bluuebunny/crossref_metadata_2025 huggingface dataset:
Rechnerische Beschreibung des Kriechverhaltens ausgewählter hochwarmfester Legierungen Teil 2: Kriechgleichung Für die Werkstoffsorte IN‐939
Authors: Kloss K. H. , Granacher J. , Pfenning A.
Published: December 2004

Zur Aufstellung einer Kriechgleichung der Werkstoffsorte IN‐939 werden aus einer umfangreichen Kriechdatensammlung mittlere Zeitdehngrenzkurven und Zeitbruchkurven gebildet und hieraus mittlere Kriechkurven abgeleitet. Auf deren Basis wird eine bereits für einen Einzelwerkstoff erstellte Kriechgleichung an das durchschnittliche Kriechverhalten der Werkstoffsorte im gesamten anwendungsrelevanten Bereich angepaßt.
Study on numerical approaches for the evaluation of J‐Integral Results in 3D problems
Authors: Grebner H.
Published: December 2004

For numerical analyses of fracture mechanics problems often a combination of the finite element method with a post processor program for the evaluation of J‐integral values is used. Instead of calculating a line integral as originally proposed by RICE it is reasonable to evaluate surface or volume integrals (for two or three dimensional calculations, respectively) in this case.

In this paper 3D‐formulations proposed by DE LORENZI and ATLURI are considered and several possibilities of the numerical realisation of these formulations are described. While the De Lorenzi proposal is contained as subroutines in the GRS‐version of the standard finite element program ADINA, the Atluri formulation is used in separate post‐processing programs developed by GRS.

As a first application three‐dimensional calculations of a compact‐tension‐shear specimen are considered.
Mathematical Model for high temperature properties of cast nickel superalloys with high content of gamma prime phase
Authors: Efimov A.
Published: December 2004

This investigation relates to structural cast superalloys with improved oxidation resistance in the temperature range of 1100–1200°C. It was tried to clarify the role of heavy metal elements on mechanical properties of an alloy in the system Ni‐17at% Al‐3at% Cr‐Mo‐Ta‐W. Solidus temperature, yield strength at 20°C, ultimate tensile strength at 1200°C of polycrystal alloys and creep‐rupture life at 1000°C and 1200°C of single crystals <001> were investigated by means of experimental design and regression analysis techniques, It was determined that solidus temperature do not depend from W content, yield strength at 20°C and ultimate tensile strength at 1200°C strongly depend on Ta and W contents. The properties sharply increase with simultaneous adding of Ta+W. At 1200°C Mo content is a critical factor. The influence of alloying with Ta and W on the creep resistance of single crystals was examined. With increase of test temperature dependence of creep resistance from refractory additives appears to increase, but interval of an optimum alloying narrows.
Barkhauseneigenspannungsmessungen an einem schadhaften Hydraulikzylinder mit tribotechnischer Funktionsschicht
Authors: Richter H.
Published: December 2004

Von der Zylinderinnenfläche eines Flugzeug‐Hydraulikzylinders war ein Schwingbruch ausgegangen und hatte zu einer Leckage geführt. Hauptursache für den Schwingbruch waren Anrisse, die bei der Endbearbitung der Zylinderinnenfläche zusammen mit Zugeigenspannungen in örtlich begrenzten Bereichen der Randschicht des Grundmaterials erzeugt worden waren. Mittels Barkhausenrauschanalyse ließen sich Eigenspannungsunterschiede an der Zylinderinnenfläche messen, ohne daß die dort aufgebrachte tribotechnische Funktionsschicht aus Chrom entfernt werden mußte. Die Ergebnisse der Barkhausenspannungsmessungen wurden durch stichprobenartige röntgenografische Eigenspannungsmessungen bestätigt.
Bewertung zyklischer Verformungsvorgänge metallischer Werkstoffe mit Hilfe mechanischer, thermometrischer und elektrischer meßverfahren Characterization of cyclic deformation behaviour by mechanical, thermometrical and electrical methods
Authors: Eifler D. , Piotrowski A.
Published: December 2004

Zyklische Verformungsvorgänge verursachen mikrostrukturelle Werkstoffveränderungen, die zum Versagen führen können. Am Beispiel normalisierter und vergüteter Stähle sowie verschiedener Sinterstähle wird gezeigt, wie mechanische, thermometrische und elektrische Meßverfahren genutzt werden können, das zyklische Verformungsverhalten umfassend zu bewerten.
Numerisch ermittelter Parameter C* zur Beschreibung des Kriechrißverhaltens
Authors: Granacher J. , Tscheuschner R. , Mao T. S. , Maile K. , Bareiß J.
Published: December 2004

In früheren Untersuchungen gewonnene umfangreiche Kriechrißergebnisse an drei warmfesten Stählen werden mit einem Parameter C* beschrieben, der aufgrund inelastischer Finit‐Element‐Analysen berechnet wird. Die Streubänder der Kriechrißeinleitungsdauer und der Kriechrißgeschwindigkeit werden für diesen Parameter ermittelt. Außerdem werden Anwendungsgesichtspunkte zur Bauteilberechnung aufgeführt.
Mikrostrukturelle, mechanische und korrosive Eigenschaften reibrührgeschweißter Stumpfnähte in Aluminiumlegierungen
Authors: Donne C. Dalle , Braun R. , Staniek G. , Jung A. , Kaysser W. A.
Published: December 2004

Das Reibrührschweißen (friction stir welding FSW) ist ein neues Fügeverfahren, mit dem auch die schwer schmelzschweißbaren, höherfesten Aluminiumlegierungen ohne große Festigkeitsverluste verschweißt werden können. Erste Ergebnisse von Untersuchungen an selbst hergestellten FSW‐Stumpfnähten der Aluminiumlegierungen 2024–T3 und 6013‐T4 werden vorgestellt. Zunächst wird das Gefüge der Naht und der Wärmeeinflußzone mikrostrukturell und durch Härteverläufe charakterisiert. Weiterhin wird mit Zug‐, Schwingfestigkeits‐ und Rißfortschrittsversuchen nachgewiesen, daß insbesondere die FSW‐Nähte der Legierung 2024‐T3 außerordentlich hohe mechanische Belastungen ertragen. Abschließende Korrosionsuntersuchungen der FSW‐Nähte zeigen eine gewisse Anfälligkeit der abschreckempfindlichen Legierung 2024‐T3 für interkristalline Korrosion und Schichtkorrosion.
Versagen von Keramik im Hochtemperaturbereich
Authors: Fett T. , Munz D.
Published: December 2004

Das Versagensverhalten keramischer Werkstoffe im Hochtemperaturbereich ist sehr komplex. Neben den schon bei Raumtemperatur wirksamen Effekten der unterkritischen Rißausbreitung und der zyklischen Ermüdung müssen noch die Effekte des Kriechens an sich sowie die Materialschädigungen beim Kriechbruch und beim Kriechrißwachstum berücksichtigt werden. Der größte Teil der Arbeit ist der Beschreibung des unterkritischen Rißwachstums und des Kriechrißwachstums gewidmet. Einer der Schwerpunkte liegt dabei auf der Beschreibung und Anwendung des C*‐Konzepts.
Allurin, a 21 kD sperm chemoattractant, is rapidly released from the outermost jelly layer of the Xenopus egg by diffusion and medium convection
Authors: Xiang Xueyu , Kittelson Andrew , Olson John , Bieber Allan , Chandler Douglas
Published: December 2004

Allurin, a 21 kD protein from Xenopus laevis egg jelly, has been demonstrated to attract sperm by video microscopy and by quantitative chemotaxis chamber assays. Here, we use immunocytochemistry to demonstrate that this sperm chemoattractant is located in the outermost layer of egg jelly (J3) and is rapidly released into the surrounding medium. SDS–PAGE analysis and Western blotting confirm the appearance of allurin in the medium within 1.5 min and separation of proteins in the medium by anion exchange FPLC, shows that nearly half of the allurin released over a 12‐hr period is discharged in the first 5 min. The kinetics of allurin release from J3 and its appearance in the medium were quantitatively accounted for, by computer simulation of mathematical diffusion and convection models. Comparison of simulation data to quantitative measurements of allurin appearance in the medium suggests that allurin, although larger than most chemoattractants, is effectively dispersed by a combination of diffusion and medium mixing at the jelly surface during spawning. Our model further predicts that the innermost jelly layer, J1, is less permeable to allurin than the other layers, allowing it to act as a “reflector” to speed up allurin discharge. Mol. Reprod. Dev. 70: 344–360, 2005. © 2005 Wiley‐Liss, Inc.
Identification of maternal mRNAs in porcine parthenotes at the 2‐cell stage: A comparison with the blastocyst stage
Authors: Hwang Kyu‐Chan , Lee Hwa‐Young , Cui Xiang‐Shun , Kim Jin‐Hoi , Kim Nam Hyung
Published: December 2004

Successful embryonic development is dependent on the temporal and stage‐specific expression of appropriate genes. Currently, information on specific gene expression during early cleavage‐stage embryos before zygotic gene activation (ZGA) is limited. In the present study, we compare gene expression between porcine 2‐cell and blastocyst stage parthenotes to identify genes that are specifically or predominantly expressed by employing annealing control primer (ACP)‐based GeneFishing PCR. Using 60 ACPs, we identified and sequenced nine differentially expressed genes (DEGs). A BLAST search revealed that cloned genes or ESTs (GDI‐2, MTMR3, MKLN1, NUP88, ePAD, CIRHIM, UPF3B, ITGA2, and CGI‐140) had significant sequence similarities with known genes (78–95%) of other species in the GenBank/EMBL database. Real‐time reverse transcriptase‐polymerase chain reaction (RT‐PCR) data disclosed that these genes were regulated upstream in metaphase II (MII) oocyte, 1‐cell, and 2‐cell stage embryos during early pre‐implantation. Similarly, upregulation was observed in MII mouse oocytes and 1‐cell stage embryos before ZGA, suggesting that these nine differentially expressed orthologous genes play important roles during early cleavage before ZGA. Further analysis of the differentially expressed genes identified in this report should provide the basis for research on early cleavage and activation of the embryonic genome. Mol. Reprod. Dev. 70: 314–323, 2005. © 2005 Wiley‐Liss, Inc.
Expression of fibroblast growth factor‐8 and its cognate receptors, fibroblast growth factor receptor (FGFR)‐3c and‐4, in fetal bovine preantral follicles
Authors: Buratini J. , Glapinski V.F. , Giometti I.C. , Teixeira A.B. , Costa I.B. , Avellar M.C.W. , Barros C.M. , Price C.A.
Published: December 2004

Paracrine cell signaling is thought to be important for ovarian follicle development, and a role for some members of the fibroblast growth factor (FGF) family have been suggested. In the present study, we tested the hypothesis that FGF‐8 and its cognate receptors (FGFR‐3c and FGFR‐4) are expressed in bovine preantral follicles. Reverse transcription‐polymerase chain reaction was used to amplify bovine FGF‐8, FGFR‐3c, and FGFR‐4 from preantral follicle samples and a variety of fetal and adult tissues. All three genes were widely expressed in fetal tissues, with a restricted expression pattern in adult tissues. FGF‐8 and FGFR‐3c were expressed in secondary follicles in 70% of fetuses examined, whereas FGFR‐4 expression was significantly less frequent (20%). FGFR‐3c expression frequency was significantly lower in primordial compared to secondary follicles, and FGF‐8 expression showed a similar trend. FGFR‐4 was only observed when all follicle classes of an individual were expressing both FGF‐8 and FGFR‐3c. We conclude that FGF‐8 and its receptors are expressed in preantral follicles in a developmentally regulated manner. Mol. Reprod. Dev. 70: 255–261, 2005. © 2005 Wiley‐Liss, Inc.
Postpartum depression and related psychosocial variables in Hong Kong Chinese women: Findings from a prospective study
Authors: Leung Sharron S.K. , Martinson Ida M. , Arthur David
Published: December 2004

Research on predictors of postpartum depression (PPD) in Hong Kong (HK) Chinese women is scant. A prospective study with 385 HK Chinese postpartum women was conducted to identify correlations between PPD and demographic variables, and antenatal depression and psychosocial variables, and to determine which of these variables were predictors of PPD. Using the Edinburgh Postnatal Depression Scale (EPDS), we classified 19.8% of participants as postnatally depressed. Fifty‐six percent of the variance in PPD was explained by social support and stress factors. However, social support factors accounted for only a small percentage of that variance. The major predictors were antenatal depression, postnatal perceived stress, and childcare stress. HK women may benefit from a culturally appropriate intervention focused on reducing stress in the postpartum period. © 2004 Wiley Periodicals, Inc. Res Nurs Health 28:27–38, 2005
Time optimal factorizations on compact Lie groups
Authors: Dirr G. , Helmke U. , Kleinsteuber M.
Published: December 2004

In this paper we study the relationship between factorization problems on SU(2n) or more generally on compact Lie groups G and time optimal control problems. Both types of problems naturally arise in physics, such as in quantum computing and in controlling coupled spin systems (NMR‐spectroscopy). In the first part we show that certain factorization problems can be reformulated as time optimal control problems on G. In the second part a necessary condition for the existence of finite optimal factorizations is discussed. At the end we illustrate our results by an example on Euler angle factorizations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Iterative Refinement Revisited
Authors: Drygalla Volker , Zielke Gerhard
Published: December 2004

Die Verfügbarbarkeit von effektiven Algorithmen zur exakten Berechnung von Skalarprodukten ermöglicht die Nachiteration von Lösungen linearer Gleichungssysteme mit direkten wie iterativen Methoden im nichtsingulären wie überbestimmten Fall und bietet weite Anwendungsmöglichkeiten für nichtlineare Gleichungssysteme, insbesondere für die Behandlung von Eigenwertaufgaben. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computing Interior Eigenvalues of Conservative Gyroscopic Problems
Authors: Markiewicz Marta , Voss Heinrich
Published: December 2004

We propose a new method for computing a large number of eigenpairs in the interior of the spectrum for conservative gyroscopic eigenproblems by the nonlinear Arnoldi method combined with a localized version of safeguarded iteration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalization of a Parametric Fixed‐Point Iteration
Authors: Popova Evgenija D.
Published: December 2004

Based on new sufficient regularity conditions, Rump's method for solving parametric interval linear systems is generalized which expands its scope of applicability over a class of co‐called column‐dependent parametric matrices. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite difference schemes for some types of boundary value problems with interfaces
Authors: Jovanović Boško S. , Vulkov Lubin G.
Published: December 2004

Stability and convergence of finite difference schemes approximating an elliptic partial differential equation with interface are examined. A convergence rate estimate compatible with the smoothness of the input data is obtained. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A constitutive model for non‐linear behavior of SMC accounting for linear viscoelasticity and micro‐damage
Authors: Oldenbo M. , Varna J.
Published: December 2004

An approach for modeling sheet molding compound (SMC) composites as viscoelastic damageable material is presented. Continuum damage mechanics theory by Chow and Wang (Int. J. Fract., 33, 3 (1987)) was used in combination with linear viscoelasticity. The model was applied to a modern SMC composite material containing both hollow glass spheres for low density and toughening additive for improved impact resistance. Tensile tests and uniaxial creep test were employed to build the constitutive model. Validation was done by comparing test data with simulations of uniaxial creep on material with different degrees of damage. The model has good accuracy at moderate damage levels under controlled time‐dependent crack propagation. Tensile testing at two different fixed strain rates was simulated using quasi‐elastic method to calculate relaxation modulus. The model predicts the stress‐strain curve with good accuracy until the region is close to failure, where new mechanisms not accounted for are taking place. Finally, a simulation of a cyclic tensile test with increasing maximum strain per cycle was performed, and since both damage and viscoelasticity are included in the model, the slope change, accumulation of residual strain, and hysteresis in the stress‐strain, loading‐unloading curve are predicted. POLYM. COMPOS., 26:84–97, 2005. © 2004 Society of Plastics Engineers
Plastic composites for electromagnetic interference shielding applications
Authors: Bigg D. M. , Stutz D. E.
Published: December 2004

Research in the past eight years has established the ability of polymer composites made with sufficient electrical conductivity to be suitable as shields against electromagnetic interference (EMI). A number of conductive fillers have been used to produce such composites. These include carbon black, carbon fibers, metal fibers, metal flakes, and metal‐coated glass fibers. Each filler offers its own set of advantages and disadvantages. An important aspect of developing polymeric composites for EMI shielding applications is measuring their shielding ability in areliable, easy‐to‐use test facility. Once a reliable test has been developed, basic data relating the bulk conductivity (or surface conductivity of coatings) can be generaated. The objective of this article is to discuss the relative utility of the different types of fillers commonly used, present an analysis of the utility of different testing approaches, and show data correlating volume resistivity with shielding effectiveness.
Hydrolysis and condensation of silanes in aqueous solutions
Authors: Savard S. , Blanchard L.‐P. , Léonard J. , Prud'homme R. E.
Published: December 2004

Aminosilanes hydrolyze rapidly in aqueous acidic solutions and exhibit good stability; however 1H NMR measurements indicate that γ‐MPS (γ‐methacryloxypropyltrimethoxy silane) hydrolyzes slowly and condenses rapidly under similar conditions. The rate constant of these two reactions depends upon the pH of the solution, and the rate constant of the condensation reaction also depends upon the initial γ‐MPS concentration. The hydrolysis is faster and the condensation slower at low pH's. These factors explain why an induction period is observed before the adsorption of γ‐MPS onto mica takes place and why it does not occur if the induction period is too long. Using the Lentz technique, it is also shown that the main species resulting from the condensation of a concentrated γ‐MPS solution is a cyclic trimer or tetramer, in agreement with literature results.
The effect of silica on the crystallization of isotactic poly(propylene oxide)
Authors: Kennedy M. A. , Brown G. R. , St‐pierre L. E.
Published: December 2004

The addition of one part, by weight, of fine particle silica to one hundred parts isotactic poly(propylene oxide) causes a retardation in the rate of radial growth of spherulites at all temperatures between 268 and 313 K. The results have been fitted empirically by use of the Hoffman‐Lauritzen equation suitably modified to account for effects due to the presence of the silica. At certain temperatures the presence of the silica also causes a change in the morphology of the spherulites.
Stress dependence of the coefficient of moisture diffusion in composite materials
Authors: Neumann Shoshana , Marom Gad
Published: December 2004

A model for the effect of external loading on diffusion into the bulk resin matrix of unidirectional composite materials is proposed. The model attributes the effect to a change in the free volume of the resin matrix, which is equal to its volume strain. The latter is calculated by substracting the volume strain of the fibers from that of the composite. The ratio of the diffusion coefficients in the stressed and unstressed states is expressed as a function of the stress level, the volume fraction of the fibers, and the angle between the applied stress and the fiber direction. Calculations for a glass‐fiber‐reinforced epoxy composites are presented.
Processing‐property relationships in compression molding of sheet molding compounds
Authors: Oh Sang Yeol , Han Chang Dae
Published: December 2004

An experimental investigation was conducted into establishing relationships between the processing variables and the mechanical properties of compression‐molded parts of sheet molding compounds (SMC). Emphasis was placed on investigating the effects on the tensile properties, impact strength, and dynamic mechanical properties of composite specimens, of low‐profile additives, and of treating glass fibers (for reinforcement) with sizing chemicals. The processing variables investigated were cure time, mold temperature, and mold pressure. It was found that: (1) An optimum cure time and mold temperature exist for achieving molded SMC composites of the greatest tensile and impact strengths; (2) Of the four different types of low‐profile thermoplastic additives employed, the poly(vinyl acetate) modified with acrylic acid gives rise to molded SMC composites having the greatest tensile and impact strengths; (3) An optimum cure time and mold temperature exist for achieving the highest glass‐transition (Tg) of the low‐profile additive; (4) The values of cure time and mold temperature that have yielded the greatest tensile and impact strengths also yield molded specimens having the highest Tg of the low‐profile additive.
Experimental verification of an optimal thermal design in a compression mold
Authors: Barone M. R. , Caulk D. A. , Panter M. R.
Published: December 2004

A production sheet molding compound (SMC) mold for an automotive hood outer panel was instrumented with 64 thermocouples to measure cavity surface temperatures along two cross‐sections in each mold half and regulate the supply of steam to each heating line. The positions and temperatures of each heating line in the mold were optimized using an in‐house computer program to produce a minimum spatial variation in cavity surface temperature during steady cyclic molding. Provision was also made to heat the mold conventionally so that optimal and conventional heating could be directly compared in the same mold. While maintaining a 78 s overall molding cycle, the conventional heating system eventually produced a 10°C temperature variation on the cavity surface. This, in turn, led to serious resin undercure and severe difficulties in removing the part from the mold. When the optimal heating design was substituted in place of the conventional system, the surface temperature variation was reduced to less than 3°C and the problems experienced with conventional heating disappeared. For the most part, the measured temperatures in these experiments agreed with the results of the computer analysis to within 1°C.
Polyetheretherketone (PEEK): Processing‐structure and properties studies for a matrix in high performance composites
Authors: Seferis James C.
Published: December 2004

The processing, structure and properties of polyetheretherketone (PEEK) semicrystalline thermoplastic as matrix polymer for high performance composites has been investigated in this work. In processing PEEK samples with different crystallinities, a specially designed mold capable of cooling the polymer in excess of 115°C/s from its melt temperature was constructed. In addition, during processing studies, a reaction of PEEK in the presence of copper was discovered. Analysis of the samples in terms of their crystallinity values also provided a new method for measuring crystallinity of the matrix in the composite. Crystallization of low crystalline samples at room temperature in the presence of methylene chloride was also confirmed for the first time with polarized microscopy. However, at the same time, the excellent hygrothermal resistance of PEEK was also confirmed. Finally, dynamic mechanical and stress‐strain experiments with samples of different crystallinities elucidated the dependence of these properties to crystallinity. However, this study also elucidated that under normal processing conditions for high performance composites, PEEK properties may not be strongly affected by different levels of crystallinity.
Melt rheology of highly loaded ferrite‐filled polymer composites
Authors: Saini D. R. , Shenoy A. V. , Nadkarni V. M.
Published: December 2004

This paper presents new experimental data on the viscosity of ferrite‐filled polymers at high levels of loading. The choice of matrix and the choice of filler and filler loading has direct relevance to commercially important systems of magnetic plastics and rubbers. The effect of shear rate, concentration, and temperature on the rheological behavior of such highly loaded systems has been discussed in detail. The differences in the relative viscosities between the filled and unfilled systems for various matrices have been explained on the basis of polymer filler affinity and filler‐filler interaction.
Electrodeposition of a polymer interphase in carbon‐fiber composites
Authors: Subramanian R. V. , Crasto A. S.
Published: December 2004

The performance of an electrodeposited interphase of poly(butadiene‐co‐maleic anhydride) (BMA) in carbon‐fiber composites is investigated. Carbon fibers are electrocoated with BMA from an aqueous solution and the coated fibers are fabricated into composite bars for evaluation of mechanical properties. These composites show superior impact strength, but lower interlaminar shear strength, compared to composites made from commercially treated fibers. It is suggested that unsaturation in the butadiene segments of the interphase polymer leads to the formation of a crosslinked layer during electrodeposition and subsequent drying. Inadequate penetration of this interphase by bulky epoxy molecules leads to a weak interphase/matrix interface which is the locus of failure, generating the observed mechanical properties. These conclusions are supported by examination of the fracture surfaces by Scanning Electron Microscopy. Further evidence of lack of matrix penetration into the interphase comes from electron microprobe line scans for bromine performed on cross‐sections of single‐filament composites, the bromine being introduced into the matrix via a brominated epoxy resin. Appropriate control of the chemical structure and physical characteristics of the interphase polymer is thus indicated, for acieving simultaneous improvements in impact and interlaminar shear strengths.
Property modification of bulk molding compounds for use in injection molding
Authors: Pritchard M. , Gibson A. G.
Published: December 2004

Although impact and flexural strength of injectionmolded bulk molding compounds increase initially with glass fiber content, these properties level out at a glass volume fraction between 0.1 and 0.2, limiting the achievable properties. Use of “special purpose” polyester resins gives no significant improvement in impact. The impact strength limitation is not worsened, however, by using the maximum processable level of filler, this being true for all fillers commonly used in polyester compounds. Replacement of a fraction of the glass by poly(ethylene terephthalate) fibers results in a substantial improvement in impact strength.
Spectroscopic studies of the gradient in the silane coupling agent/matrix interface in fiberglass‐reinforced epoxy
Authors: Hoh K.‐P. , Ishida H. , Koenig J. L.
Published: December 2004

Differential scanning calorimetry, Fourier transform infrared, and solid‐state carbon 13 nuclear magnetic resonance were used to study the silane coupling agent/epoxy resin interface. Penetration of epoxy into the hydrolyzed silane has been shown. The addition of a solvent can further increase the penetration of epoxy into the hydrolyzed silane by decreasing the viscosity of the epoxy. Bulk models of the gradient in the silane coupling agent/epoxy interface have shown that the concentration of silane and the degree of hydrolysis of the silane can determine the rigidity or mobility of the interphase region. When the silane is hydrolyzed, the possible formation of entanglements may increase the rigidity of the system and decrease the degree of phase separation through the formation of an interpenetrating network.
Mechanics of short fibers in filled styrene‐butadiene rubber (SBR) composites
Authors: Rueda L. Ibarra , Antón C. Chamorro , Rodriguez M. C. Tabernero
Published: December 2004

Different short fibers (glass, carbon, cellulose, polyamide, and polyester with aspect, length/diameter, ratio of 600, 860, 500, 83, and 330 respectively) were added to styrene‐butadiene rubber (SBR) matrix filled with an inorganic semireinforcing mineral (sepiolite). In all cases, 18 parts by volume of fiber per 100 parts by mass of rubber were added. The fiber orientation attained (more than 60%) was evaluated by a ratio of directional mechanics on uncured samples. In glass and carbon fiber composites, because of decreases in fiber aspect ratio after mixing (10 and 35 respectively), no improvements in properties were obtained. The presence of fibers yields a large increase in green strength, stress at low strain, and tear strength. Logically, the elongation at break diminishes. The uncured and cured properties present a remarkable anisotropy. The adhesive employed (resorcinol‐formaldehyde) to increase fiber‐to‐matrix adhesion enhanced the composite properties, especially in the case of polyester fiber composites. Thus, for polyester fiber composites, green strength became 15.85 kg/cm2; stress at 25% strain, 10.2 MPa; tensile strength, 6.3 MPa; elongation at break, 36%; tear strength, 70 N; and swelling in longitudinal direction, 1.06.
Radiation‐curable carbon fiber prepreg composites
Authors: Saunders Chris B. , Dickson Lawrence W. , Singh Ajit , Carmichael Alistair A. , Lopata Vince J.
Published: December 2004

Radiation processing is the utilization of ionizing radiation, usually photons or electron beams, to produce useful physical and chemical changes in a material. A potential application for electron beam processing for composite manufacturing is for curing carbon fiber prepregs. These prepregs, carbon fibers or fabrics preimpregnated with liquid polymer resin, are commonly used in the aircraft industry. Their use, however, can be time consuming and labor intensive. The advantages of radiation curing over thermal or chemical curing methods include improved rate control, reduced curing times, and curing at ambient temperature. There is no need for chemical initiators. A radiation‐curable prepreg has been designed to meet the mechanical and physical property specifications of a leading aircraft manufacturing company. The resin is a mixture of an expoxy diacrylate, polybutadiene diacrylate, and a multifunctional monomer. This resin was used to impregnate a plain weave carbon fabric, at a loading of 35 percent (by mass), using a solvent process. Preliminary characterization studies show that the cured polymer produced by irradiation in air to a dose of 40 kGy is amorphous with a maximum gel fraction of 85 percent. The softening point of the polymer varied from 228°C (30‐kGy sample) to 237°C (50‐kGy sample). The linear thermal expansion coefficient of the polymer was 1.7 × 10−4 m/m°C from 25°C to 150°C and was unaffected by varying the applied dose from 30 to 50 kGy.
Use of wood fibers in thermoplastic composites: VI. Isocyanate as a bonding agent for polyethylene–wood fiber composites
Authors: Raj R. G. , Kokta B. V. , Maldas D. , Daneault C.
Published: December 2004

Linear low density (LLDPE) and high density (HDPE) polyethylenes were reinforced with wood fibers of aspen chemithermomechanical (CTMP) pulp. The different isocyantes: (i) polymethylene (polyphenyl isocyanate), (ii) tolene –2–4‐diisocyanate, (iii) 1–6 hexamethylene‐diisocyanate, and (iv) ethyl isocyanate used as bonding agents improved the tensile properties of the composites. HDPE performed better in comparison with LLDPE composites. Also, shorter fibers (mesh size 60) produced higher tensile strength and modulus in HDPE. The comparison of HDPE reinforced with aspen, mica, and glass fibers showed the effectiveness of wood fibers in terms of their cost and performance.
Analysis of coating on glass fiber reinforcements
Authors: Drumm Charlene A. , Ulicny John C.
Published: December 2004

Several commercially available glass fiber reinforcements were analyzed to determine the amounts (“loadings”) and types of coatings applied by their manufactures. Loadings were determined by solvent extraction and pyrolysis and ranged from 0.54 to 4.22 weight percent with the heaviest amounts on random mats and the least amounts on rovings intended for filament winding and weaving. The major components of the solvent‐extracted coatings were identified by infrared (IR) and proton nuclear magnetic resonance (NMR) spectroscopies. All of the coatings analyzed could be sorted into three classes of coatings which matched the matrix types recommended by the glass manufacturers. In each case, the coating consisted primarily of a mixture of two separate materials, designated as the “unreacted resin” and the “lubricant”.
Synergism on electromagnetic inductance (EMI)‐shielding in metal‐ and ferroelectric‐particle filled polymers
Authors: Wenderoth K. , Petermann J. , Kruse K.‐D. , ter Haseborg J.‐L. , Krieger W.
Published: December 2004

In this paper the electromagnetic inductance (EMI)‐shielding of metal‐and ferroelectric‐particle filled polymers is described. The composite, containing only metallic fillers, has a shielding effectiveness comparable to conventional products. The addition of a few percent of ferroelectric material to this composite enhances the shielding behavior by several orders of magnitude—without increasing its electrical conductivity. In this three component composite the shielding effectiveness reaches a maximum close to the ferroelectric/paraelectric transition temperature. The synergetic effect, obtained by the addition of ferroelectrical particles, is related to the high dielectric losses of ferroelectric material close to its transition temperature.
Interfacial shear strength and failure modes of interphase‐modified graphite‐epoxy composites
Authors: Wimolkiatisak A. S. , Bell J. P.
Published: December 2004

Electrocopolymerization of acrylonitrile/methyl acrylate/acrylic acid, acrylonitrile/methylacrylate, and glycidyl‐acrylate/acrylonitrile interlayers onto Hercules AS4 graphite fibers was used to improve simultaneously the effective interfacial shear strength, τe, and the fracture toughness of graphite‐epoxy composite materials. With a single‐fiber fracture test, τe for these coated fibers (embedded in a diglycidyl ether of bisphenol A ‐ 4,4′‐methylenedianiline matrix) was determined at various temperatures and under various hygrothermal treatments. At room temperature, the coated samples showed slightly improved shear strength over the uncoated sample. At elevated temperatures, a plot of τe vs. temperature for the uncoated sample showed two distinctive regions: an interface‐controlled plateau region at low temperatures, and a matrix‐controlled region at high (>80°C) temperatures. Only one region, which was controlled by the matrix and the interlayer, was observed for the GA/AN coated sample. The τe values determined were slightly higher than the shear strength of the bulk matrix, possibly because of stronger matrix properties at the interface. Optical micrographs of the coated sample tested at temperatures less than 100°C showed no matrix crack perpendicular to the fiber axis, indicating that the interlayer has effectively blunted the crack tip and restricted its propagation. The effect of moisture in the sample was to reduce τe for the coated sample. Upon dehydration, the strength was partially recovered. The treatments did not affect the uncoated sample, however. The fragmentation length data were fitted well by both Gaussian and Weibull distributions.
Accelerated characterization of a chopped fiber composite using a strain energy failure criterion
Authors: Yen Shing‐Chung , Morris Don H.
Published: December 2004

The creep and creep rupture response of a chopped fiber composite material (SMC‐R50) were investigated experimentally and analytically. The goal of this research was to use the short time laboratory data to predict long time creep and creep rupture behavior. The creep response data up to 200 min duration were obtained at various constant temperature and stress levels. The short time creep data were then modeled using a modified power law equation. The modified power law equation contains the parameters of the so‐called accelerated characterization procedure. Using this power law equation, the short time creep response at the elevated temperatures were able to successfully predict the long time creep response at a lower temperature and stress level. To predict the creep rupture behavior, the modified power law equation was then coupled with a strain energy based failure criterion. It was found that the same parameters that were used in the prediction of the long‐time creep response can also be used to predict the creep rupture. At a given temperature level, the strain energy density related to creep rupture was found to be a constant. Furthermore, this strain energy density was found to increase with an increase in temperature. With a limited amount of data, it was found that the strain energy based failure criterion coupled with the modified power law equation can be used to predict long time creep rupture behavior.
Three‐dimensional stress analysis of composite structures using isodyne techniques
Authors: Pindera J. T.
Published: December 2004

It is known that the stresses in lamination planes of composite structures are pronouncedly three‐dimensional, and that criticality of the lamination defects is often very high. It is also known that the classical methods of photoelastic stress analysis are often not reliable when stress states are three‐dimensional, with the exception of the gamma‐ray stress‐freezing method. The paper presents analytical and empirical evidence that the recently developed “isodyne” techniques allow reliable determination of the 3‐D stresses existing in components of real composite structures and in lamination planes.
Time‐dependent response of aramid‐epoxy‐aluminum sheet, ARALL, laminates
Authors: Pindera M.‐J. , Williams T. O. , Macheret Y.
Published: December 2004

Selected results of an ongoing investigation aimed at characterizing the timedependent response of an aramid‐epoxy‐aluminum sheet laminate and its constitutents at 121°C are outlined in this paper. This laminate is a recently developed hybrid composite developed by the Aluminum Company of America, marketed under the ARALL‐4 tradename. The paper addresses the time‐dependent response of the above hybrid composite under creep loading. It is illustrated that ARALL‐4 laminates may exhibit substantial creep effects at stress levels below the proportional limit. The creep response is a nonlinear function of time and the applied stress level and is primarily due to the creep characteristics of the aluminum layers. An analytical model based on the assumptions of the classical lamination theory developed to model the time‐dependent response of these laminates under creep and thermal loading is shown to yield good correlation with the experimental data. It is also illustrated that the residual state of stress can influence the extent of creep. This offers the possibility of minimizing the creep effects by altering the state of residual stress with mechanical prestraining.
Rheological behavior and fiber orientation in slit flow of fiber reinforced thermoplastics
Authors: Mutel A. T. , Kamal M. R.
Published: December 2004

The flow behavior and fiber orientation in slit flow of a short fiber reinforced thermoplastic composite melt are investigated. A slit die with adjustable gap and interchangeable entrance geometries was designed and built. The slit die is fed by a single screw extruder. The bulk viscosity is calculated from the axial pressure profiles measured using three flush mounted pressure transducers. The effect of entrance geometry and gap dimensions on the fiber orientation and bulk flow behavior is specifically considered. A skin‐core composite fiber orientation is observed in the thickness direction. Fibers are oriented in the flow direction and parallel to the walls in the skin region irrespective of the entrance geometry. Different fiber orientation distributions in the core region can be realized by using different entrance geometries. However, the changes in the core fiber orientation are not fully reflected by the measured viscosities, due to highly oriented skin layer. Exit pressures obtained by extrapolation of linear pressure profiles are found to be all positive, but dependent on the die geometry and entrance conditions, even for the unfilled melts.
Viscoelastic characterization of high performance epoxy matrix composites
Authors: Woo E. M. , Seferis J. C. , Schaffnit R. S.
Published: December 2004

Dynamic mechanical analysis, stress relaxation, and creep experiments were performed to characterize the viscoelastic properties of a basic unmodified epoxy (Hercules 3501‐6) and a modified multiphase epoxy (Hercules 8551‐7), which are commonly used as matrices in high performance composites. The Arrhenius and WLF equations and a modified Standard Linear Solid (SLS) Model were used to quantify the viscoelastic behavior below, above, and at the glass transition temperatures, Tg. Both the modified and the unmodified epoxy systems exhibited a single relaxation peak above ambient temperature. The Tg of the modified epoxy at full cure was 170°C, which is 50°C lower than that of the basic epoxy. The glassy moduli of these two resin systems were found to be comparable, but the rubbery modulus of the modified epoxy was much lower than that of the basic epoxy system. However, the viscoelastic behavior of these two systems and their sensitivity to time‐temperature may be considered to be quite similar if they are compared with respect to their corresponding glass transition temperatures.
Effect of surfactant treatments on interfacial adhesion in single graphite/epoxy composites
Authors: Wu H. F. , Biresaw G. , Laemmle J. T.
Published: December 2004

Interfacial adhesion between graphite fibers and epoxy matrices is one of the important parameters in controlling composite performance. Experiments were performed to verify the idea that polymerizable and nonpolymerizable nonionic surfactants can promote wetting and increase interfacial shear strength. Using a single‐fiber‐composite (SFC) technique with a Poisson/Weibull model of fiber strength and flaws, the effective interfacial shear strength (ISS) was determined. The effect of surfactant treatments on interfacial adhesion in single graphite/epoxy composites was also compared with the effects of treatment with deionized water, absolute alcohol, and acetone. The experimental results showed that the fibers treated with the nonpolymerizable surfactant gained 37% in interfacial shear strength relative to those untreated or those treated with deionized water, absolute alcohol, or acetone. The polymerizable surfactants showed a 10% increase in interfacial shear strength. The lognormal distribution provided the best fit for critical aspect ratios obtained from the SFC tests.
A nondestructive method to determine material properties in anisotropic plates
Authors: Fällström K.‐E. , Jonsson M.
Published: December 2004

Material parameters in anisotropic rectangular plates are determined in a nondestructive way. Real‐time, TV‐holography is used to determine frequencies and shapes of the first five modes of vibration of plates with free‐free boundary conditions. According to rules given in the paper, finite element analysis is then used to determine two effective Young's moduli, the shear modulus, and the Poisson's ratio.
Deterrmining material properties in anisotropic plates using Rayleigh's method
Authors: Fällström K.‐E.
Published: December 2004

Material parameters of anisotropic plates are determined. Rectangular anisotropic plates are tuned by changing the quotient between the length of the sides, so that the second and third modes of vibration, for free‐free boundary conditions, degenerate into the well‐known cross‐shaped and ring‐shaped modes, respectively. The first three modes of vibrations for these plates are determined by optical methods. The propagation of bending waves, generated by the impact of a ballistic pendulum on the plates, has also been optically studied. It is found that bending waves generated in the middle of the tuned plates will reach the boundaries of the plates simultaneously. This gives a relationship between main material parameters. Using this relation and Rayleigh's method for the first three modes of vibrations, the main material parameters for the plates, that is, the effective two Young's moduli, the shear modulus, and the Poisson's ratio, are determined.
Effect of water absorption on the behavior of E‐glass fiber/nylon‐6 composites
Authors: Bian X. S. , Ambrosio L. , Kenny J. M. , Nicolais L. , Dibenedetto A. T.
Published: December 2004

The effect of water absorption on the stress transferability across E‐glass fiber/nylon 6 interface has been studied using the embedded single fiber composite technique. The behavior of silane coated fiber and untreated fiber composites after periods of water immersion were compared. The silane coating provided both higher interfacial shear stress transferability and protection from permanent water damage in the interphase region. It was found that water absorption in the nylon matrix reduced the shear stress transferability through plasticization of the matrix, weakening of the interface, and the development of tensile swelling stresses at the phase boundaries. In untreated materials the shear stress transferability was limited by decoupling of the matrix from the broken fiber ends by either interface slippage or local plane strain fracture in the interphase region near the fiber end. In the silane treated materials the shear stress transferability was limited by constrained yielding of the polysiloxane/nylon interphase at the fiber end, thus indicating plasticization of the matrix was the primary factor. After 20 days of water immersion, there was permanent deterioration of stress transferability in the untreated samples, but very little permanent damage in the treated samples.
The interphasial regions in interlayer fiber composites
Authors: Sanadi A. R. , Subramanian R. V. , Manoranjan V. S.
Published: December 2004

The interaction between the fiber and matrix in a fiber‐reinforced material plays an important role in determining the mechanical behavior of the composite. An efficient technique to simultaneously improve fiber‐matrix interfacial shear strength and impact behavior of the composite is to deposit a flexible interlayer onto the fiber. This results in the creation of three bulk phases, the fiber, matrix, and the interlayer and two interphasial regions. A phenomenological model that defines the variation of the fiber‐interlayer interphase and that of the interlayer‐matrix interphase has been developed. In the model, the elastic moduli of these regions vary continuously, so as to bridge the two bulk phases on either side of the interphase. The interaction between the bulk phases is also taken into consideration. The model has the potential for the use of dynamic mechanical analysis to obtain, relatively, adhesion/interaction parameters of different fiber‐interlayer‐matrix systems. These parameters can be used to determine the optimum interlayer thickness for improved toughness and good stress transfer efficiency.