Volume 55, Issue 5

The demand for lightweight construction in mechanical and civil engineering has strongly promoted the development of high strength steels with excellent damage tolerance. Nowadays, the requirements from mechanical and civil engineering are even more challenging, as gradients in mechanical properties are demanded increasingly often for components that are utilized close to the limit state of load bearing capacity. A metallurgical solution to this demand is given by composite rolling processes. In this process components with different chemical compositions were jointed, which develop after heat treatment special properties. These are actually evaluated in order to verify that structural steels with the desired gradients in mechanical properties can be processed. A numerical study was performed aiming to numerically predict strength and toughness properties, as well as the processing behaviour using Finite Element (FE) simulations with damage mechanics approaches. For determination of mechanical properties, simulations of tensile specimen, SENB sample, and a mobile crane have been carried out for different configurations of composite rolled materials out of high strength structural steels. As a parameter study, both the geometrical and the metallurgical configurations of the composite rolled steels were modified. Thickness of each steel layer and materials configuration have been varied. Like this, a numerical procedure to define optimum tailored configurations of composite high strength steels could be established.

This paper investigates the effects of surface microgeometry on coating thickness, both theoretically and experimentally. In the theoretical part of the paper, surface roughness parameters are analyzed and basic definitions and general requirements on coating quality defined. The experimental part of the paper gives a calculation for the coating quantity required in order to fill “dead volume” depending on surface roughness. Coating distribution is analyzed using scanning electronic microscopy (SEM). The paper also evaluates quality of a measuring system using magnetic method for measuring coating thickness.

In this study, sea water effect on failure behaviour was investigated for mechanically fastened composites that are oriented as [0/90/45/-60] s . The laminated composite specimens were fastened with two serial fasteners and were tested under non-immersed and immersed conditions, i. e. in sea water for 200 days. The experiments were carried out according to D 5229/D 5229M standard test method for evaluation of moisture absorption properties and equilibrium conditioning of polymer matrix composite materials. The results point out that the immersion into sea water of the composite specimens can cause a decrease in failure loads of both, pinned and bolted joints, particularly.

Die dreidimensionalen Wasserverteilungen und -transportwege in den Gasdiffusionslagen (GDL) einer Polymer-Elektrolyt-Membran(PEM)-Brennstoffzelle werden bei verschiedenen Betriebsbedingungen analysiert. Die Methode der quasi In-situ-Röntgen-Tomographie wird für eine dreidimensionale Visualisierung der Wasserverteilung sowie der Struktur der GDL genutzt. Basierend auf Ergebnissen dynamischer radiographischer Messungen werden Wassertransportwege aufgefunden und anschließend mithilfe der Tomographie im Detail untersucht. Die Kombination dieser 2D- und 3D-Techniken erlaubt eine Identifizierung der Transportwege durch die GDL. zwei Mechanismen werden auf der Kathodenseite beobachtet: zum einen Wasser, das aus der GDL in den Kanal transportiert wird, und zum anderen Wasser, das in die GDL zurückgedrückt wird.

In this work, three percentages of constant loading are used for fatigue failure assessment. Fatigue behaviour under these three percentages of constant loadings is analyzed by using a new statistical-based approach known as integrated kurtosis-based algorithm for Z-notch filter (I-kaz). Fatigue tests were performed according to ASTM E466-96 standard with a strain gauge attached to the specimen being tested. A fatigue test was conducted under three loadings between 600–700 MPa and at a frequency of 8 Hz. A set of data acquisition systems was used to collect the fatigue strain signals. The I-kaz technique, which provides an I-kaz coefficient and a three-dimensional (3D) graphic, was used to describe and to evaluate the fatigue failure activities. The trends of I-kaz coefficients and of 3D graphics were compared to explain the fatigue damage induced by the three loadings.

In this study, trochoidal type (gerotor) hydraulic pump gears were produced by powder metallurgy (P/M) technique. Several gears with different mechanical properties have been obtained by changing process variables. The tooth contact stresses were calculated analytically under particular operation conditions of the hydraulic pump. The 3D models have been obtained from real gears by using Capability Maturity Model (CMM, 3D scanning) operation and SOLIDWORKS software. Stress analyses were conducted on these 3D models by using ANSYS WORKBENCH software. It was found that the density increases by the increase of sintering duration and mechanical properties were positively affected by the increase of density. Maximum deformation takes place in the region of the outer gear where failure generally occurs with the minimum cross-section area.

β-Titanium orthodontic wires are exposed to three different artificial corrosive environments, modified Fusayama, modified Fusayama with 0.1 % NaF addition, and modified Fusayama with 1.7 % H 3 PO 4 addition, which are similar to the oral cavity conditions. Corrosion behaviours of wires are observed by using weight loss method and scanning electron microscope observations. Afterwards, surface roughness of wires is investigated in details. Consequently, it is determined that corrosion rate of β-titanium wires exposed to the modified Fusayama solutions with H 3 PO 4 addition is higher because of the acidity of this saliva. Furthermore, maximum increase in surface roughness and skewness are observed in the same environment. Hydrogen embrittlement of titanium is also an important factor for the corrosion of wires.

Die Gefährdung durch Pipelines ist in der Öffentlichkeit wegen zahl­reicher Berichte über Unfälle weitgehend präsent. Warum? Weil jeder Unfall die Gefahr von massiven Umweltschäden mit sich bringt und bei Leitungen, die durch besiedeltes Gebiet führen, sogar mit menschlichen Opfern verbunden sein kann. Thema dieses Beitrags ist ein neuartiges Ultraschall-Verfahren, das eine schnellere, sichere und kostengünstigere Prüfung derartiger Rohrleitungssysteme erlaubt.

The aim of this study is to evaluate dimensional conformity and thickness variation of a pyramid geometry obtained by negative single point incremental sheet forming. DC04 mild steel, which has been widely used in automotive and numerous applications due to high formability, was used for experimental investigations. Dimensional accuracy of whole geometry and surface roughness are investigated under the influence of toolpath parameters such as tool diameter, feed rate and vertical step down. In this paper, geometric accuracy and thickness are evaluated by production tolerances of conventional methods and results show that thickness reduction of formed sheet and geometrical deviation of side faces are out of tolerance for all cases.

In this paper, the effects of process parameters on the recycling efficiency of used aluminium beverage cans (UBCs) were investigated. In the experimental studies, separated internal workshop scraps and used aluminium beverage cans are used as charge materials for melting process. Aluminium beverage cans are thin walled parts and produced with high Mg content aluminium alloys. Thus its high oxidation affinity reduces recycling efficiency of the cans. Used can pieces were pressed to obtain briquettes for charging. To increase the recycling efficiency and to optimize the process conditions, preheating, pre-charging, and fluxing were applied. The optimum parameters that provide the maximum recycling efficiency were determined. Chemical analyses and tensile tests were carried out with the resulting as cast samples.

Iron ores located in Alswaween area, Saudi Arabia are of finely disseminated nature. They require ultrafine grinding for a considerable degree of liberation. In this paper, different upgrading techniques are described for their processing. The applied upgrading techniques included selective flocculation and column flotation as recent efficient technologies in fines upgrading. Each technique was investigated and optimized separately. Results showed that neither selective flocculation nor column flotation can be successfully used alone to produce high quality iron concentrate, especially when using iron ore of size fraction 0.075 mm (100 %). The best quality concentrate was found to have 55 % Fe and 57 % Fe when applying selective flocculation and column flotation, respectively, at their optimum operating conditions. Meanwhile, the previously obtained results can be significantly improved when grinding the ore < 45 µm first and applying selective flocculation as cleaning step for the concentrate obtained from the column flotation. Thus, it is possible to obtain a concentrate having an iron content of 63.55 % Fe with 52.3 % yield which means an iron recovery in the concentrate of about 80 %.

The diffusion reaction kinetics of weathered crust elution-deposited rare earth with mixed ammonium salts was studied. The influence of concentration of reagents and particle size of ore on diffusion rate was investigated. The results showed that the diffusion process and diffusion rate could be improved by increasing reagents concentration and decreasing diffusion flowing rate and particle size. The diffusion process could be explained with the shrinking core Model, which could be controlled by the diffusion rate of reacting reagents in porous solid layer.