bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ fracture tests in the scanning electron microscope
Authors: Roulin‐Moloney A. C. , Cudré‐Mauroux N. , Kausch H. H. 
Published: May 2005

AbstractThe experimental arrangement for conducting fracture tests in the scanning electron microscope (SEM) are described together with the particular problems in applying this technique to polymers and composite materials. Several examples are given of mechanisms of fracture in epoxy resins both unfilled and reinforced with particulate and fibrous fillers. The paper is illustrated by still photos taken from the video recording of the fracture experiments and by photos taken from the SEM raster.
Thermal expansion of organic and inorganic matrix composites: A Review of theoretical and experimental studies
Authors: Raghava R. S. 
Published: May 2005

AbstractThis paper reviews theoretical and experimental studies conducted in organic, ceramic, and metal matrix composites containing cylindrical, lamellar, and spheroidal inclusions as reinforcements. Mathematical formulations proposed to predict thermal expansion coefficients of fiber, disc, and sphere reinforced organic and inorganic matrix composites have been reviewed. Experimental studies undertaken to confirm theoretical predictions of thermal expansion coefficients of a variety of reinforcement geometry composites have also been discussed.
Orientation development in molding of short‐fiber liquid crystalline polymer composites
Authors: Kenig S. , Trattner B. , Anderman H. 
Published: May 2005

AbstractThe orientation development mechanisms that take place during molding of short‐fiber reinforced liquid crystalline polymer composites, have been analyzed and consequently the orientation development and properties distribution were studied for the case of thin wall large area components. Two factors associated with orientation development were investigated. The first is related to the melt front shape for in‐plane orientation distribution, and the second to the thickness of the skin layer where the alignment of the orientable liquid crystalline matrix and the rigid reinforcing fibers are of importance. The two basic factors were first verified by flow calculations using a computer assisted design (CAD) system and then experimentally validated. Experimental results for thin wall large area plaques have shown that the control over the melt front shape could be achieved with a narrow restrictor‐type gate and that the skin layer thickness is determined by the heat transfer processes during filling of the mold. Furthermore, a clear correlation has been established between the measured tensile properties and the ratio of skin layer to total thickness of the plaque. Such correlations should be generally developed for short‐fiber polymer composites for cases where rigidity and load bearing capabilities are of importance.
Study of epoxy resin—filler interaction
Authors: Petrović Zoran , Stojaković Nikola 
Published: May 2005

AbstractA bisphenol‐type epoxy resin cured with phthalic anhydride was filled with three types of SiO2 (untreated, silanized and smaller particle size), CaCO3, dolomite and Al2O3. Also, the concentration of silica was varied. Interaction of filler and resin was estimated by measuring the glass transition temperature (Tg) by different methods. Electron microscopy and x‐ray diffraction were used to study the structure of the boundary layer and the bulk polymer. It was found that silica forms strong bonds with the resin and that basic fillers (CaCO3, Al2O3) probably affect the crosslinking process with anhydride as hardener causing lowering of Tg.
A general strength theory for orthotropic fiber‐reinforced composite laminae
Authors: Labossière P. , Neale K. W. 
Published: May 2005

AbstractThin, orthotropic fiber‐reinforced composite laminae under plane stress loading conditions are considered. The essential conditions that must be satisfied in developing phenomenological strength criteria for such materials are first established. A new, parametric failure criterion is then presented. It is shown that this entirely general formulation encompasses all previously proposed failure theories (e.g., tensor polynomial criterion) for orthotropic laminae. Examples of application and the inherent advantages and drawbacks of the proposed parametric approach are discussed. In the past, the formulation of strength criteria for composite materials has closely paralleled the development of yield criteria in metal plasticity. The parametric approach advocated here for the failure of composite materials was inspired by a general formulation proposed by Budiansky (1) for the plastic yielding of sheet metals.
Future prospects for wood cellulose as reinforcement in organic polymer composites
Authors: Zadorecki Paul , Michell Anthony J. 
Published: May 2005

AbstractWood cellulose, a versatile and renewable natural resource, has potential for use as a reinforcement for synthetic organic polymers. During the past 80 years a number of materials using the reinforcing properties of wood cellulose have found major markets. Forms of wood cellulose proposed as reinforcements include: wood fibers, cellulose fibers, microfibillar, and microcrystalline cellulose. Recent attention has been given to them as fillers/reinforcements in thermoplastics and elastomers. Most cellulosic composites derive their existence from their comparatively low materials cost and the filling rather than reinforcing properties of cellulose. However, cellulose chains have a potential stiffness much higher than glass and in the same range as superstiff aramid fibers. This paper examines the state of the art of combining wood cellulose with synthetic organic polymers to from composites and considers new ways for better using cellulose's reinforcing potential.
The processing of fiber reinforced thermoplastics using co‐rotating twin screw extruders
Authors: Wall David 
Published: May 2005

AbstractFor short fiber reinforced thermoplastics the effect of fiber length and the fiber/matrix bond on the ultimate properties of the material are well understood. But, how the process conditions under which the composite is made affect the fiber length and the fiber matrix bond has not been so thoroughly reported in the literature. A study of this relationship has been made on a co‐rotating twin screw extruder incorporating 30 percent by weight of glass fiber into nylon 66 to make the composite.Experimental results are presented to show how machine variables such as mixing configuration and screw speed affect the material properties and process efficiency. The properties of the composite were assessed by measurement of the fiber length distribution and tensile strength.From the results in the text it is possible to select machine variables to give desired production conditions. Although most of the work concerns the twin screw extruder, some of the consequences of subsequent injection molding are also shown.
Properties of carbon/graphite fibers modified by plasma polymerization
Authors: Dagli Gulcin , Sung Nak‐Ho 
Published: May 2005

AbstractCarbon fibers and pyrolytic graphite blocks were treated with plasma of acrylonitrile (AN) and styrene (ST) monomers, using an induction‐coupled, RF‐plasma reactor. Both substrates were stable towards plasma, leading to a deposition of thin, coherent coatings of 400Å∼1000Å thickness. Both monomers produced surfaces which are substantially more polar (γc=54 dynes/cm for AN and 40 dynes/cm for ST) than the untreated surfaces (γc=32 dynes/cm). ESCA and IR studies indicate that the plasma polymers contain a high concentration of oxygen (12 percent in PPAN and 17.8 percent in PPST), in the form of CO, COOH, COC, and OH groups. Also, treated fibers exhibited slightly higher tensile strengths than the untreated counterparts, suggesting that the plasma coatings effectively heal some of the surface flaws of the fiber. The abundant surface polar groups combined with the improved tensile properties of the plasma treated fibers make them attractive reinforcements for advanced composite materials.
Effects of water sorption on the physical properties of PET, PBT, and their long fibers composites
Authors: Bastioli C. , Guanella I. , Romano G. 
Published: May 2005

AbstractThe behavior of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) on water aging has been studied above and below the glass transition temperature (Tg). The aging process is caused by: degradation of the matrix and an increase in crystallinity above Tg, and microcavitation at the amorphous/crystalline interface below Tg. Such behavior well explains the deviation of the sorption kinetics from the Fickian model. The apparent water diffusion coefficients and the transport activation energies of PET and PBT have been calculated at temperatures above and below Tg. The mechanical behavior of the two polymers on water aging has been measured by means of fracture mechanics and Izod impact tests at different stress concentration factors. An increase of toughness of PET at short aging times has been shown by mechanical tests and SEM analysis fracture surfaces of differently aged samples. Izod tests of PET and PBT composites reinforced by long glass fibers have shown the contribution of fibers to the total fracture energy.
Random glass mat reinforced thermoplastic composites. Part I: Phenomenology of tensile modulus variations
Authors: Stokes Vijay K. 
Published: May 2005

AbstractThe mechanical properties of random continuous glass mat reinforced composites, as determined by standard tensile tests, are known to have a very large scatter. To understand this scatter, new test procedures were developed to map the local tensile elastic moduli in a large plaque at 12.7‐mm (½‐in) intervals. Surprisingly, the tensile modulus in these materials can vary by a factor of two over the 12.7‐mm distance. The elastic modulus is shown to vary by a factor of three in a 150 × 305‐mm (6 × 12 in) plaque. Expressions have been obtained for the average moduli measured by tensile and bend tests. These expressions have been used to compare measured flexural moduli with values predicted by using measured tensile moduli.
Melting behavior of high performance composite matrix polymers: Poly(phenylene sulfide)
Authors: Cebe Peggy , Chung Sengshiu 
Published: May 2005

AbstractWe have been studying crystallization and melting behavior of high performance semicrystalline polymers to increase our understanding of the effects of processing on microstructure. Questions on development of morphology center around whether single or dual populations of crystals exist after melt processing, and how these crystals melt creating the multiple endotherms usually observed. We have used differential scanning calorimetry (DSC) to examine endothermic response in poly(phenylene sulfide), PPS, after various processing treatments. These include isothermal melt crystallization and crystallization from the rubbery amorphous state. For the first time, we report endothermic response of solution crystallized mats of single crystals. Our results on melt crystallized PPS are explained by a model in which different crystal populations exist in the material at room temperature prior to DSC scanning. Ability of the material to reorganize during the scan depends upon the initial state of perfection of the crystals.
Thermoforming of high performance thermoplastic composites
Authors: Muzzy John D. , Wu Xiang , Colton Jonathan S. 
Published: May 2005

AbstractMatched‐die forming of a 90° bend in a quasi‐isotropic 16 ply laminate of ICI's APC‐2, containing 61 volume % Hercules AS‐4 continuous carbon fiber in poly(etheretherketone) (PEEK), is described. To uncouple and characterize elementary deformation phenomena, a series of simple tests are developed. Single ply bending of APC‐2 tape up to 420°C has been performed to characterize elastic bending. Transverse flow, axial interply shear flow, and z direction elasticity have been characterized in an instrumented matched die mold. Interply shear flow is characterized using a simple shear test fixture. Transverse flow and interply slip are relatively easily induced. Precautions should be taken to avoid fiber buckling and to provide for laminate reconsolidation.
The Iosipescu shear test method as used for testing polymers and composite materials
Authors: Adams Donald F. 
Published: May 2005

AbstractThe Iosipescu shear test, developed initially in the 1960s for use with homogeneous, isotropic structural materials such as metals, has been adapted during the past ten years for use with composite materials. Much of this development work has taken place at the University of Wyoming, where a very efficient test fixture configuration has been developed, and extensive test results have been generated. Many other research groups have also adopted the test method during the past five years. As a result, the American Society for Testing and Materials (ASTM) is presently in the final stages of making the Iosipescu shear test an ASTM standard. The test method is described and its range of applications indicated, including examples of typical data.
Fiber length distribution effects on the fracture of short‐fiber composites
Authors: Carling M. J. , Williams J. G. 
Published: May 2005

AbstractThe effect of fiber geometry on the fracture behavior of short glass fiber‐reinforced nylons was examined. In particular a comparison was made between conventional short‐fiber composites (with feedstock made by an extrusion process) and the newer pultruded feedstock materials which have longer fiber length distributions but larger fiber diameters. The toughness of the material was measured over a wide range of loading rates, from impact conditions, using Kc and Gc type tests, to long term, slow crack growth tests. The moisture content of the materials was varied from dry to saturated. It was found that there was little difference in fracture toughness when the materials were dry. However, when moist, the longer fiber material showed significant improvements over the conventional short‐fiber‐reinforced material. This behavior is explained in terms of the changes in fiber geometry.
Polypropylene/low density polyethylene blends with short glass fibers. II: Effect of compounding method on mechanical properties
Authors: Ramos M. Arroyo , Belmontes F. Avalos 
Published: May 2005

AbstractPolypropylene/low density polyethylene blend matrices have been reinforced with short glass fibers in order to study their tensile, flexural, and impact behavior. Two‐roll milling and twin‐screw extrusion compounding methods were used to incorporate the fiber within the polymer matrices, and standard test samples were prepared by injection molding. The effects of matrix composition and fiber concentration on mechanical properties were investigated keeping in mind the matrix and fiber morphology, the latter being intimately dependent upon the compounding method employed.
The dependence of interfacial shear strength on matrix and interphase properties
Authors: Rao Venkatesh , Drzal Lawrence T. 
Published: May 2005

AbstractExperiments were conducted to determine the dependence of the interfacial shear strength on the bulk material matrix properties using model compounds based on epoxy/amine chemistry. AS4, carbon fibers were used as the subject for these measurements with both a difunctional epoxy (DGEBA) system as well as a tetrafunctional epoxy (MY720) system. Amine curing agents were carefully chosen to produce matrices which produced a range of matrix properties from brittle, elastic to ductile, plastic. The fiber‐matrix interfacial chemistry was constant throughout this study by always using a stoichiometric amount of curing agent. The results indicate that, for both the difunctional as well as the tetrafunctional epoxy system, the interfacial shear strength (as determined by the fragmentation test) decreases nonlinearly with decreasing modulus of the matrix. Linear elastic analysis yields a nearly linear relationship, for both systems, between the interfacial shear strength and the product of strain to final break and the square root of the matrix shear modulus. A linear relationship is also found between the difference in test temperature and glass transition temperature of the cured matrix and the interfacial shear strength. Additionally, the failure mode is seen to remain interfacial as the ductility of the matrix changes.
Optimizing fiber wetout for composites manufacturing
Authors: Cercone Larry 
Published: May 2005

AbstractDecreased mechanical strength in a fiber reinforced plastic part can often be traced to poor or incomplete impregnation of the reinforcing fiber with the matrix. To properly understand the impregnation process in the design of new composites manufacturing machinery (specifically in unidirectional tape machines), or to optimize wetout in existing machine designs, the raw process materials and their relationship within the process environment must be examined. The critical factors are: resin viscosity vs. temperature; the work of adhesion between the fiber and resin; and the problem of forcing the resin to completely penetrate a fiber bundle. If these factors are known, nip rolls can be designed to meet a specific process envelope, or in the case of existing equipment, the existing process envelope for specific fiber/matrix combinations can be manipulated for maximum fiber wetout.
Effect of advancement on epoxy prepreg processing—a dielectric analysis
Authors: Day David R. , Shepard David D. 
Published: May 2005

AbstractWith the relatively recent trend toward adaptive process control during processing of structural composites, there is need for an understanding of the nature of variations during cure that are encountered. Part‐to‐part variations can arise because of differences in thermal exposure arising from part placement or part thickness, or from chemical differences due to formulation or advancement. Microdielectric sensors are particularly well suited for monitoring thermoset cures from initial point of flow, through the liquid region, and on into the solid state. In this study, microdielectric sensors are used to systematically study the influence of resin advancement on cure behavior. Relationships between advancement and critical cure phenomena such as flow temperature, point of viscosity minimum, and reaction end point are discussed.
Monitoring the composite curing process with a fluorescence‐based fiber‐optic sensor
Authors: Levy R. L. , Schwab S. D. 
Published: May 2005

AbstractA novel cure sensor, based on the combination of fiber‐optic fluorometry and the viscosity/degree‐of‐cure dependence of the epoxy resin fluorescence, was developed to provide a reliable low‐cost cure‐monitoring sensor for control of composite manufacturing. The capability of the first‐generation sensor to monitor chemorheological changes that occur during the autoclave cure of carbon‐epoxy laminates was successfully demonstrated. An improved second‐generation sensor, which simultaneously monitors the changes in the epoxy fluorescence intensity and the wavelength of maximum emission, was also developed. The changes in the sensor intensity and wavelength signals, as a function of cure time, provide characteristic profiles that reveal the main chemorheological events of the cure cycle; these signals follow the changes in the degree‐of‐cure to completion. The configuration of the optrode‐laminate interface strongly affects the signal profiles and their reproducibility. A “resin cavity” optrode‐laminate interface, which improves reproducibility, was developed and tested.
Minimum‐gage, maximum‐stiffness graphite/thermoplastic spacecraft structures
Authors: Garvey R. E. , Andriulli J. B. , McKeever J. W. , Rudness R. V. 
Published: May 2005

AbstractAdvanced thermoplastic matrix composite materials have been studied for use in aircraft applications since about 1980. This Strategic Defense Initiative Organization/Air Force project was initiated in 1987 to study the suitability of this class of materials for use in spacecraft applications. This paper will report on the following work in progress: development of ultrahigh‐modulus, pitch‐fiber‐reinforced thermoplastic composites; development of thin‐ply graphite/thermoplastic materials for gage‐limited spacecraft applications; and producibility demonstrations for generic spacecraft structures including open frames and T and L members, circular and square‐tube truss configurations, and stiffened‐skin modules.
Impact damage in a composite material
Authors: Reed P. E. , Beva L. 
Published: May 2005

AbstractDamage development in plates of a glass fiber‐reinforced polypropylene is recorded, using short pulse photography, during instrumented falling weight tests using the excess energy approach. It is seen that the damage is progressive throughout the test but its initiation cannot be detected either by freeze‐frame photography or visual observation. Specimens are therefore subjected to low‐energy impact followed by microscopic observation of the tensile face. It is found that the initial damage mechanism is cracking of the matrix at the fiber‐matrix interface, the crack propagating along the fiber. The finite element method is used to estimate the stress distributions at damage initiation in 4‐ply and 8‐ply samples cut from unidirectional and cross‐ply plaques. The computed results indicate that initial damage occurs when the transverse tensile stress reaches a critical value.
Development and evaluation of surface treatments to enhance the fiber‐matrix adhesion in PAN‐based carbon fiber/liquid crystal polymer composites. Part I: Coupling agent and amine surface treatments
Authors: King Julia A. , Buttry Daniel A. , Adams Donald F. 
Published: May 2005

AbstractSeveral surface treatments, using both commercially available coupling agents and reagents containing multiple amines, were applied to commingled continuous as‐received AS4 carbon reinforcing fiber/liquid crystal polymer (LCP) matrix fibers. Unidirectional composites (normally 60 vol% carbon fiber) were prepared from as‐received and treated commingled fibers and characterized. To estimate the effect the effect of the treatments on fiber‐matrix adhesion, short beam shear (SBS) tests were conducted, the failure surfaces were examined, and spectroscopic studies wee performed. The mean SBS strength of the as‐received unidirectional AS4 carbon fiber/LCP matrix composite system was 49 MPa. The best coupling agent and amine treatments yielded increases in composite shear strength of ∼ 10 to 20%, relative to the as‐received AS4/LCP system. For the amine treatments, ESCA and FTIR analyses suggested of both the carbon and LCP fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers may have caused the increased adhesion. Moreover, SEM analysis of the failure surfaces of SBS specimens from composites prepared with the treated fibers (both with coupling agents and amines) showed that strong fiber‐matrix adhesion was present. That is, failure occurred in the LCP matrix material.