شکست ترد در نمونه‌های پلیمری دارای شیار کلیدی‌شکل تحت بارگذاری مرکب فشاری-برشی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی مکانیک، دانشگاه علم وصنعت ایران، تهران، ایران

2 دانشکده علوم و فنون نوین، دانشگاه تهران، تهران، ایران

چکیده

شکست ترد پلی استایرن تحت بارگذاری فشاری- برشی با استفاده از نمونۀ دیسک برزیلی دارای شیار کلیدی شکل به صورت تجربی و نظری مورد بررسی قرار گرفته است. نمونه‌های شیاردار توسط پارامترهای مختلف هندسی، یعنی طول و شعاع نوک شیار مشخص شده است. دو مدل پی شبینی مبتنی بر انرژی، یعنی معیار چگالی انرژی کرنشی متوسط و چگالی انرژی کرنشی متوسط براساس مفهوم ضرایب معادل به منظور پیش بینی مقادیر بار شکست تجربی قطعات پلی استایرنی آزمایش شده ارائه شده است. به منظور مقایسه کلی، نتایج تجربی و نظری مقادیر بار شکست برحسب شعاع نوک شیار برای هر حالت رسم شده است. علاوه بر این، تجزیه وتحلیل های مبتنی بر حل اجزا محدود و همچنین مشاهدات تجربی نشان دادند که اگرچه شکست ترد در نمونه های تجربی تحت بار فشاری- برشی از سمت نیروی اعمالی در شیار رخ می‌‎دهد ولی همواره خط نیمساز شیار و سمت دیگر شیار تحت تنش‌های فشاری می‌باشد. در واقع این رخداد بیانگر مفهوم بارگذاری فشاری- برشی می باشد. در نهایت، نشان داده شده است که تطابق خوبی بین نتایج بار شکست تجربی و مقادیر پیش بینی‌های نظری با استفاده از معیارهای مبتنی بر انرژی کرنشی وجود دارد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Brittle Fracture in Key-hole Notched Polymer Specimens under Combined Compressive-shear Loading

نویسندگان [English]

  • M.R. Ayatollahi 1
  • A.R. Torabi 2
  • H.R. Majidi 1
1 Fatigue and Fracture Research Laboratory, School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran
2 Fracture Research Laboratory, Faculty of New Sciences & Technologies, University of Tehran, Tehran, Iran
چکیده [English]

In the present study, brittle fracture of the general-purpose Polystyrene (GPPS) is studied experimentally and theoretically under compressive-shear loading by using the Brazilian disk specimens containing a key-hole notch. The notched specimens are specified by different geometric parameters, i.e. the notch length and the tip radius. In this investigation, 84 fracture tests reported recently by the present authors are evaluated to assess the brittle fracture of key-hole notched specimens under compressive-shear loading. Two energy-based fracture models namely, the averaged strain energy density (ASED) and averaged strain energy density based on the equivalent factor concept (ASED-EFC) are proposed to predict the fracture loads of the tested GPPS specimens. The experimental and theoretical results are plotted for each case in the form of the fracture load versus the notch tip radius. Moreover, the analyses based on the finite element method as well as the experimental observations showed that although brittle failure in the test samples under compressive-shear loading takes place from the applied load side of the notch border by local tensile stresses, the notch bisector line and the other side of the notch border sustain compressive stresses. In fact this phenomenon states the concept of compressive-shear loading. Finally, it is shown that a good agreement exists between the experimental fracture load results and the theoretical predictions evaluated by using the two strain energy-based criteria.

کلیدواژه‌ها [English]

  • Key-hole notch
  • GPPS
  • Mixed mode I/II loading
  • Brittle fracture
  • Strain energy density
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