Th. Lampke

Thermogravimetric and differential scanning calorimetric analysis of natural fibres and polypropylene

The thermal behaviour of variably separated flax and hemp fibres was characterised by means of thermogravimetric and differential scanning calorimetric analyses. Reference measurements of cellulose served to describe the degradation behaviour. Furthermore, thermoanalytic investigations on polypropylene were carried out to evaluate the thermal stability and the respective activation energy of the materials. The results prove the thermal stability necessary for the consolidation process of composite materials.

Processing of natural-fibre reinforced polymers and the resulting dynamic–mechanical properties

Abstract By means of dynamic–mechanical analysis (DMA), selected application-specific properties of flax- and hemp-fibre reinforced polypropylenes (PPs) have been determined for material characterisation. The compound samples were manufactured both by consolidation of hybrid non-wovens and compounding and injection moulding with the addition of natural fibres. The conditioning (long and short fibres), the manufacturing process and the processing parameters are the most important influencing factors on the mechanical properties of the final product. The results also reveal that the elastic properties (stiffness, storage modulus) of the composite material are dependent on the type of coupling agent. Other influencing parameters are the specific surface and the content of added fibre. The parameters mentioned can be varied by fibre separation or post-treatment procedures. The recycling behaviour of natural-fibre reinforced PP shows that multiple processing has only an insignificant influence on the fibre lengths and the mechanical properties. In addition, it is possible to very quickly draw conclusions about the quality of the composite material, such as fibre–matrix adhesion and damping behaviour. Fractographic evaluations in the scanning electron microscope (SEM) confirm the quantitative characterisation obtained from DMA.

Einfluß des Anlassens auf Gefüge und Härte warmfester 9%Cr-Stähle

An warmfesten martensitischen Stahlen mit niedrigem Kohlenstoffgehalt, 9% Chrom und den weiteren Legierungselementen Molybdan, Vanadium, Niob und z. T. Wolfram wurde der Einflus von Temperatur und Dauer des Anlassens auf Harte und Gefuge untersucht. Nach dem Austenitisieren und folgender Luftabkuhlung wurden die Stahle bei Temperaturen unter, bei und uber Ac1b unterschiedliche Zeiten angelassen und einer Harteprufung unterzogen. Anhand der Harte wurden Anlasschaubilder erstellt und der Hollomon-Jaffe-Parameter an den drei Stahlen innerhalb seiner Anwendungsgrenzen bestimmt. Gefugebilder (REM) belegen die Ausbildung der Karbide und des Martensits. Bei Anlastemperaturen unterhalb Ac1b tritt ein Harteabfall auf, bei Temperaturen oberhalb Ac1b kommt es infolge der dabei stattfindenden Teilaustenitisierung zu einem Harteanstieg. Beim Anlassen unterhalb Ac1b nimmt die Anlasbestandigkeit in der Reihenfolge P 91, NF 616, E 911 zu. Influence of tempering on microstructure and hardness of high-temperature 9%Cr-steels The influences of temperature and duration of tempering on hardness and microstructure were investigated at high-temperature martensitic and low-carbon steels with 9% chrome and the further alloying elements molybdenium, vanadium, niobium and partially tungsten. After austenitizing and subsequent air cooling the steels were tempered at temperatures below, at and above Ac1b for different times and finally a hardness test was performed. Making use of the temperature dependence of the hardness tempering diagrams were constructed and the Hollomon-Jaffe-Parameter on the three steels was determined within its application limits. Micrographs of the structure shows the formation of the carbides and the martensite. At tempering temperatures below Ac1b a decrease of hardness occurs, above Ac1b, a hardness rise due to the partial austenitizing was obtained. While hardening below Ac1b, the tempering quality increases from P 91, NF 616 to E 911.

Characterisation of Gold Nanocomposites by SEM, TEM and EBSD

Electroplated composites with incorporated nanoparticles become a key material in the fabrication of microsystem devices. A good survey of composites with nickel matrix is given in [1]. Electrodeposition of alumina particles (13 nm diameter, content around 1 Wt %) in nickel from an acidic electrolyte has been investigated using a nickel sulfamate bath with a particle loading of 10 g/l. Direct current (DC) deposition was compared to pulse-reverse plating (PRP) which can facilitate higher amounts. Details are given in [2]. Materials properties depend on the particle distribution, their bonding to the matrix and their influence on the microstructure of the matrix which has been characterized by TEM, STEM, SEM and EBSD.

Numerical simulation of the thermo-elastic behaviour for textile structured ceramic matrix composite bearings

With the aim of simulating the thermo-elastic behaviour of a slide bearing with a sleeve made of woven fabric ceramic composite material, a new approach is used to determine the material properties of the composite. Therefore a small cutout of the fabric pattern was discretised with the Finite-Element Method (FEM). The properties of the woven roving part of the model come from the well-known methods for computing unidirectional composites. The model also allows for describing porosity and determining materials behaviour more accurately than other approaches. The calculated properties have been applied to another FEM model to simulate the thermo-elastic behaviour of the bearing, combining a steel bearing box and a Ceramic Matrix Composite (CMC) bearing sleeve. The main problem arises from the different thermal expansion coefficients of both materials. In the heating stage, the bearing surface changes its shape. Without constructive changes resulting from the simulation, the dissipation loss rises and leads to galling of the bearing. The article shows that the deformation can be predicted by means of the developed model.