Filtern
Erscheinungsjahr
Dokumenttyp
Referierte Publikation
- ja (43) (entfernen)
Schlagworte
- Mechanical properties (7)
- Interface (6)
- Kristallisation (4)
- Thermoplaste (4)
- Adhesion (3)
- Carbon fibres (3)
- Composites (3)
- Elastic properties (3)
- Epoxy (3)
- Interfacial strength (3)
- Kristallisationskinetik (3)
- Modellrechnung (3)
- Nanotubes (3)
- Verbundwerkstoffe (3)
- A. Carbon fibres (2)
- Avrami (2)
- B. Interfacial strength (2)
- Cellulose (2)
- Erstarrung (2)
- Fractography (2)
- Functional composites (2)
- Interfacial shear strength (2)
- Interphase (2)
- Ionic conductivity (2)
- Multifunctional supercapacitor (2)
- Polymer (2)
- Simulation (2)
- Structural electrolyte (2)
- A. Carbon nanotubes (1)
- A. Coupling agents (1)
- A. Hybrid composites (1)
- A. Polymer-matrix composites (PMCs) (1)
- Acoustic emission (1)
- Adhesion promotion (1)
- Adhäsion (1)
- Alumina (1)
- B. Adhesion (1)
- B. Debonding (1)
- B. Interface (1)
- Bacteria (1)
- Bicontinuous morphology (1)
- Biopolymer (1)
- Carbon Fibre (1)
- Carbon fibers (1)
- Carbon fiberepoxy resin laminates (1)
- Carbon fibre (1)
- Carbon fibres nanotubes interface (1)
- Carbon nanotubes (1)
- Cellulose natural fibers (1)
- Characterisation (1)
- Composires (1)
- Composite (1)
- Composite material (1)
- Composite recycling (1)
- Concrete (1)
- Contact angle (1)
- Cooling rate (1)
- Copper (1)
- Creep (1)
- Cryogenic (1)
- Debonding (1)
- Debonding Mechanism (1)
- Desorption (1)
- Electric conductivity (1)
- Electrolyte (1)
- Electrospray ionization (ESI) (1)
- Electrospray ionization polymers (1)
- Energy release rate (1)
- Epoxy Resin (1)
- Epoxy based network (1)
- Epoxy resin (1)
- Failure (1)
- Faser (1)
- Fatigue (1)
- Festigkeit (1)
- Fiber (1)
- Fiber properties (1)
- Fiber-matrix interface (1)
- Fiber/matrix bond (1)
- Fibre Bragg grating (1)
- Fibre reinforced plastic (1)
- Fibre/matrix bond (1)
- Fibre/matrix bonding (1)
- Films (1)
- Finite element analysis (1)
- Fluorination (1)
- Four-parametric (1)
- Fracture mechanics (1)
- GFRP (1)
- Glass fibre (1)
- Glass fibres (1)
- Grafting (1)
- Haftung (1)
- Hierarchical Structures (1)
- Hierarchical composites (1)
- Hydrogel (1)
- Hydrothermal Ageging (1)
- Imaging (1)
- Indentation (1)
- Interfacial Strength (1)
- Ionic liquid (1)
- Irradiation (1)
- Keywords: Poly(ether ether ketone) (1)
- Kurzfaser (1)
- Layer topography (1)
- Light curing (1)
- Luminescent probes (1)
- Längenabhängigkeit (1)
- Mapping (1)
- Matrix adhesion (1)
- Matrix residual stress (1)
- Mechanical testing (1)
- Morphology (1)
- Nachkristallisation (1)
- Nano indentation (1)
- Nano tubes (1)
- Nanoindentation (1)
- Natural (1)
- Patch (1)
- Photocleavable organosilanes (1)
- Photocleavage (1)
- Photoconduction (1)
- Photopolymer composites (1)
- Plasma nanocoatings (1)
- Plasma polymers (1)
- Poly(acrylic acid) (1)
- Poly- (hydroxyethylmethacrylate) (1)
- Polymer Fibres (1)
- Polymer composite (1)
- Polymer-matrix composites (PMC) (1)
- Polymer-metal (1)
- Pull-Out Behaviour (1)
- Pull-out (1)
- Pull-out test (1)
- Pull-out tests (1)
- Pulsed laser treatment (1)
- Push-in (1)
- Push-out test (1)
- Recycling (1)
- Reibung (1)
- Self-healing (1)
- Short-beam strength (1)
- Silica fibres (1)
- Single carbon fibers (1)
- Single fiber pull-out test (1)
- Sphärolithe (1)
- Strain (1)
- Strength (1)
- Supercapacitor (1)
- Superstructure (1)
- Surface (1)
- Surface area (1)
- Surface modification (1)
- Synthesis (1)
- Temperature (1)
- Test method (1)
- Thermal cycling (1)
- Thermoplastic matrix (1)
- Thermoplastic prepreg (1)
- Thermosetting resin (1)
- Thin polymer layers (1)
- Transkristallisation (1)
- Unidirectional composites (1)
- Verstärkungsfaser (1)
- Water Diffusion (1)
- Wetting (1)
- Work of adhesion (1)
- Zirconia (1)
- model (1)
- o-Nitrobenzyl ester (1)
- pH sensing (1)
Organisationseinheit der BAM
Paper des Monats
- ja (1)
Carbon nanotube-grafted carbon fiber polymer composites: Damage characterization on the micro scale
(2017)
Multiwall carbon nanotubes (CNTs) e carbon fibers (CFs)hybrid materials were produced by directly growing CNTs on CFs by means of chemical vapor deposition. For the latter, the oxidative dehydrogenation reaction of C2H2 and CO2 was applied, which allows growing CNTs without damaging the CF surface. Uni-directional nano-engineered carbon fiber reinforced composites (nFRCs) were fabricated by impregnating these hybrid materials with epoxy. The nFRCs subjected to single fiber push-out tests revealed a decrease of the interfacial shear strength (IFSS) of about 36% compared to the carbon fiber composites without CNTs. By means of transverse three-point bending tests performed on pre-notched composite beams inside a scanning electron microscope, the fracturing behavior parallel to the fibers was studied in-situ. The nFRCs showed significantly reduced fiber/matrix debonding while CNTs pull-out, CNTs bridging as well as matrix failure occurred. These results demonstrate that the presence of CNTs in nFRCs affects the stress distribution and consequently the damage Initiation as well as the damage propagation. The presence of CNTs suppresses the stress concentration at the fiber/Matrix interface and reduces the debonding of CFs from the matrix. However, our results indicate that the stress concentration shifts towards the CNTs' ends/matrix interface and causes promoted matrix failure leading to lower IFSS.
Thin coatings of poly(acrylic acid) (PAA) and poly(hydroxyethylmethacrylate) (PHEMA) were deposited onto carbon fibers by means of the electrospray ionization (ESI) technique in ambient air. These high-molecular weight polymer layers were used as adhesion promoters in carbon fiberepoxy resin composites. Within the ESI process, the carbon fibers were completely enwrapped with polymer in the upper 10 plies of a carbon fiber roving. As identified with scanning electron microscopy also shadowed fibers in a bundle as well as backsides of fiber rovings were pinhole-free coated with polymers (electrophoretic effect'). Under the conditions used, the layers have a granular structure. Residual solvent was absent in the deposit. PAA and PHEMA films did not show any changes in composition and structure in comparison with the original polymers as analyzed by X-ray photo-electron spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Single-fiber pullout tests of coated fibers embedded in epoxy resin showed significantly increased interfacial shear strength. It is assumed that chemical bonds between carbon fiber poly(acrylic acid) and epoxy resin contribute significantly to the improved interactions.
The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibres and the composition of the matrix. The composition of poly(vinylidene fluoride) (PVDF) was modified by the addition of maleic anhydride grafted PVDF. The surface properties of the various matrix formulations were characterised by contact angle and electrokinetic measurements. Carbon fibres were modified by industrial electrochemical oxidation and oxidation in nitric acid, or the use of a traditional epoxy-sizing of industrially oxidised fibres. The surface composition, morphology and wetting behaviour of the carbon fibres was characterised. The interaction between modified PVDF and the carbon fibres was studied by direct contact angle measurements between PVDF melt on single carbon fibres and by single fibre pull-out tests. The best wetting and adhesion behaviour was achieved between PVDF containing 5 ppm grafted maleic anhydride (MAH) and epoxy-sized carbon fibres. The addition of MAH-grafted PVDF to the unmodified PVDF caused the apparent interfacial shear strength to increase by 184%. The apparent interfacial shear strength of this fibrematrix combination allowed for the utilisation of 100% of the yield tensile strength of PVDF.
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.
The longitudinal and transverse strength of three unidirectional thermoplastic prepreg systems: carbon fiber/polypropylene (CF/PP), polyamide 6 (CF/PA6), and polyphenylene sulfide (CF/PPS) are studied and analytical formulas are proposed for the estimation of matrix and fiber/matrix interface properties from composites properties. Since the matrices are semi-crystalline thermoplastics, the influence of cooling rate on the strength is statistically evaluated. While the 0° tensile strength is found to be independent of the cooling rate, the 90° tensile strength is strongly influenced by the matrix type and cooling rate. The matrix modulus increases as the cooling rate is decreased; the degree of crystallinity also increases. The matrix residual stress, interfacial shear strength, and mode II interlaminar fracture toughness are also found to depend on the cooling rate, with the trends different for different matrices.
After a delamination process in a C-fiber reinforced polymer composite, the identification of the polymer residue of poly-(phenylene sulphide) on carbon fiber surfaces gives important information on the composite failure mechanism. Using scanning force microscopy (SFM) in its lateral force imaging mode or with the stiffness imaging mode, it is almost impossible to distinguish the two composite components owing to a very low material-based contrast of the local friction and compliance. The new technique using contrast based on a local AC current measurement allows a clear identification of the conducting carbon fiber and the non-conducting polymer coverage.
The bond between polymer fibers and the surrounding cementitious matrix is essential for the development of concrete reinforcement. The single fiber pull-out test (SFPT) is the standard characterization technique for testing the bond strength. However, the different phases of debonding cannot be distinguished by the SFPT. This study investigates the debonding of different polymer fibers from the surrounding cementitious matrix with a modified SFPT and proposes methods to change the SFPT setup to generate more valuable information on the debonding mechanism. The SFPT was equipped with linear variable differential transformers (LVDT), digital image correlation (DIC) and acoustic emission (AE) analysis. The results demonstrate that the modified SFPT allows a better understanding of the different phases of debonding during fiber pull-out. Furthermore, bond strength values calculated by different methods reveal that the chemical bond of the investigated polymers is not different as reported by previous studies. Deformation measurements performed using LVDTs and DIC are suitable measuring techniques to characterize the debonding mechanism in SFPT. A correlation between recorded AE and debonding phases was not found.
Structural electrolytes were prepared using a fully formulated commercially available high performance epoxy resin (MTM57) and an ionic liquid based electrolyte: lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). Through a systematic study, the composition of the formulations was found to have a greater effect than the curing temperature on the morphology and properties of the resulting structural electrolytes. The presence of lithium salt is essential to form a structurally homogeneous electrolyte. Bicontinuous morphologies containing continuous (coarse) epoxy networks surrounded by connected spherical epoxy nodules were obtained with different length scales upon varying the lithium salt concentration. Increasing the LiTFSI concentration improved the miscibility of MTM57 with the electrolyte and decreased the characteristic length scale of the resulting bicontinuous microstructure. The properties of the structural electrolytes correlated with the morphology, showing increased Youngs modulus and decreased ionic conductivity with increasing lithium salt concentration. The miscibility of the epoxy system with the electrolyte was also improved by substitution of EMIM-TFSI with an equal weight of an aprotic organic solvent, propylene carbonate (PC); however, the window of PC concentrations which resulted in structural electrolytes with bicontinuous microstructures was very narrow; at PC concentrations above 1 wt %, gel-like polymers with no permanent mesoporosity were obtained.
Electrolyte systems that can carry mechanical load while allowing for high levels of ionic conductivity are an important prerequisite for structural power storage devices. Introduction of structural power storage into the variety of consumer products will allow saving in weight and volume. Moreover, using a supercapacitor/battery system in hybrid electric vehicles (HEV), the supercapacitor part will extend the battery lifetime by protecting it from the high peak currents. To successfully produce structural power storage requires the development
of multifunctional electrolytes where one has to simultaneously maximize mechanical properties and ionic conductivity.
Structural supercapacitor electrolytes based on bicontinuous ionic liquid-epoxy resin systems
(2013)
'Structural electrolytes' retain the desirable mechanical characteristics of structural (epoxy) resins whilst introducing sufficient ionic conductivity to operate as electrolytes in electrochemical devices. Here, a series of ionic liquid–epoxy resin composites were prepared to identify the optimum system microstructure required to achieve a high level of multifunctionality. The ionic conductivity, mechanical properties, thermal stability and morphology of the cured epoxy based structural electrolytes were studied as a function of phase composition for three fully formulated high performance structural epoxy systems. At only 30 wt% of structural resin and 70 wt% of ionic liquid based electrolyte, stiff monolithic plaques with thicknesses of 2–3 mm were obtained with a room temperature ionic conductivity of 0.8 mS cm-1 and a Young's modulus of 0.2 GPa. This promising performance can be attributed to a long characteristic length scale spinodal microstructure, suggesting routes to further optimisation in the future.