1,720,983 research outputs found
Effect of compressibility on the mechanics of hyperelastic membranes
Get PDFElastic membranes are usually studied assuming material incompressibility. However, in several applications they are made of compressible materials such as polymeric foams, hydrogels, and certain kinds of elastomers. Only a few works attempted to incorporate volume changes into membrane problems, but with significant limitations. The models proposed were designed for nearly incompressible materials and lacked a foundation in experimental data, leading to results of limited value. In this work, we investigate the effect of compressibility in membrane problems adopting a consistent model based on the real response of materials to large volume changes. We consider three benchmark problems of nonlinear elasticity: (i) inflation of a circular flat membrane; (ii) inflation of a thin-walled cylindrical tube; (iii) inflation of a thin-walled spherical balloon. Four types of materials divided by increasing degree of compressibility are studied. The results indicate that volumetric deformations have a significant impact on both the limit pressure and the deformed shape. The proposed solutions represent benchmarks for developing new applications of compressible membranes made of polymeric foams and hydrogels, playing an increasingly important role in engineering technologies
A strain energy function for large deformations of compressible elastomers
No full textElastomers are typically considered incompressible or slightly compressible. However, we present simple tension and bulk tests showing that, under large deformations, these materials can undergo significant volume changes. A review of the literature reveals the lack of an accurate hyperelastic model for finite volumetric deformations of elastomers. Therefore, we propose a new volumetric strain energy density (SED) that overcomes the limitations of the current models. The main advantages of the proposed SED are: (1) accurate description of the response of rubbers for both small and large volumetric deformations; (2) ability to reproduce diverse behaviors during volume shrinkage and expansion; (3) adaptability to other compressible materials, such as soft tissues, foams and hydrogels. Using the deviatoric- volumetric split of the strain energy, the proposed volumetric SED is combined with a suitable deviatoric part selected from the literature. The parameters of the combined SED are calibrated by fitting the model to the experimental data from simple tension and bulk tests. As a result, an accurate description of the response of elastomers under both shape and volume deformations is provided. The proposed SED can be implemented in numerical codes to capture the effects of volumetric deformations on the equilibrium solutions for various stress states
Analytical, numerical and experimental study of the finite inflation of circular membranes
Get PDFIn the present work we derive an analytical expression for the pressure–deflection curve of circular membranes subjected to inflation. This problem has been studied mostly from a numerical point of view and there is still a lack of accurate closed-form solutions in nonlinear elasticity. The analytical formulation is developed with a semi-inverse method by setting a priori the kinematics of deformation of the membrane. A compressible Mooney–Rivlin material model is considered and a pressure–deflection relation is derived from the equilibrium. The kinematics is approximated and therefore the obtained solution is not exact. Consequently, the formulation is adjusted by introducing an additional polynomial function in the pressure–deflection equation. The polynomial is calibrated by fitting numerical solutions of the exact system of differential equilibrium equations. The calibration is done over a wide range of constitutive parameters that covers the response of all rubber materials for technological applications. As a result, a definitive and accurate expression of the applied pressure as a function of the deflection of the membrane is obtained. The formula is validated with finite element (FE) simulations and compared with other solutions available in the literature. The comparison shows that the present model is more accurate. In addition, unlike the other models, it can be applied to compressible materials. Experimental uniaxial and bulge tests are carried out on rubber materials and the model proposed is used to characterize the Mooney–Rivlin constitutive parameters. Since the pressure–deflection formula is accurate and easy-to-use, it is an innovative tool in engineering applications of inflated membranes
Optimization of the structural coupling between RC frames, CLT shear walls and asymmetric friction connections
Get PDFThis paper focuses on the optimum design of the e-CLT technology. The e-CLT technology consists in adding cross laminated timber (CLT) walls to an existing reinforced concrete (RC) infilled frame via asymmetric friction connection (AFC). The authors carried out quasi-static and nonlinear dynamic analyses. The RC frame is modeled in OpenSees by fiber-section-based elements with force-based formulation. The contribution of the infill is simulated using a degrading data-driven Bouc–Wen model with a slip-lock element while the AFC is modelled with a modified Coulomb model. Different types of infill, aspect ratio, scaling, and member size are considered. The benefits of using e-CLT technology are discussed and the ranges of optimum performance of the AFC are estimated. A comparison of the performance of traditional infills with the e-CLT system is presented. The authors provide optimum intervals of the ratio between slip force and in-plane stiffness of the CLT panel, following energy and displacement-based criteria. The seismic displacement demand under various seismic scenario is investigated. Correlations between the RC characteristics and the optimum design ratios bestow possible criteria for the design of the AFC
Hyperelastic model for nonlinear elastic deformations of graphene-based polymer nanocomposites
Get PDFGraphene-based polymer nanocomposites (PNCs) are increasingly important in engineering applications involving large deformations. However, the nonlinear behavior of these materials has not been thoroughly studied. Current models do not address the specific nonlinear effects of graphene nanofillers under large strains, lack sufficient comparison with experimental data, and primarily focus on uniaxial behavior without exploring biaxial responses, which are relevant in technological applications. This study investigates PNCs composed of silicone elastomer and graphene nanoplatelets (GNPs). We present experimental tests conducted in both simple tension and biaxial inflation on circular membranes. A homogenized hyperelastic model is developed, incorporating distinct contributions from the matrix and the nanofiller. Specifically, we introduce a novel strain energy function for the nanofiller contribution, tailored to reproduce the observed experimental behavior. The model accurately predicts the nonlinear elastic response of the studied PNCs across varying contents of GNPs. The proposed strain energy function is implemented in MATLAB to obtain an exact numerical solution for the inflation of circular PNC membranes. Finally, to demonstrate its broader applicability, the hyperelastic model is applied to additional experimental data from other PNCs found in the literature. This model contributes to establishing a robust framework for the effective use of PNCs
Empirical formulation for the estimate of the equivalent viscous damping of infilled RC frames
No full textThe direct displacement-based design (DDBD) is based on the equivalence between the nonlinear hysteretic response of a structure and a simple linear oscillator with equivalent viscous damping (EVD). Typically the EVD is calibrated for different types of structures as a function of the ductility. However, those simple relationships exhibit a huge dispersion and uncertainty since the specific properties of the structural system are not considered. This work proposes an original approach for estimating the EVD of infilled reinforced concrete (RC) frames. We focus on a ductility demand corresponding to an ultimate limit state and we investigate the effect of the properties of infilled RC frames on the EVD. A data-driven hysteresis model proposed by the authors in a previous research is implemented in OpenSees to represent the nonlinear response of infill panels. The optimal EVD at the ultimate limit state is computed using an extensive series of time-history analyses (THAs) on a dataset of 14 infilled RC frames. Afterwards, an empirical correlation law for the estimate of the optimal EVD is calibrated as a function of the geometrical and mechanical properties of infilled RC frames. This formula is meant to be a practical tool for a preliminary design of infilled RC frames. A comparison with the EVD estimated by quasi-static tests and the EVD of bare frames is made. The methods and results presented in this work may be the basis for more robust predictions of the EVD of infilled RC structures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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