bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Processing Parameters on Consolidation Quality of GF/PP Commingled Yarn Based Composites
Authors: Bernhardsson Jonas , Shishoo Roshan
Published: June 2014

Investigations have been carried out to study the effect of processing parameters, namely holding time, temperature, and pressure, on the consolidation quality and mechanical properties of GF/PP commingled yam based composites. The consolidation quality has been defined in terms of the void content in the laminate, and the mechanical property of the composite studied was short-span flexural strength. The results show that the greatest effect on the strength is due to processing temperature, followed by holding time. The increased strength due to increased holding time has been explained in terms of a decrease in void content and increased interfacial fiber-matrix adhesion.A statistical model was developed for optimizing processing parameters, and the results show excellent prediction of the required process parameters. It can be concluded that the statistical design methodology provides a useful means of studying and optimizing the processing parameters in the production of composites.
Material Selection/Fabrication Issues for Thermoplastic Fiber Placement
Authors: Sharp Richard , Holmes Scott , Woodall Cindy
Published: June 2014

The Manufacture of Advanced Composite Submarine Structures (MACSS) program is part of the Advanced Research Projects Agency (ARPA) Maritime Systems Technology Office, Advanced Submarine Technology (AST) program. The program is developing the material product forms, processes, and equipment for automated fabrication of lowcost composite submarine structures. These developments will be demonstrated through fabrication and delivery of subscale and fullscale components of the Composite Dry Deck Shelter (CDDS).

This paper will discuss the McDonnell Douglas Aerospace (MDA) thermoplastic fiber placement process, material selection, and machine that make fabrication of largescale submarine structures possible.
A Strength Prediction Methodology in Regions of Matrix-Dominated Stress Concentrations
Authors: Gipple Karin , Nuismer Ralph , Camponeschi Eugene
Published: June 2014

A point stress criterion based on stress distribution, in conjunction with Hashin's interactive failure criteria for fiber composites, is applied to composite laminates containing throughthickness discontinuities. The point stress criterion assumes that failure occurs when the stress over some distance (characteristic distance) from the discontinuity is equal to or greater than the strength of the material without the discontinuity. The characteristic distance is determined from Vnotched beam specimens cut through the thickness of AS4/3501-6, S2 glass/3501-6, and AS4/PEEK unidirectional laminates. This characteristic distance is then used to estimate the strength of inplane Vnotched beam specimens, transverse flexure specimens, and an AS4/PEEK doublenotched cylinder loaded in axial compression. Good correlation between the predicted and measured strength was obtained for this case. Based on these results, additional investigations with other material systems and more interactive stress states are warranted.
Case Study-Design and Testing of the Brunswick Graphite Composite Ring-Stiffened Thermoset Cylinder
Authors: Leon G. F. , Hall J. C.
Published: June 2014

This paper discusses the design development of a four-foot (1.22 m) diameter graphite/epoxy composite cylindrical marine model. The cylinder was fabricated by Brunswick using an automated filament winding process and was nonautoclave cured in an oven. The paper reviews the details of the design/analysis approach and the assumed failure criteria using 2D solid axisymmetric finite element analyses with the ABAQUS code. Numerous design iterations were made to achieve a balanced design. The model is composed of 50% circumferential, 33% longitudinal, and 17% helical plies, and the ring (blade) stiffener is composed of all circumferential plies. This paper also reviews the assumed material properties used for the design and analysis, and the "asfabricated" material properties used to predict failure of the cylinder due to hydrostatic loading. The final design achieved a weight savings of 44% over an equivalent steel-stiffened cylinder. The cylindrical model was then subjected to a hydrostatic collapse test. A comparison of the test results and the failure prediction is also presented. This work was sponsored by the Maritime Systems Technology Office, Advanced Research Projects Agency.
Buckling Performance of Hydrostatic Compression-Loaded 7-Inch Diameter Thermoplastic Composite Monocoque Cylinders
Authors: Gruber Mark B. , Lamontia Mark A. , Smoot Michael A. , Peros Vasilios
Published: June 2014

The general instability, or buckling performance, of thick compression loaded composite cylinders is not well understood. Few cylinders have been hydrostatically tested that exhibit a well-controlled buckling failure. This work includes the design, fabrication, and test results for two monocoque cylinders tested in hydrostatic compression to measure buckling performance. The design focused on assuring that buckling failure would occur before a strength failure. The analysis accounted for the effects of end cap design and boundary conditions. The two cylinders were insitu thermoplastic filament wound using AS4 Graphite/PEKK and S-2 Glass/PEKK. Quality was excellent, with 1% void volume fraction and negligible waviness. Both cylinders buckled elastically in their respective tests. The test results include acoustic emissions (AE) and measured strains versus pressure. Experimental results show excellent correlation with analytical predictions.
Composite Molded Products Based on Recycled Polypropylene and Woodflour
Authors: Maldas D. , Kokta B. V.
Published: June 2014

Composite materials were prepared from recycled PP and woodflour. The effects of various factors (e.g., the particle size of the woodflour and the concentrations of woodflour, coupling agent-i.e., a mixture of maleic anhydride and dicumyl peroxide-and impact modifier) as well as fire-retardant materials [e.g., mixture of boric acid, Na-borate, and Mg(OH)2] on the mechanical properties of the composites were evaluated. In general, the mechanical properties of the surface-modified woodflour-filled composites were superior to those of unmodified ones. The effects of each component and interactions between them were also statistically analyzed based on an empirical model. The significance of the model coefficients was discussed. In most cases, good correlation of the results was obtained.
Optimization of the Extrusion Process for Glass-Fiber-Reinforced Tubes
Authors: Ausias G. , Vincent M. , Jarrin J.
Published: June 2014

The resistance of short-fiber-reinforced thermoplastic tubes to internal pressure is strongly related to fiber orientation. A new way to increase the degree of orientation in the hoop direction is presented. It consists of injecting a lubricant at the surface of a diverging die. A calculation of flow and fiber orientation in a lubricated die with a divergent final land shows that extensional deformations, which tend to orient the fibers perpendicular to the flow, take place on the entire thickness; in contrast, without lubricant, shear deformations near the surface orient the fibers in the flow direction. Various dies are tested with a 30 wt% short-glass-fiber-reinforced polypropylene. Observations show that, with the lubricated diverging die, the fibers are oriented mainly in the hoopwise direction throughout the tube thickness. Consequently, mechanical properties are increased in this direction. The resistance of the tube is increased by about 40%.
Stochastic Damage Evolution Modeling in Laminates
Authors: Dzenis Y. A.
Published: June 2014

A stochastic mesomechanics model has been developed for damage accu mulation analysis in advanced laminated composites. The model is based on a theory of excursions of random process beyond the bounds. Stochastic strains in the laminate sub jected to random Gaussian inplane loading are calculated using lamination theory and random functions theory. Probabilistic variation of stiffness and strength characteristics of plies is used in the analysis. A stochastic version of the maximum strain failure criterion is applied for damage probability calculation. A mesovolume concept is utilized in model ing stiffness degradation. The capabilities of the model are illustrated by predictions of damage accumulation and failure in a Kevlar®/epoxy [0/ 4 30/90]. laminate under quasi stationary, longterm stationary, and cyclic loading. Effects of loading rate, deviation, sta tionary level, and cyclic amplitude on damage evolution are discussed. Inversion of the in fluence of loading deviation on laminate strength with varying loading rate is revealed and interpreted. Highcycle fatigue behavior of the laminate is calculated utilizing the observed stages in failure accumulation under cyclic loading.
Thermal Analysis of Continuous Filament-Wound Composites
Authors: James Darryl L. , Black W. Z.
Published: June 2014

A transient thermal model for the continuous filament winding process using an infrared energy source has been transformed into a quasi-steady problem by working in a Eulerian reference frame. The model has been subdivided into two regimes. A one-dimensional, Cartesian coordinate, heat transfer analysis of the tape regime is coupled with a three-dimensional, cylindrical coordinate, heat transfer analysis of the composite substrate in the mandrel regime. Together, the temperature distribution of the filament winding process is predicted as a function of the power of the infrared energy source, location of the infrared spot, infrared spot size, mandrel rotational speed, and material properties.

The temperature distribution determined in the numerical analysis is then compared with temperatures measured with an infrared camera attached to a small-scale filament winding apparatus. While the infrared camera cannot determine temperatures within the composite, a measure of the accuracy of the thermal model can be obtained by comparing surface temperatures predicted by the model to experimental temperatures. The results suggest that varying the position of the lamp, changing the winding speed, or modifying the power output of the lamp can have a major impact on the temperature distribution throughout the composite during winding and consolidation.
Strain Distribution in a Taper-Taper Adhesive-Bonded Joint in a Composite Flat Plate
Authors: Helms Jack E. , Yang Chihdar , Pang Su-Seng
Published: June 2014

An analytical model of a taper-taper adhesive-bonded joint between two composite plates has been developed using a mechanics of materials approach. The derived model consists of four coupled second-order ordinary differential equations with polynomial coefficients. The equations were reduced to a set of eight coupled, first-order differential equations and integrated numerically. The solutions were obtained by using an algorithm based on the Linear Shooting Method. Analytical model results were compared with finite element analyses and a model published in 1971 by Erdogan and Ratwani. The analytical model agrees well with the other two models.
Morphology and Properties of Wood-Fiber Reinforced Blends of Recycled Polystyrene and Polyethylene
Authors: Simonsen John , Rials Timothy G.
Published: June 2014

Material properties of composites produced from recycled plastics and recycled wood fiber were compared. A blend of high-density polyethylene and polystyrene was used as a simulated mixed plastic. Stiffness was generally improved by the addition of fiber, as expected, but brittleness also increased. Pretreatment of the wood filler with phenol-formaldehyde resins did not significantly affect material properties. Differential scanning calorimetry indicated no interaction between the polyethylene phase and the other phases present in the composite. Glass transition temperatures for the various combinations of components indicated a possible interaction between the polystyrene phase and untreated wood filler. This was supported by scanning electron micrographs, which indicated a less-coalesced morphology for samples filled with treated wood flour compared to those with untreated wood flour.
Optimization of the Surface Free Energy of Carbon Fiber through Electrolytic Oxidation
Authors: Hrivnak Jeffrey A. , Mccullough R. L.
Published: June 2014

Fiber surface treatments are a method of improving fiber/matrix adhesion in composite materials. In this study, an electrolytic oxidation process was systematically optimized as a means of altering the interfacial region. A statistical experimental design was utilized to examine the effect of process variables on the surface energy of the carbon fibers. Using a Dynamic Contact Angle Analyzer, in conjunction with the Wilhelmy Plate Technique, the surface energy of each oxidatively treated fiber was determined. These data were used to develop an empirical model relating processing conditions to fiber surface energy. Fiber/matrix adhesion was then related to the polar component of the surface energy by means of the single-fiber fragmentation test.
Fracture Toughness and Damage Propagation of Ultrahigh-Modulus Polyethylene Fiber-Reinforced Composites
Authors: Xian X. J. , Poon Y. M. , Choy C. L.
Published: June 2014

The fracture toughness K&, and crack propagation of four types of ultrahighmodulus polyethylene (UHMPE) fiber-reinforced composites were investigated under conventional testing conditions and using a scanning electron microscope. The value of Kk is found to depend on the nature of the matrix and interface and the volume fraction of the fibers. The machining method has no significant effect on K,. The fracture mechanisms of UHMPE fiber composites are discussed.
Transverse Impact Behavior of Knitted Carbon-Fiber Fabric-Reinforced Thermoplastic Composite Sheets
Authors: Karger-Kocsis J. , Yuan Q. , Mayer J. , Wintermantel E.
Published: June 2014

Instrumented falling weight impact (IFWI) properties of two-dimensional (2D) weft-knitted carbon-fiber (CF)-reinforced poly(ethyl methacrylate) (PEMA) and poly(ether ether ketone) (PEEK) composites with a reinforcement content of V f≈ 35 and 51 vol.%, respectively, were studied under low-energy and perforation impact conditions. Results indicated that the transverse impact response of these thermoplastic composites strongly depends on the ductility of the matrix, on fiber/matrix adhesion, and on the stitch (rib) structure (size, stretching of the fabrics) of the knitted fabric reinforcement. The highest thickness-related perforation impact energy was found for the knitted CF-reinforced PEEK composite (≈15 J/mm) due to its high reinforcement content, high matrix ductility, and good fiber/matrix bonding.
Influence of ENF Specimen Geometry and Friction on the Mode II Delamination Resistance of Carbon/PEEK
Authors: Davies P.
Published: June 2014

Unidirectional carbon/polyetheretherketone (PEEK) composites were tested under mode II (shear) loading conditions. Three ENF (end notched flexure) specimen thicknesses have been tested, allowing a range of span length-to-thickness ratios to be examined. Analysis of the results from a first series of tests indicated a strong influence of specimen thickness on G,,, values. However, a second series of tests was then performed on similar specimens under identical loading conditions but with a folded layer of PTFE film inserted between the crack faces to reduce friction. These test results were independent of specimen thickness except for the thickest specimens at the shortest span length. It is concluded that friction can cause overestimation of G,, C values by up to 20%. A standard mode II test method must include steps to reduce this friction component.
Crystallization Mechanism in PEEK/Carbon Fiber Composites
Authors: Hachmi B. D. , Vu-Khanh T.
Published: June 2014

The non-isothermal crystallization kinetics of PEEK in the presence of carbon fibers are investigated for PEEK/carbon composites made from both prepreg and commingled systems. The crystallization kinetics under non-isothermal conditions are studied over a wide range of cooling rates, varying from 0.5°C/min to 160'C/min and compared with the pure PEEK matrix resin. For the composite materials as well as for the PEEK resin, the mechanism of crystallization is found to undergo two transitions, at about 5°C/min and 40'C/min. While the presence of carbon fibers affects the temperature and the rate of crystallization of the PEEK matrix, it does not seem to alter the basic crystallization mechanisms. The results are in agreement with some reported morphological studies on PEEK/carbon composites, suggesting that the transcrystalline structure resulting from epitaxial growth of the PEEK matrix at the carbon fiber surface constitutes a small element in the global crystallinity of the PEEK matrix in the molded composite.
Design Optimization of a Laminated Composite Femoral Component for Hip Joint Arthroplasty
Authors: Fu W. , Biggers S. B. , Latour R. A.
Published: June 2014

A multi-level optimization process has been developed specifically to design thick laminated composite structures. The large number of design variables present in this type of structure makes such a process a necessity so that reasonable computational efficiency can be achieved. At the first level, the in-plane response of a global model is optimized using the stiffnesses of an equivalent orthotropic laminate as the design variables. At the second level, stiffnesses of sublaminates are used to optimize the out-of-plane response while maintaining the in-plane performance obtained in the first level. Finally, a detailed model of a critical local region is developed based on the results from the second level. This local model is used to optimize the laminate strength using ply orientations as design variables while maintaining the in-plane and out-of-plane performance obtained in the first two levels. The optimization process has been applied to a conceptual model of a composite femoral component for total hip joint replacement. Three-dimensional finite element models are used for the analysis at each of the three levels. The required computational efficiency is achieved by controlling the complexity of the models, the number of design variables, and the nonlinearity of the optimization problem at each level.
Finite Element Based Degradation Model for Composites with Transverse Matrix Cracks
Authors: Srirengan Kanthikannan , Whitcomb John D.
Published: June 2014

A degradation model for predicting the effective homogenized threedimensional elastic constants of an interior ply with transverse matrix cracks was developed by analyzing a three-ply representative volume element using the finite element method. The degradation model was first evaluated by comparing the homogenized extensional modulus for a cracked [0/(90)3]s laminate with experimental results and finite element discrete models in which each crack was modeled discretely. Further, using the degradation model, the prediction of load redistribution for a cantilevered laminated plate with matrix cracks subjected to transverse end load was compared with a discrete crack model. Also, the prediction of load redistribution in a cracked plain weave composite subjected to uniaxial stress was compared with a discrete crack model. The degradation model showed good agreement in predicting the homogenized elastic constants and load redistributions.
An Experimental Method for Compressive Properties of Laminated Composites at High Rates of Loading
Authors: Tzeng Jerome T. , Abrahamian Ara S.
Published: June 2014

Dynamic responses of composite materials are characterized for ballistic engineering applications. An experimental method has been developed to investigate the dynamic effects on material behavior at a strain rate typically found during the launching of a projectile. An air-gun system and a test fixture with a designed crashing mechanism are used to simulate a loading condition resulting from gun firing. Methods of data acquisition and reduction have also been developed using a streak camera and a film digitization technique. The system is calibrated and verified by testing aluminum samples, and fairly good results are obtained. Finally, polymer composite laminates with lay-up constructions of interest are tested. Strain rate effects on the compressive strength are determined at strain rates of 10-100 in/sec. The failure mechanism of composite laminates is also investigated, which provides an understanding of the strengthening mechanism of composites subjected to impact.
Impact Resistance Modeling of Hybrid Laminated Composites
Authors: Abatan Ayo , Hu Hurang , Olowokere David
Published: June 2014

This paper discusses the analytical and numerical results for the impact responses of two types of plates with equal areal weights: hybrid laminated composite plates and homogeneous metallic plates. The loadings and the boundary conditions for the two types of plates are the same, and an impact load was applied at the center of each plate. An analytical solution based on Fourier expansion was developed to obtain the impact responses of the plates. The finite element method (FEM) was used to perform numerical analyses to verify the analytical solutions. The response patterns from the results were compared and a preliminary conclusion made on the impact resistance ratio between the hybrid laminates with proper interfacial bonding and that of equivalent homogeneous metallic plates. The effect of different shapes of pulse on the laminated composites was also examined. Three loading cases were considered, each being a function of time. The effect of different pulse shapes on the impact response was evaluated. Finally, a solution based on shear deformation theory was developed, and the comparison between classical plate theory results and shear deformation theory results indicates that for the problem examined classical plate theory predicts relatively accurate results.
A Simplified Method for the Geometrically Nonlinear Analysis of the Single Lap Joint
Authors: Penado F. Ernesto
Published: June 2014

A simplified method for the geometrically nonlinear analysis of the single lapjoint is presented. The method consists of first finding the force/moment boundary conditions at the joint overlap ends. This is achieved by solving the differential equations that relate the resulting moment to the applied load and the unknown transverse deflection. The solution for the deflection is eventually reduced to the solution of a system of six linear equations in six unknown coefficients. Once the force/moment boundary conditions for a given load are known, a linear finite element analysis is used to find thejoint stresses using only the overlap region of the joint. Since in many practical joints adhesive fillets exist at the ends of the overlap, the existence of these fillets is taken into account in the formulation. Also, to allow for various support conditions of the grips of the testing machine, solutions are presented for both simply supported and clamped-clamped end supports. Additional boundary conditions on the linear finite element model using multipoint constraints are also given that allow consideration of only one half of the overlap length in the analysis. This is possible due to the inherent conditions of antisymmetry that exist between the top and bottom of the joint overlap. The accuracy of the simplified method was verified by comparison of results against a full-size geometrically nonlinear finite element model, and it was found that the results were very close, within 3%. Overall, the method results in considerable savings in both solution time and modeling effort, while maintaining accuracy.
Resistive Susceptor Design for Uniform Heating during Induction Bonding of Composites
Authors: Yarlagadda S. , Fink B. K. , Gillespie J. W.
Published: June 2014

A novel susceptor concept for metal mesh susceptors, designed to achieve uniform in-plane temperatures during induction heating, is documented. The process involves redirecting eddy current flow patterns in the resistive mesh susceptor by specifically designed cut patterns in the mesh. A theoretical model was developed to predict heat generation in metal mesh susceptors with any prescribed network pattern. Initial results for meshes with cut patterns show significant changes in heating compared to an uncut mesh. Cut patterns can be optimized to reduce temperature gradients in the susceptor to within the processing window of the composite. Experimental results are presented for qualitative comparisons.
Multidisciplinary Parametric Design Optimization for Enhancing the Affordability of Molded Composites
Authors: Pochiraju K. , Chassapis C. , Manoochehri S.
Published: June 2014

The role of design optimization in assisting design decision-making and enhancing the affordability of composite products is studied in this paper. The design of composite products that meet performance, manufacturability, and cost requirements is a multidisciplinary problem. Solutions to appropriately formulated design optimization problems can assist in quickly examining several design alternatives at early conceptual design and parametric design stages. However, the candidate designs require manufacturing process, structural and material performance, and product cost evaluations. These evaluations are often conducted by several domain experts using sophisticated and diverse numerical analysis tools. The formulation of constraint and objective functions in multiple domains, the use of numerical model-based evaluation of the functions, and the solution of multidisciplinary optimization problems during the design of injection molded plastics are addressed in this paper. Numerical examples are presented illustrating the application of optimization techniques in process and exploring material alternatives as well as in parametric design of geometry with affordable cost objectives. A brief description of a software system developed to systematically integrate optimization with the domain-dependent knowledge and geometric design is also presented.
Titanium Ply Effects on the Behavior of a Hybrid Thermoplastic Composite Laminate
Authors: Veazie David R. , Badir Ashraf M. , Grover Ronald O.
Published: June 2014

An experimental-cum-analytical study was undertaken to investigate the mechanical response of four hybrid titanium composite laminate (HTCL) systems, each prepared using a graphite-fiber-reinforced thermoplastic polyimide as the adhesive in a unidirectional prepreg. Two of the four HTCL systems were fabricated with the titanium Ti15-3 alloy, while the other two systems were fabricated with the titanium Timetal fl-2 I S alloy. The improvement in mechanical properties achieved by the influence of the titanium layer was assessed by comparing the uniaxial tensile results of static strength at room temperature. An analytical study was also performed to predict the laminate strength and loaddeformation behavior based on the constituent material properties. Results included stressstrain curves, ultimate strength, longitudinal modulus, and the description of the observed modes of failure.
Design, Manufacture, and Characterization of Composites Using On-Line Recycled Thermoplastic Powder Impregnation of Fibers and In-Situ Filament Winding
Authors: Nejhad Mehrdad N. Ghasemi , Ikeda Karen M.
Published: June 2014

Recycled thermoplastic powder impregnated composites using in-situ filament winding and on-line consolidation of fibers have been successfully manufactured with the modified filament winding setup constructed in this study. Reclaimed low density polyethylene (RLDPE), reclaimed low-density polyethylene with polymer additives consisting of 0.25% by weight of Cyasorb® UV-3346 Light Stabilizer, 0.25% by weight of Cyasorb® UV-53 1 Light Stabilizer, and 0.08% by weight of Cyanox® 2777 Antioxidant (RLDPE-PA), and virgin low-density polyethylene (LDPE) were pulverized to ultrafine powders ranging from 20 to 300,um, and utilized to impregnate a separated fiberglass tow. After initial experiments, two powder-impregnated composite tubes were manufactured for each thermoplastic material system. The composites were then tested for tensile (hoop) strength and compressive bending strength under the ASTM D2290-95 and C-ring tests, respectively. This study showed that while the RLDPE composite did not perform well, composite samples made with RLDPE and polymer additives (i.e.. RLDPE-PA) performed better than RLDPE samples but not as well as composites made of virgin LDPE.

The impregnation and consolidation steps in the manufacturing process were also effective for all three systems. The composite tubes exhibited very low void contents and high fiber volume fractions, while unmelted and unconsolidated thermoplastic powders were not present in the manufactured parts. The absence of fiber waviness and fiber migration through the thickness of the composite demonstrates that the online consolidation of powder-impregnated fibers was also effective. The collection of the separated powder-impregnated fibers prior to filament winding also seemed to be sufficient.
Experimental Support for the Cell-Model Description of Hyper-Concentrated Suspensions
Authors: Burns James S. , Kirschner Susan B. , Powell James
Published: June 2014

The bulk tensile viscosity of large arrays of aligned, high-modulus, high aspect-ratio, rod-like, cylindrical fibers is a constitutive figure useful to composite manufacturers interested in exploiting the axial extensibility of ordered staple-reinforced laminar preforms. These preforms, when embedded in a highly viscous coupling fluid, form a hyper-concentrated suspension for which little applicable modeling has been accomplished. Shear coupling between long fibers during bulk axial extension was studied using a series of tests that employ mechanically driven rods embedded in a viscous Newtonian fluid (40,000 cps). The local fluid velocity field created by an axially translating fiber and this field's screening by adjacent fibers was studied by measuring viscous shear tractions. A momentum flux-capture theory previously applied to elastic solids was reformulated for creepingregime composite deformation. The effectiveness of momentum screening for 4-, 5- and 6-neighbor cells of shear-coupled rods was measured at three different effective volume fractions and compared with this theory. Results of this comparison suggest that even at low volume fractions of around 0.15, a cell-type linear superposition model may suffice for describing bulk properties based on local shear-coupling interactions. At structural volume fractions of near 0.60, the cell-model approach should permit accurate modeling of bulk tensile viscosity.
Static and Low-Velocity Impact Response Characteristics of Pultruded Hybrid Glass-Graphite/Epoxy Composite Beams
Authors: Kowsika Murthy V. , Mantena P. Raju
Published: June 2014

The influence of hybridization on the crashworthiness and energy-absorption characteristics of pultruded glass-graphite/epoxy composite beams was investigated. Lowvelocity drop weight instrumented impact tests were conducted on these hybrid composites to determine the load-deformation behavior for evaluating the impact performance in terms of the ductility index, damage initiation, propagation, and total absorbed energies. Three-point static flexural tests were also conducted to compare the static load-deformation characteristics with those of the dynamic low-velocity impact tests. The behavior under both static and dynamic loading conditions was simulated using finite element modeling procedures to identify the failure mechanisms for optimizing the performance of pultruded hybrid composites.

Experimental results show that the load and strain to failure of all-graphite/epoxy, all-glass/epoxy and other hybrid composites obtained from impact tests are significantly higher as compared to the static test data. The load-bearing capability of composites after damage initiation (which is dictated by the ductility and failure index) has shown marked improvement for the graphite-outside hybrids when compared with the all-graphite, all-glass, and glass-outside hybrids. The high strain to failure glass fibers absorb considerably higher energy before ultimate failure compared to the brittle graphite fibers; as a result, the fiber content and geometric placement of each type of fiber significantly influenced the energy-absorption characteristics of hybrids. Results indicate that the energy-absorption behavior of pultruded hybrids predicted using finite element modeling is in close agreement with the behavior characterized from experimental impact tests. The effectiveness ofhybridization to improve the impact performance of composites was demonstrated.
Phase Ultrasonic Testing of Joints in Multilayered Composite Materials
Authors: Nesvijski Edouard G.
Published: June 2014

One of the new promising methods of nondestructive testing (NDT) is the ultrasonic harmonic wave method. The method uses wave phase characteristics that can be measured with high accuracy. It has proved to be very sensitive to structural changes in materials with regular structures. The application of the harmonic waves method for testing of composite materials with irregular structures as well as for joints of materials with distinctive properties may allow characterization of a wider class of materials such as ceramics, concrete, and metal-ceramic-plastic composites. Stochastic approaches are used to analyze distribution of mechanical properties for characterization of materials. Results of mathematical simulation of ultrasonic testing ofjoints in multilayered composites are shown. The method sensitivity is analyzed and some practical applications are presented in this paper.
Experimental Characterization of Orientation Formation in a Mold Cavity with Sudden Contraction
Authors: Olivero Kristian A. , Altan M. Cengiz
Published: June 2014

Orientation formation of short fibers suspended in a flow through a planar mold cavity is experimentally analyzed. The suspension of corn syrup mixed with short fibers is injected into the mold at constant flow rate through a narrow, planar inlet gate. The mold cavity contains a sudden expansion following the inlet gate, and a three-to-one sudden contraction downstream. Orientation data are obtained using computerized image analysis on photographs of thirteen zones of interest near the sudden contraction. The photographs are taken through the transparent top mold wall, thus collecting average planar orientation data through the mold thickness. Orientation distribution histograms are generated from the individual fiber orientations to graphically depict orientation microstructure. These histograms reveal bimodal fiber orientations in nearly all zones of interest. Experiments performed at different volume flow rates and viscosities also confirmed the bimodal orientation distribution observed through the top mold wall. Orientation results are observed to be more random compared to those predicted using Jeffery's theory (He et al., 1997). Fiber size or wall effects may contribute to the formation of a more random orientation field.
Experimental Investigation of Compression Molding of Glass/PP-PP Foam Core Sandwich Components
Authors: Akermo Malin , Astrom B. Tomas
Published: June 2014

Compression molding of sandwich components made from a novel material combination, glass/polypropylene faces and expanded polypropylene foam core, has been experimentally investigated. The aim of the study was to determine the processing window for this material concept in terms of shear, transverse tensile and flexural properties of compression molded components and to evaluate the concept's processability. To enable evaluation of the influence of a large number of process parameters, the components were manufactured according to a two-level Taguchi experimental design. It is found in the study that the compatibility between faces and core results in a face-core bond strength that is always higher than that of the core, provided that the faces remain melted when placed onto the core. All the mechanical properties studied are generally improved by reduced molding pressure and time, while excessive heating of the faces significantly increases their void content and thereby reduces their strength.
Structure and Mechanical Properties of Knitted Carbon-Fiber-Reinforced Polyamide 12
Authors: Mayer J. , de Haan J. , Kirch M. , Reber R. , Wintermantel E. , Wild U.
Published: June 2014

In this study, the mechanical properties and failure behavior of multilayer knitted carbon-fiber-reinforced polyamide 12 were investigated. In the first part, the influence of the number of stacked knit layers in composites containing 2 to 8 knit double layers were tested in the wale direction. It was found that the thickness correlated linearly with the number of knit double layers in the composite. In the second part, the angle dependence of tensile strength, Young's modulus, and failure behavior were investigated at 00, 30°, 45°, 60°, and 90° in accordance to the wale direction.
Influence of Fiber Surface Treatment on the Creep Behavior of Jute Fiber-Reinforced Polypropylene
Authors: Gassan Jochen , Bledzki Andrzej K.
Published: June 2014

Improvements in the characteristic properties of jute-polypropylene composites were obtained with the application of MAH grafted PP copolymers as a coupling agent to the fiber. SEM investigations demonstrated that fiber pull-out is reduced after the modification with the coupling agent. This improved fiber-matrix adhesion further leads to a lower creep strain in the outer fibers. This was demonstrated for composites with two different fiber contents. Up to applied stresses of 5.1 N/mm2, the creep behavior for the composites with unmodified, as well as for those with MAH-PP modified, fibers obeys the creep law according to Abbott. The experimental data of creep tests at higher applied stresses were fitted more successfully by using the creep law according to Findley. The creep kinetic coefficient according to Abbott was dependent on the applied stress for both types of composites and for both fiber contents.
Effect of Strain Rate and Temperature on the Tensile Failure of Pineapple Fiber Reinforced Polyethylene Composites
Authors: George Jayamol , Thomas Sabu , Bhagawan S. S.
Published: June 2014

The dependence of temperature and strain rate on the mechanical properties of pineapple leaf fiber (PALF) reinforced polyethylene (LDPE) composites has been investigated. The effects of fiber loading, fiber orientation, and fiber treatment on the test properties were studied. The tensile strength of the composite was found to be decreased and elongation increased up to 40'C, decreasing thereafter as the temperature was increased from 40 to 80'C. Failure at low temperature and or high strain rate occurred due to brittle matrix fracture, which was evident from SEM micrographs. Activation energy of the failure was calculated using an Arrhenius equation. Failure envelope is generated in order to understand the effect of temperature and strain rate on composite properties. Composites with longitudinally oriented fibers showed higher retention of tensile properties at elevated temperatures. Fibers treated with poly(methylene) poly(phenyl) isocyanate (PMPPIC) showed maximum retention in strength at higher temperature.
Crystallizability in a Model High-Performance Thermoplastic Polyimide-Matrix Composite
Authors: Deshpande Abhijit P. , Seferis James C.
Published: June 2014

The effect of annealing and exposure to high temperatures on the crystallizability and glass transition of a model thermoplastic polyimide/carbon fiber (TPI/CF) system was investigated in this work. A varying range of crystallinity was obtained by annealing the TPI/CF prepreg at different temperatures. The relaxation of the material was observed when the prepreg was annealed at temperatures above the glass transition. On the other hand, exposure to high temperatures close to the processing temperature irreversibly affected the material, and the material lost the ability to crystallize (permanent structural changes). The loss of crystallizability was observed after the exposed materials were annealed. This loss of crystallizability was paralleled with an increase in the Tg. Both relaxation and permanent structural change effects are higher for greater times and higher temperatures. In conclusion, the response of TPI/CF to treatment at temperatures higher than the glass transition temperature was characterized in this work. The loss in crystallizability and changes in glass transition temperature were observed, which will be essential for further investigations on process modeling and performance.
Experimental and numerical research on the effects of minimum quantity lubrication in thread turning of free-cutting steel AISI 1215
Authors: An Qinglong , Liu Zhiqiang , Jiang Li , Chen Ming
Published: June 2014

As a heavy-load machining method, thread turning always requires high-performance lubrication to achieve high machining accuracy and good machined surface quality. Minimum quantity lubrication with good lubrication effects is used more and more widely in machining process for its eco-friendly and economical benefits. In this article, numerical simulations on minimum quantity lubrication flow field were first conducted by means of computational fluid dynamics, and the effects of minimum quantity lubrication in thread turning of free-cutting steel AISI 1215 were evaluated based on experimental method. The computational fluid dynamics simulation results show that the two vortexes existing in minimum quantity lubrication flow field and the micro oil droplets with high speed above 200 m/s help to enhance heat exchange and lubrication effect by improving the permeation of oil droplets into the cutting zone. The thread turning experiment results also show that the cutting forces with minimum quantity lubrication were reduced significantly, and good machined surface quality was achieved, as compared with dry cutting.
On the cutting of wood for joinery applications
Authors: Lopez de Lacalle Luis N , Fernández-Larrinoa Javier , Rodríguez-Ezquerro Adrián , Fernández-Valdivielso Asier , López-Blanco Raúl , Azkona-Villaverde Ibón
Published: June 2014

In the joinery sector, several tons of wood are processed every month. Exploitation costs must be kept low for achieving reasonable margins. Therefore, tool life is an important issue to study, looking for ways of making it longer. There are different types of wood involved in this application, and a value to establish the difficulty of machining one or the other is interesting. For this purpose, the concept of specific cutting force is introduced in this work. In the work presented here, three issues are regarded: (a) three typical woods are characterized by means of the specific cutting force as it is commonly done in the metal industry, (b) coatings are tested for high-speed steel and cemented carbide tools, and (c) tool performance is defined by admissible values of flank wear. The field tests performed showed that the coating of tools could be a good choice for this application.
Development of a method to recognize punch shapes for progressive dies
Authors: Hussein HMA , Wang F , Qudeiri J Abu
Published: June 2014

A generic method for automatic shape recognition on two-dimensional contours, particularly used for recognizing punch shapes for progressive dies, is presented in this article. In this work, shapes of two-dimensional contours are defined by shape templates using a sequence of symbols, lists, and numbers, and their definitions are stored in a specially designed database for the minimum number of shape definitions to be retrieved during shape recognition for optimal computational efficiency. When a contour is input from a computer-aided design system for shape recognition, the computer-aided design data are translated into shape components and input to the shape recognition device. Upon successful recognition of a shape, the shape code will be composed and its dimensional values will be extracted. Standard or special punch purchase code may be created automatically through this method.
Effect of friction in stretch forming and its influence on the forming limit curve
Authors: Manikandan G , Verma Rahul K , Biswas Pinaki
Published: June 2014

Formability is an important property requirement in sheet metal forming and mostly useful to automobile and aerospace industries. Every product design starts with finite element simulation before the die design and material selection stage. The forming limit curve along with finite element results acts as tool to investigate whether the design is feasible. Hence, it is of utmost importance that the forming limit curve is accurate over a wide range of strain path. Generally, a forming limit curve is derived from discrete failure strain points corresponding to different strain ratios by fitting a smooth curve. It has been observed from many studies that the generated forming limit curves are devoid of any failure points corresponding to equibiaxial strain path. This is found to be true even when the test conditions are supposed to produce biaxial state of strain. To understand the reason behind this observation, a set of forming limit diagram experiments and finite element analyses were carried out for high-strength interstitial free steel and interstitial free galvannealed steel with three different friction conditions. It was observed that friction plays an important role in right-hand side of the forming limit curve. Finite element results and experimental validation suggest that failure strain points for biaxial strain paths can be obtained only if the tests are conducted with proper lubrication system.
Formability improvement of austenitic stainless steel by pulsating hydroforming
Authors: Xu Yong , Zhang Shi-Hong , Cheng Ming , Song Hong-Wu
Published: June 2014

Pulsating hydroforming process has been verified to prevent the thickness of tube wall thinning and obtain a uniform expansion, which can improve the hydroformability effectively. In the present work, the experimental research was carried out on the influence of pulsating load on the formability of austenitic stainless steels. The results showed that the formability of austenitic stainless steel can be improved by pulsating load in which the effect on formability should be understood from two different aspects of process parameters and material properties. The mechanical property of austenitic stainless steel is obviously improved through loading and unloading mode. The fraction of the strain-induced martensite is increased by pulsating load, which leads to enhance the transformation-induced plasticity effect. Meanwhile, axial feeding process can be motivated during the process of loading and unloading. Consequently applying pulsating load with large amplitude can achieve a more uniform deformation with a more homogeneous thickness distribution beneficial for preventing excessive local thinning and an excellent die filling performance for tube hydroforming.