bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling three‐dimensional crack propagation—A comparison of crack path tracking strategies
Authors: Jäger P. , Steinmann P. , Kuhl E. 
Published: October 2008

AbstractThe development of a new finite element technique for the simulation of discontinuous failure phenomena in three dimensions is the key objective of this study. In contrast to the widely used extended finite element technique, we apply a purely deformation‐based strategy based on an independent interpolation of the deformation field on both sides of the discontinuity. This method has been applied successfully for two‐dimensional crack propagation problems in the past. However, when it comes to three‐dimensional failure phenomena, it faces the same difficulties as the extended finite element method. Unlike in two dimensions, the characterization for the three‐dimensional failure surface is non‐unique and the tracking of the discrete crack can be performed in several conceptually different ways. In this work, we review the four most common three‐dimensional crack tracking strategies. We perform a systematic comparison in terms of standard algorithmic quality measures such as mesh independency, efficiency, robustness, stability and computational cost. Moreover, we discuss more specific issues such as crack path continuity and integratability in commercial finite element packages. The features of the suggested crack tracking algorithms will be elaborated by means of characteristic benchmark problems in failure analysis. Copyright © 2008 John Wiley & Sons, Ltd.
Singularity enrichment for complete sliding contact using the partition of unity finite element method
Authors: Giner E. , Sukumar N. , Fuenmayor F. J. , Vercher A. 
Published: October 2008

AbstractIn this paper, the numerical modelling of complete sliding contact and its associated singularity is carried out using the partition of unity finite element method. Sliding interfaces in engineering components lead to crack nucleation and growth in the vicinity of the contact zone. To accurately capture the singular stress field at the contact corner, we use the partition of unity framework to enrich the standard displacement‐based finite element approximation by additional (enriched) functions. These enriched functions are derived from the analytical expression of the asymptotic displacement field in the vicinity of the contact corner. To characterize the intensity of the singularity, a domain integral formulation is adopted to compute the generalized stress intensity factor (GSIF). Numerical results on benchmark problems are presented to demonstrate the improved accuracy and benefits of this technique. We conduct an investigation on issues pertaining to the extent of enrichment, accurate numerical integration of weak‐form integrals and the rate of convergence in energy. The use of partition of unity enrichment leads to accurate estimations of the GSIFs on relatively coarse meshes, which is particularly beneficial for modelling non‐linear sliding contacts. Copyright © 2008 John Wiley & Sons, Ltd.
A 3D BEM model for liquid sloshing in baffled tanks
Authors: Firouz‐Abadi R. D. , Haddadpour H. , Noorian M. A. , Ghasemi M. 
Published: October 2008

AbstractThe present work aims at developing a boundary element method to determine the natural frequencies and mode shapes of liquid sloshing in 3D baffled tanks with arbitrary geometries. Green's theorem is used with the governing equation of potential flow and the walls and free surface boundary conditions are applied. A zoning method is introduced to model arbitrary arrangements of baffles. By discretizing the flow boundaries to quadrilateral elements, the boundary integral equation is formulated into a general matrix eigenvalue problem. The governing equations are then reduced to a more efficient form that is merely represented in terms of the potential values of the free surface nodes, which reduces the size of the computational matrices considerably. The results obtained using the proposed model are verified in comparison with the literature and very good agreement is achieved. Finally, a number of example tanks having common configurations are used to investigate the effect of baffle on sloshing frequencies and some conclusions are outlined. Copyright © 2008 John Wiley & Sons, Ltd.
Robust and direct evaluation of J2 in linear elastic fracture mechanics with the X‐FEM
Authors: Legrain G. , Moës N. , Verron E. 
Published: October 2008

AbstractThe aim of the present paper is to study the accuracy and the robustness of the evaluation of Jk‐integrals in linear elastic fracture mechanics using the extended finite element method (X‐FEM) approach. X‐FEM is a numerical method based on the partition of unity framework that allows the representation of discontinuity surfaces such as cracks, material inclusions or holes without meshing them explicitly. The main focus in this contribution is to compare various approaches for the numerical evaluation of the J2‐integral. These approaches have been proposed in the context of both classical and enriched finite elements. However, their convergence and the robustness have not yet been studied, which are the goals of this contribution. It is shown that the approaches that were used previously within the enriched finite element context do not converge numerically and that this convergence can be recovered with an improved strategy that is proposed in this paper. Copyright © 2008 John Wiley & Sons, Ltd.
Space–time approach to numerical analysis of a string with a moving mass
Authors: Bajer Czesław I. , Dyniewicz Bartłomiej 
Published: October 2008

AbstractInertial loading of strings, beams and plates by mass travelling with near‐critical velocity has been a long debate. Typically, a moving mass is replaced by an equivalent force or an oscillator (with ‘rigid’ spring) that is in permanent contact with the structure. Such an approach leads to iterative solutions or imposition of artificial constraints. In both cases, rigid constraints result in serious computational problems. A direct mass matrix modification method frequently implemented in the finite element approach gave reasonable results only in the range of relatively low velocities. In this paper we present the space–time approach to the problem. The interaction of the moving mass/supporting structure is described in a local coordinate system of the space–time finite element domain. The resulting characteristic matrices include inertia, Coriolis and centrifugal forces. A simple modification of matrices in the discrete equations of motion allows us to gain accurate analysis of a wide range of velocities, up to the velocity of the wave speed. Numerical examples prove the simplicity and efficiency of the method. The presented approach can be easily implemented in the classic finite element algorithms. Copyright © 2008 John Wiley & Sons, Ltd.
A contact algorithm for frictional crack propagation with the extended finite element method
Authors: Liu Fushen , Borja Ronaldo I. 
Published: October 2008

AbstractWe present an incremental quasi‐static contact algorithm for path‐dependent frictional crack propagation in the framework of the extended finite element (FE) method. The discrete formulation allows for the modeling of frictional contact independent of the FE mesh. Standard Coulomb plasticity model is introduced to model the frictional contact on the surface of discontinuity. The contact constraint is borrowed from non‐linear contact mechanics and embedded within a localized element by penalty method. Newton–Raphson iteration with consistent linearization is used to advance the solution. We show the superior convergence performance of the proposed iterative method compared with a previously published algorithm called ‘LATIN’ for frictional crack propagation. Numerical examples include simulation of crack initiation and propagation in 2D plane strain with and without bulk plasticity. In the presence of bulk plasticity, the problem is also solved using an augmented Lagrangian procedure to demonstrate the efficacy and adequacy of the standard penalty solution. Copyright © 2008 John Wiley & Sons, Ltd.
Numerically consistent regularization of force‐based frame elements
Authors: Scott M. H. , Hamutçuoğlu O. M. 
Published: October 2008

AbstractRecent advances in the literature regularize the strain‐softening response of force‐based frame elements by either modifying the constitutive parameters or scaling selected integration weights. Although the former case maintains numerical accuracy for strain‐hardening behavior, the regularization requires a tight coupling of the element constitutive properties and the numerical integration method. In the latter case, objectivity is maintained for strain‐softening problems; however, there is a lack of convergence for strain‐hardening response. To resolve the dichotomy between strain‐hardening and strain‐softening solutions, a numerically consistent regularization technique is developed for force‐based frame elements using interpolatory quadrature with two integration points of prescribed characteristic lengths at the element ends. Owing to manipulation of the integration weights at the element ends, the solution of a Vandermonde system of equations ensures numerical accuracy in the linear‐elastic range of response. Comparison of closed‐form solutions and published experimental results of reinforced concrete columns demonstrates the effect of the regularization approach on simulating the response of structural members. Copyright © 2008 John Wiley & Sons, Ltd.
Comparison of FDG‐PET scans to conventional radiography and bone scans in management of Langerhans cell histiocytosis
Authors: Phillips Michelle , Allen Carl , Gerson Paul , McClain Kenneth 
Published: October 2008

AbstractBackgroundWe evaluated the effectiveness of FDG‐PET scans in identifying sites of active disease and assessing response to therapy in patients with Langerhans cell histiocytosis (LCH). Changes in standardized uptake value (SUV) indicated increased or decreased disease activity before changes are evident by plain films or bone scans.MethodsOne hundred and two PET scans for 44 patients (41 children, 3 adults) with biopsy‐proven LCH were compared with 83 corollary imaging modalities and were rated for overall clinical utility: false positive or negative (“inferior”), confirming lesions identified by another imaging modality (“confirmatory”), or showing additional lesions, response to therapy or recurrence of disease activity (“superior”), in comparison to bone scans, MRI, CT or plain films.ResultsFDG‐PET was rated superior in that 90/256 (35%) new, recurrent, or lesions responding to therapy were identified via change in standard uptake value (SUV) before other radiographic changes. PET scans confirmed active LCH in 146/256 (57%). FDG‐PET was superior to bone scans in that 8/23 (34%) lesions, 11/53 (21%) comparisons to lesions found by MRI, 13/64 (20%) CT, and 58/116 (50%) plain films. PET scans confirmed lesions found by: 14/23 (61%) bone scans, 33/53 (62%) MRI, 45/64 (65%) CT, and 54/116 (46%) of plain films.ConclusionsWhole body FDG‐PET scans can detect LCH activity and early response to therapy with greater accuracy than other imaging modalities in patients with LCH lesions in the bones and soft tissues. Whole‐body FDG‐PET scanning is an important and informative study at diagnosis and for following disease course in patients with LCH. Pediatr Blood Cancer 2009;52:97–101. © 2008 Wiley‐Liss, Inc.
Process optimization of devulcanization of waste rubber powder from syringe stoppers by twin screw extruder using response surface methodology
Authors: Maridass B. , Gupta B.R. 
Published: October 2008

AbstractResponse surface methodology was used to predict the optimal processing parameters viz. barrel temperature and screw speed in a counter‐rotating twin screw extruder for devulcanization of rubber powder obtained from factory waste of medical syringe stoppers. Central composite rotatable design for two variables at five levels was chosen as the experimental design. The results obtained after measuring the responses were fitted as two‐variable second‐order equations. The corresponding contour plot, response surface plot, Pareto chart, and main effect plot were plotted and analyzed. Optimum properties were predicted at temperature 180°C and screw speed 27 rpm, which was confirmed experimentally. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Clay intercalation and influence on flammability and crystallization behaviors of POE‐based nanocomposites
Authors: Lu Hongdian , Hu Yuan , Li Ming , Song Lei 
Published: October 2008

AbstractEthylene‐octene copolymer (POE)‐based nanocomposites were prepared from POE or maleic anhydride grafted POE with organo‐modified montmorillonite (OMT) using melt blending technique. Their morphology, flammability, and crystallization behavior were investigated by X‐ray diffraction (XRD), transmission electron microscopy (TEM), cone calorimeter, and differential scanning calorimetry (DSC). XRD and TEM studies confirmed the intercalation of clay layers within the POE matrix whereas the exfoliation throughout the maleated POE matrix. Cone calorimetry results exhibited that the reduction in heat release rate of exfoliated maleated‐POE/OMT nanocomposite was greater than that of intercalated POE/OMT nanocomposite. The DSC results suggested that the nonisothermal kinetics crystallization of the exfoliated nanocomposite corresponded to tridimensional growth with heterogeneous nucleation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
The thickness dependence of elastic modulus of organosilane interphases
Authors: Jancar J. 
Published: October 2008

AbstractSeries of organosilanes with varying molecular structure was deposited onto E glass. Solution coating and rf plasma enhanced Chemical Vapor Deposition (PE‐CVD) techniques were used. Thickness of the deposited layers varied from 30 nm to 106 nm. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic modulus of the layers deposited on the glass substrate as a function of layer thickness. In all cases, increase of the Young modulus, E, of the organosilane layer with decreasing layer thickness was observed. Solution deposited layers exhibited always significantly lower elastic moduli compared to the layers deposited using PE‐CVD technique. Elastic moduli of deposited layers increased with increasing hydrocarbon chain rigidity at comparable chain length. Chlorosilane interlayers possessed always significantly greater elastic modulus compared to their ethoxy‐analogues. The observed increase of E with the decreasing layer thickness was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. It was shown that increasing the bond strength between the deposited layer and the solid E‐glass substrate resulted in immobilized region with constraints imposed by the surface spanning into a distance from the surface. This was in agreement with current models of reinforcement mechanism in nanocomposites based on the idea of immobilized entanglements. It was shown that the deposition technique plays important role in controlling the structure and properties of the deposited interphase. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
A robust shock and noise model for the manufacturing of molded LDPE foams
Authors: Chedly S. , Chettah A. , Bonnefoy H. , Ichchou M.N. 
Published: October 2008

AbstractThe article concerns the injection manufacturing process of molded foam sheets and their intrinsic shock and noise performances. The main goal is to optimize the physical performances of molded plastic foams at an early stage in their design and manufacturing. The effects of injection process parameters on the properties of molded LDPE foams are investigated. The input optimization parameters considered are: injection temperature, mold temperature, injection speed, plasticization back pressure, and screw rotation speed during the plasticization phase. The output optimization parameters considered are: density, shock absorption, and acoustic absorption. The experimental design method made use of the Taguchi table and central composition design. This allows us to identify simplified mathematical models for input/output and to detect the most influential input in the injection process. We conclude by validating the models and their robustness. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Effect of crystallite size on the deformation and fracture of poly(vinylidene fluoride‐trifluorethylene) ferroelectric copolymer films under uniaxial tension
Authors: Fang F. , Yang W. , Jia C. , Zhang F.C. 
Published: October 2008

AbstractThe deformation and fracture behavior is characterized for poly(vinylidene fluoride‐trifluorethylene) 75/25 mol% copolymer films under uniaxial tension. The films are prepared by solution casting and then annealed at 135°C for 2 h, 6 h, and at 140°C for 2 h, respectively. The results demonstrate that all the copolymer films show the typical polymeric brittle fracture behavior. The copolymer film annealed at 135°C for 2 h shows the best combination of ductility and strength, with the fracture strain reaching 9.6%. Scanning electron microscope observation and X‐ray diffraction analysis are carried out to examine the morphology and microstructure change during uniaxial tension. It is revealed that the average size of the polymer crystallites increases while the content of the crystallites hardly changes as the annealing time or temperature increases. Reduction in the crystallite size leads to enhanced fracture strain and strength for the copolymer film under uniaxial tension. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Modeling contraction flows and swell of polymer melts extruded from dies of various lengths
Authors: Jeong Jae‐Hyeuk , Leonov Arkady I. 
Published: October 2008

AbstractThis article describes isothermal contraction flows and extrudate swell, using our recent model for fast (high Deborah number) contraction flows of polymers melts. The model analyzes the polymer flow in several regions as one continuous process. This approach makes possible to evaluate the extrudate swell as a result of complex contraction polymer flow in dies of various length. Using the asymptotic matching conditions for the change in flow type at the die exit allowed us to calculate the swelling profile for extrudate in the flow direction. The present calculations performed using a multi‐mode viscoelastic constitutive equation of differential type, are compared with the experimental/direct numerical data including basic rheological tests. The presented complex model for contraction flow and swelling consists of no fitting parameter and is applicable for calculations using any viscoelastic constitutive equation. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Direct patterning of polystyrene–polymethyl methacrylate copolymer by means of laser interference lithography using UV laser irradiation
Authors: Lasagni A.F. , Acevedo D.F. , Barbero C.A. , Mücklich F. 
Published: October 2008

AbstractThe fabrication of functionalized surfaces on polymeric substrates is of importance in chemistry, biology, physics, and material science. Examples of functional surfaces are micro/nano periodic arrays that can be fabricated using different methods. However, many of these techniques require several fabrication steps. In this communication, we report the fabrication of advanced architectures in poly(methylmethacrylate)–polystyrene (PMMA–PS) copolymers using direct laser interference patterning. Because of the mixed optical properties of the copolymers, a different type of periodic architectures could be fabricated when compared with traditional pure polymers. This new type of periodic structures results from the local swelling of the copolymer due to the formation of gaseous products induced by the laser radiation. Additionally, relatively low laser fluences are necessary to initiate the ablation process of the copolymers. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Studies on epoxy blends modified with a hyperbranched polyester
Authors: Cicala G. , Recca G. 
Published: October 2008

AbstractThermomechanical and rheological properties of epoxy blends modified with different percentages of a hyperbranched polymer have been reported. The addition of the hyperbranched modifier did not alter the rheological behavior of the blend. This effect is particularly advantageous for some composite manufacturing techniques because it allows for the establishment of low viscosity during processing. Morphological development was studied under curing by hot stage microscopy. The cryo‐fractured surfaces of the cured samples were analyzed by scanning electron microscopy. The morphological analysis showed that the blends did not phase separate at any modifier percentage. This result was further supported by dynamic mechanical testing (DMTA) on cured samples. In fact, DMTA showed a single relaxation peak for all the formulations studied. The dynamic testing was also used to assess the damping properties of the systems. The blends of this study were also compared with similar systems modified with poly(ε‐caprolactone), which were the subjects of a previous article. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Use of carboxylated nitrile rubber and natural rubber blends as retreading compound for OTR tires
Authors: Pal Kaushik , Das Tanya , Pal Samir K. , Das Chapal K. 
Published: October 2008

AbstractOre transportation is one of the important unit operations in a mineral industry. In this study, three raw rubber compounds are prepared in three different blend ratios, and four types of raw rubber samples of pure NR with silica reinforced has been collected from the different tire retreading industries. Blend properties largely depend on the blend ratio and on the blending technique. The improvement in the physical properties such as cure characteristics, mechanical characterization, cross‐link density, FTIR, thermal characterization, SEM studies, and dynamic mechanical analysis has been studied in those samples. It has been found that retread rubber made with 80 phr XNBR and 20 phr NR has given the better results when compared with the other samples against all the characterization done. It is also seen that rubber made by the researchers are very good in tough, rigid and these are extremely able to withstand for using as a retread rubber for 35T dump trucks tire when compared with the retread rubber made by the tire retreading industries for different mines in India. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Processing/structure/property relationships for artificial wood made from stretched PP/wood‐fiber composites
Authors: Kim Y.S. , Guo G. , Park C.B. , Wang K.H. 
Published: October 2008

AbstractThis article presents the processing/structure/property relationships for artificial wood made from stretched PP/wood‐fiber (WF) composites that have required strength and density. The die drawing of PP/WF composites causes a unidirectional orientation of the polymer molecules and enhances the mechanical properties significantly along the stretched direction. The drawing of the composites also lowers the density of artificial wood by generating voids at the WF and polymer matrix interface. The critical processing and materials parameters are identified. The effects of these parameters on the structure and the properties are also investigated. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers