بررسی خستگی سنگ بکر بلوری تحت بارگذاری کاملاً معکوس شونده

نوع مقاله: پژوهشی

نویسندگان

1 دانشکده مهندسی معدن، دانشگاه صنعتی اصفهان

2 دانشکده مهندسی عمران، دانشگاه صنعتی اصفهان

10.29252/anm.7.13.91

چکیده

در طی پدیده خستگی جسم به علت تجمع آسیب و گسترش ترک ناشی از تکرار روند بارگذاری، در تنشی کمتر از مقاومت استاتیکی خود به‌صورت ناگهانی و ترد می‌شکند. سازندها و سازه‌های سنگی ازجمله گسل‌ها، درزه‌ها، صفحات لایه‌بندی، مخازن زیرزمینی، دیواره تونل‌ها، دیواره حائل پل‌ها، پی راه‌ها و سدها و ... می‌توانند تحت تأثیر بارهای دینامیکی ناشی از زمین‌لرزه‌های بزرگ، انفجار سنگ، آتشباری، حفاری، ترافیک قرار گیرند. در این کار تحقیقاتی رفتار سنگ‌ها تحت تأثیر بارگذاری کاملاً معکوس شونده (کشش فشار) و به کمک دستگاه آزمایش خستگی ساخته‌شده بر اساس آزمایش رایج خستگی فولاد بررسی شده است. از دو نمونه سنگ بلوری گابروی نطنز و مرمر سبز با ترکیب کانی‌شناسی و منشأ ساخت متفاوت جهت بررسی پدیده خستگی با این روش استفاده شد. نتایج به‌دست‌آمده نشان می‌دهد که در نمودار S-N برای هر دو نوع سنگ با کاهش مقدار تنش اعمالی به نمونه، تعداد دوره تحمل شده به‌صورت لگاریتمی افزایش پیدا می‌کند و نمودار هر دو سنگ از رابطه وهلر پیروی می‌کنند. همچنین امکان ارزیابی حد دوام به کمک این نوع آزمایش وجود دارد، درحالی‌که در تحقیقات قبلی این امکان وجود نداشته است. نتایج نشان می‌دهد که حد دوام برای گابروی نطنز در حدود 7/14 مگا پاسکال (53% مقاومت کششی در حالت استاتیکی) و برای مرمر سبز حدود 8/10 مگا پاسکال (60% مقاومت کششی در حالت استاتیکی) است. مقایسه نتایج حاصل‌شده با نتایج سایر مصالح تأیید می‌کند که دستگاه ساخته‌شده و روش مورداستفاده در این تحقیق برای برآورد خستگی در سنگ‌های بلوری مناسب است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluating Fatigue of Intact Crystalline Rocks under Completely Reversed Loading

نویسندگان [English]

  • Saeed Jamali Zavareh 1
  • Hamid Hashemolhosseini 2
  • Alireza Baghbanan 1
  • Mohsen Khoshkam 1
  • Hadi Haghgouei 1
1 Department of Mining Engineering, Isfahan University of Technology, Iran
2 Department of Civil Engineering, Isfahan University of Technology, Iran
چکیده [English]

Summary
The fatigue behavior under completely reversed loading for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx, which have different mineral compositions and formation conditions, were evaluated using a new developed apparatus. The obtained S-N curves followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, the endurance limit is perceived for both tested rocks as well as observed in ferrous metals. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively.
 
Introduction
During fatigue phenomenon cyclic loading causes a material to fail prematurely and suddenly like a brittle failure at a stress level less than determined strength under monotonic condition. Rock formations and structures such as faults, joints, bedding planes, underground reservoirs, tunnels walls, bridge abutments, roads and dams’ foundations, etc. can be subjected to dynamic loadings resulting from vibrations of the earth’s crust, through major earthquakes, rock bursts, rock blasting and drilling and also, traffic. Reaction of rocks to cyclic and repetitive stresses resulting from dynamic loads has been generally neglected with the exception of a few rather limited studies. In this research work, the fatigue behavior of two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were studied under completely reversed loading.
 
Methodology and Approaches
The stress-life method was applied and fatigue behavior and the existence of the endurance limit for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were evaluated using a new developed apparatus. The developed fatigue testing machine was inspired by rotating beam fatigue testing machine (R. R. Moore) which is commonly used for laboratory fatigue test in metals.
 
Results and Conclusions
The obtained results (S-N diagram) followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, results showed that both rocks have endurance limit. The results also illustrated that the endurance limits for both tested rocks are ranged between 0.4 and 0.6 of their tensile strengths. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively. The agreement between the obtained results and presented results in fatigue of other materials showed that the offered method can be applied for studying the fatigue of rocks.

کلیدواژه‌ها [English]

  • Fatigue of rocks
  • Crystalline intact rocks
  • Stress – life method
  • Completely Reversed Loading
  • Endurance limit
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