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Sintering and foaming of barium and calcium silicate glass powder compacts have been studied for different powder milling. Sintering was measured by means of heating microscopy backed up by XRD, DTA, Vacuum Hot Extraction (VHE) and electron microscopy. Foaming intensity strongly increased with decreasing glass partiefe size. Although powder compacts were uniaxially pressed and sintered in ambient air, foaming was affected by the milling atmosphere and most intensive for milfing in C02. Conformingly, VHE studies revealed that foaming of fully sintered samples was mainly driven by C02, even for powders milled in technical air, Ar and N2. Prolonged storage of air milled barium silicate glass powders in ambient air before pressing and sintering caused further increase of foaming intensity. These findings indicate that carbonaceous species are preferentially trapped to or close beneath the powder surface during milling and later storage. The temperature range of C02 degassing from fully sintered barium and calcium silicate g/ass powder compacts fits the temperature ranges of decomposition of BaC03 and CaC03 mix-milled with the respective barium and calcium silicate glass powders.
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
Der Large Hadron Collider (LHC) des europäischen Kernforschungszentrums CERN ist einer der weltweit größten und leistungsfähigsten Teilchenbeschleuniger. Um den Teilchenstrahl auf seiner Kreisbahn zu halten, werden mit Hilfe supraleitender Spulen sehr starke Magnetfelder erzeugt. Die hierzu benötigten hohen Ströme werden über Verbunddrähte aus Niob-Titan und Kupfer geleitet.
Die Drähte werden u.a. durch Ultraschallschweißungen miteinander verbunden. Eine mangelhafte Verbindung kann zur Erwärmung der Kontaktstelle und in Folge davon zum Zusammenbruch der Supraleitung führen. Auf Anfrage des CERN wurden an der BAM Untersuchungen zur Prüfbarkeit solcher Verbindungen bei Umgebungstemperatur durchgeführt. Es gelang, für einen Verbindungstypen einen Wirbelstromsensor für eine manuelle Prüfung zu entwickeln. Ein Prototyp des Sensors befindet sich beim CERN in der praktischen Erprobung. Das Sensorprinzip sowie Prüfergebnisse aus Labor und Praxis werden vorgestellt.
DIN 50100 definiert die Bedingungen für den Schwingfestigkeitsversuch, der zur Ermittlung von Kennwerten dient, die das Verhalten metallischer Werkstoffe und Bauteile bei zyklischer Beanspruchung mit einer konstanten Lastamplitude beschreiben (Wöhlerversuch). Die Norm umfasst die Versuchsdurchführung, die Versuchsauswertung sowie die Dokumentation von lastgeregelten Wöhlerversuchen im Zeit- und Langzeitfestigkeitsbereich. Mit DIN 50100 soll erreicht werden, dass die Wöhlerlinien verschiedener Prüfstellen miteinander vergleichbar und die wesentlichen Randbedingungen der Versuchsdurchführung dokumentiert werden. Da die Ergebnisse von Schwingfestigkeitsversuchen streuen, ist die Treffsicherheit für die Schätzung der Kennwerte von der Anzahl der Versuche einer Versuchsreihe abhängig. In Abhängigkeit von einer geforderten Treffsicherheit wird durch die DIN 50100 der erforderliche Stichprobenumfang vorgegeben.
The goal of the present study is to assess the feasibility to develop a first reliable database of materials parameters for Earth Block Masonry (EBM). The database is crucial when defining the materials safety factors. In the first part an experimental campaign of compressive tests were carried out on two types of earth block and two types of earth mortar. The results showed that the mean variation of the compressive strength was remarkably less than expected. This low variation is related to a production with high quality standards of the materials employed. In the second part a partial safety factor for EBM under uniaxial compression was determined through the reliability method. The results proved the reliability of a common calculation method for EBM based on partial safety factors following the current standards.
Both in developed and developing countries, modern building materials tend to be preferred to traditional earthen construction. Reasons include low durability, inadequate performance under seismic loading and, in developing countries, a wish to replace what is perceived as 'poor' with what is perceived as 'rich'. In an age when building permissions and construction standards are a must, particularly in seismic areas, even when an owner is willing to build in earth, construction approval needs to be granted: we rely on values and standards to build, but the necessary data on material properties and structural performance of earthen building techniques is scarce if compared to the abundance of data for other materials (clay brick masonry, concrete, steel) available to the engineer. At the same time, traditional builders' skills, knowledge and confidence in earthen building techniques are decreasing if not disappearing. A wallette testing campaign was thus carried out with the aim of filling this knowledge gap. Prior to the wallette campaign, material properties, including composition and physical-mechanical parameters, were determined. Compression and diagonal compression (shear) tests were then performed, and a basic analysis of the mechanical behaviour of structural elements built in cob is provided in relation to earth block (adobe) masonry and rammed earth elements. Cob, shown to have low compressive resistance, has a relatively ductile post-peak behaviour if compared to earth block masonry specimens which, as expected, show a marked brittle behaviour. In terms of shear strength, cob performs relatively well in view of its low compressive strength. The study is part of our work within the framework of the ongoing project NIKER funded by the European Commission dealing with improving the structural performance of Cultural Heritage assets in order to limit earthquake hazards.
Structural performances of earthen building materials. A comparison between different typologies
(2011)
Traditional construction techniques utilizing earthen materials are often seen as inferior compared to modern ways of building. Structural earthen elements are perceived as vulnerable towards environmental influences (moisture, frost) and in particular towards the load scenarios during earthquakes. In comparison to the recent advances in research on stone and brick masonry, knowledge on the structural performance of earthen building construction is limited and scattered. Consequently the confidence in the performance of these earthen buildings constructed in the traditional techniques during earthquakes is fairly low. The research presented here aims to make a comparison of mechanical behavior between different earth masonry material typologies, consisting of earth block masonry, rammed earth and cob. The paper has been developed in the framework of a larger research program called NIKER. BAM and other seventeen research partners from the Mediterrean area are jointly involved to develop and validate innovative materials and technologies for the systemic improvement of the seismic behavior of Cultural Heritage assets
The paper has been developed in the framework of a larger EC‐research program called NIKER, in which BAM and other seventeen research partners from the Mediterrean area are jointly involved. It aims to develop and validate innovative materials and technologies for the systemic improvement of the seismic behavior of Cultural Heritage assets. The death tolls brought about by recent catastrophes in
developing countries where many inhabitants lived in earthen dwellings (Gujarat, India 2001, Bam, Iran 2003 and Concepción, Chile 2010 Earthquakes, Tamil Nadu 2004 Tsunami) have brought about research studies aimed at improving earth construction in terms of strength, seismic resistance and speed of construction.
In comparison to the recent advances in research on stone and brick masonry, knowledge on the material properties and failure mechanisms of earthen Building construction is limited and scattered.
The research presented here by aims making a comparison of mechanical behaviour between different earth masonry material typologies, consisting of earth block masonry, rammed earth and cob.