Band 56, Heft 9

Composite materials show an extraordinary change of properties depending on service life. This implies the necessity to find tailored methods to determine strength and residual strength of composite cylinders. This determination can be done by load cycle tests [1] or, in some cases, primarily by slow burst tests [2]. The results of both test methods need statistical assessment for the precise description of strength. Especially the statistical assessment of burst related strength properties has a high uncertainty. Sample size [3] and scatter distribution were identified as major influences on uncertainty. It is unclear if a Gaussian normal distribution, a Weibull distribution or others describe the scatter behaviour correctly. An assumption has to be found and confirmed to prevent overestimation of survival rate, respectively reliability, in the interval of one failure per 10 4 to 10 8 cylinders.

This work studies the effects of Zn/Cu ratio and silicon on the improvement of mechanical properties, tarnish and corrosion resistance of 940 silver alloys. The silver alloys to be investigated are divided into 2 groups. The group 1 alloys are Ag-Cu-Zn alloys. The group 2 alloys are Ag-Cu-Zn-0.02Si alloys. The microstructures of all alloys to be tested look similar and consist of a Ag-rich matrix (α phase) and Cu-rich eutectic structure (α + β phase). The proportion of eutectic structure decreases by increasing Zn/Cu ratio. Increasing Zn/Cu ratio significantly decreases hardness, ultimate tensile strength, but markedly increases elongation. Addition of 0.02wt.- %Si to Ag-Cu-Zn alloys has no effect on hardness and ultimate tensile strength, but decreases elongation. The tarnish and corrosion resistance of Ag-Cu-Zn alloys in 1 % NaCl solution at 298 K significantly increases with increasing Zn/Cu ratio. Addition of silicon also improves tarnish resistance.

The literature review showed that honeycomb-structured fine sheet metals were not adequately investigated regarding their fatigue strength. Moreover, some development in experimental methods for fatigue strength of structured specimens will be necessary. Honeycomb-structured fine sheet metals of the deep-drawing steel DC04 with a thickness of 0.5 mm were examined. Three specimen types were prepared and tested for their fatigue strength. The fatigue tests were performed on a resonant testing machine. Analysis of the resonant frequency was used to clarify the issues of stability and degradation mechanism of the structured sheet metals. A method for characterization of honeycomb-structured sheet metals under cyclic load was developed. Adopted clamping plates were constructed and used for the experiments. The fatigue strength of honeycomb-structured sheet metals was determined. The reasons for low fatigue limit of structured sheet metals were exposed and suggestions for improvement were presented.

In this study, carbon nanotubes at 0.05–1 wt-% ratios reinforced pure copper powder. Carbon nanotubes (CNT) were used to reinforce the copper matrix, these materials were synthesized under laboratory conditions. Ultrasonic processes and ball-milling method were used to provide a homogenous dispersion during production of the Cu-CNT composite. The Cu-CNT composite powder was produced as bulk material and then, the thermal conductivity as well as the microhardness of the composite were measured. As a particular result, it turned out that the thermal conductivity and the hardness of the composite increased up to a specific ratio of the CNT reinforcement, while the reinforcement ratio exceeding this critical level provided an adverse effect.

The ternary Bi-Ga-Sb system is a potential soldering material. The gallium-based alloy systems are the subject of numerous investigations due to the constant interest of the semiconductor industry. For a more complete characterization of the ternary Bi-Ga-Sb system, alloys from the three vertical sections were investigated using microstructural analysis as well as electrical conductivity and Brinell hardness measurements. The microstructures of the alloys were investigated by light microscopy and scanning electronic microscopy equipped with energy dispersive spectrometry. Isolines of electrical conductivity and hardness for the entire Bi-Ga-Sb system were calculated using regression models. In addition, a thermodynamic assessment of the system has been carried out by calculation of the isothermal section at 100 °C and by description using the CALPHAD method. Experimental and analytical results were found to be in good agreement.

Soils stabilized by cement are found to be influenced by the environmental condition such as acid rain, seawater invasion, or industrial pollution. These adverse effects will lead to the deterioration of a structure. In order to study the process of corrosion effects including the changes of the corrosion rate of the surface, compression strength of the cemented soils and the Mg 2+ and SO 4 2− ion concentrations of the corrosive solutions have been determined. A series of experiments were conducted on the cemented soil blocks cured with different concentrations of MgSO 4 solution. Specifically, the experimental work includes photo documentation, compressive strength tests and measurements of Mg 2+ and SO 4 2− ion concentrations. The test results show that the rate of corrosion for the sample surface increases with increasing concentration of the corrosive solution, while, the compressive strength decreases accordingly. Moreover, the corrosion rate degree intensifies with corrosion time. Chemical analysis of the corrosive environment indicates that CaSO 4 reacts with the cemented soil, resulting in crystallizing corrosion products of 3 CaO ×Al 2 O 3 ×3 CaSO 4 ×32 H 2 O and CaCO 3 ×CaSO 4 × CaSiO 3 ×15 H 2 O. Mg(OH) 2 reacts with 3 CaO ×2 SiO 2 ×3 H 2 O (C-S-H) and forms new dissolving corrosive reactants such as MgO ×SiO 2 ×H 2 O (M-S-H). It is concluded that the corrosion of cemented soils in MgSO 4 solution is a complex reaction involving the resolving and crystallizing corrosive processes. Finally, a strength model for cemented soils is proposed based on the relationship between the compressive strength and the concentrations of Mg 2+ and SO 4 2− ions.

In this study, investigation was conducted on the out-of-plane fracture under repeated reversing loads of specimens of unreinforced masonry wall models, a suitable building material found worldwide, strengthened by bed joints using FRP (fiberglass reinforced plastic) with epoxy resin, by production of two separate wall samples composed of materials with identical characteristics in a 1 : 1 ratio. It was also observed that the fracture type became brittle and the pour lines indicated that it did not have tensile strength. Approximately, a 3.5 increase in withstanding breakage under seismic forces was observed in the performance of the wall strengthened by FRP with epoxy reinforcements in the bed joints. Furthermore, the shear strength of the model masonry wall was 48 % less than that attained in the wall strengthened by bed joints and it was determined that the energy absorption of the model masonry wall was 22 % less than that of the wall strengthened by bed joints. Additionally, while the masonry wall in the test which was not strengthened broke under repeated reversing loads at 65 kN, the break load of the strengthened masonry wall was ascertained to be 80 kN. The accuracy and application of the results of the studies conducted were also scrutinized by running finite element stress analysis and numerical solutions using an ANSYS computer-supported analysis program.

In this study, the fracture toughness of Fe 2 B boride layer on boronized AISI 304 stainless steel was investigated. Samples were boronized in an indirect heated fluidized bed furnace with Ekabor 1™ boronizing agent at 1123 K, 1223 K, and 1323 K for 1 h, 2 h, and 4 h, respectively. The boride phases were investigated by X-ray diffraction (XRD) analysis. Hardness and fracture toughness of borides were measured via Vickers indentation. With increasing boriding temperature and time the fracture toughness values were reduced. The boride layer thickness formed on the boronized samples ranged between 12 μm and 176 μm. The hardness of the borides ranged between 1709 HV 0.1 and 2119 HV 0.1 and fracture toughness was in the range of 2.19–4.47 MPa × m 1/2 depending on the layer thickness and hardness.

Ferrochromium is used in hardfacing alloys as carbide former. In this study, ferroboron was used with ferrochromium to investigate the effect on microstructure and wear resistance. Five different hardfacing alloys (50 % massive welding wire + 50 % powder mixture) were produced by open arc welding on AISI 1020 steel. Microstructure, SEM and XRD analysis, hardness test, and dry sand/rubber wheel abrasion test were carried out. According to the test results, as the amount of ferroboron increased, wear rate decreased. Minimum wear rate was obtained in 100 % ferroboron powder added sample.

In the present experimental study, bimetal aluminium/magnesium macro composites which contain magnesium core were fabricated via compound casting by lost foam casting process. AM50 Mg alloy prismatic core was placed into a cubic EPS foam pattern. Conventional process steps of lost foam casting were followed and A319 casting aluminium alloy was melted and poured. Experimental studies have shown that determination of casting temperature is very important to avoid melting of Mg alloy core. Microstructures of sectioned cast specimens were observed by light microscope and scanning electron microscope (SEM). Energy dispersive X-ray spectroscopy (EDS) analysis and Brinell hardness tests were carried out. Especially, transition zone and Al/Mg interface were in the focus of research.

In this study, the effect of zinc (Zn) and silicon (Si) in the industrially very important magnesium alloys AZ91 (9 % Al, 1 % Zn) and AS91 (9 % Al, 1 % Si) has been investigated, with respect to wear resistance and machinability. The hardness of the intermetallic phases found in the microstructure of the alloys AZ91 and AS91 was observed to affect the wear resistance and machinability. It turned out that Mg 2 Si found in the microstructure of AS91 alloy reduced the machinability while this intermetallic phase increased the hardness and the wear resistance.

Kurzfassung Anhand von computertomografischen Messungen und Modellrechnungen werden DIRECTT-Rekonstruktionen im Vergleich mit gefilterten Rückprojektionen bewertet. Dazu wird die Rekonstruktionsqualität mittels einer zirkular erweiterten Modulations-Transfer-Funktion (MTF) und mit integralen Kenngrößen im Radon- und im Ortsraum verglichen. Zur Überprüfung der Rekonstruktionsgenauigkeit experimenteller Daten werden Mustermessungen einfacher Probengeometrien unter definierten physikalischen Bedingungen durchgeführt. Diese beinhalten die Monochromasie, die Unterdrückung von Kantenartefakten und die radiometrische Intensitätsbestimmung. Für die Qualität der Rekonstruktionen mittels DIRECTT erweisen sich sowohl unterschiedliche Rekonstruktionsfilter als auch der Verzicht auf jede Filterung als unerheblich, im Gegensatz zur gefilterten Rückprojektion.

Kurzfassung Typische „Missing Wedge“(MW)-Artefakte in Rekonstruktionen der Computertomografie können mit dem iterativen DIRECTT-Algorithmus (Direkte iterative Rekonstruktion computertomografischer Trajektorien) unterdrückt werden. Die durch fehlende Projektionswinkel bedingten MW-Restriktionen betreffen bisher nur Sonderapplikationen der Röntgen- und Neutronentomografie, müssen in der Nanometer auflösenden Elektronentomografie jedoch als Standard akzeptiert werden. Die MW-Artefakte werden besonders effektiv mit einer spezifischen DIRECTT-Prozedur partiell diskreter Zwischenlösungen beseitigt. Für die Beurteilung der Abbildungsqualität werden Rekonstruktionen von vollständigen und unvollständigen Mess- und Modell-Datensätzen erzeugt und mit Ergebnissen anderer Algorithmen (gefilterte Rückprojektion (FBP) und ART-Methoden) verglichen. Die Fourier-Transformierten der Rekonstruktionen demonstrieren die erfolgreiche Ergänzung der fehlenden Information im MW-Bereich. Die quantitative Bewertung der lokalen Rekonstruktionsqualität mit Methoden der räumlichen Statistik ergibt auch für unterschiedliche Signal-Rausch-Verhältnisse signifikante Vorteile gegenüber FBP und ART.

Kurzfassung Gegenstand dieser Studie ist ein kommerzieller Lithium-Ionen-Kondensator (LIC), welcher einer intensiven Alterung in Form von sukzessive durchgeführten Lade- und Entladeprozessen unterzogen wurde. Die dabei auftretenden dreidimensionalen Veränderungen der inneren Struktur wurden mittels Röntgen-Tomografie analysiert. Mit ansteigender Zyklenzahl finden wir eine Ansammlung von Elektrolytflüssigkeit im Bodenbereich des Kondensators vor. Unter Berücksichtigung der beim Zyklieren aufgezeichneten elektrischen Daten ergibt sich ein klarer Zusammenhang zwischen der Elektrolytverteilung im Bodenbereich und der Leistung des LIC.

Composite materials such as fiber-reinforced composites (FRP) are extensively used in today's industries such as aerospace, automotive, and shipping because of their high specific strength and high specific stiffness. In addition, they have good thermal resistance, corrosion resistance, damping resistance, and dimensional stability. But, due to the inhomogeneous composition of these materials, machining of composite materials becomes a major concern in the industry. For the present study, machining was carried out at a CFRP composite pipe with bidirectional carbon fiber. Based on the experimental results, regression analysis was conducted to determine the input-output relationships of the process. A mathematical model was developed to predict the responses, and correlation graphs were plotted. The regression equations were then plotted and the effects of each process parameter on the response were analyzed using the response surface methodology. The process parameters were then optimized using genetic algorithm to yield minimum cutting force and minimum surface roughness.

Production and applications of both ferrous and non-ferrous bimetals have been increased due to several advantages and the respective fabrication techniques and procedures are rapidly developing. Liquid metal based fabrication techniques of bimetal production can be classified in two types, i. e., liquid-solid and liquid-liquid processes. Lost foam casting technique can be successfully employed for both liquid-solid and liquid-liquid bimetal composite productions. In this study, A380 and A6063 aluminum alloys were used to produce a bimetallic structure by conventional lost foam casting with the liquid-liquid process. There are two main principles of the liquid-liquid process. Firstly, both alloys are joined in liquid phase and solidified. Secondly, crucible tilting of he metals is carried out synchronously at the same time. The Brinell hardness of the cast specimens was measured and the microstructures of the joint were investigated by light microscope and SEM. Additionally, EDX mapping analysis of the bonding zone was carried out.

This study has focused on the Taguchi-based multi-response optimization of the pocket milling process for an optimal parametric combination to yield minimum surface roughness within a minimum machining time using a combination of Grey relational analysis (GRA) and the Taguchi method on the CNC process of DIN 1.0038 medium carbon steel. Sixteen experimental runs based on an orthogonal array of the Taguchi method were performed to derive multi-objective functions to be optimized within the experimental range. The objective functions have been selected in relation to parameters of the pocket milling process, i. e., surface roughness and machining time. The Taguchi approach was followed by Grey relational analysis to solve the multi-response optimization problem. The significance of these factors on overall quality characteristics of the pocket milling process has also been evaluated quantitatively by a variance analysis method (ANOVA). Optimal results have been verified by validation experiments to calculate the effectiveness of the method. The application of this method showed that proper selection of the milling parameters produces better surface roughness within the minimum machining time.

The inspection of the sealing weld is an important phase for the evaluation of the acceptability of final disposal canister, but the weld is only a part of the 3D shielding of copper shell. The main tasks for reliable NDT evaluation requires an extensive evaluation of the parameters – which contains typical inspection related items like repeatability, S/N ratio, POD, setting up the equipment for inspection, and all practices for inspections. The other parameters are material parameters, their variation must be taken into account in the evaluation of NDT reliability. Further parameters include human factors, i. e. human inspectors and their interaction with technical systems; their effects were studied on an example of the evaluation of eddy current data. Final parameters are related to evaluation of detected defects, which means sizing and base for acceptance and this can be done in different ways. Some examples are given and results are compared with different methods for instance between radiographic testing and ultrasonic testing by raw data analysis and PA-SAFT results. Also, preliminary curves for the evaluation of metallographic results of 55 defects will be shown by EB weld measurements. Some practical items concerning copper inspections will be also discussed related to acceptability.

Algorithms to estimate ultrasonic testing method based on the integrated use of indicators of reliability and accuracy are presented, and built according to the nature of techniques, features of their application and evaluation purposes (comparison of techniques, introduction of new methods, test procedures, etc.). On the basis of the main revision of ISO 5725-1, 5725-2 the estimation of reproducibility and repeatability of measured characteristics determine the design of reflectors and real defects, and thus the reliability of non-destructive testing, including ultrasonic inspection of railways.