Volume 60, Issue 2

A fast calculation of Wöhler or S-N curves is of major importance in the design process of complex components and for selection of optimized materials. In the context of this work, it is shown how the nondestructive testing methods, the digitalization of the measurement techniques as well as signal processing can be combined with a new short-time procedure in order to acquire potentially more information from fatigue processes, while experimental effort and costs are reduced significantly. The results of this combination show not only considerable advantages over conventional methods aimed at determining S-N curves, but also over established short-term procedures, due to the possibility to separate several material mechanisms by means of data analysis and to use this for fatigue life calculations based on the results of a few specimens only. The SteBLife approach is a new short-time calculation method developed at the Chair of Nondestructive Testing and Quality Assurance at Saarland University, Germany, which takes into account that there is no linear relation between the elastic, elastic-plastic and plastic portion of the material response in the deformation process. With respect to the test strategy, the number of fatigue tests can be reduced for SteBLife mtc and SteBLife msb to three and five, respectively, or in the case of SteBLife stc to one single constant amplitude test with a special step-shaped specimen geometry when compared with approximately 15 required fatigue tests for the conventional determination of Wöhler or S-N curves. Moreover, SteBLife msb offers the possibility to calculate scatter bands for different failure probabilities, which is an important feature, even in the case of inhomogeneous materials. Within the scope of the presented work, the change in temperature of SAE 1045 (C45E) specimens was measured during fatigue tests by an infrared camera in order to feed the thermal response back into the new SteBLife approach for a reliable fatigue life calculation.

The sports industry, in particular the ski industry, uses high strength aluminum alloys in adhesive compounds in order to achieve higher torsional stiffness, high strength and nevertheless lightweight construction. These alloys must be surface treated prior to bonding to achieve the required service properties. Subsequently, the bonding process takes place. Occasionally, there can be local defects in the bonding. The analysis of the cause of the locally appearing failures by scanning electron microscopy (SEM) is part of this study along with the testing of alternative surface treatment techniques and comparing them by using contact angle measurement (CAM). Furthermore, peeling tests are performed to determine and compare the alternative surface treatments regarding their impact on the joint strength. The focus is on achieving a high peeling resistance and a reduction of the defect rate.

In this study, effect of rotational speed on the characteristic microstructure and mechanic properties of the AISI 1030/AISI 420 stainless steel couple welded by friction welding method was experimentally investigated. The weld joints were produced with 1400, 1500, 1600 rpm rotational speed, under 40 MPa process friction pressure and 60 MPa forging pressure for a friction time of 4 s and a forging time of 6 s. After friction welding, the bonding interface microstructures of the samples were examined by scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive spectrometry (EDS) and X-Ray diffraction (XRD) analysis. Furthermore, microhardness and tensile tests were applied to determine the mechanical behavior of weld joints. In addition, fracture types of the tensile test samples were determined from the fractographic examinations by using SEM and EDS. The result of the applied tests and observations pointed out that the mechanical properties and the microstructure changed depending on the increased rotational speed.

Despite their proven record in promoting osseointegration, titanium and titanium alloys present certain other challenges to providing an optimal dental implant. Titanium and suitable titanium alloys have a higher stiffness than human bone, and therefore dental implants formed from such materials absorb most of the forces of mastication. This can lead to a phenomenon known as a stress shielding of the surrounding bone. A variety of bioceramics have been developed and used in different implants due to their excellent biological performance. However, only a few of them have been used in clinical applications, especially in low load bearing implants, due to their poor mechanical strength. Little existing research has been reported for the design of dental implants made of FGM materials. However, many researchers have studied the effect of improving the dental implant surface by coating its surface with different materials including functionally graded materials (FGM). On the other hand, the effect of coating the FGM dental implant with a homogenous material has not been studied yet. The main goal of this work is to compare the biomechanical behavior of three types of dental implant models. Three dimensional models are created. The first model is a homogenous dental implant with a homogenous coating material. The second model represents a homogenous dental implant with a FGM coating and. the third model is a functionally graded implant with a homogenous coating material. The FGM implant with homogenous coating appears as the most suitable model. It reduces the bone stress on cancellous bone by 4.6 % and by 6.5 % on cortical bone compared to homogenous implant with homogenous coating. This leads to reduction of bone stress shielding as well as reduction of the aseptic loosening of bone/implant/coating interfaces which increase the life time of the implant.

In this study, AISI 4140 steel couples 10 mm in thickness were joined using manual gas metal arc (GMAW) and synergic controlled pulsed gas metal arc (GMAW-P) welding methods. Interfacial images of welded samples were investigated using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) methods. Impact and microhardness tests were performed to determine the mechanical properties of the joined parts. In addition, the fracture surface of the broken joint with the impact test was examined using SEM. The AISI 4140 welded joints obtained by the GMAW-P method showed higher impact strength, less grain growth and narrower heat affected zone (HAZ) than by using the GMAW method. It is thought that this is caused by lower heat input.

A mechanistic exposure experiment was performed on welded samples of the commercially available Haynes ® Hastelloy ® C–4 ® Ni-Cr-Mo-Fe alloy (65 wt.-% Ni, 16 wt.-% Cr, 16 wt.-% Mo, 3 wt.-% Fe, 2 wt.-% Co, 1 wt.-% Mn, 0.7 wt.-% Ti, 0.5 wt.-% Cu, 0.08 wt.-% Si and 0.01 wt.-% C) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin-si, South Korea. The alloy samples were preoxidized at 400 °C under a stagnant air atmosphere for 24 h prior to exposure to the corrosive environment (60 % CO, 28.4 % H 2 , 2.5 % CO 2 , 0.8 % CH 4 , 600 ppm H 2 S and 110 ppm carbonyl sulfide under 2.005 MPa pressure and 170 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference of the corrosion mechanism was supplemented with morphological, compositional and microstructural analyses of the exposed samples using scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy analyses performed on the external and cross-sectional surfaces of the recovered corrosion test samples to comprehensively examine the corrosion scale. The X-ray diffraction results revealed stable corrosion products of NiO, MoNi 4 and Cr 4.6 MoNi 2.1 after a total accumulated exposure duration of 139 h to the corrosive atmosphere. Scanning electron microscopy and energy dispersive X-ray spectroscopy positively identified the formation of rather continuous and adherent preoxidation corrosion products in the alloy samples, although extensively peeled off oxides were eventually observed as corrosion scale on the post-exposure alloy samples, which were attributed to the combined effects of the evaporation of the hydrated Fe, Al and Cr chlorides and their subsequent transformation into thin (spalled) oxides.

Ash fusion temperature determines suitability of coal for the entrained flow gasification/combustion process. For this, an Indonesian “Sehwa” coal sample and its acidic ash and slag constituents have been comprehensibly characterized via X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and inductively coupled plasma optical emission spectrometry (ICP-OES) methods. For assessment of environmental impact, leachate solution was also prepared from the discharged slag for ICP-OES analysis. The experimental data were comprehensively explained by ash fusion temperature and FactSage ® thermochemical software and databases for understanding the thermodynamic fluidity properties of the coal ashes. More specifically, coal slagging behavior inside of the coal gasifier/combustor necessitated optimization of operational condition for subsequent mild slagging. The currently used coal gasification operation temperature range caused insufficient fraction of liquid available at 1200 to 1300 °C (19.7–20.1 bar). The metallic element-wise compositional analysis result via ICP-OES performed on the leachate solution therefrom excluded possibility of secondary environmental pollution from the discharged slag. This contribution continues the already published studies of the physicochemical characterization of slag waste from coal gasification syngas plants supplemented with FactSage ® thermodynamic modeling results of coal gasification slag (SiO 2 –Al 2 O 3 –TiO 2 –Fe 2 O 3 –CaO–MgO–Na 2 O–K 2 O–P 2 O 5 –MnO–SO 3 ). Besides, essentially similar experimental procedure to that employed in the already published studies was used to compare ash transformation and slagging behavior of the acidic coal feedstock.

Kurzfassung Für die Orientierung in den Tiefen der Ozeane entwickelten Wale und Delphine im Laufe der Evolution ein spezialisiertes Hörorgan für ein breites akustisches Spektrum. Die innere Anatomie des Felsenbeins (Perioticum), insbesondere die Morphologie der Hörschnecke (Cochlea) hat bei Säugetieren einen signifikanten Einfluss auf das Hörvermögen. Mittels Röntgen- und Neutronentomographie wird die knöcherne oder fossilisierte Cochlea verschiedener fossiler Repräsentanten ausgestorbener Bartenwalgruppen (wie der Cetotheriidae) sowie moderner Furchenwale (Balaenopteridae) und Glattwale untersucht, ebenso die eines Urwals und einiger Landwirbeltiere. Morphologische Veränderungen, die für die Entwicklung des niederfrequenten Hörens verantwortlich sein können, sollen so erfasst werden. Unterschiede in der Cochlea-Morphologie werden anhand morphometrischer Parameter, wie der Anzahl der Windungen, der Länge der Cochlea und des Krümmungsverlaufs des Cochleakanals bestimmt. Insbesondere die Röntgentomographie ermöglicht eine hochauflösende Darstellung des knöchernen Innenohrs.

For many decades thermally sprayed corrosion protection systems on the basis of ZnAl or Al carry out their service for structures in coastal areas, the offshore sector, as CUI (corrosion protection under insulation) or anywhere, where the properties of thermally sprayed corrosion protection systems bring important advantages in terms of durability. A thermally sprayed corrosion protection system is about to protect the structure for 25 to 30 years against corrosion. During this time it may be damaged due to factors like construction work, improper handling or simple aging. There are many standards and regulations which describe the initial design of thermal spray systems, however, there cannot be found any information regarding repair. In particular, a mending of partial regions is hardly described. Specific repair instructions are rare and if present, they differ from one another. Overall there is a lack of knowledge of the proper procedures for partial repair of thermally sprayed coating systems. This project was concerned with tangible corrosion technical issues of the coating repairs: How does the critical overlap area perform? Have organic coatings benefits? To what extent does a renewed damage affect the lifetime? The aim of this study was to develop practice relevant instructions for the repair of thermally sprayed duplex systems.

Red mud is a waste product generated by the aluminum industry and its presence has significantly damaged the environment. Interestingly, red mud has some desirable adsorptive properties and can solidify heavy metal ions. Moreover, after processing, red mud has certain cementing properties that have a positive influence on the curing effect of red mud cement-treated soil. This study examined different ratios of red mud, cement and Ca(OH) 2 by testing the electrical resistivity and unconfined compressive strength of various soils. The resistivity test indicates that the electrical current frequency has a great influence on the test results. It is recommended that a current frequency between 1 and 50 kHz is used in a resistivity test. The study also indicates that, with increasing Cu 2+ content, conductive tunnel effect occurs. However, when the ratio of curing agent and content of Cu 2+ are different, the time causing the conductive tunnel effect varies. The unconfined compressive strength of different cement-to-soil ratios decreases with increasing Cu 2+ content and the reduction extent is related to that ratio. Lastly, the study results suggest a good linear relationship between unconfined compressive strength and electrical resistivity, which is dependent on the specific ratio of contaminating materials.

In this study, iron based and copper based sintered brake materials have been investigated. Iron and copper based brake materials have been produced by powder metallurgy method. Hardness, experimental and theoretical density, porosity measurements and metallographic analysis have been performed to examine microstructure. Pin-on-disc tests have been carried out to understand friction behavior, to get the average coefficient of friction and to calculate wear rates of specimens. Pin-on-disc tests have been done at different radiuses (4, 6 and 9 mm), at different velocities (85, 100 and mm × s −1 ) and under a load of around 6.5 N. Test results show that the specimens have high porosity (25 to 26 %) because of the production methods. The phases and porosities can be also observed by metallographic analysis. Iron based brake materials have a lower coefficient of friction and lower wear rates in comparison with copper based brake materials. But copper based brake materials have a more stable abrasion profile during test period.

This study focuses on the machinability of AISI O2 cold work tool steel investigated by using different drilling parameters namely drill bit types, cutting speed and drill feed rate. Cutting temperature and chip formation were used to evaluate the surface roughness. The surface roughness of drilled holes were measured by using a profilometer. The results of the study revealed that the surface roughness was decreased with increasing cutting speed and drill feed rate. HSCo drill bits provided slightly better hole surfaces compared to HSS and HSE type drill bits. Additionally, acceptable chip formations were obtained with HSCo and HSSe drill bits operations. The cutting temperature of the holes was measured using thermocouples. The maximum temperatures were observed with HSS type drill bits, while the minimum temperatures were measured in the group of HSCo drill bits. As a result of this study, it can be evaluated that the HSCo drill bit was the best choice for the optimum drilling performance in machining of AISI O2.

This study is focused on the inhomogeneity and local heterogeneity of the particle size distributions (PSD) of granular backfilling materials (eolian sands and loess) from western mines of China under overburden strata loads. The multi-fractal spectrum and variations in corresponding parameters of PSD of granular backfilling materials were obtained under different loads using a laser particle size analyzer and an environmental scanning electron microscope (ESEM). The results indicated that the load had negligible effects on the multi-fractal characteristics of PSD of eolian sand. There were no significant variations in the capacity dimension D(0), the information entropy dimension D(1) and the bandwidth of the multi-fractal spectra (Δα) as a function of the load. In contrast, the load significantly affected the multi-fractal characteristics of the PSD of loess, and D(0), D(1) and Δα increased and then decreased (maximized at 2 MPa) as the load increased. Furthermore, there was a correlation between structural morphology parameters and multi-fractal parameters in the particle breakage process, which demonstrated that D(0), D(1) and Δα of PSD of granular backfilling materials could effectively reflect the particle breakage and the change of structural morphology parameters of backfilling materials under different loads.

This research is focused on the fabrication of aluminum alloy 8011 with 4 % fly ash (FA) composite (AA8011-4 % FA) using the stir casting method. The dry sliding wear characteristics of the composite were investigated using various sliding parameters. A three-level central composite design experiment was developed using response surface methodology with various parameters such as load, time and sliding velocity varied in the range of 5 to 15 N, 5 to 15 min, and 1.5 to 4.5 m × s −1 , respectively. Dry sliding wear tests were performed according to the experimental design using a pin-on-disc apparatus at room temperature. The obtained regression result indicated that the developed model performed well in relating the wear process parameters, and predicted the wear behavior of the composite. The surface plot showed that the wear rate increases with increase in load, time and sliding velocity. Moreover, the surface morphology of the worn-out composite was examined using a scanning electron microscope.

This study involves the multi-objective optimization of end milling process parameters during machining of Al-Si5Cu3/Si 3 N 4 functionally graded metal matrix composite that was fabricated using centrifugal casting route. The dimension of the cast sample was 150 × 150 × 20 mm 3 . The hardness of the sample was measured along the radial direction. It was found that the hardness at the outer periphery was greater than that of other points along the radial direction. Therefore, the machining experiment was carried out only at the outer periphery. Taguchi's design of experiments method was employed and sixteen levels of experiments were conducted by varying the input parameters namely the cutting speed (355, 500, 710 and 1000 rpm), the depth of cut (0.5, 0.9, 1.2 and 1.5 mm) and the feed rate (250, 315, 400 and 500 mm × min −1 ). Multi-objective optimization using grey relational analysis was performed and the optimal set of input parameters were found to be cutting speed of 1000 rpm, feed rate of 250 mm × min −1 and depth of cut of 1.5 mm. Using analysis of variance technique, it was found that cutting speed, depth of cut and feed rate have an influence of 63.57, 16.83 and 8 %, respectively, on the optimal solution.