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- Interface (12)
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Eingeladener Vortrag
- nein (33)
Hier wird der chronologische Verlauf der Kristallisation verfolgt. Sie beginnt mit den thermodynamischen Grundlagen der Keimbildung und des Wachstums, stellt anschließend Wachstumsformen in der Frühlphase der Kristallisation vor und behandelt schließlich die spärolithische Hauptkristallisation sowie die sogenannte Nachkristallisation.
Untersuchungs des Ermüdungsverhaltens glasfaserverstärkter Thermoplaste mittels Schwingungsmessungen
(1990)
Friction Measurement on fiber reinforced polymer composites with using the indentation technique
(1998)
Energy Dissipation of the Fibre-Matrix Debonding Process Investigated with the Indentation Technique
(1995)
Influence of water on the fibre-matrix adhesion investigated by the single fiber indentation method
(1998)
Characterisation of the fibre/matrix interface in reinforced polymers by the push-in technique
(1997)
The push-in test is the only micromechanical test method that is not restricted to artificial fibre/matrix arrangements, but allows the in situ characterisation of interfaces in composites fabricated and stressed under realistic conditions. However, with the application of this method to reinforced polymers some problems arise both in the mathematical model for evaluating test data and in the practical performance of the test. Because in some cases the deformation of the relatively compliant polymeric matrices cannot be neglected, an extension of the existing model is required. For this purpose, the elastic energy of the material around the debonded part of the fibre is estimated and included in the energy-balance analysis. Because of the small diameter of the fibres usually used for reinforcing polymers, a test apparatus was designed which ensures a high positioning accuracy in the xy plane as well as in the z direction. In order to minimise thermal and mechanical influences, the microscope for fibre selection and the force sensor/indenter are directly connected together and the apparatus is designed to be stiff in all components. A solid-state bending joint guarantees very precise control of the axial movement. Three examples of the application of this easy-to-handle and low-cost test apparatus are presented briefly in the paper: assess fibre/matrix combinations, measures to improve the interfacial adhesion and the influence of water on the interface.
The strength of composite reinforcement fibres is normally measured on samples of much greater length than the actual residual fibre lengths found in many composite materials. This is due to a number of limitations of the standard techniques which are employed. We present a description of a technique which enables values for the tensile strength of composite reinforcement fibres at short gauge lengths to be obtained. The technique is based on an adaptation of a micro-mechanical test apparatus for fibre pullout measurements. Data is presented which was obtained at gauge lengths of 180380 µm on E-glass and S-2 glass® fibres taken from different chopped reinforcement products. The technique can be used at gauge lengths as short as 20 µm. The data indicates that the values of average fibre strength in these products are significantly below the pristine glass strength values.
A mathematical model for the description of the overall crystallization of polymers has been developed which separates the pure geometric spreading of the semicrystalline superstructures from the increasing crystallinity inside these entities. The model uses the Avrami theory for the geometric part and a freely optional function for the increasing local crystallinity. The two functions are combined by a mathematical procedure called convolution. The free option of the local crystallinity function enables this model to permit calculation of this function, which is not accessible to direct measurement. Thus with given Avrami parameters and measured values of the time-dependent overall crystallinity, this function of the local crystallinity (secondary crystallization function) can be calculated. The model has been applied to test data produced by computer simulations.
The effect of transcrystallinity in carbon fiber reinforced poly(p-phenylene sulfide (PPS) composites on the apparent shear strength was investigated with the single fiber pull-out test. Transcrystalline zones around the reinforcing fibers do not seem to improve the adhesion level significantly. Neighbor fibers hinder the formation of the transcrystalline zone and a ductile fracture behavior can be observed. However, the apparent strength level is slightly higher for composites containing such reinforcing neighbor fibers compared with single fiber composite samples. During annealing a brittle interface can be formed in the multifiber composite yielding a higher level of the apparent shear strength.
An advanced equipment for single-fibre pull-out test designed to monitor the fracture process
(1995)
Pull-out of Single Fibres
(1994)
Investigations on the cold crystallization of pure and filled PETP by dielectric measurements
(1993)
The cold crystallization of pure and filled poly(ethylene terephthalate) (PETP) after quenching from the melt has been investigated by dielectric measurements in two different modes: The first one using constant heating-rate (in the temperature range from 320 to 480 K) and the second one under isothermal conditions (at 378 K). The complex dielectric constant (ε´, tan δ) is influenced by crystallization. Two α-relaxation regions are identified: The αa-relaxation region from the pure amorphous phase and the α´-relaxation region from the spherulitic phase. The investigations on the filled systems (PETP + 10% aramid puple, PETP + 30% short glass fibres) prove that an influence of the fillers on the time delay and rate of crystallization and on the geometry of the growing spherulites exists.
Fatigue Behaviour of High-Performance Fibre-Reinforced Composites with a Thermoplastic Matrix
(1990)
Viscoelastic properties of the interphase in fibre reinforced polymers - measurement and simulation
(1999)
Polymer-based electrolytes based on commercially available epoxy resins were prepared through the addition of a liquid electrolyte, a solution of a lithium salt in an ionic liquid. The polymer monoliths were characterized using impedance spectroscopy, 3-point bending test, scanning electron microscopy (SEM) and nitrogen adsorption (BET). The balance of ionic conductivity and flexural modulus is crucially dependent on the relative proportions of epoxy resin to electrolyte. Also the effect of the liquid electrolyte on curing kinetics and processing was assessed by complex viscosity measurements and differential scanning calorimetry (DSC). Only one out of the three resins investigated exhibited a significant acceleration effect.
For the concept of using structural materials such as carbon fibre reinforced plastics as
energy storage devices, new matrix polymers are required. These polymers must provide ionic
conductivity as well as adequate mechanical strength. In the EU-Project StorAGE this
requirements are fulfilled by adding ionic liquid to commercial polymers. The mechanical
properties of these mixtures materials were characterized by using a 3-point-bending device.
In addition, single fibre pull test were performed in order to get information on the interfacial
shear strength. Adding of ionic liquid has an impact on the mechanical performance of the
materials. A decrease of the flexural strength and modulus of less than 10% of the value of the
reference materials took part. The interfacial shear strength decreased to a value of around
one third compare to the reference material.
In Kooperation zwischen dem Institut für Kunststoffverarbeitung (IKV) und der Bundesanstalt für Materialforschung und -prüfung (BAM) wurde das mechanische Verhalten unter Druck- und Zugbelastung unterschiedlicher morphologischer Strukturen teilkristalliner Thermoplaste (PP und POM) untersucht. Im Ergebnis steigt der E-Modul sowohl der druck- wie auch zugbelasteten Prüfkörper aus spritzgegossenem PP und POM mit gröberem Gefüge an. Probekörper mit scherinduziertem Gefüge zeigen einen hohen Einfluss des Kristallisationsgrads auf den E-Modul.
A fiber Bragg grating (FBG) strain patch specially adapted for long-term and high-strain applications has been developed and characterized. The design concept for the patch is based on a glass-fiber reinforced plastic (gfrp) carrier material. The developed concept for the FBG integration into the carrier material was derived from reliable integration procedure of FBG sensors into composite structures. The patches' temperature sensitivity, strain gauge factor, fiber–matrix interface adhesion and fatigue behavior were characterized. As a result, FBG strain patches with linear temperature and strain behavior, as well as excellent fatigue resistance, were developed and can be used as part of a monitoring system for advanced composite materials in aerospace structures or wind turbine power plants.
Mikromechanische Methoden zur Messung der Faser-Matrix-Haftung in Polymermatrix-Verbundwerkstoffen
(2007)
Bestimmung der Haftfestigkeit in Verbundwerkstoffen mittels Indentations- und Durchdrückexperimenten
(2004)
Mikromechanische Testmethoden zur Bestimmung von Haftung und Reibung in Faserverbundwerkstoffen
(2004)
Mapping Epoxy Interphases
(2005)
Atmospheric-plasma fluorination was used to introduce fluorine functionalities onto the surface of carbon fibers without affecting their bulk properties. The interfacial adhesion between atmospheric-plasma-fluorinated carbon fibers and poly(vinylidene fluoride) (PVDF) was studied by means of direct wetting measurements and single fiber pullout tests. Measured contact angles of PVDF melt droplets on modified carbon fibers show that short exposure times of carbon fibers to atmospheric-plasma fluorination (corresponding to a degree of surface fluorination of F/C = 0.01 (1.1%)) leads to improved wettability of the fibers by PVDF melts. The apparent interfacial shear strength as a measure of practical adhesion, determined by the single-fiber pullout test, increases by 65% under optimal treatment conditions. The improved practical adhesion is not due to the formation of transcrystalline regions around the fibers or a change of the bulk matrix crystallinity or to an increased surface roughness; it seems to be due to the compatibilization of the interface caused of the atmospheric-plasma fluorination of the carbon fibers.