تحلیل عمر خستگی کم‌چرخة چندراهة دود با درنظرگرفتن اثر کشسان لزج دائمی (کُلد)

نوع مقاله : مقاله پژوهشی

نویسنده

دانشکده مهندسی مکانیک، واحد ورامین-پیشوا، دانشگاه آزاد اسلامی، ورامین، ایران

10.22034/er.2023.2007571.1010

چکیده

چندراهة دود به‌‏علت هندسة پیچیده و شرایط بارگذاری یکی از چالش برانگیزترین قطعات موتورهای احتراق داخلی است. این قطعه باید نوسانات چرخه‏‌های ترمومکانیکی را در طول عمر خود تحمل کند. بنابراین شبیه‏‌سازی و تحلیل ترک­‌های خستگی ضروری است. در این پژوهش، تحلیل عمر خستگی کم‌‏چرخة چندراهة دود با استفاده از روش اجزای محدود و نرم‌­افزار آباکوس به منظور پیش‌­بینی دما و تنش و سپس عمر خستگی کم‏‌چرخه با استفاده از نظریة اسمیت- واتسون- تاپر و نرم­‌افزار FE-SAFE انجام شده است. از ترکیب الگوی سخت‌‏شوندگی غیرخطی همگن-سینماتیک چابوچه با قانون تنش لزجت به منظور در نظر گرفتن اثر لزجت استفاده شده است. خواص مکانیکی چدن نرم سیلیسیم-مولیبدن با استفاده از آزمون‏­‌های خستگی کم‌‏چرخه در دماهای مختلف بدست آمده است. نتایج تحلیل اجزای محدود نشان داد که بیشینة دما و تنش در چندراهة دود 757.7 درجه سانتیگراد و 395.2 مگاپاسکال است و موقعیت آن در ناحیة همریختگاه است. نتایج تحلیل عمر خستگی نشان داد که در نظر نگرفتن اثر کشسان لزج دائمی (کُلد) باعث می‏‌شود که تعداد چرخه‏‌های گسیختگی 619 چرخه‏‏ یا حدود 5.7 درصد بیشتر از مقدار مجاز تخمین زده شود. بنابراین لازم است اثر کُلد در تحلیل عمر خستگی کم‌‏چرخة چندراهة دود در نظر گرفته شود. نتایج تحلیل عمر خستگی نشان داد که حداقل عمر خستگی کم‏‌چرخة چندراهة دود در ناحیة بحرانی همریختگاه رخ می‏‌دهد. برای بررسی صحت نتایج تحلیل ترمومکانیکی و عمر خستگی کم‏‌چرخه، نتایج شبیه‌‏سازی شده با نمونة واقعی چندراهة دود آسیب دیده مقایسه گردید و نشان داده شد که نواحی بحرانی، مطابقت مناسبی با نواحی گسیختگی در نمونة واقعی دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Low cycle fatigue life analysis for exhaust manifold considering Elastoviscoplastic effect

نویسنده [English]

  • Hojjat Ashouri
Department of Mechanical Engineering, Varamin-Pishva Branch, Islamic Azad University, Varamin, Iran
چکیده [English]

Due to the complex geometry and loading conditions, exhaust manifolds are the most challenging components among all parts of internal combustion engines. They must withstand severe cyclic thermo-mechanical loading throughout their lifetime. Thus, simulation and analysis of fatigue cracks are essential. In this paper, low cycle fatigue (LCF) life analysis of the exhaust manifold is performed by using the finite element method and ABAQUS software to predict the temperature and stresses and then LCF life by using Smith-Watson-Topper theory and FE-SAFE software. Mechanical properties of silicon-molybdenum ductile cast irons obtained by LCF tests at different temperatures. The combination of the Chaboche nonlinear isotropic-kinematic hardening model with viscous stress law is used to consider the effect of viscosity. The results of finite element analysis (FEA) showed that the maximum temperature and stress values in the exhaust manifold are 757.7 °C and 395.2 MPa and the position is at the confluence region. According to the fatigue life analysis results, neglecting the elastoviscoplastic effect caused an estimation of 619 cycles or about 5.7% higher than the limit. Therefore, it is necessary to consider the elastoviscoplastic effect in the analysis of the low cycle fatigue life of the exhaust manifold. The results of the fatigue life analysis showed that the minimum LCF life of the exhaust manifold occurs in the confluence area. Thermo-mechanical analysis and LCF life results are compared with experimentally damaged exhaust manifolds to evaluate the results appropriately. It has been shown that the critical identified area match well with the area of failure in the experimental sample.

کلیدواژه‌ها [English]

  • Exhaust Manifold
  • Finite Element Analysis
  • Low Cycle Fatigue Life
  • Elastoviscoplastic Effect
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