bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoresistenz‐Materialprüfung mittels Laser‐Simulation
Authors: Habegger H. , Steffen J.
Published: December 2004

Obschon die vorgestellte Laser‐Simulationsmethode noch nicht für alle wünschbaren Anwendungsfälle zu treffsicheren Ergebnissen führt, erlaubt sie doch für mittel‐ bis hochtemperaturresistente und nitrierte Stähle bzw. hochwarmfeste Legierunen praxisnahe Vergleichsresultate (siehe Abb. 12). Mithin ist diese Methode ein brauchbares Instrument zur Vorevaluation bzw.
Bruchmechanische Analyse des Zähigkeitsverhaltens von teilchengefüllten Thermoplasten
Authors: Grellmann W. , Bohse J. , Seidler S.
Published: December 2004

Zur Ermittlung der bruchmechanischen Zähigkeitseigenschaften von gefüllten Thermoplasten wurde der instrumentierte Kerbschlagbiegeversuch verwendet. Die Interpretation der Schlagkraft‐Durchbiegungs‐Diagramme wurde mit modernen Konzepten der Bruchmechanik durchgeführt. Die Änderung der Zähigkeitseigenschaften mit zunehmendem Füllstoffvolumenanteil wird in geeigneter Weise durch das J‐Integral‐Konzept beschrieben. Es wurde der Einfluß des Füllstoffvolumenanteils, der Teilchengröße und der Matrixart auf das kritische J‐Integral sowie die kritische Rißöffnung bei Einleitung des instabilen Rißwachstums untersucht. Anhand eines mikromechanischen Modells wird das Bruchverhalten von teilchengefüllten Thermoplasten theoretisch interpretiert, wobei energiedissipative Prozesse vor der Rißspitze einbezogen werden.
Werkstoffmechanische Beanspruchungs‐ und Lebensdaueranalyse zweistufig schwingbeanspruchter Biegeproben aus 42CrMo4
Authors: Savaidis G. , Seeger T.
Published: December 2004

Versuchsergebnisse von ein‐ und zweistufenbelasteten ungekerbten Biegeproben aus 42CrMo4 nach [1] wurden herangezogen, um exemplarisch eine vergleichende Untersuchung und Bewertung des Nennspannungskonzeptes und des Örtlichen Konzeptes mit jeweils verschiedenen Varianten vorzunehmen. Dabei wurde als Ausgangssituation angenommen, daß entweder nur die Zugfestigkeit des Werkstoffes oder aber die vollständige experimentelle Bauteilwöhlerlinie für R = 0 vorliegt. Beim örtlichen Konzept wurden der Mittelspannungen und Reihenfolgeeinflüsse erfassende pJ‐Parameter nach Vormwald und der nur Mittelspannungen berücksichtigende PSWT‐Parameter nach smith, Watson, und Topper untersucht.

Für beide Ausgangssituationen sind die Vorhersagen nach dem Örtlichen Konzept geringfügig besser als jene nach dem Nennspannungskonzept, wenn mit dem PSWT‐Parameter gearbeitet wird. Eine deutliche Verbesserung wird jedoch durch die Anwendung des PJ‐Parameters erreicht. Wird dagegen das Örtliche Konzept auf der Grundlage von PSWT und zyklischen Werkstoffdaten dem Nennspannungskonzept mit experimentellen Bauteilwöhlerlinien gegenübergestellt, dann liefert letzteres die besseren Vorhersagen. Aus diesen Befunden, die als Trends auch für andere Fälle angesehen werden, wird die Empfehlung abgeleitet, beim Örtlichen Konzept verstärkt den PJ‐Parameter einzusetzen und, wenn Bauteilwöhlerlinien vorliegen, diese zur Anpassung von P‐Wöhlerlinien zu nutzen.
Mechanisches Verhalten von kohlenstoffaserverstärkten Duromeren im Tieftemperaturbereich
Authors: Roeder E. , Ritter R. , Eckrich R. , Mayer H.‐J.
Published: December 2004

Die vorliegenden Untersuchungen charakterisieren die mechanischen Eigenschaften verschiedener kohlenstoffaserverstärkter Epoxide unter quasistatischer Beanspruchung, wobei neben Prepregs auch Naßlaminate berücksichtigt wurden. Die Prüfungen dienten zur Ermittlung einer geeigneten Faser/Matrix‐Kombination für den Einsatz bei tiefen Temperaturen, weshalb sie sowohl bei Raumtemperatur als auch in flüssiger Stickstoffatmosphäre ausgeführt wurden. Als Bewertungskriterien der Werkstoffe wurden die Kenngrößen Bruchfestigkeit, Bruchdehnung und Elastizitätsmodul herangezogen. Im Zugversuch nehmen die beiden erstgenannten Kennwerte mit sinkender Temperatur erwartungsgemäß tendenziell ab, wohingegen der Elastizitätsmodul geringfügig ansteigt. Im Druckversuch dagegen steigen alle genannten Kennwerte an. Weiterhin ist ein unterschiedlich stark ausgeprägter Einfluß der Prüftemperatur auf die mechanischen Kenngrößen der Prepregsysteme und der Naßlaminate erkennbar. Schließlich zeigen die Versuche, daß die Temperaturabhängigkeit der genannten mechanischen Eigenschaften durch die Wahl der eingelagerten Verstärkungsfasern beeinflußt werden kann. Diese Aussage trifft in besonderem Maße auf die maximal erreichbare interlaminare Scherfestigkeit zu.
Beitrag zur Abschätzung der Dauerfestigkeit nitrierter bauteilähnlicher Proben
Authors: Spies H.‐J. , Kern T. U. , Tan N. D.
Published: December 2004

Das Fehlstellenmodell von Kogaev und Serensen erfaßt den statistischen und spannungsmechanischen Größeneinfluß auf die Dauerschwingfestigkeit. Seine Verbindung mit dem Konzept der örtlichen Dauerfestigkeit auf der Grundlage des Schädigungsparameters von Smith, Watson und Topper ermöglicht die Berücksichtigung wesentlicher bauteilspezifischer Einflußgrößen auf die Schwingfestigkeit randschichtverfestigter Werkstoffe. Die Anwendbarkeit dieses Konzeptes wird mit Hilfe von Versuchen an nitrierten Probestäben unterschiedlicher Geometrie und Beanspruchung nachgewiesen.
Investigations on Load Capacity and stability of deformation of rubber cylindrical shells under internal pressure
Authors: Gasiak G.
Published: December 2004

The paper presents a wide analysis of conditions under which a loss of deformation stability can be observed as well as local bulges form in axially‐symmetric (rotational) shells of any length. Analytical relations of the theory of shells were used for the analysis. If the maximum pressure in the shell was exceeded, the deformation process was investigated too. In such a case, strains begin to develop more intensely in the central part of a long cylindrical shell and, owing to that, one or more superimposed bulges (blisters) form. Symmetry of the shell deformation in relation to the centre of its length can be disturbed. A set of algebraic equations was derived for determination of critical pressure and critical strains on the falling part of the relation between pressure and the shell radius. The analysis of deformation stability is of a general type, because the used form of elastic potential of the material is a function characteristic for all the rubber‐like materials.

The experiments proved the results obtained from the analysis of the assumed theoretical models of shells, which were cylindrical at the beginning.
Einfluß der Sinterzeit und ‐temperatur auf das Schwingfestigkeitsverhalten des diffusionslegierten Sinterstahls Fe‐4.0%Ni‐1.5%Cu‐0.5%Mo+0.6%C
Authors: Lindner K.‐H. , Sonsino C. M.
Published: December 2004

Es wurde das Festigkeitsverhalten des Sinterstahls Fe‐4.0% Ni‐1.5% Cu‐0.5% Mo+0.6%C (Ultrapac LE+0.6%C) mit der Dichte von 7.1 g/cm3 und gesintert mit 1120°C/30 min, 1120°C/120 min, 1250°C/30 min sowie 1250°C/120 min untersucht. Sowohl das Schwingfestigkeits‐ als auch das Bruchmechanikverhalten werden durch die Erhöhung der Sinterzeit‐ und ‐temperatur deutlich verbessert. Da aber eine Sinterzeit von 120 min für eine wirtschaftliche Massenfertigung zu lang ist, wird für die Herstellung von hochfesten PM′ Bauteilen eine Sinterung bei 1250°C für mindestens 30 min empfohlen.
Hochtemperaturverhalten von Werkstoffen aus neuartig gefertigten Gasturbinenschaufeln
Authors: Kloos K. H. , Granacher J. , Windecker Th.
Published: December 2004

An in neuer Technologie gefertigten Schaufeln für die mittleren bis hinteren Laufreihen von stationären Gasturbinen wurden betriebsrelevante Werkstoffeigenschaften bestimmt. Die Untersuchungen erfolgten an den Schmiedelegierungen Nimonic 101 and Udimet 720 und an zwei Feinkornvarianten der Gußlegierung IN‐792. Im Bereich der Anwendungstemperaturen wurden Langzeitstandversuche, Glühversuche, Relaxationsversuche sowie nieder‐ und hochfrequente zyklische Versuche durchgeführt.
Schnellbewertung von Dispersionsgefüge und mechanischen Eigenschaften karbidbildender Stähle
Authors: Hildebrand H.
Published: December 2004

Es wurde eine Möglichkeit für eine Gefüge‐ und Eigenschaftsschnellbewertung von C‐, Cr‐ und Mn‐legierten Stählen mit Dispersionsgefüge, das durch Ausscheidung und Vergröberung aus dem martensitischen Ausgangszustand eingestellt wurde, erarbeitet. Die schnellregistrierende Koerzitivfeldstärke HC und rasterelektronenmikroskopisch ermittelte Gefügeparameter können z. B. im Zusammenhang HC‐ Partikeldurchmesser dp für eine Gefügeschnellbewertung genutzt werden. Infolge wiederholter Keimbildungwachsen und vergröbern die M3C‐Karbide parallel und in Partikelgenerationen. Daher wird immer ein Partikelgrößenspektrum erhalten.

Eine Eigenschaftsschnellbewertung ist über den Zusammenhang HC – Streckgrenze Rp 0,2/Zugfestigkeit Rm/Härte HV möglich. Da HC auf die Größe der ausgeschiedenen Partikel reagiert und der Verlauf HC – Zeit t / Partikeldurchmesser dp / Partikelvolumen (dp/2)3 zwei Maxima einschließt, die beiderseits das Ausscheidungs‐(A) und Vergröberungsstadium (V) trennen, muß bei einem betrachteten HC‐Wert eine der Zuordnungsmöglichkeiten ausgeschlossen werden. Dies kann bei Beachtung von ermittelten Temperatur‐Zeit‐Grenzwerten erreicht werden.

Die magnetisché Meßmethode liefert mit der strukturempfindlichen Größe HC innerhalb einer Minute eine Aussage zum Gefügezustand. Der Fehler liegt bei ≤0.5%. Die Anwendung der HC‐Messung ist zeit‐ und kostensparend. Eine Probenbearbeitung ist nicht erforderlich. Der Zustand der Oberfläche geht in das Meßergebnis nicht ein. Die aufgestellten Zusammenhänge HC – Rp 0,2 / Rm / HV können für die getesteten Stahlmarken standardmäßig angewendet werden.
Numerische Untersuchung zum Verhalten von Rißwiderstandskurven: Simulation mit dem Kohäsivmodell
Authors: Lin G. , Cornec A.
Published: December 2004

Bauteile werden durch Risse infolge ihrer lokalen Beanspruchungs‐konzentration deutlich geschwächt. Zur Bewertung der maximalen Restfestigkeit wird der Widerstand eines Werkstoffs durch Rißwiderstandskurven bestimmt. Sie basieren auf global zugänglichen und meßbaren Größen. In der einfachsten Vorstellung sollte der Rißwiderstand nur vom Werkstoff abhängen. Dies trifft leider nicht zu. Mit dem GKSS spezifischen Kohäsivmodell wird der Bruchvorgang realitätsnäher konstiutiv lokal beschrieben. Durch FEM Rechnungen wird gezeigt, welche Größen den Rißwiderstand beeinflussen. Auch für die Werkstoffentwicklung ergeben sich neue Aspekte im Hinblick auf eine gezielte Auswahl oder Veränderung eines Werkstoffs.
Requirements for operational fatigue strength of high quality Cast components
Authors: Sonsino C. M. , Grubisic V.
Published: December 2004

For the fatigue design of high quality cast components the information about service loading, geometry, material behaviour depending on alloy, casting technology, heat treatment and surface state must be available. The influence of these parameters on operational strength is demonstrated on the examples of selected ductile cast iron materials, aluminium alloys and nickel base alloys as well as cast steel. The proof‐out of the components must be supported by appropriate quality requirements in design, provision of material and manufacture. However, for safty components, their functionability and fatigue life must be guaranteed by service strain measurements and fatigue tests under variable amplitudes, too.
Karbidpartikelbildung und Diffusion in Stählen
Authors: Hildebrand H. , Heger D. , Heinzel G.
Published: December 2004

Die Einstellung von Dispersionsgefügen in Cr′ und Mn‐legierten Stählen wurde mit der Ausscheidung von M3C‐Karbidpartikeln aus dem martensitischen Ausgangszustand durch Auslagerung im Temperaturbereich von T = 500° …700°C über eine Dauer von t = 1…4290 min vorgenommen. Wie bereits früher in diesem Zusammenhang festgestellt wurde, können Keimbildung, Partikelwachstum und ‐vergrößerung parallel ablaufen, wobei die Vergröberung zeitlich dominiert. Mit der Partikelvolumenzunahme gemäß r3 α t (r – Partikelradius) werden asymptotisch endliche Partikelgrößen erhalten. Die Volumenzunahme im Vergröberungsstadium kann nur aufrechterhálten werden, wenn kleine Partikel wieder aufgelöst werden. Dieser Vorgang wird mit der Ostwald‐Reifung gut beschrieben. Damit sind Ständige Konzentrationsänderungen an den Partikelkeimbildungsorten bzw. in der sich entmischenden Matrix erforderlich. Mit Hilfe der Ostwald‐Reifungsgesetze wurden effektive chemische Diffusionskoeffizienten Deff für die Legierungselemente C, Mn, Si, Mo und Cr für die Diffusion in der α‐Fe‐Matrix abgeschätzt. Deff ändert sich mit der Entmischung der Matrix um einige Gößenordnungen. Das Diffusionvermögen der Elemente hängt vom Legierungsgehalt der Matrix ab. C ist wie erwartet am beweglichsten, Cr am unbeweglichsten. Die Gittérbindung scheint dabei bedeutend zu sein.

Im weiteren konnten die Werte der Aktivierungsenergie für die Karbidausscheidung Q und die Frequenzfaktoren D0 in der Arrhenius‐Beziehung für die untersuchten Stähle ermittelt werden. Damit stehen die für eine kurz‐ bis langzeitige Wärmebehandlung erforderlichen Diffusionsdaten zur Einstellung von Vergütungsgefügen bereit. Die unteren und oberen Grenzwerte des Karbidpartikelgrößenspektrums können den Darstellungen für die Cr′ und Mn‐legierten Stähle entnommen werden.
Überlebensrate und Sicherheit von keramischen Kugelköpfen für Hüftendoprothesen
Authors: Willmann G.
Published: December 2004

Der totale Ersatz eines Hüftgelenkes mit Kugelköpfen und Pfannen aus Aluminiumoxidkeramik ist klinisch bewährt. Die in vivo Bruchrate eines Biolox Kugelkopfes liegt unter 0,02 %. Ausgelöst durch eine extrem hohe Belastung (z. B. Unfall) kann der Bruch nach unterkritischem Rißwachstum erfolgen.

An 107 Biolox Explantaten wurde die Restfestigkeit bestimmt. Es konnte keine Materialermüdung nachgewiesen werden. Dies kann mit Hilfe des Zusammenhanges zwischen der Geschwindigkeit des Rißfortschritts und der Spannungsintensität (v‐K‐Diagramm)b erklärt werden. Normal belastete keramische Kugelköpfe (z. B. beim Gehen max. 3 kN) haben in vivo Spannungsintensitäten K1 von ca. 0,6 MPa m1/2. Hiermit befindet man sich mit der Spannungsintensität im Bereich unter der Ermüdungsgrenze KIo, für die ca. 1 MPa m1/2 abgeschätzt werden kann.

Biolox Kugelköpfe sind ein Beispiel für den Einsatz von Keramik, die trotz Zugspannungen als Dauerbelastung und mit hohen Anforderungen an die Sicherheit über large Zeiten sicher im Einsatz sind.
Zur Ermittlung verformungsbedingter Makro‐ und Mikroeigenspannungen durch mechanische und röntgenographische Eigenspannungsanalysen
Authors: Kornmeier M. , Scholtes B.
Published: December 2004

An überelastisch vorverformten Zug‐ und Biegeproben aus perlitischem Stahl wurden Eigenspannungstiefenverläufe röntgenographisch nach dem sin2ψ‐Verfahren und mechanisch mit der inkrementellen Bohrlochmethode ermittelt. Nach plastischer Zugverformung wurden im Ferrit röntgenographisch Druckmikroeigenspannungen bestimmt, denen sich im Fall der Biegeproben nach Entlastung zusätzlich Makroeigenspannungen überlagern. In keinem Fall stimmen röntgenographisch und mechanisch ermittelte Eigenspannungsverläufe überein. Durch Kombination beider Meßverfahren konnten Mikroeigenspannunsanteile separiert werden. Diese sind nach reiner Zugbeanspruchung größer als in der gleich stark vorverformten Randschicht einer entsprechenden Biegeprobe.
Caloric restriction transiently improves motor performance but hastens clinical onset of disease in the Cu/Zn‐superoxide dismutase mutant G93A mouse
Authors: Hamadeh Mazen J. , Rodriguez M. Christine , Kaczor Jan J. , Tarnopolsky Mark A.
Published: December 2004

Caloric restriction (CR) prolongs lifespan in insects, rodents, and nonhuman primates, a process attributed to a reduction in oxidative stress. Transgenic mice that overexpress the mutant human Cu/Zn‐superoxide dismutase (SOD1) gene (G93A mice) are an animal model of amyotrophic lateral sclerosis showing progressively lower motor neuron weakness and increased oxidative stress. We investigated the effect of CR on motor performance, clinical onset, disease progression, and lifespan in G93A mice. Starting at 40 days of age, 14 separately caged G93A mice were randomly divided into two groups: ad libitum (AL; n = 6) and calorie‐restricted (CR; n = 8) with a diet equal to 60% of AL. The CR mice (mean ± SEM: 14.0 ± 0.7 g) weighed 31% less than the AL mice (20.3 ± 1.0 g) (P = 0.0002). From 74 to 93 days of age, the CR mice performed better on the rotarod than the AL mice: fall time, P = 0.039; fall speed, P = 0.009. The CR mice had a faster rate of reaching clinical onset than the AL mice (hazard ratio = 4.3, P = 0.0006). The CR and AL mice reached clinical onset of disease at age 99 ± 1 and 110 ± 2 days, respectively (P = 0.0003), with no significant difference in disease progression. The CR mice tended to reach endpoint sooner than the AL mice (age‐specific death: 125 ± 3 vs. 133 ± 3 days, respectively, P = 0.09). We conclude that CR diet transiently improves motor performance but hastens clinical onset of disease in G93A mice. These results suggest that CR diet is not a protective strategy for patients with amyotrophic lateral sclerosis (ALS) and hence is contraindicated. Muscle Nerve, 2005
Delayed ulnar neuropathy at the wrist following open carpal tunnel release
Authors: Pingree Matthew J. , Bosch E. Peter , Liu Patrick , Smith Benn E.
Published: December 2004

Open carpal tunnel release is a common and successful treatment of median neuropathy at the wrist (carpal tunnel syndrome). We report a case of delayed ulnar neuropathy at the wrist with onset 2 months after open carpal tunnel release. Clinical findings, electrophysiological studies, magnetic resonance imaging, and surgical exploration demonstrated ulnar nerve compression at Guyon's canal resulting from translocation of the carpal tunnel contents. To our knowledge, this is an unreported complication of open carpal tunnel release that merits wide appreciation. Muscle Nerve, 2005
Signaling satellite‐cell activation in skeletal muscle: Markers, models, stretch, and potential alternate pathways
Authors: Wozniak Ashley C. , Kong Jiming , Bock Erika , Pilipowicz Orest , Anderson Judy E.
Published: December 2004

Activation of skeletal muscle satellite cells, defined as entry to the cell cycle from a quiescent state, is essential for normal growth and for regeneration of tissue damaged by injury or disease. This review focuses on early events of activation by signaling through nitric oxide and hepatocyte growth factor, and by mechanical stimuli. The impact of various model systems used to study activation and the regulation of satellite‐cell quiescence are placed in the context of activation events in other tissues, concluding with a speculative model of alternate pathways signaling satellite‐cell activation. Muscle Nerve, 2005
Decomposition‐based quantitative electromyography: Effect of force on motor unit potentials and motor unit number estimates
Authors: Boe Shaun G. , Stashuk Daniel W. , Brown William F. , Doherty Timothy J.
Published: December 2004

Decomposition‐based quantitative electromyography (DQEMG) allows for the collection of motor unit potentials (MUPs) over a broad range of force levels. Given the size principle of motor unit recruitment, it may be necessary to control for force when using DQEMG for the purpose of deriving a motor unit number estimate (MUNE). Therefore, this study was performed to examine the effect of force on the physiological characteristics of concentric needle‐ and surface‐detected MUPs and the subsequent impact on MUNEs obtained from the first dorsal interosseous (FDI) muscle sampled using DQEMG. Maximum M waves were elicited in 10 subjects with supramaximal stimulation of the ulnar nerve at the wrist. Intramuscular and surface‐detected EMG signals were collected simultaneously during 30‐s voluntary isometric contractions performed at specific percentages of maximal voluntary contraction (MVC). Decomposition algorithms were used to identify needle‐detected MUPs and their individual MU firing times. These MU firing times were used as triggers to extract their corresponding surface‐detected MUPs (S‐MUPs) using spike‐triggered averaging. A mean S‐MUP was then calculated, the size of which was divided into the maximum M‐wave size to derive a MUNE. Increased levels of contraction had a significant effect on needle‐ and surface‐detected MUP size, firing rate, and MUNE. These results suggest that force level is an important factor to consider when performing quantitative EMG, including MUNEs with this method. Muscle Nerve, 2005
Relationship between symptoms and functional performance in COPD
Authors: Reishtein Judith L.
Published: December 2004

We studied the relationships among functional performance and three symptoms—dyspnea, fatigue, and sleep difficulty—in a sample of 100 people with chronic obstructive pulmonary disease (COPD). All participants had an FEV1 60% or less of the predicted level for age, sex, and height. Consistent with the Theory of Unpleasant Symptoms, dyspnea correlated with both fatigue and sleep difficulty. Dyspnea and fatigue both had moderate negative correlations with functional performance, while sleep difficulty had a small nonsignificant negative correlation with functional performance. After controlling for age and oxygen use, dyspnea was the only symptom to predict variance in functional performance significantly. Of the three symptoms studied, only dyspnea was related to both the other symptoms and to functional performance. Focusing on dyspnea may be the best way to improve both symptom experience and functional performance in people with COPD. © 2004 Wiley Periodicals, Inc. Res Nurs Health 28:39–47, 2005
Group‐based HIV risk reduction intervention for adolescent girls: Evidence of feasibility and efficacy
Authors: Morrison‐Beedy Dianne , Carey Michael P. , Kowalski Jeanne , Tu Xin
Published: December 2004

The purposes of this pilot study were (a) to assess the feasibility of a community‐based, small group HIV risk reduction intervention with adolescent girls, and (b) to obtain preliminary evidence of the efficacy of this theoretically‐guided intervention using a controlled design. The feasibility of the intervention was demonstrated by successfully implementing it with 33 sexually‐active, single girls. Preliminary evidence of the efficacy of the intervention was obtained using a randomized trial with 62 sexually‐active, single girls. Data obtained at a 3‐month follow‐up assessment showed that girls who received the HIV‐related intervention improved their HIV‐related knowledge and enhanced their motivation for risk reduction compared to girls who received a control (health promotion) intervention. Effect sizes suggest that the HIV intervention also reduced several risk behaviors (e.g., vaginal sex without a condom, giving oral sex, and alcohol and drug use before sex). Challenges to implementation and suggestions for intervention enhancement are discussed. © 2004 Wiley Periodicals, Inc. Res Nurs Health 28:3–15, 2005
Impact of training on work‐related assault
Authors: Nachreiner Nancy M. , Gerberich Susan Goodwin , McGovern Patricia M. , Church Timothy R. , Hansen Helen E. , Geisser Mindy S. , Ryan Andrew D.
Published: December 2004

Although training is often recommended as a part of a comprehensive approach to address occupational violence, little empirical literature exists to support this recommendation. Over 40% of nurses responding to the Minnesota Nurses Study reported being trained about occupational violence, involving seven different training topics. Although at the univariate level, an increased risk was identified for nurses trained in managing assaultive/violent patients, no statistically significant results remained at the multivariate level. This lack of protection from training is consistent with previous research, although the explanations for this lack of effect remain unclear. Additional research is necessary to obtain more specific details on occupational violence training, including training content and methods, to understand more thoroughly the impact of training on occupational violence. © 2004 Wiley Periodicals, Inc. Res Nurs Health 28:67–78, 2005
The effect of ambient moisture and temperature conditions on the mechanical properties of glass fiber/carbon fiber/nylon 6 sandwich hybrid composites consisting of skin‐core morphologies
Authors: Ishiaku U.S. , Hamada H. , Mizoguchi M. , Chow W.S. , Mohd Ishak Z.A.
Published: December 2004

The concept of skin‐core (SC) morphology was used to make sandwich hybrid composites in which the skin and core were composed of different fibers in the same matrix. The sandwich blends comprising glass skin with carbon core and vice versa were compared with those of the hybrid composite, while the respective carbon (CF) and glass fiber (GF) composites served as points of reference. The composites were compounded and fabricated into injection molded tensile specimens and 3‐mm thick plaques. The effect of ambient temperature and moisture was studied. The fracture mechanical characterization of the various materials was done by using notched compact tension (CT) specimens. Tensile properties were also used to characterize the composites. Morphogical studies based on scanning electron microscopy and light microscopy were used to elucidate fracture characteristics. Deterioration of properties was noticed under hot and humid conditions. Synergism in flexural properties was observed in the CF/GF/PA hybrid composite. The mechanical properties of the CF/GF/PA hybrid are closer to those of CF/PA, suggesting a cost advantage by substituting half of the carbon fibers with glass fibers. Dynamic mechanical analysis results revealed that synergism in Tg is attained by blending or sandwiching glass and carbon fibers. Morphological studies reaffirmed the skin‐core morphology of the composites. POLYM. COMPOS., 26:52–59, 2005. © 2004 Society of Plastics Engineers.
Processing of single polymer composites using the concept of constrained fibers
Authors: Barkoula Nektaria‐Marianthi , Peijs Ton , Schimanski Tilo , Loos Joachim
Published: December 2004

The concept of “overheating” is one of the known methods for manufacturing single polymer composites. This concept is validated on two categories of semi‐crystalline polymers: the drawable, apolar (i.e., isotactic polypropylene [iPP], ultra‐high molecular weight polyethylene [UHMWPE]) and the less drawable, polar ones (i.e., polyethyleneterephalate [PET] and polyamides [PA]). The interchain interactions in apolar polymers are relatively weak and therefore a high degree of drawability can be obtained. Polar polymers on the other hand have relative strong interchain interactions, they are therefore less drawable. A shift higher than 20°C of the melting temperature can be obtained in case of highly extended iPP (draw ratios >14). Ultra‐drawn PE shows only 10°C overheating upon constraining and this is mainly due to the change in chain mobility for PE in the hexagonal phase. In case of PET and PA6, only draw ratios of 4 could be reached; however, temperature shifts of about 10°C for constrained fibers compared to unconstrained fibers could be measured. A proof of principle of the potential of the constraining concept for the manufacturing of single polymer composites is obtained by the preparation of single fiber model composites. The effect of the post‐drawing conditions on overheating is examined in details on the example of iPP. It is concluded that both post‐drawing temperature and ultimate draw ratio have a significant influence on the degree of overheating. POLYM. COMPOS., 26:114–120, 2005. © 2004 Society of Plastics Engineers
Fatigue crack propagation in composites with spherical fillers—part 1
Authors: Gadaree K. P. , Salee G.
Published: December 2004

A study of the effect of various percentages of a spherical filler in a brittle matrix resin on fatigue crack propagation rates was carried out. The resin was a low‐molecular‐weight [Mn‐8200;Mw/Mn= 2.04] Bisphenol A‐terephthalate/isophthalate thernmoplastic copolyester. The fly ash filler had a mean diameter of 20μ. Experiments were done with 10 to 40 wt.% filler compliance method. A paris law model fits the data for the unfilled and the 10 wt.% filled compositions. At higher percentages of filler, however, a pattern of increasing and decreasing crack growth rates is observed. The pattern is unique for a given specimen. A mechanism is proposed to explain this behavior.
Some effects of matrix and interface properties on the fatigue of short fiber‐reinforced thermoplastics
Authors: Mandell J. F. , McGarry F. J. , Huang D. D. , Li C. G.
Published: December 2004

The fatigue behavior of injection‐molded tensile bars of short‐fiber‐reinforced theromplastics is described and related to the fatigue behavior of the matrices and the strength of the fiber/matrix interface. A brittle matrix system based on polyphenylene sulfide is shown to behave in a similar manner to long‐fiber composites. Glass‐fiber reinforcement in this matrix gives fatigue sensitivity that correlaes with that of unimpregnated glass fiber strands, while carbon‐fiber rein‐forcement gives better fatigue resistance. A well‐bonded, due‐tile matrix system based on nylon 6,6 gives matrix‐controlled fatigue sensitivity. Fatigue data for glass‐ and carbon‐fiber‐reinfoced nylon 6,6 superimpose on the matrix fatigue data when normalized by the ultimate tensile strength. Another ductile matrix, polyetherther ketone, is very fatigue‐resistant, but its composite progressively loses its reinforcing effect in fatigue, apparently due to interface failure. A transitional matrix, polysulfone, shifts from ductile to fatigue‐crack‐dominated failure as the cyclic stress is reduced. Its composites show an analogous failure mode shift, and the high cycle‐fatigue response is correlated with fatigue‐crack‐growth data.
Effect of fiber‐aspect ratio and orientation on the stress‐strain behavior of aligned, short‐fiber‐reinforced, ductile epoxy
Authors: Masoumy E. , Kacir L. , Kardos J. L.
Published: December 2004

In the study of complex short‐fiber‐reinforced plastics behavior, it is helpful to begin with a well‐aligned short‐fiber system. This study isolates the effects of fiber‐aspect ratio and orientation distributions on the tensile stress‐ strain behavior and failure mechanisms for a system containing 50 vol% E‐glass fiber bundles in a ductileepoxy matrix. Using a system wherein the fiber orientation distribution was well‐characterized, it is shown that the fibers reinforced as bundles rather than as individual fibers. As the bundle‐aspect ratio varied from 185 to 557 for samples tasted in the longitudinal majoralignment direction, the modulus rose from 85 to 99 percent of the value for a continuous fiber system, while the strength rose only to about 60 percent of the continuous‐fiber system. The ductility of the matrix had no effect on the modulus or the longitudinal strengths, but the off‐axis strengths were significantly higher than has been reported for a comparable brittle‐matrix system. The effects of fiber orientation on modulus and strength were successfully fit with the Leknitskii and Azzi‐Tsai equations, respectively. SCanning electron micros‐copy showed excellent adhesion and no fiber brekage, except at the highest bundle‐aspect ratio. Even at off‐axis angles below 15°, a mixed mode failure mechanism occurs because of the fiber orientation distribution.
Temperature increase of sheet molding compound (SMC‐R65) in flexural fatigue test
Authors: Hoa S. V. , Nguyen Q. B.
Published: December 2004

The temperature increase in flexural fatigue testing of sheet‐molding compound SMC‐R65 is investigated within a range of testing frequencies from 1000 cpm to 2200 cpm. Variation of the testing frequency affects the temperature increase and, based on 10 percent reduction in flexural stiffness, the effect of changing frequency on the fatigue lives was not detected. Steady‐state temperatures are obtained in the case of specimens tested in air. A temperature analysis is carried out that gives reasonable agreement with experimental values.
Interlaminar shear properties of graphite fiber, high‐performance resin composites
Authors: Varma D. S. , Needles H. L. , Kourtides D. A. , Fish R. H.
Published: December 2004

Shear properties of laminates consisting of graphite fiber (Celion 6000, Celion 3000, and T‐300) and several resins (epoxy, hot melt‐bismaleimide, solvent bismaleimide, polyimide, and polystyrylpyridine (PSP)) were measured using the short‐beam test. The interlaminar shear strength of epoxy composites was hightest. All other resin composites showed considerably lower shear properties. The shear strengths deereased with temperature, with the loss up to 100°C being more pronounced. The PSP composites did not show a loss in strength in the temperature range investigated (room temperature to 250°C). Boiling the composite samples in water for 24 h resuled in negligible reduction in shear strength in all cases. The interlaminar shear properties depended on the fiberresin interfacial bond, the wetting characteristics of the resin, and the resin meechanical properties. Attempts were made to determine to what extent each of these factors controlled the shear properties of the composites studies. Thus, the interfacial bond between the resin and the single fiber was determined. Results showed that the lower shear strength of polyimide, bisimides and PSP composites, as compared to epoxy resin composites, seemed to be due to their corresponding low interfacial bond strengths. The subsequent decrease in shear strength with temperature appeared to be directly correlated to the decrease in bond strength. The wettability of carbon fiber tow with all these resins was also determined. The small variations in wetting characteristics of the resin did not seem to justify the rather large differences in shear‐strength properties observed.
Introductory remarks
Authors: Weiss Robert A.
Published: December 2004

No Absract.
Synthesis and characterization of bisimide amines and bisimide amine‐cured epoxy resins
Authors: Scola Daniel A.
Published: December 2004

A series of novel bisimide amines were synthesized and characterized and then utilized as curing agents with a standard epoxy resin, N,N′‐ tetraglycidyl‐methylenedianiline (TGMDA), known commercially as MY720. The bisimide amines (BIA's) were synthesized by reaction of 4,4′‐hexa‐ffuoroisopropylidine (biphthalic acid dianhydride) (6F anhydride) with aromatic and aliphatic diamines in dimethyl formamide at reflux temperatures in yields ranging 24 to 99 percent. The diamines used were 3,3′‐diaminodiphenylsulfone (3,3′‐DDS), 4,4′‐diaminodiphenylsulfone (4,4′‐DDS), 1,12‐dodecanediamine (1,12‐DDA), alone and as mixtures to produce the BIA's 6F‐3,3′‐ DDS, 6F‐4,4′‐DDS, 6F‐3,3′‐DDS‐4,4′‐DDS, 6F‐3,3′‐DDS‐1, 12‐DDA with various compositions, depending on the mode of addition and stoichiometry. The BIA's are isolated as mixtures containing monomer, oligomer, and polymeric species. They were characterized by elemental analysis, and high pressure liquid chromatography (HPLC). Epoxy resin specimens were fabricated by reaction of the standard epoxy (MY720) with the BIA and in some cases, mixtures of BIA and aromatic diamine, such as 3,3′‐DDS. The bisimide amine cured epoxies (IME's) were characterized for moisture absorption, thermal properties, physical and mechanical properties. The bisimide amine epoxy (IME) resins were also characterized as matrices in Celion 6000/bisimide amine cured epoxy (IME) composites. The relative toughness characteristics of each IME formulation was measured by the 10° offaxis tensile test by measuring the uniaxial tensile, shear strengths and shear‐strain‐to‐failure of the composite systems.
Use of processing aids and coupling agents in mica‐reinforced polypropylene
Authors: Chun I. , Woodhams R. T.
Published: December 2004

Low molecular weight waxes prepared by the maleation of thermally degraded polypropylene are effective substitutes for silane coupling agents in filled polypropylene resins. The addition of 1 to 5 percent maleated polypropylene wax increased the tensile and flexural strength of mica‐filled polypropylenes without significant changes in the modulus or fracture toughness. The waxes also aided dispersion, reduced melt viscosity, and permitted direct injection molding of powder blends without precompounding. The influence of maleated polypropylene wax coupling agents on the mechanical properties is similar to the published behavior of chlorinated paraffin waxes, but without the undesirable corrosiveness. The efficient utilization of untreated micas as reinforcing fillers for general purpose polypropylene homopolymers can have important cost savings in the fabrication of mica‐reinforced automotive components.
The effect of aspect ratio of inclusions on the elastic properties of unidirectionally aligned composites
Authors: Tandon G. P. , Weng G. J.
Published: December 2004

This paper examines the influence of aspect ratio α, from zero to infinity, on the effective elastic moduli of a transversely isotropic composite. The reinforcing inclusions, which could be flakes or short fibers, are assumed to be spheroidal and unidirectionally aligned. Of the five independent elastic constants, the longitudinal Young's modulus E11 and in‐plane shear modulus μ12 appear to increase with increasing aspect ratio, while the transverse Young's modulus E22, out‐plane shear modulus μ23, and plane‐strain bulk modulus K23, generally decrease. It is further noted that E11 is more sensitive to α when α > 1 but the others are more so when α < 1. The present analysis was carried out by the combination of Eshelby's and Mori‐Tanaka's theories of inclusions.
Polypropylene composites: Fracture mechanics analysis of impact strength
Authors: Bramuzzo M. , Savadori A. , Bacci D.
Published: December 2004

An investigation according to LEFM (Linear Elastic Fracture Mechanics) principles has been carried out to determine impact resistance of PP (polypropylene) containing calcium carbonate in comparison with other types of mineral fillers. The tests have also allowed us to emphasize the strong influence of matrix brittleness or ductility on decreasing or increasing of toughness. In any case, of those materials tested, the calcium‐carbonate‐filled polypropylene is the material with the best performance. Scanning microscope (SEM) analysis and comparison of the results with the theoretical models reported in the literature made it possible to point out some particular aspects of this type of behavior.
Fracture behavior of glass‐cloth‐reinforced composites
Authors: Agrawal D. C. , Agarwal B. D. , Banerji K.
Published: December 2004

The fracture behavior of glass‐cloth‐reinforced composites has been studied. Fracture of these composites proceeds by tensile failure of fibers rather than by the shear failure of the matrix or the interface. Although the spread of damage in these composites is restricted to small distances away from the crack path due to the interweaving of the fibers, this distance is found to be appreciably larger for the samples with smaller initial crack lengths. Characteristic distances associated with the Whitney‐Nuismer criteria are, in turn, found to be smaller for these composites than for the angle ply laminates or randomly oriented short‐fiber composites reported in literature in which the spread of the damage is much greater. Analysis through the crack growth resistance also supports this correlation with the extent of damage spread and indicates that the critical crack length for these composites may be equal to the best fit value of the characteristic distance of the average stress criterion.
Statistical aspects of tensile strength of aramid fibers and unidirectional composites
Authors: Kompaniets L. V. , Potapov V. V. , Grigorian G. A. , Prut E. V. , Enikolopian N. S.
Published: December 2004

The effect of gage length and temperature on tensile strength of aramid monofilaments, yarns, and strands has been studied in view of statistical models of the theory of strength. The tensile strength of monofilaments and yarns is found to decrease as the gage length is increased. The strength of strands remains constant. The temperature resistance of strands is determined by the glass transition temperature of a polymeric matrix.
Electrical resistivity behavior of solution‐cast metal‐filled composites
Authors: Singh Rajeev R. , Roberts Robert W.
Published: December 2004

Solvent‐cast metal‐filled composites made of polymethyl methacrylate and aluminum or copper exhibited electrical resistance behavior as is predicted by the percolation and tunneling mechanisms. A precipitous change in volume resistivity of about 1010 ohm‐cm was found to be thermally dependent at volume concentration of filler in the range from 17 to 19.5 percent. Materials with compositions at the conductive‐non‐conductive threshold showed semi‐conductor behavior and exhibited memory switching.
Fracture behavior of mica‐reinforced polypropylene: Effects of coupling agent, flake orientation, and degradation
Authors: Vu‐Khanh T. , Fisa B.
Published: December 2004

The effects of such factors as flake size, orientation, and surface treatment on the fracture mechanism of mica‐reinforced polypropylene were investigated. Concepts of post‐yield fracture mechanics were used to characterize the crack initiation and propagation resistances of the composite. It was found that better flake alignment slightly increases the yield strength but does not affect the crack growth resistance of the material. Flake size degradation during processing leads to an increased crack initiation resistance but reduces the tearing capacity and the maximum crack growth resistance of the composite, due to a reduction of the extent of matrix deformation. In the same manner, the use of a coupling agent diminishes the effect of matrix drawing and the total energy dissipated during the fracture process, even though the crack initiation resistance can be increased.
The silane interphase of composites: Effects of process conditions on γ‐aminopropyltriethoxysilane
Authors: Culler S. R. , Ishida H. , Koenig J. L.
Published: December 2004

FT‐IR spectroscopy was used to collect spectra of γ‐aminopropyltriethoxy silane (γ‐APS) coupling agent deposited on KBr plates, modeling the silane interphase of composites, to study the effects of heating the γ‐APS film under various environmental conditions. This coupling agent is used in fiber‐reinforced epoxy composites. An aminebicarbonate salt forms when the sample is dried in a moist carbon dioxide environment giving rise to a series of bands from 2800 to 2000 centimeter−1 (cm−1) and bands at 1637 cm−1, 1330 cm−1, 696 cm−1, and 663 cm−1. The primary amine group is split into two bands at 1572 cm−1 and 1486 cm−1 in the NH3+ form. Heating removes the aminebicarbonate salt at temperatures above 95°C and condenses the γ‐APS polymer to a polysilsesquioxane film. The aminebicarbonate salt partially reforms if the γ‐APS film is stored in a moist CO2 environment. At temperatures above 120°C the primary amine of γ‐APS is oxidized in air to imine groups. In the process of evolving the CO2 the polymer is further condensed and the amine groups can be converted to imines if the temperatures exceeds 120°C. Both processes reduce the reactivity of the coupling agent with the epoxy resin. The structure of the silane interphase must be controlled during the processing of the composite to yield materials with maximum properties.
The effect of fiber‐matrix stress transfer on the strength of fiber‐reinforced composite materials
Authors: Dilandro L. , Dibenedetto A. T. , Groeger J.
Published: December 2004

A model for the mechanism of tensile failure in oriented fiber composites based on random fragmentation of the reinforcing fibers biased by stress concentrations at fracture sites has been developed. Single‐fiber composites and composite strands of 34 to 36 volume percent fiber were prepared from an epoxy resin reinforced with Hercules AS4, HMS4, and IM6G carbon fibers. Fiber strength distributions and single‐fiber composite fragmentation data were used to calculate theoretical composite tensile strengths, which were then compared with experimental values. The fractures in single‐fiber composites were observed in situ under cross‐polarized light, and the mechanisms of interfacial failure were discussed.
Review of methods for characterization of interfacial fiber‐matrix interactions
Authors: Narkis M. , Chen E. J. H. , Pipes R. B.
Published: December 2004

This paper reviews various common methods for studying fiber‐matrix interaction with specific evaluation of the critical fiber length method. Commonly accepted methods are often shown to be unsatisfactory because interfacial results may not be independent of fiber tensile strength properties. A new concept for measuring fiber‐matrix interaction in a single filament, or in a single uniaxially reinforced thin layer, sandwiched between two relatively thick unreinforced layers is proposed. This method relies upon variable curvature bending jigs introducing continuously changing longitudinal shear profiles across the fiber surface by clamping the sandwiched specimen onto the jig surface and also upon the availability of physical detection methods of debonding fronts.
Some studies on glass fiber‐reinforced polypropylene. Part I: Reduction in fiber length during processing
Authors: Gupta V. B. , Mittal R. K. , Sharma P. K. , Mennig G. , Wolters J.
Published: December 2004

The reduction in fiber length during extrusion and injection molding of two commercial glass fiber‐reinforced polypropylene products containing 30 percent by weight of glass fibers was studied. The first product had very small fibers of average length around 0.5 mm and also contained a coupling agent. The second product contained relatively longer glass fibers of 9 mm length and no coupling agent. In both cases, fiber attrition occurs predominantly at the solid‐melt interface in the meiting zone of the extruder. However, in the short fiber granules, the maximum of the length distribution, which for the initial sample is around 0.5 mm, moved to shorter fiber lengths along the screw channels further from the hopper. In the long fiber granules, a bimodal length distribution was obtained in the intermediate channels; the first maximum was around the original length of 9 mm and the second centered around 0.5 mm. Thus, the forces at the solid‐melt interface result in fiber breakage to lengths which are predominantly around 0.5 mm. The fiber attrition was observed to be more severe in injection molding apparently because of higher shear rates and also because the fibers had to pass through narrow channels. The measured distributions of fiber length along the screw channels for the two products are presented, and the possible mechanisms of fiber breakage are discussed. The mechanical properties of samples containing different fiber length distributions and the effects of fiber length and interfacial adhesion on properties are presented and discussed in Part II.
Mat formation and unstable flows of highly filled suspensions in capillaries and continuous processors
Authors: Yilmazer Ulku , Gogos Costas G. , Kalyon Dilhan M.
Published: December 2004

Suspensions, which are filled at loading levels approaching their maximum packing fractions, present special processing challenges. The flow and deformation behavior of such highly filled suspensions are dominated by strong slip effects. Furthermore, during pressure driven flows of these suspensions, the polymer matrix can filter out, giving rise to demixing and unstable flows. In this study, the capillary flow and extrusion of highly filled suspensions of ammonium sulfate and other salt fillers in a poly(butadiene acrylonitrile acrylic acid), PBAN matrix were investigated. The experimentally observed instabilities were elucidated in conjunction with a proposed mechanism, involving slip and filtration rates. This mechanism suggested greater affinity to unstable flows with relatively lower matrix shear viscosity, greater particle size of the filler, and greater convergence ratio; all of which were experimentally verified.