bluuebunny/crossref_metadata_2025 huggingface dataset:
Einfluß der Oberflächenbeschaffenheit auf die Schwingfestigkeit von Aluminium‐Druckguß
Authors: Kurth Bernhard , Bomas Hubert. , Mayr Peter
Published: December 2004

Oberflächenbearbeitungsverfahren wie‐das Fräsen oder Kugelstrahlen führen zu Veränderungen im Randbereich eines Werkstoffs, die durch die Änderungen des Eigenspannungszustandes, der Härte und der Oberflächenrauhigkeit beschrieben werden können. Ferner besteht die Möglichkeit, daß zusätzliche Oberflächendefekte eingebracht werden. Im vorliegenden Aufsatz wird der Einfluß dieser Randschichtveränderungen auf das Schwingfestigkeitsverhalten der Aluminium‐Druckgußlegierung GD‐AlSi8Cu3 vorgestellt. Dazu wurden Wöhlerkurven für vier Oberflächenzustände aufgestellt, die durch Fräsen, Kugelstrahlen und eine kombinierte Behandlung erzeugt wurden. Die Verbesserung der Dauerfestigkeit durch Kurgelstrahlen wird auch für diesen Werkstoff bestätigt. Der zusätzliche Einfluß einer Mittelspannung wird bestimmt. Untersuchungen der Ermüdungsbruchflächen zeigen, daß Poren und Lunker, aber auch Oberflächendefekte, die durch das Kugelstrahlen erzeugt wurden, ursächlich für Ermüdungsrißbildung sind.
Einfluß von Korngrenzenöffnungen auf die Bruchvorgänge geschweißter AlMgSi‐Werkstoffe
Authors: Winkler R. , Schwellinger P. , Hornbogen E.
Published: December 2004

Fraktographische Untersuchungen an Profilen der Legierung AlMgSi0,7 (AA6005A), geschweißt mit dem Zusatzwerkstoff SG‐AlMg5, haben gezeigt, daß die in der Wärmeeinflußzone vorhandenen Korngrenzenöffnungen das Bruchverhalten beeinflussen. Durch gezielt eingebrachte Ermüdungszyklen ist es gelungen, den zeitlichen Ablauf des Rißfortschritts auf der Bruchfläche abzubilden. Korngrenzenöffnungen verhalten sich nicht wie scharfe Anrisse im Sinne der technischen Bruchmechanik. Erst nach einer unterschiedlich großen Zahl von Lastwechseln können sich Ermüdungsrisse an Korngrenzenöffnungen bilden. Ein nach Norm zulässiger Kantenversatz kann im Vergleich zu Korngrenzenöffnungen ein wirksamerer Rißauslöser sein.
Betrachtungen über mikrobiell induzierte Korrosionsvorgänge und deren biologischen Hintergrund
Authors: Gümpel P. , Kreikenbohm R. , Neumann K.
Published: December 2004

An einem Kühlwassersystem kam es aufgrund von mikrobiell induzierter Korrosion (MIC) zu einem Schadensfall. Der bräunliche Belag, der sich in den Rohren befand, wurde nach aeroben und anaeroben Bakterien untersucht, die zu unterschiedlichen Stoffwechseltypen gehören. Betrachtet man die geringe Zufuhr an organischen Substanzen können die Kühlwasserrohre als „magerer”︁ Standort bezeichnet werden. Trotzdem kommt es unter diesen Bedingungen im Biofilm zur Entwicklung einer vielfältigen Mischpopulation von aeroben, denitrifizierenden und anaeroben Bakterien, die gemeinsam einen Biofilm auf der Rohroberfläche ausbilden. Bakterien können durch ihre Stoffwechselvorgänge einen Beitrag zu den chemischen Reaktionen leisten, die dann zur Entstehung der klassischen Korrosionsarten führen. Die Populationsdichten sind allerdings noch nicht bekannt. Deshalb ist es noch nicht möglich die Größe des Einflusses auf die Korrosion abzuschätzen. Die Studie gibt einen ersten Einblick in ein komplexes System aus anorganischen Elementen, organischen Substanzen, den darin lebenden Organismen und den Wechselwirkungen untereinander im Biofilm.
Beurteilung des Haftvermögens von PVD‐Hartstoffschichten mittels tribologischer Kurzzeit‐Tests
Authors: zu Köcker G. Meier , Hudl C.
Published: December 2004

Mit zunehmender Bedeutung der Hartstoffbeschichtungen wächst das Interesse an Beurteilungsmöglichkeitenihres Haftvermögens durch wenig aufwendige, rasch durchführbare und reproduzierbare Testmethoden. Zwar gibt es inzwischen verschiedene Standard‐Prüfverfahren, doch erweist sich die Übertragbarkeit der Ergebnisse auf den späteren Anwendungsfall oftmals als unzureichend, so daß Aussagen über das funktionelle Verhalten für den späteren praktischen Einsatz kaum möglich sind. Zur Beurteilung des Haftvermögens von PVD‐Hartstoffschichten wurden verschiedene Hartstoffschichten mit Hilfe tribologischer Kurzzeit‐Tests untersucht. Die tribologischen Kurzzeit‐Tests wurden unter Gleitreibungsbedingungen durchgeführt und die Versuchsparameter so gewählt, daß schnell qualitative Aussagen über das Haftvermögen der Hartstoffschichten möglich waren. Zur Überprüfung der mittels tribologischer Kurzzeit‐Tests gewonnenen Erkenntnisse wurden Modellverschleißuntersuchungen an Originalwerkzeugen und reale Zerspanversuche durchgeführt.

Die Ergebnisse der tribologischen Kurzzeit‐Testszeigen eine sehr gute qualitative Übereinstimmung mit den Zerspanuntersuchungen. So schneiden die untersuchten TiN und (Ti, Al)N‐Schichten, die bei den tribologischen Kurzzeit‐Tests ein schlechtes oder mäßiges Haftvermögen zeigten, auch bei den Zerspanuntersuchungen schlecht ab. Entsprechendes gilt für Schichten mit guter Haftung, die bei tribologischen Tests und Zerspanuntersuchungen übereinstimmend deutlich besser abschnitten. Demnach erscheint die tribologische Kurzzeit‐Prüfung eine interessante Möglichkeit zu sein, das Haftungsvermögen von PVD‐Schichten auf schnellem und kostengünstigem Wege qualitativ zu beurteilen.
Bio‐inerte Implantatkeramiken Teil III. Zur pulvertechnologischen Verdichtung nanoskaliger Feinstpulver aus dem Al2O3‐SiO2‐TiO2‐System
Authors: Khalil T. K. K. , Müller U. , Ondracekd̊ G.
Published: December 2004

Beschrieben wird die Charakterisierung und Verdichtung von verschiedenen Zusammensetzungen nanoskaliger Pulver aus dem Al2O3‐SiO2‐TiO2‐System. Die über das Hydrolyseverfahren und/oder Sol‐Gel‐Verfahren dargestellten Pulver werden nach chemischer Zusammensetzung und Morphologie, spezifischen Oberflächenwerten, Schütt‐, Klopf‐, Preßlings‐ und Sinterlingsdichten charakterisiert, der Einfluß der Pulvertrocknung und ‐kalzination wird gesondert ermittelt.

Es ergibt sich

daß der Trockenprozeß keinen verdichtungsrelevanten Einfluß hat

daß die Kalzination bie 1273 K/3 h zu restfeuchtefreien, agglomerierten Pulvern führt

daß die spezifischen Oberflächen der Pulver ebenso wie ihre Schütt‐, Klopf‐ und Preßlingsdichten mit steigendem SiO2‐Anteil geringer, mit steigendem Al2O3‐ und/oder TiO2‐Anteil dagegen größer werden und

daß die Agglomeratbildung die Verdichtbarkeit nicht nachteilig beeinflußt, wohl aber bevorzugte Konzentrationsbereiche für die Herstellung hochdichter, rißfreier Sinterlinge existieren.
Hartstoffauflösung und Gefügeausbildung bei der konvektionsarmen Erzeugung von Hartstoff‐Dispersionsschichten auf Stahl mittels Laserstrahlung
Authors: Fischer D. , Luft A. , Löschau W.
Published: December 2004

Mit dem Ziel, harte und verschleißfeste Dispersionsschichten zu erzeugen, wurden in die Oberfläche von Stahlproben grobkörnige TiC‐ und TiB2‐Partikel nach einem zweistufigen Prozeß mit Hilfe eines CO2‐Leistungslasers eingeschmolzen. Die Laserbehandlung erfolgte derart, daß eine Schmelzbadkonvektion weitgehend unterdrückt werden konnte. Der Einfluß des Kohlenstoffgehaltes im Stahl sowie der Art und der Gehaltes von metallischen Zusätzen und Hartstoffen in der Vorbeschichtung auf die Hartstoffauflösung und die Ausbildung der Schichtgefüge wurde mittels Lichtmikroskopie, Rasterelektronenmikroskopie und Röngenmikroanalyse untersucht. Außerdem wurden zur Schichtcharakterisierung Härtemessungen durchgeführt.
Einfluß von Sauerstoffzusätzen beim Gasnitrieren auf den strukturellen Aufbau von Nitrierschichten
Authors: Spies H.‐J. , Schaaf P. , Vogt F.
Published: December 2004

Die Wirkung kontrollierter sauerstoffhaltiger Zusätze beim Gasnitrieren von Stählen auf den strukturellen Aufbau der Nitrierschichten und den Ablauf der Nitrierreaktion unter technischen Bedingungen wurde mit metallkundlichen Untersuchungsmethoden unter Einbeziehung der Mössbauer Spektroskopie verfolgt.

Die Ergebnisse der durchgeführten Untersuchungen zeigen, daß Sauerstoffzusätze unterhalb der Oxidationsgrenze des reinen Eisens das Nitrierverhalten unlegierter Stähle etwas verbessern können. Weiter konnte gezeigt werden, daß bei legierten Stählen, die schon bei Chromgehalten ab 3% bei der konventionellen Gasnitrierung zur Passivierung neigen, die Nitrierung durch einen Sauerstoffzusatz erheblich verbessert werden kann. Die auf diesen Stählen vorhandenen Passivschichten werden beim Oxinitrieren durch eine äußere Oxidation zerstört. Diese äußere Oxidation und die innere Nitrierung laufen in der Anfangsphase des Oxinitrierens parallel ab.
Protamines in the internally fertilizing neobatrachian frog Eleutherodactylus coqui
Authors: Kasinsky Harold E. , Frehlick Lindsay J. , (Harvey) Su Hua Wei , Ausio Juan
Published: December 2004

The internally fertilizing primitive frog Ascaphus truei (family Ascaphidae) from the Pacific Northwest is the only frog with an intromittent organ. The more advanced neobatrachian frog Eleutherodactylus coqui (family Leptodactylidae) from Puerto Rico has secondarily acquired internal fertilization but mates by cloacal apposition. Nonetheless, both frogs have introsperm with an elongated head containing highly condensed chromatin. Characterization of sperm nuclear basic proteins (SNBPs) in E. coqui by acid‐urea polyacrylamide gel electrophoresis indicates that, as in A. truei, testes from a single animal contain several protamines. Amino acid analysis indicates a composition for the most rapidly moving protamine of each species as follows: in E. coqui, ARG (35.6 mol %) + LYS (3.8 mol %) + HIS (7.6 mol %) = 47 mol % total basic residues and in A. truei, ARG (42.1 mol %) + LYS (11.1 mol %) = 53.2 mol % total basic residues. Transmission electron microscopy shows that E. coqui introsperm, like those in A. truei, are elongate with highly condensed chromatin. However, E. coqui introsperm lacks an axial perforatorium that extends into an endonuclear canal. These morphological features are plesiomorphic (primitive) and shared by A. truei with urodeles and basal amniotes (Jamieson et al. (1993) Herpetologica 49:52–65). In E. coqui introsperm, the nucleoprotein complex has a cross‐sectional axis of 420 + 20 Å and shows a knobby chromatin structural organization in TEM. The presence of arginine‐enriched protamines in both a basal anuran like the ascaphid A. truei and a more advanced neobatrachian like the leptodactylid E. coqui supports the hypothesis that internal fertilization acts as a constraint on the range of SNBP diversity in animals. Mol. Reprod. Dev. 70: 373–381, 2005. © 2005 Wiley‐Liss, Inc.
Identification of differentially expressed genes in murine embryos at the blastocyst stage using annealing control primer system
Authors: Cui Xiang‐Shun , Shin Mi‐Ra , Lee Kyung‐Ah , Kim Nam‐Hyung
Published: December 2004

The identification of embryo‐specific genes would provide insights into early embryonic development. However, the current methods employed to identify the genes that are expressed at a specific developmental stage are labor intensive and suffer from high rates of false positives. Here we employed a new and accurate reverse transcription‐polymerase chain reaction (RT‐PCR) method that involves annealing control primers (ACPs) to identify the genes that are specifically or prominently expressed in mouse blastocysts compared to 4‐cell stage embryos. Using 120 ACPs, we identified and sequenced 74 of these differentially expressed genes (DEGs). Basic Local Alignment Search Tool (BLAST) searches revealed that 53 were known genes, 9 encoded ribosomal proteins, and 12 were unknown genes. Of the known genes, 14 were selected and further characterized using real‐time quantitative PCR to assess their stage‐specific expression in mouse embryos. This analysis suggests that the ACP system is a very good method for the identification of stage‐specific genes in small numbers of mouse embryos. Further analysis of the differentially expressed blastocyst genes we have identified will provide insights into the molecular basis of preimplantation development. Mol. Reprod. Dev. 70: 278–287, 2005. © 2005 Wiley‐Liss, Inc.
On Kuhn's Hungarian Method—A tribute from Hungary
Authors: Frank András
Published: December 2004

Harold W. Kuhn, in his celebrated paper entitled “The Hungarian Method for the assignment problem” [Naval Res Logist Quart 2 (1955), 83–97] described an algorithm for constructing a maximum weight perfect matching in a bipartite graph. In his delightful reminescences [“On the origin of the Hungarian method,” History of mathematical programming—a collection of personal reminiscences, J.K. Lenstra, A.H.G. Rinnooy Kan, and A. Schrijver (Editors), CWI, Amsterdam and North‐Holland, Amsterdam, 1991, pp. 77–81], Kuhn explained how the works (from 1931) of two Hungarian mathematicians, D. König and E. Egerváry, had contributed to the invention of his algorithm, the reason why he named it the Hungarian Method. (For citations from Kuhn's account as well as for other invaluable historical notes on the subject, see A. Schrijver's monumental book [Combinatorial optimization: Polyhedra and efficiency, Algorithms and Combinatories 24, Springer, New York, 2003].) In this note I wish to pay tribute to Professor H.W. Kuhn by exhibiting the exact relationship between his Hungarian Method and the achievements of König and Egerváry, and by outlining the fundamental influence of his algorithm on Combinatorial Optimization where it became the prototype of a great number of algorithms in areas such as network flows, matroids, and matching theory. And finally, as a Hungarian, I would also like to illustrate that not only did Kuhn make use of ideas of Hungarian mathematicians, but his extremely elegant method has had a great impact on the work of a next generation of Hungarian researchers. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2005.
On Preconditioners for the Borsuk Existence Test
Authors: Frommer Andreas , Lang Bruno
Published: December 2004

Existence or fixed point theorems, combined with interval analytic methods, provide a means to computationally prove the existence of a zero of a nonlinear system in a given interval vector. One such test is based on Borsuk's existence theorem. We discuss preconditioning techniques that are aimed at improving the effectiveness of this test. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isoparametric finite element approximation of the flow in magnetic fluid rotary shaft seals
Authors: Mitkova Teodora , Tobiska Lutz
Published: December 2004

The hydrodynamic behaviour of the magnetic liquid in a magnetic fluid rotary shaft seal can be described by a coupled system of nonlinear partial differential equations. A decoupling numerical solving strategy is proposed and applied to determine the flow in a magnetic fluid seal. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Turbulent Flow Through a Straight Square Channel
Authors: Shalaby Hemdan , Pachler Klaus , Wozniak Klaus , Wozniak Günter
Published: December 2004

Large Eddy Simulation (LES) of an incompressible fully developed square channel flow is described in some detail. Computations were performed for a low Reynolds number of 5000, based on the bulk velocity and the hydraulic diameter of the channel. Prandtl's secondary motion calculated by LES shows satisfying agreement with Direct Numerical Simulation (DNS) results of the literature. Additionally, the flow at a high Reynolds number of 50,000 has been studied. The numerical results of high Reynolds numbers reveal that the mechanism driving the corner secondary flows are similar to the low Reynolds number situation. The difference of the mean secondary velocity of high Reynolds number LES and low Reynolds number DNS is approximately 17%. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New linear spring stiffness definition for displacement analysis of cracked beam elements
Authors: Skrinar Matjaž , Pliberšek Tomaž
Published: December 2004

The paper describes the reasons for the derivation of a new definition of a rotational spring that can be utilised in the simplified computational model for the computation of transverse displacements of cracked beam structures due to transverse load. This definition plays an extremely important role in the inverse identification of cracks. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Factorized solution of the Lyapunov equation by using the hierarchical matrix arithmetic
Authors: Baur Ulrike , Benner Peter
Published: December 2004

We investigate the solution of the Lyapunov equation with the matrix sign function method. In order to obtain the factorized solution we use a partitioned Newton iteration, where one part of the iteration uses formatted arithmetic for the hierarchical matrix format while the other part converges to an approximate full‐rank factor of the solution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zur Berechnung von verlässlichen Außen‐ und Inneneinschließungen bei parameterabhängigen linearen Gleichungssystemen
Authors: Krämer Walter , Popova Evgenija D.
Published: December 2004

Es wird ein selbstverifizierendes Verfahren zur Berechnung von Innen‐ und Außeneinschließungen der Lösungsmenge eines parameterabhängigen linearen Gleichungssystems bei affin‐linearer Parameterabh ängigkeit besprochen. Entsprechende open‐source‐Software wird online zur Verfügung gestellt. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure Preserving Reduction of Large Second Order Models by Moment Matching
Authors: Lohmann Boris , Salimbahrami Behnam
Published: December 2004

A new approach for the reduction of large‐scale second order systems is presented, resulting in a system of second order structure. We first reduce the equivalent state space model using Krylov subspace methods and then convert the reduced model back into the second order type representation of the original model. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stopping Criterion in Order Reduction of Large Scale Systems Using Krylov Subspace Methods
Authors: Salimbahrami Behnam , Lohmann Boris
Published: December 2004

We show that order reduction by a two‐sided Krylov subspace method is equivalent to an approximate TBR in the sense of Galerkin type conditions. The Hankel Singular Values of the original system are thereby approximated by the Hankel singular values of the Krylov reduced model which are used as a stopping criterion to find a suitable order of the reduced model. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized Alternating Direction Implicit Method for Projected Generalized Lyapunov Equations
Authors: Stykel Tatjana
Published: December 2004

We generalize an alternating direction implicit method for projected generalized Lyapunov equations. Low rank versions of this method is also presented that can be used to compute a low rank approximation of the solution of Lyapunov equations with symmetric, positive semidefinite right‐hand side. Numerical example is given. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Positively invariant cones of dynamical systems under Runge‐Kutta and Rosenbrock‐type discretization
Authors: Horváth Zoltán
Published: December 2004

In this paper we consider positively invariant cones of finite dimensional dynamical systems and study conditions on the time step‐size that guarantee the discrete positive invariance of these cones under Runge‐Kutta and Rosenbrock‐type methods. We conclude quite simple sufficient conditions, which involve the positivity (or absolute monotonicity) radius of the Runge‐Kutta schemes and its generalization when the Rosenbrock‐type methods are applied. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SUPG and grad‐div stabilized finite element methods for steady weakly compressible viscous flow
Authors: Bause Markus
Published: December 2004

The extensive application of mathematical and computational methods has become an efficient and powerful approach to the investigation and solution of many problems and processes in fluid dynamics from qualitative as well as quantitative point of view. In this work a new class of advanced numerical approximation schemes to isothermal compressible viscous flow is presented. The schemes are based on an iteration between an Oseen like problem for the velocity and a hyperbolic transport equation for the density. Such schemes seem attractive for computations because they offer a reduction to simpler problems for which highly refined numerical methods either are known or can be built from existing approximation schemes to similar equations, and because of the guidance that can be drawn from an existence theory based on them. For the generalized Oseen subproblem a Taylor–Hood finite element method is proposed that is stabilized by a reduced SUPG and grad‐div technique (cf. [1, 4]) in the convection‐dominated case. Results of theoretical investigations and numerical studies are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of the three‐dimension wave equation by using wave polynomials
Authors: Maciąg Artur
Published: December 2004

The paper demonstrates a specific power series expansion technique to solve the three‐dimensional wave equation. As solving functions, so‐called wave polynomials are used. The presented method is useful for a finite body of certain shape geometry without strength restrictions. The wave polynomials are defined. Recurrent formulas for the wave polynomials and their derivatives are obtained. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An adaptive refinement method for convection‐diffusion problems
Authors: Schamberg Thomas , Heinrichs Wilhelm
Published: December 2004

An adaptive finite difference method for singularly perturbed convection‐diffusion problems is presented. The method is introduced using a first‐order upwind scheme and a suitable error estimator based on the first derivatives. To obtain the grid structure needed for the cross stencil a special refinement strategy is considered. To avoid the slave points we change the stencil at the interface points from a cross to a skew one. After the convergence of the refinement algorithm we use a combination of a first order upwind and a second order central schemes to achieve higher order of convergence. Several numerical examples show the efficiency of our treatment. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Iterative Projection Methods for Sparse Nonlinear Eigenproblems
Authors: Voss Heinrich
Published: December 2004

For the sparse nonlinear eigenproblem T(λ)x = 0 we consider iterative projection methods where the current search space is expanded by a direction having a high approximation potential for the eigenvalue wanted next. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of processing on the mechanical properties of carbon short‐fiber reinforced polycarbonate
Authors: Haskell W. E. , Petrie S. P. , Lewis R. W.
Published: December 2004

The effects of varying the injection‐molding parameters of temperature, pressure, and injection rate on the mechanical properties of commercially obtained neat and carbon‐rein‐forced polycarbonate were investigated. The test specimens contained molded‐in and drilled holes so that the effect of a weld‐line could be investigated. The breaking‐strength and modulus‐of‐toughness values are reported. The results of the Young's moduli determinations showed that the stiffness of the neat materials was invariant and that the carbon‐reinforced material was orthotropic. Gel Permeation Chromatography (GPC) results showed that the neat resin was stable at the temperature investigated. The filled resin, however, underwent a decrease in molecular weight distribution at 650°F. At elevated temperatures, the breaking strength and modulus of thoughness of the carbon‐reinforced material showed a decrease where the properties were dependent upon the resin. Fiber orientation produced during molding significantly affected the toughness. The results agreed well with theory.
Direct determination of the orientation of short glass fibers in an injection‐molded poly(ethylene terephthalate) system
Authors: Fakirov S. , Fakirova C.
Published: December 2004

A simple and new technique for direct determination of the short fibers orientation in polymer composites is described. It is based on the fact that the shape of the fibers' cross section in the plane perpendicular to the desired direction (e.g., orientation direction) depends on the orientation angle ϕ with respect to this direction. For an eliptical shape with minor and major radii r and R, the cosϕ = r/R. Using micrographs from the polished samples' cross section and assuming a planar fiber distribution, it is possible to calculate for a part or entire cross section area: (i) the ϕ‐values; (ii) the orientation parameter fp; (iii) the angular distribution (by histograms); and (iv) the number and the sizes of the layers with more uniform fiber orientation as well as the transition zones between them. It is demonstrated for commercial poly(ethylene terephthalate) (PET) reinforced with 45 percent (by weight) short E‐glass fibers (Rynite®) that each surface layer (A) takes ca. 3/16 of the sample thickness (b), the core (C)—3/16b and the boundary (B) between them occupies 3/16b. These layers are characterized, respectively, by <ϕ>A = 28°, <ϕ>B = 38°, <ϕ>C = 64°, and f = 0.51, f = 0.18, f = −0.15. For the entire thickness (A + B + C) the <ϕ>A+B+C = 44° and f = 0.17. The method described is applicable to any kind of fiber‐reinforced composites from which it is possible to obtain micrographs of a desired cross section. The thickness of the cross section studied, as well as the number of the layers, does not affect the efficiency of the method.
Thermal properties of composites with bismaleimide‐vinyl poly(styrylpyridine) blends
Authors: Kourtides D. A.
Published: December 2004

Flammability, thermal properties, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties measured included limiting‐oxygen index, smoke evolution, thermal degradation products, total‐heat release, heat‐release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. This paper describes the properties of eight different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement. The resin matrices included: XU71775/H795, a blend of vinyl poly(styrylpyridine) and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a poly(styrylpyridine). The graphite fiber used was AS‐4 in the form of either tape or fabric. The properties of these composites were compared with those of epoxy composites. It was determined that the blend of vinyl poly(styrylpyridine) and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.
Properties and processing characteristics of dielectric‐filled epoxy resins
Authors: Zee R. H. , Huang Y. H. , Chen J. J. , Jang B. Z.
Published: December 2004

A family of casting composites, epoxy resins with mineral fillers, having a range of electrical properties, are being developed. In such composites, the dielectric constant is controlled primarily by varying the filler material in composition and proportions. The present work reports on the mechanical properties of composites made with two types of filler, an alumina powder (XA3500 from ALCOA) and a BaTiO3/TiO2 ceramic powder (ATD‐50 from Ampex). Dependence of mechanical properties on curing agents was also determined. Filler contents from 0 to 40 percent volume were used. Epoxy systems contained single epoxy resin with both amine and anhydride hardeners. Processing of the anhydride‐cured systems was easier than that of the amine‐based systems because of their lower viscosity and longer gel time of the former. However, the anhydride‐cured systems required higher processing temperatures. Curing kinetics and molecular bonding were investigated using a combination of differential scanning calorimetry, dynamic mechanical thermal analysis, and scanning electron microscopy. Activation energies of 11.2 kcal/mole and 12.1 kcal/mole were obtained for the curing of the amine‐based and the anhydride‐based composites respectively, and a small difference in the glass transition temperature was also observed. These effects can be attributed to the difference in the structure of the curing agents. The epoxy resin cured with NMA is less ductile compared with those cured with MTHPA or MHHPA due to slight chemical modification on the ring structures. This dependence of ductility on curing agent was observed in specimens with different filler contents. Although the presence of the filler materials was found to enhance the mechanical properties of the epoxy, the fracture mode in these materials is still brittle.
Delamination shape effects in aramid‐epoxy‐aluminum (ARALL) laminates with fatigue cracks
Authors: Macheret J. , Teply J. L. , Winter E. F. M.
Published: December 2004

An aramid reinforced aluminum‐epoxy‐laminate, ARALL, which contains a fatigue crack and a delamination zone is analyzed. It is assumed that the interlaminar shear forces between the aluminum and aramid/epoxy layers are transmitted along the delamination boundary. The aramid/epoxy layer of the laminate is considered a series of linear springs. The tensile stress in the aramid/epoxy layer and the stress intensity factor in the aluminum layer are found for various experimentally observed delamination shapes. A residual strength criterion based on the maximum tensile stress in the aramid/epoxy layer is applied and the analytical results are correlated with the available experimental data.
Investigation of composite interphase using dynamic mechanical analysis: Artifacts and reality
Authors: Thomason J. L.
Published: December 2004

The fiber‐matrix interface is an important factor determining the overall mechanical properties of composites. This interface is no longer regarded as a sharp boundary, but is now considered to be an „interphase,”︁ i.e., a region surrounding the fiber where properties differ from those of the bulk matrix. Although the concept of the interphase is rapidly gaining acceptance, its in situ detection and characterization remains a largely unsolved problem. Dynamic mechanical analysis (DMA) is a technique known for its sensitivity in the detection of inhomogeneity in polymer morphology. Recent publications have claimed that the interphase in unidirectional fiber‐reinforced composites is detectable using DMA. We have been evaluating a Du Pont 982 DMA on its uses in characterization of composites and their individual components. We have found that using heating rates higher than 2°C/min produces an artificial peak in the DMA loss spectrum of glass‐fiberreinforced epoxy composites at temperatures above the matrix glass‐transition temperature (Tg). This peak was not present in the data from the unreinforced matrix nor in data from carbon‐fiber‐reinforced samples. This artifact could be interpreted as evidence of an interphase. However, our investigations revealed that it is in fact due to a complex interaction of the instrument, the thermal conductivity of the sample, the heating rate, and the sample modulus above Tg. Despite this artifact, the high sensitivity of the Du Pont 982 DMA enables detection of inhomogeneities in the composite matrix that are attributable to an interphase.
Room‐temperature aging of Narmco 5208 carbon‐epoxy prepreg. Part II: Physical, mechanical, and nondestructive characterization
Authors: Cole K. C. , Noël D. , Hechler J.‐J. , Cielo P. , Krapez J.‐C. , Chouliotis A. , Overbury K. C.
Published: December 2004

Samples of Narmco Rigidite 5208/WC3000 carbon‐epoxy composite prepreg were exposed to ambient temperature (22°C) and 50 percent relative humidity for different periods up to 66 days. The aging has a significant effect on prepreg physical properties such as tack, volatiles content, and gel time. A set of 4‐ply laminates made from aged prepreg was subjected to tensile testing, ultrasonic inspection, and optothermal inspection. No relationship could be discerned between laminate properties and prepreg aging time. However, variations in panel homogeneity were observed, and these correlated with thermal diffusivity and tensile modulus measurements, but not with ultimate tensile strength or elongation. A set of 6‐ply laminates was used to measure compressive properties, interlaminar shear strength, and physical properties. These panels also showed variations in porosity, again unrelated to aging, but in addition, the fiber/resin ratio was observed to decrease with aging time. Both factors were found to affect mechanical properties. The implications concerning the importance of monitoring the aging by physicochemical methods are discussed.
Continuous monitoring of the fragmentation phenomenon in single fiber composite materials
Authors: Yavin B. , Gallis H. E. , Scherf J. , Eitan A. , Wagner H. D.
Published: December 2004

A continuously monitored single‐filament composite (CM‐SFC) test was conducted to measure the stress at which successive fiber breaks occur in the single fiber fragmentation process. This exercise was performed with a limited number of samples of various types. The purpose was to explore the possibility of using this test as a simple alternative means of (i) measuring the size effect in single fibers, (ii) calculating the Weibull shape and scale parameters for fiber strength, (iii) calculating the fiber/matrix interfacial shear strength from the extrapolated value of fiber strength using the loading history of a single fragmentation test, rather than from the value of fiber strength extrapolated from extensive testing of single fibers at various gage lengths, as is usually done. These are aspects of the SFC test that have largely been ignored so far. The results presented here confirm the possibility of using the CM‐SFC test for such purposes, with a certain degree of approximation, as discussed. Additional information supplied by this test as well as a possible effect of fiber pre‐tensioning on fragmentation results (including the value of the interfacial shear strength) are also briefly discussed.
Simulation of compression molding of long‐glass‐fiber‐reinforced thermoplastic sheets
Authors: Ducloux R. , Vincent M. , Agassant J. F. , Poitou A.
Published: December 2004

An isothermal two‐dimensional shear‐thinning model of the compression molding of long‐glass‐fiber–reinforced thermoplastic is presented. A transverse isotropic behavior is introduced by considering two different pairs of power‐law coefficients. First (K1, m1) is linked to the shear deformations through the thickness and to the compression deformation; second (K2, m2) is associated to the expansion motions in the plane. K2 is significantly greater than K1 because of the influence of the glass mat structure, which resists stretching in the plane of the part. These coefficients are determined by fitting the computed and experimental mold closing forces in a circular isothermal compression‐molding test. The average velocity through the thickness is obtained by a variational method. Incompressibility is ensured by penalization. A finite element method is used, with a convected mesh and remeshing technique. The agreement between this model and experimental results (shape of the sample, mold closing force, pressure) performed on a rectangular mold is good.
Random glass mat reinforced thermoplastic composites. Part V: Statistical characterization of the tensile modulus
Authors: Bushko W. C. , Stokes V. K.
Published: December 2004

Random glass mat thermoplastic composites (GMT), which can be thermostamped to form complex deep‐drawn parts with ribs and boxes, are complex material systems in which the local elastic modulus and local strength vary widely and randomly across the material (the tensile modulus can vary by a factor of two over a 12.7‐mm length scale). And the values of these local properties depend on the length scale of measurement. The random, large‐scale point‐to‐point variations in their properties cannot be described by a single number. The broad distribution of elastic moduli in GMT has been modeled by a four‐parameter probability density function. Moments of this distribution function provide numerical measures that can be used for comparing data sets representing properties of different material samples. This statistical characterization is used to establish the consistency and the random nature of previously obtained elastic moduli data sets. The framework is also used to predict the effect of the gage length used to measure the local elastic modulus on the shape of the modulus probability density function.
Flow behavior of stampable sheet with a rib part
Authors: Hamada H. , Shonaike G. O. , Yamaguchi S. , Sato T. , Maekawa Z. , Koshimoto M.
Published: December 2004

The effect of die design on the flow characteristics of compression molded three‐layer long glass fiber reinforced polypropylene composite, known as “stampable sheet,” was investigated. The flow behavior of each layer was observed by optical and soft X‐ray photographs. The fiber flow length into the rib part was measured by an image processing system. The results showed that during compression resin exudation occurred and that this depended on the die's rib width. Thus, the larger the rib width, the lower the amount of resin exuded. Resin exudation was found to occur earlier in a die with zero fillet radius. The fiber flow length into the rib part was enhanced by using a die with a large fillet radius. The results were confirmed by a short‐shot molding process. In this process, the stamping operation was stopped short of making a complete part.

A finite element method was used to study the flow process. The results agree with the experimental results confirmed by short‐shot molding.
Hydrothermal effects on mechanically fastened glass/polypropylene composite joints
Authors: Morii Ohru , Hamada Hiroyuki , Maekawa Zen‐Ichiro , Tanimoto Toshio
Published: December 2004

This study deals with the hydrothermal effects on mechanically fastened glass fiber mat/polypropylene composite joints with different joint geometry. Three kinds of joint geometries were adopted; hole diameter was 6 mm, the length from top edge to the hole center was 18 mm (3e) and the specimen width was 12 (2w), 18 (3w), and 30 mm (5w). The joints were immersed in hot water at 60 and 80°C. The effect of water temperature on the failure load appeared clearly in 2w3ejoints. The higher water temperature induced more strength reduction. The dominant failure mode changed from the net‐tension to the bearing for the original dry joints for wider specimens. The failure mode changed from multiple to net‐tension only for 3w3ejoints, because of a remarkable tensile strength reduction. The failure strength and the failure mode were predicted by the macroscopic failure criterion, and the characteristic experimental curves, and the FEM analysis. The predicted results agreed with experiment.
Unsteady flow of dilute fiber suspensions using a Generalized Eulerian Lagrangian approach
Authors: Alexanurou Andreas N. , Aiimed Alauddin
Published: December 2004

In recent years the emphasis on the development of fiber reinforced plastics has experienced an unprecedented expansion. One of the most commonly used methods in manufacturing of plastic products is injection molding. In this work we are using a Generalized Eulerian Lagrangian (GEL) formulation to study the unsteady flow of dilute fiber suspensions in injection molding. This formulation combines the advantages of both formulations: in the same flow problem but different regions the GEL formulation allows the selective application of an Eulerian, Lagrangian or a mixture of the two formulations. The suspending fluid is considered to be Newtonian and the contribution of the fibers to the local stress tensor is obtained using a volume averaging theory. The fiber distribution tensor is expressed in terms of a second order tensor with a quadratic closure approximation. Results are shown and discussed for the filling of a cavity from a single gate under different process conditions fibers aspect ratio and content.
Elastic constants and thermal expansivity of gel‐spun polyethylene fiber and its composites
Authors: Choy C. L. , Kwok K. W. , Ma H. M.
Published: December 2004

The five independent stiffness constants, C11, C33, C44, C66, and C13, and the axial and transverse thermal expansivity of unidirectional gel‐spun polyethylene fiber reinforced composites have been measured as functions of fiber volume fraction Vf. The axial extensional modulus C33 and axial Poisson's ratio v13 follow the rule of mixtures, while the axial shear modulus C44, transverse shear modulus C66, and transverse plane‐strain bulk modulus Ct ( = C11 − C66) obey the Halpin‐Tsai equation. Extrapolation to Vf = 1 gives the five stiffness constants of gel‐spun polyethylene fiber. The tensile property of the fiber is highly anisotropic, with the axial Young's modulus about 40 times higher than the transverse Young's modulus. In contrast, the axial shear modulus exceeds the transverse shear modulus by only 5%. A similar treatment of the thermal expansivity data in terms of the Schapery equations gives an axial thermal expansivity of −1.25 × 10−5 K−1 and a transverse thermal expansivity of 11.7 × 10−5 K−1 for the fiber.
Torque rheometer evaluation of polypropylene process stability
Authors: Goodrich J. E.
Published: December 2004

A new method of treating torque rheometer test data has been developed. First, it involves converting the torque values measured over a range of temperatures to torques corresponding to a constant reference temperature. Then the log of the calculated torques is plotted against time. The method has been applied to several polypropylene grades, and the effects of numerous test variables have been explored. Correlations have been developed between torque rheometer data and fundamental polymer properties of viscosity and molecular weight. The method should also be applicable to polymers other than polypropylene.
Isothermal kinetic studies using a thermomechanical analyzer II. Rates of penetration of a polymer by a spherical indenter
Authors: Machin D. , Rogers C. E.
Published: December 2004

The use of a commercially available thermomechanical analyzer (TMA) operated in its isothermal mode is illustrated for studies of penetration of a hemispherically‐tipped probe into a material sample. Two amorphous copolymers were studied at various temperatures above their softening points. Kinetics of penetration are compared with tensile creep measurements for these viscoelastic materials. A simple semi‐empirical relationship between creep and penetration at small strains is applied and found to yield approximate although not exact agreement with experiment. It is thus possible that for homogeneous materials of this type creep data might be easily predicted with a fair degree of accuracy from penetration data and vice versa. Experimental problems involved in the TMA penetration technique are discussed.
Fracture of fiber glass laminates
Authors: Hamilton R. , Berg C. A.
Published: December 2004

The applicability of fracture mechanics to the description of initial notch extension under tension in quasi‐isotropic fiberglass laminates is tested experimentally. It is found that classical elastic fracture mechanics, without modifications of couple stress effects, as represented in the theory of Muki and Sternberg, is sufficient to describe initial notch extension in prenotched specimens which are sufficiently thick to avoid transplanar bucklings of the specimen under tension. The fracture toughness (KIC) is found to be 15 ksi √in. However, it is noted that in these specimens (0.035 in. thick) transplanar postbuckling deformation becomes pronounced well before fracture, and that different modes of buckling seen in externally notched and internally notched specimens have opposite effects on the apparent fracture toughness of the specimen. It is pointed out that the effect of transplanar buckling on fracture of fiber glass, with its high compliance and high strength, is a potential source of serious problems in design with this material.
Rheology of network forming systems
Authors: Mussatti Francis G. , Macosko Christopher W.
Published: December 2004

Viscosity and dynamic shear measurements are reported on several network forming systems as a function of reaction time and temperature. Phenolic, epoxy and EPDM rubber systems are examined. Rheological data are related to the reaction kinetics of the systems. With these relations overall activation energies, reaction orders and rate constants are interpreted from the data. These compare favorably with results in the literature.

Applications of rheological techniques to processing problems of several network forming systems are described, specifically thermoset injection molding and SBR rubber vulcanization.
Measurement of oxidation stability of polyolefins by thermal analysis
Authors: Marshall D. I. , George E. J. , Turnipseed J. M. , Glenn J. L.
Published: December 2004

Differential thermal analysis (DTA) is well known for measuring temperatures and heats of physical and chemical transitions in materials. Recent development work on improved stabilization systems for polyolefin wire insulations has required fast procedures for measuring the performance of stabilization systems. Isothermal DTA procedures have been developed into routine tools for measuring stability of polyolefins by determining the oxidative induction time at elevated temperatures.

Oxidative induction time has been used to study the stability of polyethylene and polypropylene in raw material form and on wire. The dependence on temperature and antioxidant concentration have been measured. Effects of oxidation catalysts, catalyst deactivators and various environmental exposures are readily observed. Techniques and apparatus have been developed for simultaneous testing of a multiplicity of samples, providing for economical large scale use of the method.
Infrared reflection studies of metal‐polymer interfaces
Authors: Chan M. G. , Allara D. L.
Published: December 2004

By incorporating the spectroscopic techniques of reflection‐absorption and internal reflection in the infrared region, we have been able to define and characterize overall chemical changes occurring at a metal‐polymer interface. Our initial studies have concentrated on the oxidative degradation of metal‐polymer systems. These systems are of particular importance because of the common need to retard the metal‐catalyzed degradation of the polymer. Preliminary results for copper‐polyethylene interfaces, models for polyolefin‐insulated cable, have shown the copper surface to be the site of the initial catalysis in the oxidation of the polyethylene. When copper deactivators are added to inhibit the oxidation, initial reactions between the copper surface and the inhibitor can be seen. The importance of these surface reactions highlights the necessity for studying the interface.
Time‐temperature superpositioning of viscosity‐time profiles of three high temperature epoxy resins
Authors: White R. P.
Published: December 2004

The chemo‐rheological behavior has been elucidated for three high temperature epoxy resins. Constant temperature and shear stress measurements were made on a modified Weissenberg Rheogoniometer. Curing behavior of various temperatures is unified by a time‐temperature superposition method. The curing rate of one resin, Ferro E‐293, is limited by the chemical reaction. The other resins, 3M PR‐286 and PR‐288, each have consecutively occurring reactions, both of which are diffusion limited. The chemo‐rheological information obtained for these materials is used to model viscosity for compression molding of hand‐laidup composites.
Flow visualization for injection molding of polyethylene and polystyrene melts
Authors: White James L. , Dee Henry B.
Published: December 2004

Flow patterns have been observed during the injection molding of rheologically characterized low‐density polyethylene and polystyrene melts under various molding conditions. Some studies of high‐density polyethylene were also carried out. Various mold designs were included in the study and the flow patterns investigated under both isothermal and cold cavity wall conditions. In addition to investigating injection molding of single polymer melts, flow patterns in the sandwich molding of polyethylene and polystyrene were studied.