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In the present paper, the parameters of Johnson - Cook (JC) constitutive model for two steels have been identified, based on the Hopkinson pressure bar test results. The experimental data has been taken from the split Hopkinson pressure bar data found in the literature. Using the measured strain pulses, the experimental stress - strain and deformation - time curves can be extracted. The experimental data have been processed using two different methods. In the first method strain rate assume to be constant during deformation and in the other one the deformation has been applied to a modeled specimen. In each method, an optimal set of material constants for JC constitutive model have been computed by minimizing the standard deviation of the numerically obtained stress - strain curve from the experimental data. Also a sensitivity analysis has been performed on JC constitutive model parameters and temperature changes during test have been investigated. The obtained results show that using constant strain rate method, leads to considerable error in results; for example in this study the minimum error is about 14%.

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Cemented sandy soils can be found in different parts of nature. Slopes and natural cuts are observed to be stable for long periods of time. Indeed the stability is related to the cementation and bonding between soil grains which induces an equivalent cohesion for coarse grained soil. Several experimental and theoretical studies have been performed to investigate the mechanical behavior of this category of geomaterials. In present research, a constitutive model is proposed for simulating the mechanical behavior of cemented sandy soils. The model is based on separating the mechanical behavior of cemented soil to two different parts; firstly the uncemented soil matrix and secondly the cemented bonds. The generalized plasticity model developed by Manzanal et al. (2011) is used for predicting the mechanical behavior of the uncemented soil matrix. The model is based on critical state concepts and is able to simulate the behavior of sandy soil in a wide range of confining pressures. It contains sixteen parameters which can be determined using ordinary geotechnical tests for the base soil. Also the elastic-plastic damage bond model proposed by Haeri and Hamidi (2009) is used for cemented bonds. The model has two additional parameters and is able to predict the brittle behavior of cemented bonds besides their degradation with increase in shear strain. Peak shear resistance of cemented bonds increases with confining pressure, however, the axial strain associated to the peak shear strength decreases with enhancement of confining stress. Also cement content is considered in this bond model which is its advantage in comparison with similar ones. Both components have been combined together based on deformation consistency and energy equilibrium equations. Deviatoric stress-shear strain curves besides volumetric strain-shear strain ones have been compared with the results of consolidated drained triaxial tests on a gypsum cemented sand to verify the proposed model. Also deviatoric stress-axial strain besides deviatoric stress-mean effective stress curves of model are compared with results of tests in consolidated undrained state. Results of verification indicate good performance of developed model in a wide range of cement contents and confining pressures. The proposed model has two distinct advantages. At first it considers the effect of cement content as a model parameter and shows variation of the results with this parameter. Secondly, it simulates the soil behavior in a wide range of confining pressures which enables using it in the boundary value problem in geotechnical engineering. However, it should be noted that the model predicts the mechanical behavior of cemented sand in cement contents less than floating limit. Increasing the cement content from the floating threshold changes its role from effective bonding between soil grains to a filler of voids. In this condition, the model can not predict the behavior of cemented soil due to the limitations in the elastic-plastic damage bond model applied in present constitutive model.

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Cemented sandy soils can be found in different parts of nature. Slopes and natural cuts are observed to be stable for long periods of time. Indeed the stability is related to the cementation and bonding between soil grains which induces an equivalent cohesion for coarse grained soil. Several experimental and theoretical studies have been performed to investigate the mechanical behavior of this category of geomaterials. In present research, a constitutive model is proposed for simulating the mechanical behavior of cemented sandy soils. The model is based on separating the mechanical behavior of cemented soil to two different parts; firstly the uncemented soil matrix and secondly the cemented bonds. The generalized plasticity model developed by Manzanal et al. (2011) is used for predicting the mechanical behavior of the uncemented soil matrix. The model is based on critical state concepts and is able to simulate the behavior of sandy soil in a wide range of confining pressures. It contains sixteen parameters which can be determined using ordinary geotechnical tests for the base soil. Also the elastic-plastic damage bond model proposed by Haeri and Hamidi (2009) is used for cemented bonds. The model has two additional parameters and is able to predict the brittle behavior of cemented bonds besides their degradation with increase in shear strain. Peak shear resistance of cemented bonds increases with confining pressure, however, the axial strain associated to the peak shear strength decreases with enhancement of confining stress. Also cement content is considered in this bond model which is its advantage in comparison with similar ones. Both components have been combined together based on deformation consistency and energy equilibrium equations. Deviatoric stress-shear strain curves besides volumetric strain-shear strain ones have been compared with the results of consolidated drained triaxial tests on a gypsum cemented sand to verify the proposed model. Also deviatoric stress-axial strain besides deviatoric stress-mean effective stress curves of model are compared with results of tests in consolidated undrained state. Results of verification indicate good performance of developed model in a wide range of cement contents and confining pressures. The proposed model has two distinct advantages. At first it considers the effect of cement content as a model parameter and shows variation of the results with this parameter. Secondly, it simulates the soil behavior in a wide range of confining pressures which enables using it in the boundary value problem in geotechnical engineering. However, it should be noted that the model predicts the mechanical behavior of cemented sand in cement contents less than floating limit. Increasing the cement content from the floating threshold changes its role from effective bonding between soil grains to a filler of voids. In this condition, the model can not predict the behavior of cemented soil due to the limitations in the elastic-plastic damage bond model applied in present constitutive model.

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The lateral spreading of mildly sloping ground and the liquefaction induced by earthquakes can cause major destruction to foundations and buildings, mainly as a result of excess pore water pressure generation and softening of the subsoil. During many large earthquakes, soil liquefaction results in ground failures in the form of sand boils, differential settlements, flow slides, lateral spreading and loss of bearing capacity beneath buildings. Such ground failures have inflicted much damage to the built environment and caused significant loss of life. The risk of liquefaction and associated ground deformation can be reduced by various ground improvement methods, including densification, solidification (e.g., cementation), vibro-compaction, drainage, explosive compaction, deep soil mixing, deep dynamic compaction, permeation grouting, jet grouting, piles group and gravel drains or SCs. Nowadays, using pile foundation is one of the popular solution for soils vulnerable to liquefaction. the pile with enough length more than liquefiable soil depth can reduce the large deformation and unacceptble settlements. Liquefaction and lateral deformation of the soil has caused extensive damage to pile foundations during past earthquakes. Several example of significant damages in pile foundation have been reported in the literature from the 1964 Niigata,1983Nihonkai-Chubu,1989 Manjil and 1995 kobe earthquakes. These damage have been observed mainly in coastal areas or sloping ground. evaluation of liquefaction in order to develop the northern and southern ports and implement coastal and offshore structures in Iran is of particular importance due to locating in a high seismic hazard zone and Liquefactable soil in coastal areas. Although, in recent years many studies have been conducted to understand the various aspects of this phenomenon, yet a lot of uncertainties have remained about the lateral deformations of the soil and its effects on deep foundations. In this study, behavior of pile groups (2 × 1, 1 × 3, 2 × 2 and 3 × 3) were evaluated using fully coupled three-dimensional dynamic analysis. Therefore, the influence of effective parameters such as number of piles, ground slope angle on soil and pile behavior has been studied using the finite element software Opensees SP v2.4. results indicate that most of the factors affecting the behavior of the pile, soil are not considered in the current design codes (such as JRA 2002) and these issues indicate the need to revise the current design and analysis methods.Lateral Pressures compared to that of JRA regulations show that these regulations cannot exactly predict pressures on pile and pile groups. Altogether comparing the results of numerical model of this research to various laboratory observations indicate that the use of numerical method can be reliable to predict the behavior of the soil and pile qualitatively and quantitatively using appropriate constitutive model and parameters for soil and pile. Keywords: Liquefaction soil, pile group, fully coupled numerical analysis, multi-surface-plasticity constitutive model.

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Mechanical properties of polymeric materials are significantly sensitive to the loading rate. Therefore, it is necessary to develop a dynamic constitutive model to investigate their strain rate dependent mechanical behavior. In this study, first by conducting torsion experiments the shear behavior of neat and reinforced epoxy with carbon nano-fibers (CNFs) was studied experimentally. Then, the Johnson-Cook (J-C) model has been modified to be able to model the shear behavior of neat polymers. The strain rate effects on elastic behavior of polymers were considered by introducing a material equation. Then, by combining the modified Johnson-Cook (MJ-C) model with a micromechanical model (Halpin-Tsai model) and using pure polymer experimental tesults and mechanical properties of carbon nano fiber, the strain rate dependent mechanical behavior of polymers reinforced with CNFs at arbitrary strain rates and volume farction of carbon nanofiber has been predicted. The new model presented in this research is called as the dynamic-micromechanical constitutive model. The predicted results for the neat and nano-phased polymers were compared with conducted and available experimental results. It has been shown that the present dynamic constitutive model can predict the strain rate dependent mechanical behavior of polymeric materials with a good accuracy.

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Aortic Valve simulation remains a controversial topic, as a result of its complex anatomical structure and mechanical characteristics such as material properties and time-dependent loading conditions. This study aims to integrate physiologically important features into a realistic structural simulation of the aortic valve. A finite element model of the natural human aortic valve was developed considering Linear Elastic and Hyperelastic material properties for the leaflets and aortic tissues and starting from the unpressurized geometry. It has been observed that although similar stress-strain patterns generated on Aortic Valve for both material properties, the hyperelastic nature of valve tissue can distribute stress smoothly and lower strain during the cardiac cycle. The deformation of the aortic root can play a prominent role as its compliance extremely changed throughout cardiac cycle. Furthermore, dynamics of the leaflets can reduce stresses by affecting geometries. The highest values of stress occurred along the leaflet attachment line and near the commissure during diastole. The effects of high +G acceleration on the performance of valve, valve opening and closing characteristics, and equivalent Von Mises stress and strain distribution are also investigated.

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Skeletal muscles simulation remains a controversial topic as a result of its complex anatomical structure and mechanical characteristics such as nonlinear material properties and loading conditions. Most of the current models in the literature for describing the constitutive equations of skeletal muscles are based on Hill's one-dimensional, three element model. In this paper a 3D constitutive model which is based on the hyper elastic behavior of skeletal muscle and energy function has been presented. By using the derivatives of such energy function for defining the Second Piola and Cauchy stresses, we able to describe the inactive behavior of skeleton muscles. The applied constitutive equations are an efficient generalization of Hamphury's model for the inactive behavior of skeletal muscle. In this paper using a 3D model, different modes of deformations of skeletal muscle such as simple tension, biaxial and shear tests has been investigated and material properties constants for each modes of deformation has been optimized by Genetic algorithm. Finally the results of the model simulations of each mode are compared with those obtained from experimental tests. Also, the model results are compared with the ones from two well- known hyper elastic Ogden and Mooney-Rivilin models in order to show the priority of the new developed 3D model to those aforementioned models has been shown.

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In this research, the seismic response of offshore wind turbines, considering the interaction of saturated soil-pile-structure, has been investigated using numerical method of finite element. OpenSees software has been used to consider the conditions of soil saturation and pore water pressure changes. Due to the existence of soil constitutive model in OpenSees, such as the PDMY model and coupled u-p elements, it has a good ability to model saturated soil and pore water pressure changes.For numerical verification, a centrifuge test carried out by Yu et al. was used. This test was carried out on an offshore wind turbine with tripod foundation, with a height of 13 meters and three piles, 0.5 in diameter and 3 meters in length with a triangular arrangement, and the response of the turbine tower and pore water pressure variations under the earthquake load have been investigated. In this experiment, blades, hub and Nacelle were simplified as a rigid mass on top of wind turbine tower and so large moment caused by the earthquake load was modeled on the foundation. For simulation and creating numerical model, only one half of the system was modeled using symmetry boundary condition. Soil 3D continuous medium was modeled through coupled u-p formulation correlated to saturated porous medium using PDMY constitutive model that has the ability to simulate sandy soil behaviour under cyclic loadings in drained and undrained condition. The model consisted of 14288 nodes and 12420 coupled u-p 3D elements for saturated soil part. Nonlinear beam-column elements were used for pile parts. For simulating actual size of pile cross-section, rigid beam elements perpendicular to the longitudinal axis of the piles were used. Actually these rigid elements were beam-column type that their stiffness is 10000 times larger than the stiffness of pile elements. One node of this elements was connected to the pile and the other node was tied to the soil node with same location through equal DOf constraint. Each pile with 3 meter in length consisted of 12 nonlinear beam-column elements. For half pile 65 rigid elements and for full pile 104 rigid elements was used to simulate actual size of pile cross-section. Wind load on tower is estimated by equation provided in DNV standard. Also the thrust force (force applied by the wind on the rotor of turbine) is calculated through the previous study (Leite) and using Manwell equation. Wave load is calculated by Morison equation and the kinematics of water particles are simulated by Airy wave theory (linear wave theory). After passing the verification stage, through the parametric study, the effect of other environmental loads (wind and wave load) and peak ground acceleration (PGA) on the seismic response of the offshore wind turbine are investigated. The results showed that in seismic analysis of offshore wind turbines, the interaction of environmental loads should be considered, and the Superposition Principle can not be easily applied. It was also found that the relationship between the peak ground acceleration and the turbine tower response is nonlinear. On the other hand, by increasing the PGA, the effect of soil-piles interaction on the r_u ratio increases.

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Granular materials in their natural state have an inter particle boning that is resulted from natural cementation. These bonds form a relatively strong structure in the soil mass that is called soil structure and consequently these types of material are called structured soils. Structured soils could also be produced artificially by cement or lime treatments. Volumetric compression and the stress-strain behavior of the structured materials after virgin yielding are highly nonlinear that cannot be expressed by a single line in semilogarithmic scale. The natural or artificial structure of the soil retains the void ratio of the soil in higher levels than the void ratio of the same soil in remolded state at the same stress levels. Increasing the stress level from the threshold stress of the virgin yielding initiates the crashing of the soil structure that results large amounts of volumetric strains with a small value of volumetric stiffness. Further crashing the structure of the soil and decreasing its void ratio increases the volumetric stiffness of the soil. Although this procedure is highly nonlinear, however it is a continuous phenomenon and can be formulated mathematically. Since the structure losing behavior of structured soils occurs between two known states, therefore, it could be explained based on the disturbed state concept (DSC). According to the DSC, the behavior of complex phenomena between two reference states could be described based on their behaviors in two reference states using an appropriate state function. The state function or interpolating function relates the response of the material at any level to its responses at two reference states. In this paper a constitutive model base on hierarchical single surface model (HISS) and the disturbed state concept was proposed to describe the stress-strain and the failure behavior of structured soils. The behavior of the soil at the beginning of the virgin yielding was considered as initial, relatively intact (RI), state and its behavior after fully crashed state was considered as fully adjusted (FA) state. The disturbance function derived based on the isotropic compression behavior of the material in the laboratory. A power form state function was proposed to describe the variation of the bulk modulus of the soil. The variable compression model was implemented in HISS model to capture the volumetric behavior of the structured soil. The proposed model verified based on the data from literature. The verification of the proposed constitutive model showed the ability of the model to predict the stress-strain and failure behavior of structured soils. The proposed model could be employed with any other constitutive models to introduce the effect of the structure destruction on the stress-strain and failure behavior of the soil. In the proposed model, if the initial and end modulus of elasticity are equal, the strain stress relationship is linear, and if the initial and final values of the modulus of elasticity are different, then the nonlinear stress-strain behavior is simulated. Hence the behavior of a wide range of materials can be predicted by this model. The proposed model could be utilized to predict the behavior natural structured soils, artificially cemented soils.

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In the present study, solid particle erosion of Ti-6Al-4V alloy under the impact of spherical alumina particles with a diameter of 85 microns was analyzed using experimental studies and smoothed particle hydrodynamics (SPH) modeling. The erosive behavior of this alloy was simulated as impacts on micro-scale and based on Johnson-Cook constitutive equations. This research focuses on the effect of particle velocity and impact angle on erosion rate as the most critical factors. Additionally, the results of this model are validated by empirical results under-considered conditions. At the end of the article, based on the alloy properties, the velocity of particles, and impact angle, a prediction equation was presented on erosion rate in the studied range of velocity and impact angle. This study indicates a power-law equation between the velocity of particles and the erosion rate, where the power is independent of impact angle. Furthermore, in all the velocity and angle ranges, the maximum erosion rate was associated with the angle of 45^o. Therefore, the critical angle in erosion is also independent of the velocity of particles.