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Thickness Direction (thickness + direction)
Selected AbstractsFracture analysis of composite co-cured structural joints using decohesion elementsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2004P. P. CAMANHO ABSTRACT Delamination is one of the predominant forms of failure in laminated composite structures, especially when there is no reinforcement in the thickness direction. To develop composite structures that are more damage tolerant, it is necessary to understand how delamination develops, and how it can affect the residual performance. A number of factors such as residual thermal stresses, matrix-curing shrinkage and manufacturing defects affect how damage will grow in a composite structure. It is important to develop computationally efficient analysis methods that can account for all such factors. The objective of the current work is to apply a newly developed decohesion element to investigate the debond strength of skin-stiffener composite specimens. The process of initiation of delaminations and the propagation of delamination fronts is investigated. The numerical predictions are compared with published experimental results. [source] Stress analyses of laminates under cylindrical bendingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2008Tarun Kant Abstract A semi-analytical approach for evaluation of stresses and displacements in composite and sandwich laminates under cylindrical bending subjected to transverse load has been developed in this paper. Two dimensional (2D) partial differential equations (PDEs) of such a laminate are obtained by imposing plane-strain conditions of elasticity. The fundamental dependent variables are so selected in this formulation that they satisfy the continuity of displacements and transverse interlaminar stresses at the laminate interface through the thickness. The set of governing PDEs are transformed into a set of coupled first-order ordinary differential equations (ODEs) in thickness direction by assuming suitable global orthogonal trigonometric functions for the fundamental variables satisfying the boundary conditions. These ODEs are numerically integrated by a specially formulated ODE integrator algorithm involving transformation of a two-point boundary value problem (BVP) into a set of initial value problems (IVPs). Numerical studies on both composite and sandwich laminates for various aspect ratios are performed and presented. Accuracy of the present approach is demonstrated by comparing the results with the available elasticity solution. It is seen that the present results are in excellent agreement with the elasticity solutions. Some new results for sandwich laminates and for uniform loading condition are presented for future reference. Copyright © 2006 John Wiley & Sons, Ltd. [source] A reduced integration solid-shell finite element based on the EAS and the ANS concept,Geometrically linear problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2009Marco Schwarze Abstract In this paper a new reduced integration eight-node solid-shell finite element is presented. The enhanced assumed strain (EAS) concept based on the Hu,Washizu variational principle requires only one EAS degree-of-freedom to cure volumetric and Poisson thickness locking. One key point of the derivation is the Taylor expansion of the inverse Jacobian with respect to the element center, which closely approximates the element shape and allows us to implement the assumed natural strain (ANS) concept to eliminate the curvature thickness and the transverse shear locking. The second crucial point is a combined Taylor expansion of the compatible strain with respect to the center of the element and the normal through the element center leading to an efficient and locking-free hourglass stabilization without rank deficiency. Hence, the element requires only a single integration point in the shell plane and at least two integration points in thickness direction. The formulation fulfills both the membrane and the bending patch test exactly, which has, to the authors' knowledge, not yet been achieved for reduced integration eight-node solid-shell elements in the literature. Owing to the three-dimensional modeling of the structure, fully three-dimensional material models can be implemented without additional assumptions. Copyright © 2009 John Wiley & Sons, Ltd. [source] A triangular plate element for thermo-elastic analysis of sandwich panels with a functionally graded coreINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2006M. Das Abstract A sandwich construction is commonly composed of a single soft isotropic core with relatively stiff orthotropic face sheets. The stiffness of the core may be functionally graded through the thickness in order to reduce the interfacial shear stresses. In analysing sandwich panels with a functionally gradient core, the three-dimensional conventional finite elements or elements based on the layerwise (zig-zag) theory can be used. Although these elements accurately model a sandwich panel, they are computationally costly when the core is modelled as composed of several layers due to its grading material properties. An alternative to these elements is an element based on a single-layer plate theory in which the weighted-average field variablescapture the panel deformation in the thickness direction. This study presents a new triangular finite element based on {3,2}-order single-layer theory for modelling thick sandwich panels with or without a functionally graded core subjected to thermo-mechanical loading. A hybrid energy functional is employed in the derivation of the element because of a C1 interelement continuity requirement. The variations of temperature and distributed loading acting on the top and bottom surfaces are non-uniform. The temperature also varies arbitrarily through the thickness. Copyright © 2006 John Wiley & Sons, Ltd. [source] A finite element model for thermomechanical analysis of sheet metal formingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2004G. Bergman Abstract A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin-walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature-dependent elastic,plastic model with a non-linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one-sided forming and quenching experiment. Copyright © 2004 John Wiley & Sons, Ltd. [source] Classical and advanced multilayered plate elements based upon PVD and RMVT.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002Part 2: Numerical implementations Abstract This paper presents numerical evaluations related to the multilayered plate elements which were proposed in the companion paper (Part 1). Two-dimensional modellings with linear and higher-order (up to fourth order) expansion in the z -plate/layer thickness direction have been implemented for both displacements and transverse stresses. Layer-wise as well as equivalent single-layer modellings are considered on both frameworks of the principle of virtual displacements and Reissner mixed variational theorem. Such a variety has led to the implementation of 22 plate theories. As far as finite element approximation is concerned, three quadrilaters have been considered (four-, eight- and nine-noded plate elements). As a result, 22×3 different finite plate elements have been compared in the present analysis. The automatic procedure described in Part 1, which made extensive use of indicial notations, has herein been referred to in the considered computer implementations. An assessment has been made as far as convergence rates, numerical integrations and comparison to correspondent closed-form solutions are concerned. Extensive comparison to early and recently available results has been made for sample problems related to laminated and sandwich structures. Classical formulations, full mixed, hybrid, as well as three-dimensional solutions have been considered in such a comparison. Numerical substantiation of the importance of the fulfilment of zig-zag effects and interlaminar equilibria is given. The superiority of RMVT formulated finite elements over those related to PVD has been concluded. Two test cases are proposed as ,desk-beds' to establish the accuracy of the several theories. Results related to all the developed theories are presented for the first test case. The second test case, which is related to sandwich plates, restricts the comparison to the most significant implemented finite elements. It is proposed to refer to these test cases to establish the accuracy of existing or new higher-order, refined or improved finite elements for multilayered plate analyses. Copyright © 2002 John Wiley & Sons, Ltd. [source] Processing and mechanical behavior of carbon black graded rubber compoundsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Sandeep S. Ahankari Abstract Functionally graded rubber compounds (FGRCs) were prepared by construction based method. The matrix used was natural rubber (NR). Amorphous carbon black (N-330) was used as grading material. The gradation of nanoparticles in a rectangular geometry comprised the variation of particle volume fraction along thickness direction. Its performance was evaluated for structural application through various mechanical and surface properties like tensile strength, modulus, tear strength, elongation at break, hardness, fracture surface by scanning electron microscopy, etc. At the same percentage of nanofiller loading, FGRCs show enhanced properties, i.e., modulus and tear strength (in some grades) compared to uniformly dispersed rubber compounds (UDRCs). Modulus of FGRCs, for a given particular stacking sequence of the layers, increases as much as by 275% compared to UDRCs. The ultimate properties like tensile strength and elongation at break made up for the modulus enhancement that decreases to as minimum as 50 and 80%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Novel UV-induced photografting process for preparing poly(tetrafluoroethylene)-based proton-conducting membranesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2007Masaharu Asano Abstract A novel process comprising the UV-induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton-conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with ,-ray radiation grafting, UV-induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624,2637, 2007 [source] Design, Preparation, and Characterization of Graded YSZ/La2Zr2O7 Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Hongfei Chen Large-area spallation and crack formation during service are big problems of plasma-sprayed thermal barrier coatings (TBCs), owing to their weak bond strengths and high residual stresses. Functional gradient TBCs with a gradual compositional variation along the thickness direction are proposed to mitigate these problems. In this paper, a six-layer structured TBC composed of Y2O3 partially stabilized ZrO2 (YSZ) and La2Zr2O7 (LZ), was prepared by plasma spraying with dual powder feeding ports. This coating had a gradient composition and function. Thermal conductivity of the coating was comparable with that of a single LZ coating while the coefficient of thermal expansion was nearly equal to that of YSZ single coating. The experiment was conducted to compare the thermal shock resistance of a graded coating with a conventional YSZ/LZ double-layer system. Changes in weight and morphology of specimens before and after thermal shock tests were analyzed. Results demonstrated that the thermal shock resistance of the graded coating was superior to the double-layer coating. Typically, a barely visible pimple-like spallation was present on the surface of the graded coating after 21 cycles. On the other hand, obvious delamination was observed for a double-layer coating after six to seven cycles. Special focus was also placed on a comparative investigation of stresses that are closely related to spallation via the use of numerical simulation. [source] A New Technique for Preparing a Filled Type of Polymeric Gradient MaterialMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006Yong-Bin Zhu Abstract Summary: So-called functionally gradient materials have received increased attention as a new type of composite whose microelements, including composition and structure, change spatially to optimize the gradient properties for a specific application. In this study, a new technique for continuously preparing a filled type of PGM was investigated through co-extrusion/gradient distribution/2-dimensional mixing with conventional polymeric material processing facilities. The processing line from co-extrusion, gradient distribution to 2-dimensional mixing was fulfilled by two extruders, a gradient distribution unit and 2-dimensional mixing units. The gradient distribution unit and 2-dimensional mixing units were designed separately in our group. As an example, a PE/GB PGM was prepared by using this new technique. The gradient variation of composition along the sample thickness direction was studied by TG and SEM. The TG results indicated that a gradient variation of the content of GB was formed along the thickness of the sample. The direct gradient distribution of GB came from SEM observation, which showed an increased stacking density of GB along the sample thickness. Experimental results indicated that the processing method with co-extrusion/gradient distribution/2-dimensional mixing can serve as a new way to produce a filled type of PGM and is worthy of further investigation. The prepared polyethylene/glass bead PGM; the graph illustrates the glass bead concentration gradient across the sample thickness. [source] Electrically switchable exhibition of circular Bragg phenomenon by an isotropic slabMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2006Akhlesh Lakhtakia Abstract A slab of an isotropic material with structural chirality in the thickness direction and with either 43m or 23 point group symmetry exhibits the circular Bragg phenomenon in the optical regime, only on the application of a low-frequency electric field across its two faces. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2148,2153, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21941 [source] Simulation and validation of resin flow during manufacturing of composite panels containing embedded impermeable inserts with the VARTM processPOLYMER COMPOSITES, Issue 4 2007Jeffrey M. Lawrence Modern composite materials are becoming more and more advanced as engineers are better able to take advantage of their properties. In addition to their lighter weight and net-shape manufacturing, current interest is to make these materials multifunctional. This may require one to insert various objects into the composite to achieve a variety of different goals. It is important to understand how these embedded objects will affect both the manufacturing and the structural integrity of the component. In this work, the effects of impermeable embedded inserts on the infusion stage of vacuum-assisted resin transfer molding (VARTM) will be explored. In VARTM, one places a distribution media on top of the preform to aid the filling as the resin will first fill the face of the preform in contact with the distribution media and will then infuse the preform in the thickness direction. However, if one has an embedded impermeable insert in the thickness direction, it will obstruct the flow in the region below the embedded object. Several case studies are conducted to understand the effect of the geometry and placement of the embedded insert and the distribution media lay out and properties on the impregnation of the resin into the fiber preform. Finally, an approach is outlined to modify the layout of the distribution media in order to ensure a complete saturation of the preform under all but the most extreme conditions. The approach is validated with experiments. POLYM. COMPOS., 28:442,450, 2007. © 2007 Society of Plastics Engineers [source] Heat transfer for pultrusion of a modified acrylic/glass reinforced compositePOLYMER COMPOSITES, Issue 1 2002Mariasun Sarrionandia Experimental values of the temperature on the wall and into the die were obtained for the pultrusion of a modified acrylic resin. The equation of continuity, and energy balance, coupled with a kinetic expression for the curing system, are solved using difference method to calculate the temperature and the conversion profiles in the thickness direction in a rectangular pultrusion die. The effects of the process variables (e.g. pulling rate, die temperature, die thickness and content of fibers) on the performance of the pultrusion are evaluated. [source] Effects of film and substrate dimensions on warpage of film insert molded partsPOLYMER ENGINEERING & SCIENCE, Issue 6 2010Seong Yun Kim Three-dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in-mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in-mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers [source] Hysteresis measurements and dynamic mechanical characterization of functionally graded natural rubber,carbon black compositesPOLYMER ENGINEERING & SCIENCE, Issue 5 2010S.S. Ahankari Functionally graded polymer composites (FGPCs) were prepared by construction based layering method employing natural rubber (NR) as a matrix and carbon black (CB) in graded form. CB particles were graded along the rectangular geometry polymer matrix comprising the variation of particle volume fraction along thickness direction. These FGPCs were characterized through hysteresis measurements and compared with uniformly dispersed polymeric composites (UDPCs) maintaining the same average amount of filler. Dynamic mechanical properties of these FGPCs and UDPCs were also compared. Dynamic mechanical characterization revealed that FGPCs show much higher storage modulus than the corresponding UDPCs for any given combination of stacking sequence. Loss tangent of FGPCs was also observed to be lesser when compared to UDPCs leading to less hysteretic losses followed by lesser heat buildup in the composite. Hysteresis measurements accorded with the results of dynamic mechanical characterization. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Crystal structure and orientation behavior of transversely compressed poly(ethylene- co -1-octene) filamentsPOLYMER ENGINEERING & SCIENCE, Issue 12 2008Haifeng Shan A basic study on crystal structure and orientation behavior of transversely compressed ethylene-1-octene copolymer with different 1-octene contents was described. All polymers were first melt spun under different spinline stress and subsequently transversely compressed. For the melt-spun filaments, an orthorhombic crystal structure was found for all polymers, but a pseudo-hexagonal mesophase was also found for polymers with the highest 1-octene level (13.3 mol%). For the transversely compressed filaments, several reflection peaks from a monoclinic unit cell were found for polyethylene without octene. For those with higher octene levels, the reflection peaks from monoclinic became fainter and disappeared for the one with the highest 1-octene level. After being transversely compressed, the (110) and (200) peaks of orthorhombic crystal structures became oriented along the meridian direction, which is the fiber axis direction. The reason for this appears to be that the compression deformation of the filament induces elongation along its width direction and shrinkage along its length and thickness direction, and in this change the polymer chain orients. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] An inverse estimation of initial temperature profile in a polymer processPOLYMER ENGINEERING & SCIENCE, Issue 1 2008Ali A. Ranjbar Since one of the most important parameter in polymer processing such as injection stretch blow molding is temperature distribution in the thickness direction, an inverse method has been applied to estimate this profile. This process comprises of four steps. In the first step the preform is injection molded, and in the second and third step it is stretched by a rod to its final length and then inflated and in the last step it is discharged from the mold. In such kind of polymer flows viscous dissipation plays a remarkable role in the evolution of temperature profile. Some theoretical temperature profile has been applied to confirm the validation of the inverse algorithm. Different solution techniques are applied in this article to the inverse problem under consideration, namely: the conjugate gradient and Levenberg,Marquardt method. After the preform is injection molded, which is the first step, it is removed from the mold, which corresponds to time t = 0. At this moment an infrared camera is used to record the surface temperature of the preform with a certain time step. With regard to variation of thermal properties with temperature, the inverse problem becomes nonlinear. These experimental data provided by the infrared camera are then used to estimate the temperature profile at the end of injection process before stretching and inflation took place. POLYM. ENG. SCI., 48:133,140, 2008. © 2007 Society of Plastics Engineers [source] The effect of talc on the crystal orientation in polypropylene/ethylene-propylene rubber/talc polymer blends in injection moldingPOLYMER ENGINEERING & SCIENCE, Issue 3 2001Yutaka Obata The effect of tale on the b -axis orientation of the polypropylene crystals in polypropylene (PP)/ethylene-propylene rubber (EPR)/talc blends of injection moulding was examined using the X-ray diffraction method. The b -axes of the PP crystals were most strongly oriented in the thickness direction for the injection molded PP/EPR/talc blends. The b -axis orientation in the thickness direction of injection moldings was promoted by increasing the concentration of talc, by reducing the particle size, or by purifying the tale. The dependence of the specimens' rigidity on talc content, particle size, and purity was also investigated. The rigidity depended on the degree of b -axis orientation. The result of our investigated suggest that increasing the orientation of the PP crystals that are near talc particles may improve the rigidity. [source] Controlling the properties of single-polymer composites by surface melting of the reinforcing fibers,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002D. M. Rein Abstract All-thermoplastic single-polymer composites are materials in which both the reinforcing fibrous phase and the matrix between them are made of the same thermoplastic polymer. Excellent bonding is achieved by mutual entanglement macromolecules due to controlled surface melting of the fibers. This results in a uniform structure of a single chemical entity. The physical properties of the consolidated material, such as modulus and coefficient of thermal expansion (CTE), can be controlled by the extent of melting effected in the process, which determines the fiber/matrix ratio. The fabrication technology utilizes oriented polymer fibers in various forms: unidirectional lay-up, woven fabric or chopped fibers/non-woven felt. The key element in the processing scheme is the control of the fibers' melting temperature by hydrostatic pressure. The fibers are heated under high pressure to a temperature that is below their melting point at the high pressure but above the melting temperature at some lower pressure. Reduction of pressure for controlled time results in melting of the fibers, which starts at the fiber surface. This surface melting under controlled pressure followed by crystallization produces the consolidated structure. We illustrate and describe this process using fibers of ultra-high-molecular-weight polyethylene (UHMWPE), showing the effect of the processing conditions on the flexural modulus, fiber/matrix ratio, and CTE in plane and in the thickness direction. These properties are relevant to the use of such composites as substrates for microwave antennae. Copyright © 2003 John Wiley & Sons, Ltd. [source] Dynamic stability of a porous rectangular platePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Daniel Debowski The study is devoted to a axial compressed porous-cellular rectangular plate. Mechanical properties of the plate vary across is its thickness which is defined by the non-linear function with dimensionless variable and coefficient of porosity. The material model used in the current paper is as described by Magnucki, Stasiewicz papers. The middle plane of the plate is the symmetry plane. First of all, a displacement field of any cross section of the plane was defined. The geometric and physical (according to Hook's law) relationships are linear. Afterwards, the components of strain and stress states in the plate were found. The Hamilton's principle to the problem of dynamic stability is used. This principle was allowed to formulate a system of five differential equations of dynamic stability of the plate satisfying boundary conditions. This basic system of differential equations was approximately solved with the use of Galerkin's method. The forms of unknown functions were assumed and the system of equations was reduced to a single ordinary differential equation of motion. The critical load determined used numerically processed was solved. Results of solution shown in the Figures for a family of isotropic porous-cellular plates. The effect of porosity on the critical loads is presented. In the particular case of a rectangular plate made of an isotropic homogeneous material, the elasticity coefficients do not depend on the coordinate (thickness direction), giving a classical plate. The results obtained for porous plates are compared to a homogeneous isotropic rectangular plate. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||