Showing papers in "Materialwissenschaft Und Werkstofftechnik in 2008"

Experimental studies on selective laser melting of metallic parts

Abstract: Laser assisted generative production techniques like Selective Laser Melting (SLM) are novel but complex near net shape fabrication methods. The present paper describes properties of metallic specimens generated by SLM. Therefore various process parameters were observed to evaluate their influence on certain attributes of parts fabricated by Selective Laser Melting. In addition, approaches for an improvement of density, surface quality and mechanical properties are given. Experimentelle Untersuchungen zum Laserstrahlgenerieren metallischer Bauteile Laserbasierte generative Fertigungsverfahren wie das Selective Laser Melting (SLM) sind neuartige, aber recht komplexe near-net-shape Herstellungsverfahren. Dieser Beitrag beschreibt Eigenschaftsprofile metallischer Probekorper, die mittels SLM generiert wurden. Zu diesem Zweck werden verschiedene Prozessparameter betrachtet und ihr Einfluss auf die Bauteilqualitat beurteilt. Zudem werden Optimierungsansatze zur Prozessfuhrung des SLM im Hinblick auf Materialdichte, Oberflachenqualitat und mechanische Eigenschaften aufgezeigt.

The effect of weld parameters on friction stir welding of brass plates

Abstract: More successful results have been obtained in butt- and overlap-joining of Al-alloy plates by a recently developed solid state joining technique, namely friction stir welding (FSW), than in more conventional fusion welding processes. In this joining technique, no fusion takes place in the joint area of the plates welded. This novel joining method also offers the potential to weld some other materials rather than Al-alloys, such as Mg-alloys, brasses and low strength steels. In this study, the applicability of friction stir welding to brasses, namely 90 %Cu-10 %Zn and 70 %Cu-30 %Zn alloys, has been investigated. The joint performance was determined by conducting optical microscopy, microhardness mesurements and mechanical testing (e.g. tensile and bend tests). The effect of welding speed on the joint quality at a given rotational speed of the stirring pin (i.e. 1600 rpm) was also determined for both alloys. The highest joint performances were obtained at a welding speed of 210 mm/min for both alloys.

Processing and property assessment of NiTi and NiTiCu shape memory actuator springs

Abstract: Among the multifarious engineering applications of NiTi shape memory alloys (SMAs), their use in actuator applications stands out. In actuator applications, where the one-way effect (1WE) of NiTi SMAs is exploited, SM components are often applied as helical coil springs. Ingots are generally used as starting materials for the production of springs. But before SM actuator springs can be manufactured, the processing of appropriate wires from NiTi ingots poses a challenge because cold and hot working of NiTi SMAs strongly affect microstructure, and it is well known that the functional properties of NiTi SMAs are strongly dependent on their microstructure. The objective of the present paper is therefore to produce binary Ni50Ti50 and ternary Ni40Ti50Cu10 SMA actuator springs, starting from ingots produced by vacuum induction melting. From these ingots springs are produced using swaging, rolling, wire drawing and a shape-constraining procedure in combination with appropriate heat treatments. The evolution of microstructure during processing is characterized and the mechanical properties of the wires prior to spring-making are documented. The mechanical and functional characteristics of the wires are investigated in the stress-strain-temperature space. Finally, functional fatigue testing of actuator springs is briefly described and preliminary results for NiTi and NiTiCu actuator springs are reported. Untersuchungen zur Herstellung und zu den Eigenschaften von NiTi- und NiTiCu-Aktorfedern NiTi-Formgedachtnislegierungen (FGL) zeichnen sich durch eine hohe Attraktivitat fur verschiedene Aktorik-Anwendungen aus. Dabei werden FGL haufig in Form von zylindrischen Federn verwendet, wobei der Einwegeffekt genutzt wird. Die Herstellung von solchen Aktor-Federn ist jedoch keinesfalls trivial. Sowohl die Herstellung von geeignetem Drahtmaterial als auch die Formgebungsbehandlung stellen in gewisser Weise eine Herausforderung dar. Die funktionellen Eigenschaften von NiTi-FGL hangen sehr stark von mikrostrukturellen Randbedingungen ab, und erforderliche thermomechanische Behandlungen sind mit weit reichenden mikrostrukturellen Veranderungen verbunden. Das Ziel dieser Arbeit war, eine Prozesskette zur Herstellung von Ni50Ti50 und Ni40Ti50Cu10-Aktorfedern ausgehend vom Gussmaterial zu erarbeiten und metallkundlich zu charakterisieren. Aus den Gussblocken wurden durch Rundkneten, Walzen, Drahtziehen und speziellen Formgebungsbehandlungen Aktorfedern hergestellt. Dabei wurden die mikrostrukturellen und funktionellen Anderungen der beiden FGL charakterisiert. Zum Schluss wurden die mechanischen und funktionellen Eigenschaften der verschiedenen Draht-Materialien und der fertigen Federn untersucht. Dabei wurde ein besonderes Augenmerk auf die funktionelle Ermudung der Aktorfedern gelegt.

Superplastic forming of friction stir welds in Titanium alloy 6Al‐4V: preliminary results

Abstract: The trend in design and fabrication of aerospace structure is moving rapidly towards the use of composite materials and the consolidation of many pieces into large monolithic assemblies. Titanium alloy 6Al-4V is more compatible with composite materials than aluminum alloys because of its superior corrosion resistance and closer match to the coefficient of thermal expansion. In addition, many components that are used for the newer composite based aircraft, and are subjected to high service temperatures, are fabricated from titanium using Superplastic Forming (SPF) and Diffusion Bonding (SPF/DB). However, the use of SPF titanium parts has been limited up until now due the size restriction of standard sheets from the titanium mills, which is generally available at a maximum size of 1.2 m x 3.6 m. The purpose of this study was to develop the Friction Stir Welding (FSW) process for both standard and fine grain titanium alloy 6Al-4V in a bid to find a process that would allow the joining of multiple pieces to fabricate much larger components. Further, the FSW process was refined such that the welds were made to have superplastic properties equal to those of the parent sheet. A secondary goal of this effort was to build full size SPF prototype parts of a generic jet engine nacelle Lipskin using one FSW titanium blank. SPF of 7475 aluminum had been reported previously in the literature by Mahoney, Barnes, Mishra and others. During this study, the FSW process for 5083 Superplastic grade aluminum was developed simultaneously along with titanium 6Al-4V. The aluminum material was used to reduce the cost of developing the SPF manufacturing process to fabricate full scale engine inlet test components. FSW blanks of both materials were used for the initial forming trials.

Preparation of chelating fibrous polymer by different diamines and study on their physical and chemical properties

Abstract: The present work describes a new modification process for producing a chelating ion-exchanger fibers with a distinct selectivity for toxic heavy metal ions. Acrylic fibers were reacted with different diamine compounds in similar conditions. Modified acrylic fibers were prepared by partial conversion of the nitrile groups into amino groups under two-step processes. In the first step, the pure liquid diamine was mixed with the fibers and in the second step, water was gradually added to the reaction flask to reach a predetermined 3M concentration at refluxing temperature of 91 °C. The aminated acrylic fibers (AAFs) were used as an ion adsorbent in a series of batch adsorption experiments for removal of chromium(III) and lead (II) ions. Experimental results showed that modified acrylic fiber with tetra methylene diamine (TMD) has the highest Pb(II) ion adsorption capacity. Results also showed aminated acrylic with ethylene diamine (EDA) has the most Cr(III) ion adsorption ability. Solubility tests showed, amination treatments give rise to the intermolecular crosslinkage in all samples. The Freundlich and Langmuir models simulated the adsorption equilibrium data of Cr(III) ions on modified fibers and their constants were determined.

Tensile and high cycle fatigue test of copper thin film

Abstract: This paper presents the results of tensile and high cycle fatigue tests for copper thin film Copper films coated by Sn are often used in various electro devices Especially, when the film is used in tape carrier package (TCP), the film is repeatedly exposed to mechanical or(and) thermal stresses which results often in the failure of the component Therefore, to guarantee the reliability of the electrical devices using a film, tensile and fatigue characteristics of the film are important In this study, to obtain the tensile and fatigue characteristics of the film, the specimen was fabricated by an etching process to make a smooth specimen of 2000 μm width, 8000 μm length and 1526 μm thickness The tensile and high cycle fatigue tests were performed with the specimen using the test machine developed by the authors These specimens had measured values of Young's modulus (72 GPa) and a 02 % offset yield and an ultimate strength of 358 MPa and 462 MPa, respectively A closed-loop feedback control of the magnetic-electric actuator allowed load-controlled fatigue tests with 20 Hz frequency, in ambient environment and at two levels of mean stresses The fatigue strength coefficient and exponent at 05 times of the ultimate tensile strength were 431 MPa and -00843, respectively The fatigue strength coefficient and exponent at 06 times of the ultimate tensile strength were 371 MPa and -00923, respectively The Goodman method is recommended when the fatigue life of thin film with mean stress will be estimated The fatigue strength coefficient and exponent of copper thin film modified using Goodman method were 910 MPa and -00896, respectively

Carbonated hydroxyapatite nanopowders for preparation of bioresorbable materials

Abstract: Incorporation of carbonate ions to the crystal structure of carbonated hydroxyapatite (CHAp) leads to the formation of point defects (vacancies) in Ca- and OH-sublattices as well as to microstrains revealed in CHAp nanocrystals. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO2, BET adsorption, were applied to determine an efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution. It was shown that there is insignificant incorporation of Na into the crystal structure of HAp. Over the range of 0–4% wt. (x<0.25), the substitution of OH- by CO 3 2- takes place leading to A-Type of CHAp, further increase of CO3 2- -content enhances PO4 3- -substitution giving AB-type of CHAp. According to in vitro test, the bioactivity of the samples is increasing with the growth of carbonate content due to accumulation of the defects in CHAp nanocrystals.

Beyond HCF – Is there a fatigue limit?

Abstract: The paper gives an overview to the present state of research on fatigue strength and failure mechanisms at very high number of cycles (N>107). Testing facilities are listed. A classification of materials with typical S-N curves and influencing factors like notches, residual stresses and environment are given. Different failure mechanisms, which occur especially in the VHCF-region like subsurface failure, are explained. There microstructural inhomogeneities and statistical conditions play an important role. Investigated materials are different metals with body-centred cubic lattice like low- or high-strength steels and quenched and tempered steels but also materials with a face-centred cubic lattice like aluminium alloys and copper. Gibt es eine Dauerfestigkeit bei sehr hohen Schwingspielzahlen? Der Beitrag gibt einen Uberblick zum gegenwartigen Stand der Forschung im Bereich der Schwingfestigkeit und der Versagensmechanismen bei sehr hohen Schwingspielzahlen (VHCF, N>107). Prufmoglichkeiten in diesem Bereich werden erlautert. Danach erfolgt eine Klassifizierung von Werkstoffen mit typischen Wohlerlinien. Der Einfluss verschiedener Faktoren wie Kerben, Eigenspannungen und Umgebungsmedien auf die Schwingfestigkeit wird beschrieben. Verschiedene Versagensmechanismen, die besonders im VHCF-Bereich auftreten, wie Bruchausgange unterhalb der Oberflache, werden erlautert. Dabei spielen mikrostrukturelle Inhomogenitaten und statistische Bedingungen eine grose Rolle. Die untersuchten Werkstoffe sind verschiedene Metalle mit kubisch-raumzentriertem Gitter, wie Vergutungsstahle sowie niedrig- und hochfeste Stahle, aber auch Werkstoffe, die ein kubisch-flachenzentriertes Gitter besitzen, wie Aluminium und Kupfer.

Computational modelling of irregular open‐cell foam behaviour under impact loading

Abstract: Cellular structures represent an important class of engineering materials. Typical representative of such structures are metallic foams, which are being increasingly used in many advanced engineering applications due to their low specific weight, appropriate mechanical properties and excellent energy absorption capacity. For optimal design of cellular structures it is necessary to develop proper computational models for use in computational simulations of their behaviour under impact loading. The paper studies the effects of open-cell metallic foam irregularity on deformation behaviour and impact energy absorption during impact loading by means of parametric computational simulations, using the lattice-type modelling of open-cell material structure. The 3D Voronoi technique is used for the reproduction of real, irregular open-cell structure of metallic foams. The method uses as a reference a regular mesh structure and utilises an irregularity parameter to reproduce the irregularity of real open-cell structure. A smoothing technique is introduced to assure proper stability and accuracy of explicit dynamic simulations using the produced lattice models. The effects of the smoothing technique were determined by comparative simulations of smoothed and unsmoothed lattices subjected to dynamic loading.

Preparation and thermal properties of zirconium tungstate/copper composites

Abstract: ZrW{sub 2}O{sub 8}/Cu composites were prepared by the powder metallurgy method. Electroless plating was used to deposit copper on ZrW{sub 2}O{sub 8} powder before sintering. The thermal expansion and thermal conductivity of composites were measured in the temperature range from 25 C to 200 C and compared with those predicted from various theoretical models. The results show that the coefficient of thermal expansion of ZrW{sub 2}O{sub 8}/Cu composites with a different volume fraction of ZrW{sub 2}O{sub 8} is greater than the theoretically calculated value. The thermal conductivities of ZrW{sub 2}O{sub 8}/ Cu composites increase with a higher copper content and decrease upon elevated temperature. The thermal conductivity of composites with a different volume fraction of ZrW{sub 2}O{sub 8} is lower than the theoretically calculated value. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

The influence of the electroplating parameters on the conditions of deposited nickel‐iron coatings

Abstract: Several specific electroplating parameters are varied to develop a manufacturing process for nickel-iron coatings with low residual stresses and favourable structures and hardness values. Here, the produced coating conditions on the surface are characterised according to alloy compositions, microstructures, residual stresses, texture and microhardness as well as the elastic indentation modulus. The manufacture of the coatings was carried out in a laboratory electroplating plant. The process parameters are: electroplating in electrolytic baths with and without saccharin as an additive, with different iron content as well as with various current parameters. The results show significant influences of saccharin, as a bath additive, and of the pulse frequency during the reverse current pulse procedure on the coating conditions. Supplementary investigations are scheduled for determining the distributions of the conditions through the coating thickness. Similarly, micromechanical tests are planned. Process parameters with optimal conditions can then be selected from the determined process-condition property relation. This is to subsequently serve as the basis for improving the manufacture of micro gear-wheels. The micro gear-wheels are produced by electroforming using the direct LIGA process. Einfluss von Galvanikprozessparametern auf die Zustande abgeschiedener Nickel-Eisen-Schichten Zur Entwicklung eines Herstellungsprozesses fur eigenspannungsarme Nickel-Eisen-Schichten mit gunstigen Gefugen und Hartezustanden werden gezielt einige Galvanikprozessparameter variiert. Dabei erzeugte Schichtzustande werden an der Oberflache nach Legierungszusammensetzungen, Gefugen, Eigenspannungs-, Textur- und Mikrohartezustanden sowie elastischen Eindringmoduln charakterisiert. Das Herstellen der Schichten findet in einer Laborgalvanikanlage statt. Prozessparameter sind das Galvanisieren in Elektrolytbadern mit und ohne Saccharin als Badzusatz, mit unterschiedlichen Eisengehalten sowie mit verschiedenen Stromparametern. An den Schichten ermittelte Ergebnisse zeigen signifikante Einflusse von Saccharin als Badzusatz und von der Pulsfrequenz beim bipolaren Pulsstromverfahren auf die Schichtzustande. Erganzende Untersuchungen zur Ermittlung der Verteilungen der Zustande uber der Schichthohe sind vorgesehen. Ebenso sind mikromechanische Prufungen geplant. Aus dem ermittelten Prozess-Zustands-Eigenschaftszusammenhang lassen sich dann Prozessparameter mit optimalen Zustanden auswahlen. Diese sollen spater als Grundlage zur verbesserten Herstellung von Mikrozahnradern dienen. Gefertigt werden die Mikrozahnrader durch Galvanoformung nach dem Direkt-LIGA-Verfahren.

Comparison between RVE and full mesh approaches for the simulation of compression tests on cellular metals

Abstract: Metal foams are materials of recent development and application that show interesting combinations of physical and mechanical properties. Many applications are envisaged for such materials, particularly in equipments of passive safety, because of their high capacity of energy absorption under impact conditions. The damage analysis in metallic foams is a complex problem and must be performed in a finite strain context. Considering that compression is the dominant loading in impact situations, a finite deformation simulation including damage effects of a compression test on a cellular metal sample is shown in this work. The main objective of the paper is to compare simulations considering periodic boundary conditions, by means of a representative volume element (RVE) approach, with results obtained using full meshes. It is shown that, when the imposed deformation is high, the use of RVE does not describe in a proper manner the deformation that occurs at the walls of cells. This characteristic of RVE approach results in a too stiff behavior when considering load-displacement relations. A comparison with experimental results is also presented.

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

Abstract: The effect of surface compressive residual stresses (RS) induced by surface grinding and polishing on the gigacycle fatigue behavior of medium-carbon high-chromium alloy cold work tool steel was evaluated. Two test series were performed: Specimens of series I revealed high compressive RS of about -800 MPa at the surface, resulting from grinding with fine emery paper, which treatment had definitely a beneficial influence on the fatigue endurance strength. The existence of surface RS was also revealed to be responsible for the location of the fatigue crack initiation. High compressive RS favored internal crack origins. In this case crack nucleation sites were primary carbide clusters in the interior of the specimen, forming so-called fish-eyes at the fracture surface. In contrast, specimens of test series II had only very low RS, which enabled crack initiation near/at the surface at primary carbides/clusters. Furthermore, it has been shown that the high initial RS are prone to partial relaxation through cyclic loading for which the mechanisms are currently unknown. In this case near-surface induced failure was obtained. It was possible to confirm the experimentally obtained data by the use of the concept of local fatigue strength as function of effective RS. The relaxation of high initial RS was experimentally confirmed through RS measurements at runout specimens (1010 cycles without failure). Einfluss von Oberflacheneigenspannungen auf das Ermudungsverhalten eines hochchromlegierten Kaltarbeitsstahls bei sehr hohen Lastspielzahlen Der Einfluss von Oberflachendruckeigenspannungen, eingebracht durch Schleifen der Probenoberflache, wurde auf das Ermudungsverhalten eines hochchromlegierten Kaltarbeitsstahls untersucht. Zwei Prufserien wurden durchgefuhrt: Proben der Serie I zeigten hohe Druckeigenspannungen aufgrund des Schleifvorgangs woraus eine eindeutig positive Wirkung auf die Ermudungsfestigkeit resultierte. Es zeigte sich, dass die Eigenspannungen einen bedeutenden Einfluss auf den Ort der Risseinleitung haben. Hohe Druckspannungen an der Oberflache begunstigten interne Rissentstehung an Primarkarbidclustern, was zur Bildung so genannter Fischaugenstruktur auf der Bruchoberflache fuhrte. Im Vergleich dazu hatten die Proben der Serie II nur geringe Eigenspannungen, was die Rissinitiierung an Primarkarbiden/Clustern an der Oberflache ermoglichte. Auserdem konnte gezeigt werden, dass die hohen Druckeigenspannungen durch die zyklische Beanspruchung zumindest partiell abgebaut werden. Die fur die Relaxation verantwortlichen Mechanismen bei solch harten Werkstoffen sind derzeit nicht bekannt. Nach Relaxation der Eigenspanungen trat Versagen aufgrund von Rissentstehung an Oberflachenkarbiden auf. Es war moglich, diesen experimentellen Befund mittels eines geeigneten Modells – des Konzepts lokaler Ermudungsfestigkeiten – zu bestatigen und Voraussagen uber den Ort der Risseinleitung zu ermitteln. Weiters war es moglich, den Eigenspannungsabbau experimentell durch Messung an Durchlauferproben (1010 Zyklen ohne Bruch) zu bestatigen.

Über adiabatic shearbands und die Entstehung der „Steilen Weißen Bänder”︁ in Wälzlagern

Abstract: Bei der Uberrollung von Walzelementen entstehen nach uberelastischen Beanspruchungen unter der Laufbahnoberflache strukturelle Veranderungen. Mikro- und makroplastische Verformungen des Gefuges infolge der dreiachsigen Beanspruchung begleiten den Walzermudungsprozess vom ersten Lastwechsel an. Sie bestimmen die Lebensdauer des Walzelements. Man beobachtet neben den plastischen Verformungen des Gefuges des Weiteren die sog. „butterflies” und die sog. flachen und steilen „Weisen Bander”. Diese Gefuge sind nicht anatzbar. Die weisen Bander entstehen bei Kugellagern erst nach einer groseren Anzahl von Uberrollungen und liegen im Umfangsschnitt unter ≈ 30 ° bzw. ≈ 80 ° zur Kontaktflache. Die butterflies und die weisen Bander entstehen offenbar infolge einer zweiachsigen Werkstoffbeanspruchung. Ein Einfluss auf die Lebensdauer ist nicht erwiesen. Struktur und Entstehungsmechanismus sind strittig. Es gibt Gefugeerscheinungen, die den butterflies und den weisen Bandern ahnlich sind, die sog. adiabatic shearbands. Diese entstehen nach einer lokalen Makro-Scherung des Gefuges, ausgelost durch eine einmalige, extrem kurzzeitige Druck-Scher-Beanspruchung. Blitztemperaturen nahe dem Schmelzpunkt verursachen im Scherbereich bei martensitisch geharteten Werkstoffen die Bildung von Neuhartungszonen; auch diese Gefuge sind nicht anatzbar. Der vorliegende Aufsatz beschaftigt sich mit der Frage, ob wahrend des stetig und langzeitig ablaufenden Prozesses der plastischen Verformungen eine Beanspruchungskonstellation entsteht, die die adiabatische Bildung von butterflies und von weisen Bandern ermoglicht. Berucksichtigt man jungste Erkenntnisse zur Walzermudung sowie zur Werkstoffbeanspruchung durch eine EHD-Stromung, dann darf man zumindest die „Steilen Weisen Bander” als adiabatic shearbands ansehen. About adiabatic shear bands and the generation of “high-angle white bands” in roller bearings During the rolling motion of roller components structural changes are generated by over-elastic distressing below the bearing face. Micro- and macro-plastic distortions of the microstructure due to the three-axial distressing accompany the process of rolling contact fatigue with the start from the first load cycle. They determine the life-duration of the roller component. Further structural changes in ball bearings besides the plastic deformations are the so called “butterflies” and the so called low- and high-angle “white bands”. The “white bands” you only can detect later, after an extended number of rolling actions. They are inclined to average circumferential angles at ≈ 30 ° respectively ≈ 80 °. Butterflies and white bands develop obviously due to a two-axial material stressing. An influence on the life duration is not proved. The structure and the mechanism of their generation are under discussion. There exist phenomena of the microstructure which are similar to the white bands, the so called adiabatic shear bands. These generate after a local macro-shear process of the microstructure, caused by a single, rapid shock-shear stressing. Flash-temperatures near the melting point generate in the shear zone of martensitic hardened materials the formations of new hardened zones; these microstructures cannot be etched too. The paper contributes to the question, if there exists a stress-constellation which causes the adiabatic formation of butterflies and of white bands during the steady and long during process of plastic deformation. If one considers the latest knowledge about rolling contact fatigue and stressing by EHD (elasto-hydro-dynamic) flow, he can come to the conclusion, that at least the “high-angle white bands” are adiabatic shear bands.

High resolution surface studies of superplastic deformation in shear and tension

Abstract: Despite decades of study, the fundamental mechanisms of superplasticity, particularly relating to the accommodation of grain boundary sliding, are still widely disputed. This is partly due to a lack of information on individual grain deformation and sliding events. Previous studies of superplasticity using surface markers have tended to use either diamond paste scratches, which make quantitative measurements difficult and are open to widely varying interpretation, or regular grids with spacing greater than the grain size, which prevents measurements of intragranular deformation. Recent work has shown that a Focussed Ion Beam (FIB) can be used to create regular, repeating grid marker systems with pitches varying from 0.25 to more than 50 microns. Previously published results in Sn-Pb have shown the power of this technique, particularly regarding the lack of intragranular deformation and surface grain boundary sliding accommodation mechanisms. The current study has applied the FIB technique to Al5083, a pseudo-single phase alloy. Tensile tests have been performed with elongations from 5 % to 150 %. Additionally, analogous biaxial shear tests have been performed for comparison and to limit the free surface effects. SEM images of FIB markers before and after deformation have been acquired, and quantitative measurements of the localized strains have been made using 3-D tilt reconstruction. Shear and tension results show several distinct features. However, no significant intragranular deformation is seen under either set of strain conditions. Possible accommodation mechanisms are discussed.

Effect of fluctuation and modification on microstructure and impact toughness of 20 wt.% Cr hypereutectic white cast iron

Abstract: In the present study, Fe-Cr-C hypereutectic high chromium white cast iron were prepared from industry-grade materials and subjected to the treatment of modification using Fe-Si-RE alloy, aluminum and a self-made intermediate alloy, fluctuation (ferroalloy powder), and the combination of the fluctuation and the modification respectively. The structures of the treated alloy were investigated by means of the optical microscopy (OM). The impact toughness of the specimens was also examined. The fractographs of the samples were examined by scanning electron microscopy (SEM). The results showed that, with the addition of fluctuation or modifying agents, the primary carbides were refined and the impact toughness of the alloys was improved, especially with the combination of them.

Microstructures and mechanical properties of friction stir welded dissimilar copper/brass joints

Abstract: In this study, an experimental investigation has been carried out on microstructure and mechanical properties of friction stir welded copper/brass dissimilar joints. Effect of axial tool force to welding quality has been investigated under obtained optimal tool rotation rate and tool traverse speed conditions. The tool for the dissimilar copper/brass friction stir welding manufactured from X155CrMoV12–1 cold work tool steel with material number of 1.2379. The friction stir welding quality was investigated by welding surface inspections, microstructural studies, micro hardness measurements and tensile tests. The experimental studies have shown that constant axial tool force during pre-heating and during welding process are very important. As a result, by using 2.5–3 kN of axial tool force during pre-heating and 5.5 kN of axial tool force during welding process, copper/brass dissimilar joints with well appearance and higher mechanical strength can be obtained. Mikrostrukturen und mechanische Eigenschaften von durch Ruhrreibschweisen hergestellten verschiedenartigen Kupfer-Messing-Verbindungen In dieser Studie wurde eine experimentelle Untersuchung der Mikrostruktur und der mechanischen Eigenschaften von durch Ruhrreibschweisen hergestellten verschiedenartigen Kupfer-Messing-Verbindungen durchgefuhrt. Die Auswirkungen der axialen Werkzeugkraft auf die Schweisqualitat wurden bei optimal erreichter Werkzeugumdrehungsrate und -fahrgeschwindigkeit untersucht. Das Werkzeug fur das verschiedenartige Kupfer-Messing-Ruhrreibschweisen besteht aus kaltem Werkzeugstahl X155CrMoV12–1 mit der Werkstoffnummer 1.2379. Die Qualitat des Ruhrreibschweisens wurde anhand einer Bewertung durch Augenschein der Schweisoberflachen, Mikrostrukturstudien, Mikrohartemessungen und Zugtests untersucht. Die experimentellen Studien haben gezeigt, dass eine konstante axiale Werkzeugkraft wahrend des Vorwarmens und wahrend des Schweisprozesses sehr wichtig ist. Folglich konnen mit einer axialen Werkzeugkraft von 2,5–3 kN wahrend des Vorwarmens und einer Axialwerkzeugkraft von 5,5 kN wahrend des Schweisprozesses, verschiedenartige Kupfer-Messing-Verbindungen mit gutem Aussehen und hoherer mechanischer Festigkeit erreicht werden.

Enhanced superplastic deformation behavior of ultrafine‐grained Ti‐6Al‐4V alloy

Abstract: The mechanical behavior of the Ti-6Al-4V ELI alloy in both conventional grain size (CG) and ultrafine-grained (UFG) conditions under tension and compression at elevated temperatures (500–800 °C) is considered. Grain refinement by equal-channel angular pressing (ECAP) followed by multicycle extrusion was observed to result in a considerable improvement of superplastic characteristics of Ti-6Al-4V ELI alloy. The alloy exhibits a superplastic deformation behavior already at 600 °C. The enhanced regime of superplasticity allows more efficient forming of parts and components. In addition, the UFG microstructure and, consequently, enhanced mechanical properties are kept after superplastic forming.

Dynamic analysis of the micromilling process – influence of tool vibrations on the quality of microstructures

Abstract: Micromilling is a suitable technique for the manufacturing of microstructured parts. The downscaling of the milling process leads to problems, which are caused by the low stability of microtools and their manufacturing. Tool vibrations and runout occur, resulting in poor surface qualities and undesirable surface location errors. The presented results of the experimental analysis include a stability diagram for the spindle speed range of n = 60,000–120,000 rpm and tool vibrations measured in the xy-plane. Micrographs illustrate the influence of tool vibrations on the quality of the generated surface structures. In addition, the dynamic runout is characterized and its effects are discussed. Dynamikanalyse des Mikrofrasprozesses – Einfluss von Werkzeugschwingungen auf die Qualitat von Mikrostrukturen Das Mikrofrasen ist ein geeignetes Verfahren zur Herstellung von mikrostrukturierten Bauteilen. Die Herabskalierung des Frasprozesses fuhrt jedoch zu Problemen, welche durch die geringe Stabilitat der Werkzeuge und deren Herstellung hervorgerufen werden. Es treten Werkzeugschwingungen und Rundlauffehler auf, woraus schlechte Oberflachenqualitaten und unerwunschte Form- und Masabweichungen resultieren. Die vorgestellten Ergebnisse der experimentellen Untersuchungen beinhalten neben einem Stabilitatsdiagramm fur den Drehzahlbereich von n = 60.000–120.000 1/min auch gemessene Werkzeugschwingungen in der xy-Ebene. Weiterhin werden Aufnahmen von Oberflachenstrukturen dargestellt, welche die Auswirkungen von Werkzeugschwingungen verdeutlichen. Des Weiteren wird der dynamische Rundlauffehler im untersuchten Drehzahlbereich charakterisiert und dessen Einfluss diskutiert.

Development and characterization of sol‐gel composite coatings on aluminum alloys for corrosion protection

Abstract: For several years, CrIV compounds were used as effective and inexpensive corrosion inhibitors. Studies showed that these materials were toxic and carcinogenic. This has led to extensive research to develop alternative inhibitors. Organo-silicate hybrid coatings appeared as an effective technique for forming protective layers on different metal alloys. A silane film was obtained by dip coating of the sample in sol solution prepared from the hydrolysis of 3-glycidoxypropyltrimethoxysilane (GPTM), tetraethylorthosilicate (TEOS) with acid as catalyst and water as solvent instead of VOC (volatile organic compound). The sol solution was aged at ambient temperature to to enhance the effectiveness of the solution for the hydrolysis process. The sample was cured at 150 °C to ensure cross-linking of the film. The experiments have shown that heat treatment leads to increased density and corrosion resistance of the films. Organic and inorganic inhibitors were added in different concentrations to improve the protection and self-healing properties of the coating even after long-time immersion in corrosive solution. The protection performance of the film was evaluated by electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl solution (pH value 7). The surface morphologies of the treated samples were investigated using SEM. Entwicklung und Charakterisierung von Sol-Gel-Komposit-Schichten auf Aluminium-Legierungen fur den Korrosionsschutz CrIV -Werkstoffe wurden viele Jahre lang als effektive und kostengunstige Korrosionsinhibitoren eingesetzt. Forschungen zeigten, dass diese Materialien giftig und krebserzeugend sind. Dies hat zu umfangreichen Forschungsarbeiten und zur Entwicklung alternativer Inhibitoren gefuhrt. Organo-Silikat-Hybrid-Beschichtungen haben sich als eine wirksame Technik fur die Bildung schutzender Schichten auf verschiedenen Metalllegierungen herausgestellt. Silanfilme wurden durch eine Dip-Beschichtung der Probe in einer Sol-Losung erzielt, die aus der Hydrolyse von 3-Glycidoxypropyltrimethoxysilane (GPTMS), Tetraethylorthosilicate (TEOS) mit Saure als Katalysator und Wasser als Losungsmittel anstelle von VOC (volatile organic Compound) entstehen. Die Sol-Losung wurde bei Raumtemperatur gealtert, um die Wirksamkeit der Losung fur den Hydrolyse-Prozess zu verbessern. Ebenso erfolgte eine Warmebehandlung der Probe bei 150 °C, um die Vernetzung des Films zu gewahrleisten. Die Experimente haben gezeigt, dass die Dichte der Filme und somit die Korrosionsbestandigkeit durch die Warmebehandlung ansteigt. Organische und anorganische Inhibitoren wurden in verschiedenen Konzentrationen beigemischt, um Schutz- und Selbstheilungseigenschaften der Schicht, auch bei langzeitigem Eintauchen in eine korrosive Losung, zu verbessern. Die Bewertung der Schutzwirkung des Films erfolgte durch elektrochemische Impedanz-Spektroskopie (EIS) in 0,5 M NaCl Losung (pH-Wert 7). Ebenso wurden die Oberflachenmorphologien der behandelten Proben mittels REM untersucht.

Theoretical and experimental analysis of plastic response of isotropic circular plates subjected to underwater explosion loading

Abstract: Dynamic response analysis of structures subjected to underwater explosion (UndEx) loading has been always an interesting field of study for ship designers and metal forming specialists. Understanding the deformation and rupture mechanism of simple structures plays an important role in successful designing of a reliable structure under this kind of loading. In this paper, first the major parameters of the UndEx phenomenon (peak overpressure, impulse per unit area, dimensionless damage parameter Φ, etc.) are discussed and determined by means of available experimental relations mostly offered by R. Cole. After that, the maximum deflection of a fully clamped circular plate has been calculated using a theoretical procedure assuming two different conditions: (1) neglecting the effect of strain rate, (2) considering the strain rate sensitivity of the material. Some experiments have been conducted on 5010 aluminum circular plates, using C4 as explosive. In order to simulate reality, a fixture was designed so that the plates are loaded in air-backed condition. Plates were fixed on top of the fixture, so the fully clamped condition which was assumed as the boundary condition was achieved. The test specimens were measured, not only their maximum deflection but also their thickness at different radii were determined. The results are compared to experimental-based predictions offered by Nurick and Rajendran who has conducted similar experiments. The results show reasonable agreement with theoretical predictions, especially when strain rate effects are considered. In addition, two new material constants (D, q) for this special aluminum alloy are introduced. Theoretische und experimentelle Analyse der plastischen Umformung isotroper kreisformiger Platten bei Unterwasser-Explosionsbelastung Die Analyse der dynamischen Reaktion einer Struktur bei einer Explosionsbelastung unter dem Wasser ist fur die Konstrukteure von Schiffen und Umformspezialisten eine interessante Forschungsaufgabe. Das Verstandnis der Umformung und der Bruchmechanismen einfacher Strukturen spielt eine wichtige Rolle im erfolgreichen Konstruieren einer festen Struktur gegen diese Belastungsart. In diesem Beitrag werden erstens die Hauptparameter der Explosionserscheinung unter Wasser (maximaler Druck, Impulse per Flacheneinheit, dimensionsloser zerstorender Parameter usw.) dargestellt und zweitens durch die vorhandenen Methoden, die uberwiegend von R. Cole vorliegen, berechnet. Danach ist die maximale Durchbiegung einer ganz gespannten kreisformigen Platte durch eine analytische Methode in zwei Formen bestimmt worden: (1) Vernachlassigung der Dehnungsgeschwindigkeit, (2) Berucksichtigung der Dehnungsgeschwindigkeitsempfindlichkeit des Werkstoffes. Einige Untersuchungen wurden an kreisformigen Platten aus Aluminium 5010 mittels Sprengstoff C4 durchgefuhrt. Zur Praxissimulation wurde die Spannvorrichtung so konstruiert, so dass die Platten Luft-gepuffert belastet wurden. Die Platten wurden oben auf der Spannvorrichtung vollstandig eingespannt, um Grenzbedingungen zu erhalten. Bei den Proben wurde nicht nur die maximale Durchbiegung sondern auch die Dicke in verschiedenen Radien ermittelt. Die Ergebnisse wurden mit den experimentellen Abschatzungen von Nurick und Rajendran, die ahnliche Versuche durchgefuhrt haben, verglichen. Die Ergebnisse zeigen eine gute Ubereinstimmung mit den theoretischen Abschatzungen, insbesondere bei Betrachtung der Dehngeschwindigkeit. Zusatzlich wurden fur diese spezielle Aluminiumlegierung zwei neue Materialkonstanten (D, q) eingefuhrt.

Effect of laser welding parameters on fusion zone morphological, mechanical and microstructural characteristics of AISI 304 stainless steel

Abstract: Nowadays, the Nd:YAG laser has been a promising key tool for joining thin components. In this research, mechanical and microstructural properties of laser welded thin austenitic stainless steel sheets were investigated with experimental investigations, as a function of laser welding parameters. Butt welded joints were made using a Nd:YAG laser in the pulsed wave mode. The appropriate laser welding parameters were found in order to obtain quality and strong weld seam. The pulsed laser seam welding process is controlled by a variety of parameters. We focus on the effects of the several processing parameters on mechanical and microstructural characteristics of joint and weld quality. The aim of this research was to evaluate the influence of these processing parameters on joint strength and microstructure. And also we examined the weldability of stainless steels in butt joint configuration by a pulsed Nd:YAG laser beam.

Rheologisches Verhalten hochgefüllter Kunststoffe. Einfluss der Füllstoffe

Abstract: Im Rahmen dieser Arbeit wurde das Fliessverhalten gefullter thermoplastischer Polymere untersucht. Es wurde gezeigt, dass die rheologischen Eigenschaften hochgefullter Kunststoffe im Allgemeinen vom Fliesverhalten des Matrixpolymers, den Eigenschaften und der Struktur der dispersen Phase und Wechselwirkungen zwischen Polymer und Fullstoff sowie zwischen den einzelnen Fullstoffpartikeln abhangig sind. In der Arbeit wurde das theoretische Verhaltnis zwischen der Viskositat von gefullten und ungefullten Polymeren als Funktion des Fullstoffgehalts und der Wechselwirkungen zwischen den Komponenten vorgeschlagen. Auf Basis des entwickelten Modells kann man die stochastische Struktur des gefullten Materials und die nicht linearen viskosen Eigenschaften der Kunststoffschmelze berucksichtigen.

Fatigue assessment of seam welds of automotive components by local stress approaches

Abstract: In the present paper a method is described for the fatigue assessment of multi-axial loaded welded joints in structures made from thin steel sheets. The focus is on seam welds under non-proportional loading, assuming a constant angular phase shift between cycles leading to stress components acting at the seam welds. Fatigue analyses are using a local stress approach based on stresses derived by Theory of Elasticity. Furthermore, potentials of considering statistical size effects in order to analyse weld start and end points are outlined. Schwingfestigkeitsbewertung von geschweisten Komponenten im Automobilbau mit lokalen Konzepten In dieser Arbeit wird eine Methode zur Berechnung der Schwingfestigkeit von mehrachsig belasteten geschweisten Dunnblechverbindungen aus Stahl vorgestellt. Der Fokus liegt auf dem Einfluss von nicht-proportionalen Lasten mit einer konstanten Phasenverschiebung auf die Schwingfestigkeit von Schweisnahten. Die Betrachtungen werden basierend auf dem Kerbspannungskonzept vorgenommen, das auf elastizitatstheoretischen Spannungen basiert, die mit einem Radius von rf = 0,05 mm ermittelt werden. Fur eine Bewertung von Schweisnahtenden werden Moglichkeiten aufgezeigt, wie unter Berucksichtigung des statistischen Groseneinflusses die Analysengute weiter gesteigert werden kann.

Contact stress analysis on the X‐shape ring

Abstract: A X-ring is a loop of elastomer with X-shaped cross-section used as a mechanical seal or gasket. Such a X-ring is designed to be seated in a groove and is compressed during assembly between two or more parts, creating a seal at the interface. The seal is designed to have line contact between the X-ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the X-ring shell body. This study aims to detect the contact stress and the deformed shape of a X–shaped ring shell under various compression conditions. For this analysis, four experiments were conducted to obtain material properties of the elastomer. The contact stress analysis is performed by applying material properties that we obtained through experiments. A contact stress analysis is carried out by finite element analysis.

Variable amplitude fatigue of autofrettaged diesel injection parts

Abstract: Experimental and analytical investigations of constant and variable amplitude fatigue life of not autofrettaged and autofrettaged components have been performed. In variable amplitude loading the new standardised COmmon-RAil-Load sequence CORAL has been used as well as two-level-tests with small cycles at high mean stresses interrupted by large cycles for the evaluation of load sequence effects. The results of the two level tests show that small cycles with amplitudes far below the fatigue limit cause fatigue damage. Life calculations have been performed according to the nominal stress approach with S-N-curves and improved Miner’s Rule, linear-elastic fracture mechanics with 3D-weight functions, elastic-plastic fracture mechanics applying an extended strip yield-model, and explicit 3D-FE-simulation of fatigue crack growth with predefined crack fronts. All approaches are appropriate for predicting realistic variable amplitude lives. From a practical point of view the explicit 3DFE- simulation of fatigue crack growth is too time-consuming. However, such simulations show that the approaches based on linear- elastic fracture mechanics and elastic-plastic fracture mechanics with extended strip yield-model capture the essential physics of fatigue crack growth in a realistic way. Key words: Autofrettage, variable amplitude, residual stress, fatigue crack growth Die Lebensdauer nicht autofrettierter und autofrettierter Bauteile unter einstufiger und betriebsa¨hnlicher Innendruckbelastung wurde experimentell und analytisch untersucht. Als betriebsa¨hnliche Belastung wurde die COmmon-RAil-Load sequence CORAL entwickelt. Zur weiteren Kla¨rung von Lastfolgeeinflu¨ssen wurden Zweistufenversuche durchgefu¨hrt mit dem Ergebnis, dass kleine Schwingspiele noch bei mitteldruckbewerteten Amplituden weit unterhalb der halben Dauerfestigkeit scha¨digen. Die folgenden Lebensdauervorhersagemethoden wurden u¨berpru ¨ft: Nennspannungskonzept mit Varianten der Miner-Regel linear-elastische Bruchmechanik mit 3D-Gewichtsfunktionen elasto-plastische Bruchmechanik mit erweitertem Fliesstreifen- Modell explizite 3D-FE-Simulation des Rissfortschritts mit vorgegebener Rissfront Alle Methoden eignen sich a¨hnlich gut. Fu¨r die praktische Anwendung erscheint die explizite 3D-FE-Simulation zu aufwa¨ndig, sie zeigen jedoch deutlich, dass die linear-elastische Bruchmechanik mit 3D-Gewichtsfunktionen und die elasto-plastische Bruchmechanik mit erweitertem Fliesstreifen-Modell die wesentlichen physikalischen Pha¨nomene des Rissfortschritts realistisch abbilden. Schlu¨sselworte: Autofrettage, Betriebsfestigkeit, Eigenspannungen, Rissfortschritt

Magnesium tube hydroforming

Abstract: Magnesium alloys reveal a good strength-to-weight ratio in the family of lightweight metals and gains potential to provide up to 30 % mass savings compared to aluminium and up to 75 % compared to steel. The use of sheet magnesium alloys for auto body applications is however limited due to the relatively low formability at room temperature. Within the scope of this paper, extruded magnesium tubes, which are suitable for hydroforming applications, have been investigated. Results obtained at room temperature using magnesium AZ31 tubes show that circumferential strains are limited to a maximal value of 4 %. In order to examine the influence of the forming temperature on tube formability, investigations have been carried out with a new die set for hot internal high pressure (IHP) forming at temperatures up to 400 °C. Earlier investigations with magnesium AZ31 tubes have shown that fractures occur along the welding line at tubes extruded over a spider die, whereby a non-uniform expansion at bursting with an elongation value of 24 % can be observed. A maximum circumferential strain of approx. 60 % could be attained when seamless, mechanically pre-expanded and annealed tubes of the same alloy have been used. The effect of annealing time on materials forming properties shows a fine grained structure for sufficient annealing times as well as deterioration with a large increase at same time. Hence, seamless ZM21 tubes have been used in the current investigations. With these tubes, an increased tensile fracture strain of 116 % at 350 °C is observed as against 19 % at 20 °C, obtained by tensile testing of milled specimens from the extruded tubes. This behaviour is also seen under the condition of tool contact during the IHP forming process. To determine the maximum circumferential strain at different forming temperatures and strain rates, the tubes are initially bulged in a die with square cross-section under plane stress conditions. Thereafter, the tubes are calibrated by using an optimised pressure-time curve. The IHP forming process has also been used to demonstrate practicability and feasibility for real parts by manufacturing a technology-demonstrator part using the magnesium alloy ZM21.

Size effects in the fatigue behavior of welded steel tubular bridge joints

Abstract: Tubular space trusses for bridge applications use thick-walled tubes. The reduction in fatigue resistance due to geometrical size effects is thus an important issue. In order to carry out a thorough study, both fatigue tests on large-scale specimens and advanced 3D crack propagation modelling were carried out at ICOM/EPFL. The study is limited to circular hollow sections (CHS) K-joints. An alternate current potential drop (ACPD) system is used to measure crack depth on nodes of the tested truss specimens. The results obtained from the tests are given in the paper in terms of S-N data, crack depth versus number of cycles and deduced crack propagation rates. The numerical model was developed using the dual boundary elements method (DBEM), software BEASYTM, and was validated with fatigue tests data. The stress intensity factors (SIF) along the doubly curved crack front at different crack depths were obtained.With this model, a parametric study investigates the influence of geometry, size and load case on fatigue life. The results of both proportional and non-proportional sizing effects on fatigue strength are presented. The paper shows that size effects (proportional and non-proportional) can be expressed as a function of the non-dimensional parameters and chord thickness. Keywords: Structural steel, fatigue, size effects, large-scale tests, boundary element method.

Superplasticity and high temperature deformation behaviour in nano grain Tungsten compacts

Abstract: Nano grain tungsten is fabricated by Mechanical Milling (MM) process, and its grain growth behavior and high temperature deformability is investigated. As a result, a nano grain structure, whose grain size is approximately 20 nm or less, is obtained after MM for 360ks. Those nano grains demonstrate an irregular grain boundary structure, i.e., “non-equilibrium grain boundary”, and they change to a smooth grain boundary structure by annealing at 1023 K for 3.6 ks. Compacts with nano grain structure indicate superior sintering property even at 1273 K (0.35 Tm). Rhenium addition prevents grain growth during sintering and thus the compacts indicate a further improvement in deformability. The compact is composed of equiaxed grain, whose grain size is 420 nm, and has low dislocation density even after the large deformation. The strain rate sensitivity, i.e., m-value, of 0.41 is obtained in the W-Re compact at 1473 K. Those results strongly imply that the nano grain W-Re compacts show superplasticity at less than half of the melting temperature, i.e., 1473 K (0.42 of the solidus temperature).

Experimental analysis of the flexural properties of sandwich panels with cellular core materials

Abstract: This paper addresses the flexural properties of sandwich structures with cellular core materials. Experimental three point bending tests are conducted in order to determine the flexural stiffness and the load-carrying capacity of these advanced composites. In addition, the significant failure modes after exceeding the load-carrying capacity are identified. The results of these analyses are compared for sandwich structures containing various core materials. These core materials comprise two aluminium foams, namely M-PoreJ and AlporasJ, honeycomb structures and novel metallic hollow sphere structures (MHSS).