Abstract    Two stages gas guns are used for various purposes, particularly for mechanical characterization of materials at high rate of deformations. The performance of a two stages gas gun is studied in this work using the theory of the two-stage gas gun proposed by Rajesh, numerical simulation using combined Eulerian/ Lagrangian elements in Autodyna commercial code and experiment using a two stage gas gun developed by the authors of this study. Equations governing the motion of the piston and projectile are solved using Runge-Kutta method. The effects of parameters such as chamber pressure, pump tube pressure and piston mass on the performance of gun are explored. The results of numerical simulation and analytical methods are validated by experiment. Finally, a comparison between the analytical, numerical and experimental results shows that the theory proposed by Rajesh, yields reasonable predictions for the two stage gas gun performance in the first place, and Autodyn software, using combined Eulerian/ Lagrangian elements, gives accurate estimations for gas gun parameters, in the second place. A 3-D working diagram is provided for prediction of projectile velocity for any state of pump and chamber pressures which are the most important variables for a gas gun with a fixed geometry.

Keywords    Two Stages Gas Gun; Rajesh Theory; Simulation; Projectile; Autodyn

چکیده    تفنگ‌های گازی دومرحله‌ای جهت مقاصد مختلفی به‌ویژه بررسی رفتار مواد در نرخ کرنش بالا مورداستفاده قرار می‌گیرند. در این پژوهش، عملکرد یک تفنگ گازی دومرحله‌ای توسط روابط تحلیلی بر پایه تحقیقات راجش و شبیه‌سازی عددی بر پایه روش اجزا محدود و استفاده هم‌زمان از المان‌های اویلری و لاگرانژی موردبررسی قرارگرفته است. معادلات حاکم بر حرکت پیستون و پرتابه حل‌شده و اثرات فشار مخزن، فشار لوله پمپ و جرم پیستون بر عملکرد آن موردبررسی قرارگرفته است. نتایج روش‌های عددی و تحلیلی با استفاده از دستگاه طراحی‌شده توسط نویسندگان به‌صورت آزمایشگاهی صحه‌گذاری گردیده است. مقایسه بین نتایج تحلیلی، عددی و تجربی نشان داد که نظریه پیشنهادشده توسط راجش و همچنین، شبیه‌سازی توانسته است عملکرد تفنگ گازی دومرحله‌ای را به خوبی پیش‌بینی کند. همچنین، یک نمودار سه‌بعدی برای پیش‌بینی سرعت پرتابه بر اساس فشارهای مخزن و لوله پمپ ارائه‌شده است.

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