bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Material Model for the Nonlinear Biaxial Behavior of ATJ-S Graphite*
Authors: Jones Robert M. , Nelson Dudley A.R.
Published: March 2007

A new model for the deformation behavior of ATJ-S graphite, a non linear transversely isotropic material, under initial loading is described. This material model, which is based on a new deformation theory of ortho tropic plasticity, has excellent potential for description of the biaxial softening phenomenon found in ATJ-S graphite. Biaxial softening is char acterized by the development of larger strains in biaxial tension than in uniaxial tension, in contradiction to conventional Poisson effects. The new model is examined for sensitivity to (1) a nonsymmetric compliance matrix, (2) how the material model constants are obtained, and (3) varia tions in material properties. Comparisons are made between strain values obtained with the material model incorporated in a finite element com puter analysis and strain values from biaxial test results.
Graphite/Aluminum: An Evaluation of State-of-the-Art Material
Authors: Hoover W.R.
Published: March 2007

The tensile and fracture toughness properties of a unidirectional, 28.3 volume percent graphite/aluminum composite have been measured and compared to boron/aluminum composites. The longitudinal and transverse tensile strengths in four-point bending were determined to be 105.6 ksi (728 MPa) and 7.19 ksi (49.5 MPa), respectively. The longitudinal strength is only slightly lower than that which would be expected from a boron/ aluminum composite of similar volume fraction. The low transverse tensile strength was shown to be the result of a very weak filament-matrix inter face. The apparent fracture toughness, Kc', of this graphite/aluminum com posite was found to be 23.48 ksi √in (25.83 MPa √ m) which is consider ably higher than the fracture toughness of a boron/aluminum composite with similar volume fraction. While the reason for this unexpectedly high fracture toughness is not definitively identified, the evidence suggests that the source may be the low filament-matrix interface strength.
Effect of Stacking Sequence and Lay-Up Angle on Free Edge Stresses Around a Hole in a Laminated Plate Under Tension
Authors: Rybicki Edmund F. , Schmueser David W.
Published: March 2007

One mode of failure in fiber reinforced laminated plates is delamination initiating at a free edge. Experimental results and theoretical stress investi gations found in the literature indicate that the interlaminar normal stress, σ z, is a factor in this mode of failure. In this paper, the stress behavior around a circular hole in a laminated plate is investigated using a three- dimensional finite element stress analysis. First, computed results for the tangential strain distribution around a circular hole for a (0/±45/0) s lamin ate under uniaxial loading are compared with laboratory data to provide a level of confidence in the analysis. Next, attention is focused on the inter laminar normal stress distribution around the free edge of the circular hole and the effects of changes in stacking sequence and lay-up angle. Initially, laminates with stacking sequences of (0/90) s are analyzed. Graphite/epoxy laminates of the type (02/±θ/∓θ) S, (±θ/∓θ/0 2) S, (902/±θ/∓θ) 2 , and (±θ/∓θ/902) S where θ is 30° , 45°, and 60° are also considered. Each lamin ate is subjected to a uniaxial stress loading distant to a hole.
Effect of Thickness on Single Ply Percolation and Conductivity
Authors: Joy Thomas , Ajmera Pratul , Strieder William
Published: March 2007

A single ply of unidirectional composite is modeled as a two-dimension al close packed lattice of circular fiber cross sections of infinite width and finite thickness. To introduce randomness fibers are removed at random from the lattice, leaving vacant lattice sites of matrix material, until a certain fiber volume fraction is reached. The effect of lattice thickness on the critical fiber fraction for percolation is calculated for this random, close packed fiber model. For a typical ply thickness of 24 fiber diameters, the critical fiber fraction for percolation is reduced by 20% from the infinite lattice value of 0.45 to a smaller value of 0.36. The percolation versus thickness results of the random square lattice of fibers are compared with those of the random close packed fiber model. Experimental measure ments of the increase in electrical conductivity of a single ply of graphite/ epoxy composite with decrease in ply thickness predicted by the random close packed fiber model, are presented.
Non Linear Viscoelastic Behavior of Polypropylene and Glass Reinforced Polypropylene in Creep
Authors: Vidya Bhushan Gupta  , Lahiri Jhumur
Published: March 2007

The non-linear visco-elastic behavior of various thermoplastic materials has long ago been established. A vast field, however, remains unexplored, firstly, in finding out workable theories for actual engineering applications with their limits of applicability specified, and secondly, in understanding the physical mechanisms which control the manifestation of non-linear visco elastic behavior in these polymeric materials.

An attempt to understand these phenomena has been made by performing 6 hrs isothermal creep tests on unreinforced and glass-fibre reinforced polypropylene samples under uniaxial tension. In the case of the homopolymer, experiments were performed under different stress levels and at various temperatures up to 60 °C. Stress levels were chosen in such a way that maximum strain level always remained below 3%. This was done in order to achieve complete recovery druing the successive recovery cycle. Validity of an equation of the form ε = εo + ε+tn has been tested. It is found that ε o in the above equation is approximately a linear function of stress and is weakly dependent on temperature, whereas ε+ is a non-linear function of stress and is strongly temperature-dependent. The exponent n, however, is a constant independent of both stress and temperature. With incorporation of glass fibers appreciable increase in the modulus and slowing down of time dependent deformation were achieved.
Some Observations on the Cured Shape of Thin Unsymmetric Laminates
Authors: Hyer Michael W.
Published: March 2007

This paper discusses the fact that the cured shape of thin unsymmetric laminates do not conform to the predictions of classical lamination theory. Rather than being saddle shaped, as predicted by the classical theory, the paper shows that thin unsymmetric laminates cure into a shape of a right circular cylinder. This anomalous behavior has been observed by many but the paper serves to quantify the effect and to inspire investigators to begin thinking about using the phenomenon to advantage. The paper indicates that the anomalous behavior is repeatable and that thicker laminates con form to the predictions of the classical theory. Laminates of the [0/902 /θ ] T, [02 /θ2 ] T and [04 /θ4 ] T families are investigated for this be havior and it is shown the principal curvature directions of the cylindrical shapes are predictable.
A Comparative Study of Water Absorption Theories Applied to Glass Epoxy Composites
Authors: Bonniau P. , Bunsell A.R.
Published: March 2007

Three types of glass epoxy composites have been studied and water diffu sion leading to saturation has been shown to occur under humid conditions for two of them, the third composite was seen to degrade in the presence of water. It has been found necessary to apply two different models of diffusion to explain the behavior of the first two materials. Both of the theoretical models are based on Fick's law, the first being classical single phase diffusion and the second is a two phase model for the Langmuir type. The material tested were identical except for the resin hardeners which were used which were, diamine, dicyandiamide, and anhydride. The testing conditions, were 0%-100% Relative humidity and 25°C-90°C.
Strengths and Thermal Residual Stresses of Unidirectional Composites
Authors: Ishikawa Takashi
Published: March 2007

Failure strengths of unidirectional composites are theoretically obtained by the employment of certain basic assumptions and the consideration of the strengths of the constituents and the fiber-matrix interface. The most impor tant assumption is that macro-failure occurs when one of the micro-stress levels in composites reaches a micro-failure criterion. Thermal residual stresses based on temperature-dependent material properties are considered as the initial state. An experimental verification of the residual stresses is then carried out by means of photoelasticity. A second phase of analysis involves the resolution of an external loading in an arbitrary direction into six basic loadings in the xyz-coordinates. Failure strengths of UD-composites are determined after all the stress components are superposed. The target material utilized is Carbon-Epoxy. Four kinds of micro-criteria are adopted. It is found that the Tsai-Wu theory with the minimum F12 can be best ex plained by the maximum principal stress criterion in the matrix. The thermal residual stresses do not have predominant effects on the strengths if an inter face normal strength is large.
Analysis of Creep for Metal Matrix Composites
Authors: Min B.K. , Crossman F.W.
Published: March 2007

The primary creep deformation of a unidirectional metal matrix com posite is analyzed. A continuum model is developed based on the results of experiments conducted on unreinforced and unidirectionally-reinforced aluminum. The experiments show that the longitudinal creep of Gr/Al is ef fectively inhibited by the fibers due to the extremely high elastic modulus and negligible creep properties of the latter. The transverse creep, however, is significant even at an applied stress level far below that necessary to cause creep in the unreinforced aluminum. Damage parameters, DT and Ds, related to the inhomogeneous local distribution of transverse and shear stresses, respectively, and the initial residual stress, σR are shown to account for the observed behavior quite satisfactorily.
Fracture Morphology of Graphite/ Epoxy Composites
Authors: Richards-Frandsen Rebecca , Naerheim Yngve
Published: March 2007

The delamination failure planes of graphite/epoxy composites that failed in three- point bending fatigue were examined microscopically to identify and relate fracture surface morphology to the composite microstructure and the applied loading condi tions. The failure surfaces were also examined for indications of crack initiation and propagation from manufacturing induced defects in the microstructure. The dominant failure surface features were found to be matrix cleavage, hackle formation, and wear regions. No indication of crack propagation from defects was observed. Instead, the role of intrinsic defects on fatigue lifetime seems to be one of damage enhancement around the defect.
Fatigue Failure of an Orthotropic Plate with a Circular Hole
Authors: Tsangarakis Nikos
Published: March 2007

A model describing the failure of an orthotropic plate with a circular hole at its center and subjected to fatigue is described. The model is applied to plates of FP/Al and its validity is investigated over two hole diameters. It was found that the model describes fatigue failure with reasonable accuracy. A damage zone extending on both sides of the hole was found responsible for the initiation of failure of the plate. The en durance limits, based on remote stresses, were 225 MPa and 167.5 MPa for specimens with 1.6 mm dia and 3.2 mm dia holes respectively. The endurance limit of the com posite without a hole was 330 MPa.
Design of a Composite Boxbeam
Authors: Bicos Andrew S. , Springer George S.
Published: March 2007

This paper presents an analysis for the preliminary design of boxbeams made of fiber-reinforced composites. The analysis provides deflections, bending and torsional stiffnesses, stresses, and the conditions for buckling and first-ply failure. Use of the analysis is illustrated through the example of a single cell, three bay, cantilevered box beam. This example demonstrates a design procedure for selecting the configuration which results in the required strength and stiffness at a minimum weight.
Progressive Fracture of Fiber Composites
Authors: Irvine Thomas B. , Ginty Carol A.
Published: March 2007

Refined models and procedures are described for determining progressive composite fracture in graphite/epoxy angleplied laminates. Unique Lewis Research Center capabilities are utilized including the Real-Time Ultrasonic C-Scan (RUSCAN) ex perimental facility and the Composite Durability Structural Analysis (CODSTRAN) computer code. CODSTRAN is used to predict the fracture progression based on com posite mechanics, finite element stress analysis, and fracture criteria modules. The RUSCAN facility, CODSTRAN computer code, and scanning electron microscope are used to determine durability and identify failure mechanisms in graphite/epoxy com posites. Results indicate that RUSCAN/CODSTRAN is an effective method of study ing progressive fracture of composites.
Interlaminar Fatigue Crack Growth in Random Short-Fiber SMC Composite
Authors: Wang S.S. , Miyase A.
Published: March 2007

The interlaminar fatigue crack growth behavior in a random short-fiber SMC-R50 com posite is studied. Experiments were conducted on double-cantilever-beam (DCB) composite specimens under displacement-controlled cyclic loading. Owing to large defor mation experienced in the specimen, a geometrically nonlinear fracture mechanics analy sis is employed to evaluate the associated cyclic strain energy release rate during crack propagation. The effect of mean nominal stress on interlaminar fatigue crack growth is studied. The fatigue crack growth behavior in the composite with different thicknesses and orientations is also examined. For the SMC composite studied, the interlaminar fatigue crack growth rate is found to follow a power-law relationship with the cyclic strain energy release rate. The value of the exponent in the power-law expression is much higher than those obtained for in-plane fatigue crack growth in the same composite and for the homog eneous neat resin. The significant effect of mean nominal stress on the interlaminar fatigue crack growth rate is appreciable and can be accounted for by proper modification of the power-law crack-growth expression. The influence of composite thickness on the inter laminar fatigue crack growth rate is noted, but the specimen orientation effect is negligi ble.
The Optimal Design of Symmetric Laminated Beams Considering Damping
Authors: Liao D.X. , Sung C.K. , Thompson B.S.
Published: March 2007

The task of designing symmetric laminated beams with optimal stiffness and damping is considered by incorporating the damping model of Adams, et al. into an optimization algorithm. The design variables are the fiber orientation in each ply, the stacking se quence, and also the thickness of each ply in the laminate. A recursive quadratic program ming algorithm is employed for the optimization process and numerical results are presented for several test problems including the constraint condition of invariable flexural rigidity.
The Influence of Quality of Adhesion on the Damping Characteristics of a Two-Layer Compound Beam
Authors: Theocaris P.S.
Published: March 2007

A two-layer compound beam submitted to forced extensional vibrations was used to study the quality of adhesion between the phases and its influence on the overall mechanical behaviour of the compound. The one layer consisted of an unplasticized epoxy polymer, whereas the other layer of a 20 percent plasticized with Thiokol LP3 polysulfide. It was shown, by the theory of elasticity of vibrating bodies, that the influence of the dif ferences in moduli and Poisson's ratios of the phases at each position of loading along the viscoelastic spectrum was insignificant for the combination of phases studied, so that the simple theory of extensional forced vibrations of the compound was valid. Then, the eval uation of the storage- and loss-moduli for the independent phases and the compounds with good or bad adhesion at the length of their interface along the whole viscoelastic spectrum has shown that compound specimens with good adhesion behaved exactly as if they consisted of a unique material with the properties of the compound according to its law of mixtures, whereas in the case of bad adhesion, a further reduction in the values of loss moduli and the loss factors of the compound appeared, due to the high dissociation of the phases. The positions and the extents of these quantities may be adequately ex plained by the two-term unfolding model for the mesophase, valid for forced-vibrating bodies.
Thermal Response of Radiantly Heated Kevlar and Graphite/Epoxy Composites
Authors: Fanucci Jerome Paul
Published: March 2007

The response of Kevlar and graphite/epoxy composites subjected to simulated nuclear or laser thermal loads was measured. A solar furnace was used to radiantly heat samples at flux rates of up to 55 cal/cm2/sec and total fluences of approximately 100 cal/cm2. An iterative numerical technique was used to estimate the thermophysical properties of the materials by matching observed temperature-time histories with analytical predictions. Comparison of results obtained during this program with previously published data suggests that free stream velocity, which affects smoke blockage and char layer removal, is a critical design parameter.
Analysis of Progressive Matrix Cracking In Composite Laminates II. First Ply Failure
Authors: Dvorak George J. , Laws Norman
Published: March 2007

The mechanics of transverse cracking in an elastic fibrous composite ply is explored for the case of low crack density. Cracks are assumed to initiate from a nucleus created by localized fiber debonding and matrix cracking. Conditions for onset of unstable cracking from such nuclei are evaluated with regard to interaction of cracks with adjacent plies of different elastic properties. It is found that cracks may propagate in two directions on planes which are parallel to the fiber axis and perpendicular to the midplane of the ply. In general, crack propagation in the direction of the fiber axis controls the strength of thin plies, while cracking in the direction perpendicular to the fiber axis determines the strength of thick plies. The theory relates ply thickness, crack geometry, and ply tough ness to ply strength. It predicts a significant increase in strength with decreasing ply thick ness in constrained thin plies. The strength of thick plies is found to be constant, but it may be reduced by preexisting damage. Strength of plies of intermediate thickness, and of unconstrained thick plies is evaluated as well. Results are illustrated by comparison with experimental data.
Axisymmetric Free Vibration of Orthotropic Complete Spherical Shells
Authors: Chao C.C. , Chern Y.C.
Published: March 2007

This paper presents studies of the axisymmetric free vibration of moderately thick orthotropic complete spherical shells. The mathematical model is formulated in terms of the mid-surface meridian and radial displacements, and cross-section rotation of the meridians by the improved linear elastic shell theory with the effects of transverse shear strain and rotary inertia included. By the use of the Legendre polynomials, the exact solu tion from a set of three governing partial differential equations for the transversely iso tropic case and the series solution from the Ritz method for the polar orthotropic case are obtained. Natural frequencies and modes are found from the eigenproblems by using orthogonality and some special integrals with reasonable results.
The Strain Energy Release Rate of Composite Microcracking: A Variational Approach
Authors: Nairn John A.
Published: March 2007

A variational analysis approach has been used to determine the two- dimensional thermoelastic stress state in cross-ply laminates of type [0 m/90 n] s and [90 m/ 0 n] s. The stress analysis was used to calculate the energy release rate due to formation of a new microcrack. The analysis accurately includes the effect of residual thermal stresses. When compared with experiments, the new energy release rate expressions are found to predict typical data using a single value for the critical energy release rate for microcrack ing. This critical energy release rate has a physical interpretation as a microcracking fracture toughness or as an intralaminar fracture toughness. We also used the variational solution to get an analytical expression for the longitudinal expansion coefficient of the microcracked cross-ply laminate as a function of microcrack density. Finally, variational theorems are used to show that this new microcracking fracture analysis is rigorously more accurate than previous attempts at the same problem.
Gauge Length Effect on the Strength of Silicon Carbide and Sapphire Filaments
Authors: De A.K. , Phani K.K.
Published: March 2007

A modification of the Weibull type of flaw distribution function has been suggested for analysing the strength distribution of sapphire and SiC on carbon filaments. The function provides an upper and lower strength limit and is characterised by two shape parameters. The strength distributions of sapphire and SiC filaments, reported by previous workers, were analysed in terms of the proposed distribution function. Strength distribu tion data obtained at greater lengths (254 mm) were used to predict strength distribution at shorter length of 75 mm. The predicted values were in close agreement with the ex perimental ones. The average strength values calculated down to a length of 12.5 mm also agreed with the experimental values quite well.
An Approximate Theory for Predicting the Moduli of Uni-Directional Laminates with Non-Linear Stress/Strain Behavior
Authors: Frost S.R.
Published: March 2007

An approximate theory for predicting the non-linear behaviour of long fibre composites is presented. The theory combines linear elastic fibre properties with non- linear elastic matrix properties to determine the stress/strain behaviour of a uni-directional laminate.

On comparison with experimental data for the stress/strain behaviour of a uni directional Carbon fibre/PEEK laminate, predictions agree well with measurement. For on-axis loading, fibre effects dominate and non-linear effects are unimportant. For off-axis loading, matrix effects dominate and consequently non-linear effects are significant, par ticularly the non-linear shear stress/strain behaviour.
Prediction of Process-Induced Residual Stresses in Thermoplastic Composites
Authors: Chapman T.J. , Gillespie J.W. , Pipes R.B. , Manson J.-A.E. , Seferis J.C.
Published: March 2007

A model to predict the macroscopic in-plane residual stress state of semi crystalline thermoplastic composite laminates induced by process cooling is presented. Heat transfer during processing is based upon an incremental transient formulation that consists of a finite difference heat transfer analysis coupled to the crystallization kinetics. Micromechanics is used to evaluate the instantaneous spatial variation of mechanical prop erties as a function of temperature and degree of crystallinity. Residual stresses are based upon an incremental laminate theory that includes temperature gradients, shrinkage due to crystallization and thermal contraction. Temperature dependent relaxation times are used to model first order viscoelastic effects. A parametric study is conducted to explore the sensitivity of residual stresses to process history. Input parameters varied include surface temperature history (cooling rate), the amount of shrinkage caused by crystallization and the relaxation time at the reference temperature. The model predictions were in good agreement with experimental residual stress measurements for unidirectional graphite (AS4) reinforced polyetheretherketone (PEEK) laminates.
Isothermal and Nonisothermal Fatigue Behavior of a Metal Matrix Composite
Authors: Gabb T.P. , Gayda J. , Mackay R.A.
Published: March 2007

The isothermal and nonisothermal fatigue resistance of a metal matrix com posite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 v/o continuous SiC fibers was investigated. The fibers were nominally oriented parallel to the specimen axis. Isothermal fatigue tests were performed in air at 300 and 550°C. In non isothermal fatigue tests, each load excursion at 300°C or 550°C was preceded by a tem perature excursion from 300 to 550°C at zero load.

The MMC had good isothermal fatigue resistance at 300 and 550°C at low cyclic stresses, with fatigue cracks initiating from fiber-matrix interfaces and foil laminations. At high cyclic stresses, stress relaxation in the matrix reduced isothermal composite fatigue resistance at 550°C. Nonisothermal fatigue loading substantially degraded composite fatigue resistance. This degradation was produced by a thermomechanical fatigue damage mechanism associated with the fiber-matrix interfaces.
A Fundamental Approach to Resin Cure Kinetics
Authors: Chiao Leroy , Lyon Richard E.
Published: March 2007

Thermoset polymer resins are an important class of materials, particularly when used as the matrix for advanced fiber composites. Because material performance is directly related to processing, it is useful to study the cure kinetics of these resins for use in process modeling, design and control. Several workers have attacked this problem using empirical rate laws. However, a fundamental approach can offer more flexibility without being cumbersome or impractical. In this work, amine-catalyzed epoxy reactions are studied. A kinetic model is developed and applied to experimental data from the literature, as well as from our laboratory. We show that this model is able to describe the cure reac tions of "real-world" systems, and unlike the empirical rate laws, can account for variations in the resin formulations.
High Temperature Thermomechanical Behavior of Carbon-Phenolic and Carbon-Carbon Composites, II. Results
Authors: Mcmanus Hugh L.N. , Springer George S.
Published: March 2007

Tests were conducted to validate the model and the CHAR computer code previously developed for calculating the thermomechanical behavior of carbon-phenolic and carbon-carbon composites exposed to high temperatures. Temperature distributions in and damage of rapidly heated carbon-phenolic composites were measured. The data com pared well to the results calculated by the code. Parametric studies were also performed, the results of which yield physical insights into the ply-lift phenomenon observed in solid rocket motor exit cone linings, and provide a guide in the design of parts made of carbon- phenolic and carbon-carbon composites.
Interpolative Aggregate Model for Short-Fibre Composites
Authors: Toll Staffan
Published: March 2007

A simplified aggregate model is proposed which predicts the elastic con stants of short-fibre composites in any state of fibre orientation. The only material proper ties needed are two elastic constants for one known orientation state. In essence, this implies an interpolation of elastic properties between different orientation states of the same material. Engineering moduli and fibre orientation distributions of an injection moulded nylon/glass fibre composite are measured and predictions are made. Predicted and experimental moduli correlate excellently.
Compressive Failure due to Kinking of Fibrous Composites
Authors: Lagoudas Dimitris C. , Saleh Ahmed M.
Published: March 2007

A new approach to compressive strength modeling of fibrous composites, that bridges the micromechanics relevant to compressive failure due to fiber kinking with the global characteristics of a composite structure, is presented in this work. To analyze the mechanics of kinking and calculate the critical compressive stress, a steady state kink propagation model is utilized for the layers under compression in the fiber direction. The proposed model incorporates the influence of boundary conditions, laminate thickness and lay-up configuration, as well as the importance of the micro-geometry. The analysis results are used to gain a better understanding of the influence of the macro-geometry in addition to the micro-geometry and fiber and matrix material properties. The predictions of the model for unidirectional laminates under direct compression and cross-ply laminates under four-point bending are discussed and comparisons with some experimental results for carbon/thermoplastic composites are presented.
Modeling and Analysis of Composite Laminates with Continuous Fiber around a Circular Hole
Authors: Lin H.J. , Yang S.H.
Published: March 2007

The stress distribution of glass woven roving composites containing a cir cular hole was examined. Two types of circular hole, drilled and moulded-in, were con sidered. A finite element model which used the panel method to simulate the fiber con figuration was used in the stress analysis of laminates with moulded-in circular hole. Experimental verification of strain distribution to check the accuracy of the model is also conducted. The stress distributions of [0°], [90°], [0°/90°] s and [±45°]s laminates were investigated. Numerical results show that the stress distribution σy on laminates with a moulded-in hole is smaller than that with a drilled hole when loading in the fiber direc tion, but it is reversed when loading in the perpendicular direction. The fiber configura tions and strain distributions of numerical and experimental were compared. The results agree well.
Impact-Damaged Graphite-Thermoplastic Trapezoidal-Corrugation Sandwich and Semi-Sandwich Panels
Authors: Jegley D.
Published: March 2007

The results of a study of the effects of impact damage on compression- loaded trapezoidal-corrugation sandwich and semi-sandwich graphite-thermoplastic panels are presented. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered in this study. Panels were designed, fabricated and tested. The panels were made using the manufacturing process of thermoforming, a less-commonly used technique for fabricating composite parts. Experimental results for unimpacted con trol panels and panels subjected to impact damage prior to loading are presented. Little work can be found in the literature about these configurations of thermoformed panels.
Anisotropic Permeability of Fiber Preforms: Constant Flow Rate Measurement
Authors: Chan Albert W. , Larive Douglas E. , Morgan Roger J.
Published: March 2007

Fiber preform permeability has a strong influence on the resin impregna tion behavior during polymer composites fabrication. A straightforward procedure has been developed for determining the general anisotropic in-plane permeability character of fiber preforms from constant flow rate mold filling experiments. The procedure is based on the application of Darcy's law to a two-dimensional in-plane flow situation. From ex perimental data on changes in flow front position and inlet pressure with mold filling time, the components of the in-plane permeability tensor can be calculated directly using param eters obtained from two linear plots. Experimental data for a commercial fabric confirms the applicability of the procedure. The required equipment setup and the analytical proce dure are both uncomplicated in nature. The proposed method provides a simple solution to the measurement of permeability and comparison of different preforms for polymer composites application.
Indentability of Conventional and Negative Poisson's Ratio Foams
Authors: Lakes R.S. , Elms K.
Published: March 2007

The indentation resistance of foams, both of conventional structure and of a novel re-entrant structure giving rise to negative Poisson's ratio, was studied using holo graphic interferometry. In holographic indentation tests, re-entrant foams had higher yield strengths σy and lower stiffness E than conventional foams of the same original relative density. Damage in both kinds of foam occurred primarily directly under the indenter. Calculated energy absorption for dynamic impact is considerably higher for re-entrant foam than conventional foam
Interfacial Microfracture in High Temperature Metal Matrix Composites
Authors: Mital S.K. , Murthy P.L.N. , Chamis C.C.
Published: March 2007

Two computational simulation approaches developed at NASA-Lewis Research Center are described for interfacial microfracture and its effect on high tempera ture metal matrix composites' (HT-MMC) global behavior. The first approach is based upon micromechanics and a nonlinear material behavior model to account for the material nonlinearities arising due to temperature, stress etc. The second approach is based upon a judicious use of three-dimensional finite element analysis. Both of these approaches have been used in the computational simulation of the effects of interfacial properties and microfracture on the high temperature metal matrix composite global behavior. Results presented demonstrate that computational simulation procedures can be effectively used to characterize interface/interphase and its effect on the complex behavior of high tempera ture metal matrix composites.
The Effects of Urbanization on Interpersonal Behavior
Authors: Amato Paul R.
Published: March 2007

Research conducted in Western societies has revealed urban-small town differences in a number of social behaviors, including differences in the "pace of life," affiliative behavior toward strangers, and helping behavior toward strangers. The present series of field studies was carried out in Papua New Guinea to see if similar urban-rural differences existed there. In the first series of studies, people in Port Moresby, the largest city, were found to carry out certain activities at a greater speed than people observed in two rural centers. In the second series of studies, interactions between buyers and sellers in traditional marketplaces and in European-style shops were found to exhibit less positive affect in the large city than in the rural areas. However, in the third set of studies, interactions with tourists of European descent were found to be equally positive in urban and rural areas. The findings in relation to tourist-host contacts are discussed in relation to the special role the tourist occupies in many developing countries.
A Cross-Cultural Study of Personality
Authors: Perera Mahendra , Eysenck Sybil B. G.
Published: March 2007

506 Sri Lankan men and 521 women completed the Eysenck Personality Questionnaire (EPQ) translated into Sinhala. Factor comparisons were all high enough to claim that all dimensions measured by the EPQ are virtually identical in Sri Lanka and England. Several item changes were required to produce a viable scoring key, but even then, reliabilities were unacceptably low for psychoticism but adequately high for extroversion, neutroticism and the "lie score." Cross-cultural differences, calculated by using only items in common for both Sri Lankan and British scoring keys, revealed a much higher social desirability mean for Sri Lankan subjects, but higher means on neuroticism for British subjects, with no differences found in psychoticism and extroversion scores.
Television and Self-Concept Formation in Developing Areas
Authors: Granzberg Gary
Published: March 2007

An eight-year longitudinal analysis of the impact of television in two Cree communities in northern Manitoba, Canada, reveals two differing reactions to television. In-depth anthropological investigation uncovered a linkage between these differing reactions and differing patterns of adaptation to Western pressure that promoted differing conceptions of the meanings and functions of television. These, in turn, were communicated to children by means of artfully crafted stories, analogies, and behavior models, and resulted in a heightened awareness of the sociocultural dimension of self. Those aware of self as a participant in a heritage of trickster-like adaptations to Western pressure responded to television as a great opportunity to learn Western ways and to use these ways to exploit the Western world. They became more aggressive and more out-group-oriented. Those aware of self as a participant in a heritage of avoidance relationships to the West responded to television as a threat to be resisted and became less aggressive, more fearful, and less out-group-oriented than was the case in the other community. These findings are viewed as supportive of a multilineal theory of modernization and social learning theory approach to telecommunication research.
Determinants of Hetero-and Autostereotypes
Authors: Marin Gerardo , Salazar Jose Miguel
Published: March 2007

This study analyzed the responses of 1,184 college students from seven countries in the Americas regarding their auto- and heterostereotypes. The instrument included emic scales (culture-specific) and a set of etic scales (composed of semantic differential scales). The autostereotype as measured by the etic scales was found to be fairly positive in most groups of respondents. Both auto- and heterostereotypes were highly uniform (with uniformity on etic scales decreasing in countries that had experienced mutual conflict), highly intense (primarilyamong the autostereotypes), and congruent (principally those obtained through the emic scales). Mirror-imaging stereotyping was found among conflicting nations, and highly developed countries were perceived in a more positive fashion than the respondents' own group. High levels of contact and proximity produced negative stereotyping.
Cross-Cultural Adaptation of A Developmental Test (Dial-R) for Young Children in Taiwan
Authors: Mardell-Czudnowski Carol , Chien-Hou Hwang , Tien-Miau Wang
Published: March 2007

DIAL-R (Developmental Indicators for the Assessment of Learning-Revised), a developmental test for children 2 to 6 years old, was modified minimally and translated for use in Taiwan. After it was normed on a stratified sample of 322 children in Taipei, analyses of internal consistency, construct validity, test-retest reliability, and concurrent validity all indicated that the test meets the standards of a technically adequate screening test for that culture, giving it criterion-referenced meaning. In addition, some tentative cross-cultural comparisons of young children's motoric, conceptual, and language development can be drawn. Whereras the normative data suggest that most skills develop at comparable ages in the two cultures, there are some notable exceptions, some of which develop earlier in American children, others of which develop earlier in Chinese children. These differences are discussed in context with environmental and cultural components, giving the test construct-referenced meaning.
Substituting Policies during U.S. Interventions in Internal Conflicts
Authors: Regan Patrick M.
Published: March 2007

The conditions under which states substitute across a range of foreign policy options have remained largely an unexplored area of international relations. The ability to substitute policies is evident in the response by the United States to instability in other countries. In this article, the author explores the conditions under which the United States changes its intervention strategies in civil conflicts and the type of interventions that are substituted once the decision to change has been made. He argues that the decision to change policy is rooted in domestic political risks, while the specific strategy for intervening will be a function of capabilities. Using data on U.S. interventions in the post-World War II period, the author demonstrates that domestic factors are associated with the likelihood of a change from the status quo. The specific policy option chosen, however, appears to be a result of both capabilities, which are rooted in the relationship with the target country and the amount of public attention given to the conflict in the media.
The Sources of Threat Credibility in Extended Deterrence
Authors: Danilovic Vesna
Published: March 2007

For deterrence to work, a potential attacker needs to perceive the deterrer's threats as capable and credible for retaliation. The issue of relative capabilities has been extensively analyzed, yet the core problem concerns credible intentions. The strategic literature is largely influenced by commitment theory prescribing various “manipulation of risk” strategies intended to enhance threat credibility. A few analysts, however, challenge this view and recognize the importance of “intrinsic interests” in the issues at stake (i.e., inherent credibility), which can limit the effectiveness of costly signals. These two alternative views are quantitatively tested in the cases of major-powers deterrence from 1895 to 1985. A new measure of the observable category of inherent credibility is also introduced, consisting of the regional interests of major powers in the area of dispute. The results indicate strong and significant effects of regional interests on both the onset and outcomes of extended-immediate deterrence, thus suggesting relevant theoretical and policy implications.
The Balance of Power in International History
Authors: Healy Brian , Stein Arthur
Published: March 2007

Many observers have recently noted that the international system is evolving into a multipolar world. At the same time, the notion of balance of power is being severely criticized for its vagueness and inconsistency. Seven empirically testable propositions which exemplify refined and narrowed notions of balance of power are reviewed and analyzed in this paper. These propositions, authored by A. L. Burns, M. Kaplan, D. Singer and M. Small, F. H. Hinsley, R. Rosecrance, and F. Harary concern one of four major approaches to the multipolar system: (1) the rules of a theoretical balance of power system, (2) the functioning of alliances, (3) historical systemic periodization, and (4) the application of structural balance theory to the interna tional system. The Situational Analysis Project provided the data for testing these propositions over the first twelve years of the "Bismarckian system," 1870 through 1881. The propositions did not hold up well under detailed testing. The rules of the balance of power system were violated—in particular, an "ingratiation effect" was found in place of the balance-restoring mechanism; alliances led to a lessening of cooperation and attention between allies; and historical periodization was found to be inaccurate. The findings, however, did support the fundamental assumption underlying the structural balance theory. Since the future may be quite like the nineteenth century in terms of structure, a reevaluation of the Bismarckian system is not an irrelevant exercise but rather an inquiry into the functioning of a system we may actually have to operate.
Collective Protest and Legitimacy of Authority
Authors: Worchel Philip , Hester Philip G. , Kopala Philip S.
Published: March 2007

A theory of collective protest is proposed in which distrust and the erosion of the legitimacy of authority are postulated to be a function of frustrations perceived as inequitably imposed and arbitrary. The present study tested the predictions that protest groups would have a significantly lower evaluation of authority, be more willing to participate in violence, and have a greater sense of competence than nonprotest groups. Two separate studies were conducted. The first study compared attitudes of an activist protest group, the Young Socialist Alliance, with two nonprotest groups, an active voter registration group and a nonactive student group at the University of Texas. The second study dealt with the attitudes of the campus activist Mexican-American Youth Organization (MAYO) and a Mexican-American non-MAYO group. The following instruments were administered individually and anonymously: a semantic differential to evaluate traditional and legitimate author ities; a participation questionnaire requesting willingness to participate in negotiation, protest, and violent confrontation with authority; a credibility-rating scale to measure the trustworthiness of information issued by authority, and a modified internal-external scale to provide an indirect assessment of competence. The results supported the hypotheses derived from the theory of collective protest.
The Effectiveness of a Pacifist Strategy in Conflict Resolution
Authors: Reychler Luc
Published: March 2007

To find out to what extent the violence and exploitative behavior of the opponent of a pacifist strategist could be controlled, the author tested within a laboratory context the impact of eight variables. Together these variables accounted for more than 50% of the behavior of the opponents. The predictions concerning the controlled variables were confirmed. A pacifist strategy tends to be most effective in reducing violence and exploitative behavior when the human distance between the subject and opponent is small, the subject is well informed about the intentions of the pacifist, the subject is required to justify his behavior post-facto, and when a partial third party is present. Male and female subjects did not differ with respect to the use of violence, but it was found that females had a higher propensity to stalemate, with a consequent reduction of their own and the pacifist's winnings. The strongest predictors of the effectiveness of the pacifist strategy were the demand characteristics and the image of the pacifist held by the opponent. A discussion of the controllability of these last two variables is included.
Nice Guys Finish Last—Sometimes
Authors: Behr Roy L.
Published: March 2007

Recent articles in this journal demonstrated that cooperation until provocation is the best approach to iterated Prisoner's Dilemma when the goal is the maximization of payoffs. However, analysis of the tournament results discussed in these previous works shows that this same strategy is not necessarily beneficial when the desired end is outscormg the opponent. In the environment considered here, when either consistent victory or maximum average margin of victory is the predetermined policy objective, strategies which usually cooperate until provoked, but occasionally take advantage of cooperative opponents are clearly most successful. Even when playing a game as straightforward as Prisoner's Dilemma, strategies must be specifically tailored to fit objectives.
Riot Contagion in Latin America, 1949-1963
Authors: Govea Rodger M. , West Gerald T.
Published: March 2007

This article investigates the possibility of a contagion effect in each of fourteen Latin American republics from 1949 through 1963. Using a data set drawn from the Hispanic American Report, riot frequencies are compared with the Poisson and contagious Poisson distributions. The authors find evidence of contagion in six countries, and suggest that contagion as a concept encompasses a variety of behavioral processes. In addition, the authors attempt to reconcile contagion studies with more traditional studies of political violence.
Resistance to Affirmative Action
Authors: Jacobson Cardell K.
Published: March 2007

Despite the decade-long debate in the media and in the social science literature over affirmative action programs, relatively little information has appeared about attitudes toward these programs. In this article racial threat or self-interest, new symbolic racism, and old-fashioned racism are examined as predictors of attitudes about affirmative action programs. The data are from a national survey conducted in the late fall of 1978 by Louis Harris and Associates for the National Conference of Christians and Jews. Self-interest, new symbolic racism, and old-fashioned racism are all found to be related to attitudes about affirmative action programs and remain so when a variety of control variables are included in the regression analyses. The new racism scale was clearly the best predictor of attitudes about affirmative action programs but is shown to have many underpinnings from traditional sources of racism. Possible reasons for the effect of self-interest on attitudes about affirmative action programs that had not been related to racial attitudes in earlier studies are discussed.