The Chaboche kinematic hardening model is generally used for modeling the plastic behaviour of material under quasi-static cyclic and monotonic loadings. This model is independent of strain rate and its constants are normally determined through quasi-static tests. Therefore, it cannot predict material behavior under high strain rate condition. On the other hand, the dynamic behaviour of materials even in some cyclic loadings is usually strain rate sensitive. In this investigation, the constants of Chaboche model are identified at various strain rates through quasi-static and dynamic tests and using these constants the effect of strain rate is incorporated in the Chaboche model. Moreover, the stress-strain diagrams at different strain rates are predicted using artificial neural network (ANN) and the results are compared with the experimental data. The results from the strain rate dependent Chaboche model shows reasonable agreement with the experimental data and the prediction from ANN. It is also shown in this work that the constants of Chaboche plasticity model are strain rate dependent and if the neural network is trained properly, it can be used for interpolating between the experimental data.

Nanocrystalline materials show a higher strain-rate sensitivity in contrast to the conventional coarse-grained materials and a different grain size dependency. To explain these phenomenon, a finite element model is constructed that considers both grain interior and grain boundary deformation of nanocrystalline materials. The model consist of several crystalline cores with different orientations and grain boundary phase. The nonlinear behavior of the nanocrystalline core is implemented by a grain size dependent crystal plasticity. The boundary phase is assumed to have the mechanical properties of quasi-amorphous material. The constitutive equations for both grains interior and boundary phase are implemented into the finiteelement software Abaqus. A calibration procedure was used to tune some parameters of the model with the previously published experimental data on the nanocrystalline copper. Then the model is used to predict the material behavior in various strain rates and grain sizes. The stresses obtained from these simulations match well with the experimental data for nanocrystalline copper at different strains and strain rates. Deviation from the Hall-Petch law and inverse Hall-Petch effect are also well illustrated by the model.

For the purpose of determining the effects of strain rate on the complete load-displacement curves of specimens containing a single joint when subjected to gradually increasing compressive loading, a series of tests was conducted at constant strain rates of 2.08 x 10(-6)/s (slow rate), 4.17 x 10(-5)/s (medium rate) and 8.33 x 10(-4)/s (fast rate). Triaxial tests were carried out under satisfactory end-specimen conditions on two types of sandstone from various locations by a 5 MN servo-controlled stiff testing machine up to 30 MPa confining pressure. For intact specimens in zero confining pressure (uniaxial test) a higher strain rate resulted in a higher modulus of elasticity (steeper positive slope before strength failure) and in a higher failure stress of the specimens. Increased confining pressure reduced the strain rate effects. strain rates had no similar effect on the jointed specimens of different rocks under uniaxial condition. Change of strain rate from slow to fast resulted in a higher stress value at the initiation of sliding for both rock types under different confining pressures. The behavior varied in different rocks when sliding continued. strain rate had a significant effect on the modes of failure for both the intact and jointed specimens.

dependency is one of the significant relations in syntactic elements. In subordination, a unit is subordinated to another. One kind of subordination is complement clauses. In this study, the rate of semantic and syntactic integration is discussed. Relying on semantic factors, successfulness of main clause verb, co-reference and co-temporality of main clause and complement clause, complement-taking verbs of Farsi are put in different classes of dependence. the presence or absence of complementizer in complement clauses, co-lexicalization or case-marking of the subject and the object are marked in clauses to see which verbs show the most bond in main clauses and complement clauses by studying the semantic factors including the tense of complement clauses. The complement clauses with the most bonds dealing with main clauses tend to join to in a single sentence. It is revealed in this research that manipulation verbs have the most bonds between complement clauses and main clauses and their tendency in such verbs to join in a single sentence is high, so, they are placed above the complementation continuum. beside manipulation verbs, modality verbs with the same bonds are placed in the category, then, below complementation continuum, perception-cognition-utterance verbs are placed afterwards which have the lowest bond between main clause and complement clause. While studying semantic factors dealing with complement clauses and main clauses, it is revealed that Persian doesnot use co-lexicalization joined with complement clauses. This research provides a continuum of complement-taking verbs in Persian and the effect of iconicity on linking these verbs.

The fiber-reinforced polymer (FRP) composites under different dynamic loads experienced various strain rates. Since mechanical behaviors of fiber-reinforced polymer composites vary with the strain rate, the transient response of most of the composite structures will be dependent on the strain rate. In the present research, a comprehensive review of the previously published studies on the topic of strain-rate dependent properties of glass fiber and its fiber-reinforced composites, as the most common FRP composite, under dynamic loading was presented. At first, studies that presented the mechanical properties of the long glass fibers at various strain rates were extensively investigated. Furthermore, experimental studies on the effects of strain rate on different types of glass fiber reinforced polymer composites were categorized and presented. Also, the strain-rate dependent behavior of the thermoset polymers was investigated. The various analytical and numerical models of macro-mechanics and micromechanics presented for this type of composites were reviewed comprehensively.

Background: Pulmonary arterial hypertension (PAH) is a leading cause of death in systemic sclerosis (SSc) patients. Early detection of systolic failure in SSc patients will facilitate early treatment and improve the survival rate of these patients.Objectives: In this study, besides studying the RV function in SSC patients, attempts have been made to find a new possible noninvasive echocardiographic test for early diagnosis of systolic failure as a PAH complication.Methods: 30 patients with at least a 2-year history of diffuse SSc confirmed by an expert rheumatologist were enrolled in this study.All the patients underwent transthoracic echocardiography by an echocardiologist. Fractional area change (FAC) of the right ventricle (RV), tricuspid annular plane systolic excursion (TAPSE), RV lateral wall strain and strain rate (Base, Mid, Apex), RV-EDD and RV pressure with respect to inferior vena cava (IVC) diameter as well as Left Ventricle’s Ejection Fraction (LVEF) were evaluated.Results: The prevalence rate of PAH was reported 36.6% in this study. There was no significant relationship between LVEF and RV parameters. LVEF was found to be significantly higher in women whereas RV strain turned out to be higher in men. Besides, there was a significant relation between pulmonary arterial pressure (PAP) and Basal (P=0.03), mid RV strain (P=0.002), RV strain rate (P=0.001) and RV diameter (P=0.02). Also, an inverse relation was observed between RV systolic (P=0.01) and diastolic functions (P= 0.007) with PAP. In addition, no significant relationship was found between LVEF and body mass index (BMI) and RV parameters (P> 0.05). Moreover, Apical RV strain and LVEF were found to be higher in males and females respectively. Furthermore, a significant relationship was found between RV strain and age (P=0.027). Finally, the results did not show any relationship between RV systolic and diastolic functions and gender.Conclusions: This paper states the likely advantages of strain and strain rate echocardiography in identifying patients with more diffused and severe SSc and the need for further longitudinal studies based on the mentioned method for early diagnosis of myocardial impairment.

Today thorium based fuels are being investigated as possible alternatives in fuel technology. However, the majority of thorium fuel research studies are limited to reactor physics investigations, and there are concerns about dose evaluation and shielding of such spent fuels. The present work investigates burn-up behavior of thorium oxide fuel in Tehran research reactor. The fuel gamma dose rates are calculated at different burnups and cooling times. A comparison between the reactor routine fuel and the thorium oxide fuel is conducted to reveal shielding challenges of the thorium-based fuel application. Despite the U3O8-Al routine fuel, the obtained results showed that ThO2 gamma dose rates are completely dependent on the burn-up values. In addition, for transporting the spent ThO2 fuel with the routine transport casks, there is a necessity for the higher cooling times compared with that of U3O8-Al. Otherwise, construction of thicker transport casks is needed to transport the thorium-based spent fuel in shorter times.

A model of freshwater ice behavior under impact compression is suggested. To obtain the parameters (mechanical properties of ice at high-speed loading) of the model the Kolsky method is used. The necessary parameter data are obtained at a strain rate of 1. 4×103 s-1. A new procedural approach and an experimental data filtering algorithm are proposed. In addition, a phenomenological model of ice is offered, which makes it possible to obtain a relationship between the measured force and the parameters of the material. The verification of the model is performed according to the results of experiments in which forces are obtained in the study of the destruction of ice samples for high strain rates. It is shown that the analytical force model describes the experimental data well.

Advanced high strength steels (AHSS) have recently attracted great attention because of their superior mechanical properties. A modern group of these steels, known as twinning induced plasticity (TWIP) steels, shows a unique combination of strength and ductility even at high rates of strain. In order to examine the functionality of such steels in dynamic loading conditions, their mechanical behavior should be characterized by high strain rate experiments. Regarding the precision of its results and characteristics of the loading pulse, the torsional Kolsky bar experiment has well-known advantages over similar high rate experiments. In this study, a high strain rate torsional testing machine was designed and constructed. By using high strain rate torsional experiments in the range of strain rates from 500 to 1700 /s, mechanical behavior of two high manganese steels with different levels of carbon (0.49 and 0.07 wt%) was surveyed. Through the experiments, it was observed that the phenomenon of adiabatic temperature rise considerably decreased the work hardening rate during the dynamic testing of the high-carbon steel, whereas the low-carbon steel showed a definitely higher hardening rate. The influence of pre-straining on the dynamic mechanical behavior of this low-carbon steel was also studied.