Volume 61, Issue 2

Electrical connectors for signal applications in the automotive sector are subjected to stringent requirements. These systems must ensure dependable signal transmission throughout the service life of a vehicle, even under high stress conditions. To this end, redundantly structured contact systems with several lamellas are often used. Stress due to vibrations during vehicle operation can lead to relative displacements between the electrical contact partners, especially in the resonant frequency range of the connector. Fretting corrosion then leads to increased electrical resistance at the connection and to failure of the system when a certain resistance threshold is exceeded. For studying the durability of electrical contacts, a fretting test bench was developed that allows the emulation of stress due to vibrations on a contact system with test frequencies of up to 300 Hz. The Wöhler model was used for describing the durability as a function of the relative motion. The test procedure and evaluation for determining the model parameters were based on the pearl string method. The test unit was qualified as electrically failed if the resistance exceeded the 15 mΩ threshold. The studies showed that the lifetime of the redundantly structured contact system can be described via an analytic approach based on the methodology for determining Wöhler curves. The distribution function was based on a logarithmic normal distribution. With the aid of scanning electron microscopic analyses in combination with element distribution images from energy dispersive X-ray spectroscopy, it was possible to attribute electrical failure to the oxidation of the base material in the wear track.

Reliability-based design optimization (RBDO) is an effective method for structural optimization due to its ability to take into consideration uncertainties in design variables. Performance measure approach (PMA) based methods are commonly utilized to evaluate the probabilistic constraints of RBDO problems. The advanced mean value (AMV) method is a very commonly used due to its simpleness and effectiveness. However, the AMV method sometimes produces unstable and inefficient results for concave and highly nonlinear limit-state functions. In order to improve robustness and efficiency, many methods have been developed, for example, chaos control based and conjugate gradient-based methods. These methods lead to more stable results as compared with the AMV approach but they are inefficient for use in complex and convex limit-state functions. The RBDO of structural components is often a difficult issue due to complicated constraints. In this paper, a novel hybrid approach, referred to as “hybrid gradient analysis (HGA)” is introduced for the evaluation of both convex and concave constraint functions in RBDO. The HGA method combines AMV and conjugate gradient analysis (CGA). The robustness, simpleness and effectiveness of the proposed HGA method are compared with various PMA methods aimed at reliability such as AMV, chaos control (CC), conjugate mean value (CMV), modified chaos control (MCC), hybrid mean value (HMV) and CGA methods by means of several nonlinear convex/concave limit-state functions and structural RBDO problems. Reliability analysis and RBDO results point out that the HGA approach introduced here is more effective and robust than the well-known approaches.

The chemical and microstructural heterogeneities of arc welded joints of duplex stainless steel (X2CrNiMoN22-5-3) and chromium-molybdenum (13CrMo4-5) low alloy steel have been investigated. Rutile coated electrodes containing chromium and molybdenum amounts similar to that of duplex stainless steel but with a higher nickel content have been selected for the manual welding of the joints. The higher nickel content has been chosen, since nickel promotes the formation of austenite and induces an approximately equal proportion of ferrite and austenite in the weld. At the interface between the low alloyed steel and the weld metal as well as in the cross section of the weld metal, chemical and microstructural variations have been determined.

Pre-cracked 304 stainless steel compact tension specimens were repaired by a CO 2 laser at the crack tips with the addition of different weight fractions of nano-Al 2 O 3 . Crack opening displacements were measured by a digital image correlation system for the evaluation of fracture performance. Microstructures of the repaired areas were examined by scanning electron microscopy equipped with an energy dispersive spectrometer. Results indicated that laser repair with the addition of 1.0 wt.-% nano-Al 2 O 3 resulted in metallurgical bonding at the interface and fine columnar crystal in the repair layer. The addition of nano-Al 2 O 3 increases sites of heterogeneous nucleation, which acts as a fine-grain strengthener. In addition, the uniform distribution of nano-Al 2 O 3 plays a role in dispersion strengthening, resulting in improved fracture performance by approximately 10 % to 30 % as applied loads varied from 1 to 20 kN. However, the excessive addition of nano-Al 2 O 3 gives rise to the agglomeration and micro-cracks in the repair layers and clear detachment are observed at the interface.

The scarcity of fossil fuels may lead to a depletion of coal, oil and natural gas in the near future. Alternative fuels, especially biofuels, are receiving considerable attention for their environmental benefits. Biodiesel is a renewable and clean burning fuel that is made from waste vegetable oils, animal fats, or recycled restaurant grease for use in diesel vehicles. Biodiesel produces fewer toxic pollutants and greenhouse gases than petroleum diesel. Many biofuels have been extracted and synthesized but little has been undertaken to study their effects on corrosion. The present investigation aims to evaluate the wet corrosion behavior of copper in used groundnut oil (UGNO) as a biofuel. The varieties of its blending ratios with commercial diesel (5, 10 and 20 %) were studied in accord with the mass loss method for a period of 100 h. The corrosion rate of the metal was evaluated according to mass loss and electrochemical methods. The corrosivity and conductivity of the test media were positively correlated. Wettability studies also supported the non-corrosive nature of biodiesel.

Centrifugal pumps play an important role in the fluid engineering industry due to their high energy conversion capabilities. It is important to understand form to achieve a successful pump design. In the scope of this research paper, a novel approach to the performance evaluation of a centrifugal pump was used. A precise design of the pump components should be considered a key factor for increasing the pressure-induced performance. The aim of this investigation is to produce an innovative pump and to compare its actual performance with the results derived from numerical analysis. A novel pump was designed, analyzed, manufactured and then tested. Test results indicate that the numerical efficiency was close to 91.72 vol.-% of the virtual experimental efficiency thanks to our precision approach. The operational parameters of the pump are illustrated, and crucial points emphasized to facilitate an understanding of the decision-making process. This novel method may be beneficial for those looking for alternative pump designs.

Friction stir welding frequently produces a superior microstructure and mechanical properties than conventional methods for welding nonferrous materials and alloys. In this study, friction stir welding was used to join sheets of the aluminum alloy AA7075 with commercially pure copper cpCu. Two rotational speeds, 660 and 920 rpm, and three welding speeds, 18, 32 and 54 mm × min −1 , were studied to determine the effects of these parameters on the structure and mechanical properties of friction stir welded AA7075-cpCu. The joint performance was investigated by conducting optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), by microhardness measurements and mechanical testing (e. g. tensile tests). A maximum tensile strength of 224 MPa and percentage elongation of 2.49 were obtained when friction stir welding process parameters, namely rotational speed and welding speed, were kept at 660 rpm and 32 mm × min −1 , respectively.

The aim of this research is to investigate the mechanical properties of a new bio-filler particle reinforced composite reinforced by recycled waste mussel shells. To this purpose, waste mussel shells were collected from a mussel trader and recycled in two stages: coarse processing using a hammer and fine processing by means of a rod mill. A size distribution analysis was conducted for the mussel shell particles after the recycling process. According to the results of the analysis, the particles were 74 μm in mean diameter with a 60 μm standard deviation. Vacuum assisted resin infusion molding, which is generally used to produce fiber reinforced composites, was used as the method of production. Subsequently, test specimens were prepared according to related standards and the mechanical properties of the composites such as micro-hardness, tensile strength, compression strength and flexural strength were investigated experimentally. Thetests were repeated five times for each mechanical property. It was determined from these experiments, that recycled mussel shell particle reinforced epoxy composites have a micro-hardness of approximately 170 HV, 24 MPa ultimate tensile strength, 112.8 MPa ultimate compression strength and 75 MPa flexural strength. Furthermore, flexural modules of the composites were calculated at 36.72 GPa. All experimental results are presented in graphs and tables. Finally, the results determined for these new bio-filler reinforced composites were compared with results pertaining to other alternative fillers available in the literature.

In the present work, the mechanical properties of banana fiber – vinyl ester composite were investigated. The stacking of the layers was accomplished by hand-lay-up techniques and composites were produced by compression molding. The effect of the layering sequence on the mechanical properties, namely tensile, flexural and impact, was analyzed and is discussed in this paper. The natural fibers were extracted and processed locally. It was observed that the hardness of the samples was influenced by an increase in banana fiber content in the composite. Thus, banana fiber composite could be considered for applications in areas where high impact strength is a requirement such as in some automobile parts.

The effects of the rare earth elements Ce, La and Sm on the microstructure and mechanical properties of a die-cast aluminum alloy were studied. First, the optimal percentage content of the main elements in the alloy was determined by a single factor and by orthogonal experiments based on the composition range of ADC12 aluminum alloy. The results showed that the optimal percentage content of the main elements in ADC12 die-cast aluminum alloy were 11 wt.-% Si, 2.5 wt.-% Cu, 0.5 wt.-% Mn and 0.3 wt.-% Mg. The tensile strength was 285 MPa and the fracture strain 2.23 %. Then, three rare earth elements of varied contents were added to the above-mentioned aluminum alloy. The tensile strength and elongation of the alloy were increased through the addition of rare earth elements. The comprehensive mechanical property of the alloy was best when Ce, La and Sm levels were at 0.6, 0.4 and 0.2 wt.-%, respectively, in the single factor test. Sm had the largest influence on the comprehensive mechanical properties of the alloy, followed by Ce and La which had the least influence.

The role of MnS in the nucleation of intragranular acicular ferrites (IAF) has been explored in Ti-Mg treated steel sample through scanning electron microscope (SEM) and energy dspersive spectrometer (EDS). When compared with a non-treated sample, Ti-Mg treatment evolves from Al-Mn-Si-O inclusion to Ti-Mg bearing inclusion and causes a reduction in pure MnS. In addition to this reduction in pure MnS, a precipitation of MnS around the Ti-Mg bearing inclusion can be observed. Moreover, after etching, it can be found that Ti-Mg bearing inclusions can induce IAF nucleation. Based on EDS line analysis and a comparison with Al-Mn-Si-O inclusion in non-treated sample, this effect can be explained by the presence of an Mn-depletion zone (MDZ) caused by the vacancy property and crystal structure of the inclusion. It should be added, however, that in the same sample, a similarly induced nucleation effect as well as an MDZ have not been observed around pure MnS. This comparison implies that the formation of an MDZ may be independent of MnS precipitation.

The continual usage of computers produces excessive heat, which directly affects the processor. The main reason for computer failure is an increase in chip temperature which degrades the performance, reliability and the lifespan of a computer. In order to avoid these limitations, excessive heat should be transferred to the environment. This research article proposes to analyze heat transfer in microprocessors through graphene layer coating. Heat transfer in pure and graphene coated microprocessors, based on 0 %, 50 % and 75 % central processing unit (CPU) usage, has been investigated. Initially, graphene was mixed with ethanol and spin-coated on the surface of microprocessor. Scanning electron microscopy (SEM) analysis confirms the deposition of a graphene layer on the substrate. Applying graphene to the surface of the substrate significantly improves heat transfer due to high thermal conductivity. A maximum of a 5.6 °C difference in heat transfer has been achieved by introducing a graphene layer on the substrate. This experimental analysis proves that graphene is a suitable material for electronic applications.

The Taguchi procedure is an important method for obtaining high quality without increasing the cost in the optimization of the process parameters. In the Taguchi procedure, the orthogonal planes of the maximum effects of the controllable process parameters and the minimum effects of the uncontrollable process parameters were used. In this study, B 4 C, SiC, and FeCrC powders were alloyed on the surface of an AISI 430 ferritic stainless steel by plasma transfer arc (PTA) welding. The abrasive wear of the various specimens was measured by the mass loss at a load between 10 and 16 N using SiC abrasive paper with a 60 and 240 mesh and over distances between 20 and 30 meters. The effects of the parameters with respect to the lowest wear behavior as an important criterion were optimized by the lowest-the best control characteristic of the Taguchi method. The results were analyzed by graphical methods.

The thermal degradation behavior of poly(vinyl chloride) (PVC) and poly(N-vinylpyrrolidone) (PVP) blends was investigated using potentiometric measurements of the released HCl gas during the degradation process, estimating the degree of discoloration of the degraded samples and measuring the thermal stability (Ts) values. The influence of the PVP percentage in the blend and, moreover, of the addition of commercial dibasic lead carbonate stabilizer to the blend was studied with regard to thermal stability. It turned out that the dehydrochlorination rate of the blend was promoted by increasing the PVP concentration in the blend.