The Role of Heterogeneous Constitutive Properties on Mechanical Behavior of Advanced High Strength Steel Spot Welds

Recent publications have shown that the load bearing capability of resistance spot welds (RSW) made from dual-phase (DP) and martensitic (MS) Advanced High Strength Steels (AHSS) does not scale linearly with the tensile strength of their base metals. Although this degradation of welds strength has been linked by researchers to a phenomenon known as heat affected zone (HAZ) softening, the individual role of HAZ softening in different grades of AHSS has not yet fully understood. This work attempts to explain the above nonlinearity in spot welds performance by using a local to global approach to understand the role of HAZ softening on the strength of DP and MS spot welded samples. Material heterogeneity in Tension-Shear (TS) and Cross-Tension (CT) samples made from six grades of AHSS is studied by using microhardness measurements on spot welds and mechanical testing and digital image correlation (DIC) on thermally simulated samples in Gleeble machine. Results showed that the HAZ softening occurs in both subcritical and intercritical HAZ and the lowest yield stress exists in the ICHAZ making this region a candidate for plastic strain concentrating and failure initiation site.Results from FE simulations showed that both the spot weld’s nugget diameter and the HAZ softening play role in the performance of TS and CT samples. Nugget diameter showed to have a dominant effect on the strength of spot welds, and it is shown that the nonlinearity between the strength of spot welds and base metal tensile strength is related to the change in failure type in sample, as the nugget diameter increases. Results also showed that the HAZ softening have a complex and different role in performance of the welds. While it reduced the peak load and extension at peak load in DP spot welds, it played an opposite role and improved the same metrics in MS spot welds. The results also suggest that the lower strength (peak load) of MS spot welds compared to DP steels, is related to the intrinsic brittle behavior of their base metal as the HAZ softening showed to increase the peak load in MS spot welds

Reduction process of Cu/Sn nanocomposite by plasma furnace

Pre-milled copper and tin powder was subjected to heat treatment to investigate the effect of polyethylene glycol surfactant powder on it. The existing thermographic shows that the delta value of the copper-tin phase powder formation reaction is much higher than other chemical reactions, and this increase in energy is related to the new phase formation. Results of the DTA heat test in the direction of temperatures 300, 600, and 1000 °C were selected for this heat treatment and after that non-destructive and mechanical tests were performed on it, the phases Copper and tin are formed with great intensity and the particle size is reduced to 5 µm. On the other hand, the hardness of the resulting powder is greatly increased and about 220 HV0.1, all of which are due to the effects of adding a surfactant to copper and tin powder and ceramic phase made in this alloy.Peer ReviewedPreprin

Self-Efficacy After Life Skills Training: A Case-Control Study

Background: Nursing students’ self-efficacy is a predictor for their educational progress. Students, who believe that they can be successful in their studies, are more confident. Therefore, many universities have focused on life skills training programs to improve the mental health of their students. Objectives: This study was conducted to evaluate and compare self-efficacy in two groups of nursing students of Tehran University of Medical Sciences (TUMS). One group of students was trained on life skill programs, and the second group was not trained on the issue. Materials and Methods: A case-control study was conducted on two groups of nursing students in TUMS in the late 2012. The case group (n = 112) had passed life skills training course, and the control group (n = 139) was not trained on the issue. Data was collected using a questionnaire containing 12 questions about demographic features, and the Sherer’s general self-efficacy questionnaire. Data analysis was performed using independent sample t-test, Chi-square, odds ratio, and Fisher’s exact test. Results: In the untrained and trained groups, 23% and 8% of the students had very high self-efficacy, respectively. The overall mean scores of self-efficacy were 41.99 ± 9.31 and 38.99 ± 10.48 in the trained and untrained groups, respectively (P = 0.015), and the higher mean score indicates lower level of self-efficacy. A significant difference was also found between the self-efficacy and family income (P = 0.029). Conclusions: The present study showed that life skills training program did not affect self-efficacy of nursing students. Perhaps, the methods used in education were influencing and then, more effective techniques such as role-play and group discussion should be substituted in life skills training

Modification of as-cast Al-Mg/B4C composite by addition of Zr

Zirconium was used in Al-Mg/B4C composite to improve compocasting efficiency by increasing particle incorporation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results revealed that by addition of zirconium a reaction layer containing Zr, Al, B and C is formed on the interface of B4C-matrix. X-ray diffraction (XRD) analysis of extracted particles unveiled that the ZrB2 phase is the main constituent of this layer. Formation of ZrB2 is an exothermic reaction which can rise temperature locally around particles and agglomerates. Rising temperature around agglomerates in conjunction with turbulent flow of melt facilitates agglomerates wetting and dissolving into molten aluminum. As the result, final product contains more uniformly distributed B4C particles. Besides enhancing compocasting efficiency, addition of Zr and formation of reaction layer by improving particle matrix bonding quality, led to increase in ultimate tensile strength and elongation of the composite around 8% and 30%, respectively. SEM observations of the fracture surfaces confirmed that a proper bonding presents at the interface of particles and matrix in presence of Zr.Peer ReviewedPostprint (author's final draft

RELATIONSHIP BETWEEN THE DEMOGRAPHIC CHARACTERISTICS AND THE EFFECTIVENESS OF E-BANKING TRAINING COURSES BASED ON KIRKPATRICK MODEL FOR EMPLOYEES OF MASKAN BANK BRANCHES IN TEHRAN, IRAN

This study was carried out aimed to measure the Relationship between demographic characteristics and the effectiveness of e-banking training courses for employees of Maskan Bank Branches in Tehran province. The research method in terms of objective is considered as an applied research and information collection method is descriptive-survey. The statistical population of this research includes all employees of Maskan Bank Branches in Tehran Province who have participated in e-banking courses and have a population of about 1100 people. The statistical population of this study includes all employees of Maskan Bank Branches in Tehran Province who have participated in e-banking training courses and have a population of about 1100 people. 285 people were selected using Morgan table and by simple random sampling method. The tool measurement used was questionnaire based on the Kirkpatrick model in four levels of reaction, learning, behavior and results, which its reliability was calculated using Cronbach's alpha coefficient, 0.89 and it was confirmed. Descriptive and inferential statistical methods (one-way t-test, one-way ANOVA and Pearson correlation coefficient) were used in order to analyze the obtained data. According to the results of t-test, e-banking training courses were effective for employees of Maskan Bank Branches in Tehran province. Also, the analysis of demographic findings based on the results of the one-way between-subjects ANOVA showed that employees' attitudes at different positions, work experience or education level were not significantly different towards the factors affecting the effectiveness of e-banking training courses and none of them should be omitted from e-banking courses

Fundamental analysis of liquid breakup mechanism in a rotary atomizer with square discharge orifice

[EN] An experimental investigation of breakup mechanism in a rotary atomizer with square shape discharge orifice at ambient condition has been performed. The effects of a high aspect ratio noncircular discharge channels, particularly a square shape discharge channel, are considered. The motivation of this study is the use of this type of orifice in some small gas turbine engines as well as non-existing observation in literature concerning about high aspect ratio of discharge channel. Visualization experiments are conducted by high speed shadowgraph imaging technique with pulsed light illumination for the first time. The effects of rotational speed and volume flow rate are studied on the breakup structure. The visualizations indicates that the liquid film formed along the channel is pushed to one side of it due to Coriolis force which is dominant in this type of atomizer. Accordingly a crescent shaped liquid film is formed at the square channel exit covering two corners of the square, resulting the combination of Coriolis induced stream mode and surface tension induced stream mode breakup. Observations of the breakup process for different volume flow rates and rotational speeds indicate that the breakup of liquid film stream is dependent on injection conditions and the corresponding cross flow velocity created by atomizer rotation. The breakup regime map is provided as a function of weber number and momentum flux ratio. Four distinct regimes are identified: Rayleigh breakup, bag breakup, multimode breakup, and shear breakup. The present results leads to understanding atomization performance and creating some idea to improved spray quality in this type of atomizer.Ghorbanhoseini, M.; Rezayat, S.; Farshchi, M. (2017). Fundamental analysis of liquid breakup mechanism in a rotary atomizer with square discharge orifice. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 496-503. https://doi.org/10.4995/ILASS2017.2017.5640OCS49650

Characterization and optimization of Cu-Al2O3 nanocomposites synthesized via high energy planetary milling: a morphological and structural study

This study examines the synthesis and characterization of a copper–alumina nanocomposite powder. Mechanical milling is employed to synthesize the powder, and a holistic analysis is conducted to evaluate its morphological and structural properties. TEM analysis reveals the presence of alumina particles within the copper matrix, indicating the formation of both coarse and fine particles at different stages of synthesis. XRD analysis demonstrates a reduction in copper’s crystallite size with increasing milling time, attributed to defects generated within the crystal lattice during milling. Additionally, statistical analysis is utilized to determine the significance of different factors influencing the synthesis process. ANOVA analysis reveals that milling time has a significant impact on the particle size of the nanocomposite powder, while temperature and their interaction do not exhibit significant effects. Optimization techniques are utilized to identify solutions that meet the specified constraints for milling time, temperature, particle size, and differential thermal response, resulting in favorable solutions within the desired ranges. The study highlights the efficacy of mechanical milling for producing nanocomposite powders with enhanced mechanical properties, offering promising prospects for advanced materials in various industries. Additionally, the characterization results provide valuable insights into the microstructure and phase distribution of the nanocomposite powder. The application of the Williamson–Hall method proves to be effective in determining the crystallite size of the synthesized powder.Peer ReviewedPostprint (published version

Exploring the effects of laser surface modification on AISI 301LN steel: a micro-mechanical study

This article investigates the surface hardening capability of a metastable austenitic TRansformation Induced Plasticity (TRIP) stainless steel, particularly on AISI 301LN, by laser texturing. This technology produces microstructural surface changes in terms of both phase transformation and grain size modification and, as a direct consequence, the laser influences the surface characteristics, mainly hardness and roughness. In this sense, the key parameters (laser power, scanning speed and position of the focal length) were investigated by using a Design of Experiments (DoE) in detail to better understand the correlation between texturing parameters, microstructural and mechanical changes, always at the superficial level. From all the aforementioned information, the results show that the maximum surface hardening is obtained by increasing the laser power and decreasing the scanning speed. Furthermore, by reducing the focal distance, the depth of the microstructural evolution layer is more significant, while the width is less affected. Finally, a suitable model was developed to correlate the processing parameters here investigated with the resulting surface integrity, in terms of mechanical properties, by means of a regression equation.This research was funded by AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca), grant number FI-SDUR 2020.Peer ReviewedPostprint (published version

ElectroCatalytic Activity of Nickel Foam with Co, Mo, and Ni Phosphide Nanostructures

In this study, the electrocatalytic activity of nickel foam, which is activated by cobalt, molybdenum, and nickel phosphide nanostructures, is prepared by the plasma hydrothermal method for use in the release of hydrogen and oxygen. The morphology and crystallographic structure of the synthesized phosphide specimens were examined by means of scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. Moreover, the electrolysis activity for these sets of specimens was investigated using the Tafel polarization curve or linear sweep voltammetry, cyclic voltammetry, as well as by means of the electrochemical impedance spectroscopy technique. Preliminary results show that nickel phosphide presents the highest electrocatalytic activity than the other phosphides developed in this research. In this regard, it presents an electrocatalytic activity to release hydrogen and oxygen of around -1.7 and 0.82 mV, which is measured at a current density of 100 mA·cm-2, respectively.Peer ReviewedPostprint (published version