Volume 52, Issue 6

Kurzfassung Bei der Anwendung des inkrementellen Bohrlochverfahrens zur Eigenspannungsanalyse sind zur Bestimmung von Spannungsverteilungen aus den gemessenen Deformationen Kalibrierfunktionen notwendig, welche die Empfindlichkeit der verwendeten Dehnungsmessstreifenanordnung im Hinblick auf die Dehnungsauslösung durch die Bohrung berücksichtigen. Üblicherweise werden diese aus elastischen FE-Rechnungen gewonnen, wobei als Geometrie eine dicke Platte ohne Randeffekte zugrunde gelegt wird. Aus diesem Grund müssen bei Eigenspannungsanalysen an realen Bauteilen bestimmte Restriktionen im Hinblick auf die Bauteilgeometrie beachtet werden. Dies schränkt in der Realität die Anwendbarkeit des Verfahrens bzw. die Aussagefähigkeit der Messungen ein. In der vorliegenden Arbeit wird vorgeschlagen, geometriespezifische Kalibrierfunktionen zu verwenden, um die genannten Probleme zu vermeiden. Es werden Ergebnisse von FE-Simulationen von Bohrlochexperimenten vorgestellt, welche die Auswirkungen realer Bauteilgeometrien auf die ermittelten Spannungen zeigen und die Verbesserungen der Messgenauigkeit bei Verwendung geometriespezifischer Kalibrierfunktionen im Vergleich mit der konventionellen Vorgehensweise belegen.

The paper contains considerations on fatigue life determined on the basis of tests performed under uniaxial stress state. Specimens made of a 18G2A steel were tested. The calculated fatigue lives were compared with those obtained from the tests. The calculations were performed according to the ASTM standard, i. e. plotted as S-N characteristic (the Wöhler curve), and in the scatter for the assumed significance level of 5%, typical for fatigue tests. The results of the calculations are consistent to the experimental results within the whole range

An attempt has been made to determine the suitability of the conventional Jominy end quench test for assessing the quenching behaviour of heat treatable aluminium alloys. Hence it was decided to apply the Jominy test initially on specimens of 6061, 2024, and 7075 alloys possessing considerable differences in quenching response. The Jominy test with slight modification was found to be successful in revealing the quenching response of the alloys studied. Experimental results have indicated that the quench sensitivity of these alloys increases in the order of 6061, 2024, and 7075. The quench sensitivity of Al alloys is primarily governed by two factors. Firstly, the increase in the concentration of the alloying elements increases the quench sensitivity. Secondly, the elements that form high temperature intermetallics make aluminium alloys more quench sensitive.

Si 3 N 4 /C composites were prepared with carbon black and α-Si 3 N 4 powder by a novel sintering method, i.e. spark plasma sintering. SiC particles formed through reactions between the carbon particles and the SiO 2 on the Si 3 N 4 surface. The samples were sintered at 1650 °C for 5 minutes in a nitrogen atmosphere. The microstructure, phase composition, mechanical properties, and dielectric properties of the composites were investigated. The relative densities of the C/Si 3 N 4 composites decreased from 99 to 85% when the carbon black content increased from 0 to 20 wt.-%. Bending strength, hardness and dielectric properties were found to be influenced by the amount of carbon black introduced into the silicon nitride matrix.

Metal foams are a new class of materials with low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Aluminum foams especially show potential for use in lightweight structures, for energy absorption, and for thermal management. Open cell aluminum foams with tailored porous morphology were synthesized by a space-holder method. In these foams, the pore shape is predominantly controlled by the initial shape of the space-holder particles that are used to produce the preform. In this study, resin bonded sand and gypsum bonded ceramic space holder particles are used in the open cell foam production. This paper describes the space-holder method for manufacturing open cell aluminum foams and characterizes the density as well as the compressive property of the foams.

Kurzfassung This study presents the new development in the 1.8l Eagle shape of an edible oil bottle made of polyethylene terephthalat (PET) virgin resin. The study refers to an increasing of the stretch ratio between the bottle and the preform. The new preform design offers several advantages including light-weight, reduced electrical consumption, maintaining good quality level and improvement of some mechanical properties (ductility and toughness) for many bottle applications. Mainly, the study has been divided into two parts, i.e. experimental work and finite element analysis. Regarding the experimental work, substantial modifications of the injection unit have been made to produce the new preform fitting to the new stretch ratio. The modification comprises the pair of injection cores, cavity, guide ring, and two pairs of split insert. Also, in the experimental work 126 tension tests with standard samples from bottles before and after the modification have been performed. The specimens have been taken from seven areas of the bottle and have been loaded in two directions (axial and hoop). Finally, the new bottle quality level has been experimentally checked by load tests, stacking tests and center closure leak tests. For the finite element simulations, solid modeling of the complex bottle shape by SolidWorks has been carried out, followed by finite element analyses with Abaqus to calculate the stress and displacement in the bottle areas and also to compare the behavior of the stress distributions for old and new bottles. Among others, as the major result of this study a 16.2% reduction in the bottle weight has been achieved which will reduce the material cost. Regarding the mechanical properties for the new bottle, like ductility and toughness, a number of significant improvements have been made in many bottle areas. In the most critical area, the ductility has been improved by 180% and the toughness by 35%. The non-linear finite element analyses have revealed a maximum stress reduction of 36% as compared to the old bottle.

In order to improve the spatial resolution of computed tomography reconstructions which suffer from un-sharpness due to an extended source size a new procedure of de-smearing has been developed. As the width of the source related smearing function of the projections may even double between the position near and far from the detector the desmearing procedure has to be variable. In contrast to the essentially wrong approach of de-convolution by a constant smear kernel for all voxel positions an implicit desmearing is established. The pre-known position dependent smearing is applied to the iteratively repeated projections of partial reconstructions obtained from the DIRECTT reconstruction algorithm. This approach of variable desmearing from sinograms of a pixel model with smearing from one to five pixel FWHM achieves a spatial resolution near one pixel.

Kurzfassung Zur Abschätzung von Versagensbeanspruchungen von Komponenten mit Fehlstellen ist die Kenntnis der Bruchzähigkeit hilfreich. Die Ermittlung des Widerstandes gegen Rissausbreitung bei sehr hohen Temperaturen an metallischen Hochtemperatur-Werkstoffen wird gezeigt. Das Bruchverhalten von metallischen Hochtemperaturlegierungen lässt sich bei hohen Temperaturen mit einer Kombination der Gleichstrompotenzialsonde und einer Probenheizung mit einem Gasbrenner ermitteln. Die sehr hohen Genauigkeitsanforderungen des Teilentlastungsverfahrens lassen sich umgehen. Die grobkörnigen Nickelbasislegierungen führen zu deutlich größeren Messwertstreuungen als bei feinkristallinen Stählen üblich ist. Die Rissfront beinhaltet nur wenige Körner mit unbekannter Kristallorientierung. Es empfiehlt sich, mehrere Proben bei derselben Temperatur zu prüfen, um einen Anhaltswert für die zu erwartende Streuung zu erhalten.