Abstract in English:Abstract In this study the use of short glass, carbon and hybrid glass-carbon fibers reinforced polymeric composites in power transmission coupling is investigated. The presented work is generalized to thermoplastic and thermoset polymeric matrix composites. The effects of the constituents weight percentages, and average fibers length on the composite tensile strength and modulus are studied using the Taguchi design of experiments method. A new approach of Finite Element analysis is introduced to model the effect of the hybrid fibers random distribution and average fibers length among the volume of the matrix. Each fiber is simulated independently in the model as a three dimensional truss element embedded in the matrix. The FEA model is applied on the tensile specimen and then on the power transmission coupling simulation. Finally, the new approach of finite element analysis results on the coupling are validated.
Abstract in English:Abstract A study on the seismic response of a free-standing marble column, including rocking and sliding effects, is presented in this paper. The rocking-sliding model implemented for the development of the analyses corresponds to the basic theoretical and numerical simulation of the dynamic phenomenon. The assessment procedure adopted for the application of the model to the non-linear dynamic incremental time-history investigation is checked by comparison with simplified rigid body-based analytical predictions of the rocking-onset response acceleration and the overturning critical velocity. The results show a high seismic vulnerability of the column, as identified by severe damage at the basic design earthquake level, and an overturning-related near-collapse response at the maximum considered earthquake level.
Abstract in English:Abstract The prediction of plastic instability in sheet metals during forming processes represents nowadays an ambitious challenge. To reach this goal, a new numerical approach, based on the loss of ellipticity criterion, is proposed in the present contribution. A polycrystalline model is implemented as a user-material subroutine into the ABAQUS/Implicit finite element (FE) code. The polycrystalline constitutive model is assigned to each integration point of the FE mesh. To derive the mechanical behavior of this polycrystalline aggregate from the behavior of its microscopic constituents, the multiscale self-consistent scheme is used. The mechanical behavior of the single crystals is described by a finite strain rate-independent constitutive framework, where the Schmid law is used to model the plastic flow. The condition of loss of ellipticity at the macroscale is used as plastic instability criterion in the FE modeling. This numerical approach, which couples the FE method with the self-consistent scheme, is used to simulate a deep drawing process, and the above criterion is used to predict the formability limit of the studied sheets during this operation.
Abstract in English:Abstract This paper presents an exact model for studying the global buckling of concrete-filled steel tubular (CFST) columns with compliant interfaces between the concrete core and steel tube. This model is then used to evaluate exact critical buckling loads and modes of CFST columns. The results prove that interface compliance can considerably reduce the critical buckling loads of CFST columns. A good agreement between analytical and experimental buckling loads is obtained if at least one among longitudinal and radial interfacial stiffnesses is high. The parametric study reveals that buckling loads of CFST columns are very much affected by the interfacial stiffness and boundary conditions.
Abstract in English:Abstract In the present paper, orthotropic elasto-plastic constitutive formulations for sheet metal forming based on non-associated flow rule that assume distortion of yield function/plastic potential with ongoing deformation process are analyzed. The yield function/plastic potential are considered as two different functions with functional form as orthotropic quadratic Hill or non-quadratic Karafillis-Boyce stress function. Based on the principle of plastic work equivalence, anisotropy parameters of the utilized yield function/plastic potential are set as functions of the equivalent plastic strain. In the constitutive formulation, for this internal variable, evolution equation consistent with the same principle of plastic work equivalence is introduced. For DC06 sheet sample with reported significant variation of the incremental r-values with straining, predictions of the evolution of the yield stress and r-value directional dependences with straining obtained by the analyzed models are presented. The algorithmic formulations of the analyzed constitutive models are derived by application of the implicit return mapping algorithm. For the derived stress integration procedures the accuracy is investigated by calculating iso-error maps. The maps are compared according to the flow rule and involved orthotropic stress functions. It has been revealed that although there is a difference in maps configuration there is no prominent difference in error magnitudes.
Abstract in English:Abstract In this paper, forming limit diagrams (FLDs) for an aluminum alloy are predicted through numerical simulations using various localized necking criteria. A comparative study is conducted for the FLDs determined by using the Lemaitre damage approach and those obtained with the modified Gurson-Tvergaard-Needleman (GTN) damage model. To this end, both damage models coupled with elasto-plasticity and accounting for plastic anisotropy have been implemented into the ABAQUS/Explicit software, through the user-defined subroutine VUMAT, within the framework of large plastic strains and a fully three-dimensional formulation. The resulting constitutive frameworks are then combined with four localized necking criteria to predict the limit strains for an AA6016-T4 aluminum alloy. Three of these necking criteria are based on finite element (FE) simulations of the Nakazima deep drawing test with various specimen geometries, while the fourth criterion is based on bifurcation theory. The simulation results reveal that the limit strains predicted by local criteria, which are based on FE simulations of the Nakazima test, are in good agreement with the experiments for a number of strain paths, while those obtained with the bifurcation analysis provide an upper bound to the experimental FLD.