Volume 53, Issue 1-2

Kurzfassung Aktuelle Untersuchungen an der TU Kaiserslautern beschäftigen sich im Rahmen der DFG-Forschergruppe 524 mit dem Fügen hybrider Strukturen aus C-Faser-Kunststoff-Verbunden und Leichtmetallen. Am Lehrstuhl für Werkstoffkunde (WKK) wurde hierzu erstmals die Metall-Ultraschallschweißtechnik genutzt. An den erzeugten Verschweißungen wurden umfangreiche Untersuchungen zum mechanischen Verhalten der Leichtbauwerkstoffverbunde durchgeführt. Dabei wurden insbesondere die erreichbaren Festigkeiten bei unterschiedlichen Beanspruchungsarten (Quer-Druck und Schub) in Abhängigkeit von der Temperatur- und Prüfgeschwindigkeit untersucht. Am Institut für Verbundwerkstoffe GmbH (IVW) wurden quasistatische Versuche bei automobiltypischen Betriebstemperaturen sowie Hochgeschwindigkeitsversuche durchgeführt, um das Verformungsverhalten der geschweißten Leichtbaustrukturen detailliert zu beschreiben.

A crucial problem in the development of new hydrogen technologies is the need for lightweight and safe storage of acceptable amounts of hydrogen, in particular for portable or mobile applications. A new and innovative technology based on capillary arrays has been developed. These systems ensure the safe infusion, storage, and controlled release of hydrogen gas, even when storage pressures of up to 1200 bar are applied. This technology enables the storage of a significantly higher amount of hydrogen than other approaches. It has already surpassed the US Department of Energy's 2010 target, and is expected to meet the DOE's 2015 target in the near future. The main determinant in this storage technology is the pressure resistance of glass capillaries. It is well known that quartz, for example, is three times stronger than steel. At the same time, the density is about three times lower which means that much less material is necessary to reach the same pressure resistance. The pressure resistance of single capillaries has been determined in relation to various capillary materials and dimensions, wall thicknesses etc. in order to find out optimal parameters for the “final” capillaries.

The particularities of joining surface hardened steels (carburized, nitrided and induction hardened) using friction welding are analyzed in order to assess the influence of the wear protection layers on the welding process. The joint influence of the friction speed, friction pressure and time, as well as the upsetting pressure is evaluated for joints made out of carburized, nitrided and carburized with nitrided steels, respectively. The investigation of microstructure and properties allows an optimization of the friction welding parameters. The friction stroke appears to be the main parameter for welding carburized and nitrided steels, respectively. For welding carburized with nitrided parts, remains of carbon and nitrogen enriched materials are still present in the joining plane, regardless of the axial pressure and the friction stroke. Only a limited diffusion of the two components in the axial direction can be detected.

In this work the lock-in-thermography was tested for crack detection capabilities. Instead of an external heat source the thermo elastic effect induced by the mechanical loading is used for cyclic thermal stimulation. This procedure was applicable for crack detection in an aluminium centre cracked tension specimen (CCT) during a running fatigue test. As lock-in input signal the force as well the signal of a strain gauge, placed in the surrounding of an estimated crack initiation site, can be used, respectively. This strain gauge can also be attached perpendicular to the loading direction.

Pb(Zr,Ti)O 3 (PZT) powder modified SrBi 2 Ta 2 O 9 (SBT) ceramics, hereafter called SBT-PZT, were prepared by the solid phase synthesis method. With the aid of atomic force microscopy and x-ray diffractometry, the SBT-PZT ceramics were found to exhibit an enhanced c -axis orientation compared with SBT ceramics. Ferroelectric and dielectric properties of SBT-PZT ceramics were revealed to be anisotropic by relevant measurements. Because of differences in heteropolar valence and ionic radius between SBT and PZT, the PZT may be introduced into SBT as a heterogeneous system and embedded in the SBT grain boundaries. The large differences in crystal structures between SBT and PZT were proposed to be responsible for the SBT-PZT grain orientation mechanism. Obviously, the grain orientation resulted in electrical anisotropies of SBT-PZT ceramic. The internal stress, which was induced by heterogeneous system doping, was considered to affect the polarization reversal of SBT-PZT ceramics.

Effects of binder and water contents on extrusion behavior of a 100 CPSI (cells per square inch) square lattice channel honeycomb-type zeolite monolith support with 0.59 mm wall thickness and an overall cross-sectional square area of 100 cm 2 have been studied. Process variables for successfully processing the green-body were first optimized, but drying condition of the green body turned out to be more crucial in successful fabrication of the calcined honeycomb-type support. Overall, the addition of processing additives such as 2.4 wt.-% of organic binder, 17.6 wt.-% of distilled-water to 60.0 wt.-% natural zeolite paste exhibited low exit pressure and contributed to successful fabrication of honeycomb-type zeolite monolith green body. The green bodies thus fabricated were dried for about 140 h under 95% relative humidity at 60 °C before final calcination treatment for 2 hr at 600 °C.

Tungsten inert gas welding (TIG) is one of the most important material-joining processes widely used in industry. AISI type 304L stainless steel plates with 8 and 10mm thicknesses are widely used in the fabrication of pressure vessels and other components. These plates are mostly joined together by multipass welding methods. The temperature distribution that occurs during multipass welding affects the material microstructure, hardness, mechanical properties, and the residual stresses that will be present in the welded material. Very limited experimental data regarding temperature distribution during multipass welding of plates is available in the literature. Experimental work was carried out to find out the temperature distribution during multipass welding of the AISI 304L stainless steel plates. The temperature distribution curves obtained during the experiments are presented. The average maximum temperature rise during each pass of welding is calculated and plotted against the distance from the weld pad centre line. From these plots, the maximum temperature rise expected in the base plate region during any pass of welding operation can be estimated.

The Vickers micro-hardness of three different sea mollusc shell structures has been determined as a function of the indentation load. The following shells from the Adriatic Sea have been investigated: abalone (Haliotis tuberculata) , smooth clam (Callista chione) , and warty venus (Venus verrucosa) . The results show that the measured micro-hardness depends on the load for all of the investigated seashell structures, which indicates the influence of the indentation size effect (ISE). The load dependence of micro-hardness has been analyzed by using the known Meyer's Law, the proportional specimen resistance model (PSR), and the modified proportional specimen resistance model. The best correlation between measured values and used models has been achieved by using the modified PSR model.

In this study, the effect of the PVA amount on the SiC preform properties was investigated. SiC particulates that have 60 μm average grain size were used as preform constituent. In order to produce SiC preforms, slurries that contains SiC, PVA, and colloidal silica were prepared with different amount of PVA and were dried at room temperature for 24 hours. Dried specimens were sintered at 1000°C for 3 hours. Also, specimens were characterized by Archimedes' tests for porosity. Mechanical and microstructural tests were carried out by bending and SEM analysis, respec- tively.

A method for independent prediction of creep damage accumulation on the basis of damage at short term loading and long-term strength is verified for the case of fiber/matrix debonding of injection moulded short glass fibre reinforced polyoximethylene. Small angle scattering X-ray refractometry is applied for damage registration. The method is applicable to materials which display delocalised damage prior to fracture. The predicted damage is compared with the experimental data for damage accumulation in creep.