In this paper, nonlinear vibration and instability response of an embedded pipe conveying viscose fluid is investigated. The pipe is considered as a Timoshenko beam embedded on an elastic foundation which is simulated by spring constant of the Winkler-model and the shear constant of the Pasternak-model. The external flow force, acting on the beam in the direction of the flexural displacement is described by the well-known Navier-Stokes equation. The corresponding governing equations are obtained using Hamilton's principle considering nonlinear strains and first shear deformation theory. In order to obtain the nonlinear frequency and critical fluid velocity for clamped supported mechanical boundary condition at two ends of the pipe, Differential quadrature method (DQM) is used in conjunction with a program being written in MATLAB. The effect of dimensionless parameters such as aspect ratios of length to radius of the pipe, Winkler and Pasternak modules, fluid velocity and viscosity as well as the material type of the pipe on the frequencies and instability of pipe are investigated. Results indicate that the internal moving fluid plays an important role in the instability of the pipe. Furthermore, the nonlinear frequency and instability increases as the values of the elastic medium constants  and viscosity of fluid increases. پرونده مقاله

امروزه مواد فوق ریز دانه به دلیل خواص کم نظیر خود جایگاه ویژه ای در صنایع مختلف پیدا کرده اند. با کاهش اندازه دانه، سهم اتم‌های موجود در مرز دانه‌ها افزایش‌یافته و زیادشدن مرز دانه ها موجب جلوگیری از حرکت نابه جایی ها و بالا رفتن استحکام می-شود. یکی از روش های تولید مواد فوق ریز دانه، اعمال تغییر شکل پلاستیک شدید می باشد. جهت اعمال تغییر شکل پلاستیک می-توان از روش های بسیاری استفاده نمود که در این پژوهش از کانال های زاویه دار موازی استفاده می شود. جهت بررسی عددی این فرایند از نرم افزار المان محدود آباکوس و جهت بهینه سازی نتایج از روش شبکه عصبی و الگوریتم ژنتیک استفاده شده است. در این پژوهش اثر پارامتر های قالب که شامل زاویه کانال، طول لوله، افزایش اختلاف قطر و ضریب اصطکاک می باشد، بررسی می شود. نتایج نشان داد که ضریب اصطکاک و طول لوله مورد آزمایش هر کدام جداگانه بر همگن شدن توزیع کرنش بسیار نقش داشته است، به طوری که با افزایش مقدار ضریب اصطکاک تعریفی و کاهش میزان طول لوله، توزیع کرنش به سمت همگنی و یکنواختی سوق پیدا خواهد کرد. تفاضل افزایش قطر لوله و زاویه کانال قالب تاثیر چندانی بر بهبود یکنواختی توزیع کرنش نخواهند داشت. از سوی دیگر افزایش ضریب اصطکاک، طول لوله و افزایش قطر لوله هر کدام جداگانه منجر به افزایش نیروی فرایند می شوند درحالی که افزایش زاویه کانال قالب منجر به کاهش نیروی شکل دهی شد. پرونده مقاله

One of reasons that researchers in recent years have tried to produce ultrafine grained materials is producing lightweight components with high strength and reliability. There are disparate methods for production of ultra-fine grain materials,one of which is severe plastic deformation method. Severe plastic deformation method comprises different processes, one of which is Parallel tubular channel angular pressing. The aim of this study is optimizing parameters of the noticed process die just by utilizing neural network and genetic algorithm methods that at first for this purpose, by using ABAQUS finite element software, the numerical analysis of the die parameters is performed and the impact of each die parameter on the force of the process and the equivalent strain is examined. Finally, for gaining optimal parameters, MATLAB and neural network optimization methods and genetic algorithm are used. The use of neural network and genetic algorithm illustrated that to achieve the ideal possible situation in order to achieve a flawless super-fine tube, it is imperative to use the friction coefficient of 0.05, tube length of 40 mm, channel angle of 140 degrees and diameter increase difference of 1.5 mm. With such values, strain fluctuations reach 0.23, lowest value, and also the force reaches 0.49 KN and the amount of applied strain reaches its highest value to 2.37. پرونده مقاله

Fracture assessment of U- and V-notches is important in mechanical engineering. One can use the J-integral as fracture parameter in order to predict the critical fracture load in notches. The critical value of the J-integral in cracks is a function of the material properties. In notches, however, the material properties as well as the notch dimensions affect this critical value (named fracture toughness). So, one should carry out a complex and time-consuming experiment in order to find the fracture toughness. In this paper, a practical equation has been derived to evaluate the critical value of the J-integral in blunt V-notches under Mode I loading. By means this new expression, only the notch dimensions and the critical value of the J-integral in cracks should be known. In this paper, the effect of the notch angle, the control volume radius to the notch root radius ratio (Rc/ρ), and the Poisson’s ratio on the J-integral and the critical value of the J-integral have been studied. Results have shown that by increasing the notch angle and the Poisson’s ratio, the fracture toughness decreases. However, the fracture toughness increases by increasing the Rc/ρ ratio. پرونده مقاله