Frischbetondruck bei Verwendung von Selbstverdichtendem Beton

Formwork Pressure Asserted by Self‐Compacting‐Concrete On the basis of tests on the friction and deformation behaviour of Self‐Compacting Concrete (SCC) in the fresh state, analytical models to calculate the formwork pressure on vertical formwork were developed. One model, which is based on silo theory and takes into account time dependent material parameters of fresh concrete, as well as a simplified model makes it possible to estimate the fresh concrete pressure during setting. A proposal for the design of formwork, based on semi‐probabilistic safety concept was developed. It was noted that even for SCC, in the design of formwork and scaffolding the load is often less than hydrostatic concrete pressure. The pressure can be best controlled on site by limiting the casting rate.     

Methoden zur mechanischen Charakterisierung von modifizierten Implantatoberflächen in der Orthopädischen Chirurgie

Methods for the mechanical characterisation of modified implant surfaces in orthopaedic surgery Nowadays, on average approximately 10 % of all hip and knee endoprostheses have to be exchanged within the first 10 years. Implant revision is often necessary following aseptic or septic loosening. Hence, today implants for orthopaedic surgery are increasingly being coated for better osseointegration. Coatings have to be biocompatible and meet high mechanical requirements, whereby the adhesive strength and the abrasive wear resistance of the coatings take on a key role. This study presents different methods to asses these parameters experimentally using two innovative coatings (TiN, TiO2‐Cu) exemplary. The adhesive bonding strength of the coatings was investigated using different standardised methods, such as the arbour bending test, scratch test and the standard adhesive test. Wear resistance was determined after 1.5 million cycles in a special testing machine. The investigations showed for both coatings, TiN and TiO2‐Cu, good adhesive strength and wear resistance. The adhesive strength and wear resistance of bio‐active, wear reducing or anti‐allergenic surface coatings can be determined reliably using the above‐mentioned methods.     

Optimization of Dielectric Properties of Suspension Plasma Sprayed Hydroxyapatite Coatings

Conventional plasma torch was adapted to spray very fine Ca₅ (PO₄)₃OH (hydroxyapatite, HA) precursors having sizes ranging from a few hundreds of nanometers to a few micrometers. The powders were put in suspension with distilled water and antidispersive agent. A home made suspension feeder, including two peristaltic pumps, delivered the suspension into atomizer and therefrom injected into plasma jet. The suspension flow rate was electronically controlled. The resulting coatings had the thickness of a few tenths of μm. The electrical properties of the coatings including breakdown voltage and loss factor of suspension sprayed hydroxyapatite coatings sprayed onto aluminium substrates were also tested. The influence of such experimental factors as power input to plasma, pressure of atomizing gas, spray distance and suspension feed rate on the responses being the electrical properties was investigated using a 2⁴ design of experiments (DOE). The mathematical models relating the responses with the factors were created and the significant factors were selected.     

Fabrication of hydrothermal ageing resistant of 3 mol % yttria-stabilised tetragonal zirconia polycrystalline via microwave sintering

The influence of microwave sintering on the densification, mechanical performances, microstructure evolution and hydrothermal ageing behaviour of pure 3 mol % yttria-stabilised tetragonal zirconia polycrystalline (3Y-TZP) ceramics was compared with conventional sintered samples. Green bodies were sintered via conventional pressure-less and microwave sintering method between 1200 °C to 1400 °C with dwelling time and firing rate at 120 min, 10 °C/min and 1 min, 20 °C/min. Result showed that reduced processing temperature and holding time is possible with microwave sintering technique for fabricating good resistant zirconia sample with bulk density, Young's modulus, and Vicker's hardness that are comparable to samples sintered with conventional method. However, the microwave sintered samples suffered from hydrothermal ageing where their average grain size is above critical size. The enhancement of hydrothermal ageing resistance of the sintered samples is associated with the decreasing grain size of the sintered samples instead of sintering method.     

Effective thermal properties of an isotactic polypropylene (α‐iPP) injection moulded part by a multiscale approach

In injection moulding processes, the melt undergoes a complex deformation and cooling history, which results in an inhomogeneous distribution of crystalline superstructures in semi‐crystalline thermoplastics, which significantly influences their final mechanical and thermal properties. In this paper we describe the determination of local effective thermal properties of a moulded part via a multiscale simulation approach. First a macroscopic filling and heat transfer simulation is performed followed by a microstructure evolution calculation on the micro‐scale. Then, the effective thermal properties are derived via a two‐level homogenization scheme. The results show that the effective thermal conductivity is anisotropic and that it varies asymmetrically over the analysed plate sections.     

Einfluss und Bedeutung chemischer Entmischungen auf mechanische Eigenschaften thixogeformter Bauteile

Chemical Segregation Effect on Mechanical Properties of Thioxo Formed Components Thixoforming is a near net shape forming process of semi solid billets with a stiffness, which is comparable to “butter”. Advantages of conventional forming and casting processes can be combined due to this modern forming process technology. The objective of this investigation is to identify the effect of local chemical segregation regarding the microstructure and mechanical properties in various parts of a component. Different components and component regions – with diverse cross‐sections and flow lengths – have been tested. Tensile, charpy and fatigue tests are completed by metallography and local chemical analysis. The investigation was focused on AlSi7Mg0.3 and AlSi6Cu3 aluminium casting alloys. It can be confirmed, that chemical composition of the raw material and segregation are important effects on mechanical properties of components. Chemical segregation can be caused by abrupt changes in cross‐section. The inhomogeneity verified by chemical analysis and metallography are important effects on mechanical properties of Thixoforming components. In future the counteract between metal structure and processing steps regarding mechanical properties of components must be examined more intensively. The aim is to create a fundamental understanding of the relationship between the structure, chemical composition, homogeneity and characteristics of aluminium materials.     

Friction stir welding of AISI 304 austenitic stainless steel

The objective of this work is to demonstrate the feasibility of friction stir welding (FSW) AISI 304 austenitic stainless steels. The tool used was formed of a tungsten‐based alloy. The specimens were welded on an 11 kW vertical milling machine. Defect‐free welds were produced on 2.5 mm plates of hot‐rolled AISI 304 austenitic stainless steels at travel speeds ranging from 40 to 100 mm/min with a constant rotating speed of 1000 rpm. Tensile strengths and hardness values of the weld interface were determined and microstructure features of these samples were investigated.