Volume 59, Issue 5

The main purpose of this experiment is to study the effect of batch annealing atmospheres on oxide scales by annealing in air, hydrogen and nitrogen at 1123 K for 72, 90 and 108 ks. Grazing incidence x-ray diffraction (GIXRD) and energy dispersive X-ray (EDX) were used to characterize oxide scales after batch annealing process. The morphology and oxide scale of the studied specimens were investigated by scanning electron microscopy (SEM) and optical microscope. Result obtained by GIXRD showed Fe 3 O 4 and spinel FeCr 2 O 4 oxide scales on the as-received hot-rolled specimens. After batch annealing in air, Fe 2 O 3 and (Fe,Cr) 2 O 3 oxide scales were found. Whereas after batch annealing in hydrogen, Fe 3 O 4 and spinel FeCr 2 O 4 oxide scales were found. In addition, after batch annealing in nitrogen, Fe 3 O 4 , (Fe,Cr) 2 O 3 and spinel FeCr 2 O 4 oxide scales were seen. Oxide scales after batch annealing in air are thicker than the scales after batch annealing in hydrogen, however thinner than those scales after batch annealing in nitrogen. The oxide scales thickness after batch annealing in hydrogen is quite equivalent to that found in the as-received hot-rolled oxide scales. Cracks were observed perpendicular to the rolling direction. Weight change after batch annealing in air is higher than that after batch annealing in nitrogen and hydrogen, respectively.

In this research, a newly developed moth-flame optimization algorithm (MFO) is presented for solving optimization problems in manufacturing industry. A well-known milling optimization problem is solved to emphasize the effectiveness of the MFO in the optimization of manufacturing problems. In the optimization problem solved in this paper, the main aim is to maximize the profit rate for multi-tool milling operations considering difficult constraints. The results demonstrate that the MFO is an effective optimization method for the solution of manufacturing optimization problems.

Important objectives when using high strength steel materials in the automotive industry are to reduce the weight and therefore the energy consumption of motor vehicles. Suitable test methods must be used to characterize the material specific properties in relation to hydrogen induced effects so that the materials can be used safely in body structures. Strained bend specimens and 4-point loaded specimens were used for this work. Both test methods have specific advantages and disadvantages and provide meaningful results in regard to the time delay in hydrogen assisted brittle fractures. Fundamental insights were obtained regarding the test procedure and the development of test methods for the impact of hydrogen on steel during manufacture and operation of respective components.

The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on “Concrete 1” (compressive strength f c = 80 MPa) and “Concrete 2” (f c = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 f c (Concrete 1) and 0.38 f c (Concrete 2) delivered specimen failures above 10 9 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.

In this study, wear behavior of ultrasonic impact treated S235JR steel was investigated. Samples were peened for different times (5, 15 and 30 minutes) by ultrasonic impact treatment. It was found that triple layers (nanocrystallization, plastic deformation and residual stress) formed on the treated surface. The thickness of the layers treated samples increased with increasing treatment time. It was also determined that surface roughness of treated samples decreased with increasing treatment time. All treated samples have significant surface hardness. Nanocrystallization layer on top of the treated surface has the highest hardness values in comparison with the hardness of the other layers. The treatment increases not only surface hardness, but also wear resistance of all treated samples. The maximum wear resistance was observed for the 30 min treated samples due to the high hardness and thickness of the nanocrystallization layers.

In this study, FeCrC, SiC and B 4 C powders were alloyed on the surface of AISI 430 ferritic stainless steel by plasma arc welding. The mass losses of the abrasive wear of the AISI 430 substrate were examined under the loads of 6, 10 and 16 N and in the distances of 10, 20 and 30 m by using Taguchi design method. The results of abrasive wear test were optimized by the minimum optimal control characteristics of the Taguchi procedure and the results were analyzed by using graphical methods. The Taguchi procedure is an important approach to achieve high quality without increasing the cost during the optimization of process parameters. The orthogonal planes of maximum effects of the controllable process parameters and minimum effects of uncontrollable process parameters were employed in the Taguchi method.

In the automotive industry, optimum design must be achieved to compete with strong competitors. Thus, it is aimed to reduce the cost, increase the quality and reduce the total production time. In this study, the natural frequency optimization of a vehicle sliding door linkage used to open and close the sliding doors on vehicles was made. In the optimization study for determining the optimum design model of the vehicle sliding door linkage, natural frequency was increased by 22.8 % using internal search algorithm.

In this paper, composite parts bonded with embedded single lap joint (SLJ) subjected to tensile load were analyzed by using 3D finite element method (FEM). In the analysis, the composite parts are carbon/epoxy (AS4/3501-6) with different fiber orientation angles and the adhesive is DP 410. The models for the numerical analyses were generated by using ANSYS software package. The finite element analyses (FEA) were carried out to predict the failure loads. Stress in x-, y- and z-directions, shear stresses and the von-Mises stresses on adhesive were obtained at the time of the failure for predetermined parameters. Consequently, the effects of orientation angles, overlap widths and length, and adhesive layer were examined. The most effective parameters were determined for composite parts adhesively bonded with embedded single lap joint.

Kurzfassung Zum Vergleich der Polyethylenformstoffe für eine Bauart von Gefahrgutverpackungen und IBC (Intermediate Bulk Container) wurden die folgenden Materialkennwerte der DIN EN 15507 (Verpackung – Verpackungen zur Beförderung gefährlicher Güter – Vergleichende Werkstoffprüfung von Polyethylensorten) ausgewählt: Schmelze-Massefließrate MFR, Dichte D, Kerbschlagzähigkeit a cN bei −30 °C, Spannungsrissbeständigkeit (bestimmt mit dem Full Notch Creep Test) und Beständigkeit gegen oxidativen Abbau Ox (bestimmt durch den prozentualen Anstieg des MFR in Salpetersäure). Das Ziel der Untersuchungen war die Auswahl eines Kennwertes für die Bestimmung des mechanischen Leistungsniveaus von Polyethylenformstoffen, da unter Druck Verpackungen beulen oder knicken. Zur Auswahl standen drei Prüfverfahren: a) Bestimmung der Biegesteifigkeit S nach DIN 53350 (Prinzip von Ohlsen), b) Bestimmung der Biegefestigkeit σ fM und Biegedehnung ∊ fM nach DIN EN ISO 178 und c) Bestimmung der Druckkraft F max und Verformung dL bei F max nach DIN EN ISO 604. Die Prüfmethode zur Bestimmung der Biegesteifigkeit nach DIN 53350 eignet sich zum Vergleich des mechanischen Leistungsniveaus der Formstoffe. Zur Verbesserung der Reproduzierbarkeit der Ergebnisse sollte der Skalierungsbereich der Prüfapparatur erweitert werden, um genauere Messergebnisse zu erzielen. Der Dreipunktbiegeversuch nach DIN EN ISO 178 eignet sich bei verformungsfähigen Kunststoffen, wie dem Polyethylen, zur Bestimmung der Biegefestigkeit σ fM . Dieser Versuch besitzt den Nachteil, dass am Ort des maximalen Biegemoments in der Randschicht, wo auch die maximale Biegespannung erzeugt wird, zusätzlich der Biegestempel angreift. Die Messergebnisse haben gezeigt, dass die Druckprüfung nach DIN EN ISO 604 sich sehr gut zur Bewertung des mechanischen Verhaltens der Polyethylenformstoffe unter Druckbelastung (Stapeldruckprüfung der Verpackungen) eignet.

This study explores the influences of laminates stacking sequence configuration on the mechanical behavior of hybrid composites. The woven carbon, Kevlar and S-glass fibers with epoxy resin were used to produce hybrid composite specimens in addition to full composites. The hybrid specimens were prepared by introducing different fiber volume fractions between carbon/glass, carbon/Kevlar, glass/Kevlar and carbon/glass/Kevlar fibers. Stacking sequence and fibers in outer skin of the laminates obviously showed the effective influence on tensile and flexural strength with modulus. The maximum change in tensile strength due to hybridization effect was achieved with carbon/glass epoxy laminate by replacing the two face sheets of the carbon fibers with glass fibers, resulting in an increase of tensile strength by 60 % according to full carbon/epoxy laminates. On the other hand, flexural strength of glass/Kevlar hybrid laminates showed the highest hybrid effect, resulting in 78 % increase according to full Kevlar/epoxy composites.

Numerical parameters have significant impact on the results of finite element simulations. Wrong selection of these parameters causes erroneous results and too long computation time in the analyses. Therefore, numerical parameters should be selected properly in order to obtain accurate results in the finite element simulations. In this study, the effects of the numerical parameters used in finite element simulations are investigated. Deep drawing of a double bowl sink is modeled and simulations are done with different parameters. Influences of element size and refinement level on the blank, the effect of the number of elements on the die radius and dynamic effects are investigated and optimum parameters are determined. The results obtained are compared with experimental data, and a good agreement is observed.

The toughness U T and shear modulus S of polyacrylamide (PAAm) – multiwalled carbon nanotube (MWNTs) composites were studied with various MWNT contents. These composites were prepared via free radical crosslinking copolymerization with different amounts of MWNT varying in the range between 0.1 and 50 wt.-%. The MWNT content dependency of the shear modulus of the composites due to volume phase transition was measured using tensile testing at 30 °C. It was observed that the composite preserves the ability to undergo the volume phase transition and its elastic modulus is strongly dependent on the MWNT content. The observed shear modulus first increased and then decreased above 1 wt.-% MWNT content during such loading tests. The toughness showed exactly the reverse behavior dependent on the MWNT content, as compared to the elasticity and as expected.

Wear characteristics of composites, Al matrix reinforced with B 4 C particles percentages of 5, 10,15 and 20 produced by the powder metallurgy method were studied in this study. For this purpose, a mixture of Al and B 4 C powders were pressed under 650 MPa pressure and then sintered at 635 °C. The analysis of hardness, density and microstructure was performed. The produced samples were worn using a pin-on-disk abrasion device under 10, 20 and 30 N load through 500, 800 and 1200 mesh SiC abrasive papers. The obtained wear values were implemented in an artificial neural network (ANN) model having three inputs and one output using feed forward backpropagation Levenberg-Marquardt algorithm. Thus, the optimum wear conditions and hardness values were determined.

For speeding up motor vehicles, new brake disk materials with higher frictional need to be developed. Brake disks work under very difficult thermomechanical conditions due to high temperature and wear. As most of commercial disks have high wear rate and low braking performance, there is a need for development and manufacturing of new disks-brake linings to reduce wear and to increase braking performance in motor vehicles. Ceramic coated disks have shown good stability in friction coefficient at a high speed and high energy braking conditions. Therefore, flame spraying technique for cermet coating materials has been chosen as a good method to produce coatings on a metallic substrate. In this study, a sample cast iron disk with ventilation channels coated with NiCrBSi-%35W 2 C powder by the flame spraying method were investigated. The braking performances of uncoated disk and coated disk were tested according to SAE J2430 test standard. It was found out that the coated disk had lower surface roughness and higher coefficient of friction than the uncoated disk. The NiCrBSi-%35W 2 C coated disk exhibited less wear, a higher coefficient of friction and longer life than the uncoated disk. As a result, the NiCrBSi-%35W 2 C coated disk could be a much better alternative for a new generation of brake disks in the motor vehicles than the uncoated disk.