Bauweise mit Zukunft: Durch und durch mineralisch —Wärmedämmendes Mauerwerk mit mineralischem Putz

Hat Mauerwerk eine Zukunft? Oder dienen Wände bald nur noch als Trägermaterial für Dämmschichten? Dabei ist gerade wärmedämmendes Mauerwerk aus gutem Grund im Wohnungsbau nach wie vor die Nummer Eins — und wird es nach Einschätzung der Fachleute auch bleiben. Dieser Beitrag schildert aktuelle Entwicklungen und beleuchtet Hintergründe. Construction with a future — theral insulating brick with mineral plaster. Does brickwork has a future? Couldn’t it be that walls will soon only serve as backing material for insulation layer? However, there are good reasons that heat insulating brickwork is still the number one in domestic constructions — according to experts this will remain so. The following article will characterize current developments und backgrounds.     

Reasons for Melting of Chemical Elements and some Consequences

When studying the causes for melting, solid chemical elements are considered to be the simplest systems. Data of the melting enthalpy, ΔH_m, and entropy, ΔS_m, taken from the literature are investigated as well as the molar specific heat capacities immediately below and above the melting temperature, T_m. In many cases, the molar specific heat capacity at constant volume exceeds the classical limit for the lattice vibrations C_V = 3R above the Debye temperature. This excess specific heat is due to electronic transitions of bonding electrons and of the electrons near the Fermi‐edge to states with higher energy. The wave functions of the electrons in these higher states are different from those of the original lower states causing the core ions to be attracted to different new positions. In addition, the vibrations may modify the local potential of the electrons and thus their wave‐functions with similar results. Melting occurs if sufficient core ions relax to new positions within the lifetime of the excited states and if their order and arrangement is changing according to the random time series of the different occupied electronic states with their respective wave‐functions. This mechanism can also be applied to explain diffusion, thermal expansion and the glass transition temperature.     

Performance of Multipor WI as exterior insulation

Multipor WI is a mineral‐based interior insulation system with excellent insulation properties. It is dimensionally stable, vapor permeable, and nonflammable. In this paper the investigation of the processability and functionality of Multipor WI WLF 042 as an exterior insulation system is reported. On the campus of Technische Universität Kaiserslautern, a building was constructed with a new exterior insulation system of Multipor WI WLF 042, of 14 cm thickness. This insulation, which has so far only been used in the building interior, has a heat conductivity of λ = 0.042 W/(mK) and a density of ρ = 90 kg/m³. Its thermal expansion coefficient is α = 10^–5/K and its specific heat capacity is c = 0.85 kJ/(kgK). It has a lower density and compression strength than Multipor mineral insulation boards for exterior use do. Temperature sensors were implemented in different layers of the building envelope, both in undisturbed areas and at thermal bridges. The building will be monitored for several years. First heat transfer simulations of two thermal bridges of the building demonstrate the excellent insulation properties of WI WLF 042. The investigation of the processability and functionality of Multipor WI WLF 042 as an exterior insulation system is presented. First simulations show the excellent insulation properties of the insulation. The building will be monitored for several years to provide data about the processability and functionality of Multipor WI WLF 042 as an exterior insulation system.     

Die Werkstoffermüdung bei Wälzbeanspruchung – Eine Hypothese zum Mechanismus

Materials fatigue by rolling contact stressing – A hypothesis of the mechanism Research in Rolling contact fatigue produced plenty of experimental observations and theoretical knowledge. By considering all these detailed informations a hypotheses for/describing the mechanism of the fatigue process was developed and will be presented. The fatigue process may be devided up in three phases. In phase 1 and 2 the structure will be deformed microplastically. The strength localy becomes smaller. Residual compressive stresses grow. Added to the load stresses, the stressing continual change. In phase 2 the deformations nearly stop. There is a critical point by material behaviour and stressing when phase 2 attains phase 3. The microplastic deformation changes to a macroplastic deformation. The structure “flows” in the direction of the relative tension stress, more and more (in direction) towards the surface. At both sides of the track vaults arise. In the middle of the track a vault also tends to arise, but it will be smoothed by over rolling. So normal to the raceway residual tensile stresses are created. They become biger and biger. Finally they start the subsurface cracks. By the hypotheses nearly all phenomena detected in rolling contact fatigue research can be explained. The thesis reveals chances, rolling contact systems to optimize.     

On the solid state heat transport phenomena measurement

The paper deals with theoretical and experimental aspects of lumped capacitance model (LCM) application for the study of heat transport in different materials. Patented construction of the measuring chamber together with special software the fundamental features of which are presented here allows evaluating thermal conductivity k, specific heat capacity c_p and thermal diffusivity α. Obtained results are in relatively very good agreement with those obtained from independent measurement or table values.     

Investigation on the transferability of algorithms for the numerical optimization of cooling channel design in injection molding on metal gravity die casting

The thermal mold design and the identification of a proper cooling channel design are primordial steps in the development of complex molds for injection molding. In order to find a suitable cooling channel system, a lot of effort is needed to avoid part warpage after solidification. In current research, a simulative procedure to optimize the cooling channel layout iteratively is being developed at the Institute of Plastics Processing. These algorithms are transferred to the metal gravity die casting process, which has several similar requirements to the mold. Effectively, the simulation is simplified to a heat conduction problem. Instead of water, high temperature resistant oil is deployed and the casted material is a A356 aluminum alloy instead of semi‐crystalline plastics. The algorithm is adapted to these changed boundary conditions and the calculation of the optimized heat distribution is performed. Aim of this procedure is the construction of a mold producing parts with less warpage than a conventional mold.     

Development of a clinker brick façade to exploit solar thermal energy / Entwicklung einer Klinkerfassade zur Nutzung solarer Wärmeenergie

The featured research project was intended to develop and test a specially modified brick façade, which would convert solar radiation on the façade into thermal energy for heating purposes. The main objective was to measure the energy extraction potential but all other issues concerning technical feasibility also had to be taken into account. To this end a masonry structure had to be developed, which allowed integration of the inserted pipe to dissipate the energy introduced, while allowing simple, practicable installation. Various tests were carried out on masonry walls and individual bricks. On sunny winter days, an energy extraction potential of 1.9 kWh per square metre of façade and day was measured. During summer days, an extraction potential of up to 2.6 kWh/(m²·d) could be observed. The initial findings allow the assumption that this energy could be utilized with the use of a heat pump.     

Thermal conductivity issues of EB‐PVD thermal barrier coatings

The thermal conductivity of electron‐beam physical vapor deposited (EB‐PVD) thermal barrier coatings (TBCs) was investigated by the Laser Flash technique. Sample type and methodology of data analyses as well as atmosphere during the measurement have some influence on the data. A large variation of the thermal conductivity was found by changes in TBC microstructure. Exposure at high temperature caused sintering of the porous microstructure that finally increased thermal conductivity up to 30 %. EB‐PVD TBCs show a distinct thickness dependence of the thermal conductivity due to the anisotropic microstructure in thickness direction. Thin TBCs had a 20 % lower thermal conductivity than thick coatings. New compositions of the ceramic top layer offer the largest potential to lower thermal conductivity. Values down to 0.8W/(mK) have been already demonstrated with virgin coatings of pyrochlore compositions.     

An analytical model for the prediction of hot roll temperatures in a hot rolling process

Temperature variations in the hot roll during a hot rolling process were analysed by solving heat conduction equations for boundary conditions using an analytical method. The analysis was conducted in a steady‐state regime, taking into account the effects of process parameters such as the contact surface, roll velocity and various cooling boundary conditions. Assuming the periodicity of the process, the development of a solution in the Fourier series was employed to solve the governing equations. The temperature and its gradient distributions in the roll depth were analytically expressed according to the process parameters. The accuracy of the predicted results was examined through comparison with predictions presented in the literature (finite element solutions and measurements). Results showed that an increase in the rolling speed leads to a shorter contact time, which decreases the temperature field in the work‐roll.     

Auf Zukunft gebaut — Projektbericht eines Neubau‐Zweifamilienhauses als EnergieWertHaus

Bereits im Jahre 2007 wurde von Xella die EnergieWertHaus‐Initiative gestartet. Aktueller Anlass war die aufkommende Klimaschutzdiskussion und die damals schon angekündigte Verschärfung der Anforderungen an die Energieeffizienz in 2009 und weiter ab 2012. Es wurden Bauträger und Komplett‐/Schlüsselfertig‐Hausanbieter von Ein‐ und Zweifamilienhäusern zu Workshops eingeladen, mit dem Ziel, ein hochwertiges, zukunftsfähiges massives Hauskonzept zu entwickeln. Diese landesweit angebotenen Workshops wurden durch ein Expertenteam aus den Bereichen Bauphysik, Anlagentechnik, Baubiologie, Mehrwertverkauf und Finanzierung begleitet und die Ergebnisse zu einem Kriterienkatalog für EnergieWertHäuser zusammengefasst. Bei weiteren Workshops und Informationstreffen wurden neue Partner für das Konzept gewonnen und das Konzept ständig verbessert. Im folgenden Beitrag werden die besonderen Eigenschaften des EnergieWertHauses am realisierten Objekt eines Zweifamilienhauses erläutert. Rely on the future ‐ Project report of a new building two‐family house as an energy‐value‐house. In the Year 2007 Xella already started the energy‐value‐house‐initiative. The topical reason was the uprising discussion about climate protection and the announcement for further tightening of the energy efficiency requirements in 2009 and following from 2012. With the aim to develop a prime quality and sustainable solid housing concept, builders of family‐homes were invited to workshops. These workshops were offered nationwide and were accompanied by an expertise‐team from the fields of building physics, heating and ventilation engineering, building biology, value added sales and finance. The results of these workshops were summarised in a catalogue of criteria’s for energy‐value‐houses. In the following workshops and information meetings, new partners were attracted to join the concept and the concept was continuously improved. In the following paper the extraordinary qualities of an energy‐value‐house will be showed on a realized object of a two‐family‐house.     

Simulation der Wärmebehandlung von Stählen am Institut für Werkstoffkunde I

Simulation of the heat treatment of steels at the Institut für Werkstoffkunde I The simulation of manufacturing processes is an important tool in simultaneous engineering. The aim is to cut the time necessary for development and to optimize processes by simulation of the complete manufacturing chain. The field of heat treatment offers a large variety of applications for the use of simulation tools. The geometry of the part, the composition of the material, the heat treatment process as well as the initial state of the parts interact with each other in complex ways and have an influence on the distortion of the part. The calculation of the microstructure and of the hardness distribution helps to determine suitable charging and quenching conditions as well as plant engineering. Calculated residual stresses and distortions can be taken into account in the development and construction of new parts. The Institut für Werkstoffkunde I of the Universität Karlsruhe (TH) is engaged in research programms in this field dealing with numerical as well as experimental problems for almost 30 years.     

Untersuchungen zur Wälzermüdung nach induktivem Kurzzeitanlassen

Ball bearing fatigue after inductive short time tempering To improve toughness, machiniability and to avoid distortion under operating conditions inductive hardened components often were additional tempered in an oven. As a general rule tempering is applied when grinding is required. According to tempering conditions the present hardness, toughness and the microstructure will change. In the present studies it is shown, that with optimized inductive short term tempering conditions it was possible to achieve even better mechanical properties in comparison with oven tempered components. Ball bearing fatigue testings showed an improvement of wear resistance. The achieved findings opens the possibility for numerous applications to exchange the previous oven tempering through the more rapid and more low‐cost inductive short‐term inductive surface layer hardening.     

Hochfrequenzschweißen von Feinblech aus mikrolegiertem Stahl mit integrierter thermomechanischer Nahtbehandlung

High frequency welding of low alloyed sheet steel with integrated thermo‐mechanical treatment Described are the seam characteristics of high frequency welded low‐alloyed sheet steel blanks. The focus of the investigations is directed to static and fatigue strength. In addition, a possibility to perform a thermo‐mechanical treatment of the welding seam will be presented. Also the effect of the thermo‐mechanical treatment on the cold formability of the welding seam is analysed.     

Die Werkstoffbeanspruchung im Wälzkontakt bei hoher Flächenpressung,ermittelt nach Hertz und nach der EHD‐Strömungshypothese

Material stressing at rolling contact with high specific load determined by HERTZian‐ and elastohydrodynamic‐ (EHD) flow hypothesis For the calculation of the material stressing at rolling contact HERTZian distribution of the normal stresses and the tangential stresses within the contact area, which are proportional to the normal stresses, are assumed. This numerical explication is based upon the calculation of the contact fatigue endurance. Taking in consideration the real stress distribution of forces at EHD contact, it can be explained by the EHD flow hypothesis, that at special load constellations the materials stressing leads to higher values.     

Gefügemäßige Bewertung der Schweißeignung von Stahlgusssorten unter Berücksichtigung der Kaltrissbeständigkeit

Microstructural evaluation of weldability of cast steels considering the sensitivity to cold cracking The behaviour of different types of cast steel at welding of structures is widely determined by the specialities of the microstructure in the heat affected zone (HAZ). The identification of the different areas of microstructure depends on the alloying system of the cast material. At the evaluation of the weldability of cast steels with high or low carbon contents high attention should be drawn to the sensitivity to cold cracking, which correlates with the chemical composition as well as with the inhomogenieties of the initial microstructure.     

Heat conduction in closed‐cell cellular metals

The purpose of this research was to describe the thermal transport properties in closed‐cell cellular metals. Influence of cell size variations with different pore gases has been investigated with transient computational simulations. Heat conduction through the base material and gas in pores (cavities) was considered, while the convection and radiation were neglected in the initial stage of this research. First, parametric analysis for defining the proper mesh density and time step were carried out. Then, two‐dimensional computational models of the cellular structure, consisting of the base material and the pore gas, have been solved using ANSYS CFX software within the framework of finite volume elements. The results have confirmed the expectations that the majority of heat is being transferred through the metallic base material with almost negligible heat conduction through the gas in pores. The heat conduction in closed‐cell cellular metals is therefore extremely depended on the relative density but almost insensitive regarding to the gas inside the pore, unless the relative density is very low.     

Effect of Multipor interior insulation on flanking sound transmission / Einfluss einer Innendämmung aus Multipor auf die flankierende Schallübertragung

In order to improve the energy efficiency of an existing building, it is necessary, among other things, to improve the thermal insulation provided by that building’s external walls. If the additional insulation required for this cannot be fitted on the outside, then it will need to be applied on the inside instead. To avoid the need for complex designs, insulating materials with a considerably reduced susceptibility to damage should be used, for example the mineral insulation panel Multipor. Xella Technologie‐ und Forschungsgesellschaft mbH has conducted a study in cooperation with Xella Deutschland GmbH to determine whether, and if so, how, Multipor affects structure‐borne sound transmission when used as interior insulation. The study, the results of which are presented in this article, involved testing flanking sound transmission in a laboratory at the Hochschule für Technik (HFT) in Stuttgart, Germany.     

Modeling of Transient Thermal Contact Resistance out of Conjugate Gradient Method

Temperature profile at contacting pairs of any material combination is crucial in many engineering applications. A new experimental approach is suggested to estimate the contact heat transfer coefficient as well as the thermal contact resistance. This method is based on temperature infrared measurements of contact bodies and then solve the inverse problem with conjugate gradient method. Different affecting parameters are studied namely; surface roughness, presence of interlayer, applied pressure and bodies temperature difference. The time dependant heat transfer coefficients resulting from the proposed method need to be validated by a computer model. Close results are shown with slight deviation by the increase of the applied pressure and the temperature difference.