bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method for Compression After Impact Strength Prediction of Composite Laminates
Authors: Puhui Chen , Zhen Shen , Junyang Wang
Published: April 2003

A new method to determine the compression after impact (CAI) strength of composite laminates was presented. In this method, an impact damage zone was modeled as an equivalent hole. The most outstanding characteristic of the method was that the simplification of the impact damage was based on the compressive failure mechanisms of impacted laminates. Such a simplification has not been discussed in the literature before. A technique was established for determining the shape and size of the equivalent hole. To the authors’ knowledge, it is the first practical method for simplifying the impact damage as a hole, and also the present work was the first attempt to predict the CAI strength by modeling the impact damage as a hole. The stress distribution around damage was calculated using the complex potential method and the classical lamination theory. A lay-up independent failure criterion was used to predict CAI strength. The predictions of the present approach were compared to test results and found to be in very good agreement over a wide variety of materials. The study indicated that the width of damage zone was a key factor governing CAI strength. The influence of damage area, impact energy, impactor shape and dimension, etc. on CAI strength can be essentially characterized by their effects on the damage width. The study provided a very simple and effective approach for CAI strength prediction compared with previous methods.
The Effect of Eccentric Loads on the Macroscopic Strain and Stress Distributions in Woven Fabric Composite Iosipescu Specimens
Authors: Searles K. , Odegard G. , Kumosa M.
Published: April 2003

Thispaper documentsthe resultsof work undertaken to evaluate the effects of eccentric loading conditions on the surface shear strains and stress distributions in layered quasi-laminar composite on opposite faces of the specimen as well as more pronounced shear stress gradients through-thickness. It has also been shown in this research that the effect of eccentric loads on the through-thickness shear stress and strain gradients in the Iosipescu specimens depends very strongly on the loading block geometries.
Quantitative Evaluation of Interlaminar-Toughened CFRP Composite by Ultrasonic Wave Propagation Characteristics
Authors: Okabe Yoji , Takeda Nobuo
Published: April 2003

The interlaminar-toughened CFRP composite, T800H/3900-2, has interlaminar resin layers, whose thickness is about 20 mm. The interlaminar layer was evaluated quantitatively using an ultrasonic micro-spectrometer (UMSM) for the determination of the elastic constants, which is quite difficult by other techniques. At first, the composite was ground to remove the outermost CFRP layer, and the interlaminar layer was exposed. Then the acoustic reflection coefficients at a small spot on the surface of the interlaminar layer were measured using the UMSM. The magnitude of the reflection coefficients is related to the properties of the layer. Hence, the elastic constants of the interlaminar layer were obtained appropriately through the fitness of theory to the magnitude of the reflection coefficients. Moreover, the obtained Young’s modulus was compared with that measured by tensile tests.
Neuro-Fuzzy Modeling of Fatigue Life Prediction of Unidirectional Glass Fiber/Epoxy Composite Laminates
Authors: Jarrah M. A. , Al-Assaf Y. , Kadi H. El
Published: April 2003

Fatigue behavior of unidirectional glass fiber/epoxy composites under tension–tension and tension–compression loading is important in the design of composite structures. Adaptive neuro-fuzzy modeling was successfully used to model the relationship between the input/output variables of fatigue behavior of unidirectional glass fiber/epoxy composites. The experimental input variables were the maximum stress, fiber orientation, and stress ratio, while the output variable was the number of cycles to failure. In comparison with previous results obtained using neural networks only, the proposed hybrid neuro-fuzzy method gave more accurate fatigue life predictions.
Modeling Relaxation of a Polymeric Composite during Loading and Unloading
Authors: Kim Wiedae , Sun C. T.
Published: April 2003

Polymeric composites exhibit highly nonlinear and rate dependent behavior during loading and unloading in off-axis directions. In this study, off-axis specimens were used to study this behavior in AS4/PEEK thermoplastic composite. The equilibrium states of stress during loading and unloading were determined by stress–relaxation and stress–recovery tests, respectively. It was found that the equilibrium stress–strain curves for loading and unloading are basically the same for the same loading–unloading rate. A one-parameter plasticity model was used to generate a master equilibrium plastic stress–strain curve for both loading and unloading. Stress relaxation curves and recovery curves were obtained during loading and unloading cycles, respectively, for various strain rates. Similarity between relaxation and recovery curves was noted, and the effective stress defined from the one-parameter plastic potential function was able to describe both curves.
Dimensional Accuracy of Thermoset Composites: Shape Optimization
Authors: Zhu Qi , Geubelle Philippe H.
Published: April 2003

We present a design sensitivity analysis, which supports the shape optimization of the tool used in thermoset composite manufacturing. The method provides a systematic way to predict the optimal tool geometry that leads to the minimum difference between desired and final shapes of the manufactured part. The design process is formalized by integrating process modeling, design sensitivity analysis, and numerical optimization into a single framework. The process modeling is based on a transient coupled thermo-chemo-viscoelastic finite element scheme, which accurately capturest he evolution of residual stresses throughout the manufacturing process, and their effect on the final shape of the composite part. Design sensitivity information is extracted efficiently from the primal analysis using an analytical, direct differentiation method. The sensitivities are then provided to a numerical optimization program to improve the tool design. Optimization results are presented for two specific applications involving mold design for cross-ply laminates and L-shaped composite parts.
Approximate Analysis of Mid-Plane Symmetric Rectangular Composite Plates
Authors: Veres Istvan A. , Kollar Laszlo P.
Published: April 2003

The paper compares the ‘‘exact’’ solution of mid-plane symmetric rectangular plates to approximate ones obtained by assuming orthotropy or Huber orthotropy. It shows under which conditions the approximate solutions can be used for the bending, buckling and vibration analyses of composite plates.
An Improved Thermal Lamination Model for Analysis of Heat Transfer in Composite Structures
Authors: Pantano Antonio , Averill Ronald C.
Published: April 2003

A new thermal lamination model and its associated finite element model are presented for analysis of heat transfer in laminated composite structures. The form of the present model closely resembles that of recent zig-zag sublaminate structural laminate theories. The through-thickness distribution of temperature is assumed to vary linearly within each ply, and continuity of transverse flux at ply interfaces is enforced analytically. Thus, the number of computational degrees-offreedom (DOFs) is made independent of the number of plies in the sublaminate. In its present form, the model contains only two computational DOFs in each sublaminate–the temperature at the top and bottom surface of the sublaminate. This model lends itself well to development of convenient and efficient finite element models, as demonstrated herein. Both linear and nonlinear numerical results are presented to demonstrate the effectiveness of the present approach.
Energy Absorption in Polymer Composites for Automotive Crashworthiness
Authors: Jacob George C. , Fellers John F. , Simunovic Srdan , Starbuck J. Michael
Published: April 2003

The energy absorption capability of a composite material is critical to developing improved human safety in an automotive crash. Energy absorption is dependent on many parameters like fiber type, matrix type, fiber architecture, specimen geometry, processing conditions, fiber volume fraction, and testing speed. Changes in these parameters can cause subsequent changes in the specific energy absorption (ES) of composite materials up to a factor of 2. This paper is a detailed review of the energy absorption characteristics in polymer composite materials. An attempt is made to draw together and categorize the work done in the field of composite energy absorption that has been published in the literature in order to better understand the effect of a particular parameter on the energy absorption capability of composite materials. A description of the various test methodologies and crushing modes in composite tubes is also presented. Finally, this paper raises certain design issues by examining the work rate decay necessary to keep the deceleration below 20g during an impact crash.
Effect of Thermal Cycling on Microcracking and Strength Degradation of High-Temperature Polymer Composite Materials for Use in Next-Generation SST Structures
Authors: Shimokawa Toshiyuki , Katoh Hisaya , Hamaguchi Yasumasa , Sanbongi Shigeo , Mizuno Hiroshi , Nakamura Hiroyuki , Asagumo Ryoji , Tamura Hirobumi
Published: April 2003

The objective of this study was to investigate the effect of thermal cycles encountered by an SST in service on the cumulative frequency of microcracks and degradation of open-hole-compressive (OHC) strength in high-temperature polymer-matrix composite materials. One cycle of thermal cycling was designated as the sequence from room temperature (RT) to 54C, up to +177C, and back to RT. Thermal-cycling tests were conducted up to 10,000 cycles on two kinds of carbonfiber/thermoplastic polyimide composite material: IM7/PIXA, IM7/K3B, and up to 1000 cycles on G40-800/5260 carbon fiber/bismaleimide composite material. At scheduled thermal cycles, transverse microcracks initiated on the sectional surface of the laminates were observed and counted using an optical microscope. Static mechanical tests at RT provided OHC strength before and after thermal cycles. In addition, a simple and approximate finite element model (FEM) analysis using basic lamina data of the T800H/PMR-15 carbon fiber/polyimide composite was conducted to estimate the thermal stresses generated in the laminate.

Major results obtained by the tests and FEM analysis are as follows: A fairly large number of microcracks were initiated, though the number as a function of thermal cycles varied according to the material; OHC strength before and after thermal cycles did not change during the course of this study; thermal cycles and transverse microcracks did not affect OHC strength; the calculated thermal-stress level in layers generated by one thermal-cycle of 231C temperature difference was under the limit for crack initiation of the T800H/PMR-15.
Low-Velocity Impact and Damage Process of Composite Laminates
Authors: Guan Zhidong , Yang Chihdar
Published: April 2003

Several important issues regarding damage simulation of composite laminates due to low velocity impact were investigated including contact law, damage initiation and the corresponding change of stiffness, and damping. Continuum damage mechanics was applied to account for the change of mechanical properties of damaged materials. The Hertzian contact law was modified in order to accommodate the serious damage in the plate. A semi-empirical delamination damage criterion was introduced. A finite element program was written in FORTRAN using twenty-noded solid elements with layered structure to analyze the transient dynamic response of composite laminates. In the simulation computations, variable material damping coefficients were applied to the elements according to damage in order to stabilize the computation. Damage in the forms of matrix cracking, delamination, and fiber breakage were included and analyzed. Results including the force history and delamination areas were found to correlate well with the experiments.
Micro-and Macrostresses in a Cold-Rolled Al–SiC Composite
Authors: Li Alex , Lodini Alain
Published: April 2003

The method of the neutron diffraction has been widely applied to determine the residual stresses in composite materials. In this work,the neutron diffraction technique is used to determine the stresses in 7075 aluminum alloy reinforced with 27% volume fraction SiC whiskers that was treated by the coldrolling technique. The strains in Al matrix and in SiC phase have been converted to stresses by applying a stress separation technique. The elastic and the thermal or plastic mismatch stresses due to cold-rolling treatment and manufacture in the Al matrix and in the SiC phase are estimated. The stresses in the Al matrix and in the SiC phase of the first order are different from the stresses of the second order. The stress values of the thermal or plastic are tensile in Al matrix and compressive in SiC reinforcement.
Strain Rate Dependent Analysis of a Polymer Matrix Composite Utilizing a Micromechanics Approach
Authors: Goldberg Robert K. , Stouffer Donald C.
Published: April 2003

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. The Ramaswamy–Stouffer viscoplastic constitutive equations for metals have been modified to model the strain rate dependent inelastic deformation of ductile polymers, including hydrostatic stress effects. These equations have been incorporated into a mechanics of materials based micromechanics model that was developed to analyze uniaxial composites at various fiber orientation angles. The Hashin failure criteria have been implemented into the micromechanics to predict ply failure strengths. The deformation response and ply failure strengths for the representative composite AS4/PEEK have been successfully predicted for a variety of fiber orientations and strain rates.
Stiffness Degradation of FRP Strengthened RC Beams Subjected to Hygrothermal and Aging Attacks
Authors: Li Guoqiang , Pang Su-Seng , Helms Jack E. , Mukai David , Ibekwe Samuel I. , Alaywan Walid
Published: April 2003

The past decade has witnessed an ever increasing interest in strengthening, repairing, retrofitting, andu pgrading of deterioratedco ncrete structures using fiber reinforcedplastics (FRP). Enhancedload carrying capacity by FRP strengthening has been observedby a large number of researchers through experiments at ambient environments. In a harsh environment, however, FRP will degrade. This may result in structural degradation of FRP strengthened concrete members. The possible structural degradation has become a major obstacle for the wide-spread acceptance of this new strengthening technique. In the present study, boiling water and ultraviolet (UV) radiation were used to study the structural degradation of concrete beams strengthened with GFRP and CFRP fabrics. A total of eighteen 170 7.62 15.2 cm steel reinforcedconcrete (RC) beams were prepared as control specimens, conditioned specimens, and unconditioned specimens. Finite element modeling was used to analyze stiffness degradation of FRP layers. The tested and calculated results showed that environmental attacks had a considerable effect on the structural degradation of FRP strengthened concrete beams. 57–76% of the strengthening efficiency and43–48% of the stiffness of FRP were lost after conditioning.
Fracture Behavior of Woven Composites Containing Various Cracks Geometry
Authors: Khashaba U. A.
Published: April 2003

Recently, polymeric composite materials are widely used in automotive applications for reducing structural weight, saving fuel, and improving performance. Accidentalimpact damage is an important issue in the use of these composite materials as body components. The damages or cracks in the present work were represented by notched specimens. The test specimens were fabricated from polyester resin reinforced by woven E-glass fiber. A series of tests were conducted to measure the notched strength of composite laminates with various types of through-the-thickness cracks such as central normal notch (CNN), center inclined notch (CIN), single edge notch (SEN) and double edge notch (DEN). A Modified Point Stress Criterion (MPSC) was proposed for predicting the tensile strength of composite laminates with various aspect ratio (a/w), that is, notch length to specimen width ratio.

The results show that the load–elongation diagrams of notched and unnotched glass fiber reinforced polyester (GFRP) specimens have a nonlinear behavior, with clear “Knee”, associated with audible noises. For the same notch length, the notched strength of GFRP specimens with symmetric cracks (CNN, CIN and DEN) is quite consistent. The lowest notched strength is for SEN specimens. An excellent agreement is found between the experimentalresults of centralnotched specimens (CNN and CIN) and the predicted values using the MPSC than the reviewed published theories. The critical stress intensity factor ( KIC) was determined from the centralnotched specimens and used to predict the notched strength of edge notched specimens (SEN and DEN). The type of the central notch (inclined or normal) insignificantly affects the values of the stress intensity factor, KIC.
Nondestructive Characterization of Thermal Shock and Oxidation-Induced Damage by Flash Diffusivity
Authors: Graham Samuel , McDowell David L. , Lara-Curzio Edgar , Dinwiddie Ralph B. , Wang Hsin , Porter Wallace
Published: April 2003

The effect of thermal shock and oxidation-induced damage on the thermal diffusivity of unidirectional Nicalon-LAS glass–ceramic composites is presented in this study. The data presented show that thermal diffusivity measurements provide a sensitive nondestructive method whereby damage progression may be assessed. Samples were exposed to isothermal oxidation and thermal shock environments. In addition, combined cycles of oxidation and thermal shock were also evaluated. The thermal diffusivity transverse to the fibers was measured to detect changes in material integrity. Significant decreases up to 23% were observed in the thermal diffusivity of the material.
Lamb Wave Interaction with Impact-induced Damage in Aircraft Composite: Use of the A0 Mode Excited by Air-coupled Transducer
Authors: Kaczmarek H.
Published: April 2003

A novel technique has been experimented involving the use of an air-coupled transducer to excite Lamb mode in composite material, a pinducer to pick-up local response and a turn-table set-up to reveal impact damage-induced anisotropy.

So, a fundamental antisymmetric A0 Lamb mode has been excited under unusual conditions. Its efficiency for detecting impact-induced damage in a multilayered thin quasi-isotropic carbon–epoxy composite laminate has been demonstrated and the knowledge on the A0 Lamb mode interaction with the damage has been improved using an original mapping.

Some material characteristics have been obtained. Intrinsic material attenuation of this guided mode at a frequency of 370 kHz and a frequency-thickness product of 740 kHz mm has been assessed and in-plane energy distribution of the A0 mode has been mapped, revealing a relatively directive acoustic field. However, the composite material exhibits slightly anisotropic acoustic behaviour due to a lack of fibres in certain directions. Interactions between the A0 mode and multidelamination of the critical area were also investigated. In-plane mappings of the ultrasonic field have revealed two main phenomena: attenuation and scattering due to damage. Splitting of the ultrasonic wave was observed, creating a region of geometric shadow where attenuation occurs. It is shown on the mappings that the energy lost in this direction of propagation appears in other directions. An increase in the received energy was detected in certain directions, showing that the damage can be considered as a soft scattering centre.
A Model of Damage Initiation in Singly Oriented Ply Fiber Metal Laminate under Concentrated Loads
Authors: Nam H. W. , Jung S. W. , Jung C. K. , Han K. S.
Published: April 2003

Damage initiation is modeled in singlyoriented ply(SOP) Fiber Metal Laminate (FML) under concentrated loading conditions. The finite element method (FEM) is used based on the first order shear deformation theoryfor modeling damage initiation in SOP FML. The failure indices of the fiber prepreg and the metal laminate were calculated using the Tasi–Hill failure criterion and the Miser yield criterion respectively. To verify the model, failure analysis was conducted under uniaxial loading and cylindrical bending, then under concentrated loading. Results show that the model is good.

An indentation test was then conducted to compare the damage initiation load with the calculated failure index. The test was conducted under two side clamped conditions in order to studythe fiber orientation effect. The indentation curve was fitted using the Hertz equation, and the damage initiation load was defined as the point of divergence of the fitted curve from the real indentation curve. The damage initiation loads were obtained for various fiber orientations and were compared with the calculated failure index. The experiment results closelymatched the calculated failure index. It follows that the present method accuratelycaptures damage initiation of SOP FML.
Microstrip Antenna for SAR Application with Composite Sandwich Construction: Surface-antenna-structure Demonstration
Authors: You C. S. , Hwang W. , Park H. C. , Lee R. M. , Park W. S.
Published: April 2003

A 5.3 GHz microstrip antenna for use in synthetic aperture radar (SAR) systems was developed with a composite sandwich construction, using composite laminates, Nomex honeycomb and aluminum alloy. This is the surface-antenna-structure (SAS) for application to load-bearing structural surfaces. The design concept originated from a composite sandwich structure and a multi-layer microstrip antenna. Design, fabrication and validation of structural/electrical performances were all demonstrated. To verify the structural rigidity, flexural behavior was observed under the three-point bending test and was compared with two kinds of composite sandwich beams consisting of CFRP–GFRP skins and Nomex honeycomb core. Electrical measurements of the fabricated antenna array were in good agreement with design requirements, and a comparative study found that SAS has good mechanical characteristics. The SAS concept can be extended to give a useful guide to manufacturers of structural body panels as well as antenna designers, promising innovative future communication technology.
Damage Mechanism of Hybrid Composites with Nonwoven Carbon Tissue Subjected to Quasi-static Indentation Loads
Authors: Lee Seung-Hwan , Aono Yuuta , Noguchi Hiroshi , Cheong Seong-Kyun
Published: April 2003

Damage mechanisms of hybrid composites with nonwoven carbon tissue (NWCT) are investigated under a quasi-static indentation loading condition with a steel ball as an indentor. The damage level corresponds to an initial stage of damage due to an indentation loading, which leads to a strength degradation of the composite.

The hybrid composites consist of the CFRP prepreg and the NWCT prepreg, which are made byinterleaving the NWCT prepreg into the CFRP layer interfaces. Four kinds of cross-plylaminates are studied; i.e., CFRP laminates ([05/905/05] and [03/903/03/903/03]) and hybrid laminates ([05//905//05] and [03//903//03//903//03]). Here, the symbol “//” means that the NWCT prepreg is located at an interface between CFRP layers. The hybrid effect is examined by investigating the delamination area and the absorption energyof two cross-plylaminates. As it has been recognized that the quasi-static indentation damage agrees well with the low velocity impact test results, the present static test results can then be used to understand the damage mechanism of low-energyimpact.

The damaged parts of the specimens were observed bythe deplytechnique and the cut method which used a microscope. The NWCT interleaving’s effect was clarified based on the observation of the damage for the hybrid specimen’s cross-sections after indentation testing. The delamination area of the hybrid composites was reduced to about a half of the CFRP’s byindentation loading. It was clarified that the Mode II interlaminar fracture is predominant in the delamination bythe impact.
Bond Parameters to Improve Tensile Load Bearing Capacities of Co-Cured Single and Double Lap Joints with Steel and Carbon Fiber-epoxy Composite Adherends
Authors: Shin Kum Cheol , Lee Jung Ju
Published: April 2003

A co-cured joining method has several advantages over an adhesivelybonded joining method for its simple manufacturing process. It requires neither an adhesive nor surface treatment of the composite adherend and uses excess resin to bond both adherends, including composite adherend.

In this paper, the effects of bond parameters, including surface roughness on the steel adherend, stacking sequence of the composite adherend, and manufacturing pressure in the autoclave during the bonding process, on tensile load bearing capacities of plate-type co-cured single and double lap joints were investigated experimentally. Bond parameterswere related to interfacial parameterssuch asa contact area and adhesive thickness, which affected the joint strength. Experimental results were explained with respect to all of interfacial parameters and bond parameters through investigating failure surfaces of the steel adherend and a lot of data of tensile load bearing capacities. In order to predict tensile load bearing capacities of co-cured single and double lap joints, we considered two different failure models using stress distributions in both co-cured lap joints obtained from finite element analysis. Finally, optimal conditions to improve the joint strength of co-cured single and double lap joints have been presented.
The Behavior of Compressively Loaded Stiffener Runout Specimens – Part I: Experiments
Authors: Falzon Brian G. , Davies G. A. O.
Published: April 2003

The development of the next generation of civil and military transport aircraft will inevitably see an increased use of advanced carbon fibre composite material in the primary structure if performance targets are to be met. One concern in this development is the vulnerability of co-cured and co-bonded stiffened structures to through-thickness stresses at the skin–stiffener interfaces, particularly in stiffener runout regions. These regions are a consequence of the requirement to terminate stiffeners at cutouts, rib intersections, or other structural features which interrupt the stiffener load path.

This work presents the results of an experimental programme investigating the failure of thick-sectioned stiffener runout specimens loaded in uniaxial compression. For all tests, failure initiated at the edge of the runout and propagated across the skin–stiffener interface. It was found that the failure load of each specimen was greatly influenced by intentional changes in the geometric features of these specimens. High frictional forces at the edge of the runout were also deduced from a fractographic analysis, indicating a predominantly Mode II initial failure mode.
Numerical Modeling of Heat Transfer for Squeeze Casting of MMCs
Authors: Jung C. K. , Jung S. W. , Nam H. W. , Han K. S.
Published: April 2003

A finite element model is developed for the process of squeeze casting of metal matrix composites in cylindrical molds. The fluid flow and the heat transfer are fundamental phenomena in squeeze casting. To describe heat transfer in the solidification of molten aluminum, the energy equation written in terms of temperature and enthalpy are applied in an axisymmetric model which is similar to the experimental system. A 1-D flow model simulates the transient metal flow. A direct iteration technique was used to solve the resulting nonlinear algebraic equations, using a computer program to calculate the enthalpy, temperature and fluid velocity. The cooling curves and temperature distribution during infiltration and solidification were calculated for pure aluminum. Experimentally, the temperature was measured and recorded using thermocouple wire. The measured time–temperature data were compared with the calculated cooling curves. The resulting agreement shows that the finite element model can accurately estimate the solidification time and predict the cooling process.
Effect of Transverse Matrix Cracks on the Relaxation Moduli of Linear Viscoelastic Laminates
Authors: Noh Jae , Whitcomb John
Published: April 2003

A finite element based degradation model was employed to study the effect of cracks on the relaxation moduli of linear viscoelastic laminates. In the current study, the relaxation moduli are expressed in terms of the elastic moduli, the fully relaxed moduli, and the relaxation functions. The degradation behavior of a viscoelastic lamina due to cracks was examined and compared with that of an elastic lamina. The study shows that the degradation behavior of a viscoelastic lamina can be predicted by that of an elastic lamina. The effect of other parameters such as adjacent lamina orientation on the properties of a cracked lamina in a viscoelastic analysis is found to be very similar to that for an elastic analysis. It was found that the cracks affect the elastic and fully relaxed moduli but do not affect the relaxation functions. The study also shows that the variation of the stress state of a viscoelastic laminate depends on the instantaneous crack density, not on the time-history of cracking. Based on the study, an efficient method has been developed for the progressive damage analysis of viscoelastic materials. The method allows accurate prediction of the stress state of a viscoelastic laminate utilizing the degradation information obtained from an elastic analysis. This method is very efficient and accurate.
The Behavior of Compressively Loaded Stiffener Runout Specimens – Part II: Finite Element Analysis
Authors: Falzon Brian G. , Hitchings D.
Published: April 2003

The termination of stiffeners in composite aircraft structures give rise to regions of high interlaminar shear and peel stresses as the load in the stiffener is diffused into the skin. This is of particular concern in co-cured composite stiffened structures where there is a relatively low resistance to through-thickness stress components at the skin–stiffener interface. In Part I, experimental results of tested specimens highlighted the influence of local design parameters on their structural response. Indeed some of the observed behavior was unexpected. There is a need to be able to analyse a range of changes in geometry rapidly to allow the analysis to form an integral part of the structural design process.

This work presents the development of a finite element methodology for modelling the failure process of these critical regions. An efficient thick shell element formulation is presented and this element is used in conjuction with the Virtual Crack Closure Technique (VCCT) to predict the crack growth characteristics of the modelled specimens. Three specimens were modelled and the qualitative aspects of crack growth were captured successfully. The shortcomings in the quantitative correlation between the predicted and observed failure loads are discussed. There was evidence to suggest that high through-thickness compressive stresses enhanced the fracture toughness in these critical regions.
Stochastic Collusion and the Power Law of Learning
Authors: FLACHE ANDREAS , MACY MICHAEL W.
Published: April 2003

Concerns about models of cultural adaptation as analogs of genetic selection have led cognitive game theorists to explore learning-theoretic specifications. Two prominent examples, the Bush-Mosteller stochastic learning model and the Roth-Erev payoff-matching model, are aligned and integrated as special cases of a general reinforcement learning model. Both models predict stochastic collusion as a backward-looking solution to the problem of cooperation in social dilemmas based on a random walk into a self-reinforcing cooperative equilibrium. The integration uncovers hidden assumptions that constrain the generality of the theoretical derivations. Specifically, Roth and Erev assume a “power law of learning”—the curious but plausible tendency for learning to diminish with success and intensify with failure. Computer simulation is used to explore the effects on stochastic collusion in three social dilemma games. The analysis shows how the integration of alternative models can uncover underlying principles and lead to a more general theory.
Power Parity, Alliance, Dissatisfaction, and Wars in East Asia, 1860-1993
Authors: KIM WOOSANG
Published: April 2003

Original power transition theory is extended by relaxing the restrictive assumption of the method of augmenting national power. The occurrence of war in East Asia from 1860 to 1993 is examined to see if the revised power transition argument holds for the conflicts in East Asia. Results show that conflicts in East Asia occur under the same general conditions that lead to war in the international system and that war is most likely when the dissatisfied challenger approximates the dominant power. The evidence also suggests that the role of alliances is crucial for mitigating or militating the risk of war, contrary to the standard power transition formulation. Because alliances play a central role in the risk of wars, the dangers of such a conflict in East Asia (or elsewhere) can be managed through skillful strategies of alignment and de-alignment.
Domestic Strife and the Initiation of International Conflicts
Authors: DAVIES GRAEME A. M.
Published: April 2003

The effects of domestic strife on the likelihood of an international conflict are tested empirically. A rare-events logit model with corrections for temporal dependence to assess whether domestic strife is related to the initiation of international conflicts is used to test the validity of the diversionary conflict thesis. Results suggest that decision makers do initiate international conflicts when the state is undergoing domestic strife, although not in a predicted manner. The results indicate that violent domestic strife increases the likelihood of a diversionary conflict, whereas nonviolent strife increases the likelihood of repression. The research also presents evidence that calls into question some of the claims made in previous studies and demonstrates that domestic strife in a target state increases the likelihood of being attacked.
On the Incidence of Civil War in Africa
Authors: COLLIER PAUL , HOEFFLER ANKE
Published: April 2003

An econometric model of civil war is applied to the analysis of conflict in sub-Saharan Africa. Results show that Africa has had a similar incidence of civil conflict to other developing regions, and, with minor exceptions, its conflicts are consistent with the global pattern of behavior. However, the structure of risk differs considerably from other regions. Africa's economic characteristics have made it more vulnerable to conflict, but this has been offset by social characteristics that make its societies atypically safe. The contrasting trends of conflict are analyzed: rising in Africa and declining in other regions. Results show that these trends are predicted by the model. Africa's rising trend of conflict is due to its atypically poor economic performance.
Ethnicity, Political Systems, and Civil Wars
Authors: REYNAL-QUEROL MARTA
Published: April 2003

The effect of ethnic division on civil war and the role of political systems in preventing these conflicts are analyzed, using the importance of religious polarization and animist diversity to explain the incidence of ethnic civil war. Findings show that religious differences are a social cleavage more important than linguistic differences in the development of civil war, and being a consociational democracy significantly reduces the incidence of ethnic civil war.
Third-party Interventions and the Duration of Intrastate Conflicts
Authors: REGAN PATRICK M.
Published: April 2003

Recent research has begun to focus on the role of outside interventions in the duration of civil conflicts. Assuming that interventions are a form of conflict management, ex ante expectations would be that they would reduce a conflict's expected duration. Hypotheses relating the type and timing of outside interventions to the duration of civil conflicts are tested. The data incorporate 150 conflicts during the period from 1945 to 1999, 101 of which had outside interventions. Using a hazard analysis, the results suggest that third-party interventions tend to extend expected durations rather than shorten them. The only aspect of the strategy for intervening that reduces the likelihood that a conflict will end in the next month is that it be biased in favor of either the opposition or the government. In effect, neutral interventions are less effective than biased ones.
The Temporal Links between Conflict and Economic Activity
Authors: BLOMBERG S. BROCK , HESS GREGORY D.
Published: April 2003

Data from 152 countries from 1950 to 1992 are used to estimate the joint determination of external conflict, internal conflict, and the business cycle. Results show that the occurrence of a recession alone will significantly increase the probability of internal conflict, and when combined with the occurrence of an external conflict, recessions will further increase the probability of internal conflict. These results are obtained from estimates of a Markov probability model in which transitions between states of peace and conflict influence each other and the state of the economy. Strong evidence emerges that the internal conflict, external conflict, and the state of the economy are not independent of one another. The results suggest that recessions can provide the spark for increased probabilities of internal and external conflict, which in turn raise the probability of recessions. Such dynamics are suggestive of a poverty-conflict trap-like environment.
Recruitment and Allegiance
Authors: GATES SCOTT
Published: April 2003

Civil war is fought between two political organizations, the state and a rebel group. Myriad theories of civil war have examined the role of state institutions and state strength, but little attention has been devoted to theorizing about rebel organizations themselves. The organizational structure of rebel groups is examined to understand patterns of recruitment and allegiance. Drawing on principal-agent analysis of participation and incentive compatibility constraints and the analytical tradition of rent-seeking contests, a model is developed to demonstrate that three factors—geography, ethnicity, and ideology—play an important role in determining military success, deterring defection within the rebel group, and shaping recruitment.
Looting and Conflict between Ethnoregional Groups
Authors: AZAM JEAN-PAUL
Published: April 2003

A game-theoretic model is analyzed for discussing the determination of looting and fighting activity during a civil war between two ethnoregional groups. The Nash equilibrium of this game emphasizes population size, production capacity and productivity, and access to external funding as the main determinants of the size of the armies and the intensity of looting activity. The Nash equilibrium of the game between the two warlords involves an excessive level of looting. Some lessons are drawn from this framework to bring out the minimum redistribution of resources between groups that must take place in a peaceful equilibrium.
Honest Threats
Authors: GUISINGER ALEXANDRA , SMITH ALASTAIR
Published: April 2003

Traditional arguments that link credibility to a reputation for resolve, power, or strength are contrasted with a model that posits that credibility arises from the expectation of future, continued gains from retaining an honest record. Diplomatic statements are believed only if a country's or leader's credibility is unmarred. Leaders keep their word so that they are believed in later crises. Two environments are contrasted: one in which a country's record for honesty resides within the country as a whole and another in which reputation resides with individual leaders. In this latter case, citizens have an incentive to remove leaders caught bluffing. More robust than previous reputation theories, this model also offers comparative statics for when diplomacy will be more effective—namely, when leaders are domestically accountable.
Foreign Policy and the Rational Public in Comparative Perspective
Authors: ISERNIA PIERANGELO , JUHÁSZ ZOLTÁN , RATTINGER HANS
Published: April 2003

The aggregate changes in public opinion attitudes toward foreign policy issues in three West European countries during the cold war decades (1954-1990) are analyzed. The stability hypothesis is addressed from different angles to ascertain the amount of change in public opinion attitudes toward foreign policy issues in France, Germany, and Italy. Results reveal a low level of volatility in public opinion that corresponds with the findings for the American public. On the other hand, French, German, and Italian public opinion shows a somewhat higher level of fluctuation than in the United States. Attitudes toward NATO, the United States, and the Soviet Union closely reflect the evolution of world politics and therefore represent a reasonable reaction to international events and crises.
The End of Geography?
Authors: GREIG J. MICHAEL
Published: April 2003

Globalization and the expansion of communications carry important consequences for culture in the international system. The effect of the expansion of communications on cultural change is examined using simulations based on Robert Axelrod's adaptive culture model. Findings show that the expansion of communications increases the rate at which cultures change and the level of cultural homogeneity in the system, but limited expansion of communications promotes the development of cultural diasporas. The expansion of communications also reduces the extent to which the most common cultural attributes tend to predominate after interaction.
Integrative Complexity of South-north Korean Correspondences
Authors: KOO JASOOK , HAN JOON , KIM JUNGHYUN
Published: April 2003

Integrative complexity signifies the complexity of conceptual and cognitive rules that people use in processing information. People with high complexity take diverse approaches in evaluating situations and making decisions, and those with low integrative complexity rely on simplistic and dichotomous reasoning. An integrative complexity coding scheme is used to analyze correspondences exchanged between South and North Korea. Time-series models are used to predict mean levels of integrative complexity in South and North Korea for each half-year period between 1984 and 1994. Results show that trends in South-North Korean relations exert significant influence on integrative complexity levels, and major coordinative events are associated with a decline in complexity in the following half-year period. During presidential elections in South Korea, complexity levels decline in both South and North Korea.
How Much War Will we see?
Authors: ELBADAWI IBRAHIM , SAMBANIS NICHOLAS
Published: April 2003

Quantitative studies of civil war have focused on war initiation (onset) or war duration and termination and produced important insights into these processes. An empirical analysis of civil war prevalence is used to show that the prevalence or amount of war observed at any given time is important. Civil war prevalence is defined as the probability of observing either a new war onset or the continuation of an ongoing war or both. Two economic theories of war onset and duration are combined to estimate the prevalence of civil war across more than 150 countries and over 40 years. The analysis is consistent with the findings of earlier studies on war onset and duration. New findings that result from slight improvements in the data and estimation methods show that democracy and ethnic diversity are significant determinants of civil war prevalence.
The Influence of Advisers on Foreign Policy Decision Making
Authors: REDD STEVEN B.
Published: April 2003

The influence of advisers on foreign policy processes and choice and on how decision strategies affect foreign policy outcomes are examined. Using the poliheuristic theory of foreign policy decision making and process-tracing techniques in an experimental setting, the effects of the presence of advisers on strategy selection and choice and the influence of strategy selection on choice in a foreign policy scenario are tested. The findings show that decision makers are highly sensitive to and cognizant of the political ramifications of their decisions. Specifically, political information and advice influenced information processing and foreign policy choices. The findings have significant implications for the study of foreign policy decision making and the understanding of real-world foreign policy decisions.
Motivations for Choice
Authors: ROUSSEAU DAVID L.
Published: April 2003

Realists assume that individuals are obsessed with relative gains and that cooperation is the exception rather than the norm in international relations. In contrast, liberal institutionalists assume that, in many situations, individuals are motivated by absolute gains. These critical assumptions are examined. Results show that the salience of relative gains varies with the beliefs of the individual, the nature of the opponent, and the context of the situation, and that individuals often employ alternative pure strategies (e.g., equity) or mixed strategies (e.g., relative gains in the domain of gains and absolute gains in the domain of losses). Decision strategies (e.g., relative gains, absolute gains, joint gains, equality, and altruism) are linked to the growing constructivist literature in international relations.
Views to a Kill
Authors: DAVENPORT CHRISTIAN , BALL PATRICK
Published: April 2003

To investigate the implications of source selection, three different sources regarding Guatemalan state terror are compared: newspapers, human rights documents, and interviews with eyewitnesses. Results show that each source pays attention to diverse types and aspects of repression in line with the objectives of the observer, the characteristics of the repressive events, and the overall political context within which events take place. Who is consulted influences what is observed/recorded. Suggestions are presented for understanding sociopolitical behavior through diverse data sources, especially behavior related to contentious activity and/or occurring within contexts that are not easily penetrable.
The Law of Small Numbers
Authors: LEBOVIC JAMES H.
Published: April 2003

Armed with a new threat and promising technology, advocates of national missile defense (NMD) have framed the debate by presenting NMD as a break from traditional deterrence principles. The assumption that the United States faces new adversaries that cannot be deterred by U.S. offensive options and whether adversaries can and will use nuclear weapons to coerce the United States, given its inclination and ability to retaliate, are assessed. The effectiveness of NMD against various offensive threats is simulated. Conclusions indicate that NMD advocates have not made their case that cold war-era deterrence principles are ill suited to U.S. relations with fledgling nuclear states and that the expected value of a missile defense of any type and scale is low because it is unlikely to enhance global security above levels offered by retaliatory deterrence.