مهندسی مکانیک مدرس

مهندسی مکانیک مدرس

ارتعاشات آزاد پیچشی نانو ذره کروی با استفاده از تئوری الاستیسیته سطح گورتین

نویسنده
مدیر گروه مهندسی مکانیک
چکیده
حل تحلیلی ارتعاشات آزاد پیچشی نانو ذرات کروی با بکارگیری تئوری الاستیسیته سه بعدی دقیق همراه با مدل گورتین- مرداک برای وارد نمودن اثرات سطح مورد مطالعه قرار گرفته است. برای بدست آوردن معادلات حرکت، معادلات ناویر برای یک محیط مادی نوشته شده و با استفاده از جداسازی هلمهولتز، معادلات ناویر به معادلات برداری موج تبدیل شده است سپس با استفاده از فرضیاتی که برای حرکت پیچشی کره مفروض است معادلات برداری موج در سیستم مختصات کروی بصورت دقیق حل شده و میدانهای جابجایی و تانسور تنش استخراج شده است. در ادامه با استفاده از تئوری گورتین- مرداک، اثرات انرژی سطح که بنوعی مبین اندازه نانو برای کره است در شرایط مرزی مساله وارد می‌شود. نهایتا با اعمال شرایط مرزی معادله مشخصه فرکانسی استخراج می‌شود. با در نظر گرفتن نانو کره از جنس آلومنیوم و دو نوع سطح مختلف متاثر از جهت‌های کریستالوگرافی، چندین مثال عددی مورد بررسی قرار گرفته است تا تاثیر انرژی سطح و به ویژه اندازه شعاع داخلی نانو کره بر روی فرکانس‌های طبیعی پیچشی سیستم نشان داده شود. مشاهده می‌شود برای نانو کره آلومنیوم با اندازه کمتر از 50 نانومتر تاثیرات انرژی سطح بر فرکانس طبیعی قابل توجه است
کلیدواژه‌ها

عنوان مقاله English

Free torsional vibration analysis of Nano-spherical particle using Gurtn surface elasticity model

نویسنده English

yaser mirzaei
head of mechanical engineering department
چکیده English

The torsional vibrational characteristics of nano-scale sphere using an exact size-dependent elasticity solution based on Gurtin-Murdoch’s surface elasticity model are studied. In the absence of body forces, the displacement field is governed by the classical Navier’s equation. Helmholtz decomposition is used to separate the dynamic equations of motion into the decoupled vector wave equations. The motion under consideration is assumed to be torsional and vector wave equation exactly is solved and displacement field and stress tensor are obtained. Size-dependent elasticity solution based on Gurtin-Murdoch surface energy model is employed to incorporate the surface stress terms into the pertinent boundary conditions, leading to frequency equations involving spherical Bessel functions. Isotropic aluminum with two different set of surface properties corresponding to the crystallography directions are considered and extensive numerical calculations have been carried out to illustrate the size effect of the nano-sphere on the first and second dimensionless vibrational natural frequencies. The numerical results describe the imperative influence of surface energy and radii ratio on vibrational characteristic frequency of nano-sphere. In particular, the surface energy is much important when inner radius is smaller than 50 nm

کلیدواژه‌ها English

natural frequency
Nano-sphere
Nano-particle
Surface energy
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