bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Short Glass-Fiber Volume Fractions in Compression Molded Thermoset Composites—Experimental
Authors: Cheon Jae-Seung , Im Yong-Taek
Published: April 2011

Prediction of volume fraction of short glass-fibers in compression molded thermoset composites parts such as sheet molding compounds (SMC) is of importance since their distribution affects the mechanical property and surface quality. In the present study, a simple approach based on digital image processing technique was applied in determining the fiber volume fraction distribution in the compression molded flat plate of SMC. Although the present digital image processing approach does not have the resolution to distinguish individual fiber diameters, it is capable of determining fiber concentrated regions, and thus an effective means of determining the global distribution of fibers in a single process is provided. As molding conditions, two different molding temperatures and velocities as well as two different compression ratios were investigated to determine the influence of molding parameters on the glass-fiber volume fraction distributions. It was found that a rather uniform distribution of glass-fibers was obtained under the condition with smaller compression ratios and faster mold closing speeds, whilst the effect of mold temperature on volume fraction distribution being negligible. The validity of the proposed scheme was estimated by comparing the predicted volume fraction distribution with the experimental result obtained from the conventional burning-test measurement. The comparison clearly demonstrates the simplicity and capability of the digital image processing technique applied under the present condition.
Preliminary Study on Composite Hip Prostheses Made by Resin Transfer Molding
Authors: Reinhardt Andreas , Advani Suresh G. , Santare Michael H. , Miller Freeman
Published: April 2011

Metal hip implants used in arthroplastic surgery have an elastic modulus which is an order of magnitude higher than the modulus of the surrounding cortical bone. Therefore the metal implant assumes most of the applied loads resulting in resorption of the unloaded bone material by the human body which can cause the impant to loosen. In addition, patients may experience allergic reaction due to the release of metal ions or particles caused by friction, wear or enzymatic effects. Composite materials offer potential benefits such as tailorable mechanical properties, enhanced damage tolerance and fatigue life and improved biocompatibility.

Based on structural analysis and mold filling simulation, prototypes of a hip prosthesis were manufactured using the resin transfer molding process. The preform of the prototype consists of braided high strength carbon fiber socks which are wrapped around a balsa wood insert. Two fiber architectures with different fiber angles (20° and 15° relative to the stem axis) were used. The maximum average fiber volume fraction obtained was about 38%.

The mechanical performance of the composite hip prostheses was evaluated by static, fatigue and impact testing. Static testing verified that composite prostheses with the 20° braid carbon fiber preform exhibited an ultimate load of 7.5 kN, which is ten times the body weight of a 75 kg person. Fatigue testing showed that two million load cycles can be performed with a maximum load of 5 kN for the implants with the 20° reinforcement and 5.5 kN with 15° preform. The use of this type of prostheses in press fit applications was verified by conducting impact tests, simulating the hammer blows executed during the surgery.

The study lays out the scientific base for a new manufacturing technique for composite hip prostheses using the resin transfer molding process and shows that prostheses with similar stiffness to the surrounding bone can be manufactured. All steps of the development cycle, including design, structural analyis, mold filling simulation, manufacturing and evaluation of performance, were performed on a basic level. The mechanical performance, especially fatigue and impact resistance were found to be excellent. The design of the implant and the mold need further revision in order to enhance mechanical performance, to ease manufacturing and to improve quality.
Modeling of Diffusion in a Micro-Cracked Composite Laminate Using Approximate Solutions
Authors: Roy Samit , Bandorawalla Tozer
Published: April 2011

A set of approximate solutions for predicting through-thickness diffusivity and solvent uptake behavior of micro-cracked composite laminates is presented. In order to maintain solution tractability, Fickian diffusion is adapted as the basic framework of the model. Starting with the assumption of a uniform micro-crack array on the exposed faces of the laminate, an RVE (representative volume element) approach is employed to estimate the laminate through-thickness diffusivity as a function of crack depth and crack density. It is also established that, for the Graphite/Epoxy material system under consideration, the rate of moisture ingress into micro-cracks due to capillary imbibition does not have an appreciable long-term influence on the laminate diffusivity and uptake. The approximate solutions are verified by comparison with available test data from moisture uptake experiments and with finite element predictions.
Performance of Fiber-Reinforced Plastic Tapered Poles under Lateral Loading
Authors: Polyzois D. , Ibrahim S. , Raftoyiannis I. G.
Published: April 2011

An extensive research project is currently being carried out at the University of Manitoba to develop lightweight poles for use in transmission lines. In this project, the failure modes of tapered fiber-reinforced plastic (FRP) poles with hollow circular cross-section subjected to cantilever bending are being investigated experimentally and theoretically. The poles are made of vinylester reinforced with E-glass fibers and are produced by the filament winding process. To date, twelve bending tests have been conducted on scaled poles up to failure. Test parameters included the wind angle, and the number of layers. Local buckling and/or material failure, very likely to appear in thin-wall cross-sections, are also investigated. The analysis was conducted through a nonlinear finite element program using superparametric layered cured shell element. The coupling phenomenon between flexural bending and in-plane stretching and the effect of shear deformation were included in the finite element model. The analytical results obtained in this study are compared to experimental results obtained for various thickness and reinforcement specimens of composite poles. The finite element model was used to design a series of FRP poles with different safety factors.
Analysis of a Quasi-Isotropic MMC Laminate Using Iosipescu Shear Test
Authors: Zhang Ke , Newaz Golam , Ahmad J. , Chandu S.
Published: April 2011

The shear constitutive response and deformation mechanisms of a quasi-isotropic [0/+45/-45/90], laminate made from TIMETAL 21 S/SCS-6 MMC were investigated using the Iosipescu test. A combination of mechanical measurement, microstructure analysis and finite element method were used to investigate the inelastic deformation mechanisms of the composite. Loading-unloading experiments provided significant insight into the nature of damage/plasticity in the quasi-isotropic MMC laminate. Shear-induced inelastic deformation is dominant due to plasticity which is associated with slip bands, and damage which includes matrix grain boundary cracks, reaction zone cracks, debonding and fiber cracks. A method of finite element analysis was developed on oriented ply-stacked quasi-isotropic laminate based on an existing inelastic constitutive model from literature. The prediction for the constitutive response using finite element analysis fits test data very well. The correlation of predicted results with experimental data shows that Iosipescu shear test is a valid method for investigating shear properties of quasi-isotropic MMC laminates which can experience complex damage modes under pure shear loading.
Effect of Cylindrically Orthotropic Carbon Fibers with Transversely Isotropic Core on Effective Thermal Conductivity of Unidirectional Composites
Authors: Rodríguez Alfonso Corz , Cabeza José M. Gutiérrez
Published: April 2011

Carbon fibers can be considered cylindrically orthotropic. Depending on the arrangement of basal planes, predominant configurations are circumferential and radial, but in the core of the fiber, the alignment is undetectable, and consequently it is considered as transversely isotropic. In composites reinforced with these types of fibers, the effective thermal conductivity transverse to the fiber direction will be affected by the core and by the thermal resistance between the fiber and the matrix. The analytical models available are not adequate because they assume that the fiber is totally homogeneous.

In this paper, a model of finite elements is presented, which allows combination of the effects of core with the cylindrical orthotropic of the fiber and the thermal contact resistance between the fiber and the matrix. The effective conductivity of composites with orthotropic and inhomogeneous fibers are compared to those with orthotropic and homogeneous fibers. This allows evaluation of the effect for the different morphology of the fibers. The model reveals a significant effect for radially orthotropic fibers (pitch-based). The model also contributes to a better understanding of the heat flux paths in cylindrically orthotropic and inhomogeneous fibers. Finally, this numerical simulation can be of interest first, in the microstructural studies focused on the relationship between the transverse thermal conductivity of carbon fibers and some microstructural parameters, and secondly, in the studies designed to estimate the interfacial contact resistance.
Theoretical and Experimental Investigation of Progressive Failure of Woven Composite Panels
Authors: Feng Zheng-Nong , Allen Howard G. , Moy Stuart S. J.
Published: April 2011

Progressive failure of laminated panels containing stacks of unidirectional non-woven composite laminae has been widely studied in recent years. However, there are few reports about the progressive failure analysis of woven composite panels. The present paper provides a methodology for the progressive failure analysis of such woven composite panels under high transverse pressure. The method incorporates the results from micro-structural analysis of a woven composite unit [1] into the macro analysis of the woven composite panel. The effect of stress concentrations due to interlacing and undulation of the woven fabrics on the strength of the material is considered. The Hashin failure criterion is used in the analysis. Three types (two woven and one non-woven) of composite panels are analysed as examples and the predicted results are compared with tests on panels. Good agreement is demonstrated.
Studies on Polymer-Wood Interface Bonding: Effect of Coupling Agents and Surface Modification
Authors: Razi P. S. , Portier R. , Raman A.
Published: April 2011

Mechanical properties of composites are a direct function of the interface bonding between strengthening fiber and the matrix. This study investigates the influence of surface modification of wood chips and presence of different interface coupling agents on the interface bonding of wood-polyethylene composites. Single wood-polyethylene interfaced samples were prepared by introducing extruded polyethylene from a twin extruder to bond to the rip surface of a rod-shaped wood specimen. Sodium hydroxide and sulfuric acid were used as surface modifiers for wood. The bond-modifying properties of three silane coupling agents were investigated. The coupling agents used were vinyltrimethoxysilane, 98%, 3-(tri-methoxysilyl)propylmethacrylate, 97%, and 3-glycidoxypropyltrimethoxy silane, 96%. Direct measurement of the interfacial bond strength was carried out using an Instron tensile test machine. Individually, the acidic modifier showed adverse effect on the interface. However, sodium hydroxide improved the interface bonding and enhanced the bond strength by a factor of 1.3 to 1.5. Basically, all of the coupling agents individually increased the interface bonding; vinyltrimethoxysilane, (H2C=CHSi(OCH3)3), had the greatest effect. Also, surface modifiers and coupling agents applied together showed a synergistic effect which contributed to an improved polymer/woodstock interface bond.
An Experimental Investigation of High Velocity Impact and Penetration Failure Modes in Textile Composites
Authors: Flanagan M. P. , Zikry M. A. , Wall J. W. , El-Shiekh A.
Published: April 2011

The dynamic failure evolution of textile composites, which were subjected to impact velocities up to 1100 m/s, was investigated. Specialized machines were used to fabricate composites from combinations of Spectra®, Kevlara®, and Twaron® fibers and two- and three-dimensionally woven, braided, and needle-punched nonwoven fabrics. This control of fabrication and processing enabled us to characterize response as a function of areal density, fabric finish, and consolidation techniques. Failure was categorized in terms of material layers, debris mass, matrix cracking, fiber failure, and shear-plugging. Results indicate that shear-plugging occurs at velocities corresponding to decreases in debris mass.
Bound Solution for Residual Stress Due to Thermal Mismatch in Particle Reinforced Composites
Authors: Park S. J. , Earmme Y. Y.
Published: April 2011

The residual stress in the particle reinforced composite (both phases isotropic) is studied by both the self-consistent method (SCM) and the generalized self-consistent method (GSCM). Two models of GSCM are employed: Model I is the inclusion phase surrounded by the matrix phase, which is embedded in the effective medium, while in Model II the positions of the inclusion and matrix are interchanged. The results are summarized as follows: (1) SCM yields the residual stress in between the bounds of the residual stress given by the GSCM in the present study. (2) The residual stress from the well known modified equivalent inclusion method (MEIM) and composite sphere model (CSM) reduces to the lower bound of the GSCM (i.e., Model I in the present study) if the inclusion is stiffer than the matrix. If the matrix is stiffer, Model II results in the lower bound, which is equal to the result by MEIM and CSM. (3) The result by Kreher, who expressed the residual stress in terms of the effective bulk modulus (in addition to the elastic properties of the inclusion and matrix) can be reduced to the present bound solutions by GSCM if the bound for the effective bulk modulus is used for the Kreher's work and a proper choice of Model I or Model II of GSCM with a proper choice of the bound for the effective bulk modulus is made.
Predictor-Corrector Procedure for Displacements, Stresses and their Sensitivity Coefficients in Composite Panels
Authors: Park Jin Woo , Kim Yong Hyup
Published: April 2011

A predictor-corrector procedure is presented for the accurate recovery of stresses, displacements and their sensitivity coefficients of multilayered composite panels subjected to mechanical and thermal loads. It is a post-processing procedure combined with the finite element model based on the first order shear deformation theory. The predictor procedure provides only the accurate transverse shear stresses of the panel, in the thickness direction. The corrector procedure following the predictor procedure is adopted in the present study and enhances the accuracy of displacements, in-plane stresses and transverse normal stress in the thickness direction by using the results from the predictor procedure and the finite element analysis. The corrector procedure enables the recovery of higher order distributions of the results in the thickness direction. The sensitivity coefficients of the displacements and the stresses with respect to material properties can be evaluated in a similar manner. The numerical examples are conducted to demonstrate the effectiveness of the present procedure. The basis of comparison is the exact solutions of the three-dimensional thermoelasticity equations.
Finite Element Analysis of the Arcan Specimen for Fiber Reinforced Composites under Pure Shear and Biaxial Loading
Authors: Hung S. C. , Liechti K. M.
Published: April 2011

Linearly elastic finite element analyses were used to examine the effects of fiber orientation, notch angle and notch root radius on the stress distribution in Arcan specimens in order to optimize the specimen geometry for the unidirectional, fiber reinforced composite AS4/PEEK under shear and biaxial loadings. Two fiber orientations, three notch angles and five notch root radii were examined. A comparison between butterfly-shaped and circular S-shaped specimens was also made. For specimens with fibers running across the specimen from grip to grip (1-2 orientation), a 1340 notch angle was found to be the best choice due to superior stress uniformity along the gage section and minimum transverse normal stress along the notch flank. However, specimens with fibers running from notch to notch (2-1 orientation), required a 900 notch angle for optimum stress uniformity along the gage section and minimum transverse normal stress along the specimen notch. It was also found that, along the gage section, the largest shear stress concentration occurred near the notch roots of the 1-2 specimen, yet it was not seen in the 2-1 specimen. This made the 2-1 specimen a better candidate for determining the shear properties of fiber reinforced composites. It was also found that the butterfly-shaped specimen bonded to steel grips provided much more uniform normal stresses than the original circular S-shaped specimen did. As a result, a butterfly-shaped Arcan specimen with a 2-1 fiber orientation, a 900 notch angle, a 2.38 mm root radius and bonded to steel grips was found to be very suitable for examining the longitudinal deformation behavior of this particular fiber reinforced composite under both shear and biaxial loading. Strain distributions from the finite element analyses were also compared to those obtained from moire measurements. At low load levels, there was excellent agreement between the two. Nonlinear effects mitigated stress concentrations at higher load levels.
Modeling of Anomalous Moisture Diffusion in Polymer Composites: A Finite Element Approach
Authors: Roy Samit
Published: April 2011

Theory of irreversible thermodynamics is applied to derive governing equations for history-dependent diffusion in polymers and polymer matrix composites from first principles. A special form for Gibb's free energy is introduced using stress, temperature, and moisture concentration as independent state variables. The resulting governing equations are capable of modeling the effect of interactions between complex stress, temperature, and moisture histories on the diffusion process within an orthotropic material. Since the mathematically complex nature of the governing equations precludes a closed-form solution, a variational formulation is used to derive the weak form of the nonlinear governing equations which are then solved using the finite element method. For model validation, the model predictions are compared with published experimental data for the special case of isothermal diffusion in an unstressed graphite/epoxy symmetric angle-ply laminate.
Simultaneous Measurement of Two Strain Components in Composite Structures Using Embedded Fiber Sensor
Authors: Jin X. D. , Sirkis J. S. , Chung J. K. , Venkat V. S.
Published: April 2011

This paper uses an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg grating to simultaneously measure axial and transverse strain components inside a cantilever beam fabricated from a graphite/epoxy composite material. The ILFE and Bragg grating sensor signals are demultiplexed using a variation of coherence division multiplexing, and then demodulated using a Pseudo-Heterodyne scheme. Composite cylinders models are developed that allow the optical measurements to be related to the strains in the host composite material. Experimental results show that both of the measurement errors of the two strain components are approximately 5 uE.
Influence of Delamination Growth and Contact Phenomena on the Compressive Behaviour of Composite Panels
Authors: Perugini P. , Riccio A. , Scaramuzzino F.
Published: April 2011

A numerical analysis, providing a realistic insight on the compressive behaviour of composite panels with through-the-width delaminations, was performed by means of an in-house Finite Element Method (FEM) based code able to analyse the influence of delaminations' growth and contact phenomena on the load carrying capability of these kinds of structures. First of all a sensitivity analysis was carried out to underline the influence of delaminations' position along the thickness and their growth on panels' compressive behaviour. Then comparisons with experimental data available in bibliography were performed to test the effectiveness of new numerical techniques. Finally a panel with two delaminations was investigated to point out the need of a numerical tool able to take into account contacts between sublaminates in order to evaluate the real structure's response under compressive load.
Optimal Design of a Hybrid Composite Flywheel with a Permanent Magnet Rotor
Authors: Ha Sung K. , Yang Hyun-Ik , Kim Dong-Jin
Published: April 2011

A design method to optimize the dimensions of a hybrid composite flywheel rotor and a permanent magnet is presented. The flywheel rotor consists of multiple rims of advanced composite materials with a permanent magnetic rotor attached inside the flywheel. The pressure distribution at the inner surface from the centrifugal forces of the magnet is considered together with the centrifugal body forces in the flywheel rotor. The size of the magnet also maintains the required induced voltage. An analytical solution of the displacements and stresses for each ring has been obtained and expressed in terms of a symmetric stiffness matrix. Using the stiffness matrix, the continuity conditions between the rings and the pressure due to the magnet can be easily considered. An optimum design is thus performed maximizing the total stored energy (TSE) with the size of the magnet and the thickness of each composite ring as design variables. For that purpose, the sensitivities of TSE and the Tsai-Wu failure index with respect to the design variables are derived by using the global stiffness matrix and the relationship of the magnetic size and the induced voltage. As a result, the optimal design using the hybrid composite rims has significantly reduced the stresses in a rotor and attained about 2 times the total energy of cases of using each material alone. The present optimization approach can be used to develop an efficient flywheel rotor for various applications.
Fatigue Strength Prediction under Multiaxial Stress
Authors: Philippidis T. P. , Vassilopoulos A. P.
Published: April 2011

A multiaxial fatigue failure criterion for composite materials is presented in this paper along with an assessment of the capability it offers for design under multiaxial constant or variable amplitude stresses. The applicability of this criterion, based on the well known quadratic failure tensor polynomial criterion for static loading, is validated through comparisons with uniaxial and multiaxial fatigue experimental data. Static and fatigue tests were carried out during this study on glass/polyester specimens cut off-axis from a multidirectional laminate at different angles. The agreement between experimental values and theoretical predictions is good. The proposed criterion is also compared to existing fatigue criteria and an overall assessment of their performance is given. Some theoretical design considerations for the case of irregular stress spectra, introducing the concept of multiaxial Miner coefficient, are finally presented.
Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers
Authors: Alsayed Saleh H. , Alhozaimy Abdulrahman M.
Published: April 2011

A total of 18 concrete beams were tested to study the influence of adding steel fibers (SF) to concrete mix on the ductility of concrete beams reinforced with fiber reinforced plastics bars (FRP beams). The main variables in the study were the type and volume fraction of the steel fiber. The study also investigated the accuracy of an available model, developed originally to predict the flexural strength of concrete beams reinforced with SF and steel bars (SF-steel beams), after modification in estimating the flexural capacity of the fibrous FRP beams (SF-FRP beams).

The results indicate that the ductility of FRP beams is less than 50% of that of the respective steel beams. The results also reveal that the ductility of SF-FRP beams is directly related to the fiber content. In addition, the test results show that inclusion of 1% of hooked SF can improve the ductility of FRP beams to be the same as that of the steel beams. Furthermore, comparison between the predicted and measured flexural capacity of SF-FRP beams shows that the modified model can predict the measured results within a reasonable accuracy.
Strength Prediction of Random Fiber Composite Beams using a Phenomenological-Mechanistic Model
Authors: Zhang Y. , Sikarskie D. L.
Published: April 2011

A phenomenological-mechanistic model, referred to as a lamini model and reported in a previous paper [8] for homogeneous stress states, is used to predict random fiber composite beam strength in this paper. This model divides a random fiber composite panel into a stack of thin transversely isotropic layers (laminas) with each lamina constructed from a series of unidirectional layers (laminis). As the number of laminis and laminas approach infinity, the convergence of the extensional stiffness matrix [A] and the bending stiffness matrix [D] is proved. These two stiffness matrices also satisfy the relationship established for isotropic materials, thus ensuring the transverse isotropy typical of random fiber composite plates (and beams). Due to the difficulty in determining lamini post-peak stress-strain behavior, in this paper only bounds on the damage growth and ultimate strength of a random fiber composite beam have been determined. The lower bound is obtained by assuming the stress falls to zero immediately after it reaches its peak value, i.e., zero residual strength in the failed layers. The upper bound is based on the assumption that the stress remains constant after the peak value is reached. This is analogous to a perfectly plastic material. Both bound predictions follow the four point bend load-strain experimental curves closely until the failure process begins to dominate with the lower bound predicting failure load approximately 39% below the experimental results while the upper bound predictions are approximately 37% higher. The model also quantitatively predicts the failure initiation and damage growth behavior in the composite beam which were observed in the previous high sensitivity laser Moire interferometry experiments [6].
Influence of Matrix Chemistry on the Short Term, Hydrothermal Aging of Vinyl Ester Matrix and Composites under Both Isothermal and Thermal Spiking Conditions
Authors: Verghese K. N.E. , Hayes M. D. , Garcia K. , Carrier C. , Wood J. , Riffle J. R. , Lesko J. J.
Published: April 2011

Moisture absorption in vinyl ester (Derakane 441-400) resin and vinyl ester/glass fiber (EXTREN®) composites has been investigated. Moisture uptake for the neat polymer under short term isothermal aging conditions in water was found to obey Fick's second law. Information on moisture uptake in the polymer at different water bath temperatures namely, room temperature, 45°C, 66°C and 84°C was used to compute the diffusion coefficients and the Arrhenius activation energy for the diffusion process. In this study, glass transition (Tg) of the polymer aged to different extents in a water bath at 66°C was monitored as a function of moisture content using a dynamic mechanical analyzer (DMA) run in fixed frequency mode. Chemical structure changes were also monitored for both unaged and fully saturated thin film specimens aged under similar conditions using Fourier transform infrared spectroscopy (FTIR). Specific interactions in the form of hydrogen bonding with water were found to exist. In addition to isothermal aging, the effects of short term thermal spiking on the equilibrium moisture content was studied both for polymer and composite. Samples were aged in water under a 66°C-room temperature-66°C temperature profile, wherein changes in exposure temperature were made only upon saturation at the previous temperature. The reverse thermal effect (RTE) was found to exist. The activation energy for the process was experimentally computed and compared with that of typical hydrogen bonding to find excellent correlation confirming that hydrogen bonding was occurring. Moisture uptake at 66°C was also monitored on a model resin system (i.e., CH3-GMA) similar in chemical structure to vinyl ester except for the absence of hydroxyl (-OH) groups on the backbone and FTIR tests were performed on this new resin. The absence of the "-OH" peak in the unaged specimen and the resulting shift upon aging motivated the above mentioned thermal spiking experiment to be performed on the system. The RTE was not observed for this resin, and it was concluded that along with the previous work that the RTE related phenomenon could be attributed to hydrogen bonding. In addition to the neat polymer, quasi-static tensile properties were found to deteriorate as a function of equilibrium moisture content for E-glass/vinyl ester composites aged under RTE conditions.
Elasto-Plastic Analysis of the Iosipescu Shear Test
Authors: Odegard G. , Kumosa M.
Published: April 2011

It has been shown in this research that the effect of non-linear material behavior has a large effect on the mechanical response of 00 unidirectional graphite/epoxy Iosipescu shear test specimens. The Iosipescu specimens with and without axial splits at the roots of the notches have been numerically investigated. Using a non-linear finite element analysis and an anisotropic plasticity model, numerical load-displacement and shear stress-strain diagrams that closely match the experimentally obtained curves have been obtained. In addition, stress distributions have been numerically determined for the Iosipescu specimens assuming the presence of three different non-linearities, namely material non-linearity, geometric non-linearity, and boundary contact non-linearity (specimen sliding within the fixture). It has been found that the material non-linearity is primarily responsible for the non-linear behavior of the specimens subjected to shear. Both the geometric and boundary contact non-linearities have an essentially insignificant effect on the load-displacement diagrams and internal stresses in the specimens subjected to small shear deformations. The non-linear material behavior significantly reduced the internal stress concentrations at the roots of the notches. For the proper evaluation of the shear strength of unidirectional graphite/polymer composite materials using the Iosipescu shear test, the non-linear material behavior must be considered in a finite element analysis. However, it has also been shown in this research that the shear strength of unidirectional graphite/epoxy composites can be quite accurately determined from the experimental load-displacement data.
Interlaminar Shear Behavior of Thick Carbon/Epoxy Composite Materials
Authors: Oh Je Hoon , Kim Jin Kook , Lee Dai Gil , Jeong Kwang Seop
Published: April 2011

The interlaminar shear behavior of thick carbon/epoxy composite laminates was investigated using the Iosipescu shear test. In order to manufacture thick test specimens, both the conventional autoclave cure cycle recommended by prepreg manufacturer and the modified autoclave cure cycle incorporating cooling and reheating steps were used.

A 3-dimensional linear finite element analysis was performed to assess the uniformity of the shear stress field in the test section as well as to predict the failure mode of the specimen. For more accurate analysis of the stress field, contact elements were used between the specimen and the fixture, and the shear stress field in the thickness direction was taken into account. From the analysis, the failure region in the specimen was predicted and the correction factor was calculated to compensate for the non-uniformity of the shear stress field in the gage section.

From the shear test, the interlaminar shear strength and shear modulus were obtained, and the interlaminar properties of the specimens manufactured by the conventional autoclave cure cycle were compared with those of the specimens manufactured by the modified autoclave cure cycle.
A New Test Method for Measuring the Longitudinal and Shear Moduli of Fiber Reinforced Composites
Authors: Jalali S. Javad , Taheri Farid
Published: April 2011

A new test method for the simultaneous evaluation of the longitudinal and the shear moduli of fiber reinforced plastic composites (FRPC) is introduced. Under the proposed method, specimens with different span to depth ratios (Llh) are subjected to three-point bending. Therefore, we name the method the "Varying Span Method" (VSM). The method builds on the inherent low shear modulus characteristics of FRPC. This characteristic leads to a flexural modulus which is a function of LMh. Eliminating the effect of local deformation from the test results, the flexural modulus (beside the geometry of the specimen) is a function of the longitudinal and the through-the-thickness shear moduli. These moduli can be obtained from the results of at least two tests on specimens with different Llh. For this, two distinctly different theories are introduced. A special apparatus is used to eliminate the effect of local deformations. The factors that may affect the accuracy and efficiency of the results are investigated and discussed. The validity of the proposed method is demonstrated by theoretical and experimental evaluations. The moduli of graphite/epoxy and Kevlar/epoxy composites, as measured by VSM, are reported. The measured values were found to be in very good agreement with the values evaluated by other standard methods.
A Progressive Damage Methodology for Residual Strength Predictions of Notched Composite Panels
Authors: Coats Timothy W. , Harris Charles E.
Published: April 2011

The translaminate fracture behavior of carbon/epoxy structural laminates with through-penetration notches was investigated to develop a residual strength prediction methodology for composite structures. An experimental characterization of several composite materials systems revealed a fracture resistance behavior that resembles the R-curve behavior exhibited by ductile metals. Fractographic examinations led to the postulate that the damage growth resistance was primarily due to fractured fibers in the principal load-carrying plies being bridged by intact fibers of the adjacent plies. The load transfer associated with this bridging mechanism suggests that a progressive damage analysis methodology will be appropriate for predicting the residual strength of laminates with through-penetration notches. A progressive damage methodology developed by the authors was used to predict the initiation and growth of matrix cracks and fiber fracture. The residual strength predictions for different panel widths, notch lengths, and material systems were in reasonable agreement to the experimental failure loads.
A Progressive Damage Model for Mechanically Fastened Joints in Composite Laminates
Authors: Camanho P. P. , Matthews F. L.
Published: April 2011

A three-dimensional finite element model is developed to predict damage progression and strength of mechanically fastened joints in carbon fibre-reinforced plastics that fail in the bearing, tension and shear-out modes. The model is based on a three-dimensional finite element model, on a three-dimensional failure criterion and on a constitutive equation that takes into account the effects of damage on the material elastic properties. This is accomplished using internal state variables that are functions of the type of damage. This formulation is used together with a global failure criterion to predict the ultimate strength of the joint. Experimental results concerning damage progression, joint stiffness and strength are obtained and compared with the predictions. A good agreement between experimental results and numerical predictions is obtained.
Optimal Design of Filament Winding Using Neural Network Experimental Design Scheme
Authors: Chen Junghui , Jang Shi-Shang , Wong David Shan Hill , Ma Chen-Chi M. , Lin Jia-Min
Published: April 2011

The goal of this paper is to design the filament winding in composites materials based on our previous developed technique. The most significant parameters in design and construction of composites prepared by filament winding are resin temperature, fiber tension and winding angle. The three variables depict nonlinear relationship; thus a nonlinear modeling technique is required. The proposed methodology enjoys many of the advantages claimed for the artificial neural network (ANN), random search optimization, fuzzy classification and information theory for the sequential design filament winding. The neural network is used to construct a model based on the currently available experimental data. Random search generates a number of candidates of the next batch of experiments. Fuzzy classification and information analysis are defined to balance the need of better classification and the relevance of each class in optimization. The test results of the proposed method show that the abilities of the proposed methodology handle multivariable experimental design and also help experimenters discuss complex trade-offs between practical limitation and statistical preferences in the experiment.
The Political Contradictions of Incremental Innovation: Lessons from Pharmaceutical Patent Examination in Brazil
Authors: Shadlen Kenneth C.
Published: April 2011

Neodevelopmental patent regimes aim to facilitate local actors’ access to knowledge and also encourage incremental innovations. The case of pharmaceutical patent examination in Brazil illustrates political contradictions between these objectives. Brazil’s patent law includes the Ministry of Health in the examination of pharmaceutical patent applications. Though widely celebrated as a health-oriented policy, the Brazilian experience has become fraught with tensions and subject to decreasing levels of both stability and enforcement. I show how one pillar of the neodevelopmental regime, the array of initiatives to encourage incremental innovations, has fostered the acquisition of innovative capabilities in the Brazilian pharmaceutical sector, and how these new capabilities have altered actors’ policy preferences and thus contributed to the erosion of the coalition in support of the other pillar of the neodevelopmental regime, the health-oriented approach to examining pharmaceutical patents. The analysis of capability-derived preference formation points to an endogenous process of coalitional change.
Same-Day Substance Use in Men and Women Charged With Felony Domestic Violence Offenses
Authors: Friend John , Langhinrichsen-Rohling Jennifer , Eichold Bernard H.
Published: April 2011

This archival study reviewed 196 closed felony domestic violence files from a large southern city from the years 1999—2006. The purpose was to provide information on the co-occurrence of substance use and intimate partner violence (IPV) for male and female perpetrators on the day of the violent incident. Results indicated that of the 141 of 196 cases in which there was documentation about drug or alcohol involvement, 67.4% ( n = 95) of the cases confirmed that there was drug or alcohol use on the day of the incident. Male perpetrators were significantly more likely to have been involved with alcohol and/or drugs the day of the violent episode than were female perpetrators. Sex of offender and race analyses revealed that the percentage of female IPV perpetrators (42.9%) was substantial and African Americans, particularly women, were overrepresented in IPV felony charges. Implications and suggestions for further research are discussed.
Accuracy of Person-Fit Statistics
Authors: St-Onge Christina , Valois Pierre , Abdous Belkacem , Germain Stéphane
Published: April 2011

Using a Monte Carlo experimental design, this research examined the relationship between answer patterns’ aberrance rates and person-fit statistics (PFS) accuracy. It was observed that as the aberrance rate increased, the detection rates of PFS also increased until, in some situations, a peak was reached and then the detection rates of PFS decreased with increases in aberrance rates. Furthermore, the results suggest that ECI2Z was somewhat more robust to high levels of aberrance than lz, HT, and U3 when cheating was simulated. The results of this study shed light on a limitation of PFS analysis.
A Comparison of Mortality and Cardiac Biomarker Response between Three Outbred Stocks of Sprague Dawley Rats Treated with Isoproterenol
Authors: Schultze A. Eric , Main Bradley W. , Hall D. Greg , Hoffman Wherly P. , Lee H.-Y. Cindy , Ackermann Bradley L. , Pritt Michael L. , Smith Holly W.
Published: April 2011

The authors compared the mortality and cardiac biomarker responses in three outbred stocks of Sprague Dawley rats (CD/IGS, Sasco, Harlan) treated with isoproterenol hydrochloride. Cardiac injury was confirmed by histologic evaluation, and increases in cardiac troponin I concentration in serum were measured by two methods. CD/IGS rats had a higher incidence and earlier mortality compared with Sasco or Harlan rats. Harlan rats had lower severity scores for cardiomyocyte degeneration/necrosis compared with the other stocks. Post–isoproterenol treatment cardiac troponin I concentrations were greater in CD/IGS and Sasco rats compared with Harlan rats. Concentrations of cardiac troponin T followed a similar pattern to that of cardiac troponin I in rats treated with isoproterenol. Myosin, light chain 3 concentrations increased in all rats treated with isoproterenol, but there was no difference between the three stocks in the magnitude or pattern of the dose response. Increases in fatty acid binding protein 3 concentrations were detected in only the highest dose group at the earliest timepoint postdose for all three stocks of rats. Results of these studies illustrate the need for investigators to recognize the potential differences in response between stocks of Sprague Dawley rats treated with cardiotoxicants or novel chemical entities.
Clinical and Pathologic Predictors of Recurrence and Survival in Spindle Cell Squamous Cell Carcinoma
Authors: Spector Matthew E. , Wilson Kevin F. , Light Emily , McHugh Jonathan B. , Bradford Carol R.
Published: April 2011

Objective

To determine clinicopathologic predictors of recurrence and survival in patients with spindle cell squamous cell carcinoma (SpSCC).

Study Design

Historical cohort study.

Setting

Tertiary care hospital.

Subjects and Methods

Forty‐eight patients (mean age, 65.2 years; 35 men, 13 women) who underwent definitive treatment for pathologically confirmed SpSCC between 1987 and 2009 were identified and reviewed. The main outcome measures were time to recurrence and overall survival, while controlling for clinical and pathologic parameters (age, sex, TNM classification, stage, tumor subsite, smoking status, treatment modality, margin status).

Results

Of 48 patients, there were 25 oral cavity, 15 laryngeal, 7 oropharyngeal, and 1 maxillary sinus tumors. Treatment included surgery in 32, radiation in 9, and concurrent chemoradiation in 7 patients. The 3‐year overall survival for the cohort was 62% with a median follow‐up of 59 months; 52.1% (25/48) of patients developed a recurrence, and 88% (22/25) recurred locally or locoregionally. Recurrence occurred within 2 years in 72% (18/25) of patients. Age, sex, initial T and N classification, overall stage, tumor subsite, smoking status, treatment modality, and margin status were not predictive of recurrence or overall survival.

Conclusion

Patients with SpSCC are at high risk of developing locoregional recurrence, but no measured clinical or pathologic parameter was predictive of survival. Although overall survival is similar to that of patients with conventional SCC, closer follow‐up should be considered in these patients to allow earlier detection and treatment of these locally aggressive tumors.
Second Primaries after Major Salivary Gland Cancer
Authors: Megwalu Uchechukwu C. , Shin Edward J.
Published: April 2011

Objectives

To evaluate the risk of second primary cancers in patients with major salivary gland cancer using a large population database and to examine the effects of sex, salivary gland cancer histology, and radiation therapy on the risk of second primaries.

Study Design

Population‐based study using the Surveillance, Epidemiology, and End Result (SEER) cancer database.

Subject and Methods

The subjects were 15,572 men and women ages 15 and above, diagnosed with cancer of the major salivary glands from 1973 to 2006.

Results

There was an increased risk of oral cavity (standardized incidence ratio [SIR] = 3.48, P <. 05), salivary (SIR = 9.97, P <. 05), lung and bronchus (SIR = 1.60, P <. 05), kidney (SIR = 1.68, P <. 05), and thyroid (SIR = 2.66, P <. 05) cancers. Men had an increased risk of developing kidney cancer (SIR = 1.70, P <. 05) compared with women (SIR = 1.64, P >. 05). Patients with mucoepidermoid carcinoma had an increased risk of a second salivary gland cancer (SIR = 8.97, P <. 05) and thyroid cancer (SIR = 3.97, P <. 05). Patients with adenoid cystic carcinoma had an increased risk of oral cavity (SIR = 3.76, P <. 05) and nasopharyngeal (SIR = 16.88, P <. 05) cancers. Patients with acinar cell carcinoma had an increased risk of salivary (SIR = 31.36, P <. 05), kidney (SIR = 2.98, P <. 05), and thyroid (SIR = 3.85, P <. 05) cancers. Patients who received radiation therapy had a higher incidence of lung and bronchus (SIR = 2.11, P <. 05), laryngeal (SIR = 3.08, P <. 05), and thyroid (SIR = 2.95, P <. 05) cancers compared with patients who did not receive radiation therapy (SIR = 1.18, 0.48, and 2.39, respectively; P >. 05). Patients had an increased risk of developing second primaries, even 10 years after diagnosis of primary salivary gland cancer.

Conclusions

Patients with major salivary gland cancers are at a risk for certain second primary cancers. This highlights the need for long‐term surveillance in these patients, not only for recurrence but also for second primary cancers.