مهندسی مکانیک مدرس

مهندسی مکانیک مدرس

بررسی المان محدود آزادسازی حرارتی تنش پسماند در Ti-6Al-4V تحت کوبش لیزری چندگانه

نویسندگان
سهیل نخودچی 1
محمدامین پورمیر 2
مجید صادقی غریب دوستی 2
1 عضو هیات علمی/استادیار دانشگاه صنعتی خواجه نصیرالدین طوسی
2 کارشناس ارشد، مهندسی مکانیک، دانشگاه صنعتی خواجه نصیرالدین طوسی، تهران
چکیده
ایجاد تنش پسماند فشاری در قطعاتی که در تحت بارگذاری خستگی قراردارند، راه حلی اقتصادی جهت افزایش استحکام می باشد که در واقع تمام و یا قسمتی از تنش های کششی اعمال شده به قطعه خنثی می گردد. این در حالی است که تنشهای پسماند در دمای بالا عموما کاهش یافته و یا کلا از بین می روند. لذا همواره نقش این تنش های پسماند در عملکرد قطعات در دمای بالا مورد سئوال بوده است. لذا ابتدا میدان تنش ناشی از روش کوبش لیزری چندگانه مدلسازی شده و سپس تاثیر دمای کاری قطعه که منجر به پدیده ی آزادسازی دمایی این میدان تنش می گردد، بررسی شده است. ماده ی مورد استفاده آلیاژ Ti-6Al-4V بوده و جهت اعمال اثر رفتار غیر خطی ماده در نرخ کرنش های بالا از مدل ماده ی جانسون-کوک استفاده شده است. نتایج حاکی از آن است که میدان تنش پسماند ناشی از این فرآیند به مراتب عمیق تر از روش های مشابه مانند ساچمه زنی بوده و با اعمال کوبش لیزری چندگانه به یک نقطه می توان از حداکثر تنش فشاری 640 مگاپاسکال در یک سیکل کوبش لیزری به 834 مگاپاسکال در دو سیکل و 889 مگاپاسکال در سه سیکل دست یافت. با اعمال دمای 600 درجه سانتیگراد به قطعه نیز مشاهد شد تنش پسماند آزاد شده حرارتی در سطح نمونه ی تحت کوبش لیزی یگانه، دوگانه و سه گانه به ترتیب 28.13%، 41.37% و 43.87% مقدار اولیه تنش پسماند قبل از اعمال حرارت می باشد.
کلیدواژه‌ها
کوبش لیزری
جانسون-کوک
Ti-6Al-4V
تنش پسماند
آزادسازی حرارتی

عنوان مقاله English

A finite element study of thermal residual stress relaxation in multiple laser shock peened Ti-6Al-4V

نویسندگان English

mohammad amin poormir 2
majid sadeghi gharibdusti 2
2 Department of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran
چکیده English

Creation of a compressive residual stress in specimen that are exposed to fatigue induced failure, is considered to be a beneficial solution in order to neutralize all or some parts of the external force. Using components with this residual field stresses in high temperature applications can lead to reduction and termination of residual stress field and the effectiveness of this residual stress fields in high temperature is always questioned. So this paper aimed to simulate and study residual stress field made by multiple laser shot peening which is a novel method to create in depth residual stress. Thermal relaxation of this residual stress field due to working conditions was also investigated by FEM simulation in ABAQUS. Ti-6Al-4V was the employed material and since high strain rates were involved in dynamic loading process of simulation, Johnson-Cook material model was used to count for nonlinear material behavior. Results showed that created residual stress field from this method is much deeper than similar conventional shot peening process and by using multiple laser shot peening on the same spot, it is possible to achieve 640 MPa in one loading cycle, 834 MPa in two cycle loading and 889 MPa in three cycle loading. By applying 600 ℃ on specimen, it was observed that for each of single shot, double shot and triple shot specimens, a surface residual stress relaxation of 28.13%, 41.37% and 43.87% occurred, respectively.

کلیدواژه‌ها English

Laser shock peening
Johnson-Cook
Ti-6Al-4V
Residual Stress
Thermal relaxation
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مهندسی مکانیک مدرس
دوره 18، شماره 3
خرداد 1397
صفحه 38-44