Development and Processing of Continuous Flax and Carbon Fiber-Reinforced Thermoplastic Composites by a Modified Material Extrusion Process

Additive manufacturing, especially material extrusion (MEX), has received a lot of attention recently. The reasons for this are the numerous advantages compared to conventional manufacturing processes, which result in various new possibilities for product development and -design. By applying material layer by layer, parts with complex, load-path optimized geometries can be manufactured at neutral costs. To expand the application fields of MEX, high-strength and simultaneously lightweight materials are required which fulfill the requirements of highly resilient technical parts. For instance, the embedding of continuous carbon and flax fibers in a polymer matrix offers great potential for this. To achieve the highest possible variability with regard to the material combinations while ensuring simple and economical production, the fiber-matrix bonding should be carried out in one process step together with the actual parts manufacture. This paper deals with the adaptation and improvement of the 3D printer on the one hand and the characterization of 3D printed test specimens based on carbon and flax fibers on the other hand. For this purpose, the print head development for in-situ processing of contin uous fiber-reinforced parts with improved mechanical properties is described. It was determined that compared to neat polylactic acid (PLA), the continuous fiber-reinforced test specimens achieve up to 430% higher tensile strength and 890% higher tensile modulus for the carbon fiber reinforcement and an increase of up to 325% in tensile strength and 570% in tensile modulus for the flax fibers. Similar improvements in performance were achieved in the bending tests

Central quantitative measurements of achievement and qualitative school development. The effects of High Stakes tests in the USA

Der Autor geht der Frage nach, "ob und wie sich zentrale quantitative Leistungsmessungen mittel- und langfristig" auf das Schul- und Bildungssystem auswirken. "Nach [einer] kritisch-distanzierten Bilanzierung der Testphilosophie und der Testpraxis in den USA" formuliert er Bedingungen "für sinnvolle Modelle und Verfahren von Leistungsmessung..., die pädagogischen, entwicklungspsychologischen und lerntheoretischen Begründungen" standhalten können. (DIPF/Orig./Un)In the USA experiences with central achievement tests are vehemently discussed. Evaluations show that such selective and prominent examinations do not promote the behavior of the teachers and the learners. Conclusions for a more productive handling of achievement expectations should be drawn. (DIPF/Orig.

Neuro sciences and learning. Implications on the contribution of neuro sciences for the organization of instruction

Aus gehirnbiologischer Sicht bedeutet Lernen die Herstellung von Bedeutung sowie die Entwicklung von neuronalen Mustern, Verbindungen, Strukturen und Netzen. Bei der Suche nach tragfähigen Ansätzen für eine Qualitätsverbesserung von Unterricht können neurobiologische Ergebnisse mit dazu beitragen, das Nachdenken über lernergerechte Gestaltungsformen von Lehr- und Lernprozessen zu intensivieren. (DIPF/Orig.)In neurobiological studies the acquisition of knowledge is seen as a process of constructing meaning by developing neuronal patterns, connections and networks. These insights can contribute to intensify the discussion of teaching and learning formal education in school with the aim to adapt them to the learners\u27 needs. (DIPF/Orig.

Advances in Understanding The Ability of Sapstaining Fungi To Produce Cell Wall-Degrading Enzymes

The ability of selected sapstaining fungi to produce the enzymes cellulase, xylanase, mannanase, pectinase, and amylase was investigated in vitro. While all test fungi secreted low amounts of xylanase (up to 1.64 μmoles/min/ml) and pectinase (up to 0.11 μmoles/min/ml) into the growth medium, extracellular cellulase was not detected. Furthermore, mannanase was produced only by Ophiostoma piceae (Münch) Syd. & P. Syd. (0.29 μmoles/min/ml). To the best of our knowledge, this is the first report of mannanase activity for any Ophiostoma sp. Amylase activity was higher than xylanase, mannanase, and pectinase activities for all test fungi. This confirms that sapstaining fungi preferentially metabolize readily accessible, nonstructural wood components, such as starch. Possible roles of the enzymes detected are discussed

Experimental analysis of the thermal energy storage potential of a phase change material embedded in additively manufactured lattice structures

Recent literature introduced novel additively manufactured porous metallic structures designed to deliver enhancement of the thermal conductivity of organic phase change materials. Among these, so-called lattice structures are of particular interest for application in lightweight components. Originally investigated for their attractive mass-specific mechanical properties, these geometries were recently proposed, in alternative to metallic foams, as a conductive matrix of phase change materials. However, the geometrical parameters of a lattice structure differ from the ones of a metallic foam and no established data exist in the literature about the influence of the lattice cell geometry on the transient heat transfer enhancement of a phase change material. This work presents an experimental comparison of the thermal behaviour of a composite based on an n-Octadecane paraffin wax embedded in four different aluminium lattices with varying unit cell topology (f2ccz, bcc, bccz, f2bcc), but showing the same cell size, aspect ratio and strut diameter. It is noticed that the unit cell topology affects the transient thermal behaviour beyond its direct effect on the cell porosity. To address this, a specific thermal performance parameter is identified. The sample based on the f2ccz topology represents the best candidate. The influence of orientation with respect to gravity on the heat transfer is also investigated. While the samples show relatively low porosity, ranging from 70.7% to 83.4%, the wide pore diameters lead to a high impact of melt convection on the thermal behaviour of most samples. Up to 28% wall temperature variation is evidenced for different heating orientations

Werteerziehung und Schulentwicklung. Konzeptuelle und organisatorische Ansätze zur Entwicklung einer demokratischen und sozialen Lernkultur

Der Schule fällt vermehrt die Aufgabe zu, neue Lernformen zu initiieren, die die soziale und moralische Entwicklung der Kinder und Jugendlichen sowie den Erwerb sozialer Kompetenzen fördern. Dazu muss sich Schule auf drei Ebenen ändern: Unterricht, Schulleben und Öffnung der Schule in ihr soziales Umfeld