In this work, the influences of fiber orientation and weld lines on the morphological structures and the mechanical behavior of polyamide 6.6 (PA6.6-GF35) are investigated. In quasistatic and fatigue tests tensile and 3-point-bending loads are applied. Test temperatures vary between RT and 150 C. Two different specimen types are produced by using injection moulding process to create different fiber orientations as well as weld lines. Fiber orientations are determined using computer tomography. Scanning electron microscopy is used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation and temperature. Transversely oriented fibers in weld lines result in brittle failure mechanisms and decreased mechanical properties. Different stress distributions in the specimens under tensile and flexural loads have influence on the material behavior as well.

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Generally, wood chipping represents an important procedure in the wood processing and forestry industry. To improve structural components like chipping tools, knowledge of the properties of local timber including resistance against chipping as well as the dynamically acting process forces is of utmost significance. The aim of this work is to experimentally evaluate service-induced stresses on machinery parts to create a numerical material model, which is capable of revealing similar resistance against cutting as natural wood. To this end, a small-scale cutting machine has been designed, incorporating a bladeholder with strain gauges applied, measuring the resulting mechanical stresses during the chipping process by focussing on different wood species. Spruce is utilized as a variety with a lower density and European beech for higher density timber applications. The test results demonstrate a distinct difference by cutting both materials, whereby European beech indicates more than twice the resistance against chipping compared to spruce. Setting two different, relatively acute rake angles on the cutting tool does not reveal a fundamental difference for chipping. To evaluate the numerical wood material model, an isotropic ductile damage model, usually applied to ductile metals, was implemented in this study. Based on a sensitivity study of the material properties in the course of the numerical simulation, a possible approach is presented that explains how to change the cutting resistance, depending on the blade movement direction and the angle of the main grain of the timber. In a comparison of different types of mechanical stress from the numerical analysis and experimental tests, the

KurzfassungAufgrund der überragenden Bedeutung des Leichtbaus im Fahrzeugbau versucht man heutzutage immer mehr Bauteile aus Metall durch kurzfaserverstärkten Kunststoff zu ersetzen. Für die betriebsfeste Bauteildimensionierung benötigt man Wöhlerlinien, welche jedoch stark von Faserorientierung, Temperatur, Feuchtigkeit und anderen Einflüssen abhängen. Dazu wurden umfangreiche Probenversuche im Rahmen eines Forschungsprojektes durchgeführt. Für die Lebensdauervorhersage wurden Methoden entwickelt und ein Simulationsprozess etabliert, der Faserorientierung und Faserverteilung als Ergebnis einer Spritzgießsimulation berücksichtigt. Anhand von Praxisbauteilen mit vorhandenen Versuchsergebnissen wurden die neuen Verfahren verifiziert.

The prediction of fatigue strength and fatigue life of materials was the key motivation in this study. Several approaches for fatigue limit prediction at mesoscopic scale have been proposed. All of them incorporate microstructure and grain features. For the purpose of studying plastic local strain accumulation and therefore fatigue behaviour at the grain scale a new testing rig was developed. A key point for understanding fatigue behaviour and crack initiation even at higher load cycles is basic knowledge on strain localization in the grain structure of the material. Till now low testing frequencies of SEM in-situ testing rigs limited tests at higher load cycles. The developed in-situ tension-compression testing apparatus for in-situ SEM use allows testing at higher frequencies and therefore to perform even higher load cycles with less time consumption. Oxygen free high conductivity copper (OFHC) grade 99,99% was chosen for investigation. In addition cuts with a focus ion beam (FIB) were made in distinct orientations representing material defects to get an idea of the influence of micro notches on fatigue behaviour and crack initiation. The results of in-situ fatigue tests will be presented.