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UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications,but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or Ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and/or 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
Manufacturing and deformation behavior of alumina and zirconia helical springs at room temperature
(2023)
Ceramic helical springs with identical dimensions were produced by hard machining from alumina, alumina toughened zirconia (ATZ), and tetragonal zirconia polycrystals (TZP) stabilized with different oxides. According to the results of the spring constant determination under deformation rates of 3 mm/min, the deformation behavior of all ceramic springs obeys to Hook’s law. However, variation of the deformation rate, tests under constant load, and spring recovery behavior revealed differences in the deformation behavior of alumina, TZP, and ATZ springs. Alumina springs exhibited time-independent deformation in all tests. In contrast, anelastic deformation at room temperature was demonstrated in all springs containing TZP. This deformation is completely reversible over a period of several days. Anelastic behavior is particularly pronounced in Y-TZP springs, whereas Ce-TZP springs exhibit comparatively very low but still reliably detectable anelasticity. Oxygen vacancies in the TZP ceramic are considered the most likely explanation for the anelastic behavior of TZP springs at room temperature.
One of the holy grails in chemistry is to reconstitute some of life’s functions with or within synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
One of the holy grails in chemistry is to reconstruct some of life’s functions with synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
The present study aims at the development of photodegradable epoxy based materials comprising o-nitrobenzyl ester links that undergo well defined bond cleavage in response to UV irradiation. New bi-functional epoxy based monomers bearing o-nitrobenzyl ester groups are synthesized and thermally cured with an anhydride hardener to yield photosensitive polymers and duromers. The UV induced changes in solubility are exploited for the preparation of positive-type photoresists. Thin patterned films are obtained by photolithographic processes and characterized by microscopic techniques. The results evidence that sensitive resist materials with good resolution and high contrast behavior can be accomplished. Along with resist technology, the applicability of o-nitrobenzyl chemistry in the design of recyclable polymer materials with thicknesses in the millimeter range is evaluated. By monitoring the thermo-mechanical properties upon UV illumination, a distinctive depletion of storage modulus and glass transition temperature is observed with increasing exposure dose. Additionally, single fiber pull-out tests are carried out revealing a significant decrease of the interfacial adhesion at the fiber-matrix interface due to the phototriggered cleavage reaction.
Plasma polymers and electrospray-ionization (ESI) polymer layers are compared for most efficient adhesion promotion in carbon fiber-epoxy resin composites. The ultra-thin ESI layers (2–30 nm) of commercial poly(acrylic acid) and poly-(hydroxyethylmethacrylate) produce an significant increase of adhesion measured by single-fiber pull out tests.
However, plasma Treatment has also advantages, such as simultaneous activation of the fiber substrate. Chemical structure and composition are rather far from the regular structure of commercial polymers as deposited by ESI processing.
Vesicles self-assembled in water from natural and synthetic phospholipids (liposomes), amphiphilic block copolymers (polymersomes), and more recently amphiphilic Janus dendrimers (dendrimersomes) as hollow soft structures in the nano size regime have attracted increasing interest as they can mimic primitive and contemporary biological membranes, and can be configured into biomimetic nanocapsules with application in nanomedicine such as gene, proteins and drug carriers or theranostics.
Compared to other amphiphilic structures, the molecular structure of Janus dendrimers can be precisely controlled: by using the vast range of tools from organic chemistry their size, architecture, density, generation as well as the number of end groups of the individual dendrons can be modified as desired.
Unfortunately, the controlled production of the supramolecular aggregates made thereof is still a challenging task. Conventional batch-based techniques such as the solvent injection method or the film hydration method typically go along with a lack of control over mixing and thus over size, morphology and size distribution. The micromixer technology is a promising method for the controlled preparation of supramolecular assemblies as it allows control of mixing at microscale level. In addition, such microfluidic systems benefit from a high mixing efficiency, a low mixing time as well as from a reproducible and continuous synthesis.
Herein, we report on the microfluidic-controlled self-assembly of Janus dendrimers as dendrimersomes and the impact of the mixing parameters on the self-assembly process.
Structural Health Monitoring of composite materials gains in importance with the increasing use of Composite structures for safety-related applications, e.g. in aerospace. Because of the material properties of composites, defects often occur inside the structures and raise the demand for integrated sensors. The advantages of optical fibres predestine them not only for the surface-application on composite structures but also for the Integration into composite structures. Even without quasi-distributed sensors such as FBGs or LPGs, the optical fibre itself can be used to measure the structure and occurring events over the entire fibre length by distributed sensing techniques. This paper presents the surface-application of polyimide coated silica optical fibres onto PEEK specimens and the integration of copper and polyimide coated silica optical fibres into an AS-4/PEEK Composite to be used as distributed fibre optic sensors for SHM. Results from distributed measurements by optical backscatter reflectometry based on Rayleigh backscattering are shown.
The strength of laminates distinctly depends on the transverse strength of the laminas. The transverse failure is dominated by the adhesion between fiber and matrix. Usual strength criteria however do not take into account the adhesive strength explicitly. The determination of the interface strength is performed on the micromechanical scale using single fiber specimens. The fibers are loaded under off-axis loading while the debonding is monitored under a microscope. The stresses acting in the Interface are calculated by finite element analyses. It is found that for off-axial angles up to 35° interfacial debonding is the dominant failure mode while fiber breakage takes place at lower angles. The occurrence of fiber breakage and debonding under off-axis loading shows that the restriction to two potential failure planes - perpendicular or parallel to the fibers - as applied in common failure criteria has to be put in question.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
Vesicles self-assembled in water from natural and synthetic phospholipids (liposomes), amphiphilic block copolymers (polymersomes), and more recently amphiphilic Janus dendrimers (dendrimersomes) -5 as hollow soft structures in the nano size regime have attracted increasing interest as they can mimic primitive and contemporary biological membranes, and can be configured into biomimetic nanocapsules with application in nanomedicine such as gene, proteins and drug carriers or theranostics.
Compared to other amphiphilic structures, the molecular structure of Janus dendrimers can be precisely controlled: by using the vast range of tools from organic chemistry their size, architecture, density, generation as well as the number of end groups of the individual dendrons can be modified as desired.
Unfortunately, the controlled production of the supramolecular aggregates made thereof is still a challenging task. Conventional batch-based techniques such as the solvent injection method or the film hydration method typically go along with a lack of control over mixing and thus over size, morphology and size distribution. The micromixer technology is a promising method for the controlled preparation of supramolecular assemblies as it allows control of mixing at microscale level. In addition, such microfluidic systems benefit from a high mixing efficiency, a low mixing time as well as from a reproducible and continuous synthesis.
Herein, we report on the microfluidic-controlled self-assembly of Janus dendrimers as dendrimersomes and the impact of the mixing parameters on the self-assembly process.
Vesicles self-assembled in water from natural and synthetic phospholipids (liposomes), amphiphilic block copolymers (polymersomes), and more recently amphiphilic Janus dendrimers (dendrimersomes) -5 as hollow soft structures in the nano size regime have attracted increasing interest as they can mimic primitive and contemporary biological membranes, and can be configured into biomimetic nanocapsules with application in nanomedicine such as gene, proteins and drug carriers or theranostics.
Compared to other amphiphilic structures, the molecular structure of Janus dendrimers can be precisely controlled: by using the vast range of tools from organic chemistry their size, architecture, density, generation as well as the number of end groups of the individual dendrons can be modified as desired.
Unfortunately, the controlled production of supramolecular aggregates made thereof is still a challenging task. Conventional batch-based techniques such as the solvent injection method or the film hydration method typically go along with a lack of control over self assembly/mixing and thus over size, morphology and size distribution of the vesicles.
The micromixer technology is a promising method for the controlled preparation of supramolecular assemblies as it allows control of mixing at microscale level. In addition, such microfluidic systems benefit from a high mixing efficiency, a low mixing time as well as from a reproducible and continuous production of soft nanoparticles. Herein, we report on the microfluidic-controlled self-assembly of Janus dendrimers as dendrimersomes and the impact of the mixing parameters on the self-assembly process.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
This presentation is a summary of the work from the past 20 years’ development of PMC-testing at the BAM-FB 5.3 with respect to safety-relevant design of advanced light weight structures in aircraft, wind turbine and automotive applications. The talk begins with wood as an example from nature, and emphasizes that load case, fiber architectural design and the production process and quality have to go hand in hand to generate an advanced light weight structure. Since PMC-relevant basic findings of mankind span across hundreds of years, high-performance composite applications today are based more on long term experiences than on breakthrough inventions of modern days.
In the second part of the talk, future plans and projects of FB-5.3 are presented, specifically addressing H2-safety, circular economy, recycling by design and digitalization of PMC-technologies.
Tooth wear induced by abrasive particles is a key process affecting dental function and life expectancy in mammals. Abrasive particles may be plant endogenous opal phytoliths, exogene wind-blown quartz dust or rain borne mineral particles ingested by mammals. Nano-indentation hardness of abrasive particles and dental tissues is a significant yet not fully established parameter of this tribological system. We provide consistent nano-indentation hardness data for some of the major antagonists in the dental tribosystem (tooth enamel, tooth dentine and opaline phytoliths from silica controlled cultivation). All indentation data were gathered from native tissues under stable and controlled conditions and thus maximize comparability to natural systems. Here we show that native (hydrated) wild boar enamel exceeds any hardness measures known for dry herbivore tooth enamel by at least 3 GPa. The native tooth enamel is not necessarily softer then environmental quartz grit, although there is little overlap. The native hardness of the tooth enamel exceeds that of any silica phytolith hardness recently published. Further, we find that native reed phytoliths equal native suine dentine in hardness, but does not exceed native suine enamel. We also find that native suine enamel is significantly harder than dry enamel and dry phytoliths are harder than native phytoliths. Our data challenge the claim that the culprit of tooth wear may be the food we chew, but suggest instead that wear may relates more to exogenous than endogenous abrasives.
Poly (ether ether ketone) (PEEK) has a high continuous service temperature, excellent mechanical properties, and good solvent and abrasion resistance, which can be further improved through the addition of carbon nanotubes (CNTs). CNT-PEEK nanocomposites are promising matrices for continuous carbon fibre composites; powder processing can mitigate the high melt viscosities in these systems. In this study, model single fibre (hierarchical) composites were produced by embedding sized and desized carbon fibres in nanocomposite CNTPEEK powders followed by single fibre pull-out tests to assess interfacial characteristics. Carbon fibre-PEEK interfacial shear strength is typically 40–45 MPa. Increasing CNT loadings increased fibre-matrix interfacial shear strength linearly up to ~70 MPa at 5.0 wt%, which was attributed to the CNT-based mechanical modification of the PEEK matrix. Apparent interfacial shear strength was inversely correlated with the embedded fibre length irrespective of carbon fibre sizing or CNT loading, indicating brittle fracture of the fibre-matrix interface.
Pulled out carbon fibres were still coated with the matrix, which indicated strong adhesion at the interface in all samples, likely related to a transcrystalline region. Adhesion was, however, negatively affected by the presence of epoxy sizings. Frictional shear strength was independent of embedded fibre length and CNT content for all samples.
One of the holy grails in chemistry is to reconstruct some of life’s functions within synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
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.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and/or 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
Der Vortrag widmet sich der Kratzbeständigkeit-Prüfmethoden und deren Bewertung und beschreibt Begriffe/Definitionen, Wirtschaftliche Bedeutung der Kratzbeständigkeit, Mess- und Prüfverfahren – allgemein (Anwendbarkeit, Messunsicherheit, Validierung), Mess- und Prüfverfahren – speziell die Erzeugung, Prüfverfahren von Einzel- und Vielfach-Kratzern, die Charakterisierung von Verkratzungen und eine zusammenfassende Bewertung im Einzelnen
Jahresbericht 2013
(2014)
This work presents a further development of the methods of simultaneous determination of temperature and axial strain using a single fibre Bragg grating (FBG). The reflected spectrum of composite-embedded FBG sensors has been analyzed in order to separate temperature and load effects. We found out that during the curing process of the laminates, a superstructure has been introduced on the FBG. Analyzing this effect, a temperature and strain separation was implemented by simply calculating and comparing the integrated intensity of the spectral response signal. A mathematical four-parametric model has been developed to calculate the reflected spectrum of a superstructured fibre Bragg grating. The mathematically achieved data has been evaluated with experimentally determined data from fibre Bragg gratings embedded in glass-fibre reinforced composite materials.
Das Ziel des Gesamtvorhabens bestand darin, einen neuartigen kapazitiven Sensortyp zur hochauflösenden Bestimmung von Masse- und Gravitationskraftänderungen zu entwickeln. Bisherige Technologien nutzten dafür Federn oder Biegebalken aus gehärteten metallischen Werkstoffen, deren Alterungsverhalten die Präzision der Kräftemessung begrenzen. Grundprinzip des neuen Sensortyps ist es, eine auf die keramische Feder einwirkenden Änderung der Gewichts- oder Gravitationskraft durch eine Erfassung der Kapazitätsänderung am Sensor zu bestimmen. Dazu muss die durch Stauchung oder Dehnung der Feder entstehende Kapazitätsänderung mit hoher Auflösung reproduzierbar gemessen werden. Neben einem geeigneten Sensordesign waren Lösungen für Messsignalerfassung und -auswertung (Elektronik/Software) und die Systemintegration zu entwickeln.
Die wichtigsten im Rahmen des BAM-Teilvorhabens erzielten Ergebnisse sind:
- Ausgehend von kommerziellen High-end Keramikpulvern wurden durch Optimierung der keramischen Technologie nahezu porenfreie Al2O3, ZrO2 und Si3N4-Werkstoffe hergestellt und bezüglich Gefüge und Phasenbestand sowie mechanischen, thermischen und elektrischen Eigenschaften bewertet. Insbesondere die defektfreie Herstellung von nanostrukturierten Werkstoffen erforderte umfangreiche Variationen der Prozessparameter. Geeignete Werkstoffvarianten wurden für die Federherstellung ausgewählt.
- Gemeinsam mit den Projektpartnern wurden Layoutvarianten für Schraubendruckfedern mit rechteckigem Windungsquerschnitt und für die Federeinbindung in das Sensorsystem erarbeitet.
- 4 Federvarianten wurden an der BAM durch Hartbearbeitung von gesinterten Hohlzylindern umgesetzt. Fertigungstoleranzen von < ±10 µm für Windungsbreite, Windungshöhe und Windungsabstand und dünnfilm-kompatible innere Windungsflächen (Ra < 0,2 µm) wurden erreicht. Al2O3- und ZrO2-Federn können rissfrei und mit sehr guter Kantenqualität gefertigt werden, bei Si3N4-Federn konnten Kantenschädigungen nicht vollständig verhindert werden.
- Mit der entwickelten Herstellungstechnologie können sowohl „harte“ als auch sehr „weiche“ Federn produziert werden. Federkonstanten zwischen 0,02 N/mm und 10 N/mm wurden realisiert. Die Reproduzierbarkeit der Federfertigung ist gegeben, innerhalb einer Charge unterschieden sich die Federkonstanten der gefertigten Federn nur um etwa +/- 1%.
- An einem speziell entwickelten Versuchsstand wurden die Federn unter zyklischer Druckbelastung im Temperaturbereich von -20 bis +80 °C untersucht. An den Al2O3- und ZrO2-Federn wurden keine Schädigungen beobachtet, die Federkonstante wird durch die zyklische Langzeitbelastung nicht verändert.
- Die Eignung der keramischen Federn für den Applikationsfall wurde mit zahlreichen Spannungs-Dehnungs-Experimenten, teilweise an speziell aufgebauten Versuchsapparaturen, untersucht. An Al2O3- und Si3N4-Federn wurde – wie erwartet – gefunden, dass die Federkonstante unabhängig von der Belastungsgeschwindigkeit ist und unter konstanter Last auch über lange Zeiträume keine Verformung auftritt. Überraschenderweise zeigten ZrO2 (TZP)-Federn ein zeitabhängiges Verhalten unter Last. Dieses ist besonders stark bei Y-stabilisierten Werkstoffvarianten ausgebildet, wurde aber mit Hochpräzisionsmessungen auch bei Ce-stabilsierten Werkstoffen nachgewiesen. Die Deformation ist reversibel, eine vollständige Relaxation wird erst nach Tagen erreicht. Aufgrund der zeitabhängigen Verformung können ZrO2 (TZP)-Federn, trotz ihrer hervorragenden Festigkeit und Bruchzähigkeit, nicht für die konzipierten Sensorfedern eingesetzt werden.
- Das durch die Fa. Siegert TFT entwickelte Metallisierungs-Schichtsystem, bestehend aus aufgesputterten Ti-, Pt- und Au-Schichten verstärkt durch eine galvanisch aufgebrachte Au-Schicht, wurde an der BAM umfassend bewertet. Die Schichten sind untereinander und mit der Keramik weitgehend defektfrei verbunden, die lokale Schichtdicke schwankt jedoch bedingt durch Abschattungseffekte während der Beschichtungsvorgang. Es wurden Schichtwiderstände zwischen 50 und 90 Ohm und damit die Zielvorgabe des Projektes (< 100 Ohm) erreicht. In statischen und dynamischen Belastungstests wurden keine Veränderungen der Leitungswiderstände festgestellt.
- Zur Erhöhung der Kapazität des Kondensators kann der Raum zwischen den Federwindungen statt mit Luft mit einer Flüssigkeit mit hoher Dielektrizitätskonstante gefüllt werden. Als geeignete Flüssigkeit wurde Propylencarbonat mit einer Dielektrizitätskonstante von 65, einem hohen Siedepunkt und einer geringen Viskosität identifiziert. Um eine noch höhere Dielektrizitätskonstante zwischen den Federwindungen zu erreichen. wurden Suspensionen aus Silikonöl und nanokristallinem Bariumtitanat hergestellt und bezüglich ihrer Langzeitstabiltät charakterisiert.
- Gemäß den Anforderungen des Projektpartners KOMPASS wurden maßgeschneiderte Al2O3-Federn mit einer Federkonstante < 0,1 N/mm hergestellt und für den Aufbau des finalen Demonstrator eingesetzt.
Die prinzipielle Funktionsfähigkeit des neuen Sensorkonzeptes auf Basis keramischer Federn wurde mit dem im Projekt aufgebauten Demonstrator nachgewiesen. Die Umsetzung der F+E-ergebnisse in eine industrielle Nutzung zur Herstellung von Gravimetern wird vom Projektpartner KOMPASS angestrebt und ist bereits mit detaillierten Zeitplänen untersetzt.
Self-healing polymers have been developed to improve durability and reduce costs associated with maintenance during service. The addition of thermoplastics to thermosets to produce mendable polymers appears as a promising selfhealing technique. In this study, poly (ethylene-co-methacrylic acid) (EMAA) was added to epoxy resin and the effects of EMAA addition on epoxy properties were evaluated. Specimens with two different contents of thermoplastic and particles sizes were manufactured. A two-level full factorial experimental design was used to evaluate the effect of particle size and particle content on properties of epoxy modified with addition of EMAA. Tensile tests and dynamic mechanical analysis (DMA) were used and the evaluated responses were tensile strength, modulus of elasticity, and glass transition temperature (Tg). X-ray computed tomography (XCT) was used to investigate particle size and concentration after manufacturing. It was found that the particle concentration has greater effects on stress–strain behavior of epoxy while Tg was not significantly affected by neither of the analyzed entrance variables.
AbstractTwo‐photon polymerization (2PP) additive manufacturing (AM) utilizes feedstocks of ceramic nanoparticles of a few nanometers in diameter, enabling the fabrication of highly accurate technical ceramic design with structural details as small as 500 nm. The performance of these materials is expected to differ from conventional AM ceramics, as nanoparticles and three‐dimensional printing at high resolution introduce new microstructural aspects. This study applies 2PP‐AM of yttria‐stabilized zirconia to investigate the mechanical response behavior under compressive load, probing the influence of smallest structural units induced by the line packing during the printing process, design of sintered microblocks, and sintering temperature and thereby microstructure. We find a dissipative mechanical response enhanced by sintering at lower temperatures than conventional. The pursued 2PP‐AM approach yields a microstructured material with an increased number of grain boundaries that proposedly play a major role in facilitating energy dissipation within the here printed ceramic material. This microplastic response is further triggered by the filigree structures induced by hollow line packing at the order of the critical defect size of ceramics. Together, these unique aspects made accessible by the 2PP‐AM approach contribute to a heterogeneous nano‐ and microstructure, and hint toward opportunities for tailoring the mechanical response in future ceramic applications.
AbstractTwo‐photon polymerization (2PP) additive manufacturing (AM) utilizes feedstocks of ceramic nanoparticles of a few nanometers in diameter, enabling the fabrication of highly accurate technical ceramic design with structural details as small as 500 nm. The performance of these materials is expected to differ from conventional AM ceramics, as nanoparticles and three‐dimensional printing at high resolution introduce new microstructural aspects. This study applies 2PP‐AM of yttria‐stabilized zirconia to investigate the mechanical response behavior under compressive load, probing the influence of smallest structural units induced by the line packing during the printing process, design of sintered microblocks, and sintering temperature and thereby microstructure. We find a dissipative mechanical response enhanced by sintering at lower temperatures than conventional. The pursued 2PP‐AM approach yields a microstructured material with an increased number of grain boundaries that proposedly play a major role in facilitating energy dissipation within the here printed ceramic material. This microplastic response is further triggered by the filigree structures induced by hollow line packing at the order of the critical defect size of ceramics. Together, these unique aspects made accessible by the 2PP‐AM approach contribute to a heterogeneous nano‐ and microstructure, and hint toward opportunities for tailoring the mechanical response in future ceramic applications.
Fluorescence imaging microscopy is an essential tool in biomedical research. Meanwhile, various fluorescent probes are available for the staining of cells, cell membranes, and organelles. Though, to monitor intracellular processes and dysfunctions, probes that respond to ubiquitous chemical parameters determining the cellular function such as pH, pO2, and Ca2+ are required. This review is focused on the progress in the design, fabrication, and application of photoluminescent nanoprobes for sensing and imaging of pH in living cells. The advantages of using nanoprobes carrying fluorescent pHindicators compared to single molecule probes are discussed as well as their limitations due to the mostly lysosomal uptake by cells. Particular attention is paid to ratiometric dual wavelength nanosensors that enable intrinsic referenced measurements. Referencing and proper calibration procedures are basic prerequisites to carry out reliable quantitative pH determinations in complex samples such as living cells. A variety of examples will be presented that highlight the diverseness of nanocarrier materials (polymers, micelles, silica, quantum dots, carbon dots, gold, photon upconversion nanocrystals, or bacteriophages), fluorescent pH indicators for the weak acidic range, and referenced sensing mechanisms, that have been applied intracellularly up to now.
BAM Report 2019
(2020)
Dieser BAM-Report erscheint zwischen zwei historischen Jubiläen: dem 30. Jahrestag des Mauerfalls am 9. November 1989 und dem der staatlichen Einheit Deutschlands am 3. Oktober 1990.
Für unser Land bedeuten beide Daten eine glückliche Zäsur. Und auch für die Bundesanstalt für Materialforschung und -prüfung (BAM), die in den Jahren der Teilung ihren Sitz im westlichen Teil Berlins behalten hatte, waren sie mit guten Veränderungen verbunden: Zur BAM sind über 500 Wissenschaftler*innen des ostdeutschen Amtes für Standardisierung, Messwesen und Warenprüfung sowie aus den Instituten der Akademie der Wissenschaften in Berlin-Adlershof dazugekommen. Die BAM hat damals neue Tätigkeitsschwerpunkte gewonnen, vor allem auf dem Gebiet der Analytischen Chemie, und konnte sich als Teil des sich auch heute noch rasant entwickelnden Wissenschaftsstandortes Berlin-Adlershof positionieren.
Blicken wir heute auf die bewegten und bewegenden Monate vor 30 Jahren zurück, so tun wir dies aus einer deutlich veränderten Gegenwart: Aktuell beschäftigen uns große gesellschaftliche Herausforderungen wie die digitale Transformation, Energiesicherheit, demografische Veränderungen und der Klimawandel. Berlin ist inmitten dieser Herausforderungen ein Ort der Innovation und des Aufbruchs in der Mitte Europas. Dafür steht beispielhaft die Ansiedlung des Werner von Siemens Centre for Industry & Science, das in den kommenden Jahren im Nordwesten der Stadt wachsen wird. Die BAM ist auch hier Partner des Zukunftsprojekts.
Sicherheit in Technik und Chemie zu gewährleisten - unser Kernauftrag bleibt inmitten dieses beschleunigten Wandels unverändert gültig. Aber er bezieht sich heute auf die Sicherheit von Nanopartikeln, von Werkstücken aus dem 3D-Drucker oder die Speicher von Wasserstoffautos und morgen auf ganz neue Technologien. Dazu forschen wir in unseren fünf Themenfeldern Energie, Infrastruktur, Umwelt, Material und Analytical Sciences weltweit vernetzt.
Über alle Umbrüche hinweg leitet uns dabei eine Idee: Sicherheit macht Märkte. Technologischer Wandel, Kreativität und Erfinder*innengeist ermöglichen den Wohlstand unserer Gesellschaft. Zugleich aber gilt: Erst die Verlässlichkeit neuer Technologien und Materialien schafft das Vertrauen der Menschen in den Wandel und sichert so langfristig unsere Zukunft.
Charakterisierung von Glas-Polymer Verbundmaterialien fur die Hochdruckspeicherung von Wasserstoff
(2017)
In der vorliegenden Arbeit werden Glaskapillaren und Strukturen aus Borosilikatglas (Simax) f¨ur die Hochdruckspeicherung von Wasserstoff betrachtet. Um die mechanischen Belastungen zu analysieren und anschließend ein optimiertes Speicherdesign abzuleiten, findet die Finite Element Methode (FEM) Einsatz.
Die notwendigen Materialkennwerte werden zuvor experimentell ermittelt. Dazu geh¨oren die Festigkeit, die Schubfestigkeit der Grenzfl¨ache Klebung/Glas, der Wasserstoffpermeationskoeffizient, das Temperatur-Zeit-abh¨angige Verhalten, sowie die obere Temperatureinsatzgrenze.
Die Glasfestigkeit ist stark abh¨angig von der Oberfl¨acheng¨ute. Daher werden in dieser Arbeit Kapillaren selber gezogen und beschichtet. Der Einfluss auf die Festigkeit wird mit Hilfe von Berstversuchen untersucht. Die eingesetzten Polymere werden zus¨atzlich mit dem Push-out Versuch, der dynamisch mechanischen Analyse und der Permeationsmessung charakterisiert.
Dar¨uber hinaus wird aus den DMA Versuchen ein viskoelastisches Materialmodell abgeleitet, womit der Temperatur- und Zeiteinfluss auf die mechanische Belastung simuliert wird.
Unter Beachtung der experimentell gewonnenen Erkenntnisse, sowie der durchgef¨uhrten Simulation ist es m¨oglich, ein optimiertes Speicherdesign zu erstellen und Aussagen ¨uber die Einsatzgrenzen zu treffen.
Jahresbericht 2006
(2007)
Jahresbericht 2009
(2010)
The epoxy/metal interface regions are recognized as crucial for the mechanical reliability of composite materials. In particular, the spatial stress distribution is governed by modulus variations, which may result from the physical-chemical interactions between epoxy and the metal surface. The properties of the interphase between bulk polymer and metal were analyzed in nanometer scale. It was aimed to characterize the stiffness gradient of the polymeric interphase, which was formed by a thermoset being cured in contact with a metal surface.
Jahresbericht 2004
(2005)
Jahresbericht 2008
(2009)
Jahresbericht 2007
(2008)
Jahresbericht 2002
(2003)
Die Werkstoffgruppe der Faser-Kunststoff-Verbunde (FKV) hat sich aufgrund ihrer hervorragenden Leichtbaueigenschaften unter anderem im Sportgerätebau, in der Luft- und Raumfahrt und in der Windenergieindustrie etabliert. Die so hergestellten Strukturen sind in der Regel nicht nur mechanischen Belastungen, sondern auch thermischen Lasten in einem breiten Temperaturspektrum ausgesetzt. Dennoch ist die Auswirkung des Temperatureinflusses bei einer Kombination von thermischer und mechanischer Last auf die Lebensdauer von Strukturen aus FKV bisher nur wenig untersucht.
Im Rahmen dieser Arbeit wird der Einfluss von Temperaturen zwischen 213 K und 343 K auf einen Glasfaser-Epoxidharz-Verbund experimentell untersucht. Das Material wird in diesem Temperaturbereich eingehend charakterisiert: Es werden sowohl die thermomechanischen Eigenschaften von Faser- und Matrixwerkstoff als auch die des Verbundes ermittelt. In einem weiteren Schritt wird dann der Einfluss der Temperatur auf die Schädigungsentwicklung im quasi-statischen Lastfall sowie unter schwingender Ermüdungsbeanspruchung bei verschiedenen FKV-Mehrschichtverbunden analysiert.
Basierend auf den experimentellen Daten wird ein Zusammenhang zwischen der Schädigung und der Anstrengung der Matrix innerhalb der Einzelschicht demonstriert. Die Matrixanstrengung wird mithilfe eines mikromechanischen Modells unter Berücksichtigung der thermomechanischen Eigenspannungen analytisch berechnet. Bei Querzugbeanspruchung kann gezeigt werden, dass eine Vorhersage der Schädigung in Abhängigkeit der Volumenänderungsenergie innerhalb der Matrix getroffen werden kann.
Mithilfe des Konzepts der Matrixanstrengung ist eine Vorhersage der Lebensdauer des Werkstoffs unter schwingender Ermüdungsbeanspruchung in Abhängigkeit der Einsatztemperatur möglich.