bluuebunny/crossref_metadata_2025 huggingface dataset:
Plate Theory Model for Thickness Tapered Composite Laminates
Authors: Trethewey Bruce R. , Gillespie John W.
Published: August 2002

The influence of induced interlaminar loads on the structural performance of thickness-tapered laminates is investigated using an energy-based damage tolerance methodology. An analytical model based on the assumptions of shear deformation plate theory is presented. The model employs linear-elastic fracture mechanics to determine the strain energy release rate characteristic of delamination growth from an embedded flaw. The solution is general in terms of taper thickness, delamination size, laminate fiber orientation and material interlaminar fracture toughness. As such, the model provides a preliminary design tool for the evaluation of interlaminar performance of symmetric tapered composite laminates.
Evaluation of the Maximum Configuration Factor for Cylindrical Flame Hazard Calculation
Authors: He Yaping
Published: August 2002

This work reviews solutions for the maximum configuration factor between a cylindrical body representing a fire flame and a differential area element. A solution expressed in terms of the configuration factors between the cylinder and three orthogonal differential areas is compared quantitatively with other expressions obtained in the literature.
Neonatal Chronic Lung Disease
Authors: Avent Minyon , Coile Diana , Mathai Letha
Published: August 2002

Chronic lung disease (CLD), formerly known as bronchopulmonary dysplasia, is presently defined as the need for oxygen therapy either at 28 days of age or greater than 36 weeks postmenstrual age. Clinical signs and symptoms include tachypnea, retractions, apnea, and radiographic findings of poorly inflated lungs with reticulogranular opacities. The disease develops as a result of chronic pulmonary inflammation and continuous lung injury induced by oxygen, positive pressure ventilation, and other causes. Fifty to sixty-five percent of neonates with CLD are rehospitalized with respiratory problems, and 21% of very low birth weight neonates are diagnosed with asthma or other respiratory disorders by the age of five. These infants are at risk of adverse neurodevelopmental sequelae as they have a more complicated neonatal course. Many studies have explored various preventive therapies including α1-proteinase inhibitors, superoxide dismutase, antioxidants, and ventilatory management. Although the results from these trials are promising, further studies are needed to define which patients are most likely to benefit from preventive therapy. Two preventive treatment approaches that have shown a decrease in morbidity and an improvement in mortality are antenatal steroids and surfactant therapy. Postnatal corticosteroid therapy continues to be the mainstay of treatment for CLD, however, there are a number of detrimental side effects associated with this treatment. Due to the increased incidence in periventricular leukomalacia, early treatment of steroid therapy cannot be recommended. The optimal time to start steroid therapy appears to be after the first week of life. In addition, the lowest dose and shortest duration of treatment needs to be implemented in order to minimize potential complications. Although bronchodilators and diuretics continue to be used extensively in infants with CLD, there are surprisingly few well-controlled studies that have evaluated the clinical impact of this therapy. Further trials are needed in order to support the routine use of these therapies in CLD. Unfortunately, inhaled steroids have not shown an improvement in long-term outcomes of CLD, however, they have shown a decrease in systemic steroid usage. CLD is a complex disease with many unanswered questions. Further studies are needed to evaluate the effects of various treatment modalities with particular focus on the long-term outcomes such as oxygen and ventilator dependency as well as the incidence of CLD.
Elasto-Plastic Stress Analysis of Thermoplastic Matrix Composite Laminated and Perforated Plates under In-Plane Loading
Authors: Arlsan N. , Pihtili H. , Gur M.
Published: August 2002

The study presents an elasto-plastic stress analysis in symmetric and antisymmetric cross-ply reinforced thermoplastic matrix composite laminated plates. The thermoplastic matrix composite layer reinforced by long stainless steel fiber is manufactured by using moulds under the action of 2 MPa pressure and heating up to 200°C. A laminated and perforated plate consists of four thermoplastic matrix layers is reinforced cross-ply and bonded symmetrically or antisymmetrically. The first-order shear deformation theory and nine node Lagrangian finite element are used. The residual stresses and the expansions of plastic regions are illustrated for various cases. The in-plane load and the layer orientation angle are increased gradually.
The Susceptibility to Failure of the Constituents of Particulate Two-Phase Composites
Authors: Antretter T. , Fischer F. D.
Published: August 2002

In many composites consisting of hard and brittle inclusions embedded in a ductile matrix, failure can be attributed to particle cleavage followed by ductile crack growth in the matrix. Both mechanisms are significantly sensitive to the presence of residual stresses.

On the one hand, particle failure depends on the stress distribution inside the inclusion which in turn is a function of various geometrical parameters such as the aspect ratio and the position relative to adjacent particles as well as the external load. On the other hand, it has been observed that the absolute size of each particle plays a role as well and will therefore be taken into account in this work by means of the Weibull theory. Unit cells containing a number of randomly oriented elliptical inclusions serve as the basis for the finite element calculations. The numerical results are then correlated to the geometrical parameters defining the inclusions. The probability of fracture has been evaluated for a large number of inclusions and plotted versus the particle size. The parameters of the fitting curves to the resulting data points depend on the choice of the Weibull parameters. Similarly, the distribution of matrix stresses has been recorded depending on the particle content and the external loading conditions.

A method to determine the Weibull parameters based on the numerical results will be pointed out. Residual stresses due to quenching of the material tend to reduce the risk of particle cleavage but promote fracture of the matrix.
A Finite Element Analysis of Second Order Effects on the Frequency Response of a SAW Device
Authors: Xu Guanshui , Jiang Qing
Published: August 2002

Electrode perturbation of the surface may cause significant second order effects on the frequency response of surface acoustic wave (SAW) devices for high frequency applications. These effects in a Y-Z lithium niobate filter are analyzed using a recently developed finite element model. In this model, the equations of wave propagation in piezoelectric materials are discretized using the Galerkin method, in which an implicit algorithm of the Newmark family with unconditional stability is implemented. The Rayleigh damping coefficients are included in the elements near the boundary to reduce the interference of reflected waves. The frequency response of the filter is obtained through the Fourier transform of the impulse response, which is solved directly from the finite element simulation. The analyses have shown that for aluminum electrodes of fixed thickness, the second order effects on the frequency response become increasingly significant as the device is scaled smaller to have higher central frequencies. Typically, for aluminum electrodes of thickness 2000 Å, the frequency response is significantly distorted for the device of the central frequency at above 2 GHz. Quantitative analyses of the second order effects in the device of various center frequencies provide insights for designing high performance SAW devices for high frequency applications.
Design Issues of a High-Stroke, On-Blade Piezostack Actuator for a Helicopter Rotor with Trailing-Edge Flaps
Authors: Lee Taeoh , Chopra Inderjit
Published: August 2002

A compact actuator to oscillate blade trailing-edge flap on a full-scale helicopter has been investigated for vibration suppression. The actuator consists of piezoelectric stacks and a dual-stage mechanical stroke amplifier. It is recommended that commercially available piezostack be used for timely manufacturing and maintenance rather than a custom-designed piezostack. An analytical approach to estimate the maximum actuator force requirement for the rotor in hover condition is discussed first. A piezostack down-selection through the experimental evaluation is presented, which is to select a piezostack with high stiffness as well as good strain/block force output among twelve commercial piezostacks. The design requirements of on-blade piezoelectric actuator are discussed, and one-dimensional stiffness modeling and finite element beam modeling are presented to evaluate the analytical/numerical actuator performance. The prototype actuator with a double-lever stroke amplifier was fabricated and tested on bench-top as well as in vacuum chamber. An amplification factor of 19.4 and the consistent actuator output up to 600 g of centrifugal loading were obtained. An improved actuator has been designed with a design refinement to reduce structural losses.
Fiber Optic Sensors and Smart Fabrics
Authors: El-Sherif Mahmoud A. , Yuan Jianming , Macdiarmid Alan
Published: August 2002

This paper presents novel work on developing fiber optic micro-sensors and integrating them into soldiers’ uniforms. These fiber optic sensors can be used to sense various battlefield hazards in real-time, such as chemical and biological warfare threats, above-normal field temperatures, and other hazards. The developed fiber optic sensors use multifunctional materials as modified cladding materials, which can sense various environmental conditions. Appropriate materials can be chromogenic materials, chemical or biological agent, conducting polymer and others. The sensing function is based on their ability to change the light propagation characteristics of optical fibers.

Two types of materials, (1) thermochromic material, segmented polyurethane-diacetylene copolymer (SPU) [synthesized at the University of Akron (UA)], and (2) conducting polymer, polyaniline [synthesized at the University of Pennsylvania (U of P)], have been successfully used in this feasibility study to prove the concept of the design and development of the optical fiber sensors. Segmented polyurethane-diacetylene copolymer was selected as the thermochromic material for temperature sensor application. Polyaniline was chosen as the photo-chemical polymer for chemical sensor application. The developed methodology for building these sensors includes modifying the regular optical fibers, by replacing the fiber passive cladding with those sensitive materials. The integration of the sensory system into textile structures, done in collaboration with the North Carolina State University (NCSU), also showed good progress. An overview on the developed methodology and technical achievement is presented.
Characteristics and Their Intelligent Control of Nanostructured Materials
Authors: Yamazaki Yoshitake , Watanabe Tadao , Tani Junji , Alyoshin Vladislav , Krasilnikova July , Krasilnikov Ilya
Published: August 2002

Nanostructured materials (NSM) belong to a completely new class of materials with important characters, covering a wide field of applications in the near future. Their properties come from peculiar features of their structure. The NSMs consist of small crystalline grains (CG) the order of a few nanometers. There are large amount (about 50%) of atoms in defect positions near the boundaries of the CGs, called the interfacial component (IC). Compositions of both the nm-sized IC and CGs yield different characteristic properties of NSMs from those of usual bulk materials.

To develop advanced sharp, functional materials, we need to study the fundamental rules of their behavior by means of both field-theoretical (FT) and microcanonical-MetropolisMonte Carlo (M3C) methods. In two dimensional (2D) and 3D NSMs the following main characteristics were derived: (1) structural properties and their intelligent control, (2) behavior of annealing, i.e., temperature-cycle, (3) the hysteresis phenomena, and (4) nonequilibrium behavior of the hierarchically metastable states and their intelligent control. Here control-mechanisms of grain interface were also found.
The Mechanical Behavior of Vascular Grafts: A Review
Authors: Salacinski Henryk J. , Goldner Sean , Giudiceandrea Alberto , Hamilton George , Seifalian Alexander M. , Edwards Alan , Carson Robert J.
Published: August 2002

The development of intimal hyperplasia (IH) near the anastomosis of a vascular graft to artery is directly related to changes in the wall shear rate distribution. Mismatch in compliance and diameter at the end-to-end anastomosis of a compliant artery and rigid graft cause shear rate disturbances that may induce intimal hyperplasia and ultimately graft failure. The principal strategy being developed to prevent IH is based on the design and fabrication of compliant synthetic or innovative tissue-engineered grafts with viscoelastic properties that mirror those of the human artery. The goal of this review is to discuss how mechanical properties including compliance mismatch, diameter mismatch, Young’s modulus and impedance phase angle affect graft failure due to intimal hyperplasia.
The Persistence of Electrostatically Seeded Endothelial Cells Lining a Small Diameter Expanded Polytetrafluoroethylene Vascular Graft
Authors: Bowlin Gary L. , Meyer Andrew , Fields Charles , Cassano Anthony , Makhoul Raymond G. , Allen Cynthia , Rittgers Stanley E.
Published: August 2002

Purpose: The purpose of this study was to evaluate the persistence of electrostatically seeded endothelial cells (ECs) lining an expanded polytetrafluorethylene (e-PTFE) graft after one week exposure to in vivo circulation in a canine femoral artery bypass model. This was accomplished by visualizing the PKH 26 (red fluorescent) label placed in the EC membranes prior to the seeding procedure. Furthermore, this study was performed to confirm that thesourceof the ECs lining thegraft werethosefrom theinitial inoculum.

Methods: This evaluation consisted of harvesting autologous, canine jugular vein ECs, PKH 26 labeling of the ECs, electrostatic EC seeding the e-PTFE grafts (4 mm GORE-TEX®, Length = 6 cm), implanting thegrafts (femoral artery model) for one week, and explanting the grafts for light, fluorescent and scanning electron microscopy evaluations of the luminal surface.

Results: The unseeded grafts (controls) had a mean fluorescence surface coverage of 6.82 ± 7.19%, while the EC seeded grafts had a mean of 90.3 ± 14.3% which is significantly (p<0.001) different from the controls. Overall, the seeding timeincluding the EC harvesting and PKH 26 labeling protocol was approximately 75 min.

Conclusions: The electrostatically seeded ECs persisted after implantation of the graft as demonstrated by the PKH 26 labeling data. The fluorescent data also demonstrated that the neointima formed (EC luminal surface coverage) one week after implantation was in fact derived from the ECs initially seeded as determined by the abundance of the labeled ECs.
Improved Properties of Stoichiometric LiNbO3 for Electro-Optic Applications
Authors: Furukawa Yasunori , Kitamura Kenji , Takekawa Shyunji , Niwa Kazuo , Hatano Hideki
Published: August 2002

High quality stoichiometric LiNbO3 single crystals, 40 mm in diameter and 80-100 mm in length, have been successfully grown by the double crucible Czochralski method equipped with automatic powder supply system using radio-frequency heating and automatic diameter control system. Although some difficulties still exist in growing 3 inch size single crystals from offcongruent composition melts, our results demonstrate that stoichiometric LiNbO3 crystals containing much less nonstoichiometric defects than congruent LiNbO3 exhibit some advantageous properties for holographic data storage applications. This was confirmed by the results of two-beam coupling experiment and digital hologram test. In digital holographic data storage, we have demonstrated that stoichiometric LiNbO3 shows more than 10 times larger photorefractive sensitivity than congruent LiNbO3 In order to interpret the high performance of stoichiometric LiNbO3, we compared several relevant parameters such as electro-optic constants, photoconductivity, and photogalvanic constants between stoichiometric and congruent LiNbO3 crystals. We report that material parameters are strongly dependent on the density of nonstoichiometric defects and control of these defects is of key importance in improving and tailoring those properties.
Micro-Scale Electrohydrodynamic Pumped High Performance Actuation
Authors: Kashani R. , Kang S. , Hallinan K. P.
Published: August 2002

A new type of actuation device has been conceptualized that meets the needs of both large displacement force and bandwidth within a package more compact than the currently available magnetostrictive and stack-type piezoelectric actuators of similar rating. This concept relies on micro-scale electrohydrodynamic (EHD) pumping of a dielectric liquid within small channels. Configured as an actuator, the EHD pump(s) would be used to move fluid between two reservoirs—each having a compliant membrane that interfaces to the world to provide the means to achieve vibration cancellation or micro actuation.

Ordinarily limited to generating flow in macroscale applications, the EHD pump, when operating in a thermal induction mode, is shown to exhibit an exciting scaling law as its size is reduced. As the pump volume to surface area decreases, the energy going toward increasing pressure in the pump has an increasingly larger effect. Since the volume/surface area is proportional to 1/ a, where a is the characteristic width or diameter of the channels comprising the pump, the pressure head generated scales similarly. Analytical and numerical studies have shown the EHD-pumped actuator to be capable of delivering equal force and bandwidth to magnetostrictive and stack-type piezo actuators, but with considerably greater displacement and a smaller size. Further, this type of actuator offers the possibility for deployment in active vibration control or micro actuation applications at significantly greater temperatures than for piezoelectric and magnetostrictive devices.
Measurement of Fiber Density by Helium Pycnometry
Authors: Rude T. J. , Strait L. H. , Ruhala L. A.
Published: August 2002

Fiber and void volume fractions of polymeric composite materials are often measured as indicators of part quality. However, accurate fiber and void volume fraction measurements require that the fiber density be known to a high degree of accuracy. Helium pycnometry offers the potential for accurate fiber density measurements. In this study, helium pycnometry was used to measure the density of E-glass, S2-glass, and carbon fibers. Results were compared with those of other fiber density measurement techniques. The density of E-glass was determined to be 2.6173 g/cc. S2-glass was found to have a density of 2.4858 g/cc. Measured carbon fiber densities were 1.7635 g/cc for Toray T300, and 1.7758 g/cc for Hercules IM7.
Dynamical Mechanical Thermo Analysis of High Performance Composites-Influences and Problems
Authors: Wolfrum J. , Ehrenstein G. W. , Avondet M. A.
Published: August 2002

A sensitive method to characterize the thermomechanical behavior of fiber reinforced composites is the dynamic mechanical thermo analysis (DMTA) method. A Round-Robin-Test with five different institutes was conducted to determine the role of the fiber orientation, processing conditions, test apparatus, mode of loading as well as the fiber and matrix materials on the determination of the glass transition temperature ( T g). The results show that the DMTA is a suitable method to analyze T g of long fiber composites; however some major problems have to be taken into consideration. A direct comparison between the results obtained from different DMTA-systems is not possible since the real temperatures in the specimens deviated from the temperatures displayed by the DMTA measuring system. Therefore, no clear and common evaluation method for the glass transition temperature can be established. The significant influences on the T g is proven by the performed statistical analysis.
Application of Ultrasonic Sensors in the Study of Physical Foaming Agents for Foam Extrusion
Authors: Sahnoune Abdelhadi , TatibouËt Jacques , Gendron Richard , Hamel AndrÉ , PichÉ Luc
Published: August 2002

The extrusion foaming process involves several critical steps, in which the physical foaming agent plays a significant role: plasticization, solubility, nucleation and bubble growth. Although these aspects can be studied by different techniques, a novel method based on ultrasonic sensors has proven to provide valuable information with respect to the thermoplastic foaming process. This technique can be either used off-line as a characterization tool to improve our understanding of the foaming agent characteristics, or it can be installed in-line, on the extrusion line, as a control device. Review of the different applications of this technique will be covered in this paper, with numerous examples given to the mixture of PS with CO2. The degree of plasticization of the polymer as a function of the blowing agent concentration will be addressed first, followed by the detection of the conditions prone to induce nucleation, in terms of pressure, temperature, type of nucleating agents and flow conditions. The evaluation of the kinetics of bubble growth will also be explored.
The Influence of “Enzymatic Hydrolysis of Cellulosic Substrates” on the Final Quality of Coated Fabrics
Authors: Zadhoush A. , Khoddami A. , Aghakhani M.
Published: August 2002

Finishing of textile fabrics used in directly coated fabrics plays an important role in the final quality of the products. The amount of surface fibres in the textile substrate is directly related to the amount of surface defects in the final coated fabrics.

In this research work defuzzing was carried out on the selected fabrics by common industrial procedures, such as shearing and singeing. Biopolishing was carried out on loom state fabrics and defuzzed samples. The rate of hydrolysis was studied by measuring the weight loss as well as microscopical analysis. Quantitative analysis of the surface defects was carried out by image analysis. The results obtained show clearly the influence of defuzzing, particularly biopolishing, on the enhancement of the surface quality of PVC coated fabrics.
Management of Allergic Rhinitisand Sinusitis
Authors: Blake Kathryn , Larsen Julie
Published: August 2002

Allergic rhinitis and sinusitis are chronic conditions of the airway and cause significant morbidity. Both can require pharmacotherapy with nonprescription products to relieve symptoms or with prescription products to treat the underlying pathophysiology. Because these diseases are prevalent conditions, the pharmacist is in the unique position of being the first health professional contact for many patients. The pharmacist can assist the patient in selection of nonprescription antihistamines, decongestants, and nasal saline sprays as well as provide instruction on the use of steam therapy, aromatic vapors, and warm compresses for the relief of symptoms. Equally important, the pharmacist can encourage patients to seek care from a physician when treatment with intranasal corticosteroids, antibiotics, and nonsedating antihistamines are needed.
On the Flammability of the Electron-Beam-Induced Grafting of ABS and SBS Copolymers, Studied by LOI/CONE/XPS
Authors: Wang Jianqi , Wu Shaoli
Published: August 2002

Pre-irradiation of the ABS and SBS copolymers, grafting of monomers (MAA and AA) onto both copolymers (ABS/SBS-g-MAA/AA) and ion exchange of the resulted grafts with cations, such as, Na+, K+, Mg2+, Ca2+(ABS/SBS-g-MAA/AA-S(Na+, K+/Mg2+, Ca++) were involved in grafting. A study has been made using the elevated temperature LOI and CONE in this paper focusing on appraisal of the halogen- and phosphorus-free approach imparting flame retardancy to ABS and SBS copolymers and confirmation of carbon accumulation, extent of cross-linking and onset of charring as functions of temperature by the XPS technique. LOI technique at elevated temperatures and cone calorimetry based on the oxygen consumption principle give parameters definitely associated with the grafting rate (Gr), such as TI,, pk-HRR, SEA, EHC, etc., for each step in grafting. Flammability tests show that the grafting induced by electron beam has led to a large increase in LOI [e.g., ABS-MAA-S(Ca2+), +16.5 units], TI [e.g., SBS-g-MAA-S(Mg2+), +42.8°C]; cone (25 kW.m-2): TTI [e.g., ABS-MAA- S(Na+2), +28%] and dramatic decreases in pk-HRR [e.g., ABS-MAA-S(Na+2), -67%), pk-MLR [e.g., ABS-MAA-S(Ca+2), -73%], SEAF [e.g., SBSMAA-S(Ca+2), -65%], etc. Most experimental data were studied and confirmed by XPS data.
Flexible Fixture Device with Magneto-Rheological Fluids
Authors: Tang X. , Zhang X. , Tao R.
Published: August 2002

In manufacturing, fixtures are required to locate parts in a correct position to ensure machining accuracy. Especially for machining on irregular-shaped work-pieces and fine parts, flexible fixtures are in demand to reduce non-machining time. The quick phase change and strong yield strength of MR fluids lead us to investigate the possibility to produce MR-fluid-flexible-fixture. The yield strength and pre-yield elastic modulus are the key issues for a flexible fixture. However, a typical MR fluid currently has yield stress about 100 kPa that is not sufficient for flexible fixtures. To overcome the difficulties, we apply pressure to force single chains into thick columns. This produces a structure-enhanced yield stress. MR fluids in this process produce a yield stress of 800 kPa or above under a moderate magnetic field. The three-dimensional load capacity of MR fluids in this process is strong enough to ensure precision manufacturing. In addition, MR-fluid-flexible-fixtures are environmentally friendly and work at room temperature.
Review: Bacteriocins of Lactic Acid Bacteria
Authors: Cintas L. M. , Casaus M. P. , Herranz C. , Nes I. F. , Hernández P. E.
Published: August 2002

During the last few years, a large number of new bacteriocins produced by lactic acid bacteria (LAB) have been identified and characterized. LAB-bacteriocins comprise a heterogeneous group of physicochemically diverse ribosomally-synthesized peptides or proteins showing a narrow or broad antimicrobial activity spectrum against Gram-positive bacteria. Bacteriocins are classified into separate groups such as the lantibiotics (Class I); the small (<10 kDa) heat-stable postranslationally unmodified non-lantibiotics (Class II), further subdivided in the pediocin-like and anti Listeria bacteriocins (subclass IIa), the two-peptide bacteriocins (subclass IIb), and the sec-dependent bacteriocins (subclass IIc); and the large (>30 kDa) heat-labile non-lantibiotics (Class III). Most bacteriocins characterized to date belong to Class II and are synthesized as precursor peptides (preprobacteriocins) containing an N-terminal double-glycine leader peptide, which is cleaved off concomitantly with externalization of biologically active bacteriocins by a dedicated ABC-transporter and its accessory protein. However, the recently identified sec-dependent bacteriocins contain an N-terminal signal peptide that directs bacteriocin secretion through the general secretory pathway (GSP). Most LAB-bacteriocins act on sensitive cells by destabilization and permeabilization of the cytoplasmic membrane through the formation of transitory poration complexes or ionic channels that cause the reduction or dissipation of the proton motive force (PMF). Bacteriocin producing LAB strains protect themselves against the toxicity of their own bacteriocins by the expression of a specific immunity protein which is generally encoded in the bacteriocin operon. Bacteriocin production in LAB is frequently regulated by a three-component signal transduction system consisting of an induction factor (IF), and histidine protein kinase (HPK) and a response regulator (RR). This paper presents an updated review on the general knowledge about physicochemical properties, molecular mode of action, biosynthesis, regulation and genetics of LAB-bacteriocins.
Cure Characteristics and Mechanical Properties of Natural Rubber—Short Nylon Fiber Composites
Authors: Sreeja T. D. , Kutty S. K. N.
Published: August 2002

Cure characteristics and mechanical properties of short nylon fiber reinforced natural rubber composites have been studied. Minimum torque, (maximum-minimum) torque and cure rate increased with fiber concentration. Scorch time and cure time decreased by the addition of fibers. Properties such as tensile strength, tear strength, elongation at break, heat build up and abrasion resistance were studied both in specimens with both longitudinal and transverse orientation of fibers. Tensile strength showed a marked minimum at 10 phr of fiber loading beyond which it increased with fiber content. Tear strength, abrasion resistance and heat build up increased with the addition of fibers, whereas elongation at break decreased with fiber content. Ageing resistance of the composites was better than that of the gum compound.
Design of Laminated Composite Plates Containing a Hole under In-Plane Loadings
Authors: Anlas Günay , Tüzer Ömer
Published: August 2002

In this work, the design of a symmetric laminated composite plate with a circular opening subject to in-plane loading is considered. Stresses are calculated using Lekhnitskii’s complex variable approach with finite width correction. To take care of the variation of stresses around the hole, Tsai-Wu quadratic failure criterion is modified with a characteristic length defined in terms of the hole size and the laminate configuration; as a result, a procedure like point stress criterion developed by Whitney and Nuismer is followed. Comparisons of strength predictions and experimental data for certain layup are presented to see the validity of the failure model developed. Optimum laminate configuration is obtained by considering the maximum first ply failure strength. An effective, quick and easy method is provided.
Functional Imaging for the Monitoring of Clinical Outcomes of Pharmacotherapy
Authors: Bednarczyk Edward M.
Published: August 2002

Functional and anatomic imaging have been used almost exclusively for diagnostic purposes. Because pharmacotherapy is expected to alter organ function, functional imaging is ideally suited to assess drug effects. The application of functional imaging techniques for this purpose has recently emerged. This paper reviews application of radiopharmaceuticals and nuclear imaging techniques to the assessment of pharmacologic effects in neurology, psychiatry, cardiology, and oncology.
Frequency-Shaping with Spatial Compensators
Authors: Smith G. Clark , Clark Robert L.
Published: August 2002

Practical realizations of adaptive structures should be designed and implemented to maximize performance, robustness and efficiency. A method of frequency-shaping the compensation of an adaptive structure is developed for increased performance, system robustness and efficiency. Robustness is defined as reduced coupling to out-of-bandwidth modes, where model fidelity frequently suffers, and to in-bandwidth modes that are considered not important for control. This method utilizes an open-loop metric of system coupling, through Hankel singular values of the controllability and oberservability Gramians, to determine the optimum transducer placements and sizes. The design metric is maximized with genetic algorithms. This optimum design process is computationally efficient. Results demonstrate that optimizing the design metric with genetic algorithms yields better performance and efficiency when compared to previous optimization methods and forms a basic method of “loop-shaping” by spatial design.
New Technology for Viscoelastic Foam
Authors: Hager Stan , Skorpenske Richard , Triouleyre Sebastien , Joulak Faouzi
Published: August 2002

The production and use of slow recovery “viscoelastic” polyurethane foams have increased rapidly over the past few years. Their unique performance characteristics, which include shape conformance, vibration and sound damping, and energy and shock absorption, make these the foams of choice for many diverse applications such as pillows, mattress toppers, automotive trim, sports and medical equipment, and ergonomic cushions and pads. These diverse applications require a wide range of foam grades with tailored performance properties. New polyol and formulating technology is being developed to meet the increased demands for improved processing, wider grade latitude and improved performance properties of viscoelastic foam. This paper reports the results of systematic experimental design studies that were conducted in the laboratory to help develop this technology. A key advance is the development of polyol compositions that enable the production of high quality, soft viscoelastic foams at 100 index and above. This eliminates processing inconsistencies associated with low index foaming, and yields foams with superior performance characteristics such as improved compression sets, reduced discoloration, and finer cell structure with improved feel. The design studies also identified formulating routes to optimize key foam performance features such as low resilience, slow but complete recovery, maintenance of slow recovery characteristics with use, reduced temperature sensitivity, good airflow, and good strength properties. The results of machine foam studies will be presented along with additional foam performance results.
Effects of Friction on Three-Dimensional Contact Stresses in Pin-Loaded Laminated Composites
Authors: Zhang Chao , Ganesan R. , Hoa Suong V.
Published: August 2002

An investigation is performed to study the effects of friction on the three-dimensional (3D) stress state around pin-loaded holes in laminated composites. The composite pinned joints are modeled as a linear elastic contact problem with friction; therefore, the interactions between the pin with the laminate follow the law of Coulomb friction. An analytical solution for the 3D stress state involved in this problem is developed based upon the variational principle of complementary energy. Compared to the previous research based on a two-dimensional stress assumption, the present solution is innovative, since the out-of-plane effects (i.e., edge effects) near the pin-loaded holes are considered. The present formulations are restricted to the laminated composites with bi-directional fiber orientations, because all the traction and displacement boundary conditions can be satisfied in such type of laminates. Numerical results for pin-loaded cross-ply laminates with different coefficients of friction are presented. It is shown that the effects of friction on the magnitude and distribution of the 3D stress state around pin-loaded holes in laminated composites are significant.
Thermal Conductivity of Unidirectional Reinforced Composite Materials—Experimental Measurement as a Function of State of Cure
Authors: Bailleul J.-L. , Delaunay D. , Jarny Y. , Jurkowski T.
Published: August 2002

The thermal conductivity of a thermosetting polymeric matrix-based composite material is a thermophysical parameter, which varies significantly during the transformation of the matrix. These variations have a considerable effect on heat transfers within a thick piece in the process and therefore on transformation kinetics of the polymer. In order to address the analysis method used to determine the parameter variations according to both temperature and state of cure of the transformation, the experimental device developed by the authors is first described. Then, the results, experimentally obtained by inverse heat conduction with a composite of Fiberglas® and epoxy resin, are compared with those given by an effective thermal conductivity model.
Limitations of Using Membrane Theory for Modeling PVDF Patches on Inflatable Structures
Authors: Williams R. Brett , Austin Eric M. , Inman Daniel J.
Published: August 2002

An underlying goal in structural modeling is to use the simplest mathematics possible that captures the physics of a problem accurately. Inflatable structures are normally fabricated from thin films, so they are often modeled as membranes, i.e., structural elements that cannot resist bending moments. Researchers have recently been looking at active control of inflated structures, so this raises the question of whether membrane theory can account for the effects of surface-mounted piezopolymer patches used as either sensors or actuators. This work discusses these effects on the dynamic behavior of a flat, rectangular coupon section and assesses the patch’s ability to sense and actuate transverse deflections of the thin film substrate using traditional membrane theory. The Rayleigh-Ritz method was employed to approximate the natural frequencies and mode shapes of this layered system. While including the additional mass of the patch, traditional membrane theory was unable to account for the added stiffness of the patch layer. When the piezoelectric behavior of the patch was considered, membrane theory failed to model the PVDF as a useful sensor. Also, excitation of transverse vibrations was not possible using membrane theory, which does not allow application of bending moments. However, PVDF actuation was modeled as an applied in-plane force, which allowed the patch the ability to suppress out-of-plane disturbances by altering the tension in the base layer as a function of applied voltage. This article discusses the limitations associated with using traditional membrane theory to analyze the dynamic behavior of thin-layered systems as well as model the interaction between an active PVDF patch and the torus substrate.
Progressive Failure Analysis of Laminated Knitted Fabric Composites Under 3-Point Bending
Authors: Huang Zheng-Ming , Teng X. C. , Ramakrishna S.
Published: August 2002

The bending behavior of laminated beams reinforced with differently arranged plain-weft knitted fabrics has been investigated in this paper. Experiments were carried out to measure the bending stiffness and strength of six layers knitted fabric rein-forced epoxy composite laminates under 3-point bending. The laminate lay-ups of [0/0/0/0/0/0], [90/90/90/90/90/90] and [0/-45/45/45/-45/0] have been taken into account, where 0 denotes that the fabric wale direction is arranged along the beam axial direction. A simulation procedure is presented to analyze the bending property of the laminated beams based on the bridging micromechanics model and the classical lamination theory. It has been found that the use of a stress failure criterion only is no longer enough for estimating the ultimate bending strength of the laminate. An additional critical deflection condition is also required. By using only the constituent properties, which were measured using bulk material specimens independently, and the fabric knitting and lay-up parameters, the predicted stiffness and strength agree favorably with the experimental data.
The Absorption of Cephalosporin on Vinyl Polymers to Form Antibacterial Surfaces
Authors: Marconi W. , Monopoli G. , Piozzi A. , di Rosa R.
Published: August 2002

In order to obtain antimicrobial polymer compositions potentially suitable for catheter fabrication, a cephalosporin was bonded to ethylene-vinyl alcohol copolymers and to their derivatives containing hydrophilic positively or negatively charged groups. The polymers were characterized by chemical and physico-chemical techniques. The antibiotic was adsorbed at a density of 1.3 mg/cm2 onto the unaffected polymer surface. The density was increased up to 1.78 mg/cm2 when the polymer was derivatized. The elution rate of the antibiotic from the surfaces and its antimicrobial activity were determined. The underivatized polymer has shown antimicrobial activity for 24 h whereas the carboxylated polymer was active for 72 h. During this time 32% of the antibiotic was eluted from the underivatized polymer and approximately 15% from the derivatized polymer.
Shrinkability and Microstructural Properties of Composites Based on Low-Density Polyethylene (LDPE) and Polyurethane (PU) Rubber
Authors: Chowdhury S. Ray , Mishra J. K. , Das C. K.
Published: August 2002

The heat shrinkability of polymers, which depends on their elastic memory, is being utilized in various applications, mainly in the field of encapsulation. The elastic memory can be introduced into the system by the addition of an elastomeric phase. From the technological point of view, low-density polyethylene (LDPE) is an important polymer. Polyurethane shows excellent properties in terms of solvent resistance, oil resistance, and abrasion resistance. Here the blends of low-density polyethylene (LDPE) and polyurethane (PU) were studied with reference to their shrinkability introducing crosslinking in both phases. Various microstructural parameters have been examined to determine their effect on shrinkability. Shrinkability decreases with increase in elastomer content and with increase in cure time in the case of blends of fixed ratio, for all blends. Generally, the crystallinity of a high-temperature (H-T) stretched sample is higher than that of low-temperature stretched samples, which is again higher than that of the original sample. From the continuous cure characteristics studied by Monsanto Rheometer, torque was found to increase with increase in elastomer content. From high-temperature DSC it is found that with increase in PU content stability increases, and further high temperature processing decreases the initial degradation temperature but enhances the rate of degradation.
Toward Smart Surfaces Using High-Density Arrays of Silicon-Based Mechanical Oscillators
Authors: Bourbon Gilles , Minotti Patrice , Htlin Philippe , Fujita Hiroyuki
Published: August 2002

Computer chips and other electronics have been getting faster and cheaper for a long time. But, often overlooked, they are also getting smaller and therefore allowing wearable high-technology to be developed on the near future. Current miniaturization and integration trends will result in the need to assemble ever-smaller systems and to handle smaller and smaller chips and other components that will be too small for humans to manipulate and assemble. As a consequence, the automation infrastructure of the future electronics assembly industry will have to scale with the technology, using fully and entirely automated micromachines such as manipulators and intelligent conveyance systems. The paper investigates, consequently, rapid and accurate positioning systems that will allow very small chips and components to be conveyed and automatically sorted. High-density arrays of silicon-based electrostatic actuators particularly are analyzed, according to their ability to move parts locally with high speed and sub-micrometer positioning accuracy. Actuator densities as high as 1000 actuators/mm are investigated, therefore allowing micrometer silicon based components to be manipulated. Lower densities involving larger actuation cells are also investigated in order to move millimeter size components on a few cm square motive surface. Very first design steps toward future smart surfaces are finally discussed. The paper shows how arrayed silicon based sensors, that can be easily distributed along with arrayed actuators, may provide tactile information from the external world, therefore allowing intelligent conveyance systems to be realized on the near future.
Effects of Shear Stress and Pressure Drop Rate on Microcellular Foaming Process
Authors: Chen Lee , Sheth Himanshu , Wang Xiang
Published: August 2002

The effect of shear stress and pressure drop rate on cell nucleation density during the foaming process has been studied using a foaming process simulator. The major part of this simulator is a test chamber that can be temperature controlled and pressurized with gas. Shear stress can be applied to the polymer melt through a rotor. With this simulator, the effects of shear stress and pressure drop rate can be investigated separately. The three materials tested were PS, unfilled HDPE, and HDPE filled with 5% talc. It was found that both shear stress and pressure drop rate have significant effect on cell nucleation density, although shear stress is generally dominant. The effect of shear stress or pressure drop rate becomes more critical when the saturation pressure is low. The transition pressure is about 1500 psi with PS or unfilled HDPE. The transition pressure reduces to about 500 psi with the filled HDPE, since the filler acts as a nucleation agent and reduces the requirement on saturation pressure for sufficient nucleation.
Polyblend Systems of Polyurethane Rubber and Silicone Rubber in the Presence of Silane Grafting Agent
Authors: Maity M. , Khatua B. B. , Das C. K.
Published: August 2002

Polyurethane elastomer (AU) and silicone rubber (VMQ) form immiscible blends with a low compatibility. In order to improve the compatibility and physical properties of the blends, VMQ was first grafted with vinyl triacetoxy silane (VTAS) by using dicumyle peroxide (DCP) as a grafting initiator; subsequently, it was blended with AU. The state of cure is improved in the case of AU/grafted-VMQ blends. Physical properties like hardness, modulus and tensile strength increased for the AU/grafted-VMQ blend compared to the AU/VMQ blend. IR spectral analysis suggested the probable interaction between the grafted silicone rubber and polyurethane elastomer. High temperature DSC study showed the increment of thermal stability of AU/grafted-VMQ blend. The extraction of single phase in solvent is restricted for AU/grafted-VMQ blend, indicating the interchain crosslinking as confirmed by SEM study.
On the Flash Point of Benzoic Acid—Part 2: Experimental Measurements
Authors: Godefroy J. , Jones J. C. , Fowler G.
Published: August 2002

A previous paper in which it was shown that the widely accepted value for the flash point of benzoic acid cannot be correct was followed by some experimental tests on the compound with a flash point apparatus.
Damage Accumulation During Multiple Stress Level Fatigue of Short-Glass-Fiber Reinforced Styrene-Maleic Anhydride
Authors: Hoppel Christopher P. R. , Pangborn Robert N. , Thomson Robert W.
Published: August 2002

Multi-stress fatigue of short-glass-fiber-reinforced styrene-maleic anhydride (S/MA) composite materials has been studied. Specimens were tested in tension-tension fatigue ( R = 0.1) in two patterns: high-stress fatigue followed by low-stress fatigue (high-low) and low stress followed by high stress (low-high). Results were analyzed using the Palmgren-Miner cumulative damage law. High-low fatigue gave Miner’s sums very close to unity, and Miner’s sums below unity were obtained for low-high fatigue. A minimum value below unity for low-high fatigue corresponded to a regime in which the first block of cycling was carried to 15% of the life.

These results were interpreted by evaluating the evolution of damage and the role of plastic deformation in the fatigue behavior. The high-stress fatigue created a more extensive region of crazing in the matrix material. This plastic deformation increased the mechanical clamping force on the short fibers, making the composite more resistant to subsequent low-stress fatigue testing. When specimens were tested in low-stress fatigue first, cracking occurred in the composite without as much plastic deformation. These cracks were extended by subsequent high-stress fatigue, leading to earlier failure of the composite.