considered as the input parameter, whereas the wear rate and friction of coefficient as the output parameters. The predicted results were compared with experimental results by simulating a linear process for each MoS2 content of the material, and it was found that the results obtained from such linear process modelling were satisfactory. The results showed that the linear process model represents an useful tool for the prediction of the brake lining material properties, and that it is more effective than timeconsuming experimental procedures.

Characterization of Boron Doped 316L Powder Metallurgy (PM) Stainless Steel

Abstract Powder Metallurgy (PM) is a shaping technology which is based on forming powder particles in a mold under high pressure. This method influences cost of parts significantly due to direct molding. Sintering is one of the most critical steps of a PM process. Mechanical and physical properties of the final product are enhanced by the optimisation of sintering conditions (temperature, time, and type of the atmosphere). The demand for PM products with high performance is increasing day by day. In this context, one way to increase the strength of the part is to perform sintering process by alloying powder. Boron was found to be useful for the activation of sintering process of iron powder in the previous study. In recent times, research is increasingly focused on the Boron addition to improve the density of PM stainless steel parts after sintering process. In this study, the influence of Boron addition into PM 316L stainless steel materials on the microstructure and properties of the final part has been investigated in detail. Boron addition is varied from 0.2 to 1 wt.-%, and the effect of Boron on the densification and distortion behaviour of stainless steel has also been studied. All samples are characterised by using several techniques such as SEM, EDX, image analysis.

Suggestion of an Indicator to Evaluate Material Deposition in Resistance Spot Welding: Weld–Surface Interaction Index

Resistance spot welding (RSW) is still leading joining process in the automotive industry due to the simplicity and speed of the process. On the other hand, galvanized steel sheets provide improvement in corrosion resistance of the auto body. Material deposition has an influence on the corrosion resistance and weld strength; however, in the literature very little effort has been made to identify any weld–surface interaction numerically. In this study, a numerical approach called “Weld–Surface Interaction Index” (IWSI) has been introduced to investigate the effect of material deposition on the corrosion sensitivity of the welding zone and its periphery. A systematic investigation was carried out to better understand the effects of an electrode cap–galvanized steel sheet interface on the corrosion resistance of spot-welded steel. The chemical composition of DP600 steel sheet and Z-Trode electrode cap was analyzed by using a spectrometer. The specimens were then joined by using same caps up to 1200 welds. SEM–EDS analysis was also performed on the chosen specimens to determine the weight percentages (wt.%) of Fe, Zn and Cu. EDS analysis results and coefficient of variation wt.% of Fe, Zn and Cu were used to compose IWSI formula. In the proposed formula, wt.% of Zn represented resistivity of the cover to corrosion, while wt.% of Fe represents the vulnerability.

Modeling of Storage Modulus of Graphene Epoxy Nanocomposites

In this work, the storage modulus of epoxy and graphene-epoxy nanocomposites are modeled using a temperature and rate dependent modulus formulation. The stiffening effect of reinforcements is included to the elastic modulus formulation for the modeling of nanocomposite materials. Simulation results are compared to experimental data from Acar et al. [1]. Keywords—graphene, epoxy, storage modulus.