Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2018 (211) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (195)
- Beitrag zu einem Tagungsband (14)
- Buchkapitel (2)
Referierte Publikation
- ja (211) (entfernen)
Schlagworte
- SAXS (11)
- Residual stress (10)
- Additive manufacturing (9)
- Mechanochemistry (7)
- Microstructure (7)
- Small-angle X-ray scattering (7)
- Creep (6)
- Friction (6)
- MALDI-TOF MS (6)
- Welding (6)
- Cyclization (5)
- High-strength steels (5)
- In situ (5)
- Nanoparticle (5)
- Upconversion (5)
- Wear (5)
- Corrosion (4)
- Laser beam welding (4)
- Laser metal deposition (4)
- Niobium carbide (4)
- Polymer (4)
- Silver nanoparticles (4)
- XRD (4)
- 3D-Printing (3)
- Additive Manufacturing (3)
- Computed tomography (3)
- Femtosecond laser (3)
- Fracture mechanics (3)
- Hydrogen (3)
- Laser welding (3)
- Neutron diffraction (3)
- Polyester (3)
- Polylactide (3)
- Process parameters (3)
- Residual stresses (3)
- TEM (3)
- Weldments (3)
- X-ray diffraction (3)
- Active thermography (2)
- Alkali-Kieselsäure-Reaktion (2)
- All-optical switching (2)
- Alloy 31 (2)
- Alloys (2)
- Aluminium alloys (2)
- Aluminum alloys (2)
- Asymmetric coupler (2)
- Austenitic stainless steel (2)
- BAMline (2)
- Bacteria (2)
- Betonfahrbahndecke (2)
- Carbon fiber reinforced polymers (2)
- Catalysts (2)
- Ceramic (2)
- Cermet (2)
- Composite (2)
- Composite materials (2)
- Coupled generalized nonlinear Schrödinger equation (2)
- Crack closure (2)
- Creep-resistant steel (2)
- Damage (2)
- Deformation (2)
- Diffusion (2)
- Digital image correlation (2)
- Dimensional accuracy (2)
- Discotic liquid crystals (2)
- Dual-core photonic crystal fiber (2)
- Electron microscopy (2)
- Fatigue crack growth (2)
- Fatigue crack propagation (2)
- Fatigue crack propagation threshold (2)
- Fatigue strength (2)
- GMA welding (2)
- Hardness (2)
- Heat treatment (2)
- High temperature corrosion (2)
- Humidity (2)
- Hysteresis (2)
- IN718 (2)
- In situ studies (2)
- LIBS (2)
- Large-scale test (2)
- MOF (2)
- Mechanical properties (2)
- Nanopatricle (2)
- NbC (2)
- Non-destructive testing (2)
- Oxidation (2)
- Photooxidation (2)
- Plastic deformation (2)
- Polyethylene (2)
- Polymers (2)
- Quenching (2)
- Rare earth nanoparticles (2)
- Restraint (2)
- Ring-opening Polymerization (2)
- Ring-opening polymerization (2)
- Rubber (2)
- Selective laser melting (2)
- Serial sectioning (2)
- Short cracks (2)
- Small-angle x-ray scattering (2)
- Soft glass (2)
- Solid lubricants (2)
- Solidification cracking (2)
- Stainless steels (2)
- Steel (2)
- TPU (2)
- Thermal expansion (2)
- Thermography (2)
- Titanium (2)
- Transesterification (2)
- UV radiation (2)
- Ultrafast soliton fission (2)
- Ultrasound (2)
- Welding simulation (2)
- ZfP (2)
- 3D printer (1)
- 3D printing (1)
- 3D-finite element modeling (1)
- 9%Ni steel (1)
- ADXRD (1)
- AISI 304L (1)
- AM (1)
- ASR modelling (1)
- Ab initio calculation (1)
- Absorption spectrometry (1)
- Abwasser (1)
- Accelerated concrete prism test (1)
- Accelerated temporal integration (1)
- Accelerator magnet coils (1)
- Accelerator magnets (1)
- Active fibers (1)
- Adaptive control (1)
- Adaptive welding beam oscillation (1)
- Additive manufacturing (AM) (1)
- Adhesion (1)
- Ageing (1)
- Aging (1)
- Al-Cu-Li-alloy (1)
- Alkali-activated slag (1)
- Alkali–silica reaction (1)
- Aluminium oxide (1)
- Aluminum Alloys (1)
- Anisotropic fiber orientation (1)
- Annealing treatment (1)
- Antikensammlung Berlin (1)
- Artificial digestion (1)
- Artificial weathering (1)
- Atomic Scale (1)
- Austenitic (1)
- Automated expansion measurement (1)
- Automated manufacturing (1)
- Automatisierte Fertigung (1)
- Automotive application (1)
- BET (1)
- Baltic Sea (1)
- Behavior (1)
- Beschichtung (1)
- Beta-eucryptite (1)
- Biaxial strength (1)
- Binder jetting (1)
- Bio Ceramic (1)
- Biofouling (1)
- Biogeochemistry (1)
- Biomaterials (1)
- Biomedical application (1)
- Bisphenol A (1)
- Bitter technique (1)
- Blends (1)
- Bone grafting (1)
- Bone regeneration (1)
- Bone substitutes (1)
- Borosilicate glass (1)
- Boson peak (1)
- Brillouin (1)
- Broadband dielectric spectroscopy (1)
- Brunauer-Emmett-Teller (1)
- Build-up strategy (1)
- C-C coupling (1)
- CCT diagrams (1)
- CCUS, supercritical/dense phase CO2, carbon steels, martensitic steel, superaustenite steel, droplet corrosion (1)
- CEC-L-103 (1)
- CFD model (1)
- CFRP (1)
- COSMO (1)
- CT (1)
- Calcination (1)
- Calcium Cobaltite (1)
- Calcium monofluoride (1)
- Carbon (1)
- Carbon footprint (1)
- Carbon steel (1)
- Cement (1)
- Changes with time (1)
- Chemical composition (1)
- Clad steels (1)
- Climate (1)
- Coarse grained heat affected zone (1)
- Coastal protection (1)
- Coating (1)
- Cobald based alloy (1)
- Cohesive finite elements (1)
- Cold-welding (1)
- Complex Molecular Systems (1)
- Computed Tomography (1)
- Computed tompgraphy (1)
- Concrete (1)
- Condition monitoring (1)
- Conductor-like screening model (1)
- Constraint (1)
- Cooling rate (1)
- Coordinate measurement machine (1)
- Copper hydroxide (1)
- Cordierite (1)
- Core shell structure (1)
- Core-shell nanoparticles (1)
- Corrosion resistance (1)
- Corrosion testing (1)
- Coupling (1)
- CrN/NbN (1)
- Crack closure mechanisms (1)
- Creep mechanisms (1)
- Creep resistant steel (1)
- Critical strain (1)
- Crosslinking (1)
- Cryogenic temperature (1)
- Crystallographic texture (1)
- Cupriavidus metallidurans (1)
- Cyclic J-integral (1)
- Cyclic R-curve (1)
- Cyclic R-curve analysis (1)
- Cyclic stress-strain curve (1)
- Cyclisation (1)
- DED (1)
- DIC (1)
- DNA origami (1)
- Damage evolution (1)
- Defects (1)
- Deformed geometry (1)
- Degradation (1)
- Density measurement (1)
- Deposition rate (1)
- Design of experiments (1)
- Destabilization (1)
- Diaspore (1)
- Die-cast aluminum (1)
- Dielectric ceramic (1)
- Dielectric heating (1)
- Digitalisierung (1)
- Digitization (1)
- Dilatometry (1)
- Disorder (1)
- Dissimilar metal weld overlays (1)
- Dissimilar welds (1)
- Duplex (1)
- Dynamic recrystallization (1)
- Dynamic vapor sorption (1)
- EBSD (1)
- EPR (1)
- ESI-TOF-MS (1)
- ESR (1)
- Early stages (1)
- Eddy current (1)
- Editorial (1)
- Education (1)
- Effective properties (1)
- Einzelzellanalyse (1)
- Elastic follow-up (1)
- Elastic-plastic fracture mechanics (1)
- Electric conductivity (1)
- Electrical connectors (1)
- Electrical resistance (1)
- Electro-plated nickel coatings (1)
- Electrochemical potentiokinetic reactivation (1)
- Electroless Ni-P (1)
- Electromagnetic influence (1)
- Electromagnetic weld pool support (1)
- Electron back-scattered diffraction (1)
- Embrittlement (1)
- Emission (1)
- Endurance limit (1)
- Engine combustion (1)
- Engine performance (1)
- Environment (1)
- Environmental stress cracking (ESC) (1)
- Epitaxial thin films (1)
- Equivalent heat source (1)
- Equivalent stress concentration factors (1)
- Excess surface work (1)
- Expanding cavity model (1)
- FIB Tomography (1)
- FRET (1)
- FTIR (1)
- Fast Scanning Calorimetry (1)
- Fast measurement (1)
- Fe2TiO5 (1)
- Femtosecond laser ablation (1)
- Ferritic steels (1)
- Ferromagnetic steels (1)
- Feuchtemessung (1)
- Fiber laser (1)
- Fiber-reinforced composite (1)
- Fiber-reinforced concrete (1)
- Finite element method (FEM) (1)
- Finland (1)
- Fire (1)
- Flue gas desulphurisation facilities (1)
- Fluorescence (1)
- Fluorescence lifetime (1)
- Fluorophore (1)
- Formaldehyde (1)
- Fourier series (1)
- Fractal Microstructure (1)
- Fracture (1)
- Fracture resistance (1)
- Free weathering (1)
- Fresnel reflection (1)
- Friction stir processing (1)
- Full notch creep test (FNCT) (1)
- Full penetration (1)
- Fungi (1)
- Fusion zone size (1)
- Fusion zone, nickel alloys (1)
- GC-FID (1)
- GFRP (1)
- GMAwelding (1)
- GMR (1)
- GMR sensors (1)
- GTAW (1)
- Gamma irradiation (1)
- Gap bridging (1)
- Gas solubility (1)
- Geosynthetics (1)
- Geotextiles (1)
- Glass (1)
- Glass crystallization stress (1)
- Glass transition (1)
- Glass-ceramics definition (1)
- Glasses (1)
- Gleeble testing (1)
- Gold (1)
- Grade S960QL steel (1)
- Gradient-enhanced fatigue model (1)
- Grain Boundary Corrosion (1)
- Grain size (1)
- Graphene (1)
- Graphite furnace (1)
- Greek curse tablets (1)
- Green-Death solution (1)
- Growth defects (1)
- HR-CS-MAS (1)
- HSLA (1)
- HSLA steel (1)
- Hard metals (1)
- Hardmetal (1)
- Heat affected zone (1)
- Heat diffusion (1)
- Heat flow (1)
- Heat-affected zone (1)
- Heizöllagerbehälter (1)
- Henry's law constant (1)
- Hessian analysis (1)
- High brightness (1)
- High interstitial austenitic steel (1)
- High power (1)
- High strength steel (1)
- High-power laser beam (1)
- High-strength steel sheets (1)
- Hipims (1)
- Hohlprofilknoten (1)
- Hot steam (1)
- Hybrid laser-arc welding (1)
- Hydrocarbons (1)
- Hydrogen assisted cracking (1)
- Hydrophilicity (1)
- ICP-MS (1)
- IR (1)
- Image processing (1)
- Impact (1)
- Impact absorbed energy (1)
- Impact factor (1)
- Impact wear (1)
- In situ diffraction (1)
- In situ strain (1)
- In-situ SEM micro shear deformation (1)
- In-situ characterization of GDLs (1)
- In-situ synchrotron X-ray computed tomography (1)
- In-situ synchrotron X-ray radiography (1)
- Inclusions (1)
- Indentation (1)
- Inorganic polymers (1)
- Interdiffusion (1)
- Interfacial strength (1)
- Internal Sulfidation (1)
- Internal friction (1)
- Internal stress (1)
- Inverse analysis (1)
- Ionic liquid (1)
- Ionic liquid crystalls (1)
- Iron oxide films (1)
- Iron speciation (1)
- Iron–chromium–nickel alloy (1)
- Isostatic hot pressing (HIP) (1)
- Isotope dilution mass spectrometry (1)
- Katalysator (1)
- Kerbspannungskonzept (1)
- Kitagawa-Takahashi diagram (1)
- Knoevenagel condensation (1)
- LTT Weld Filler Materials (1)
- Laboratory X-ray diffraction (1)
- Laminography (1)
- Lanthanide-doped nayf-4 (1)
- Laser keyhole welding (1)
- Laser scanning microscopy (LSM) (1)
- Laser surfacing (1)
- Laser-induced X-ray emission (1)
- Laser-induced periodic surface structures (1)
- Layer-by-Layer (1)
- Lead isotopes (1)
- Life prediction (1)
- Life sciences (1)
- Light curing (1)
- Liquid metal embrittlement (1)
- Liquid phase sintering (1)
- Low carbon steel (1)
- Low heat input Gma welding (1)
- Low transformation temperature filler materials (1)
- MAG welding (1)
- MRFA (1)
- Machining (1)
- Magnesium (1)
- Magnetic domain distribution (1)
- Magnetic stray field (1)
- Magnetic stray fields (1)
- Magnetomechanical effect (1)
- Magnetpartikel (1)
- Marble deterioration (1)
- Marble sculptures (1)
- Marine atmosphere (1)
- Mars (1)
- Martensitic stainless steel (1)
- Martensitic transformation (1)
- Material modeling (1)
- Material science (1)
- Measurement (1)
- Measuremment uncertainty (1)
- Mechanical analysis (1)
- Melt pool dynamics (1)
- Mesoporosity (1)
- Metal Magnetic Memory (1)
- Metal magnetic memory (1)
- Metal matrix composite (1)
- Metal matrix composites (1)
- Metal-organic frameworks (1)
- Methane (1)
- Mg1-xZnxTiO3 (1)
- Micro analysis (1)
- Microalloyed steels (1)
- Microcracked ceramics (1)
- Micromechanical modeling (1)
- Microstructur (1)
- Microstructure Tensile strength (1)
- Microstructure and texture (1)
- Microstructure evolution (1)
- Microwave synthesis (1)
- Microwaves (1)
- Milling (1)
- Mobility (1)
- Modal analysis (1)
- Modeling (1)
- Molecular Organic Frameworks (1)
- Molybdenum disulphide (1)
- Monotonic and cyclic crack driving force (1)
- Multi-pass welding (1)
- Multiaxial deformation (1)
- Multifunctional efficiency (1)
- Multilaysers (1)
- Multiple crack initiation (1)
- Multiple cracking (1)
- NGS (1)
- NIR (1)
- Nano-scratch test (1)
- Nanocomposite (1)
- Nanocrystals (1)
- Nanomaterial (1)
- Nanomedicine (1)
- Nanoparticles (1)
- Nanophotonics (1)
- Nanopores (1)
- Nanoscale multilayers (1)
- Nanostructuring (1)
- Narrow gap welding (1)
- Nasschemie (1)
- Natural silver wires (1)
- Near infrared (1)
- Near-infrared light (1)
- Neural networks (1)
- Neutron scattering (1)
- NiTi (1)
- Nickel (1)
- Nickel foam (1)
- Niobium carbide (NbC) (1)
- Nitric acid (1)
- Non lienear processes (1)
- Nondestructive testing (1)
- Nonferrous slag (1)
- Nonlinearity (1)
- Notch (1)
- Notch stress approach (1)
- Nuclear Magnetic Resonance (1)
- Nuclear power plants (1)
- Number density (1)
- Numerical simulation (1)
- Numerical welding simulation (1)
- Optical centrifugation (1)
- Optical measurement (1)
- Order parameter (1)
- Organic/inorganic block copolymer (1)
- Orientation (1)
- Orientation distribution (1)
- Outdoor weathering (1)
- Oxide (1)
- PAEKs (1)
- PUR (1)
- PVD hard coating (1)
- Partial penetration (1)
- Passive film (1)
- Passive thermography (1)
- Passivity (1)
- Pb isotopes (1)
- Peroxy-fuels (1)
- Pest control (1)
- Phase transformation (1)
- Phase-contrast microscopy (1)
- Photocatalysis (1)
- Photocatalytic activity (1)
- Photonic devices (1)
- Photophysics (1)
- Photosensitizer (1)
- Physical aging (1)
- Physical vapor deposition (PVD) (1)
- Physical vapour deposition (PVD) (1)
- Pinholes (1)
- Pitting corrosion (1)
- Plume heating (1)
- Polyacrylamide (1)
- Polycondensation (1)
- Polycrystals (1)
- Polyelektrolyt (1)
- Polyethylen (1)
- Polylactides (1)
- Polymer of intrinsic microporosity (1)
- Polymer optical fibre (1)
- Polymer particles (1)
- Polymeric Materials (1)
- Polymerization (1)
- Polymers with intrinsic microporosity (1)
- Polymorphism (1)
- Polymorphs (1)
- Polyurethane (1)
- Porcelain (1)
- Porosity (1)
- Porosity reduction (1)
- Post Weld Heat Treatment (PWHT) (1)
- Preceramic polymer (1)
- Precipitation (1)
- Pressure tanks (1)
- Pressure vessel (1)
- Process simulation (1)
- Pseudobrookite (1)
- Quantum Yield (1)
- Quantum dot (1)
- Quantum yield (1)
- R-curve analysis (1)
- RAMAN (1)
- Radar (1)
- Radiation protection (1)
- Radio waves (1)
- Raman spectroscopy (1)
- Ratiometric sensing (1)
- Reaction-sintering (1)
- Reciprocating sliding (1)
- Reconstructed ion chromatograms (1)
- Reference (1)
- Reference measurements (1)
- Reference organisms (1)
- Relaxation (1)
- Residual Stresses (1)
- Resistance (1)
- Resistance spot welding (1)
- Robust nano objects (1)
- Rod-like liquid crystals (1)
- S-Phase (1)
- SEM (1)
- SLM (1)
- SSTC Model (1)
- Sample holder (1)
- Scanning acoustic microscopy (SAM) (1)
- Scattering (1)
- Schmelze-Masse-Fließrate (1)
- Schweißnahtgeometrie (1)
- Schädigungsgrad (1)
- Seal performance (1)
- Secondary heat source (1)
- Secondary stresses (1)
- Segregation (1)
- Selective Laser Melting (1)
- Self-Assembly (1)
- Self-assembly (1)
- Semiconductive layer (1)
- Sensing (1)
- Sensor (1)
- Shape memory alloys (1)
- Shear testing (1)
- Short crack propagation (1)
- Silbernanopartikel (1)
- Simvastatine (1)
- Single photon and quantum effects (1)
- Single-crystal (1)
- Singulettsauerstoff (1)
- Sintering (1)
- Slow crack growth (SCG) (1)
- Slurry optimization (1)
- Smart industry (4.0) (1)
- Soft-templated (1)
- Solid-State-Synthesis (1)
- Solvation properties (1)
- Spark plasma sintering (1)
- Spatial analyses (1)
- Specific heat spectroscopy (1)
- Spectroscopy (1)
- Spirocyclic (1)
- Spray drying (1)
- Stainless steel (1)
- Standards (1)
- Steam oxidation resistance (1)
- Stoichiometric phases (1)
- Strain difference (1)
- Strain hardening (1)
- Strain rate (1)
- Strain rates (1)
- Strain-rate (1)
- Strength mismatch (1)
- Stress Coupling (1)
- Stress Relief Cracking (SRC) (1)
- Stress-strain behavior (1)
- Stress-strain relations (1)
- Stress-strain-behavior (1)
- Structural steel (1)
- Sulfidation (1)
- Sulphidation (1)
- Superalloy (1)
- Superalloy single crystals (1)
- Supercapacitor (1)
- Superconducting (1)
- Superconducting magnet (1)
- Superconducting magnets (1)
- Support configurations (1)
- Supramolecules (1)
- Surface cracks (1)
- Surface defects (1)
- Surface nucleation (1)
- Sustainability (1)
- Synchrotron (1)
- Synchrotron X-ray diffraction (1)
- Synchrotron X-ray refraction (1)
- Synchrotron X-ray refraction radiography (1)
- Synchrotron diffraction (1)
- Synthesis (1)
- T1 precipitate (1)
- THz Spectroscopy (1)
- TIG (1)
- TIG-welding (1)
- Tausalz (1)
- Temperature (1)
- Temperature distribution (1)
- Tensile load (1)
- Theranostics (1)
- Thermal conductivity (1)
- Thermal desorption analysis (1)
- Thermal-desorption spectroscopy (1)
- Thermoelectric (1)
- Thermoelectrics (1)
- Thermoresponsive polymer (1)
- Thick-walled steel (1)
- Thickening (1)
- Ti-6Al-4V (1)
- Ti-based colloids (1)
- TiMgN (1)
- Titanium alloy (1)
- Titanium nitride (1)
- ToF-SIMS (1)
- Tool (1)
- Topography (1)
- Toughness (1)
- Traceability (1)
- Transformable steels (1)
- Transient heat transfer (1)
- Transmission electron microscopy (1)
- Tribooxidation (1)
- Tricalcium Phosphate (1)
- Tubular joints (1)
- Turbine components (1)
- Turning (1)
- Twinning (1)
- UCST-type polymer (1)
- UHPC (1)
- UPLC (1)
- Ultra high molecular weight (1)
- Ultrafine particles (1)
- Ultrahigh-performance concrete (UHPC) (1)
- Ultrashort laser material interaction (1)
- Ultrasonic testing (1)
- Ultrasonic velocities (1)
- Ultrasonics (1)
- Upconverting nanoparticles (1)
- VOC (1)
- VOx catalyst (1)
- Vacuum (1)
- Vapor recondensation (1)
- Viscoplasticity (1)
- Volume fraction (1)
- WAXS (1)
- Water (1)
- Water droplet erosion resistance (1)
- Water/alcohol mixtures (1)
- Wear mechanisms (1)
- Weld geometry (1)
- Weld pool (1)
- Weld seam geometry (1)
- Welded joints (1)
- Welding residual stresses (1)
- Wood (1)
- Wood protection (1)
- X-ray absorption near-edge structure (1)
- X-ray absorption spectroscopy (1)
- X-ray absorption tomography (1)
- X-ray computed tomography (1)
- X-ray computed tomography (CT) (1)
- X-ray diffraction (XRD) (1)
- X-ray laminography (1)
- X-ray photoelectron spectroscopy (1)
- X-ray radiography (1)
- X-ray refraction (1)
- XAFS (1)
- Xerogel (1)
- Yield strength (1)
- Young`s modulus (1)
- Young’s modulus (1)
- ZIF (1)
- Zeolithe (1)
- Zinc (1)
- Zirconium (1)
- contour method (1)
- dipolar polarization (1)
- gold (1)
- magnesium (1)
- nanoparticle (1)
- neutron diffraction (1)
- permittivity (1)
- residual stress analysis (1)
- space charge polarization (1)
- subgrain structure (1)
- Ägyptisches Museum Berlin (1)
- Äquivalente Spannungskonzentrationsfaktoren (1)
Organisationseinheit der BAM
- 9 Komponentensicherheit (63)
- 6 Materialchemie (50)
- 5 Werkstofftechnik (42)
- 8 Zerstörungsfreie Prüfung (39)
- 7 Bauwerkssicherheit (26)
- 9.4 Integrität von Schweißverbindungen (25)
- 6.3 Strukturanalytik (24)
- 1 Analytische Chemie; Referenzmaterialien (21)
- 8.5 Röntgenbildgebung (21)
- 9.3 Schweißtechnische Fertigungsverfahren (21)
In order to satisfy the growing requirements towards lightweight design and resource efficiency in modern steel constructions, e.g., mobile cranes and bridges, high-strength steels with typical yield strength ≥ 690 MPa are coming into use to an increasing extent. However, these steels require special treatment in welding. The susceptibility for degradation of the mechanical properties
in the presence of hydrogen increases significantly with increasing yield strength. In case of missing knowledge about how and the amount of hydrogen that is uptaken during welding, hydrogen-assisted cracking (HAC) can be a negative consequence.
Moreover, modern weld technology like the modified spray arc process enables welding of narrower weld seams. In this context,
a reduced number of weld beads, volume, and total heat input are technical and economical benefits. This work presents the influence of welding parameters on the diffusible hydrogen content in both (1) single-pass and (2) multi-layer welds. Different
hydrogen concentrations were detected by varied contact tube distance, wire feed speed, arc length, and varied arc type (transitional
arc and modified spray arc). The results show that all welding parameters have significant influence on the diffusible hydrogen concentration in the single-pass welds. By increasing the number of weld beads in case of multi-layer welding, the
hydrogen concentration has been reduced. Whereby, differences in hydrogen concentrations between both arc types are present.
Powder X-ray diffraction is a time-consuming and challenging task, especially for preparation of sensitive phases like ettringite and calcium-silicate-hydrate (C-S-H) phases. Fine-grained ultrahigh-performance concrete (UHPC) with an average grain size <100 μm could be investigated directly without time-consuming milling. As a proof of concept, small UHPC cylinders with plain surfaces were investigated with a newly designed sample holder. The comparison with conventionally prepared powder shows the feasibility of fast qualitative phase analysis using this approach. As a great benefit, a depth-dependent analysis, as well as a comparison of surface layers and core material, was carried out.
Slags from the nonferrous metals industry have great potential to be used as feedstocks for the production of alkali-activated materials. Until now, however, only very limited information has been available about the structural characteristics of these materials. In the work presented herein, synthetic slags in the CaO–FeOx–SiO2 system, representing typical compositions of Fe-rich slags, and inorganic polymers (IPs) produced from the synthetic slags by activation with alkali Silicate solutions have been studied by means of X-ray absorption near-edge structure (XANES) spectroscopy at the Fe K-edge. The iron in the slags was largely Fe2+, with an average coordination number of approximately 5 for the iron in the amorphous fraction. The increase in average oxidation number after alkali-activation was conceptualized as the consequence of slag dissolution and IP precipitation, and employed to calculate the degrees of reaction of the slags. The degree of reaction of the slags increased with increasing amorphous fraction. The iron in the IPs had an average coordination number of approximately 5; thus, IPs produced from the Fe-rich slags studied here are not Fe-analogs of aluminosilicate geopolymers, but differ significantly in terms of structure from the latter.
Time-resolved phase-contrast microscopy is employed to visualize spatio-temporal thermal transients induced by tight focusing of a single Ti:sapphire fs-laser pulse into a solid dielectric sample. This method relies on the coupling of the refractive index change and the sample temperature through the thermo-optic coefficient dn/dT. The thermal transients are studied on a timescale ranging from 10 ns up to 0.1 ms after laser excitation. Beyond providing direct insights into the laser–matter interaction, analyzing the results obtained also enables quantifying the local thermal diffusivity of the sample on a micrometer scale. Studies conducted in different solid dielectrics, namely amorphous fused silica (a-SiO2), a commercial borosilicate glass (BO33, Schott), and a custom alkaline earth silicate glass (NaSi66), illustrate the applicability of this approach to the investigation of various glassy materials.
Meso-Lactide was polymerized in bulk at 60, 80, and 100 °C by means of three different types of catalysts: dibutyltinsulfides (2,2-dibutyl-2-stanna-1,3-dithiolane and 2,20-dibutyl-2-stanna-1,3-dithiane), dibutyltin derivatives of substituted cate-chols (BuCa, CyCa, and BzCa), and dibutyltin derivatives of2,2 dihydroxybiphenyl (SnBi) and 2,2-dihydroxy-1,10-binaphthyl(SnNa. Only the latter two catalysts were active at 60 °C. The architecture of the resulting polylactides depends very much on the structure of the catalyst and on the temperature. At the lowest temperature (60 °C), SnBi and SnNa mainly yielded even-numbered linear chains, but SnNa also yielded even-numbered cycles at 100 °C and short reaction times. In contrast,BuCa, CyCa, and BzCa mainly yielded odd-numbered cycles, although the same catalysts yielded even-numbered linear chains when benzylalcohol was added.
Calcium cobaltite is one of the most promising oxide p-type thermoelectric materials. The solid-state reaction (or calcination, respectively), which is well known for large-scale powder synthesis of functional materials, can also be used for the synthesis of thermoelectric oxides. There are various calcination routines in literature for Ca3Co4O9 powder synthesis, but no systematic study has been done on the influence of calcination procedure on thermoelectric properties. Therefore, the influence of calcination conditions on the Seebeck coefficient and the electrical conductivity was studied by modifying calcination temperature, dwell time, particle size of raw materials and number of calcination cycles. This study shows that elevated temperatures, longer dwell times, or repeated calcinations during powder synthesis do not improve but deteriorate the thermoelectric properties of calcium cobaltite. Diffusion during calcination leads to idiomorphic grain growth, which lowers the driving force for sintering of the calcined powder. A lower driving force for sintering reduces the densification. The electrical conductivity increases linearly with densification. The calcination procedure barely influences the Seebeck coefficient. The calcination procedure has no influence on the phase formation of the sintered specimens.
Partial penetration welding with fiber laser on 20mm thick plates was carried out in horizontal position to study the role of secondary heating in modeling of high power fiber laser welding. Experiments were carried out using 18.8kW laser with 1.5 m/min welding speed at Ar assist gas flow rates of 0, 17, 29, and 40 l/min, all four cases show similar bead shape with bright emission of vapor plume. Numerical simulations were performed using volume of fluid method by considering three different models as models A–C. Model A considers only Fresnel reflection inside the keyhole using real time tracking of free surface. Model B considers vapor recondensation flux inside keyhole along with model A. Finally, model C is used, which considers vapor plume heating at 4100K temperature along with models A B. Secondary heating by recondensation and vapor plume is vital in modeling of high power fiber laser welding; especially, the upper part of the bead is more influenced due to secondary heating. Tungsten particles are also used to visualize the flow pattern of melt pool.
Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl–C60 derivative, molecule 1, in n-hexane, n-decane and toluene as a function of concentration and temperature. Results point to an associative mechanism of aggregation similar to other commonly associating molecules, including non-ionic surfactants or asphaltenes in non-aqueous solvents. Little aggregation is detected in toluene, but small micelle-like structures form in n-alkane solvents, which have a C60-rich core and alkyl-rich shell. The greatest aggregation extent is found in n-hexane, and at 0.1 M the micelles of 1 comprise around 6 molecules at 25 °C. These micelles become smaller when the concentration is lowered, or if the solvent is changed to n-decane. The solution structure is also affected by temperature, with a slightly larger aggregation extent at 10 °C than at 25 °C. At higher concentrations, for example in solutions of 1 above 0.3 M in n-decane, a bicontinuous network becomes apparent. Overall, these findings aid our understanding of the factors driving the assembly of alkyl–π-conjugated hydrophobic amphiphiles such as 1 in solution and thereby represent a step towards the ultimate goal of exploiting this phenomenon to form materials with well-defined order.
Proline has been widely used for various cocrystallization applications, including pharmaceutical cocrystals. Combining enantiopure and racemic flurbiprofen and proline, we discovered 18 new crystal structures. Liquid-assisted grinding proved highly efficient to explore all the variety of crystal forms. A unique combination of stateof-the-art characterization techniques, comprising variable temperature in situ X-ray diffraction and in situ ball-milling, along with other physicochemical methods and density functional theory calculations, was indispensable for identifying all the phases. Analyzing the results of in situ ball-milling, we established a stepwise mechanism for the formation of several 1:1 cocrystals via an intermediate 2:1 phase. The nature of the solvent in liquidassisted grinding was found to significantly affect the reaction rate and, in some cases, the reaction pathway.
We demonstrate ultrafast soliton-based nonlinear balancing of dual-core asymmetry in highly nonlinear photonic crystal fiber at sub-nanojoule pulse energy level. The effect of fiber asymmetry was studied experimentally by selective excitation and monitoring of individual fiber cores at different wavelengths between 1500 nm and 1800 nm. Higher energy transfer rate to non-excited core was observed in the case of fast core excitation due to nonlinear asymmetry balancing of temporal solitons, which was confirmed by the dedicated numerical simulations based on the coupled generalized nonlinear Schrödinger equations. Moreover, the simulation results correspond qualitatively with the experimentally acquired dependences of the output dual-core extinction Ratio on excitation energy and wavelength. In the case of 1800 nm fast core excitation, narrow band spectral intensity switching between the output channels was registered with contrast of 23 dB. The switching was achieved by the change of the excitation pulse energy in sub-nanojoule region. The performed detailed analysis of the nonlinear balancing of dual-core asymmetry in solitonic propagation regime opens new perspectives for the development of ultrafast nonlinear all-optical switching devices.
Combining experiments and all-atom molecular dynamics simulations, we study the conformational behavior of polyacrylamide (PAM) in aqueous alcohol mixtures over a wide range of temperatures. This study Shows that even when the microscopic interaction is dictated by hydrogen bonding, unlike its counterparts that present a lower critical solution temperature (LCST), PAM shows a counterintuitive tunable upper critical solution temperature (UCST)-type phase transition in water/alcohol mixtures that was not reported before. The Phase transition temperature was found to be tunable between 4 and 60 1C by the type and concentration of alcohol in the mixture as well as by the solution concentration and molecular weight of the polymer. In addition, molecular dynamics simulations confirmed a UCST-like behaviour of the PAM in aqueous alcoholic solutions.
Additionally, it was observed that the PAM is more swollen in pure alcohol solutions than in 80% alcoholic solutions due to y-like behaviour. Additionally, in the globular state, the size of the aggregates was found to increase with increasing solvent hydrophobicity and polymer concentration of the solutions. Above ist Phase transition temperature, PAM might be present as individual polymer chains in the coil state (r10 nm). As PAM is a widespread polymer in many biomedical applications (gel electrophoresis, etc.), this finding could be of high relevance for many more practical applications in high performance pharmaceuticals and/or sensors.
Analytical flaw assessment
(2018)
The paper provides a review on analytical flaw assessment methods with the focus on fracture under monotonic loading and fatigue crack propagation. The first topic comprises linear elastic as well as elastic-plastic fracture mechanics approaches. It essentially follows their historical development. Topics which are separately discussed are reference/Limit loads, the treatment of secondary stresses, strength mismatch, constraint, unstable crack propagation (monotonic R-curve analyses) and statistical aspects. With respect to fatigue crack propagation the analytical treatment of crack closure and constraint and the Determination of the cyclic elastic-plastic crack driving force is discussed. Finally, cyclic Rcurve analyses are briefly addressed.
The in situ analysis of the damage evolution in a metal Matrix composite (MMC) using synchrotron X-ray refraction radiography (SXRR) is presented. The investigated material is an Al alloy (6061)/10 vol% Al2O3 MMC after T6 heat treatment.
In an interrupted tensile test the gauge section of dog bone-shaped specimens is imaged in different states of tensile loading. On the basis of the SXRR images, the relative change of the specific surface (proportional to the amount of damage) in the course of tensile loading was analyzed. It could be shown that the damage can be detected by SXRR already at a stage of tensile loading, in which no Observation of damage is possible with radiographic absorption-based imaging methods.
Moreover, the quantitative analysis of the SXRR images reveals that the amount of damage increases homogeneously by an average of 25% with respect to the Initial state. To corroborate the experimental findings, the damage distribution was imaged in 3D after the final tensile loading by synchrotron X-ray refraction computed tomography (SXRCT) and absorption-based synchrotron X-ray computed tomography (SXCT). It could be evidenced that defects and damages cause pronounced indications in the SXRCT images.
Severe fires at the Friedrichshain flak bunker in May 1945 destroyed or severely damaged an important part of the collection of the Kaiser-Friedrich-Museum, Berlin, today’s Bode Museum. Fragments of two marble sculptures by Tullio Lombardo, sculptor of the Italian renaissance, have survived and are now stored in the Bode Museum. In preparation for restoration, the condition of the sculptures has been documented in detail in 2010. The study revealed that the fragments are not stable enough to exhibit them in a horizontal nor in an upright position. The intention of a further study in 2012 was to find a correlation between ultrasonic velocity and mechanical properties of burned Carrara marble as a basis for stabilization measures. The results and numerous supplementary experiments show that the current condition of the sculptural fragments can not only be explained by the exposure to fire.
Research and development of WC grades is 90 years ahead of niobium carbide-based hard materials, which showed already as light-weight and unexplored material a very high potential for many technical applications, especially for wear protection and machining. NbC evoluted recently from lab scale to pilot scale, especially in areas where established WC-based materials are causing economic, environmental or technical concerns. Benchmark trials of NbC-based hard metals indicated already a favorable performance in machining of steel components.
Dynamics and ionic conductivity of ionic liquid crystals forming a hexagonal columnar mesophase
(2018)
For the first time, the molecular mobility of two linear-shaped tetramethylated guanidinium triflate ionic liquid crystals (ILCs) having different length of alkyl chains were investigated by a combination of broadband dielectric spectroscopy (BDS) and specific heat spectroscopy (SHS). By self-assembly, these ILCs can form a hexagonal ordered mesophase besides plastic crystalline phases and the isotropic state. Three dielectric active processes were found by BDS for both samples. At low temperatures, a γ-process in the plastic crystalline state is observed which is assigned to localized fluctuations of methyl groups including nitrogen atoms in the guanidinium head. At higher temperatures but still in the plastic crystalline state, an α1-process takes place. An α2 process was detected by SHS but with a completely different temperature dependence of the relaxation times than that of the α1-relaxation. This result is discussed in detail, and different molecular assignments of the processes are suggested. At even higher temperatures, electrical conductivity is detected and an increase in the DC conductivity by four orders of magnitude at the phase transition from the plastic crystalline to the hexagonal columnar mesophase is found. This result is traced to a change in the charge transport mechanism from a delocalized electron hopping in the stacked aromatic systems (in the plastic phase) to one dominated by an ionic conduction in the quasi-1D ion channels formed along the supermolecular columns in the ILCs hexagonal mesophases.
Abstract: Hybrid silicon-based organic/inorganic (multi)block
copolymers are promising polymeric precursors to create
robust nano-objects and nanomaterials due to their sol–gel active moieties via self-assembly in solution or in bulk. Such nano-objects and nanomaterials have great potential in bio-medicine as nanocarriers or scaffolds for bone regeneration as well as in materials science as Pickering emulsifiers, pho-
tonic crystals or coatings/films with antibiofouling, antibac-
terial or water- and oil-repellent properties. Thus, this Review outlines recent synthetic efforts in the preparation of these hybrid inorganic/organic block copolymers, gives an
overview of their self-assembled structures and finally presents recent examples of their use in the biomedical field and
material science.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, the vibrational density of states (VDOS) for PIM-1, the prototypical polymer with intrinsic microporosity, is investigated by means of inelastic neutron scattering. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid). The measured data show the characteristic low frequency excess contribution to VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers. For an annealed PIM-1 sample, the Boson peak shifts to higher frequencies in comparison to the un-annealed sample. These changes in the VDOS of the annealed PIM-1 sample are related to changes in the microporous structure as confirmed by X-ray scattering.
Multifunctional efficiency: Extending the concept of atom economy to functional nanomaterials
(2018)
Green chemistry, in particular, the principle of atom economy, has defined new criteria for the efficient and sustainable production of synthetic compounds. In complex nanomaterials, the number of embedded functional entities and the energy expenditure of the assembly process represent additional compound-associated parameters that can be evaluated from an economic viewpoint. In this Perspective, we extend the principle of atom economy to the study and characterization of multifunctionality in nanocarriers, which we define as “multifunctional efficiency”. This concept focuses on the design of highly active nanomaterials by maximizing integrated functional building units while minimizing inactive components. Furthermore, synthetic strategies aim to minimize the number of steps and unique reagents required to make multifunctional nanocarriers. The ultimate goal is to synthesize a nanocarrier that is highly specialized but practical and simple to make. Owing to straightforward crystal engineering, metal−organic framework (MOF) nanoparticles are an excellent example to illustrate the idea behind this concept and have the potential to emerge as next-generation drug delivery systems. Here, we highlight examples showing how the combination of the properties of MOFs (e.g., their organic−inorganic hybrid nature, high surface area, and biodegradability) and induced systematic modifications and functionalizations of the MOF’s scaffold itself lead to a nanocarrier with high multifunctional efficiency.
The present work offers an explanation for the variation of the power-law stress exponent, n, with the stress r normalized to the shear modulus G in aluminum alloys. The approach is based on the assumption that the dislocation structure generated with deformation has a fractal nature. It fully explains the evolution of n with r/G even beyond the so-called power law breakdown region. Creep data from commercially pure Al99.8%, Al-3.85%Mg, and ingot AA6061 alloy tested at different temperatures and stresses are used to validate the proposed ideas. Finally, it is also shown that the fractal description of the dislocation structure agrees well with current knowledge.
Defect recognition in CFRP components using various NDT methods within a smart manufacturing process
(2018)
The manufacturing process of carbon fiber reinforced polymer (CFRP) components is gaining a more and more significant role when looking at the increasing amount of CFRPs used in industries today. The monitoring of the manufacturing process and hence the reliability of the manufactured products, is one of the major challenges we need to face in the near future. Common defects which arise during manufacturing process are e.g. porosity and voids which may lead to delaminations during operation and under load. To find irregularities and classify them as possible defects in an early stage of the manufacturing process is of high importance for the safety and reliability of the finished products, as well as of significant impact from an economical point of view. In this study we compare various NDT methods which were applied to similar CFRP laminate samples in order to detect and characterize regions of defective volume. Besides ultrasound, thermography and eddy current, different X-ray methods like radiography, laminography and computed tomography are used to investigate the samples. These methods are compared with the intention to evaluate their capability to reliably detect and characterize defective volume. Beyond the detection and evaluation of defects, we also investigate possibilities to combine various NDT methods within a smart manufacturing process in which the decision which method shall be applied is inherent within the process. Is it possible to design an in-line or at-line testing process which can recognize defects reliably and reduce testing time and costs? This study aims to show up opportunities of designing a smart NDT process synchronized to the production based on the concepts of smart production (Industry 4.0). A set of defective CFRP laminate samples and different NDT methods were used to demonstrate how effective defects are recognized and how communication between interconnected NDT sensors and the manufacturing process could be organized.
In an increasing number of modern steel applications, high-strength structural steel grades are demanded to meet specifications regarding a high load-bearing capacity and a low operating weight. Lightweight design rules enhance the safety requirements, especially for welded joints. Besides a higher cracking risk for high-strength steel welds, the formation of tensile residual stresses might lead to fracture due to overloading or premature failure if not adequately considered. In this study, a stress-strain analysis was conducted at component-related structures from S960QL using digital image correlation while preheating, welding and cooling adjacent to the weld seam. X-ray diffraction analysis of the local residual stresses in the weld seam showed a good comparability with global analyses using either a DIC system or a special testing facility, which allowed in situ measurements of welding loads. By analysing two different seam geometries, it could be shown that lower multi-axial stresses arise if a narrower weld groove is used. Comparative analyses revealed a direct correlation of the local residual stresses in the weld with transverse shrinkage restraint, whereas the residual stress level in the HAZ is significantly affected by the bending restraint of the weld construction and the occurring bending stresses, respectively.
A three-dimensional multi-physics numerical model was developed for the calculation of an appropriate equivalent volumetric heat source and the prediction of the transient thermal cycle during and after fusion welding. Thus the modelling process was separated into two studies. First, the stationary process simulation of full-penetration keyhole laser beam welding of a 15 mm low-alloyed steel thick plate in flat position at a welding speed of 2 m/min and a laser power of 18 kW was performed. A fixed keyhole with a right circular cone shape was used to consider the energy absorbed by the workpiece and to calibrate the model. In the calculation of the weld pool geometry and the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature were taken into account. The obtained local temperature field was then used in a subsequent study as an equivalent heat source for the computation of the transient thermal field during the laser welding process and the cooling stage of the part. The system of partial differential equations, describing the stationary heat transfer and the fluid dynamics, were strongly coupled and solved with the commercial finite element software COMSOL Multiphysics 5.0. The energy input in the transient heat transfer simulation was realised by prescription of the nodes temperature. The prescribed nodes reproduced the calculated local temperature field defining the equivalent volumetric heat source. Their translational motion through the part was modelled by a moving mesh approach. An additional remeshing condition and helper lines were used to avoid highly distorted elements. The positions of the elements of the polygonal mesh were calculated with the Laplace’s smoothing approach. Good correlation between the numerically calculated and the experimentally observed weld bead shapes and transient temperature distributions was found.
Hydrogen-assisted cracking is a critical combination of local microstructure, mechanical load and hydrogen concentration. Welded microstructures of low-alloyed creep-resistant Cr-Mo-V steels show different hydrogen trapping kinetics. This influences the adsorbed hydrogen concentration as well as the diffusion by moderate or strong trapping. A common approach to describe hydrogen traps is by their activation energy that is necessary to release hydrogen from the trap. In the present study, Cr-Mo-V steel T24 (7CrMoVTiB10-10) base material and TIG weld metal were investigated. Electrochemically hydrogen charged specimens
were analyzed by thermal desorption analysis (TDA) with different linear heating rates. The results show two different effects. At first, the microstructure effect on trapping is evident in terms of higher hydrogen concentrations in the weld metal and increased activation energy for hydrogen release. Secondly, it is necessary to monitor the real specimen temperature. A comparison between the adjusted heating rate and the real specimen temperature shows that the calculated activation energy varies by factor two. Thus, the trap character in case of the base material changes to irreversible at decreased temperature. Hence, the effect of the experimental procedure must be considered as well if evaluating TDA results. Finally, realistic temperature assessment is mandatory for calculation of activation energy via TDA.
During Rutherford cable production the wires are plastically deformed and their initially round shape is distorted. Using X-ray absorption tomography we have determined the 3D shape of an unreacted Nb3Sn 11 T dipole Rutherford cable, and of a reacted and impregnated Nb3Sn cable double stack. State-of-theart image processing was applied to correct for tomographic artefacts caused by the large cable aspect ratio, for the segmentation of the individual wires and subelement bundles inside the wires, and for the calculation of the wire cross sectional area and shape variations. The 11 T dipole cable cross section oscillates by 2% with a frequency of 1.24 mm (1/80 of the transposition pitch length of the 40 wire cable). A comparatively stronger cross sectional area variation is observed in the individual wires at the thin edge of the keystoned cable where the wire aspect ratio is largest.
Additively manufactured test specimens made of polyamide 12 (PA 12) by Laser Sintering (LS) as well as of acrylnitril-butadien-styrol (ABS) by Fused Layer Modeling (FLM), were tested with active thermography. For this, two different excitation methods (flash and impulse excitation) were used and compared, regarding the suitability for the detection of constructed and imprinted defects. To increase the quality of the thermograms, data processing methods like thermal signal reconstruction (TSR) and Fourier-Transformation were applied. Furthermore, the long-term stability of the probes towards environmental stress, like UV-radiation, heat, water contact and frost is being investigated in the presented project with artificial weathering tests.
We synthesized and characterized a set of ultrasmall hexagonal-phase NaGdF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles with core diameters of 3.7 ± 0.5 nm. In order to assess passivation effects and the influence of possible core−shell intermixing and to identify optimum particle structures for combined imaging in the visible and near-infrared (vis−NIR: 410−850 nm) and short-wave infrared (SWIR: 1520 nm), NaYF4 shells of varying thicknesses (monolayer to 10 nm) were introduced and the influence of this parameter on the upconversion and downshifting photoluminescence of these particles was studied at different excitation power densities. This included excitation power-dependent emission spectra, slope factors, quantum yields, and excited state decay kinetics. These measurements revealed enhancement factors of the upconversion quantum yield of >10 000 in the low power region and an excitation power density-independent quantum yield of the downshifted emission at 1520 nm between 0.1 and 14%. The optimized shell thickness for combined vis and SWIR imaging was identified as 5 nm. Moreover, lifetimes and quantum yields can be continuously tuned by shell thickness which can be exploited for lifetime multiplexing and encoding. The fact that we did not observe a saturation of the upconversion quantum yield or the excited state decay kinetics with increasing shell thickness is ascribed to a strong intermixing of the active core with the inert shell during the shelling procedure. This indicates the potential of spectroscopic tools to detect cation intermixing.
Two new catalysts (SnNa and SnBi) were prepared from dibutyltin oxide and 2,2′-dihydroxybiphenyl or2,2′dihydroxy(1,1′-binaphtyl). These catalysts enabled rapid polymerizations of L-lactide at 160 or 180 °C in bulk, whereby almost exclusively cyclic polylactides were formed. These polymerizations were free of racemization and yielded pol(L-lactide)s having weight average molecular weights (Mw's) up to 140 000 g mol−1. The Mw's varied little with the Lac/Cat ratio as expected for a ring expansion polymerization (REP). Polymerizations performed in bulk at 140, 120 and 102 °C yielded cyclic polylactides with lower molecular weights. At 102 °C a strong predominance of even-numbered cycles was found with SnNa as catalyst. SnNa can also catalyze alcohol-initiated ROPs yielding linear poly(L-lactide) free of cyclics.
Dye-stained micrometer-sized polymer beads are important tools in the life sciences with applications in biomedical, biochemical, and clinical research. Here, bead-based assays are increasingly used, for example, in DNA sequencing and the detection of autoimmune diseases or pathogenic microorganisms. Moreover, stained beads are employed as calibration tools for fluorescence microscopy and flow cytometry methods with increasing complexity. To address the requirements concerning the relevant fluorescence features, the spectroscopic properties of representative polymer beads with diameters ranging from about 1 to 10 μm stained with varying concentrations of rhodamine 6G were systematically assessed. The observed dependence of the spectral properties, fluorescence decay kinetics, and fluorescence quantum yields on bead size and dye loading concentration is attributed to different fluorescence characteristics of fluorophores located in the particle core and near-surface dye molecules. Supported by the fluorescence anisotropy measurements, the origin of the observed alteration of fluorescence features is ascribed to a combination of excitation energy transfer and polarity-related effects that are especially pronounced at the interface of the bead and the surrounding medium. The results of our studies underline the need to carefully control and optimize all Parameters that can affect the fluorescence properties of the dye-stained beads.
Quantification of impact damages in CFRP and GFRP structures with thermography and ultrasonics
(2018)
The extent of damage caused by impacts in fibre reinforced composites depends on the energy of the impacts, on the velocity and the shape of the impacting body, on the material and structure of the composite and on the geometry of the structure. Here, mainly the thickness of the component is essential. The non-destructive evaluation of these damages can be carried out using both ultrasound and active thermography methods. A comparison of the detection sensitivity of these methods for the different damages is carried out in this paper depending on the fibre composite material used (CFRP and GFRP), the thickness of the material and the impact energy. The NDT methods used after the damage are supplemented by thermographic measurements with high temporal resolution, which were already recorded during the impact.
Solubility data of carbon dioxide (CO2) in the two ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] and 1-butyl-3-methylimidazolium tetrachloroferrate [BMIM][FeCl4] at T = (273.15-413.15) K and pressures up to p = 4.5 MPa are presented. In Addition to the experiments, a literature review was done to compare the new results with published solubility data. The measurements were carried out using an isochoric method which operates in decrements of deltaT = 20 K within the investigated temperature range and at selected four different pressure steps ranging from a pressure p of around 4.5 MPa to around 0.5 MPa. The solubility of CO2 decreases in both ionic liquids with increasing temperatures. Within the p,T-range investigated, CO2 displayed a solubility in [BMIM][BF4] from a mole fraction x = 0.0117 and a corresponding molality m = 0.0526 mol/kg at T = 413.15 K and p = 0.417 MPa up to x = 0.4876 and m = 4.2094 mol/kg at T = 293.15 K and p = 4.349 MPa. The corresponding values for the solubility in [BMIM][FeCl4] start at a mole fraction x = 0.0268 and a corresponding molality m = 0.0818 mol/kg at T = 413.15 K and p = 0.443 MPa and end at x = 0.5126 and m = 3.1216 mol/kg at T = 293.15 K and p = 4.478 MPa. At a constant temperature, CO2 is better soluble in [BMIM][FeCl4] than in [BMIM][BF4] and the mean value of the solubility difference related to mole fraction x over the pressure range investigated amounts to about 4 % at T = 273.15 K and monotonously increases to about 92 % at T = 413.15 K. Henry's law constant as well as derived thermodynamic properties, such as the Gibbs energy of solvation, the enthalpy of solvation, the entropy of solvation, and the heat capacity of solvation, were calculated and discussed regarding the solute-solvent molecular interactions.
Fiber-reinforced concretes (FRCs) offer significant improvements in tensile strength and durability compared to most other concrete mixes.
However, for safe and efficient use of FRC in large structures, anisotropy of fiber orientation needs to be understood and properly controlled. In this project, both cored samples extracted from a FRC slab and FRC samples cast individually in molds were assessed using X-ray computed tomography (CT) and measurements of fiber orientation were extracted from the resulting CT images. These results showed that fibers within the slab were highly anisotropic in orientation while fibers in individually cast samples showed a much more heterogeneous distribution of orientations.
This indicates that fiber orientation is highly dependent on the casting process and suggests that FRC can only be safely and efficiently utilized if anisotropic fiber orientation is properly accounted for during design and optimized casting methods are used during construction.
Water vapor sorption surface areas and sorption energies of untreated
and thermally modified Norway spruce [Picea abies (L.) Karst.], sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelcior L.) were investigated by means of dynamic vapor sorption (DVS) measurements and excess surface work (ESW) evaluation method, respectively. Adsorption and desorption experiments in the hygroscopic range and desorption tests from water saturation were conducted.
Thermodynamically, ESW is the sum of the surface free energy and the isothermal isobaric work of sorption. From the amount adsorbed in the first Minimum a specific surface area similar to the BET surface area can be obtained. The results show that untreated spruce has a significantly higher specific water vapor Sorption surface and sorption energy compared to both hardwoods maple and ash. Thermal modification of the woods leads to a significant reduction of water vapor Sorption surface and sorption energy. The determined surface area and energy are higher in desorption direction than in adsorption direction, whereby the highest values in Desorption direction from water saturation, especially for maple and ash, were obtained.
The surface areas calculated by means of the ESW method are similar to the surface areas calculated by means of the BET method, particularly in adsorption direction.
One of the main factors affecting the use of lasers in the industry for welding thick structures is the process accompanying solidification cracks. These cracks mostly occurring along the welding direction in the welding center, and strongly affect the safety of the welded components. In the present study, to obtain a better understanding of the relation between the weld pool geometry, the stress distribution and the solidification cracking, a three-dimensional computational fluid dynamic (CFD) model was combined with a thermo-mechanical model. The CFD model was employed to analyze the flow of the molten metal in the weld pool during the laser beam welding process. The weld pool geometry estimated from the CFD model was used as a heat source in the thermal model to calculate the temperature field and the stress development and distributions. The CFD results showed a bulging region in the middle depth of the weld and two narrowing areas separating the bulging region from the top and bottom surface. The thermo-mechanical simulations showed a concentration of tension stresses, transversally and vertically, directly after the solidification during cooling in the region of the solidification cracking.
We present an in situ triple coupling of synchrotron X-ray diffraction with Raman spectroscopy, and thermography to study milling reactions in real time. This combination of methods allows a correlation of the structural evolution with temperature information. The temperature information is crucial for understanding both the thermodynamics and reaction kinetics. The reaction mechanisms of three prototypical mechanochemical syntheses, a cocrystal formation, a C@C bond formation (Knoevenagel condensation), and the formation
of a manganese-phosphonate, were elucidated. Trends in the temperature development during milling are identified. The heat of reaction and latent heat of crystallization of the product contribute to the overall temperature increase. A decrease in temperature occurs via release of, for example, water as a byproduct.
Solid and liquid intermediates are detected. The influence of the mechanical impact could be separated from temperature effects caused by the reaction.
The knowledge of the temperature-induced changes of the superconductor volume and of the thermomechanical behavior of the different coil and tooling materials is required for predicting the coil geometry and the stress distribution in the coil after the Nb3Sn reaction heat treatment. In this paper, we have measured the Young’s and shear moduli of the HL-LHC 11 T Nb3Sn dipole magnet coil and reaction tool constituents during in situ heat cycles with the dynamic resonance method. The thermal expansion behaviors of the coil components and of a free standing Nb3Sn wire were compared based on dilation experiments.
Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, onedimensional charge carrier mobilities along the columnar axes, making them prominent model systems for functional, self-organized matter.We show by high-resolution optical birefringence and synchrotron-based x-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly propagates layer by layer towards the pore center in the supercooled domain of the bulk isotropic-columnar transition and thus allows one to switch on and off reversibly single, nanosized rings through small temperature variations. By establishing a Gibbs free energy phase diagram we trace the phase transition quantization to the discreteness of the layers’ excess bend deformation energies in comparison to the thermal energy, even for this near room-temperature system.
Monte Carlo simulations yielding spatially resolved nematic order parameters, density maps, and bondorientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.
A series of Ca-based coordination polymers were prepared mechanochemically by milling Ca(OH)2 with phthalic acid (H2oBDC), isophthalic acid (H2mBDC), and terephthalic acid (H2pBDC). The hydrated compounds [Ca(oBDC)(H2O)], [Ca(mBDC)(H2O)3.4], and [Ca(pBDC)(H2O)3] were prepared for the first time via mechanochemical routes. The refined structures were validated by extended X-ray absorption data. The new dehydrated compound [Ca(oBDC)] (1-H2O), obtained after the thermal post-treatment of 1 in a reversible phase transition process, was determined ab initio based on the powder X-ray diffraction (PXRD) data. The materials were thoroughly characterized using elemental analysis, thermal analysis, and spectroscopic methods: magic-angle spinning NMR and attenuated total reflection-infrared spectroscopy. The specific surface areas and sorption properties of the hydrated and dehydrated samples were determined using the isotherms of gas sorption and dynamic vapor sorption measurements.
A glass of the composition 37BaO·16CaO·47SiO2 wt% produced on an industrial scale is crystallized at 970 °C for times ranging from 15 min to 2 h. The crystallization at the immediate surface as well as the crystal growth into the bulk are analyzed using scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) as well as X-ray diffraction in the Θ–2Θ setup (XRD). The immediate surface shows the oriented nucleation of walstromite as well as the formation of wollastonite and an unknown phase of the composition BaCaSi3O8. All three phases also grow into the bulk where walstromite ultimately dominates the kinetic selection and grows throughout the bulk due to a lack of bulk nucleation. Walstromite shows systematic orientation changes as well as twinning during growth. A critical analysis of the XRD-patterns acquired from various crystallized samples indicates that their evaluation is problematic and that phases detected by XRD in this system should be verified by another method such as EDXS.
In present chapter, the potential usage of peroxy-fuels (usually known as organic peroxides) either in technically pure or in a blended form in engine combustion processes are explored. Although as additives (in small quantities <5% to conventional fuels, e.g., diesel, gasoline) peroxy-fuels are well known for many years their commercial applications as a main or primary fuel are not investigated in detail as such except a few. Their thermal instability and energy density demand great care during processing, which restricts their commercial exploitation. However, once the issues with safety are resolved they can be much more advantageously employed than conventional fuels. Some of these advantages are significant amount of fuel saving, reduction in amount of inducted air, or even the complete absence of air, i.e., anaerobic combustion, smaller volume of combustion (chamber), oxygenated fuel quality, and low emissions. An idea to develop the components of an engine operating solely on peroxy-fuels is also introduced. The engine concept is based on single and multiple injectors in a cylinder with special material coating to ensure a temperature-controlled processing.
An approach to develop an arc sensor for gap width estimation during automated NG-GMAW with a weaving electrode motion is introduced by combining arc sensor readings with optical measurements of the groove shape to allow precise analyses of the process. The two test specimen welded for this study were designed to feature a variable groove geometry in order to maximize efficiency of the conducted experimental efforts, resulting in 1696 individual weaving cycle records with associated arc sensor measurements, process parameters and groove shape information. Gap width was varied from 18 mm to 25 mm and wire feed rates in the range of 9 m/min to 13 m/min were used in the course of this study. Artificial neural networks were applied as a modelling tool to derive an arc sensor for estimation of gap width suitable for online process control that can adapt to changes in process parameters as well as changes in the weaving motion of the electrode. Wire feed rate, weaving current, sidewall dwell currents and angles were defined as inputs to calculate the gap width. The evaluation of the proposed arc sensor model shows very good estimation capabilities for parameters sufficiently covered during the experiments.
The copper alloyed stainless steel 1.4542 (X5CrNiCuNb16-4) is used in different areas due to its good mechanical properties and corrosion resistance. Strength and corrosion resistance can be adjusted by the heat treatment, which is of importance for the application of this alloy. The mechanical properties (strength and hardness) are attributed to the dispersive precipitation of the copper rich ε–Phase. The additional precipitation of chromium carbides can reduce the corrosion resistance. Different ageing states were produced to investigate the precipitation behaviour with various methods. Furthermore, the influence of cold-rolling on the precipitation behaviour was studied in comparison to a solution annealed state without deformation. The microstructure was studied by SEM and the variations of hardness and magnetic proportion were characterised. The electrochemical potentiodynamic reactivation
(EPR) was used to determine the corrosion resistance and detect chromium depletion in all heattreated states. The results show that a work hardening accelerates the precipitation rate, while ageing at 600 °C reduces the corrosion resistance due to chromium depletion.
We investigated the possibility of minimizing tensile matrix residual stresses in age hardenable aluminum alloy metal matrix composites without detrimentally affect their mechanical properties (such as yield strength).
Specifically, we performed thermal treatments at different temperatures and times in an age-hardenable aluminum matrix composite 2014Al-15vol%Al2O3. Using X-ray synchrotron radiation diffraction and mechanical tests, we show that below a certain treatment temperature (250 °C) it is possible to identify an appropriate thermal treatment capable of relaxing residual stress in this composite while even increasing its yield strength, with respect to the as processed conditions.
The indication-oriented Dental Bone Graft Substitutes (DBGS) selection, the correct bone defects classification, and appropriate treatment planning are very crucial for obtaining successful clinical results. However, hydrophilic, viscoelastic, and physicochemical properties’ influence on the DBGS regenerative potential has poorly been studied. For that reason, we investigated the dimensional changes and molecular mobility by Dynamic Mechanical Analysis (DMA) of xenograft (cerabone®), synthetic (maxresorb®), and allograft (maxgraft®, Puros®) blocks in a wet and dry state. While no significant differences could be seen in dry state, cerabone® and maxresorb® blocks showed a slight height decrease in wet state, whereas both maxgraft® and Puros® had an almost identical height increase. In addition, cerabone® and maxresorb® blocks remained highly rigid and their damping behaviour was not influenced by the water. On the other hand, both maxgraft® and Puros® had a strong increase in their molecular mobility with different damping behaviour profiles during the wet state. A high-speed microscopical imaging system was used to analyze the hydrophilicity in several naturally derived (cerabone®, Bio-Oss®, NuOss®, SIC® nature graft) and synthetic DBGS granules (maxresorb®, BoneCeramic®, NanoBone®, Ceros®). The highest level of hydrophilicity was detected in cerabone® and maxresorb®, while Bio-Oss® and BoneCeramic® had the lowest level of hydrophilicity among both naturally derived and synthetic DBGS groups. Deviations among the DBGS were also addressed via physicochemical differences recorded by Micro Computed Tomography, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, X-ray powder Diffractometry, and Thermogravimetric Analysis. Such DBGS variations could influence the volume stability at the grafting site, handling as well as the speed of vascularization and bone regeneration. Therefore, this study initiates a new insight into the DBGS differences and their importance for successful clinical results.
In recent years, laser beam welding has found wide applications in many industrial fields. Solidification cracks are one of the most frequently encountered welding defects that hinder obtaining a safe weld joint. Decades of research have shown that one of the main causes of such cracks are the strain and the strain rate. Obtaining meaningful measurements of these strains has always been a major challenge for scientists, because of the specific environment of the measurement range and the many obstacles, as well as the high temperature and the plasma plume. In this study, a special experimental setup with a high-speed camera was employed to measure the strain during the welding process. The hot cracking susceptibility was investigated for 1.4301 stainless steel, and the critical strain required for solidification crack formation was locally and globally determined.