In the last three decades, the constitutive modeling of concrete evolved considerably. This paper describes various developments in this field based on different approaches such as elasticity, plasticity, continuum damage mechanics, plastic fracturing, endochronic theory, microplane models, etc. In this article the material is assumed to undergo small deformations. Only time independent constitutive models and the issues related to their implementation are discussed.      

1. Introduction: Soil reinforcement with cement results in improvement of compressive and shear strengths, but adding the cement to soil causes more brittle behavior of soil. Fibers are used to solve this problem. The mechanical behavior of cemented granular soils is between soil and rock materials. Constitutive models for these materials should have the simulation capability of their special specifications. Up to now, different constitutive models for cemented soils have been presented. However, regarding the soil constitutive models with capability of considering the effects of cement and fiber, no study has been done. Constitutive models with capability of considering the effects of cement and fiber can be applied in geotechnical softwares to evaluate the correct behavior of such materials. However, representing a constitutive model for predicting the behavior of fiberreinforced cemented soils is an effective step in geotechnical analysis...

In this study, a constitutive equation based on the hyperbolic sine Arrhenius-type model has been developed to describe the hot deformation behavior of a Fe-17Cr-7Ni (17-7PH), semiaustenitic precipitation hardening stainless steel. The experimental data obtained from hot compression tests at temperature range of 950-1100 C and strain rates of 0. 001-1 s-1 were used to establish the constitutive equation. The material constants of α , A, n, and Q were calculated, using the developed model related to the applied strain by 6th order polynominal relationships. The average absolute relative error (AARE) and correlation coefficient (R) were used to evaluate the accuracy of the constitutive equation. The average values obtained for AARE and R were 5. 17% and 0. 9904, respectively. The results indicated that the developed constitutive equation can predict the flow stress behavior of the studied alloy with good accuracy over a wide range of experimental conditions. The model can be, therefore, recommended for analysis of hot deformation mechanism and microstructure evolution.

In this paper, an elastoplastic constitutive model is presented for predicting sandy soil behavior under monotonic and cyclic loadings. The model is based on the CJS3 model that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule in deviatoric mechanism is non-associated and a kinematic hardening law controls the evolution of the yield surface. In the present study, the critical state surface and history surface separating the virgin and cyclic states in the stress space are defined. Hardening modulus and stress-dilatancy law for monotonic and cyclic loadings are effectively modified. Taking the hardening modulus as a function of deviatoric and volumetric plastic strain, the model will be capable of predicting sand behavior once the history surface and stress reversal are defined. All model parameters have clear physical meanings and can be determined simply from laboratory tests. The results of homogeneous tests on Hostun sand are used to validate the model. The results of validation indicate the capability of the proposed model.

Background and Aim: When using improper recording materials during the fabrication of dentures, the whole process could be compromised in spite of the precision administered during the rest of the procedure. The aim of this study was to compare the flow of Pars Wax, Azardent, Crystal and Asia Wax with the Dental Modelling Wax Detry (Manufactured in Dentsply) according to standard indices of ADA, specification no. 24.Materials and Methods: All flow tests were conducted in accordance with the corresponding ADA specifications. Two samples of each wax (10 mm wide x 6 mm heigh) were prepared. A force of 19.6N (2kg) was applied on each specimen at three different temperatures: 23, 37 and 45°C. The geometric changes were accurately measured with a micrometer and compared to those obtained prior to the tests. The ratios of the dimensions after force application to the initial dimensions were determined. Based on these ratios, wax flows were compared to standard indices. Results: The amount of flow at 23°C and 45°C, obtained for all studied waxes was in accordance with the corresponding standard values, proposed by ADA. However, at 37°C the flow of none of the studied waxes was in the range of the ADA standards.Conclusion: Considering that the tested waxes demonstrated conflicting results at different temperatures when compared with the standard values, further investigation using different batch numbers is suggested.

New techniques in seismic design of structural systems are based on flexibility and energy dissipation approach. In this approach, the role of energy dissipaters is quite important. The behaviors of these devices and the way they dissipate energy have always been a concern for many researchers to improve the efficiency of these important parts of the structural systems. There has been a large number of investigations on behavioral aspects of energy dissipating devices capable of using in seismic design of structural systems.The concept of adding dissipating supplemental devices to a structure assumes that much of the energy imposed to the structure from a transient will be absorbed, not by the structure itself, but rather by supplemental damping elements. Among them, viscous devices have received considerable attention. The behavior of these energy dissipaters are dependent, not only on the relative velocity, but also on a large number of other parameters including relative displacement, compressibility of fluid, internal friction etc.The behavior of viscous devices are also dependent on the frequency of excitation and their thermal conditions. Determination of mechanical characteristics of these devices is usually based on experimental studies including cyclic tests in different amplitudes and frequencies.In this study, a new type of viscous dashpot in which the main body of the device has been made of contractible steel bellows (developed in IIEES) is chosen for experimental studies. The viscous device has the capacity of 500 kN and axial deformability of ±150mm. The tests have been carried out using an actuator capable of providing axial forces up to 300 kN in cyclic tests with displacement range of ±120mm. Axial forces on dashpot and resulted deformations on the device during experiments have been used to find the relationships between applied forces and induced relative displacement and velocity on the device.According to the results, the dashpot shows a dominant viscous behavior. It also represents a small frictional behavior in order of 10 kN (on average). The device also shows a frictional feature that is proportional to its internal fluid pressure. This feature is due to a small asymmetry in manufacturing some parts of the device, but it can be used later to improve the behavior of contractible dashpots. To be able to develop a model for this device, the test results are used in the form of cyclic behavior and time series. The time series results show the fact that there is not a linear proportionality between forces and velocity experienced by the dashpot in all the range of excitation frequencies. In addition, according to the test results, damping constants for this device is also dependent on the excitation frequency. Different types of behavioral models have been examined for the device. The proper model is proposed based on the three element type Maxwell model. The model can be further improved to represent the pressure dependent frictional forces in this dashpot.

Due to the stochastic nature of wind energy, allocating an appropriate investment incentive for wind generation technology (WGT) is a complicated issue. We propose an improvement on the traditional incentive, known as capacity payment mechanism (CPM), to reward the wind generators based on their performance exogenously affected by the wind energy potential of the location where the turbines are installed, and therefore, lead the investments towards locations with more generation potential. In CPM, a part of investment cost of each generator is recovered through fixed payments. However, in our proposal, wind generators are rewarded according to dynamic forecasts of the wind energy potential of the wind farm where they are located. We use an auto-regressive moving average (ARMA) model to forecast the wind speed fluctuations in long-term while capturing the auto-correlation of wind velocity variation in consecutive time intervals. Using the system dynamics (SD) modelling approach a competitive electricity market is designed to examine the efficiency of the proposed incentive. Performing a simulation analysis, we conclude that while a fixed CPM for wind generation can decrease the loss of load durations and average prices in long-term, the proposed improvement can provide quite similar results more efficiently.

The present paper deals with the theory of Ibn Sina's certain judgmental knowledge in terms of determining its constituent parts. Given Ibn Sina's existing ideas, these constitutive elements include belief, bi-dimensionality of belief, stability, and existence of middle term (in non-axioms). Nevertheless, regarding the notion of truth, we should say that Ibn Sina's considering it a constituent part creates several problems. The writer believes that since this point has not been directly stated in Ibn Sina's views, truth is necessary for a specific type of certain affirmative knowledge. Truth is neither a constituent of certain judgmental knowledge nor something external to it, rather, it is necessary for it.

Constitutive model of passive myocardium of lamb: Experimental tests and equations on the continuum mechanics are used in order to obtaining the constitutive models of soft tissue using in predictive heart simulation. Considering the myocardium as one of the important tissues, in this paper first the morphology and structure of myocardium has been reviewed and the mechanical response of passive form of this tissue has been investigated. The myocardium of left ventricle was considered as non linear elastic, in-compressible and non homogeneous material and using of bi-axial test in 3 lambs myocardium on fiber direction; a constitutive model of this tissue has been proposed. The model so constructed is then evaluated against the biaxial data, and values of the material constants have been obtained by curve fitting so the final model states the strain-energy function as cauchy's invariants which can be helpful in heart simulation.