摘要:

AbstractElectrical conductivity for polyether and polyimide‐carbon fiber composites was measured using different fiber types. The microstructure was characterized by X‐ray diffraction methods. D.C. conductivity measurements were carried out in directions perpendicular, parallel, and at varying angles to the fiber axis. The influence of the distance between electrodes on the conductivity was examined. The dependence of the frequency and the temperature upon conductivity has been, likewise, investigated. Experimental results support the concept of a conduction mechanism in the composites occurring in the carbon fibers, which built up a highly interconnected conducting network. It is also shown that the high degree of fiber orientation is consistent with the conspicuous anisotropic behavior of the electrical conductiv

ISSN:0272-8397    

DOI:10.1002/pc.750160202

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractFiber orientations caused by the flow in the thickness plane during injection molding of short fiber reinforced polymer composites has been simulated. The Lagrangian scheme was employed for the finite element analysis. Flow fields were solved by using a penalty method with Uzawa's scheme and orientation fields were also solved by using the second order orientation tensor. A generalized Newtonian fluid whose rheological behavior is independent of fiber orientation was assumed. Automatic mesh generation using an elliptic grid generator was developed for quadrilateral elements. Mold filling and orientation analyses were performed for a cavity of rectangular cross section. To determine the orientation state in other cross‐sectional geometries, numerical analyses were also performed for two different typical cross sections. As the result, orientation of short fibers in the flow field was analyzed qualitatively and quantitatively. According to the state of short fiber orientation in the thickness plane, the orientation field can be classified into three regions in the flow direction and three layers in the thickness direction. Orientation of short fibers was mainly influenced by elongational and shear flows. It was observed that critical values are present for upper limits of orientation. Effects of initial orientation at the inlet on the orientation field were examine

ISSN:0272-8397    

DOI:10.1002/pc.750160203

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA simple lab‐scale weaving method was used to produce multidirectional fiber preforms to improve the delamination resistance and damage tolerance of composites. Mechanical properties measured in this study included short‐beam shear strength and damage tolerance of 2‐D and 3‐D woven composites. The constituents of fiber and matrix in these composites are Kevlar‐29 (Du Pont) and Epon 828 (Shell Chemical Co.) epoxy. Attention was directed to the differentiation of deformation and failure mechanisms in these composites as a function of material parameters and loading conditions. The sequence of failure mechanisms differ between 2‐D and 3‐D composites. Results indicated that 3‐D woven composites exhibited higher shear strength than 2‐D woven composites. Also, 3‐D composites absorbed more impact energy than 2‐D composites. Failure mechanisms of composites subjected to repeated impacts were observed intermittently by using scanning electron microscopy and light microscopy. The failure of 2‐D composites was due to a combination of shear and tensile mode, but in 3‐D composites the failure was

ISSN:0272-8397    

DOI:10.1002/pc.750160204

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractTo improve the simulation of viscoelastic behavior of composites, an approximate and incremental method for the determination of Poisson's complex ratio of the polymer matrix is proposed. This method is based on the fact that many polymers exhibit a slight variation of their bulk modulus throughout, at their main relaxation temperature. We examine different parameters that affect the proposed method. It is shown that (i) the Poisson's complex ratio of the matrix and the complex modulus of the composite depend significantly on the initial values of the incremental method and (ii) the Poisson's complex ratio of the matrix allows for the effects of filler content on the magnitude of the mechanical relaxation.

ISSN:0272-8397    

DOI:10.1002/pc.750160205

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractWe examine the applicability of the conformation tensor to describe the fiber orientation and rheology of moderately concentrated fiber‐filled thermoplastics subjected to large deformation flow. To retain computational simplicity, we assume a Newtonian matrix. We present a model that can account for orientation effects, Brownian motion, semiflexibility, and interactions through excluded volume effect, of the fibers. The model predicts a wide variety of rheological effects. We present predictions of steady shear viscosity, primary normal stress and the creep functions, as well as uniaxial elongational viscosity, due to the fibers. We have compared rheological data for 9.54 wt% carbon fibers in polyethylene and 30 wt% glass fibers in polypropylene, with the model predictions. By defining an “effective fiber concentration,” we have been able to correlate the model well with data. With fitting parameters from the steady state viscosity vs. shear rate data, we have been able to predict the steady state primary stress coefficient data as well as the creep

ISSN:0272-8397    

DOI:10.1002/pc.750160206

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractAn investigation into the effect of isothermal aging on the development of transverse cracks in cross‐ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640–800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross‐ply configuration [02/90n]s, in whichnequals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640–800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence o

ISSN:0272-8397    

DOI:10.1002/pc.750160207

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractEvidence is presented relating the interfacial bonding strength and the optical transmission of transparent glass fiber reinforced PMMA composites. The temperature dependent (20° to 50°C) optical transmission of composites that contained uncoated 13 μm glass fibers and 13 μm glass fibers coated with divinyltetramethyl disilazane or 3‐(trimethoxysilyl)propyl methacrylate was found to decrease in the same order as the bond strength of the PMMA/glass fiber interface, namely, trimethoxy silane coated fiber, disilazane coated fiber, and uncoated fiber. SEM photographs showed similar fracture surfaces, clean fiber pull‐out, and no apparent bonding of the glass fiber to the PMMA for the composites containing uncoated and disilazane coated fiber, whereas, the composite containing trimethoxy silane coated fiber showed virtually no clean fiber pullout. Additional evidence for differences in the bonding strength is seen in the degradation (penetration of water and fiber whitening) on aging at 23°C in air or water for composites containing uncoated fiber (most degradation), disilazane coated fiber (slight degradation), and trimethoxy silane coated fiber (no degradation). The optical transmission between 20° and 30°C at 600 to 800 nm for the composite containing trimethoxy silane coated fiber decreased the least with increasing temperature (from ∼85% to 70%) while the composite containing uncoated fiber decreased the most (from

ISSN:0272-8397    

DOI:10.1002/pc.750160208

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe viscoelasticity of latex/PS beads composites, having the same volume content of latex and PS beads, but various porosity ratios and specific surfaces of particles has been investigated in the glass temperature range of the latex matrix. In order to give evidence for the main factors governing the viscoelastic properties, data were compared to numerical simulations based on the Christensen and Lo model and Skorokhod's approach. Such modelings were performed by considering either the latex matrix of the PS beads as the continuous phase. It was concluded that the glassy modulus is mainly governed by the volume fraction of porosity, while the rubbery modulus is controlled by both the interactions between phases and the void volume content. The location of the mechanical relaxation seems to be governed by the mechanical coupling between phases, which implies some local phase inversion. The magnitude of the mechanical relaxation depends not only on the chemical coupling induced by the interactions between phases, but also on the mechanical coupling.

ISSN:0272-8397    

DOI:10.1002/pc.750160209

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractPitch‐based carbon fiber surfaces were modified using a nickel‐catalyzed, dry oxygen etch (NCDO) and a dry oxygen etch (DO), both of which were applied using a continuous process. The treatments differed in that DCDO produced preferential pitting on fiber surfaces at nickel particle sites. Tensile strengths of all etched fibers were slightly lower than values for untreated, or “as received” (AR), fibers. Reductions in tensile strength were independent of the type of treatment administered, indicating that most degradation resulted from damage produced by the mechanics of the continuous process, not the etching treatments. Fiber‐matrix interfacial shear strengths (IFSS) of AR and etched fibers were evaluated using the Microbond test. At first glance, Microbond test data indicated that NCDO produced large increases in IFSS. However, inconsistencies in the data raised questions regarding the validity and usefulness of the Microbond test when applied to this system. Only after detailed analysis of the data for this series of fibers was it concluded that NCDO did indeed produce an increase in IFSS over AR fibers and

ISSN:0272-8397    

DOI:10.1002/pc.750160210

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

ISSN:0272-8397    

DOI:10.1002/pc.750160201

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY