Needle graphite electrodes are one of the main parts used in electric arc furnaces. These electrodes have a significant impact on melt quality and product quality, and their consumption is one of the most important parameters of steel production cost in EAF furnaces. Therefore, reducing the consumption of needle graphite electrodes in these furnaces is very important. The main reasons for continuous use of needle graphite electrodes in arc furnaces are oxidation of the sidewalls and sublimation of their tips, and many solutions have been proposed to reduce them. In the present study, the effect of coating consisting of TiO2/SiC/SiO2 elements on the wear rate of the needle graphite electrode in the sublimation state is investigated using EDM (Electrical Discharge Machining- Spark device). For this purpose, the effect of voltage, current, pulse on time and pulse off time on the electrode wear rate are investigated and in this regard, Taguchi design method has been used to reduce the number of experiments. Based on the test results, TiO2/SiC/SiO2 coating reduces the wear rate of the needle graphite electrode due to sublimation. تفاصيل المقالة

A variety of parameters influence the performance of piezoelectric sensors and actuators, such as support and concentrated mass. This paper presents a finite element formulation for piezoelectric structures and studies the effect of parameters on them. This method was developed based on the Bernoulli-Euler beam and the model is considered for use as a beam structure using the Variation Principle. The model was used for static and vibration analysis. The effects of support on the deflection of the piezoelectric beam were studied. Modal analysis was also carried out for the electromechanical coupling and uncoupling beams, and the effect of the concentrated mass was deduced. The finite element model was developed with FORTRAN programming Language and was implemented with MATLAB software. A comparison of the results between the analytical method, engineering software, and this program, showed acceptable accuracy. تفاصيل المقالة

امروزه لوله‌های خمیده با شعاع خم گوناگون، کاربرد بسیاری در صنایع خودروسازی، هوافضا و کشتی‌سازی دارند. در خم‌کاری لوله‌ها، هر چه میزان شعاع خم کوچک‌تر و ضخامت دیواره لوله کمتر باشد احتمال ایجاد عیوبی نظیر چین و چروک و گسیختگی بیشتر می‌شود. برطرف کردن این عیوب، یکی از مسایل مهم می‌باشد. به این منظور جهت کاهش چروکیدگی و گسیختگی نیاز به بررسی تأثیر پارامترهای هندسی ابزار خم‌کاری، قالب و مندرل‌های مورد استفاده در لوله می‌باشد. نوع مندرل استفاده شده در فرایند خم‌کاری لوله می‌تواند علاوه بر کاهش عیوب موردنظر در بهینه کردن نیروی قالب خم‌کاری تاثیرگذار باشد. این مقاله شبیه‌سازی و آزمایش تجربی فرآیند خم دورانی لوله‌های فولادی با قطرهای مختلف با استفاده از مندرل‌های الاستومری پلی‌یورتان و NBR را ارائه می‌دهد و آنگاه بررسی نیروی خمکاری و انرژی‌های داخلی و جنبشی انجام می‌گردد. از جمله نوآوری‌های این پژوهش حصول پارامترهای بهینه به منظور خم‌کردن لوله بدون پارگی و گسیختگی و بررسی تاثیر نوع مندرل بر نیروی قالب می‌باشند. آزمایش تجربی جهت صحت‌سنجی نتایج با دقت مناسبی انجام شده است. تفاصيل المقالة

An elastic-perfectly plastic middle crack tension aluminum 2024-T3 alloy was used under plane stress, plane strain and 3D analysis to determine stabilized crack-opening stresses for different R-ratios and stress levels. The stabilized crack-opening stresses of a 3D analysis locate between those values of plane stress and plane strain conditions. Using the above strategy, one can determine crack-opening stresses for any desired thickness value using interpolating scheme. Two and three dimensional programs were developed based on small strain elasticity theory incorporating linear strain isoparametric elements. The plasticity part of the analysis uses initial stress approach. The crack was extended one element size as the applied load reached the maximum value of each load cycle. Crack opening and closure stresses of nodes on the crack surface plane after some cyclic crack extensions are demonstrated. Based on the obtained results, for the three-dimensional finite-element analysis, the calculated stabilized crack opening stresses always locate between those of plane stress and plane strain conditions. تفاصيل المقالة