Nanocomposite structures of polypyrrole derivatives and poly (acrylonitrile‐co‐itaconic acid) produced by in situ polymerization as carbon nanofiber precursor

This study aimed to produce nanoparticles of poly (acrylonitrile‐co‐itaconic acid) (P (AN‐co‐IA)) containing conjugated polymers of pyrrole, N‐Methylpyrrole, 2,5‐dimethylpyrrole, and 1‐(Triisopropylsilyl)pyrrole which were synthesized by emulsion polymerization. Nanocomposite structures of P (AN‐co‐IA)/polypyrrole and polymer of pyrrole derivatives were produced via in situ polymerization, and the nanoparticle formation were followed by morphologic and ultraviolet‐visible (UV‐Vis) spectroscopic methods. Characterizations were made by Fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) and Raman spectroscopy. Atomic force microscopy (AFM) was used for investigating the surface characteristics of the nanoparticles. Characterization results revealed that nanoparticles containing conjugated polymers had rougher surface than P (AN‐co‐IA) nanoparticles. It was also observed that the nanoparticles were well‐distributed although having some agglomerates. Moreover, depending on the type of monomer of conjugated polymer, the shape and size of the produced nanoparticles differed by conjunction with their polymerization rate. These findings can be used as a startup information for production of carbon nanofibers (CNFs) with desired properties after oxidation and carbonization, and as a high‐performance and cost‐effective flame and heat‐resistant material (oxidized copolymers of polyacrylonitrile nanofiber).     

Synthesis and characterization of poly (acrylonitrile‐co‐acrylic acid) as precursor of carbon nanofibers

Synthesis of a co‐polymer of polyacrylonitrile (PAN) producing a carbon nanofiber out of PAN and co‐polymer of PAN and comparison between these products were examined. Free‐radical solution copolymerization of acrylonitrile (AN) with acrylic acid (AA) was studied. In this perspective, AA, and AN were used as a precursor for polymerization reactions; then copolymers were synthesized by using ammonium persulfate (APS) as an oxidant and carried in water/dimethylformamide (DMF) mixture. These polymers were used to obtain corresponding electrospun nanofibers. Synthesized P(AN‐co‐AA) was investigated by Fourier transform infrared spectroscopy‐attenuated total reflection (FTIR‐ATR) spectroscopy, and characteristic peaks for AN unit, AA were achieved. Thermal behavior was examined by using differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), and results indicated that addition of monomers to AN unit reduced the Tg value of homopolymer PAN compared to P(AN‐co‐AA), which provides improvement to the cyclization and the formation of a thermally stable aromatic ladder polymer chain formation. In order to prevent the shrinkage and maintain the molecular orientation on nanofiber webs during stabilization, tension was applied to the samples, and thermal oxidation varies at 200–300°C for different duration of times. Surface morphology of the fibers was observed with scanning electron microscope (SEM), and average nanofiber diameter was found 550 nm, and after carbonization it was reduced to 320 nm for homopolymer PAN, and for poly(AN‐co‐AA) average nanofiber diameter was found as 220 nm and reduced to 130 nm, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Simulation von Einspiel- und Rißbildungsvorgängen in Faserverbundwerkstoffen mit metallischer Matrix

Übersicht Faserverbundstrukturen mit metallischer Matrix sind oft Belastungen ausgesetzt, die zu einer Plastifizierung der Matrix führen. Wird die Struktur zudem zyklisch belastet, so kann sie als Folge fortschreitender Plastifizierung versagen. Vor diesem Hintergrund ist besonders die Einspielneigung und die Rißbildung der Struktur von großem Interesse. In der vorliegenden Arbeit werden daher verschiedene Faser/Matrix-Kombinationen in einer numerischen Simulation untersucht. Der Zugang erfolgt dabei über die Finite-Element-Methode.

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Study of shakedown and crack initiation in fibre composites with metallic matrices

Summary Composite materials with a metal matrix are often subjected to loads which lead to plastification of the matrix. If, in addition, the structure undergoes cyclical loading, it may fail as a result of the continuing plastification. Under these circumstances, the shakedown and the crack growth of the structure are of special interest. Hence, in the present work various fibre/matrix combinations have been investigated by numerical simulation using the finite element method.

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Herrn Prof. Dr.-Ing. E. h. Th. Lehmann zum 70. Geburtstag am 10. August 1990 gewidmet.     

Calculus of functors,operad formality,and rational homology of embedding spaces

Let M be a smooth manifold and V a Euclidean space. Let [`(\textEmb)] \overline{{{\text{Emb}}}} (M,V) be the homotopy fiber of the map Emb(M,V) → Imm(M,V). This paper is about the rational homology of [`(\textEmb)] \overline{{{\text{Emb}}}} (M,V). We study it by applying embedding calculus and orthogonal calculus to the bifunctor (M,V)↦ HQ ∧ [`(\textEmb)] \overline{{{\text{Emb}}}} (M,V)₊. Our main theorem states that if

Numerical Determination of Damping in Metal Matrix Composites

Damping in metal matrix composites is mainly caused by inelastic matrix deformation induced by the great difference in the mechanical properties of the single constituents of the materials. In this study, the finite-element method in combination with a highly accurate material model is employed to examine the effects of both the fiber volume fraction and the external loading amplitude on the energy dissipation process in an Al/SiC composite under a cyclic mechanical load.     

Numerische Untersuchung des elastisch-plastischen Verhaltens eines Fadenverbundwerkstoffes mit metallischer Matrix Eine Fallstudie

Übersicht Die Fehlervorhersage eines einachsigen Fadenverbundwerkstoffes mit metallischer Matrix erfordert die Kenntnis des nichtlinearen elastisch-plastischen Verhaltens in mikroskopischer Abmessung. Als Fallstudie wurde ein spezieller Verbundwerkstoff mit einem FEM-Programm untersucht. Im plastischen Bereich wurde das klassische, v. Mises Potential' mit dem neuen Übergangsfließpotential unter Berücksichtigung der plastischen Volumendehnung verglichen. Unter transversaler Normalbelastung zeigte der Verbund deutliche Unterschiede in der Zunahme und der Ausdehnung der lokalen plastischen Zonen. Alle kritischen Verformungsstadien wurden von dem Übergangsfließpotential bei geringerer Belastung erreicht.

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Numerical investigation of the elastic-plastic behaviour of a fibre-reinforced composite with a metallic matrix

Summary Failure prediction of unidirectional fibre-reinforced composite with a metallic matrix needs knowledge about the nonlinear elastic-plastic behaviour in a microscopic scale. A specific composite was investigated using a FEM-program as a case study. In the plastic range the classical v. Mises Potential was compared with the new Transition Flow Potential, taking into account the plastic volume dilatation. Subjected to transverse normal loading the composite showed evident differences in the increase and the spread of locally plastic regions. All critical deformation states were reached by the Transition Flow Potential at lower loading.

     

Modelling of the micromechanical behaviour of unidirectional fibre-reinforced ceramics by the example of SiC/SiC

Summary The modelling of the mechanical properties of a substructure, based on the properties of the individual phases and their interactions, is presented on the example of the unidirectional SiC fibre-reinforced SiC composite. The substructure is selected in such a way that the total structure can be modelled from a wide number of substructures. The numerical evaluation of the model is accomplished by means of the finite element method (FEM). Finally, in numerical simulations of a particular example, the statistically verified events of damage in the substructure are described.