bluuebunny/crossref_metadata_2025 huggingface dataset:
Processing and characterization of ablative composites used in rocket motors
Authors: de Almeida LEN , Cunha FAL , Batista NL , Rocco JAFF , Iha K , Botelho EC
Published: June 2014

The main objective of this research work was to obtain two formulations of ablative composites. These composites are also known as ablative structural composites, for applications in atmospherically severe conditions according to the high-temperature, hot gaseous products flow generated from the burning of solid propellants. The formulations were manufactured with phenolic resin reinforced with chopped carbon fiber. The composites were obtained by the hot compression molding technique. Another purpose of this work was to conduct the physical and chemical characterization of the matrix, the reinforcements and the composites. After the characterization, a nozzle divergent of each formulation was manufactured and its performance was evaluated through the rocket motor static firing test. According to the results found in this work, it was possible to observe through the characterization of the raw materials that phenolic resins showed peculiarities in their properties that differentiate one from the other, but did not exhibit significant differences in performance as a composite material for use in ablation conditions. Both composites showed good performance for use in thermal protection, confirmed by firing static tests (rocket motor). Composites made with phenolic resin and chopped carbon fiber showed that it is a material with excellent resistance to ablation process. This composite can be used to produce nozzle parts with complex geometry or shapes and low manufacturing cost.
Tension design of heated-mandrel winding process based on analytical algorithm
Authors: Xu Jiazhong , Miao Yanan , Qiao Ming , Li Shuang
Published: June 2014

Resin matrix filament wound composite shells are widely applied in the fields of military, aerospace, energy transportation, pressure vessel, and civil engineering. The curing and winding are regarded as the necessary procedures during molding, and they are the key factors affecting the final performance of the composite shells. This paper discusses the application of a new molding process called the heated-mandrel winding process, to take the place of the traditional molding process, which has a two-step procedure. It is proved that the heated-mandrel winding process can not only improve the product quality and production efficiency, but can also reduce the labor cost, without moving the wound shell from the winding machine to the oven. In contrast to the traditional molding process, some properties of the composite formed with the heated-mandrel winding process, including the curing degree and elastic modulus, will be changed because of the heat conduction from the heated mandrel during winding. Therefore, the traditional winding tension system design method is no longer suitable for this new process. Taking the temperature changes into account, this paper uses a theoretical investigation and calculations to suggest a tension system model that describes the relationship between the changeable parameters and the winding tension and to calculate the appropriate tension values for winding, based on the heated-mandrel winding process. The accuracy of the model is verified using an experiment. This paper applies an analytical algorithm based on simple iterative steps to design the tension system. The calculation procedures are simplified, and fewer calculation cycles are required in the analytical algorithm proposed in this paper because it is easier to calculate a few simple linear equations rather than complex nonlinear differential equations under the condition that some initial parameters can be known. As seen during practical application, the model is suitable for a tension system design based on the heated-mandrel winding process and provides further quality improvement in the molding shells.
Social and Environmental Influences on Daily Activity Pattern in Free-Living Subterranean Rodents
Authors: Šklíba Jan , Lövy Matěj , Hrouzková Ema , Kott Ondřej , Okrouhlík Jan , Šumbera Radim
Published: June 2014

Predictable daily activity patterns have been detected repeatedly even in mammals living in stable environments, as is the case for subterranean rodents. Whereas studies on activity of these rodents under laboratory conditions almost exclusively have concerned themselves with the influence of light, many field studies have revealed signs of an association between the activity pattern and daily fluctuations of temperature under the ground. This would assume that behavioral thermoregulation is probably involved. The only exceptions to the relationship between temperature and activity are 2 eusocial mole-rats of the genus Fukomys (Bathyergidae, Rodentia), which indicates that activity patterns could be affected also by social cues. To better understand how social and environmental factors influence the activity pattern in a eusocial mole-rat, we monitored the outside-nest activity in another species of this genus, the Ansell’s mole-rat ( Fukomys anselli), which has a relatively small body mass, high conductance, and more superficially situated burrows. Its daily activity had 1 prominent peak (around 1400 h), and it was tightly correlated with the temperature measured at depth of foraging burrows. Since F. anselli has high thermoregulatory requirements to maintain stable body temperature below the lower critical temperature, we conclude that the observed pattern is probably the result of minimizing the cost of thermoregulation. There were no significant differences in the daily activity patterns of breeding males and females and nonbreeders. Members of the same family group tended to have more similar activity patterns, but consistent activity synchronization between individuals was not proven. From the comparison of available data on all subterranean rodents, we assume that social cues in communally nesting mole-rats may disrupt (mask) temperature-related daily activity rhythms but probably only if the additional cost of thermoregulation is not too high, as it likely is in the Ansell’s mole-rat.
Behavioral Masking and cFos Responses to Light in Day- and Night-Active Grass Rats
Authors: Langel Jennifer , Yan Lily , Nunez Antonio A. , Smale Laura
Published: June 2014

Light not only entrains the circadian system but also has acute effects on physiology and behavior, a phenomenon known as masking. Behavioral masking responses to bright light differ in diurnal and nocturnal species, such that light increases arousal in the former and decreases it in the latter. Comparisons made within a species that displays both diurnal and nocturnal patterns of behavior may provide insight into how masking differs between chronotypes and the association between mechanisms controlling masking and the circadian drive for activity. Nile grass rats ( Arvicanthis niloticus) provide a useful model for studying such issues because when these animals are housed with running wheels, some run primarily during day, while others run at night. Here we compared behavioral masking responses to 2-h pulses of light and darkness given across a 12:12 light/dark cycle in day-active (DA) and night-active (NA) grass rats. Both wheel-running activity (WRA) and general activity (GA) were monitored. Light pulses at night tended to increase both WRA and GA overall in the DA grass rats, while in NA grass rats, light pulses significantly reduced WRA but had no effect on GA. Dark pulses during the day tended to decrease both WRA and GA in the DA grass rats, while in the NA grass rats, they tended to increase WRA in the early day but had no effect on GA overall. Next, we measured cFos expression within 2 brain areas potentially involved in masking, the intergeniculate leaflet (IGL) and the olivary pretectal area (OPT), of DA and NA grass rats either sacrificed on a control night or after a 1-h light pulse at ZT14. In DA grass rats, light at ZT14 induced cFos in the IGL and OPT, whereas in NA grass rats, cFos levels in both structures were high at ZT14 and were not altered by a 1-h light pulse. Overall, these results suggest that masking responses to light and darkness are dependent on the chronotype of the individual and that the responsiveness of the IGL and OPT to light may depend on or contribute to the behavioral response of these animals.
Effects of TWIN-OF-EYELESS on Clock Gene Expression and Central-Pacemaker Neuron Development in Drosophila
Authors: Glossop Nicholas R.J. , Gummadova Jennet O. , Ghangrekar Indrayani , Hardin Paul E. , Coutts Graham A.
Published: June 2014

Circadian oscillators are autonomous molecular rhythms that reside in cells to align whole-organism physiology and behavior to the 24-h day. In flies, as in mammals, the oscillator operates in cells that coexpress CLOCK (CLK) and CYCLE (CYC). Recent work in Drosophila has shown that CLK is unique in its ability to generate heterologous oscillators, indicating that Clk gene expression defines the circadian cell fate. Here, using standard in vitro and in vivo techniques, we show that TWIN-OF-EYELESS (TOY; dPax6) regulates Clk expression in small ventrolateral neurons (s-LNvs) that coordinate sleep-wake cycles. Crucially, toy binds multiple sites at the Clk locus, is expressed independent of CLK-CYC in LNvs, regulates CLK protein levels under optimal photoperiodic conditions, and sets clock-speed during endogenous free-run. Furthermore, TOY is necessary for the onset of Clk expression in LNvs during embryogenesis. We propose that TOY contributes to a transcription complex that functions upstream of the oscillator to promote Clk expression in s-LNvs.
Toujours plus, toujours mieux ? Effet contre-intuitif de l’évaluation des attributs environnementaux du produit par le consommateur
Authors: Jongmans Éline , Jolibert Alain , Irwin Julie
Published: June 2014

L’objectif de cet article est d’étudier l’influence du nombre d’attributs environnementaux d’un produit de consommation sur le poids associé à ces attributs. Les résultats de deux expérimentations montrent que les consommateurs tendent à systématiquement sous-évaluer les attributs environnementaux (certifiés ou non) lorsqu’ils sont présentés ensemble, par rapport à une évaluation des mêmes attributs présentés séparément. Cet effet non rationnel, appelé effet d’inclusion, est plus fort pour les individus davantage préoccupés par l’environnement et impliqués envers les écolabels. Les conclusions de cette étude remettent en question l’intérêt de cumuler de tels attributs pour les consommateurs de produits pro-environnementaux.
Les perspectives culturelles de la recherche en marketing en faveur du développement durable dans les pays en développement
Authors: Arnould Eric J.
Published: June 2014

A travers son expérience de recherches dans des pays en développement, Eric Arnould rappelle que l’origine des questionnements sur le développement durable est notamment liée aux problèmes des pays du Sud à accéder aux processus de développements sains et aptes à assurer le bien-être de leurs populations. Dès lors, penser et agir le marketing dans une perspective de développement durable nécessite de poser les problèmes à deux niveaux : le niveau macro pour comprendre les liens entre les marchés locaux et internationaux, puis le niveau culturel pour comprendre les comportements des acteurs économiques dans leurs contextes institutionnels spécifiques.
Hemocompatibility evaluation of small elastomeric hollow fiber membranes as vascular substitutes
Authors: Mercado-Pagán Ángel E , Ker Dai Fei Elmer , Yang Yunzhi
Published: June 2014

One of the main challenges for clinical implementation of small diameter vascular grafts (SDVGs) is their limited hemocompatibility. Important design specifications for such grafts include features that minimize the long-term risks of restenosis, fouling, and thrombus formation. In our lab, we have developed elastomeric hollow fiber membranes (HFMs), using a phase inversion method, as candidates for SDVGs. Here, we present our results for in vitro hemocompatibility testing of our HFM under flow and static conditions. Our results showed that the polymer-based HFMs do not damage the integrity of human red blood cells (RBCs) as shown by their low hemolytic extent (less than 2%). When analyzed for blood cell lysis using lactate dehydrogenase (LDH) activity as an indicator, no significant differences were observed between blood exposed to our HFMs and uncoagulated blood. Analysis of protein adsorption showed a low concentration of proteins deposited on the surfaces of HFM after 24 h. Platelet adhesion profiles using human platelet-rich plasma (PRP) showed that a low level of platelets adhered to the HFMs after 24 h, indicating minimal thrombotic potential. Under the majority of conditions, no significant differences were observed between medical-grade polymers and our HFMs. Eventual optimization of hemocompatible elastomeric HFM vessel grafts could lead to improved tissue vascularization as well as vascularized, tissue-engineered scaffolds for organ repair.
Assessing cement injection behaviour in cancellous bone: An in vitro study using flow models
Authors: Bou-Francis Antony , López Alejandro , Persson Cecilia , Hall Richard M , Kapur Nikil
Published: June 2014

Understanding the cement injection behaviour during vertebroplasty and accurately predicting the cement placement within the vertebral body is extremely challenging. As there is no standardized methodology, we propose a novel method using reproducible and pathologically representative flow models to study the influence of cement properties on injection behaviour. The models, confined between an upper glass window and a lower aluminium plate, were filled with bone marrow substitute and then injected (4, 6 and 8 min after cement mixing) with commercially available bone cements (SimplexP, Opacity+, OsteopalV and Parallax) at a constant flow rate (3 mL/min). A load cell was used to measure the force applied on the syringe plunger and calculate the peak pressure. A camera was used to monitor the cement flow during injection and calculate the following parameters when the cement had reached the boundary of the models: the time to reach the boundary, the filled area and the roundness. The peak pressure was comparable to that reported during clinical vertebroplasty and showed a similar increase with injection time. The study highlighted the influence of cement formulations and model structure on the injection behaviour and showed that cements with similar composition/particle size had similar flow behaviour, while the introduction of defects reduced the time to reach the boundary, the filled area and the roundness. The proposed method provides a novel tool for quick, robust differentiation between various cement formulations through the visualization and quantitative analysis of the cement spreading at various time intervals.
Antimicrobial megaprostheses supported with iodine
Authors: Shirai Toshiharu , Tsuchiya Hiroyuki , Nishida Hideji , Yamamoto Norio , Watanabe Koji , Nakase Junsuke , Terauchi Ryu , Arai Yuji , Fujiwara Hiroyoshi , Kubo Toshikazu
Published: June 2014

Deep infection associated with implants remains a serious complication of orthopedic surgery. We developed iodine coating for titanium implants. In this study, we performed a clinical trial of iodine-coated megaprostheses to evaluate its safety and antibacterial effects. Forty-seven patients with malignant bone tumor or pyogenic arthritis were treated using iodine-supported titanium megaprostheses between July 2008 and May 2013. The mean age was 53.6 years (range, 15–85 years). Twenty-six patients were males and 21 were females. The diagnoses included malignant bone tumor in 29 cases, infected total knee arthroplasty in 11 cases, chronic osteomyelitis due to pyogenic arthritis in six cases and loosening of total knee arthroplasty in one case. The iodine-supported implants used were 42 Kyocera Limb Salvage System and five KOBELCO K-MAX K-3. These megaprostheses were used to prevent infection in 21 patients, treat active infections in 26 patients. The mean follow-up period was 30.1 months (range, 8–50). Infection was prevented in 20 out of 21 patients. Only one patient had surgical site infection caused by Pseudomonas aeruginosa and was cured by intravenous administration of antibiotics alone without removal of the implant. In 26 treatment cases involving one- or two-stage revision surgery, infection subsided without any additional surgery. In all cases, there were no signs of infection at the time of the last follow-up. White blood cell and C-reactive protein levels returned to normal within four weeks after surgery. To confirm systemic effects of iodine, thyroid hormone levels in the blood were examined. Abnormalities of thyroid gland function were not detected. Loosening of the implants was not observed. Excellent bone ingrowth and ongrowth were found around iodine-supported megaprostheses. The iodine-supported titanium megaprostheses are highly effective and show promise for the prevention and treatment of infections in large bone defects. No cytotoxicity or adverse effects were detected with this treatment.
A Review and Correction of the Errors in Loftus and Guyer on Jane Doe
Authors: Olafson Erna
Published: June 2014

There are so many errors among those facts that can be checked in the Loftus and Guyer articles under review that they cast doubt on the accuracy of the alleged facts in these articles that cannot be easily checked. Loftus’s and Guyer’s two articles, published in a newsstand magazine instead of a peer-reviewed journal, show a pattern of inaccuracy that casts doubt on their claims to have conducted a skeptical, objective inquiry. Some, but not all of these errors, were corrected in a 2009 article Geis and Loftus published in a peer-reviewed journal, although Loftus does not acknowledge in that article her earlier inaccuracies. This article corrects the record about the conclusions drawn in the Corwin and Olafson article published in 1997 and clarifies the history about Corwin’s involvement in the Taus case.
Protecting Scientists, Science, and Case Protagonists
Authors: Dalenberg Constance J.
Published: June 2014

This article is a discussion of the articles by Nicole Taus Kluemper, Erna Olafson, Frank Putnam, Laura Brown, Ross Cheit, and Gerald Koocher. The papers center on the issues raised by a decision by two psychologists to break the confidentiality of a case study published by David Corwin and Erna Olafson to gather information to support an alternative theoretical view of the case. The article reviews best understandings of the justifications proposed by the psychologists, who saw themselves as investigative reporters, discusses the papers that have been submitted, and proposes enhanced ethical guidelines and increased professional discussion of these issues.
Composite Beams on Elastic Foundations
Authors: Naik Nikhila
Published: June 2014

The behavior of deep composite beams on elastic foundation under transverse concentrated load has been evaluated using higher order shear deformation theory. A trigonometric term is utilized to accurately describe shear deformation. The deformation and the induced stress state as a function of beam mechanical properties have been investigated.
Dynamic Mechanical Analysis of Low-Density Polyethylene with Glass Beads
Authors: Liang J. Z. , Li R. K. Y. , Tjong S. C.
Published: June 2014

Glass bead-filled low-density polyethylene (LDPE) composites have been analyzed employing dynamic mechanical analysis. The storage moduli of the composites decrease rapidly in a temperature range from-150 to-1 00I C and from-50 to 00C, and then decrease gently with a rise of temperatures. The mechanical damping increases with a rise of temperatures and decreases with increasing the weight fraction (4)) of glass beads when 4) is greater than 1 0%. The glass transition temperature varies with 4) and is the lowest at 4) = 10%. Under the same test conditions, the storage modulus of the LDPE filled with glass beads pretreated with a silane coupling agent is greater than that of the unpretreated system but is contrary to mechanical damping. The relative storage modulus calculated by using an equation presented in previous work was close to that measured from the composites under the test conditions.
Inclusion Method in the Work-Hardening Behavior of Transversely Isotropic Composites
Authors: Chao Lu-Ping , Huang Jin H.
Published: June 2014

This study presents the work-hardening behavior of fibrous composite materials in uniaxial tension for embracing the variational principle and the equivalent inclusion method. The linear work-hardening rate is forecast with the composite matrix perfectly plastic and the fibers (inhomogeneities) plastically nondeforming. Notably, when both the matrix and inhomogeneities are transversely isotropic with different elastic moduli, the yielding stress and the work-hardening rate are obtained in closed forms with the shapes of the inhomogeneities being elliptical, ribbon-like, rod-shaped, and penny-shaped. The results of the study show that the work-hardening rate is proportional to the volume fraction of the inhomogeneities. Meanwhile, the work-hardening rate and the yielding stress are dependent on the shape and the volume fraction of the inhomogeneities but not on the size of the inhomogeneities.
Tertiary Recycling of Automotive Plastics and Composites
Authors: Allred R. E. , Busselle L. D.
Published: June 2014

The use of engineering plastics and composites in automotive applications is increasing to achieve weight reductions and the accompanying performance increases. These materials are difficult to recycle using conventional technologies because they are contaminated with metals and paints or are cross-linked polymer structures. A novel tertiary recycling process is being developed as an economical means for recycling scrap automotive plastics and composites. Early development work on this process for recycling scrap aerospace composites and electronics shows that it can convert a variety of polymers and composites into low-molecular-weight hydrocarbons at temperatures near 300'C. The hydrocarbons produced can then be reused as chemicals, fuels, or monomers. Metal, glass, fillers, and fibers are separated from the hydrocarbons during the process and can be reclaimed for reuse. Initial feasibility studies have shown that the proposed catalytic conversion process is effective for recycling plastics and composites used in automotive parts. This process does not require presorting of plastic wastes and allows fibers and fillers to be reclaimed for reuse. Conversion products from recycling sheet molding compounds (SMC), auto shredder residue (ASR), and scrap mixtures of automotive plastic body panels show that commercial recycling plants based on the catalytic conversion process should be an economical alternative to landfilling.
Determination of Stress Intensity Factors in Cracked Bonded Composite Joints
Authors: Penado F. Ernesto
Published: June 2014

In this paper, a method is presented that facilitates the determination of stress intensity factors in composite bonded joints with interfacial or interlaminar cracks. The method is based on a global/local concept, where the displacements and stresses away from the crack tip are found by a conventional finite element analysis. In the neighborhood of the crack tip singularity, where the finite element results alone no longer converge, an elasticity solution is constructed using an eigenfunction expansion of the stresses and displacements. It was shown that the method allows accurate determination of stresses and stress intensity factors at the crack tip (within 5% of reference solutions) with a relatively small computational effort by using a coarse FE mesh. In addition, the method does not require special finitelements and can be used with any existing finite element code. An equivalent intensity factor [ILLEGIBLE] that captures the combined effect of KI and KII on failure was defined. Numerical results indicated that, out of various interfacial and interlaminar cracks studied, the largest value of the equivalent intensity factor occurs at the interlaminar crack in the first ply interface of the adherend near the adhesive, but not at the adherend-adhesive interface. These results are consistent with the experimental observation that failure of composite bonded joints typically occurs by delamination of the adherend near, but not at, the adhesive.
A Unified Micromechanical Model for the Mechanical Properties of Two Constituent Composite Materials. Part I: Elastic Behavior
Authors: Huang Zheng Ming
Published: June 2014

This series of papers reports a new, general, and unified micromechanical model for estimating the three-dimensional mechanical properties of a composite made from two isotropic constituent materials, i.e., continuous fiber and matrix. The present paper focuses on model development and its application to the prediction of the composite elastic property. The most important feature of this model is that the stresses generated in the constituents in a representative volume element of the composite are correlated with a bridging matrix. Based on this bridging matrix, those required quantities for the composite follow easily. A general routine to determine the bridging matrix elements is presented, and a set of explicit expressions of them for simulating a transversely isotropic composite is given. The bridging matrix depends on the physical as well as the geometrical properties of the fiber and matrix materials. For a fixed geometry, the bridging matrix can depend only on the physical properties of the constituents. This feature makes it easy to extend the present bridging matrix to include any inelastic deformation effect from the constituents and to establish a unified model to simulate, in addition, the plastic, strength, rubber-elastic, and laminate failure behaviors of fibrous composites, which will be addressed subsequently. Only linear elastic properties are considered in the present paper. The model has been applied to estimate the elastic properties of two unidirectional composites and a knitted-fabric-reinforced composite. Good agreement has been found between the predicted and available experimental data.
Fracture and Damping of Ionomer Interleaved Epoxy Composites
Authors: Akimoto A. , Shonaike Gabriel O. , Usui Y. , Aoki Y. , Murakami A. , Matsuda S. , Hojo M. , Ochiai S.
Published: June 2014

A study was conducted on the effect of interleaving on laminated composites. An ethylene-based ionomer of various compositions and a silane-modified ethylene-vinyl-acetate were selected as the interleaving materials. The glass transition temperatures (Tg) of the ethylene-based polymers ranged from-24 to 50'C. The fracture toughness (GIc), impact performance, and damping properties of the composites were evaluated. G1c of interleaved composites was about 3-5 times higher than that of non-interleaved. However, G1c was sensitive to the composition of the interleaf. The silane-modified ethylenevinyl-acetate had the highest fracture toughness. The impact properties of the interleaved materials were superior to those of non-interleaved, as evident from CAI testing where delamination occurred at an early stage in non-interleaved samples. The damping ratio of interleaved materials was found to be more than 100 times higher than in the original material.
Compression Molding of Warp-Knitted PET/GF Based Composites: Influence of Forming Temperature on Consolidation Quality and Impact Properties
Authors: Bernhardsson Jonas , Shishoo Roshan
Published: June 2014

The objective of this work has been to study the influence of processing temperature during compression molding on the consolidation quality and mechanical properties of warp-knitted fabric-based composites made of commingled yams containing glass fiber (GF)/polyethylene terephthalate (PET). The consolidation quality in terms of void content and uniformity of fiber distribution was studied on unidirectional and cross-ply laminates. The mechanical properties studied were flexural strength, flexural modulus, Izod impact strength, and drop-weight impact resistance. The influence of forming temperature on fiber-matrix adhesion was studied by measuring the transverse flexural strength and SEM analysis. SEM analysis was also used to analyze the mode of fracture during impact. The results in this paper suggest that consolidation quality as defined by fiber distribution is strongly dependent on molding temperature. The transverse strength increased significantly with processing temperature, indicating an increase in fiber-matrix interfacial adhesion with increasing processing temperature. The increased interfacial adhesion influenced the Izod strength and drop-weight impact behavior of the laminates.
Performance of a Filament Wound Graphite/Thermoplastic Composite Ring-Stiffened Pressure Hull Model
Authors: Lamontia Mark A. , Gruber Mark B. , Smoot Michael A. , Sloan Jay , Gillespie John W.
Published: June 2014

The design, analysis, manufacture, and hydrostatic testing results of a 24- inchdiameter ringstiffened pressurehull model are presented. The AS-4 graphite/PEEK cylinder is manufactured using a nonautoclave insitu filament winding and tape laydown process. The cylinder incorporates 5 hoopwound rings and a shell (hoop/axial construction) that are integrally wound during manufacture. Ultrasonic inspection in conjunction with optical microscopy of end rings indicates that high quality is achieved with a void content of less than 1%. Translation of coupon data into the structure is quantified by subcomponent tests that measure insitu properties (A and Bbasis allowables) including shell axial compressive stiffness and strength and interlaminar shear strength. Analysis of the structure indicates that high interlaminar shear stress exists in the ring fillet areas. Subcomponent tests with supporting analysis to design the test method indicated that this failure mode was not critical. Design and analysis efforts focused on midbay and endbay performance. Axial compressive stress concentrations in the endbay were reduced by incorporating local increases in shell thickness and a steel insert ring that provided radial constraint of the shell to reduce the probability of an endbrooming failure mode. Steel hemispherical heads were designed and manufactured to further reduce axial compressive stress concentrations in the endbay. The test model was instrumented with strain gages and acoustic emission sensors and tested at Carderock Division, Naval Surface Warfare Center (CD-NSWC). Increments in pressure were followed by a 5-minute dwell time. Acoustic emission ceased for all pressures except the last two increments at 5250 and 5500 psi. The collapse pressure of 5500 psi was within 3% of our Bbasis prediction. The cylinder weight-to-displacement ratio, W/D, was 0.212 (unitless). Axial compression failure occurred in the cylinder midbay in agreement with our analysis.
Predictions and Experimental Verification of Residual Stresses in Thermoplastic Composite Cylinders
Authors: Tzeng Jerome T.
Published: June 2014

A model was proposed to predict residual stresses in thermoplastic composite cylinders fabricated using in-situ consolidation processes. A series of poly-ether-ketone-ketone (PEKK)-based glass and graphite composite cylinders with various layup constructions were fabricated to verify the residual stress predictions. The resin viscosity and storage modulus of the polymer were measured for analysis. A "split ring experiment" shows a fairly reasonable agreement between the predictions and test data from an application point of view.
Effect of Testing Temperature on Interlaminar Fatigue Crack Growth in Fabric-Reinforced Thermoplastic Composites
Authors: Christopoulos G. C. , Paipetis S. A. , Walter R. , Friedrich K.
Published: June 2014

The interlaminar fatigue crack growth under mode I and mode II loading conditions in a temperature testing environment from 60'C to + 80°C has been investigated. Materials used to perform the mechanical tests were fabric-reinforced composite systems with either semicrystalline or amorphous thermoplastic matrices. For reference purposes, traditional epoxy-matrix composites reinforced with the same type of fibers were used. As a general conclusion, it can be stated that the fracture process is a complex interaction of parameters such as the matrix and fiber type, the loading conditions, and the testing temperature environment.
Self-Reinforced Prepregs, Laminates and Injection Moldings of LCP/LCP Blends
Authors: Ding R. , Isayev A. I.
Published: June 2014

Self-reinforced prepregs (sheets) were prepared by stretching sheets made of blends of two LCPs. LCP1 was based on 6-oxy-2-naphthoyl, and p-oxybenzoyl moieties. LCP2 was based on p-oxybenzoyl, terephthaloyl, and hydroquinone moieties. LCP's were blended, at the temperature at which both components were melt processible, by a single-screw extruder followed by a static mixer, coat-hanger die and stretching device. The prepared prepregs were laid up in multi-layers in the stretching direction and 45 degrees with respect to each previous layer. The lay-ups were compression molded into laminates at a temperature below the melting point of LCP2 but above that of LCP1. The formation of self-reinforcement of one LCP by the other as a function of the processing conditions was studied. The LCP blends in the form of prepregs and pellets of unstretched blends were also injection molded at the barrel temperature below the melting point of LCP2. The rheological and thermal properties and the morphology of the blends were investigated. The mechanical properties of prepregs, laminates with controlled anisotropy, and injection molded samples were measured. Structure-processing-property relationships were analyzed, and the differences in behavior of LCP/LCP and LCP/thermoplastics systems were identified.
Structural Similitude and Scaling Laws for Buckling of Cross-Ply Laminated Plates
Authors: Simitses G. J. , Rezaeepazhand J.
Published: June 2014

The increasing use of laminated composite components for a wide variety of applications in aerospace, mechanical, and other branches of engineering requires extensive experimental evaluation of any new design. Thus, it is extremely useful if a fullscale structure can be replaced by a similar scaled-down model, which is much easier to work with. The objective of this study is to investigate problems associated with the design of scaled models. Similitude theory is employed to develop the necessary similarity conditions. Both complete and partial similarity are discussed. The procedure consists of systematically observing the effect of each parameter and corresponding scaling laws. Then acceptable intervals and limitations for these parameters and scaling laws are discussed. In each case, a set of valid scaling factors and corresponding response scaling laws that accurately predict the response of prototypes from experimental models is introduced. Particular emphasis is placed on the cases of buckling of rectangular cross-ply laminated plates under uniaxial compressive and shear loads. This analytical study indicates that distorted models with a different number of layers and different material properties and geometries from those of the prototype can predict the behavior of the prototype with good accuracy.
Quasi-Continuous Fibrils in Blends of Liquid Crystalline and Thermoplastic Polymers at Low LCP Concentration
Authors: Roetting O. , Hinrichsen G.
Published: June 2014

A new technique for blending liquid crystalline polymers (LCPs) with thermoplastic polymers is described. With poly(ethylene terephthalate) as the matrix and Vectra B950 as the LCP, fibers containing quasi-continuous LCP-fibrils can be produced even when the LCP-concentration is very low (1 wt.-% LCP or less). Fragmentation tests show excellent bonding between the components. The elastic modulus of the LCP-containing fibers is significantly increased.
Random-Damage Finite Element for Studying Micromechanical Failure Mechanisms in Advanced Composites
Authors: Slattery Kerry T.
Published: June 2014

A finite element procedure for simulating damage progression in an advanced composite material loaded in fiber-direction tension has been developed. The eight-node, eight-degree-of-freedom element is used to model a small cell of a composite, the properties of which were determined from micromechanical simulations. A Monte Carlo simulation technique is used in the micromechanical simulation to characterize the random degradation paths that this cell can follow when subjected to axial tension. These results are synthesized using a neural network to efficiently determine the expected value and variance of the degradation of the random-damage finite element given the current state of the element. Results from failure simulations of Kevlar/epoxy composites are presented and compared to experimental results.
The Effect of GFR (Glass-Fiber Reinforcement) on the Composition-Property Balance of Compatibilized Recycled Polyolefinic Blends
Authors: Adewole Akin , Dackson Keith , Wolkowicz Mike
Published: June 2014

The effect of 20% glass-fiber reinforcement on the composition-property balance of compatibilized HDPE (post consumer) and an industrial waste PP was investigated in a two-stage compounding process, using statistical design of experiments. Glass-fiber reinforcement strongly altered the physical properties of the compatibilized blend; it eliminated the previously observed [6] two factor interactions between HDPE and the Kraton rubber compatibilizer.
Physical Aging of Glass-Fiber-Reinforced Nylon 6,6 in Automobile Underhood Parts
Authors: Bigg D. M. , Kanellopoulous V.
Published: June 2014

The use of polymers for under-the-hood automobile parts is growing rapidly. During driving, these parts are exposed to a wide range of potentially harmful conditions, including high temperatures and corrosive chemicals. Such exposure conditions can cause changes in a polymer that might affect its long-term performance. The aging of polymers subjected to the environmental conditions existing under the hood of an automobile has not been extensively investigated. In fact, there has been little quantification of the exact conditions experienced by most of the parts used under the hood of automobiles. This study was conducted to determine the physical aging characteristics of glass-fiberreinforced nylon 6,6. This material is widely used in automobile underhood applications. Two specific glass-fiber reinforced nylon 6,6 parts were examined: a radiator header and an oil cap. The program has determined the environmental thermal stresses experienced by these parts during an instrumented driving run. The physical aging behavior of the glass-fiber-reinforced nylon 6,6 parts was investigated under controlled, accelerated laboratory conditions and after actual use in automobiles driven for various distances.
Tensile and Compressive Deformation of a Short-Glass-Fiber-Reinforced Liquid Crystalline Polymer
Authors: Li R. K. Y. , Lu S. N. , Choy C. L.
Published: June 2014

Results of tensile and compression tests on a short-glass-fiber-reinforced thermotropic liquid crystalline polymer are presented. The effect of strain rate on the compression stress-strain characteristics has been investigated over a wide range of strain rates e between 10-4 and 350 s'l. The low-strain-rate tests were conducted using a screw-driven universal tensile tester, while the high-strain-rate tests were carried out using the split Hopkinson pressure bar technique. The compression modulus was shown to vary with log10 (ė) in a bilinear manner. The compression modulus is insensitive to strain rate in the low-strain-rate regime (ė = 10-4 - 10-2 s-'), but it increases more rapidly with ė at higher ė. The compression strength changes linearly with log10 (ė) over the entire strain- rate range. The fracture surfaces were examined by scanning electron microscopy.
Energy Absorption Behavior of Carbon-Fiber-Reinforced Thermoplastic Composite Tubes
Authors: Ramakrishna S. , Hamada H. , Maekawa Z. , Sato H.
Published: June 2014

The primary objective of this work was to study the energy absorption characteristics of carbon-fiber-reinforced thermoplastic composite tubes. Composite tubes with different thermoplastic matrices-polyetheretherketone (PEEK), polyetherimide (PEI), polyimide (PI), and polyarylsulfone (PAS) -have been investigated. Fiber orientations of 0°,±5°±10°, ±15°, ±20°, ±25° and ±30° with respect to the axis of the tube were used. Among the thermoplastic tubes investigated, the carbon fiber/PEEK tubes displayed the highest specific energy absorption capability. This was attributed to the superior fracture toughness of the carbon fiber/PEEK composite material and a large number of frond splits and fractured fibers in the crush zone. The specific energy absorption capability was dependent on the fiber orientation. Efforts have been made to relate the change in specific energy to the variation of microfracture processes in the crush zone.
Buckling of Moderately Thick Composite Cylindrical Shells under Destabilizing Loads
Authors: Tabiei Ala
Published: June 2014

The instability of perfect, laminated, circular cylindrical shells with fixed ends under the action of uniform axial compression, lateral pressure, and torsion is investigated. The analysis is based on nonlinear kinematic relations where the effect of transverse shear deformation is taken into account. Three theories (higher order shear deformation theory, first-order shear deformation theory, and classical) are compared to determine their range of applicability in predicting critical conditions for moderately thick cylindrical shells under the action of various loads. Also, the effects of stacking sequence, radius-to-thickness ratio, and length-to-radius ratio are assessed. The results obtained indicate that the first-order shear deformation theory with a proper shear correction factor is a good candidate for the analysis of moderately thick laminated cylindrical shells.
A Technique for Coating Aramid Fibers by Recycling of Aramid-Based Thermoplastic Composites
Authors: Poulakis J. G. , Arvanitopoulos C. D. , Papaspyrides C. D.
Published: June 2014

Recycling of thermoplastic composites may simultaneously result in coating the reinforcing fibers contained within a thermoplastic film. Such a coating is created when recycling is based on the solution/reprecipitation method as follows: The composites are exposed to a dissolution process, and consequently the polymer/fiber solution is filtrated, causing the reinforcing agent and the polymer matrix to be separated. The polymer content remaining on the fibers decreases when the washing conditions become more vigorous. The concept was applied to ionomer-based composites containing 15% w/w aramid fibers in a random in-plane orientation. The so-recycled aramid fibers, being coated with ionomer, were then incorporated in the same polymer matrix but of virgin quality. In this paper, results on the tensile performance of these second-generation composites are presented, revealing a considerable improvement in agreement with previous studies on glass-based thermoplastic composites.
An Overview of Recycling Issues for Composite Materials
Authors: Henshaw John M. , Han Weijian , Owens Alan D.
Published: June 2014

A review of the major issues surrounding the postuse disposal of polymer composite materials is presented. Composites are compared to unreinforced plastics in terms of production volume and the technologies available for reprocessing. Not surprisingly, composites comprise a very small fraction of the plastics waste stream. In highvolume applications such as automobiles, however, there are reasons to be concerned about composites recycling. The fundamental categories of dealing with waste (burning, burying, reusing, or using less in the first place) are described in relation to plastics and composites. Reprocessing technologies with applications for composites are reviewed. For thermosetmatrix composites, processes involving regrinding waste materials and using them as filler for other polymer processes show promise. For thermoplasticmatrix composites, processes involving grinding and remolding by injection or compression molding are promising. Applications for recycled composites, without which reprocessing is futile, are also reviewed.
The Influence of Cooling Conditions on the Mechanical Properties of Commingled Yarn Composites
Authors: Shonaike G. O. , Hamada H. , Maekawa Z. , Matsuda M. , Yuba T. , Matsuo T.
Published: June 2014

The influence of cooling conditions on the bending properties and Mode I interlaminar fracture toughness of commingled PET/GF and PA6/GF composites was investigated. The morphology and thermal properties of the composites were studied using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC).

The results show that cooling conditions had no major effect on bending properties, but the fracture toughness (GC) was affected; i.e., fracture toughness of gradual cooling was lower than rapid cooling. The bending properties are not significantly affected by crystallinity, but GC is strongly influenced by the level of crystallinity in the matrix resin.
Predicting Warpage of Injection Molded Fiber-Reinforced Plastics
Authors: Zheng R. , McCaffrey N. , Winch K. , Yu H. , Kennedy P.
Published: June 2014

This paper describes a computational model for the warpage analysis of injection molded short-fiber-reinforced thermoplastics. In the analysis, the molded part's warpage is predicted from the calculated fiber orientation, the volumetric shrinkage, and the thermo-mechanical properties of the fiber and the polymer. Results for a real injection molded part are presented to demonstrate the application of the method. Predicted warpage results are in good agreement with experimental observations. The analysis allows isolation of the cause of warpage, and the fiber orientation effect was found to be dominant.
Moisture-Induced Degradation of Glass/Epoxy Filament-Wound Composite Tubes
Authors: Chiou P. -L. , Bradley W. L.
Published: June 2014

The effect of simulated seawater exposure on the burst strength and stress rupture strength of glass/epoxy filament-wound composite tubes has been examined using hydraulic burst and stress rupture tests. The absorption of 5 wt% simulated seawater during aging prior to testing has a reduction on the burst strength of the tube by 20% compared to unaged composite tubes. Strain gages and acoustic emission techniques were used to monitor the tests. The acoustic emission characteristic is different for the aged tube, giving indications of damage initiation at a much lower level of pressurization. In stress rupture tests, times to rupture of tubes tested in air and tested in simulated seawater immersion were found to be similar. This surprising result is thought to be due to the significant incipient void content introduced during manufacture of the tubes.