bluuebunny/crossref_metadata_2025 huggingface dataset:
Herstellung von verschleißfesten WC‐Co Schichten durch Hypersonic Flammspritzen
Authors: Wagner N. , Kreye H. , Kestel H.
Published: December 2004

Das Hypersonic Flammspritzen, ein neuartiges Verfahren zur thermischen Beschichtung von Oberflächen, wird kurz beschrieben. Es werden Spritzversuche mit zwei WC‐Co Pulvern durchgeführt, die die gleiche chemische Zusammensetzung und Korngrößenverteilung, aber eine unterschiedliche Morphologie aufweisen. Die Untersuchung der Schichten zeigt, daß sich bei beiden Pulvern in einem relativ breiten Bereich von Spritzparametern Schichten mit hoher Dichte, hoher Härte und hoher Haftfestigkeit herstellen lassen. Deutliche Unterschiede hinsichtlich der Mikrostruktur dieser Schichten lassen sich weniger über eine Variation der Spritzparameter als über die Morphologie der verwendeten Pulver erzielen.
Numerische Auswertung von Zugversuchen an CuZn 40 mit Ausgleichskurven
Authors: Peiter A. ,   Mitarbeiter
Published: December 2004

Es werden gemessene Spannung‐Dehnung‐Kurven von Messing CuZn 40 durch zwei Ausgleichsfunktionen angenähert und daraus dann E‐ und Tangenten‐Modul, Arbeitsvermögen und Dehngrenzen errechnet. Die Übereinstimmung wird mit der Standardabweichung beurteilt. Am besten eignet sich die Langevin‐Funktion.
Potentiodynamic and cyclic voltametric studies on the Passivity of Tin in neutral phosphate buffer
Authors: Ammar I. A. , Darwish S. , Khalil M. W. , Galal A.
Published: December 2004

Passivity of tin has been investigated in phosphate buffer (pH 6.7) using potentiodynamic and cyclic voltammetric techniques. The formation of thin transparent electronically conducting passive film on which O2 is evolved in the transpassive range is indicated. The solution remains clear. Potentiodynamic measurements performed from −1.2 to 2.5 V (SCE) and backward at scan rates between 1 and 100 mV/sec give one anodic peak. In the reverse scanning, two cathodic peaks appear at low scan rates and disappear completely at higher rates. Values of the open dircuit potential, the corrosion potentials Ecor (forward and reverse), the anodic peak potential Ep and the anodic peak cd Ip are recorded. The results are compared with our previous work in neutral chloride, bromide, iodide, and sulphate solutions. Thermodynamic data are used to predict the possible oxidized species constituting the anode film.

Cyclic voltammetric measurements have been carried out in the potential range between H2 and O2 evolution, and in limited potential ranges at scan rates between 1 and 200 mV/sec. One anodic peak is detected in all cases. While a short arrest and a cathodic peak appear in the results between H2 and O2 evolution, two distinct cathodic peaks appear up to 100 mV/sec in the results taken between –1.2 and −0.224 V. Plots of Ip vs the square root of scan rate are linear, and indicate diffusion‐controlled kinetics for the reactions initiating passivity. Linear relations are observed for Ep vs log scan rate indicating the irreversible nature of the anodic processes. While the formation of SnO and SnO2 is predicted from thermodynamics at potentials more negative than Ep, the formation of Sn(OH)4 is predicted at potentials more positive than Ep. The conclusions drawn from the results obtained with the two different techniques are generally the same. The results are compared with and discussed on the light of previous work using cyclic voltammetry.
Einfluß des Makroaufbaus von Stahl/Polymer‐Faserverbundwerkstoffen auf den Abrasivverschleiß
Authors: Gahr K. H. Zum
Published: December 2004

Der Makroaufbau von Stahl/Polymer‐Verbundwerkstoffen wurde systematisch variiert. Gemessen wurde der abrasive Verschleißwiderstand der Verbundwerkstoffe gegen Flint und SiC in einem Modellprüfsystem. Wichtige Parameter im Makroaufbau der Verbundwerkstoffe waren der Flächenanteil, der Durchmesser und die Härte der Stahlfasern sowie die freie Weglänge zwischen den Fasern. Daneben wurde der Einfluß der Eigenschaften der Polymer‐Grundmasse, wie Härte und chem. Aufbau, untersucht. Es werden quantitative Beziehungen zwischen Parametern des Makroaufbaus und dem abrasiven Verschleißwiderstand angegeben.
Probleme der zerstörenden Prüfung von Proben mit sehr geringer Verformung
Authors: Grimminger H.
Published: December 2004

Bei Materialien mit sehr geringer Bruchverformung, beispielsweise Keramik und Graphit, muß die Steifigkeit der Prüfmaschine eindeutig zu definierende, nachprüfbare Forderungen erfüllen, um Fehler im Prüfergebnis zu vermeiden. Neben empfindlichen Prüfgrößen gibt es auch solche, die invariant gegenüber der Federsteifigkeit der Prüfeinrichtung sind. Der Einfluß auf die gebräuchlichen Belastungsmodi (vo = const.; \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm F}\limits^. = {\rm const}{\rm .} $\end{document}) wird untersucht. Korrekturmöglichkeiten werden diskutiert und entsprechende Algorithmen angegeben.
Einfluß des Fe‐Gehalts und der Auslagerungszeit auf mechanische, elektrische und magnetische Eigenschaften der Legierung CuNi 10(Fe)
Authors: Luger R. , Schütze M.
Published: December 2004

An 6 Versuchsschmelzen des technischen Werkstoffs CuNi 10 Fe mit Fe‐Gehalten von 0,04 bis 1,52 Gew.‐ % wurde der Einfluß des Fe‐Gehalts und der Auslagerung bei 400 ° auf die Härtewerte, die Kerbschlagzähigkeit, die Warmfestigkeit, die relative Magnetisierbarkeit und den spezifischen elektrischen Widerstand untersucht. Darüberhinaus wurden Zeitstandversuche mit kontinuierlicher Dehnungsmessung mit Laufzeiten bis zu 3000 h bei 400 °C durchgeführt. Wie die Ergebnisse zeigen, werden bei Auslagerung bei 400 ° sowohl die mechanischen als auch die untersuchten physikalischen Eigenschaften vom Fe‐Gehalt in der Legierung CuNi 10 Fe wesentlich beeinflußt. Deutlich zeigt sich dieser Einfluß auch unter Zeitstandbelastung bei 400 °. Eine Erklärung für dieses Verhalten wurde in der Bildung von Ni‐Fe‐reichen Ausscheidungen auf den Korngrenzen sowie im Korninneren in allen Legierungsvarianten mit Ausnahme derjenigen mit den niedrigsten Fe‐Gehalten gefunden.
Verhalten von Gasturbinenschaufelwerkstoffen bei mechanischer Langzeitbeanspruchung unter Heißgaskorrosion – Teil I. Mechanisches Langzeitverhalten
Authors: Kloos K. H. , Granacher J. , Struth U.
Published: December 2004

An unbeschichteten und beschichteten Schaufelwerkstoffen für Gasturbinen wurde das Zeitstandverhalten und das LCF‐Verhalten unter gasturbinenspezifischen Korrosionsbelastungen im Bereich relativ hoher Temperaturen untersucht. Dabei trat unter scharfer Heißgaskorrosion teilweise eine Absenkung der Zeitstandfestigkeit auf, die nicht mehr durch den korrosionsbedingten Querschnittsverlust erklärbar war. Unter Heißgas betriebsähnlicher Korrosivität wurde dies nicht beobachtet und die Schutzschichten zeigten kein vorzeitiges Versagen. Das LCF‐Verhalten folgte dem Zeitstandfestigkeitsverhalten, wobei aber unter Heißgaskorrosion ein verstärkter Angriff erfolgte.
Explosive Compaction of powders, principle and prospects
Authors: Prümmer R.
Published: December 2004

The explosive compaction method consisting of a cylindrical container surrounded by a proper type and amount of explosive is an inexpensive method to achieve high densities close to theoretical density. The explosive's parameters have to be adjusted to the type of the powder to be compacted. The required explosive's pressure is linearly related to the Vickers hardness of the metal powder particles. If higher pressures are applied, an “explosive liquid phase sinter” ‐ process can be achieved, allowing the welding of individual particles. The residual properties of the material are characterized by a high defect structure and by dislocation densities and subgrain sizes comparable to those after heavy plastic deformation. The same is true of compacted ceramic powders. Enhanced sinter reactivity, chemical and catalytic reactivity may be the result of high values of stored energy observed in the ceramic materials, shock wave treated under conditions of explosive compaction. The properties of materials produced by shock‐wave synthesis or by shock‐wave transformation are also determined by a high‐density defect structure.
Dehnungsinduzierte Spannungsrißkorrosion in der Flüssigzinkphase bei der Hochtemperaturverzinkung von HV‐Schrauben der Festigkeitsklasse 10.9 mit großen Abmessungen Teil 1: Untersuchung von Schadensfällen
Authors: Beyer St. , Dünkel V. , Landgrebe R.
Published: December 2004

In Schadensuntersuchungen an HV‐Schrauben der Festigkeitsklasse 10.9 wurde herausgefunden, daß bei der Hochtemperaturverzinkung ab der Abmessung M30 an den kritischen Kerbstellen im Kopf/Schaft‐Übergang und im Gewindeauslauf der Mechanismus der dehnungsinduzierten Spannungsrißkorrosion in der Flüssigzinkphase auftreten kann. Derart vorgeschädigte Schrauben sind sprödbruchanfällig und besitzen insbesondere im Betrieb eine stark erhöhte Gefährdung gegenäber wasserstoffinduzierter Spannungsrißkorrosion. Durch eine Normaltemperaturverzinkung der gefährdeten Schraubenabmessungen ab M27 können solche Sprödbrüche sicher vermieden werden. Die Kenntnis dieser Zusammenhänge macht eine Überprüfung und Neubewertung von bisher angewendeten Maßnahmen zur Vermeidung von Sprödbrüchen an HV‐Schrauben der Festigkeitsklasse 10.9 zwingend erforderlich. Insbesondere müssen aus heutiger Sicht einige der in der Vergangenheit festgeschriebenen Maßnahmen zur Vermeidung wasserstoffinduzierter Sprödbrüche relativiert werden.
Mechanisches Verhalten des Schutzschicht‐Grundwerkstoff‐Verbundes von Gasturbinenschaufeln unter betriebsähnlicher zyklischer Beanspruchung
Authors: Kloos K. H. , Granacher J. , Kirchner H.
Published: December 2004

Mit einer speziell entwickelten Prüftechnik wurden zur Untersuchung der thermomechanischen Beansprunchung von Gasturbinenschaufelwerkstoffen anisotherme betriebsähnliche Dehnwechselversuche an verschiedenen Schutzschicht‐Grundwerkstoff‐Kombinationen durchgeführt. Zum Vergleich wurden isotherme Standarddehnwechselversuche an einer ausgewählten Schutzschicht‐Grundwerkstoff‐Kombination durchgeführt. Bei dieser Kombination wurde mittels Finit‐Element‐Rechnung auch die Schichtbeanspruchung errechnet.
Festigkeitsverhalten von Schweißverbindungen unter kombinierten phasengleichen und phasenverschobenen mehrachsigen Beanspruchungen
Authors: Sonsino C. M.
Published: December 2004

Geschweißte Kreuzproben aus dem Feinkornbaustahl StE 290 und Flansch‐Rohr‐sowie Rohr‐Rohr‐Verbindungen aus dem Feinkornbaustahl StE 460 mit unbearbeiteten und bearbeiteten Nähten wurden unter biaxialer Belastung mit konstanten Amplituden im Bereich von 103 bis 5 · 106 Anriß‐ bzw. Durchrißschwingspielzahlen untersucht. Um bei der Bewertung der Ergebnisse einen Einfluß von Eigenspannungen auszuschließen, wurden alle Verbindungen spannungsarmgeglüht. Phasengleiche Beanspruchungen können zufriedenstellend mit Hilfe von konventionellen Hypothesen (Gestaltänderungsenergie oder Schubspannung) auf der Basis von Nenn‐, Struktur‐ order örtlichen Beanspruchungen bewertet werden. Im Falle einer Phasenverschiebung überschätzen aber die konventionellen Hypothesen die Lebensdauer. Die vorgestellte Hypothese der wirksamen Vergleichsspannung hingegen liefert befriedigende Abschätzungen. Hierbei ist die Kenntnis der örtlichen Beanspruchung erforderlich, die in Abhängigkeit der Schweißnahtgeometrie durch Boundary‐Elemente‐Berechnungen ermittelt werden können. Diese Hypothese behandelt den Einfluß einer Phasenverschiebung dadurch, daß Sie die gegenseitige Beeinflussung von örtlichen Schubspannungen in verschiedenen Richtungen eines Oberflächenelementes berücksichtigt. Darüber hinaus erfaßt diese Hypothese den Größeneinfluß infolge der Schweißnahtgeometrie und Belastungsart.
Berechnung von Bauteilwöhlerlinien unter Berücksichtigung der statistischen und spannungsmechanischen Stützziffer
Authors: Liu J. , Zenner H.
Published: December 2004

Im vorliegenden Beitrag wird ein Modell zur Dauerfestigkeitsberechnung in [11] auf den Zeitfestigkeitsbereich erweitert. Berücksichtigt werden der statistische Größeneinfluß nach dem Fehlstellenmodell und die spannungsmechanische Stützwirkung infolge der plastischen Verformung im Kerbgrund. Das vorgestellte Modell wird für die Grenzfälle besonders analysiert und mit Versuchsergebnissen aus der Literatur verifiziert. Nach dem vorgestellten Modell ist die Neigung der Wöhlerlinie von der Wechselfestigkeit des Werkstoffes und von der Kerbgrundgröße abhängig und unabhängig von der Formzahl. Die Wöhlerlinie wird desto flacher, je größer die Kerbgrundgröße ist und je höherfester der Werkstoff ist.
Quantitative Analyse von nichtstöchiometrischen Titannitrid‐Schichten
Authors: Stock H.‐R. , Höhl F. , Mayr P.
Published: December 2004

Stahlbleche wurden mittles Gleichstrom‐Magnetron‐Sputtern mit Titannitrid beschichtet. Durch Variation des Stickstoffdurchflusses konnten Schichten mit unterschiedlicher chemischer Zusammensetzung erhalten werden. Die Schichten wurden mittels Gimmentladungsspektroskopie und einer naßchemischen Methode quantitativ analysiert. Für die naßchemische Analyse wurden die Schichten vom Substrat getrennt, aufgeschlossen und nachfolgend die Elemente Titan mittels Atomabsorptionsspektroskopie und Stickstoff nach Kjeldahl bestimmt. Die Analysenergebnisse zeigen signifikante Unterschiede zwischen den beiden Verfahren, die durch die unterschiedlichen verwendeten Standards verursacht werden. So ergibt die GDOS‐Analyse im Vergleich zur naßchemischen Analyse für unterstöchiometrische TiNx‐Schichten (x < 1) zu niedrige Stickstoffgehalte und für etwa stöchiometrische Schichten (x ≈ 1) zu hohe. Aufgrund der Standards kann geschlossen werden, daß die naßchemische Analyse mit einem geringeren systematischen Fehler behaftet ist. Sie ist aber in der Handhabbarkeit der GDOS‐Analyse weit unterlegen und eignet sich damit besser für die Kalibration von speziellen Proben, die nachfolgend bei der GDOS‐Analyse als Standard eingesetzt werden können.
Tribologisches Verhalten von Kunststoffen bei tiefen Temperaturen
Authors: Franke R. , Haase I.
Published: December 2004

Bei Gleitlagern, die während ihrer Funktionsdauer tiefen Temperaturen ausgesetzt sind, treten immer wieder Schwierigkeiten mit den herkömmlich eingesetzten Schmierstoffen auf. Besonders bei Anlaufvorgängen nach längeren Stillstandzeiten wie etwa bei Turbinenlagerungen, Generatoren, Elektromotoren und Gebläsen versagen die meisten Mineralöle. Im Austausch eingesetzte synthetische Schmierstoffe auf der Basis von Polyalphaolefinen und Estern erreichen häufig auch ihren Stockpunkt und sind somit für Tieftemperaturanwendungen nur bedingt einsetzbar. Bisherige Lösungen sehen Vorkehruntgen zur Temperaturerhöhung im Gleitlager bzw. in der gesamten Anlage vor und sind mit erhöhten Kosten und Energiverbrauch verbunden. Ein Lösungsweg zu dieser Problematik ist der Einsatz von sogenannten selbstschmierenden Gleitlagerwerkstoffen auf Kunststoffbasis. Hochleistungskunststoffe mit unterschiedlichen Verstärkungsmaterialien und Gleitmodifikatoren sind aussichtsreiche mechanisch hochbelastbare Gleitlagermaterialien, für die obere Dauereinsatztemperaturen von etwa 200°C angegeben werden. Weitgehend unbekannt ist das Verhalten von selbstschmierenden Gleitlagerwerkstoffen bei Temperaturen unterhalb von 0°C. Anliegen der Arbeit ist es deshalb, apparative Möglichkeiten vorzustellen, um das Gleitreibungsverhalten dieser Werkstoffe bei tiefen Temperaturen im Modellversuch zu ermitteln und vergleichend darzustellen.
Ultrafine ZrO2 powder by Laser Evaporation: Preparation and properties
Authors: Michel G. , Müller E. , Oestreich Ch. , Staupendahl G. , Henneberg K. H.
Published: December 2004

Ultrafine oxide powders were produced by CO2 laser evaporation of coarse ZrO2 powder or compact stabilized ZrO2 material

The 10.6μm radiation in the power range 1–4kW was generated by a transversal flow Co2 laser which can oscillate in cw and pw operation

The vaporization rate depends on the relative position of the focal plane to the surface of the ZrO2 powder, the laser intensity and the supplied energy input.

At a laser intensity of 4.2 · 105 Wcm−2 the optimum vaporization rate is 130 g · h−1 (cw‐operation of the laser).

The produced powders consist of spherical particles; their diameters vary in the range from 5 to 200 nm can be controlled by the process conditions. The surface area (BET) is adjustable from 10 to 30 m2 · g−1.

The powders of unstabilized zirconia show an unusual high content of the tetragonal phase. In case of chemically stabilized zirconia the composition can change during the process of evaporation and recondensation.
Herstellung und Optimierung der Festigkeit aktivgelöteter Metall/Keramik‐ und Keramik/Keramik‐Verbunde
Authors: Wippel V. , Holzner G. , Cerjak H.
Published: December 2004

HPSN‐Keramik wurde mit HPSN und dem Stahl X23 CrNi17, jeweils mit den Abmessungen 3,5 × 4,5 × 30 mm, mittels zweier kommerziell erhältlicher Silber bzw. Silber‐Kupfer Aktivlote unter Variation aller essentiellen Lötparameter verlötet. Die Verbunde wurden auf ihre Festigkeit mit der 4‐Punkt Biegebruchmethode, sowie lichtmikroskopisch, mit REM und EDAX untersucht. Die Auswertung erfolgte nach den Bruchspannungen mittels Weibullstatistik, nach dem Bruchaussehen, sowie nach den Dicken der Reaktions‐ und Lötzonen. Es zeigte sich eine sehr hohe Qualität der Silber‐Kup fer‐Lot‐Proben, wobei eine geringe Beeinflussung durch Variation der Lötparameter festzustellen war. Die Silberlot‐Proben zeigten deutlich niedrigere Festigkeitswerte, welche überdies stark von der Lotabdampfung und Spannungsrelaxation während des Abkühlens während der Lötung abhängig sind. Weiter zeigten Proben artgleicher Keramik/Keramik Lötpartner deutlich höhere Festigkeiten als Metall/Keramik Proben.
Fundamental significance of specific phosphodiesterases in the control of spontaneous meiotic resumption in porcine oocytes
Authors: Laforest Martin F. , Pouliot Éric , Guéguen Laëtitia , Richard Fraņois J.
Published: December 2004

The meiosis of mammalian oocytes begins during the fetal life and stops at the dictyate stage. This study has assessed the role of specific phosphodiesterase (PDE) inhibitors on the control of meiotic resumption in porcine oocytes investigating the influence of PMSG‐hCG and cAMP stimulation. Cumulus‐oocytes complexes (COCs) and denuded oocytes (DOs) were collected from gilt ovaries obtained at a local slaughterhouse. Oocytes were cultured in NCSU23 with different PDE inhibitors. The EC50 for oocytes maintained in germinal vesicle (GV) stage was evaluated using different doses of both cilostamide (CIL), PDE3 inhibitor and 3‐isobutyl‐1‐methylxanthine (IBMX), a nonspecific PDE inhibitor. In presence of PMSG‐hCG, meiotic resumption is observed after 24 hr of culture. Both CIL and IBMX reversibly blocked meiotic resumption. In absence of PMSG‐hCG, meiotic resumption is reduced after 24 hr of culture. After 48 hr of culture, only CIL significantly blocked meiotic resumption. Still in absence of PMSG‐hCG, significant effect of treatment was only observed in COCs using the combination of CIL and rolipram (PDE3 and PDE4 inhibitor, respectively) compared to the use of IBMX. To assess the contribution of cAMP synthesis, a low dose of an adenylyl cyclase (AC) stimulator, forskolin, has been used in combination with CIL showing a significant effect of this combination. In CIL‐treated COCs and DOs, significant higher percentages of oocytes were maintained in GV stage when cultured in combination with forskolin instead of PMSG‐hCG. In conclusion, these results demonstrate that the control of meiotic resumption in porcine oocytes is highly regulated by cAMP. Both the degradation by specific PDE3 enzyme and the synthesis by an active AC are highly involved. Mol. Reprod. Dev. 70: 361–372, 2005. © 2005 Wiley‐Liss, Inc.
Expression of Sox8, Sf1, Gata4, Wt1, Dax1, and Fog2 in the mouse ovarian follicle: Implications for the regulation of Amh expression
Authors: Salmon Nicholas A. , Handyside Alan H. , Joyce Ieuan M.
Published: December 2004

Anti‐Müllerian hormone (Amh) is expressed in the granulosa cells of growing and preovulatory follicles in the mouse ovary where it acts to decrease responsiveness to follicle stimulating hormone (FSH) and plays a role in inhibiting primordial follicle recruitment. Recently, co‐culture of isolated oocytes and granulosa cells has demonstrated that Amh expression is up‐regulated in the presence of oocytes and, at preantral stages, this effect is dependent upon close contact. In Sertoli cells, Amh expression is regulated by several transcription factors including SOX9, SF1, GATA4, WT1, and DAX1, which, with the exception of SOX9, are also expressed in granulosa cells where GATA4 is known to up‐regulate Amh expression antagonised by FOG2. Here, we demonstrate that Sox8, which is closely related to Sox9 and encodes the protein SOX8 which can transactivate Amh, is expressed in the postnatal mouse ovarian follicle but is not co‐expressed with Amh in the granulosa cells of preantral follicles. Sox8 expression was found only in the oocytes of preantral follicles and in the oocytes, cumulus cells, and mural granulosa cells of preovulatory follicles. Also, increased expression of Amh in granulosa cells co‐cultured with oocytes was not associated with increased mRNA levels of the transcription factors Sf1, Gata4, Wt1, Dax1, or Fog2. These findings reveal Sox8 expression in the ovarian follicle and show that oocyte regulation of Amh expression is not due to oocyte regulation of Sf1, Gata4, Wt1, Dax1, or Fog2 expression in granulosa cells. Mol. Reprod. Dev. 70: 271–277, 2005. © 2005 Wiley‐Liss, Inc.
Development of cloned pig embryos by nuclear transfer following different activation treatments
Authors: Kim Yang‐Sil , Lee Sung‐Lim , Ock Sun‐A , Balasubramanian S. , Choe Sang‐Young , Rho Gyu‐Jin
Published: December 2004

This study compared the effects of activation treatments on the development and ploidy of nuclear transferred (NT) pig embryos. After in vitro maturation of oocytes collected from the slaughterhouse, oocytes were enucleated and reconstructed by transfer of donor cells and fusion with three DC pulses (1.4 kV/cm, 20 μsec). Oocytes were pulsed thrice electrically with 1.4 kV/cm for 20 μsec and NT eggs were divided into three treatment groups: Group 1 (no further treatment), Group 2 (10 μg/mL cycloheximide [CHX], 3 hr), and Group 3 (1.9 mM 6‐dimethylaminopurine [DMAP], 3 hr). All the eggs were cultured in sets of 30 in 60 μL drops of NCSU‐23 supplemented with 4 mg/mL fatty acid free BSA, and compared for the rates of development and ploidy. The rates of cleavage, development, and total cell number of parthenotes in Group 3 were significantly (P < 0.05) higher than those in Groups 1 and 2. Cleavage rates of NT embryos in Group 1 were significantly (P < 0.05) lower than those in Groups 2 and 3 (73% vs. 81% and 82%, respectively). Development into blastocyst stage and total cell number of NT embryos in Group 3 were significantly (P < 0.05) higher than those in Groups 1 and 2. Although the embryos in Group 3 had higher development, ∼58% of NT embryos evaluated were abnormal ploidy (6% haploidy, 9% polyploidy, and 42% mixoploid). The results suggested that although DMAP enhanced development and higher cell number, due attention should be paid to abnormal ploidy in pig NT embryos. Mol. Reprod. Dev. 70: 308–313, 2005. © 2005 Wiley‐Liss, Inc.
Indomethacin preserves muscle mass and reduces levels of E3 ligases and TNF receptor type 1 in the gastrocnemius muscle of tumor‐bearing mice
Authors: Hitt Andrew , Graves Erin , McCarthy Donna O.
Published: December 2004

Tumor‐induced skeletal muscle wasting involves tumor necrosis factor (TNF) and the ubiquitin‐proteasome pathway of muscle protein degradation. In this study, growth of the colon‐26 adenocarcinoma in mice was associated with diminished gastrocnemius muscle mass and increased muscle levels of actin, ubiquitin‐conjugated proteins, free ubiquitin, E3 ubiquitin ligases, and the type 1 TNF receptor (TNFR1). Indomethacin at 1 or 5 mg/kg/day reduced tumor growth and muscle levels of TNFR1. However, only the 5 mg dose of indomethacin reduced muscle wasting and muscle levels of the E3 ligases and actin. These data suggest that the beneficial effects of indomethacin in the treatment of tumor‐induced skeletal muscle wasting may involve inhibition of TNF‐ and ubiquitin‐mediated pathways of muscle protein degradation. These data also demonstrate that E3 ligases, which are involved in disuse atrophy, also are associated with tumor‐induced skeletal muscle wasting. © 2004 Wiley Periodicals, Inc. Res Nurs Health 28:56–66, 2005
Error estimations for some meshless boundary interpolation methods
Authors: Gáspár Csaba
Published: December 2004

Meshless methods have become quite popular in numerical treatment of partial differential equations because of their simplicity and the fact that they require neither domain nor boundary mesh. In general, however, they convert the original problem to a highly ill‐conditioned linear system of algebraic equations with a dense matrix. Recently, a special technique has been proposed which circumvents this computational difficulty. This method, called Direct Multi‐Elliptic Interpolation Method, is based on a scattered data interpolation which defines the interpolation function as a solution of a higher order multi‐elliptic equation. Here the boundary version of this meshless method which is based on a multi‐elliptic boundary interpolation is considered. Error estimations are derived justifying the interpolation function to be a good approximation of the solution of the original boundary value problem as well. At the same time, the problem of large, dense and ill‐conditioned matrices as well as the mesh generation are completely avoided. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On The Atmospheric Boundary Layer Flow Modelling
Authors: Sládek I. , Kozel K. , Jaňour Z.
Published: December 2004

The paper presents a mathematical and numerical investigation of the flow in the atmospheric boundary layer (ABL) over complex topography. The flow is supposed to be viscous, incompressible, turbulent and stationary. Two different mathematical–numerical approaches are briefly mentioned. Both models have been used to simulate a flow and pollution dispersion over a complex surface coal field in the North Bohemia which is supposed to be partially covered by a high forest stand. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
More About Geršgorin‐type theorems
Authors: Cvetković Ljiljana , Kostić Vladimir
Published: December 2004

In the recent book of R.S. Varga, [3], one of two main recurring themes is that a nonsingular theorem for matrices gives rise to an equivalent eigenvalue inclusion set in the complex plane, and conversely. If such nonsingularity result can be extended via irreducibility, usually this can be used for obtaining more information about the boundary of the corresponding eigenvalue inclusion set. Here we will start with one of Geršgorin‐type theorem for eigenvalue inclusion, given in [1], (for which exists corresponding equivalent statement about nonsingularity of a particular class of matrices) and use it for proving necessary conditions for an eigenvalue to lie on the boundary of localization area. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Treatment of Catenary Systems
Authors: Teichelmann Gunnar
Published: December 2004

Simulation is of great importance in the development of railway cable systems. Mathematical models and numerical methods for the computation of both static equilibria and dynamic oscillations of railroad catenaries are being derived. These cable systems form a complex network of string and beam elements and lead to coupled partial differential equations in space and time where constraints and corresponding Lagrange multipliers express the interaction between carrier, contact wire, and pantograph head. For computing static equilibria, two different algorithms are presented, while the dynamic case is treated by a finite element method in space, combined with stabilized time integration of the resulting differential algebraic system. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Least‐Squares Formulation for the Shallow Water Equations with Small Viscosity
Authors: Danisch Garvin
Published: December 2004

A least‐squares finite element method for the shallow water equations with viscosity parameter μ > 0 is proposed and studied. The shallow water equations are reformulated as a first order system by adding a new variable for the velocity flux. The reformulated first order system is combined with a characteristic‐based time discretization and a least squares approach. For the correct boundary treatment in the limit case μ → 0, a trace theorem is presented. For the numerical computation of the velocity, the finite element spaces introduced recently by Mardal, Tai and Winther (SIAM Journal on Numerical Analysis 40, pp. 1605–1631) are used. The degrees of freedom in these spaces can be identified with the normal and tangential components, respectively. Numerical results for some test examples are shown. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On‐line mixing during injection and simultaneous curing in liquid composite molding processes
Authors: Devillard Mathieu , Laut Antoine , Advani Suresh G.
Published: December 2004

Liquid composite molding (LCM) processes such as resin transfer molding (RTM) and vacuum assisted RTM (VARTM) are used to manufacture high quality and net‐shape fiber reinforced composite parts. All LCM processes impregnate fiber preforms packed in a mold cavity with a thermoset resin. After the preform is fully saturated, the injection is discontinued but the resin continues to cure. Once the curing step is complete, the part is de‐molded. The resin has to be mixed with a curing agent to cure. Typically, the resin and the curing agent are mixed together in a pressure pot before the injection. This has several disadvantages, such as storage of large amounts of hazardous polymerizing resin, wastage, and cleaning of cured resin from the injection line. This paper proposes the implementation and calibration of an alternative to this technique. The approach is to mix the curing agent with the resin as the resin enters the mold through a separate system featuring two feed‐lines. Such a system will enable one to maintain a uniform gel time throughout the part by varying the mixing ratio of resin and the catalyst during the injection. An experimental study of such on‐line mixing to obtain simultaneous curing and to reduce the overall curing time is conducted and presented in this paper. Implementation of a control scheme that varies the curing agent during injection and its effect on cure time is benchmarked with the process in which the percentage of curing agent is held constant. The gel time for the fabricated parts was reduced by 20–25% by continuously varying the percentage of curing agent during injection. POLYM. COMPOS., 26:74–83, 2005. © 2004 Society of Plastics Engineers
Salicylic acid modified high performance epoxy matrices
Authors: Ibrahim A. Mahammad , Seferis James C.
Published: December 2004

This study focuses on the processing‐structure‐property relations for salicylic acid modified high performance epoxy matrix systems for carbon fiber composites. Differential scanning calorimetry and dynamic mechanical data have shown that as the concentration of salicylic acid increases, the degree of cure first increases, reaches a maximum, and then decreases steadily. Analysis of the results indicated that small amounts of salicyclic acid accelerates the amine‐epoxide reactions resulting into crosslinked networks with increased degree of cure; increasing amounts, however, give rise to networks with reduced crosslinking by reducing the net available diaminodiphenyl sulfone (DDS) content in the system by a reaction of the DDS with salicylic acid. Overall, this study has demonstrated that salicyclic acid modification offers the potential for monitoring and controlling amine‐epoxide reactions that may influence the application and usage of epoxy matrices in composite systems.
Optimization of polyester sheet molding compound. Part II: Theoretical modeling
Authors: Fan J. D. , Lee L. James
Published: December 2004

A mechanistic kinetic and heat transfer model is used to describe the cure of sheet molding compounds (SMC). Kinetic parameters such as rate constant of initiator decomposition and rate constant of propagation are estimated from the induction time and the time to reach the peak exotherm of isothermal reaction curves measured by the differential scanning calorimetry (DSC). Temperature and conversion profiles inside plate sections of SMC parts during molding are measured. The predicted results compare well with the experimental data except the limiting conversion. A set of predictive parameters are proposed from this model as guidelines for the optimal molding of SMC. Several moldability diagrams are also constructed which can be easily used to design the optimum SMC recipe for a given processing condition.
The effect of the applied field on the electrical properties of metal polymer composites
Authors: Nobile M. R. , Nicodemo L. , Nicolais L. , Egiziano L. , Lupo G. , Tucci V.
Published: December 2004

The effect of filler content and applied electrical field on the electrical resistivity of poly(methyl methacrylate) (PMMA) filled with aluminum particles was investigated. The resistivity of such composite suddenly decreases by several orders of magnitude at a critical volume concentration ϕc. In addition, for filler contents lower than ϕc, the PMMA/Al composite undergoes a transition from a high to a low resistance material in correspondence of a critical value of the external applied electrical field. This value has been related to thermal breakdown occurring in the regions between conductive particles. Moreover, the permittivity spectrum as a function of frequency is reported for composites of several filler contents, and the Lal and Parshad law was used to correlate the experimental data.
A boundary element analysis of flow in sheet molding compound
Authors: Barone M. R. , Osswald T. A.
Published: December 2004

A new boundary element method has been developed for analyzing the flow of sheet molding compound (SMC) during compression molding. The boundary element equations can be used to determine the velocities on the perimeter of the charge. Successive flow front configurations are then generated by a simple explicit updating procedure. This approach was used to predict the flow front progression for elliptical, rectangular, and L‐shaped charges. Comparisons with experimental data for elliptical and rectangular charges were encouraging. The fact that it was possible to obtain reasonable agreement for charges with different shapes and thicknesses lends support to the underlying flow model. Furthermore, valuable insight regarding knit line formation was acquired by analyzing the L‐shaped charge. Results from the boundary element analysis showed that the initial thickness of the charge has a pronounced effect on knit line development. Even though there is considerable industrial experience in making SMC parts, the important role of charge thickness on knit line formation appears to have been largely overlooked. Prior analyses gave no indication of this effect because they were based on lubrication models that were independent of charge thickness.
Effect of the textural characteristics of the new silicas on the dynamic properties of styrene‐butadiene rubber (SBR) vulcanizates
Authors: Rueda L. Ibarra , Hernandez L. González , Anton C. Chamorro
Published: December 2004

It is possible to obtain silicas with different textural characteristics from natural silicates by means of an acid treatment, where the textural characteristics of the new silicas obtained are greatly influenced by the reaction conditions. The mechanodynamical behavior of compounds filled with these silicas and based on Styrenebutadiene rubber (SBR) matrices was studied. The influence of the textural characteristics on dynamic properties is explained in terms of the stiffness, porosity, and structure of the silica particles. Silicas obtained at drastic reaction conditions yield compounds with a higher storage modulus, E′, at low strain amplitudes, but with a lower storage modulus at high strain amplitudes. The maximum loss factor, tanδ, is a function of the silica external surface area.
A note on polymeric inner‐layered single fiber interfacial strength determination
Authors: Davé Raju , Lorenzo Luis
Published: December 2004

The role of inner‐layer (interphase) in fiber‐reinforced composites is often assessed by measuring the interfacial shear strength of single fibers embedded in matrix blocks. Interfacial shear strength is calculated using simple shear lag analyses (Kelly and Tyson model). This paper shows that application of Kelly and Tyson's equation may result in gross overprediction of interfacial shear strengths if the thickness of the inner‐layer is not negligible in comparison with the fiber diameter.
Interfacial shear strength studies using the single‐filament‐composite test. I: Experiments on graphite fibers in epoxy
Authors: Netravali A. N. , Henstenburg R. B. , Phoenix S. L. , Schwartz P.
Published: December 2004

The failure of the interface in a carbon fiber‐epoxy system was studied for six different epoxy blends using the single‐filament‐composite technique. The blends were formulated to yield a wide range of stiffnesses, and their effect on interfacial failure was examined. Specimens were made from Hercules IM6‐G carbon fiber and the different blends of epoxy, and then strained to obtain a distribution of fiber fragment lengths. Birefringence patterns near the fiber breaks were observed and recorded. Some of the specimens were strained until they failed and the resulting fracture surfaces were observed under a scanning electron microscope to determine fracture patterns and the existence of debonding. The fragment length distributions were interpreted using a Monte‐Carlo simulation of a Poisson/Weibull model for fiber strength and flaw occurrence. The results were used to calculate an effective interfacial shear strength. From this analysis we conclude that one cannot accurately predict the interfacial properties of a composite based solely upon conventional single fiber and bulk matrix properties. Local matrix properties and fiber/matrix interactions, on a microscale, play a key role in composite strength.
Dilatancy of concentrated suspensions with Newtonian matrices
Authors: Yilmazer Ulku , Kalyon Dilhan M.
Published: December 2004

Suspensions filled close to their maximum packing fraction present special challenges in their processing and in their rheological characterization. In this report, the literature in the area of dilatancy of concentrated suspensions is reviewed. Furthermore, the shear viscosity of a Newtonian polymeric liquid filled with 60 vol. percent of ammonium sulfate has been investigated. Both capillary and parallel disk torsional flows, were employed, spanning three decades in shear stress. Upon correction for slip, the suspension exhibited shear thinning at low shear stresses and shear thickening at higher shear stresses. Above a critical wall shear stress, the shear viscosity of the suspension increased unboundedly and the flow became pluglike with apparent slip at the wall. These findings have important ramifications in the processing of composites from such concentrated suspensions.
Issues in diaphragm forming of continuous fiber reinforced thermoplastic composites
Authors: O'Brádaigh Conchúr M. , Pipes R. Byron , Mallon Patrick J.
Published: December 2004

A literature survey is presented on sheet‐forming methods and mechanisms for continuous fiber reinforced thermoplastics. The diaphragm forming process is shown to be one of the more promising fabrication routes for complex‐curvature structures. The primary deformation mechanisms involved in the sheet‐forming processes are identified and discussed. Earlier approaches to develop mathematical models either have been kinematically based or have treated only one of the primary deformation mechanisms. A promising constitutive model for the highly anisotropic behavior of the composite at forming temperature is examined. The composite sheet is assumed to behave as a transversely isotropic Newtonian fluid that is both incompressible and inextensible in the fiber direction. The second section of the paper treats the experimental development of the polymeric diaphragm forming process for thermoplastic composites. The viscoelastic properties of the diaphragm material are characterized by dynamic mechanical analysis. The rate sensitivity of the phenomenon of shear‐buckling during forming of certain cross‐ply and quasi‐isotropic composite laminates is investigated, using a shallow female mold. Finally, the interface condition between the diaphragm and the composite during forming is examined.
The electromagnetic interference shielding of polypyrrole impregnated conducting polymer composites
Authors: Ruckenstein E. , Park J. S.
Published: December 2004

A lightweight conducting polymer composite was prepared by the incorporation of conducting polypyrrole in the pores of a host polymer to form a conductive network. The inclusion of polypyrrole in a porous cross‐linked polystyrene host polymer, prepared by the concentrated emulsion polymerization method, was carried out by imbibing the host polymer with a pyrrole solution (or oxidant solution), partially drying the saturated host polymer, and imbibing it again with the oxidant solution (or pyrrole solution) for 2 h. The conductivity of the polymer composite is as high as 0.5 S/cm and the shielding effectiveness of the composite reaches 26 dB in the frequency range from 1.0 to 2.0 GHz.
Instrumented thermoforming of advanced thermoplastic composites. II: Dynamics of double curvature part formation and structure development from PEEK/carbon fiber prepreg tapes
Authors: Cakmak M. , Dutta A.
Published: December 2004

Poly(ether ether ketone) (PEEK) carbon fiber prepreg tapes (APC‐2) have been thermoformed into a hemispherical double curvature part under a variety of processing conditions. Conventional matched die molding using aluminum molds (at 200°C) were not successful in thermoforming acceptable parts. Parts with severe wrinkling and folding were obtained. A novel three‐piece (steel) mold with built‐in sheet clamping arrangement was, therefore, designed and fabricated. This mold was used at 400°C temperature to thermoform parts from preheated preconsolidated laminates. More interestingly, using the above conditions, 8‐ and 16‐ply unconsolidated laminates could be directly thermoformed into parts that were microstructurally sound and exhibited good shape conformity. Results suggest a cycle time of 15 min, with scope for further reduction, if mold cooling is employed. Notwithstanding the simplicity of the thermoforming process, such a short cycle time compares quite favorably with cycle times of several hours for conventional thermosetting resin based composites.
Mechanical behavior of angle‐ply PEEK/carbon fiber laminates: Theory/experiment correlation
Authors: Cervenka A. , Sheard P.
Published: December 2004

Regular symmetrical laminates of the {+α/−α/+α/−} sym. type were manufactured and tested using established methods. Tensile characteristics—elastic modulus and the ultimate stress/strain characteristics—were determined in the form of angular dependences on the ply‐angle α. The same mechanical properties were also simulated adopting a reported theoretical model. The correlation between the experimental and the predicted values shows an excellent agreement for the laminate stiffness. On the other hand, the fit for the ultimate properties was unsatisfactory except under conditions of linear, elastic response encountered for α→ O and 90°. Generally, a qualitative correlation has been obtained for the ultimate strength, but no relation has been established for the ultimate strain. A mechanism of fiber reorientation during loading, i.e. closing of the ply angle with the increasing strain has been found to be responsible for exceptionally non‐linear stress‐strain response in the range 30<α<60°. Coupon width and strain rate have both been found to have little effect on the ultimate properties.
Random glass mat reinforced thermoplastic composites. Part VI: Methodology for predicting the stiffness of parts
Authors: Bushko W. C. , Stokes V. K.
Published: December 2004

Random glass mat reinforced composites have large variations in mechanical properties, requiring a statistical characterization of their elastic properties. The broad distribution of elastic moduli is modeled by a probability density function that determines the statistical characteristics of the material property data. This characterization is used to develop a framework for predicting the stiffness of parts made of these composites. The effective elastic modulus and the structural stiffness of parts have been defined in a statistical sense, and the main properties of the effective moduli have been discussed. The effective elastic modulus, if it exists, is shown to be a system property that must be considered in conjunction with the geometry of the part and the boundary conditions.
Fiber/Matrix load transfer in cyanate resin carbon fiber systems
Authors: Armistead J. P. , Snow A. W.
Published: December 2004

Comparative single fiber fragmentation test measurements are used to charcterize cynate and epoxy resin interface load transfer with high modulus (HMS4) and high strength (AS4) carbon fibers. The HMS4 fiber forms a weak interface with a fiber controlled failure mode, and the AS4 fiber forms a strong interface with the resin properties, apparently determining the level of load transfer. The resin properties examined are critical surface energy for wetting, cure shrinkage, thermal shrinkage, and mechanical modulus and strength. The cynate and epoxy resins display no significant difference in critical surface energy. Cure shrinkage has a negligible effect on load transfer. The compressive force from thermal shrinkage is significant, but the larger Tg to testing temperature range of the cyanate resin is offset by the larger thermal expansion coefficient of the epoxy, resulting in a near equal compressive force for the two resins. There is little difference in modulus between the two resins but a significant difference in shear strength. This difference is reflected in the larger load transfer measurement for the cyanate resin. A comparison of simple one‐dimensional elastic and plastic models for the fiber fragmentation experiment resulted in better conformity with the plastic model. This would indicate that interfacial failure occurs by plastic deformation of the resin for the systems of this study.
Flow and void characterization of stitched structural composites using resin film infusion process (RFIP)
Authors: Shim Sang‐Beom , Ahn Kyujong , Seferis James C. , Berg Arvid J. , Hudson William
Published: December 2004

The resin film infusion process (RFIP), which is similar to resin transfer molding (RTM), was applied to investigate the possibility of manufacturing high performance stitched composites. With the objective of understanding the resin flow mechanisms and void formation in stitched fibrous perform, two recent technological developments in homogeneous tough resin and bendable stitching fibers were incorporated in producing stituched composites with RFIP. These included new lightly crosslinked thermosets (LXT) that were phenolic or amine based. Second, bendable carbon stitching reinforcement (T‐900) was utilized as a stitching fiber. Flow characteristics were inferred by ultrasonic C‐scan analysis of cured panels. Microscopic studies indicated that voids were distrubuted along the stitching fiber because of low consolidation pressure in the resin‐rich area (stitching fiber region) where the fiber volume content was lower. In contrast to stitched composites, non‐sitiched composites contained lower void content and irregular void distribution because of uniform fiber compaction. Microscopic studies of partially resin infused quasi‐istropic stitched composites demonstrated that the resin flows along the stitching fiber region and then infuses into the fibrous preform. These infusion phebnomena were the result of anistropic permeability in the preform. Consequently, anisotropic resin flow in the stitched fibrous preform was found to be related to the heterogenous textile structure caused by the stitching process.