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In the present study, the frequency analysis of a smart sandwich plate is investigated using the finite element method. The sandwich plate is consisted of a magnetorheological elastomer (MRE) layer between two cross ply composite elastic faces. MRE is a smart material with controllable properties and a short time response when subjected to a magnetic field. This property can be used for improvement of the dynamic behavior of the structure. To model the sandwich plate with MRE layer, a complex shear modules is used to show the pre-‌yield behavior of MRE layer. In this study, effect of imperative parameters are discussed. In the present paper, the effect of different parameters such as applied magnetic field, the stacking sequences of the cross ply laminated faces in the sandwich plate and applying different boundary conditions on the natural frequencies and modal loss factors of the smart sandwich plate with MRE is investigated. The results show that considering special value for magnetic field, the stacking sequences of the composite layers of the sandwich plate and the boundary condition of the sandwich structure can lead to the satisfactory design of the sandwich plate.

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This paper briefly reviews Fiber Reinforced Elastomeric Isolators (FREIs) as a relatively new type of elastomeric bearings. In comparison with conventional Steel Reinforced Elastomeric Isolators (SREIs) that are reinforced with steel plates, FREIs utilize fiber fabric layers as the reinforcement material. The fiber reinforcement is employed to prevent the lateral bulging of elastomer layers when the bearing is subjected to vertical compression. Fiber reinforced isolators are categorized in two groups, namely, “bonded-“ and “unbonded-“ FREIs, depending on the boundary conditions at top and bottom surfaces of the bearing. The main objective of this paper is to simulate the lateral load-displacement hysteresis loops of unbonded-FREIs. In an unbonded-FREI, no bonding is provided between the bearing and its top and bottom contact supports. As such, shear forces are transferred via friction at the contact surfaces. When an unbonded-FREI is deformed laterally, portion of its contact surfaces roll off the contact supports, and the bearing exhibits a specific deformation called “rollover deformation”. As a result of rollover deformation, the effective lateral stiffness of the bearing is decreased significantly. This in turn improves the seismic isolation efficiency due to the increased base isolated period of bearing. The ultimate lateral displacement in an unbonded-FREI may achieve when the originally vertical faces of the bearing contact top and bottom supports. Lateral load-displacement response in an unbonded-FREI is characterized with a gradual softening (due to rollover deformation) that is followed by a stiffening behavior at the ultimate stage of lateral bearing displacement. Under a cyclic excitation, the response characteristics of the bearing during the first load-cycle are different than the subsequent cycles of the same load amplitude. This phenomenon that is specific to elastomeric materials is known as Mullins’ effect. In this paper an extended Bouc-Wen model is developed to simulate the lateral load-displacement hysteresis loops of unbonded-FREIs. The model captures the gradual softening and ultimate stiffening behavior in the load-displacement curve of the bearing, and addresses the Mullins’ effect in the simulation of hysteresis loops. The proposed model comprises two simultaneous coupled equations which employ six constant coefficients altogether. To determine these coefficients, the model is fitted to experimentally-evaluated load-displacement hysteresis loops of prototype bearings. The experimental loops are obtained from cyclic shear tests that are conducted on the bearing while it is subjected to constant vertical compression. In order to account for Mullins’ effect, an individual set of coefficients corresponding to unscragged loops (the first cycle of each displacement amplitude) are evaluated. The second set of coefficients is attributed to scragged response (subsequent cycles of each displacement amplitude) of the bearing. To simulate the load-displacement hysteresis loops, the proposed model switches between the first and the second set of coefficients depending on the unscragged or scragged state of the elastomer, respectively. A constraint is imposed on the model to assure its continuity when the model coefficients are alternated. Comparison between analytical and experimental results (shake-table test data) indicates that the proposed model is accurate in dynamic response simulation of the unbonded-FREIs studied in this paper.

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An experimental procedure is used to determine the transient response of an elastomeric isolator under the impact loading conditions and a numerical procedure is developed to evaluate the corresponding acceleration transmission ratio and shock response spectrum. In the experimental analysis the elastomeric isolator is connected to a resonance beam subjected to the shock loading of a pendulum striker and the shock level is measured using acceleration sensors mounted along three orthogonal directions in the basement and free end of isolator. The shock response spectrum diagram and the level of wave attenuation are determined based on the measured acceleration levels for a wide frequency range. Finite element model based on mode superposition approach is developed to analyze the impact response of elastomeric isolator using the mode shapes with frequency in range of impact excitation spectrum. Due to the importance of longitudinal response of isolators, the numerical model is employed to evaluate the longitudinal output acceleration time history of isolator. The number of elements, time step for motion equation integration and the number of mode shapes are studied and the optimized corresponding values are selected based on the convergence of the numerical results. The calculated results for wave attenuation level and shock response spectrum diagrams correlate well with the experimental measurements under two different impact loading conditions and the present model can be used to evaluate the performance of isolators depending on the level of impact loads and transmission acceleration and displacement ratios in the output of elastomeric isolators.

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Bulging with elastomer tool has been used in the production of integrated hollow parts as one of flexible forming methods. Nowadays, most industries such as Aerospace and military are using flexible die forming methods due to their flexibility, high quality and lower cost. In this research, finite element simulation has been implemented by ABAQUS software to investigate the behavior of stainless steel 304 tube bulging process using elastomer tool. By comparing the geometry of deformed tubes in experimental tests and simulation results, the FEM model was verified. The aim of this study is to determine the process factors and their effects on the average thickness and depth of bulged tube. In this regard, design of experiment (DOE) was performed using a full factorial method and the results were interpreted using analysis of variance (ANOVA). Also a regression model was presented to predict these responses. Results showed that among the studied factors, friction (between tube and rubber), rubber height, punch displacement and tube axial feeding have significant effects on the process. Finally, the optimal values for significant factors were presented.

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Elastomers are a group of polymeric materials that have unique properties, including time-dependent behavior and time-independent, the mechanical behavior of this material is affected by various factors. In this study, the effect of increasing the silica nanoparticles and strain rates in two quasi-static and dynamic states on the tensile behavior of HDPE / POE has been investigated. For this purpose, an elastomeric material was first created with 40% HDPE and 60% POE mixing ratio. Then with increasing Nano silica particles, 4 sample types including 3 samples 0.7%, 1% and 1.4%, and one sample of HDPE/POE was fabricated. The samples were loaded at strain rate of 0.04 1⁄s, 0.07 1⁄s , 0.1 1⁄s , 0.14 1⁄s , 0.17 1⁄s in a quasi-static tensile state. In dynamic mode, tensile load with a strain rate of 160 1⁄s and 100 1⁄s was applied to the specimens using a new fixture designed on the low velocity impact test machine (Drop weight impact test machine). In the dynamic loading, the behavior of the elastomeric material is extremely dependent on the strain rate, with increasing the strain rate the level of stress and forces in both quasi-static and dynamic loads will be increase. The increase in force levels in dynamic loading is much more than static. Also, the new designed mechanism provides access to dynamic tensile data at different strain rates in a low velocity impact machine. On the other hand, with increasing Nano silica percentage, the tensile strength of the samples is noticeably increased.

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In this study, the energy absorption capacity of kevlar/elastomer composites under high-speed impact loading has been investigated experimentally and numerically. The compliance of the mechanical behavior of elastomeric composites with the theory of hyperelasticity will complicate the analytical study. Therefore, numerical simulation due to the different and complex mechanisms of failure, has gained the largest share in the design of composite structures. In the present study, the most advanced method of modeling the finite element of composites Abaqus / Explicit has been used to determine their behavior during impact impact. For this purpose, planer shell elements were used to model the composite layers and to determine the behavior of the elastomeric composite failure model, the material model of the formable material and the material model of the vumat were used based on one of the damage criteria such as von mises stress. Due to the lack of criteria mentioned in the commercial versions of the software and the importance of considering such damages in numerical simulation for these composites, the criterion was written using coding in the Fortran software environment and the analysis of the penetration phenomenon in composite structure was added to the software capability. In order to validate this model, an experimental test was performed on the kevlar/elastomer composite by a Gas gun device. Also, the study of deformation and output velocity projectile and absorpted energy have been reported as results. The simulation results show a very good agreement with the experimental results.
 

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In the present research, classic micromechanical methods and their application as constitutive models in conjugation with incremental theory were developed. Using the modified Eshelby model, the Eigen strain concept in polymeric composite, and a modified form of self-consistent model the elastic properties of nanocomposites were predicted. Also, the stress-strain behavior of elastomer nanocomposites was calculated and validated by the experimentally determined ones. The results showed that the new model can predict the stress-strain behavior of elastomer nanocomposite at different particle volume fractions.