سعیدفعلی

In recent years, multi-cellular structures have gained significant attention as energy absorbers in automotive engineering to mitigate occupant injuries in collisions. This paper investigates the energy absorption of square shape thin-walled structures with constant thickness and functionally graded thickness under dynamic axial impact loading using both analytical and numerical methods. Four types of square profiles, including single-cell, two-cell, four-cell, and five-cell profiles, were studied. Simulations were conducted using the Finite Element Analysis Abaqus software to obtain force-displacement and energy-time curves. In the analytical method, equations for absorbed energy and axial collapse force were derived based on the folding theory and extended to profiles with functionally graded thickness. There is good agreement between analytical and numerical methods. Results of the analytical and numerical methods showed that five-cell profiles performed significantly better than single-cell profiles. In numerical simulations and analytical solutions, five-cell profiles absorbed 66% and 56% more energy, respectively, compared to single-cell profiles in both constant and functionally graded thickness conditions. The average collapse force in the analytical method was compared with numerical results, and the computational error was less than 9%.

In this paper, the low velocity impact response of sandwich panels with composites face sheets and aluminum based corrugated cores is modeled with numerical simulation, and the amount of energy absorption, contact force, deformation of the impact area and dimensions of the damage area are calculated and compared with experimental results. Sandwich panels with composite face sheets reinforced with carbon fibers and glass fibers and corrugated aluminum-based cores are in square, trapezoidal, arched, sinusoidal and triangular shapes. Through numerical simulations ten examples have been analyzed. Dimensions and weights of face sheets and cores of the samples are the same. The obtained results show that in the sandwich panel with trapezoidal and square corrugated cores, the contact force is applied to a larger area and the energy absorption and dimensions of the damage area are greater. Also, sandwich panels with arc and sinusoidal wave shape cores have the greatest displacement at the point location compared to other sandwich panels.

In this study, the synergistic influence of reduced graphene oxide and multi-walled carbon nanotubes  on the mechanical properties of epoxy nanocomposites was investigated. In the first step, the epoxy nanocomposite specimens reinforced with 0.02, 0.04, 0.06, 0.08 and 0.1 multi-walled carbon nanotubes weight percentages fabricated using direct homogenization technique. The mechanical properties were obtained via a tensile test setup. The results showed the 35.7%, 21.7% and 12.47% increase in Young's modulus, ultimate stress and yield stress of the 0.04% multi-walled carbon nanotubes reinforced specimen. In the second step, the epoxy reinforced with 0.2, 0.4, 0.6, 0.8 and 1 reduced graphene oxide weight percentages fabricated. For the 0.6% reduced graphene oxide reinforced specimen, 37.6%, 18.1% and 13.14% increase in Young's modulus, ultimate stress and yield stress were seen. Next, the effect of different reduced graphene oxide content on 0.04% multi-walled carbon nanotubes reinforced epoxy was investigated. The obtained results demonstrated the increase in the mechanical properties of 0.04% multi-walled carbon nanotubes -0.4% reduced graphene oxide (Mixing ratio 1: 10). Due to this mixing ratio for 0.06% multi-walled carbon nanotubes -0.6% reduced graphene oxide specimen, 42.2%, 25.88% and 18.97% increase in Young's modulus, ultimate stress and yield stress were seen. The analysis of specimens' fracture surface was performed to observe the failure modes and dispersion of nanoparticles in the epoxy matrix. The results revealed that mechanical properties can change significantly by adding two different nanoparticles, simultaneously.

In this paper an analytical model is presented to investigate the dynamic response of the nano-curved plate under impact loading of nanoparticles. Unlike the macroscale, long-range interatomic interactions, such as the Van der Waals (vdW) force, are considered at the nanoscales. The impact load on the nano- curved plate is considered as an interaction between the nanoparticle and the nano-plate. The vdW force between the carbon nanoparticle and silicon nano-curved plate is determined by the Lennard-Jones potential. The Love-Kirchhoff plate theory and Double Fourier series are used for determining the displacement field of the nano-plate. Also the governing equations of the nano-curved plate are derived by considering the residual surface stress, Gurtin and Murdoch relations and Hamilton's principle and are solved for a simply supported nano-curved plate by using the Rung-Kutta’s fourth order method in MATLAB. The analytical model results are validated with an analytical model that has investigated the dynamic response of the nanoparticle impact on a rectangular nano-plate. The effects of geometrical parameters such as curvature, thickness, mass and velocity are investigated. Also the surface effects of the nano-plate on the vdW force and the dynamic response of the nano-curved plate are studied. The results show that by increasing the radius of curvature, the maximum deformation at a constant curvature angle is decreased. Also, by considering the surface effect, the maximum displacement of the center of the nano-plate is reduced and the role of the surface effect on the maximum deflection of the nano-plate decreases with increasing nano-plate thickness.

In this paper, an analytical model has been developed for modeling high velocity impact on ceramic/nanocomposite targets. In this model, penetration resistance of ceramic is determined based on cavity expansion analysis and variables during perforation of projectile onto ceramic are considered. Also the force of ceramic-composite interface is modified. Ballistic performance of the ceramic/composite target is investigated with adding and dispersing of nano particles of zirconia (ZrO2) in the matrix of back up composite. Ballistic impact tests were performed to validate the analytical predictions. These tests were performed by firing 10 mm steel flat ended projectile onto ceramic/composite target. Front layer is alumina ceramic and composite laminates of back up made of E-glass/epoxy with and without nano-zirconia particle of 5 wt%. The effect of nano-zirconia dispersion in the matrix for different failure modes is discussed. Experimental results revealed an improvement in the ballistic performance of samples with nano-zirconia particle. The analytical predictions of ballistic limit velocity and residual velocity of projectile are found to be in good agreement with the experimental results.

In this paper, a new analytical model has been presented for energy absorption of aluminum-foam sandwich panels under ballistic impact. The panels consist of hexagonal honeycomb core sandwiched between two aluminum skins. In analytical model cylindrical rigid projectile with flat ended has been considered. In the quasi-static loading, by using the springs-mass model, energy absorption of Aluminum skins with considering difference energy absorption mechanisms calculated. Energy absorption of honeycomb has been determined by wierzbicki model. Energy balancing equation has been employed for determination the ballistic limit and residual velocity of striker. The results of ballistic limit and residual velocity of striker computed by new model have good agreement with experimental results. Also the effects of projectile mass and diameter and cell diameter of honeycomb in energy absorption of sandwich panel has been investigated.

In this paper, a new analytical model has been presented for energy absorption calculation of aluminum-foam sandwich panels under high velocity impact. The panels consist of foam core sandwiched between two aluminum skins. In analytical model, cylindrical rigid projectile with flat ended has been considered. In the quasi-static loading, by using the springs-mass model, energy absorption of aluminum skins with considering difference energy absorption mechanisms has been calculated. Also foam absorbed a partial of projectile energy by crushing. Energy absorption of aluminum-foam sandwich panel was calculated and energy balancing equation has been employed for determination the ballistic limit and residual velocity of projectiles. The results of ballistic limit and residual velocity computed by new model presented good agreement with experimental and numerical results. Also the effects of foam density, projectile mass and diameter in energy absorption of sandwich panel has been investigated.

In this paper, an analytical model has been presented for energy absorption of sandwich panels under ballistic impact. Aluminum-foam and composite-foam sandwich panel are investigated in this paper. In analytical model three types of sticker including cylindrical projectile with flat, hemispherical and conical ended have been considered. It is supposed that top and bottom skins and foam core failure by mean resistive pressure. Energy absorption of sandwich panels is the sum of the energy absorbed by the skins and foam. Energy absorption of sandwich panel is calculated and energy balancing equation has been employed for determination the ballistic limit and residual velocity of projectiles. The results of ballistic limit and residual velocity computed by new model have good agreement with experimental results. Also the effect of projectile shape in energy absorption of sandwich panel has been investigated.

Implementation of Land Consolidation Project (LCP) in Mazandaran province has faced problems in respect to farmers’ participation. This study aimed at identifying effective factors on paddy farmers’ non-participation in LCP. The target group included the paddy farmers who had not participated in LCP in Mazandaran province; and among them، 259 farmers were selected using cluster sampling method. As shown by the study results، non-delivery of consolidated land timely، probability of decreasing farming land after consolidation، and access to water resources were the main reasons of farmers for non-participation in LCP. Factor analysis results showed that ten general factors were main barriers of participation among farmers، including heritage law، population increase، financial issues، land topography، education، governmental factors and finally، agricultural issues. These factors could explain 62 percent of the variance of resistance to participate in LCP in Mazandaran province.

The purpose of this study was to identify external factors affecting the Iranian Agricultural Extension System (IAES) by 2025 using agricultural extension authorities’ viewpoints. Results of this qualitative study were obtained by using a modified Delphi technique to reach group consensus. The target population was 20 policy makers that selected by judgment sampling. It is noted that the validity of questionnaire was confirmed by panel of experts. Results of study indicated the probability of occurring sixteen external factors affecting IAES by 2025 was at “moderate to high” level that consensus was reached on fourteen external factors affecting IAES. These factors, respectively, in seven categories of "infrastructure, ecology, economic, cultural, institutional, scientific and technological revolution and the population" were reduced.

In this paper, a new analytical model has been presented for energy absorption of aluminum-honeycomb sandwich panels under high velocity impact. In high velocity impact, striker with initial velocity penetrates into target and perforates it completely and exits by residual velocity. The panels consist of hexagonal honeycomb core sandwiched between two aluminum skins. In analytical model cylindrical projectile with flat ended have been considered. It is supposed that aluminum skins failure by mean resistive pressure. Energy absorption of honeycomb has been determined by wierzbicki model. Energy balancing equation has been employed for determination the ballistic limit and residual velocity of striker. The results of ballistic limit and residual velocity of striker computed by new model have good agreement with experimental results. Also the effects of projectile mass and diameter and cell diameter of honeycomb in energy absorption of sandwich panel has been investigated.

Students’ cheating on exams is one of the common problems in higher education system in Iran. The investigations indicated that the condition of academic cheating in Iran has come to a crisis phase. The purpose of this study was to identify effective factors in Gorgan Islamic Azad University students’ cheating. The research method was descriptive-correlational survey. The target population included all bachelor’s students in Gorgan Islamic Azad University (N=401). By using simple sampling method and Krejcie & Morgan’s table، 196 people were selected and finally 180 filled questionnaires were collected. The research instrument was structural questionnaire with close-ended questions which its validity and reliability was confirmed by panel of experts and Cranach’ sapha test، respectively. Descriptive and nonparametric statistical methods were used to analyze information. The descriptive results showed that the main methods of respondents for cheating on exams were as follows: “permitting other students to see my paper” (86. 70%)، “coping fromother students’ exam sheet with their cooperation” (80%)، and “using sign language especially fingers for correct choices” (70%). The results of correlation coefficient showed that there was a statistically significant relationship between respondents’ demographic and psychological variables with their cheating behaviors. The results of the bivariate regression revealed that 39 percent of variability in students’ cheating behavior stems from attitude toward cheating on exams، motivation for cheating on exams، age، and years at the university.

The main aim of this study was to identify factors affecting the linkage between research and extension based on agricultural experts opinions.. The research instrument was a structured questionnaire. The validity of questionnaire was obtained by a panel of experts. The reliability of questionnaire was obtained by pilot test. The Cranach's alpha coefficient for questionnaire was 0.86. The population of this research consisted of agricultural experts in West Azerbaijan province of Iran (N= 381). By using a stratified –cluster randomized sampling technique 180 people were selected. The findings show that adaptability of research findings with culture, values and needs of the rural community, felt needs and responsibility of extension agents in establishing linkage and ability of extension agents to identify problems of rural population was the main solutions in linkage between research and extension. By using factor analysis methods, affective factors for linkage between agricultural extension and research was summarized in nine factors, namely motivation of research and extension agents to work together, capability and expertise of extension agents and research units, applied research findings, joint planning activities, inter organizational competition between extension and research, sufficient number of extension and research agents, structural stability of research and agricultural extension, research and education organization, willingness between the two organizations to communicate together and providing extension services only by extension units. These factors could explain 74 percent of affective factors for linkage between research and extension.

Considering the low participation of rural women in extension-education programs, in order to transfer information to this social group, agricultural extension organizations have no choice but to identify the information sources used by them. Therefore, this research, which was conducted in 2011-2012 cropping season, aims at identifying the influencing factors on the use of information sources among rural women in Mazandaran province. For this purpose, using multistage cluster sampling method, 300 rural women from this province were selected to involve in the research process. Results from the descriptive statistics show that spouse, household members, and other women in the village are the most important sources of information for the rural women. In addition, results from the analytic statistics proves the statistically significant correlation between some of the individual and professional characteristics of rural women and their use of the information sources. Furthermore, results from the multiple regression analysis show that 68 percent of the variance of the dependent variable is explained by the identified independent variables.

In this paper, a new analytical model has been presented for energy absorption of aluminum-foam sandwich panels under ballistic impact. The panels consist of foam core sandwiched between two aluminum skins. In analytical model two types of sticker including cylindrical projectile with flat and hemispherical ended have been considered. It is supposed that aluminum skins failure by mean resistive pressure. Also foam absorbed a partial of projectile energy by crushing. Energy absorption of aluminum-foam sandwich panel is calculated and energy balancing equation has been employed for determination the ballistic limit and residual velocity of projectiles. The results of ballistic limit and residual velocity computed by new model have good agreement with experimental results. Also the effects of projectile mass and diameter in energy absorption of sandwich panel has been investigated.

In this research the effect of the tumbling perforation of blunt-faced cylindrical projectiles in moderately thick aluminum plates is presented. The perforation process – depend on the impact angle in normal and oblique impact – consists of four stages: erosion, plugging, hole enlargement and petaling. The modeling in the plugging stage consists sequentially of cratering, plug formation, plug separation, plug slipping and post perforation deformation. In this analytical model, the target material is considered to be rigid perfectly plastic, while the projectile is regarded as adeformable. material Projectile deformation depend on relative velocity of projectile occurs in three mode: erosion, flattening and rigid projectile. The effect of the frictional force is considered too. The new analytical results were found to be in good agreement with experimental results.

The main purpose of this research was to identify obstacles components related to Saffron’ processing، marketing and export. A questionnaire was designed to gather data needed for the study. Its validity was acquired using a panel of experts. A reliability analysis was conducted، Cronbach´s alpha value being reported to be 0. 89. Population of this study was Jihad-Agriculture’s staff in Torbat-e-Heidariyeh (N=89) that 79 questionnaires were filled out and analyzed by take census (n=79). By applying of Factor Analysis Technique، obstacles of Saffron’ processing، marketing and export were reduced to six factors. These six factors expressed 75. 12% of the total variance of the variables. Nearly 25% of reminder variance was related to factors or variables which had not been seen in this research.

In this paper, an analytical model for impact of flat-ended projectiles onto the composite – foam sandwich panel is presented. The panels consist of foam core sandwiched between two composite skins. In the quasi-static loading, by using the springs-mass model, the load at failure of top composite skin and the energy absorbed due to failure of the top skin have been determined. The absorbed energy during the perforation of the sandwich panel is calculated and the energy balancing equation has been employed for determination the ballistic limit and residual velocity of projectiles. The load at failure of top composite skin, energy absorbed due to the top skin failure, ballistic limit and residual velocity have been compared with the available experimental results. The good agreement between analytical model and experimental results has been observed.

The main objective of this study is to identify structural changes in Iran’s agriculture up to 2025 based on experts views. The study applies Delphi technique to reach to a consensus among the experts. The statistical population consists of all policy makers in agricultural sector. Through a purposive sampling a sample size of 20 is selected to respond to the main question of research. The experts predict 16 changes for the sector and they reach to a consensus about the type of change - decrease or increase. The changes can be classified in 6 themes: type of crop production, production equipments, market demand, quality of cultivation, size and number of farm plots, and human factor in production.

The purpose of this correlational research was to assess students’ attitude and behavior on plagiarism. The research instrument was a structural questionnaire including close-ended questions and its validity was established through a panel of experts. The reliability of questionnaire was determined by calculating the Cronbach's alpha coefficient (α=.81-89). The target population included all Faculty of Agriculture’s master and doctoral students in Tarbiat Modares University who were enrolled at least two terms (N=559). A sample size of 225 was selected using Krejcie & Morgan’s table and stratified sampling techniques. The descriptive finding of this study indicated that the majority of the students’ attitude and behavior were relatively unfavorable and moderate respectively. Moreover, findings revealed a statistically significant difference between students’ plagiarism behavior of those who participated and those who did not participated in the article writing workshops.

In this paper based on the plastic stress wave propagation theory, a new analytical model is presented for impact of the cylindrical projectiles on the rigid surface. In this analytical model, Johnson-Cook material behavior equation,Mie–Grueneisen equation of state, Johnson-Cook strain at fracture equation and kinematics equations of motion, are used. Also, the conservation equations of mass, momentum and energy in front of plastic stress wave are determined.For solving the governing equations, a computer program is developed. The values of stress, strain, strain rate,velocity and length and radius of rigid and deformed region of projectile were determined. Using new model proposed in this paper, the compressive stress at different plastic strain and strain rates were determined. The results of the new model have been compared with ABAQUS finite element simulations and available experimental results.It shows that the length and radius of deformed region of projectile predicted by the new model have good agreements with experimental results and ABAQUS FE simulations. Furthermore, the compressive dynamic stress is determined as a function of the final projectile dimensions and material behavior coefficients.

The purpose of this correlational research was to investigate the factors influencing satisfaction whith sprinkler irrigation systems (SIS) as perceived by the adopting farmers. The research instrument was a structural questionnaire with close-ended questions, the validity and reliability of which were confirmed. The target population included all the adopting farmers who cultivated and harvested at least one crop with SIS applied in Kurdistan Province, Iran (N=297) from among whom, a number of 139 were selected as the statistical prototype in a stratified sampling method. Findings of the study indicated that a majority (103 individuals or 74.10%) of the farmers’ satisfaction of SIS stood at a ‘moderate’ level. There were statistically significant relationship observed between age, experience in farming, number of land plots under cultivation, number of plots under cultivation and irrigated thuough SIS, system design, after-sales services, extension-education supports after following SIS installation and the level of farmers’ satisfaction with SIS. The results of the multivariate regression revealed that 67.5 percent of variations in the level of farmers’ satisfaction with SIS stemmed from system design, extension-education supports following installation of SIS, number of plots under cultivation, as well as organization's supports for installation and maintenance of SIS.