s. feli

In this paper, a sequentially coupled 3-D thermal-metallurgical-mechanical analysis is developed to predict welding residual stresses and distortion during single-pass tungsten inert gas arc welding (TIG) of low and medium carbon steel pipes (S45C and S15C). The axial and hoop residual stresses and welding deformation by allowing volumetric change due to solid-state phase transformation are determined. In ABAQUS finite element simulation, the moving heat source is modeled by a user subroutine [DFLUX], and a user subroutine [UEXPAN] is applied for computing the fraction of martensite and volume change during heating and cooling. The simulation results show that for the S15C pipe, solid-state phase transformation has an insignificant effect on welding residual stress and distortion but for the S45C pipe the solid-state phase transformation reduces the axial residual stress in the fusion (FZ) and heat-affected zones (HAZ). Also, the sign of hoop residual stress changes in FZ, and its value of it decreases in HAZ.

In this paper by using the three-point bending and low velocity impact tests, the impact damage response of Polyurethane cored sandwich panels with hybrid nanocomposites face-sheets is investigated. The face-sheets are made of epoxy/woven-fiberglass/ nano-silica composite. Three-point bending test is used for determination of static threshold delamination force, and static and dynamic Interlaminar Shear Strength has been calculated. Furthermore, low velocity impact tests are performed on a sandwich panel and contact forces history, lateral deflection of the contact point and the absorbed energy of top face-sheets are obtained. The dynamic threshold delamination force has been used to predict the delamination damage mode in low velocity impact tests on sandwich panel. Finally, the delamination damage area is investigated theoretically and experimentally and the correction factor is associated with allowable shear stress is determined. Moreover, the effect of nano-silica particles on delaminations threshold forces, Interlaminar Shear Strengths, contact force, contact duration, deflection of contact point, energy absorption of top face-sheet and damage area caused by delamination is studied.

  Academic failure is of paramount importance for medical students because it might lead to a decline in scientific level of the community of physicians in the future. This study was conducted to investigate the predictors of academic failure in medical students of Lorestan University of Medical Sciences using classification tree.

In this cohort study, academic records of all medical students of Lorestan University of Medical Sciences during the academic years of 1999-2008 were selected by census and were followed up until September 2016. Academic failure was defined as having at least one of the components of appropriate grade point average, prolonged graduation, academic probation, dropout, expulsion, and any failure in ccomprehensive exams and the CART classification tree was adopted using the SPSS 22 software to predict it.

The cumulative incidence of academic failure was 26.4% and the most prevalent components were prolonged graduation (21.7%) and academic probation (15.0%). The probability of academic failure was 0.449 in subjects taking guest courses, 0.220 in subjects with no history of guest courses admitted to courses with less than 40 students and admission quotas of zone 1 or 3, and 0.456 in subjects with no history of guest courses admitted to courses with more than 40 students and males.

With respect to identifying the predictors of academic failure, it is suggested that these students be referred to consulting centers of the university or educational supervisors’ moreover, the regulations of taking guest courses in other universities should be revised.

By using of multilayer targets instead of monolithic layer one with equal total thickness; it is possible to increase the perforation ballistic resistance. As a result, for the same perforation ballistic resistance, the total thickness of the multilayer targets would be smaller. In this paper, a new analytical model for oblique penetration of blunt projectile into the multilayer metallic target is developed using the plastic stress wave propagation theory and equation of momentum. The base of this model is Felli’s model for oblique penetration of blunt projectile into monolithic layer target. The penetration processes are defined in nine stages. The first stage is cavity expansion in the target and then penetration continues with plug formation. For each stage, equations of motion for projectile and target are derived and solved to obtain penetration parameters. The analytical results of this paper are in good agreement with experimental results of the other investigators.