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FE Models (fe + models)
Selected AbstractsFatigue-relevant stress field parameters of welded lap joints: pointed slit tip compared with keyhole notchFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2009P. LAZZARIN ABSTRACT The notch stress intensity factor (NSIF) based analytical frame is applied to the slit tips (or weld roots) of welded joints with inclusion of the T-stress component. This T-stress can be determined from FE models evaluating the ligament stresses close to the pointed slit tip. An alternative analytical frame is presented for the corresponding keyhole notches based on analytical solutions from the literature, which are applied to the ligament stresses. In the slit tip models, the mean local strain energy density (SED) with inclusion of the T-stress effect is determined analytically and numerically in comparison, using two different fatigue-relevant control radii,,R0= 0.28 mm and,R0= 0.15 mm, the former value well proven for thick-sheet welded joints made of structural steel. The latter smaller value is tentatively proposed for thin-sheet welded joints, in the direction suggested in the recent literature where a reduction of the microstructural support length for laser beam welds and resistance spot welds is recommended. The FEM-based and analytical stress concentration factors (SCF) for the lap joint keyhole model and also the SED values for the corresponding pointed slit tips are found to be in good agreement. The,J -integral consisting of the first and second component (the latter containing the T-stress) is compared with the corresponding SED values. [source] Micromechanical viscoelasto-plastic models and finite element implementation for rate-independent and rate-dependent permanent deformation of stone-based materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2010Qingli Dai Abstract This paper presents parallel and serial viscoelasto-plastic models to simulate the rate-independent and the rate-dependent permanent deformation of stone-based materials, respectively. The generalized Maxwell viscoelastic and Chaboche's plastic models were employed to formulate the proposed parallel and serial viscoelasto-plastic constitutive laws. The finite element (FE) implementation of the parallel model used a displacement-based incremental formulation for the viscoelastic part and an elastic predictor,plastic corrector scheme for the elastoplastic component. The FE framework of the serial viscoelasto-plastic model employed a viscoelastic predictor,plastic corrector algorithm. The stone-based materials are consisted of irregular aggregates, matrix and air voids. This study used asphalt mixtures as an example. A digital sample was generated with imaging analysis from an optically scanned surface image of an asphalt mixture specimen. The modeling scheme employed continuum elements to mesh the effective matrix, and rigid bodies for aggregates. The ABAQUS user material subroutines defined with the proposed viscoelasto-plastic matrix models were employed. The micromechanical FE simulations were conducted on the digital mixture sample with the viscoelasto-plastic matrix models. The simulation results showed that the serial viscoelasto-plastic matrix model generated more permanent deformation than the parallel one by using the identical material parameters and displacement loadings. The effect of loading rates on the material viscoelastic and viscoelasto-plastic mixture behaviors was investigated. Permanent deformations under cyclic loadings were determined with FE simulations. The comparison studies showed that the simulation results correctly predicted the rate-independent and rate-dependent viscoelasto-plastic constitutive properties of the proposed matrix models. Overall, these studies indicated that the developed micromechanical FE models have the abilities to predict the global viscoelasto-plastic behaviors of the stone-based materials. Copyright © 2009 John Wiley & Sons, Ltd. [source] The fast Gauss transform for non-local integral FE modelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2006E. Benvenuti Abstract Originally developed for fast solving multi-particle problems, the fast Gauss transform (FGT) is here applied to non-local finite element models of integral type (FEFGT). The focus is on problems requiring fine geometry discretization, as in the case of solutions that exhibit high gradients or boundary layers. As shown by one- and two-dimensional examples, the FEFGT algorithm combines the robustness of the finite element method with the outstanding computational efficiency of the FGT. Copyright © 2005 John Wiley & Sons, Ltd. [source] Improving the efficiency of finite element formulations in laminated compositesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2002Kostas P. Soldatos Abstract This communication extends the principles of an advanced smeared laminate plate theory towards the development of corresponding FE models and codes. The present FE numerical results are compared with those based on exact elasticity solutions, as well as those of corresponding FE models based on three conventional laminate plate theories. These comparisons show that, compared to those conventional FE codes, the proposed FE formulation that uses also a small and fixed number of nodal degrees of freedom improves substantially the accuracy of stress predictions. They also show that the present numerical results are particularly accurate even for very thick laminates. Copyright © 2002 John Wiley & Sons, Ltd. [source] Failure of heterogeneous materials: 3D meso-scale FE models with embedded discontinuitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2010N. Benkemoun Abstract We present a meso-scale model for failure of heterogeneous quasi-brittle materials. The model problem of heterogeneous materials that is addressed in detail is based on two-phase 3D representation of reinforced heterogeneous materials, such as concrete, where the inclusions are melt within the matrix. The quasi-brittle failure mechanisms are described by the spatial truss representation, which is defined by the chosen Voronoi mesh. In order to explicitly incorporate heterogeneities with no need to change this mesh, some bar elements are cut by the phase-interface and must be split into two parts. Any such element is enhanced using both weak and strong discontinuities, based upon the Incompatible Mode Method. Furthermore, a dedicated operator split solution procedure is proposed to keep local any additional computation on elements with embedded discontinuities. The results for several numerical simulations are presented to illustrate the capabilities of the proposed model to provide an excellent representation of failure mechanisms for any different macroscopic loading path. Copyright © 2010 John Wiley & Sons, Ltd. [source] Numerical simulation of the microscale impregnation in commingled thermoplastic composite yarnsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010R. Gennaro Abstract The impregnation of a glass woven fabric with an amorphous polyethylene terephthalate copolymer (PET- g) matrix was investigated using a finite element (FE) model for interbundle and intrabundle flow of the matrix. Micrographs of samples obtained by film stacking of PET- g to impregnate the glass fabric have confirmed the occurrence of interbundle and intrabundle flow, taking place as separate steps. On the basis of this evidence, two different mechanisms for the fiber impregnation were postulated. The first flow process is associated with a macroscale interbundle impregnation, whereas the second is associated with microscale intrabundle impregnation. Two different FE models were developed to simulate the microscopic and macroscopic flow of the matrix, considering a large number of different random fiber arrangements. Both models could account for the non-Newtonian rheological behavior of the thermoplastic matrix. The microscale impregnation of fibers was simulated by using randomly spaced and nonoverlapping unidirectional filaments. The effect of the number of filaments and the number of random distributions necessary to achieve an adequate accuracy of the method was assessed. The results obtained from the simulation showed that at low pressures, the polymer melt exhibits Newtonian behavior, which makes it possible to predict the tow permeability by the Darcy law. A more difficult situation arises at high pressures because of the non-Newtonian behavior of the melt. This requires the introduction of a value for the permeability that is also dependent on the rheological properties of the melt. The same non-Newtonian behavior of the matrix was observed for macroscale impregnation of bundles. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:122,130, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20179 [source] Are ectoparasite communities structured?JOURNAL OF ANIMAL ECOLOGY, Issue 6 2006Species co-occurrence, null models, temporal variation Summary 1We studied temporal variation in the structure of flea communities on small mammalian hosts from eastern Slovakia using null models. We asked (a) whether flea co-occurrences in infracommunities (in the individual hosts) in different hosts as well as in the component communities (in the host species) demonstrate a non-random pattern; (b) whether this pattern is indicative of either positive or negative flea species interactions; (c) whether this pattern varies temporally; and (d) whether the expression of this pattern is related to population size of either fleas or hosts or both. 2We constructed a presence/absence matrix of flea species for each temporal sample of a host species and calculated four metrics of co-occurrence, namely the C -score, the number of checkerboard species pairs, the number of species combinations and the variance ratio (V -ratio). Then we compared these metrics with the respective indices calculated for 5000 null matrices that were assembled randomly using two algorithms, namely fixed-fixed (FF) and fixed-equiprobable (FE). 3Most co-occurrence metrics calculated for real data did not differ significantly from the metrics calculated for simulated matrices using the FF algorithm. However, the indices observed for 42 of 75 presence/absence matrices differed significantly from the null expectations for the FE models. Non-randomness was detected mainly by the C -score and V -ratio metrics. In all cases, the direction of non-randomness was the same, namely the aggregation, not competition, of flea species in host individuals and host species. 4The inclusion or exclusion of the uninfested hosts in the FE models did not affect the results for individual host species. However, exclusion of the uninfested host species led to the acceptance of the null hypothesis for only six of 13 temporal samples of the component flea communities for which non-randomness was detected when the uninfested hosts were included in the analysis. 5In most host species, the absolute values of the standardized size effect of both the C -score and V -ratio increased with an increase in host density and a concomitant decrease in flea abundance and prevalence. 6Results of this study demonstrated that (a) flea assemblages on small mammalian hosts were structured at some times, whereas they appeared to be randomly assembled at other times; (b) whenever non-randomness of flea co-occurrences was detected, it suggested aggregation but never segregation of flea species in host individuals or populations; and (c) the expression of structure in flea assemblages depended on the level of density of both fleas and hosts. [source] Trabecular Bone Tissue Strains in the Healthy and Osteoporotic Human Femur,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 10 2003B Van Rietbergen Quantitative information about bone tissue-level loading is essential for understanding bone mechanical behavior. We made microfinite element models of a healthy and osteoporotic human femur and found that tissue-level strains in the osteoporotic femoral head were 70% higher on average and less uniformly distributed than those in the healthy one. Introduction: Bone tissue stresses and strains in healthy load-adapted trabecular architectures should be distributed rather evenly, because no bone tissue is expected to be overloaded or unused. In this study, we evaluate this paradigm with the use of microfinite element (,FE) analyses to calculate tissue-level stresses and strains for the human femur. Our objectives were to quantify the strain distribution in the healthy femur, to investigate to what extent this distribution is affected by osteoporosis, to determine if osteoporotic bone is simply bone adapted to lower load levels, and to determine the "safety factor" for trabecular bone. Materials and Methods: ,FE models of a healthy and osteoporotic proximal femur were made from microcomputed tomography images. The models consisted of over 96 and 71 million elements for the healthy and osteoporotic femur, respectively, and represented their internal and external morphology in detail. Stresses and strains were calculated for each element and their distributions were calculated for a volume of interest (VOI) of trabecular bone in the femoral head. Results: The average tissue-level principal strain magnitude in the healthy VOI was 304 ± 185 microstrains and that in the osteoporotic VOI was 520 ± 355 microstrains. Calculated safety factors were 8.6 for the healthy and 4.9 for the osteoporotic femurs. After reducing the force applied to the osteoporotic model to 59%, the average strain compared with that of the healthy femur, but the SD was larger (208 microstrains). Conclusions: Strain magnitudes in the osteoporotic bone were much higher and less uniformly distributed than those in the healthy one. After simulated joint-load reduction, strain magnitudes in the osteoporotic femur were very similar to those in the healthy one, but their distribution is still wider and thus less favorable. [source] THERMAL PROCESS EVALUATION OF RETORTABLE POUCHES FILLED WITH CONDUCTION HEATED FOODJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2002MARCELO CRISTIANINI ABSTRACT Two models using the finite element technique (FE) and another using an analytical solution to solve the 3-dimensional heat conduction equation for a finite plate were built. FE models were built considering the actual pouch shape and retort temperature profile. Chi-square and regression lines were obtained for each set of temperatures generated by the models against experimental data. A mass average sterilizing value of 9.9 min was estimated when a critical point sterilizing value was at 8.7 min using the 3-Dimensional FE model. Close agreement was found among the three models for heating phase. Using actual retort temperature profile made FE models more accurate than the one using analytical solution, especially for cooling phase. [source] An effective strategy for the multibody simulation of jointed FE models in the framework of the floating frame of reference formulation.PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Wolfgang Witteveen In multibody systems (MBS), where elastic bodies are represented in the frame work of the ,floating frame of reference formulation' (FFRF), structural deformation is usually computed by the superposition of time invariant trial vectors (commonly called ,modes'). However, the mode bases, which are discussed in the literature, do not take joints into special account at the stage of mode generation. In the presented paper we propose a problem,oriented extension of classical mode bases in order to consider the presence of joints. In the novel extension which we call ,Joint Interface Modes' (JIMs), Newton's 3rd law across the joint is taken into account at the stage of mode generation, which leads to a superior convergence at the stage of mode based computation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||