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Rock dynamics as a branch of rock mechanics deal with dynamic behavior of rocks under high loading rates. Considering that many problems in rock engineering including earthquackes, explosions and projectile penetrations deal with high loading rates, rock dynamics has been of high significance to explore. In order to design and stability analysis of many of defense and military structures constructed on and in rocks, designating of dynamic behavior of rocks under different loading rates is essential. However, detailed understanding of rock dynamics has been of high challenge due to the additional ‘4th’ dimension of time. The split Hopkinson pressure bar test (SHPB) is the most applicable and famous technique in determination of dynamic behavior of materials under high loadin rates. In this thechnique, a pressure wave with a high domain is dispatched to the specimen and the reflected and transmitted waves of specimen will be captured by means of strain gauges glued on the bars of Hopkinson apparatus. A dynamic stress-strain curve will be obtained for the specimen applying some known equations upon physical conditions of SHPB test. A great majority of studies have been shown that dynamic strength of rocks increases with an increase in loading rate. Also, it has been shown that inertial and heterogeneity effects are the most impressive factors on dynamic strength increase of rocks under high loading rates. It is of note that Inertial effect boils down to a sudden increase in inner pressure of rock. Although, heterogeneity causes a more proper dynamic stress equilibrium as well as an increase in strain rate of specimen before the failure relative to those of homogenous one. The more the loading rate is, the more the strength of rock increases. In the present study, efforts have been applied to explore the effect of loading rate on dynamic behavior of rocks using split Hopkinson pressure bar as the most known and common apparatus in studying dynamic behavior of materials under high loading rates. The specimens have been cored of the same block of sandstone with a diameter of 21.5 mm and aspect ratio of 2. First of all, some quasi- static tests including uniaxial and Brezilian have been done to obtain uniaxial compressive strength, Young’s modulus, poison’s ratio and tension strength. In the meantime, Ultra-sonic test has been applyied to group the specimens of same p-wave velocity before doing Hopkinson test. The dynamic stress-strain curves for the specimen under different loading rates have been gained after capturing incident, reflected and transmitted waves by the strain gauges. Results show that there is an intense dependence of dynamic strength of sandstone to the loading rate so that with imposing the strain rate of 150 s^(-1) on the specimen, the dynamic strength of sandstone has been increased to 260 MPa from 160 MPa in quasi-static conditions. That’s why DIF, as the ratio of quasi-static strength to the dynamic one, has been obtained 1.6 at the 150 s^(-1) strain rate.

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Gas launchers are important part of impact testing apparatus which have many applications in material parameters identification. Some experiments call for very high velocity that are beyond the limit of one-stage gas launchers; thus, two-stage gas launchers are employed. Several parameters affect the operation of such launchers. For optimum adjustment of such parameters, modeling and simulation is necessary and inevitable. To this end, in this paper, a one dimensional model for a two-stage light gas launcher is proposed and utilized for performance optimization. To simulate combustion, experimental data for burning rate has been used. The proposed model is verified by comparing its predictions with the available experimental data. It is shown that the proposed model is accurate enough to predict the two-stage light gas launcher performance. The results of one dimensional model can be used in the basic design of the launcher, investigating the feasibility of manufacturing and estimating the costs. Moreover, the model is used to optimize the launcher performance as well as to determine optimum parameters. The statistical method of response surface is employed to find suitable second order polynomial models to predict the projectile velocity and maximum base pressure. The presented models are used to maximize the projectile velocity as well as to minimize the maximum projectile base pressure. To this end, Simplex method is employed to minimize the maximum base pressure in different conditions. Finally, the table of optimum conditions is presented to simplify the optimum use of the two-stage light gas launcher.

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Magnetic shape memory alloys (MSMAs) are a new class of smart materials that exhibit characteristics of large recoverable strains and high frequency. These unique characteristics, make MSMAs interesting materials for applications such as actuators, sensors, and energy harvesters. This paper presents a two-dimensional phenomenological constitutive model for MSMAs, developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold for variant reorientation is introduced which improves the model accuracy in multiaxial loadings. Preassumed kinetic equations for magnetic domain volume fractions, decoupled equations for magnetization unit vectors and appropriate presentation of the limit function for martensite variant reorientation lead to a simple formulation of the proposed constitutive model. To investigate the proposed model capability in predicting the behaviors of MSMAs, several numerical examples are solved and compared with available experimental data as well as constitutive models in the literature. Demonstrating good agreement with experimental data besides possessing computational advantages, the proposed constitutive model can be used for analysis of MSMA-based smart structures.

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Additive manufacturing methods and/or 3D printing have become increasingly popular with a particular emphasis on methods used for metallic materials. Selective Laser Melting (SLM) process is one of the additive manufacturing methods for production of metallic parts. The method was developed in particular to process metal parts that need to be more than 99 percent dense. In this method, according to a predefined pattern, the top surface of the powder layer is scanned by the laser and a local (selective) melt pool is produced in the place of the laser spot which results in a fully dense layer after solidification. In this study, a semi-coupled thermo-mechanical simulation of SLM process is carried out in ABAQUS finite element software. In order to simulate the moving heat flux and update material properties from the powder to the dense solid, the ability of the software for employing user-defined subroutines is employed. Investigation of the residual stress distribution and distortion of a part built using SLM process are the main objectives of this simulation. Results which are presented for two different mechanical boundary conditions show that when the bottom face of the layer is clamped, the top face of the built layer deforms in a concave shape, while the lateral faces of the layer have simply-supported boundary conditions and the bottom face of the layer is free, the part is warped.

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In this study a novel solution method for dynamic analysis of clamped-free shape memory alloy beams is presented. It is assumed that the beam is entirely made of shape memory alloy. Based on Euler-Bernoulli beam theory the governing equations of motion and corresponding boundary conditions are derived by using extended Hamilton principle. In the derived PDEs the transformation strain is behaved as external force that changes with time and position. The Galrkin approach is employed to convert PDEs to ODE system equations of motion. The derived equations of motion are solved by using Newmark integration method. The shape memory alloy constitutive model that presented by Souza is applied for specifying the phase of material all over beam. The transformation strain as internal variable that is coupled with states of equations of motion is identified in every time and every position of beam by using return map algorithm. A parametric study on the control variables has been adopted and the results of parametric study are discussed. The results show that the hysteresis damping is increased by increasing the operating temperature. Moreover the damping of system is faster by increasing the initial displacement in free vibration.

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In most semiarid and arid areas, fresh water shortage compels managers to use low quality water sources with high salinity to irrigate turf and landscape. Recent research has noticed that management of nitrogen fertilization can alleviate salinity effects on plants. This greenhouse sand culture experiment was conducted in order to investigate morphological and physiological responses to salinity stress in Kentucky bluegrass (Poa pratensis L.) grown using different nitrogen sources. Three salinity levels (0, 40 and 80 mM NaCl) and three NO₃^-/NH₄⁺ ratios (6/0.5, 6/1 and 6/2) were applied in nutrient solutions. Under non saline conditions, higher ammonium concentration increased Turf Quality (TQ), leaf NO₃^-, proline content, Nitrate Reductase Activity (NRA), shoot and root growth. On the other hand, leaf potassium (K⁺) sodium (Na⁺) and MalonDiAldehyde (MDA) content were not affected. During the first week, the 40 mM NaCl treatment showed that the positive effects of NH₄⁺ on salinity tolerance were still perceptible. However, the 80 mM NaCl treatment showed that the adverse effects of high salinities were more pronounced when turf received high ammonium rate nutrient solution, as manifested by the decrease of TQ, NO₃^-, NRA, K⁺/Na⁺ ratio, shoot and root growth and by the increase of leaf MDA content. This suggests that effects of NO₃^-/NH₄⁺ ratio on salt tolerance varies with salinity levels.