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Leichtbau und Ressourcenschonung sind zentrale Themen des 21. Jahrhunderts. Hybridverbunde mit Naturfasern (z.B. Flachs, Kenaf) sind Stand der Technik und werden v.a. im Automobilbau verwendet. Durch Hybridverbunde lassen sich die Vorteile von Spritzguss und Pressverfahren kombinieren (Funktionalisierung bei hoher Eigensteifigkeit). Obwohl Holzfasern diverse Vorteile gegenüber Naturfasern bieten (z.B. geringere Rohstoffrisiken), sind sie in diesem Bereich noch nicht umfassend untersucht.
Leichtbau und ressourcenschonende Herstellungstechnologien sind zentrale Themen des 21. Jahrhunderts. Thermoplastische Hybridverbunde mit endlosfaserverstärkten Einlegern spielen dabei eine große Rolle, sogenannte Organobleche. Auch Hybridverbunde mit Naturfaserverstärkung sind seit langem Stand der Technik und werden vor allem in der Automobilindustrie verwendet. Holzfasern sind in diesem Bereich jedoch noch nicht umfassend untersucht.
Der Vortrag befasst sich mit dem Potenzial von Holzfasern für thermoplastische Hybridverbunde im Vergleich zu Naturfasern. Dabei wird ein Einblick auf prozess- und materialtechnische Untersuchungen gegeben. Bei den Versuchen kommen diverse Technologien zum Einsatz. Holzfasern werden über ein Air-Lay-Verfahren mit Kunststofffasern zu einem Vlies gelegt. Bei der Weiterverarbeitung der konsolidierten Vliese zu Hybridverbunden, werden diese mit direkt compoundierten Holzfasern über einen In-Mould-Compounder angespritzt. Es zeigt sich, dass Faserverbunde mit Holzfasern vielversprechende Eigenschaften haben. Weitere Untersuchungen sind nötig, um ein tiefgreifendes Verständnis für die Werkstoffe und die Prozesse zu entwickeln.
Soil nailing systems are a common way to stabilize slopes and construction pits. Their design is usually based on the mechanical equilibrium of a rigid body motion and therefore, only tensile stresses are considered and accompanying forces like bending (shear stresses) in the soil nails are neglected. Continuous strain measurements along nails could verify this assumption, but may not be performed using conventional sensing technologies.
This paper reports about monitoring of a soil nailed slope stabilization using distributed fiber optic sensing. Soil nails in different anchoring horizons were instrumented and autonomously monitored over several weeks, in which the construction pit was excavated continuously. After the excavation, the final load bearing capacity of one selected nail was determined within a classical geotechnical load test. In addition to the field measurements, the bending behavior of the instrumented nail system was analyzed under laboratory conditions.
The presented studies demonstrate the high potential of distributed fiber optic sensing systems and their capability to extend traditional measurement methods in foundation engineering applications.
Laminated veneer lumber poles for temporary soil nailing ‐ investigation of material properties
(2016)
Within a current research project at Rosenheim University of Applied Sciences and Graz University of Technology the possibilities of using beech wood laminated veneer lumber poles as soil anchors for temporary soil nailing systems are investigated. Therefore tensile and bending properties of laminated veneers with high moisture and permanent cement contact concerning the influence of veneer bending rectangular to the fibre are determined. For investigation of material properties under different climate conditions tensile tests on small and faultless single beech wood veneers as well as tensile tests on 6 layered 3 mm samples and 9 layered 2 mm samples were carried out.
Therefore all samples were stored in extreme climate conditions like high moisture content and permanent cement contact. Six layered samples with 3mm thick veneers show a slightly higher strength and stiffness under dry conditions as well as at a moisture content of the samples above fibre saturation. A strength reduction factor concerning temporary geotechnical applications is suggested which considers the influence of long term loading, veneer bending, water saturation and
cement destruction on tensile properties of laminated veneer lumber poles.
Within a current research-project the possibility of using laminated veneer lumber beech wood poles as temporary soil anchors in foundation engineering is investigated. Within this project adhesive properties of laminated veneer lumber beech wood poles are determined. For
use in temporary ground applications the influence of veneer bending, veneer thickness and intensive cement contact is concerned. As standard version two different adhesive systemsmelamine formaldehyde resin (MUF) and a 1-component polyurethane adhesive (PUR) were investigated and compared.
Melamine formaldehyde resin glued samples with 3 mm thick veneers and 1.0N/mm² press force show a higher tensile shear strength but also a higher adhesive failure percentage than polyurethane glued samples. In case of melamine formaldehyde resins the closed time has a great influence on bond line quality. A long closed time reveals a low penetration of adhesive in the cells and a low embedding on the wood surface. For curved structures best results were achieved with a bonding pressure of 1.0 N/mm². A significant difference in strength between the concerned MUF and PUR adhesive system was not recognized.