bluuebunny/crossref_metadata_2025 huggingface dataset:
A Finite Element Analysis of Laminated Anisotropic Tubes
Authors: Rizzo R.R. , Vicario A.A.
Published: March 2007

To gain needed insight into the effects of thickness to diameter ratio ( t/D i), length to diameter ratio (l/Di ), and helical angle (α) on the response of laminated tubes in material characterization tests, a unique new elasticity finite element program has been implemented which can deal with the general three-dimensional nature of axisym metric composite bodies. The program, which is utilized here to analytically predict the response of unidirectional composite tube specimens to uniaxial tension/compression, differs from the usual finite element formulations in that it accounts for general anisotropy. In particular, it deals with all shear coupling terms and all six com ponents of stress. The effects of different gripping methods are also considered. Similar studies of torsion and internal pressurization tests will be reported in subsequent notes.

This first phase of the study shows that while the response of axial and hoop wrapped tubes (α = 0°, 90°) is essentially indepen dent of length and thickness ratios, the effects of these ratios and helix angle can be significant for uniaxial off-axis specimens. In addition to axial stress, hoop and in-plane shear stresses are also present in the gage section, even when the grips are free to rotate. More importantly, however, the t/D i and l/Di ratios can significantly affect the mode of stress distribution. For example, the stresses are nonuniform across the tube thickness; the nonuniformity increases as the t/D i ratio is in creased, with maximum stress occurring at the inner radius. For the material considered (boron) the distributions will be effectively linear for t/Di < 0.1, while for t/Di > 0.1 they will be nonlinear. When t/D i < 0.02, the trends are nearly uniform outside the transition zones and can thus be characterized by classical shell theory formulations. The transition length ( lt) measured in from the gripped ends is ap proximated as a function of the thickness and length ratios and is given in expression (4). Interlaminar shear and radial stresses, for all practical purposes, are non-existent in the gage length (for uniaxial layups) and are of consequence only in the grip section.
Fracture Mechanics Approach to Adhesive Joints
Authors: Trantina G.G.
Published: March 2007

This study investigates the problem of applying fracture mechanics to the opening mode fracture of a two-material (aluminum-epoxy-aluminum) system. The results of a finite element analysis of a two-material, single- edge-notch (SEN) plate are used with a compliance method in order to obtain strain energy rates, g, and with a displacement method to obtain stress intensity factors, K. Approximate relationships between the homo geneous system and the adhesive system for both K and g are determined. The relationship between K and g for the adhesive system is obtained. The experimental investigation provides an experimental compliance calibration for the same adhesive system and loading. Good reproducibility of the fracture toughness values obtained for the two-material system with SEN and tapered DCB specimens indicates the geometry independence of the fracture toughness. The effect of the notch root radius and proper specimen preparation are also considered.
Axial Impact of an Orthotropic Cylindrical Membrane
Authors: Counts J. , Brickley James J.
Published: March 2007

A semi-infinite, cylindrical membrane of helically oriented fiber- reinforced material is considered. The equations of motion are solved by the method of characteristics for a membrane impacting a rigid wall. Results are presented for various fiber orientations using representative material properties.
Some Remarks Concerning Heterogeneous Anisotropic Plates
Authors: Schumann Walter , Wuthrich Willy , Teichmann Gilles
Published: March 2007

Paper gives some illustrative aspects of the theory of laminated aniso tropic plates in general, mcluding a remark on a variational principle, boundary conditions and finite elements. In particular, a problem of a rectangular plate under some special edge conditions is outlined.
Some Remarks Concerning Heterogeneous Anisotropic Plates
Authors: Schumann Walter , Wüthrich Willy , Teichmann Gilles
Published: March 2007

Paper gives some illustrative aspects of the theory of laminated aniso tropic plates in general, including a remark on a variational principle, boundary conditions and finite elements. In particular, a problem of a rectangular plate under some special edge conditions is outlined.
Fracture Analysis of Unidirectional Composites
Authors: Sih G.C. , Chen E.P.
Published: March 2007

The concept of fracture mechanics is applied to analyze the brittle fracture of unidirectional composites. The analytical prediction based on the newly developed Sc-theory agrees well with the experimental data on Scotchply 1002 where crack propagation occurs along the fiber direction. The Sc-theory represents a departure from the classical stress-intensity factor Kc concept in that it is designed to treat the mixed mode fracture problem while the Kc-theory is limited to Mode I crack extension.
Strength Optimization for Cylindrical Shells of Laminated Composites
Authors: Chao C.C. , Sun C.T. , Koh S.L.
Published: March 2007

Optimum fiber orientations in symmetrically laminated cylindrical shells under combined loadings are investigated. The theory of maximum work is used as the strength criterion. A modified golden section method is employed for the optimization. The glass-epoxy composite is taken for numerical examples.
Moisture Content of Composites Under Transient Conditions
Authors: Springer George S.
Published: March 2007

The moisture content and moisture distribution of a fiber reinforced composite were calculated under conditions simulating the typical, 20 year service life of an aircraft. The results indicate that the complete transient analysis of the problem must be performed in order to establish a) the long term moisture effects, b) the conditions for accelerated testing, c) the "worst case" design conditions, and d) methods to interpret field monitor ing programs on moisturing gain.
Biaxial Fatigue Loading of Notched Composites
Authors: Francis Philip H. , Walrath David E. , Sims David F. , Weed Donald N.
Published: March 2007

Thin-walled, 2.54-cm diameter tubular specimens of graphite/epoxy (Fiberite T300/1034) were fatigue cycled in combinations of axial, torsion al, and internal pressure loading. Two different four-ply layup configura tions were tested: [0/90] s and [±45]s; each tube contained a 0.48-cm diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experi mental data proved to be remarkably good.
Statistical Fatigue of Graphite/Epoxy Angle-Ply Laminates in Shear1
Authors: Yang Jann N. , Jones Douglas L.
Published: March 2007

A three-parameter fatigue and residual strength degradation model has been proposed to predict statistically the fatigue behavior of composite laminae under axial shear loadings. The fatigue behavior includes the fa tigue life and the fatigue damage expressed in terms of the residual strength degradation. An experimental test program using graphite/epoxy [±45°] 2s laminates has been conducted to generate statistically meaningful data in order to examine the validity of the theoretical model. It is shown that the correlation between the theoretical predictions and the test results on the statistical distributions of the fatigue life and the residual strength is excel lent. Test results on the shear modulus degradation are also presented and discussed in detail in order to provide insight for the establishment of a shear modulus degradation model.
Interlaminar Stresses in Symmetric Composite Laminates
Authors: Wang James T.S. , Dickson John N.
Published: March 2007

Interlaminar stresses and displacements of each layer satisfying geo metrical boundary conditions are represented in series of Legendre poly nomials. The extended Galerkin procedure is used for each layer, and the final solutions are obtained by requiring the satisfaction of continuity conditions at each interface and the stress boundary conditions at exterior planes. A computer program has been prepared, and numerical results are presented and compared with existing data.
Electrical Hazards Posed by Graphite Fibers
Authors: Springer George S. , Mashtizadeh Safer A. , Keller Robert B.
Published: March 2007

The direct electrical resistance and the electrical contact resistance of graphite fibers released from both burned and unburned Fiberite T300/1034 composites were measured. The voltage at which arcing oc curs due to fibers settling on electrical conductors was also determined. On the basis of results obtained, an assessment was made of the hazards posed by graphite fibers to electrical equipment.
Analysis of a Bonded Joint in a Composite Tube Subjected to Torsion
Authors: Graves Stanley R. , Adams Donald F.
Published: March 2007

The stress state in the bonded joint region of a laminated composite tube subjected to torsional and hygrothermal loadings is analyzed. A finite ele ment solution technique is utilized. The composite can be modeled ply-by-ply, and the adhesive as a separate elastic layer. All six stress components are pre sent in a generally orthotropic material subjected to torsion, and the coupling effects between shear and normal components can become significant. Because of the low interlaminar normal strength of most composites, the in duced stress components may lead to failure. Several example problems are presented.
Notched Unidirectional Boron/Aluminum: Effect of Matrix Properties
Authors: Reedy E.D.
Published: March 2007

The manner in which matrix properties affect the notched behavior of unidirectional boron/aluminum is assessed. Data are presented for center- notched tensile specimens of as-fabricated boron reinforced 1100 and 6061 aluminum. Results are also given for a heat-treated B/6061. The notched response of these materials shows significant differences. A shear-lag analysis, formulated for finite-dimensioned monolayers made from work-hardening constituents, is shown capable of explaining such effects. The calculated rela tion between load and notch opening displacement for a uniform traction boundary condition is indistinguishable from that for a displacement condition when the matrix yield strength is sufficiently high. For such cases, the predicted relation is in excellent agreement with experiment. Specimens with a relatively low matrix yield strength exhibit different behavior: the predicted relation be tween load and notch opening displacement depends strongly on the type of boundary condition applied. This is a consequence of widespread matrix yielding. These two predictions bound the experimental data. Also discussed are calculations which indicate that nonuniform fiber spacing and flaw geometry have little effect on fiber stresses. The growth of shear cracks does ap pear, however, to substantially alter the response of notched boron/aluminum.
Energy Absorption in Composite Tubes
Authors: Thornton P.H. , Edwards P.J.
Published: March 2007

The collapse characteristics and energy absorption of a variety of tubes made in glass, graphite and Kevlar fiber composites have been examined. Tubes made from glass or graphite fibers collapsed by a fracture mode. There was a critical range of tube geometry over which stable collapse occurred with high energy absorption; thinner wall tubes tended to collapse in an unstable manner with lower energy absorption. Changes in the lay-up which increased the modulus increased the energy absorption of the tube. Tubes made from, or including Kevlar fiber, tended to collapse in an unstable mode by buckling rather than by fracture, which led to low values for specific energy absorption.
Mode I Interlaminar Fracture Toughness of Composites Using Slender Double Cantilevered Beam Specimens
Authors: Keary Paul E. , Ilcewicz Larry B. , Shaar Casey , Trostle Jess
Published: March 2007

The use of slender double cantilever beam specimens for measuring the mode I in terlaminar fracture toughness was critically evaluated. Experiments were performed with unidirectional composites to judge the validity of using data from multiple crack jumps on a single specimen. Three approaches for calculating the strain energy release rate were compared. These included an energy rate determination of the JI-integral, a compliance calibration procedure and an analytical equation based on linear beam bending. The fracture toughness was overestimated by the latter two approaches. Per manent deflection was seen to accumulate in the arms of the double cantilever beam specimens as the cracked surface area increased. This component of deflection must be accounted for in all forms of analysis with DCB specimens.
Interplay of Physical and Chemical Aging in Graphite/Epoxy Composites
Authors: Mijovic Jovan
Published: March 2007

Effects of pressure and temperature on time-dependent changes in physical/ mechanical properties of graphite/epoxy composites were investigated. Samples from an eight-ply thick laminate of commercially used composites were cured, post-cured and then quenched to environments of various temperature and pressure. Time- dependent changes in their properties were analyzed by calorimetric and dynamic mechanical measurements. An increase in the glass transition temperature was found to occur at longer aging times. The rate of this process was enhanced by an increase in temperature and/or a decrease in pressure. An explanation was offered in terms of types and mechanisms of molecular events that occur in the glassy state. Physical aging, i.e. a time-dependent decrease in free volume (and enthalpy) takes place during the first stage of aging, but is not the sole mechanism responsible for the observed in crease in T g. Here, experimental results were checked against theoretical predictions based upon the free volume concept. After a certain period of time (which depends on T and P of the environment), however, chemical aging, i.e. additional crosslinking, ap pears to take place.
On Interfacial Failure in Notched Unidirectional Glass/Epoxy Composites
Authors: Newaz Golam M.
Published: March 2007

The splitting mechanism in notched unidirectional glass/epoxy composites under tensile loading has been studied to gain insight into this failure process. An already- available mathematical expression based on the J-integral technique proposed by Tirosh [1] has been used for this purpose. This expression relates the length of the split crack to the in-plane elastic constants of the composite, original notch length, inter facial shear yield stress, and the applied tensile stress. This model has been used to distinguish between the quality of fiber-matrix bonding in two E-glass fiber-reinforced epoxy composites by evaluating their interfacial shear yield stress using transversely edge-notched unidirectional composites. The experimental results demonstrate that an important requirement to control the length of the split crack is higher fiber-matrix in terfacial shear yield stress. Also, the Tirosh model is found to effectively predict the progression of splitting in notched unidirectional composites.
Inhomogeneity Effect on the Stress Intensity Factor
Authors: Chiang C.R.
Published: March 2007

In contrast to the macromechanical analysis in which a composite material is usually taken to be homogeneous, a simplified analysis model is proposed in this article to ex amine the inhomogeneity effect on the stress intensity factor of the crack embedded in a fiber-reinforced composite material. Two composite materials (glass/epoxy and boron/epoxy) are used to illustrate the theoretical predictions, and the primary finding is that the crack size should be at least 3 orders of magnitude larger than the fiber diameter to vindicate the homogeneity assumption.
The In Situ Ply Shear Strength Distributions in Graphite/Epoxy Laminated Composites
Authors: Chang Fu-Kuo , Chen Ming-Huei
Published: March 2007

An experimental and analytical investigation was performed to study the in situ ply shear strength in fiber-reinforced laminated composites. The effects of ply orientation and laminate thickness on the ply shear strength in laminates were the major concerns of the study. T300/1034-C Graphite/Epoxy cross-ply laminates were selected for the tests, and a rail shear fixture was used for measuring ply shear strengths. A three-dimensional finite element program was also developed to analyze the interlaminar stress distributions in the specimens. The results of test data strongly indicate that the ply orientation and laminate thickness significantly influence the in-plane shear strengths of the laminates. This effect could be attributed to the inherent flaws introduced during manufacturing processes and to interlaminar stresses in laminates. As a consequence, ply shear strength should not be regarded as an intrinsic property of fiber-reinforced laminates. Due to the free edge effect, the results of shear strength distributions measured from the rail shear fixture were conser vative.
Compressive Response of Kevlar/Epoxy Composites
Authors: Yeh J.R. , Teply J.L.
Published: March 2007

A mathematical model is developed from the principle of minimum potential energy to determine the longitudinal compressive response of unidirectional fiber composites. A theoretical study based on this model is conducted to assess the influence of local fiber misalignment and the nonlinear shear deformation of the matrix. Numerical results are compared with experiments to verify this study; it appears that the predicted compressive response coincides well with experimental results. It is also shown that the compressive strength of Kevlar/epoxy is dominated by local shear failure.
Impact Induced Stresses, Strains, and Delaminations in Composite Plates
Authors: Wu Hsi-Yung T. , Springer George S.
Published: March 2007

A method is presented for calculating the locations and sizes of delaminations which oc cur in a rectangular, fiber reinforced composite plate sujected to non-penetrating (low velocity) impact of a solid object. The plate may be simply supported or clamped along its edges. In-plane loads or in-plane strains may be imposed on the plate during the im pact. The method includes two steps. First, the stresses and strains in the plate are calculated by a three-dimensional, transient finite element method using 8-node brick ele ments with incompatible modes. Second, the locations, lengths, and widths of delamina tions inside the plate are predicted by means of a proposed failure criterion, which is based on the concept of dimensional analysis. The finite element method and the failure criterion were implemented by a computer code which can be used to calculate the impactor posi tion and velocity, the displacements of the plate, the stresses and strains inside the plate during the impact, and the locations and dimensions of the delaminations after the impact. Parametric studies were performed to illustrate the information which can be generated by the computer code.
Damage Characteristics in Notched Carbon Fiber Composites Subjected to Fatigue Loading—Environmental Effects
Authors: Morton J. , Kellas S. , Bishop S.M.
Published: March 2007

Several destructive and non-destructive methods were used to study the effect of ab sorbed moisture and/or heat on the tension-compression fatigue properties of notched, 0°/±45°, carbon fiber reinforced plastic laminates. The main objective was the understanding of the nature of fatigue damage around notches (sharp slits and circular holes), under hot and/or wet conditions. The fatigue performance of the notched laminates was assessed mainly by means of residual strength measurements. It was found that the shape and extent of fatigue damage around the notches were highly dependent upon the environments considered. Furthermore, it was shown that the residual strength or fatigue life depended upon the lay-up for a given environment.
A Simple Model for the Compressive Failure of Weakly Bonded, Fiber-Reinforced Composites
Authors: Steif Paul S.
Published: March 2007

A model for the compressive failure of fiber-reinforced composites with brittle, weakly bonded constituents is presented. This model is an extension of the classic fiber micro buckling analysis to situations in which slippage occurs at the fiber-matrix interface when the interfacial shear stress reaches some critical value. Slippage is found to eliminate the support usually offered by the matrix to the fiber and, thereby, leads to substantially lower predictions of compressive strength. An explicit formula for the compressive strength in terms of the interfacial shear strength and the degree of fiber misalignment is derived, and comparisons with experiments are discussed.
Composite Parameters and Mechanical Compatibility of Material Joints
Authors: Suga T. , Elssner G. , Schmauder S.
Published: March 2007

The elastic behaviour of a bimaterial interface with interfacial cracks, misfit dislocations and interfacial thermal stresses can be described in a simple manner by using the com posite parameters α and β, and the effective modulus of elasticity E*, assuming a plane deformation of ideally bonded isotropic materials. A coefficient KT for the thermally in duced stress intensity at the interface serves as a measure of the mechanical compatibility of two bonded materials. An examination of these parameters for many composite materials shows that the values of the composite parameters α and β are limited to a nar row range and that the material transition can be classified into six groups with regard to their mechanical compatibility.
Calculation of Wave Propagation in Composite Materials Using the LAMB Wave Concept
Authors: Noiret D. , Roget J.
Published: March 2007

Over recent years the development of the use of composite materials has led to growing activity in the nondestructive testing field.

Widely known techniques such as acoustic emission and ultra-sound have found a new field of application here and new techniques such as acousto-ultrasonics which have recently appeared have shown some interesting results in detecting defects in composite structures.

However, acoustic emission for defect localisation and acousto-ultrasonics have sometimes shown a lack of reliability; very little is known about theoretical aspects of wave propagation in these materials, nor about the interaction existing in the material between acoustic waves and defects as the wave propagates.

On the basis of some assumptions, theoretical calculations have been made on the prop agation of a steady wave in unidirectional composite plates and compared successfully to experimental results found in the literature.
Analysis and Experimental Characterization of the Center Notch Flexural Test Specimen for Mode II Interlaminar Fracture
Authors: Maikuma Hironori , Gillespie John W. , Whitney James M.
Published: March 2007

The interlaminar Mode II critical strain energy release rates of unidirec tional graphite/epoxy, graphite/polyetheretherketone (PEEK), and graphite/epoxy with interleaf material were characterized using the End Notch Flexural (ENF) and Center Notch Flexural (CNF) test specimens. The CNF test method was developed specifically for this study. Compliance and strain energy release rate expressions of the CNF are derived and are in good agreement with finite element results for a wide range of crack lengths. Mode II critical energy release rates for both test methods were found to be in quite good agreement.
Spatial Strength Variation of Laminated Orthotropic Composites
Authors: Deodatis George , Shinozuka Masanobu , Neal Donald
Published: March 2007

A probabilistic model for the spatial variation of the strength of materials used for laminated orthotropic composites is introduced. The principal idea lies in the in terpretation that the material strength can be idealized as a multi-dimensional stochastic field. Under such an assumption, the type of statistical distribution followed by the strength of laminated orthotropic composite plates in uniaxial tension is found to follow a Weibull distribution, with the aid of Monte Carlo simulation techniques. Another conclu sion is the statistical size effect which is a well-known phenomenon for materials of this kind.
Effects of Friction in Ceramic Coating/Fiber Composites
Authors: Lu Mei-Chien , Hsueh Chun-Hway
Published: March 2007

The effect of frictional interaction at a weakly bonded or unbonded coating/ fiber interface is analysed by studying a single fiber with a finite length of uniform coating on its central region. Residual thermal stresses and applied tensile loads at the fiber ends are considered. The effects of the coefficient of friction at the interface and the thermo mechanical mismatch of the system on the stress transfer from the fiber to the coating are revealed. Through the analysis, a method to predict the residual thermal stress and to eval uate the coefficient of friction is suggested. The possibility of extending this method to evaluate general residual stresses is also addressed.
Biaxial Flexing of a Fiber Reinforced Aluminum Composite
Authors: Tsangarakis Nikos , Pepi Marc S.
Published: March 2007

Disks of silicon carbide continuous fiber reinforced ([0°/90°]4s) aluminum were supported circumferentially on one side and loaded at the center of the other side with a pin. Maxima principal tensile surface strains were determined during flexing with strain gages.

Failure under monotonic loading initiated on the convex side of the disks with the for mation of multiple breaks in the first layer of fibers. With further flexing cracking extended to inner fiber layers. Finally, fracture extended through the convex surface layer of the alu minum matrix. On cyclic flexing, fiber cracking was found to be the failure mechanism whenever the cyclic principal surface strain range was 0.0035 or greater. For cyclic strain ranges less than 0.0035, slip bands and cracks were formed in the matrix in addition to the cracks formed in the fibers. The cyclic strain range limit for 10 6 cycles of life was found to approach 0.0015. The latter limit corresponded to a maximum cyclic fiber strain of 0.00132, which is only 15 % of the fiber strain to failure under monotonic uniaxial compos ite loading.
Non-Axial Crushing of E-Glass/Polyester Pultruded Tubes
Authors: Czaplicki Michael J. , Robertson Richard E. , Thornton Peter H.
Published: March 2007

Two types of non-axial crushing, off-axis crushing and angled crushing, have been identified and significant differences found between the E-glass/polyester pultruded tubes crushed in these different configurations. Energy absorption for the two types of crushing was found also to vary significantly with the angle of inclination, with the difference being largest at high angles of inclination. Reasons for energy absorption differences between the crushing configurations include the initiation of different crack patterns, different loading of individual fibers, and altered friction. For all angles, the load required for continued crushing was found to fluctuate more for off-axis crushing than for angled crushing.
Variation of Elastic Moduli with Strain in Carbon/Epoxy Laminates
Authors: Stecenko Tatjana B. , Stevanovi Momčilo M.
Published: March 2007

The strain dependence of tensile and compressive elastic moduli in carbon fibre/epoxy resin unidirectional and multidirectional composites is presented. Examined composites were made from prepregs supplied by two producers. Values of relative varia tions of modulus with unit strain are given. All of the examined composites, except (±45)4s show modulus increase with the rise of tensile strain and modulus decrease with increasing compressive strain. Modulus increase and decrease of composites is attributed to the modulus change of carbon fibre, mainly.
On-Line Cure Monitoring of Epoxy/Graphite Composites Using a Scaling Analysis and a Dual Heat Flux Sensor
Authors: Perry Mark J. , Lee L. James , Lee C. William
Published: March 2007

On-line cure monitoring of an epoxy/graphite composite was studied. A scaling analysis derived the dimensionless Damkohler number for cure monitoring. A dual heat flux sensor was designed from a pile of three thermocouples to provide on-line estimation of thermal diffusivity and to measure change in heat flux for calculating the Damkohler number. Verification of this cure monitoring technique was made using differ ential scanning calorimetry. A simplified cure model was developed for a commercial epoxy/graphite prepreg. Conventional model-assisted cure cycle design was compared to the on-line monitoring technique.
A Modified DCB Specimen for Mode I Testing of Multidirectional Laminates
Authors: Robinson P. , Song D.Q.
Published: March 2007

A detailed study of the Mode I interlaminar fracture toughness measure ment of multidirectional laminates is presented. The use of a novel DCB specimen is pro posed in which the conventional DCB specimen is delaminated along its edges by the in corporation of inserts in addition to the usual delamination at the loaded end. Investigations using this specimen to examine the fracture toughness at +45°/+45° and +45°/-45° interfaces indicate that the appropriate width of edge delamination can sup press the crack jumping and fibre bridging which occur in the conventional DCB speci men. Preliminary tests show that GIC for +45°/+45° and +45°/-45° interfaces in multidirectional laminates are significantly higher than the GIc measured for a 0°/0° inter face in a unidirectional laminate.
Application of Reliability and Fiber Probabilistic Strength Distribution Concepts to Composite Vessel Burst Strength Design
Authors: Cohen David
Published: March 2007

With the expanding use of composite vessels, including space and tactical applications, accurate prediction of performance becomes increasingly important. A criti cal parameter in performance prediction is the burst strength as measured by the delivered fiber ultimate strain-to-failure. This paper discusses a composite pressure vessel design approach that is based on reliability and probabilistic fiber strength distribution concepts.1 The method is based on the fiber strain-strength interference reliability theory. A substan tial part of this paper examines how fiber strength distribution parameters generated by tow tensile tests of impregnated carbon fiber strands can be used in pressure vessel strength design. The fiber statistical strength distribution is analyzed using the Weibull distribution function. It is shown that the bimodal Weibull distribution function fits the impregnated fiber strand strength distribution data much better than the single mode Weibull function. This is particularly important because the bimodal function gave a much more accurate representation of the lower tail of this distribution. According to the strain- strength interference theory, the lower tail of the fiber strength distribution is the most sig nificant in pressure vessel strength reliability calculations.

The impregnated fiber strand strength distribution agrees well with the strength distribu tion of 4-in. biaxial composite tubes manufactured from the same carbon fiber lot. Good agreement was also shown with the strength distribution of pooled fiber lot tow tensile data and hydroburst strength distribution of full-scale composite pressure vessel manufactured from these lots. In this comparison, the A-basis fiber strength allowable calculated from the strand data was slightly lower (3%) than those calculated from the full-scale pressure vessel strength data, whereas, the B-basis allowables calculated from the strand and the full-scale pressure vessel strength data were the same. However, because A-basis and/or B-basis allowables require many data points from many material lots, the use of fiber lot qualification data is advantageous because it meets these requirements.
Study on Strength and Nonlinear Stress-Strain Response of Plain Woven Glass Fiber Laminates under Biaxial Loading
Authors: Fuj Toru , Amijima Sadao , Fan Lin  , Sagami Taisuke
Published: March 2007

Strength and stress-strain properties are investigated for plain woven glass fiber laminates using thin tubular specimens under biaxial static and cyclic loadings. Some composites show large distortion and fiber reorientation close to failure under biaxial load ing. For such composites the usage of the 2nd Piola-Kirchhoff stress instead of the nominal stress is proposed for strength evaluation. The experimental result reveals that the Tsai-Wu criterion fits the biaxial strength expressed by the 2nd Piola-Kirchhoff stress much better than the strength expressed by the nominal stress. Strong interaction between axial and shear deformations is found beyond the knee/yield points while, within the elastic range no interaction is found between the axial and shear stiffness. Fiber misalignment with the loading axis affects the observed stress-strain behavior under cyclic loading. More than two S-S curves are distinguishable when the fiber misalignment is higher than 2°. Such stress-strain relations are successfully simulated using an incremental method in conjunc tion with updating fiber orientation. Good agreement between the calculated result and ex perimental one confirms that the proposed model which considers fiber misalignment can explain the observed stress-strain response under biaxial fatigue loading.
Non-Dimensional Analysis of an Idealized Thermoset Composites Manufacture
Authors: Pitchumani Rangarajan , Yao Shi-Chune
Published: March 2007

Modeling the cure of thermoset composites has been the subject of many investigations in the literature. However, the studies have focused on specific composite systems and product specifications. Consequently, extending the results based on one com bination of process and product parameters to another is not obvious, and the choice of cure cycles in practice remains predominantly heuristic-based. This work presents a gen eralized analysis of the cure, based on an idealized expression for the cure kinetics, in terms of four dimensionless groups formed of the process and product parameters— the Damkohler number (Ko), the dimensionless activation energy (Eo), the adiabatic reac tion temperature (Bo) and the Biot number (Bi). The non-dimensional approach reduces the large number of process and product variables involved, to the few dimensionless groups, and eliminates the need for a system-specific or product-specific modeling. Fur ther, the article addresses the problem of selecting the best cure cycles for achieving a desired product quality. With regard to the manufacture of partially cured composite systems, optimal cure cycles which yield a homogeneous cure in the product, in the mini mum possible time, are obtained as a function of the non-dimensional parameters. Design plots for the optimal cure temperature and duration are presented, and their use in practi cal situations is illustrated in the context of a commercially available graphite-epoxy pre preg from Hercules, which is widely used in the aerospace industry.
Effective Thermal Conductivity of Uniaxial Composite with Cylindrically Orthotropic Carbon Fibers and Interfacial Thermal Barrier
Authors: Hasselman D.P.H. , Donaldson K.Y. , Thomas J.R.
Published: March 2007

The theories of Hasselman et al. and Benveniste et al. were extended to derive expressions for the longitudinal and transverse effective thermal conductivity of an isotropic matrix uniaxially reinforced with dilute concentrations of cylindrically orthotro pic fibers for finite interfacial thermal conductance values. The transverse thermal conduc tivity of the composite was found to be a function of both the radial and tangential compo nents of the transverse thermal conductivity of the fibers. Comparison with the effective thermal conductivity of an isotropic matrix reinforced with isotropic fibers indicates the effective thermal conductivity of cylindrically orthotropic fibers equals the geometric mean of the radial and tangential transverse thermal conductivity. As for isotropic matrices reinforced with isotropic fibers, a finite value for the interfacial thermal conductance in composites reinforced with cylindrically orthotropic fibers leads to a lowering of the com posite transverse thermal conductivity and also introduces a dependence on fiber diameter. Based on experimental data for the transverse thermal conductivity of a uniaxial carbon fiber-reinforced aluminoborosilicate glass matrix composite in nitrogen at atmospheric pressure and in vacuum, estimates of the interfacial thermal conductances indicate that in nitrogen at atmospheric pressure interfacial gaseous heat transfer contributes about one- third of the total interfacial thermal conductance. The theory should be applicable to other isotropic matrices reinforced with cylindrically orthotropic fibers.
The Effect of Fiber Concentration on the Thermal Conductivity of a Polycarbonate/Pitch-Based Carbon Fiber Composite
Authors: Demain A. , Issi J.-P.
Published: March 2007

Results of measurements of the thermal and electrical conductivities of polycarbonate samples as a function of chopped pitch-based carbon fiber concentration are reported. The fibers, roughly 500 μm long, were found to be strongly oriented in the composite leading to a highly anisotropic thermal conductivity. Longitudinal thermal con ductivities comparable to that of metallic alloys are obtained in the direction of the fibers, while in the transverse direction only a small increase in the thermal conductivity is observed. We proposed a new model which is a derivation of equations used for con tinuous fibers composites. This model is quite well in accordance with the linear de pendence of the longitudinal thermal conductivity on the fiber concentration of our data. Taking into account the effect of the polymeric matrix, the importance of contact resis tances between fibers and their maximum packing as well as the qualitative differences be tween thermal and electrical conduction is discussed.
Optimum Design of Composite Structures for Shape, Layer Angle and Layer Thickness Distributions
Authors: Fukunaga Hisao , Sekine Hideki
Published: March 2007

This article treats an optimum design of laminated composite structures subject to in-plane loading. A simplified design approach is developed to optimize layer angle and layer thickness distributions. First based on the minimum strain energy crite rion, an explicit optimal relation is derived for layer angles and layer thickness ratios in a single-element laminate. Using the optimal relation in the single-element laminate, an optimization approach is developed for determining layer angle and layer thickness distri butions in multi-element composite structures with strength constraints. The present ap proach can determine a rough structural shape in addition to layer angle and layer thick ness distributions. It is shown that the optimal structure can be obtained with a small number of finite element analyses.
Locus of Control and Academic Achievement
Authors: Kishor Nand
Published: March 2007

In an attempt to unravel reasons for ethnic discrepancies in academic achievement, this study investigated the locus of control orientation of Fijians and Fiji-Indians and examined its influence on their academic performance. Data on academic performance, locus of control, and social background were collected from 272 Fijians and 273 Fiji-Indians. In comparison to Fijians, the Fiji-Indians showed greater internal locus of control orientation and performed better on achievement tests, despite their poorer socioeconomic background. The relationship of internal orientation to academic performance was significant in both groups but stronger for Fijians than for Fiji-Indians. The results are interpreted as meaning that locus of control, a culturally influenced factor, is one variable underlying the disparity in the academic success of the two ethnic groups.
Are the Rules of Address Universal?
Authors: Kroger Rolf O. , Wood Linda A. , Beam Thelma
Published: March 2007

Our basic question was: Does the alleged universality of Brown's Invariant Norm of Address (1965) extend to Greek usage? 56 Greek speakers forming a diverse sample reported actual address usage received from and sent to 28 categories of interactants. Their answers were coded in terms of three quantitative indices which measure the degree of reciprocity, solidarity, and inequality in dyadic address exchanges. The indices permit the precise comparison of empirical results with theoretical expectations. The results provided strong support for Brown's description of the structure of address exchange such that we may add Greek to the languages that jointly support the claim for the university of the rules of address.
Ethnic Group Differences in Educational Achievement in Fiji
Authors: Basow Susan A.
Published: March 2007

Over 600 Form IV (tenth grade) students in Fiji were tested on measures of achievement orientation, self-esteem, sex typing, and certain demographic variables to determine why ethnic Fijians have relatively low educational achievement compared to other ethnic groups. Although ethnic Fijians scored relatively high on Competitiveness, Mastery, and Work Orientation, and relatively low on Personal Unconcern and Self-Esteem, none of the variables adequately predicted scores on the Fiji Junior Exam, taken seven months later, for the native groups. It is likely that factors relating to the meaning of achievement are more important in understanding ethnic group differences in achievement in Fiji than are measures of individual achievement orientation.
Maternal Strategies for Regulating Children's Behavior
Authors: Sinha Sudha R.
Published: March 2007

The present study is a replication in India of a study by Conroy et al. (1980) on Japanese and American mothers' regulating their children's behavior. Sixty Indian mothers having one to three children were given six hypothetical compliance-relevant situations and were asked to report how they would behave in those situations to make their children comply. Their responses were classified into two categories: cognitive structuring and psychological space. The findings were compared with those of Conroy et al. The results revealed that although the American mothers reported using their own authority and power for compliance from their children, the Indian and Japanese mothers reported appeals on the basis of feelings and consequences. The American and Japanese mothers used an imperative approach as compared to the Indian mothers.
The Psychosocial Adjustment of the Southeast Asian Refugee
Authors: Nicassio Perry M.
Published: March 2007

This article summarizes the clinical and research literature on the psychosocial adjustment of the Southeast Asian refugees in the United States and proposes the adoption of theoretical models that may be helpful in explaining individual differences in adjustment processes. Available evidence indicates that depression and stress-related symptoms are commonly found in refugees, whereas age, English proficiency, and socioeconomic indicators have been correlated with adjustment variables. Acculturation, learned helplessness, and stress management models appear to be beneficial in conceptualizing refugee adjustment problems and in providing a rational foundation for future research efforts.
Temperament in Australian, American, Chinese, and Greek Infants
Authors: Prior Margot , Kyrios Michael , Oberklaid Frank
Published: March 2007

Ratings of temperament in 4-to 8-month-old infants were compared across four cultural groups (American, Chinese, Australian, and Greek-Australian)using the revised Infant Temperament Questionnaire. Significant differences were found on all dimensions, with American and Australian infants being most alike and Greek and Chinese being very different from these two groups Generally, positive or "easy" temperament profiles characterized American and Australian infants while a "difficult" profile emerged for Greek-Australian infants. Biological and cultural explanations were considered in interpretations of the obtained differences. It is concluded that there are important cultural effects on temperament ratings but that such effects are effects are complex and require more careful investigation.
First Conversations
Authors: Trevathan Wenda R.
Published: March 2007

Conversations of 48 mothers were recorded with audiotapes while they interacted with their newborn infants in the first 10 minutes after birth in an El Paso, Texas, birth center. Of the women recorded, 34 were Hispanic; 14 were Anglo. Analysis of verbal content revealed that, unlike previously reported studies, comments about the infant's eyes or resemblance to family members were rare or lacking entirely. Far more frequent than reported by others were questions or comments about the infant's gender. It is postulated that differences in verbal content among studies of these first "conversations" may be due to (1) different time intervals for recording or (2) different sociocultural backgrounds of the women observed (mother-infant interaction, language, and ethnicity).
Objective Moral Judgment in Hong Kong, Mainland China, and England
Authors: Ma Hing Keung
Published: March 2007

Rest's Defining Issues Test was administered to subjects in Hong Kong, Mainland China, and England. It was found that the mean profile and age correlation pattern of the stage scores in the Hong Kong and England samples were consistent with the theoretical prediction. Results of principal components analysis of the stage scores in Hong Kong and England samples also provided fairly good support to the claim of an ordered sequence of Kohlberg's stages measured by the Defining Issues Test. However, the results of the Mainland China Study were less obvious. A cultural difference in perceiving the Stage 4 (S4) issue-statements was found between the Hong Kong Chinese and the English subjects. The Chinese tended to regard the S4 statements as more similar to the S5 and S6 ones, while the English tended to regard the S4 statements as more similar to the S2 and S3 ones.
Measuring the Effectiveness of International Environmental Regimes
Authors: Helm Carsten , Sprinz Detlef
Published: March 2007

Although past research has emphasized the importance of international regimes for international governance, systematic assessments of regime effects are missing. This article derives a standardized measurement concept for the effectiveness of international environmental regimes. It is based on a simultaneous evaluation of actual policy against a no-regime counterfactual and a collective optimum. Subsequently, the empirical feasibility of the measurement concept is demonstrated by way of two international treaties regulating transboundary air pollution in Europe. The results demonstrate that the regimes indeed show positive effects—but fall substantially short of the collective optima.
Elicitation of Cooperation by Retaliatory and Nonretaliatory Strategies in a Mixed-Motive Game
Authors: Gruder Charles L. , Duslak Robert J.
Published: March 2007

The relative effectiveness of pacifistic and retaliatory strategies in eliciting cooperating in a mixed-motive game is unclear due to confounded manipulations of these strategies and inadequate experimental designs in earlier research. In an attempt at clarification, subjects in the present studies were exposed to opponents programmed with one of three strategies: nonretaliatory (pacifist), low retaliatory, or high retaliatory. A multivariate analysis of repeated measures in experiment 1 revealed an effect of strategies and an interaction of strategies by trial blocks. The low retaliatory strategy elicited the most cooperative behavior, the high retaliatory next, and the nonretaliatory least, these differences increasing over trials.