دانشگاه صنعتی امیرکبیر نشریه مهندسی عمران امیرکبیر 2588-297X 50 4 2018 10 23 The Experimental Investigation of the Effect of Heating-Cooling Cycle Number of Rock on Mode I Fracture Toughness بررسی آزمایشگاهی اثر تعداد سیکل های گرم شدن- سردشدن سنگ بر روی چقرمگی شکست حالت I 793 800 1965 10.22060/ceej.2017.12659.5245 FA احمد جباری گروه مهندسی معدن، دانشگاه بین المللی امام خمینی )ره(، قزوین، ایران مهدی حسینی گروه مهندسی معدن، دانشگاه بین المللی امام خمینی )ره(، قزوین، ایران Journal Article 2017 03 13 There are small cracks in rocks; therefore, when rocks undergo loading, stresses are concentrated at the tip of cracks causing rock fracture before reaching its ultimate strength. The critical value of the stress intensity factor at the crack tip is called fracture toughness. The tensile strength of rocks is weak; therefore, Mode I (tensile mode) is the most critical loading mode. In some cases, rocks continuously experience heating-cooling. Therefore, it is necessary to determine the effect of heating-cooling cycle number on mode I fracture toughness, which is the objective of this research. To achieve this objective, we conducted three-point bending test on semi-circular specimens of three types of natural rock including sandstone, limestone and andesite to determine the mode I fracture toughness. A series of concrete specimen was also tested for further investigation. Petrography and X-ray diffraction analysis (XRD) were conducted to understand the rock composition. The specimens were heated up to 700° C in 1, 5 and 10 cycles and then cooled. A series of experiments were also conducted on the specimens at room temperature (25°C). According to the rising of temperature in firing process, the rate of temperature rise for specimens in the electric furnace is determined to be 15 ° C per minute. Fracture toughness of andesite rock, sandstone and limestone specimens decreases under cyclic conditions. Results indicate the generation and expansion of micro fractures in some rocks after undergoing cycles of heating-cooling, which causing an increase in the effective porosity and decrease in the P-wave velocity in rocks. <span lang="AR-SA" dir="RTL">در</span><span lang="AR-SA"> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">ترک‌های</span> <span dir="RTL">ریزی</span> <span dir="RTL">وجود</span> <span dir="RTL">دارد،</span> <span dir="RTL">هنگامی</span> <span dir="RTL">که</span> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">تحت</span> <span dir="RTL">بارگذاری</span> <span dir="RTL">قرار</span> <span dir="RTL">می‌گیرند</span> <span dir="RTL">تنشها</span> <span dir="RTL">در</span> <span dir="RTL">نوک</span> <span dir="RTL">ترک‌ها متمرکز</span> <span dir="RTL">شده</span> <span dir="RTL">و</span> <span dir="RTL">باعث</span> <span dir="RTL">گسیخته</span> <span dir="RTL">شدن</span> <span dir="RTL">سنگ</span> <span dir="RTL">قبل</span> <span dir="RTL">از</span> <span dir="RTL">رسیدن</span> <span dir="RTL">به</span> <span dir="RTL">مقاومت</span> <span dir="RTL">نهایی</span> <span dir="RTL">آن</span> <span dir="RTL">می‌شود</span></span><span>. <span lang="AR-SA" dir="RTL">به</span><span lang="AR-SA"> <span dir="RTL">مقدار</span> <span dir="RTL">بحرانی</span> <span dir="RTL">ضریب</span> <span dir="RTL">شدت</span> <span dir="RTL">تنش در</span> <span dir="RTL">نوک</span> <span dir="RTL">ترک،</span> <span dir="RTL">چقرمگی</span> <span dir="RTL">شکست</span> <span dir="RTL">گفته</span> <span dir="RTL">می‌شود</span></span>. <span lang="AR-SA" dir="RTL">مقاومت</span><span lang="AR-SA"> <span dir="RTL">کششی</span> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">ضعیف</span> <span dir="RTL">است</span> <span dir="RTL">به</span> <span dir="RTL">همین</span> <span dir="RTL">دلیل،</span> <span dir="RTL">حالت</span> </span></span><span>I </span><span>)<span lang="AR-SA" dir="RTL">حالت</span><span lang="AR-SA"> <span dir="RTL">کششی</span></span>(<span dir="RTL"> <span lang="AR-SA">بحرانی‌ترین</span></span><span lang="AR-SA"> <span dir="RTL">حالت</span> <span dir="RTL">بارگذاری</span> <span dir="RTL">است</span></span>. <span lang="AR-SA" dir="RTL">در</span><span lang="AR-SA"> <span dir="RTL">برخی</span> <span dir="RTL">مواقع</span> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">به</span> <span dir="RTL">طور</span> <span dir="RTL">مداوم</span> <span dir="RTL">گرم شدن</span></span>- <span lang="AR-SA" dir="RTL">سرد</span><span lang="AR-SA"> <span dir="RTL">شدن</span> <span dir="RTL">را</span> <span dir="RTL">تجربه</span> <span dir="RTL">می‌کنند</span></span>. <span lang="AR-SA" dir="RTL">از</span><span lang="AR-SA"> <span dir="RTL">این</span> <span dir="RTL">رو تعیین</span> <span dir="RTL">اثر</span> <span dir="RTL">تعداد</span> <span dir="RTL">سیکل</span> <span dir="RTL">های</span> <span dir="RTL">گرم</span> <span dir="RTL">شدن</span></span>-<span lang="AR-SA" dir="RTL">سرد</span><span lang="AR-SA"> <span dir="RTL">شدن</span> <span dir="RTL">بر</span> <span dir="RTL">روی</span> <span dir="RTL">چقرمگی</span> <span dir="RTL">شکست</span> <span dir="RTL">حالت</span> </span></span><span>I </span><span lang="AR-SA" dir="RTL">که</span><span lang="AR-SA"> <span dir="RTL">هدف</span> <span dir="RTL">این</span> <span dir="RTL">تحقیق</span> <span dir="RTL">است</span> <span dir="RTL">لازم</span> <span dir="RTL">و</span> <span dir="RTL">ضروری است</span></span><span>. <span lang="AR-SA" dir="RTL">برای</span><span lang="AR-SA"> <span dir="RTL">رسیدن</span> <span dir="RTL">به</span> <span dir="RTL">این</span> <span dir="RTL">هدف</span> <span dir="RTL">بر</span> <span dir="RTL">روی</span> <span dir="RTL">نمونه‌های</span> <span dir="RTL">نیم دایرهای</span> <span dir="RTL">سه</span> <span dir="RTL">نوع</span> <span dir="RTL">سنگ</span> <span dir="RTL">طبیعی</span> <span dir="RTL">شامل</span> <span dir="RTL">ماسه سنگ،</span> <span dir="RTL">سنگ آهک</span> <span dir="RTL">و</span> <span dir="RTL">آندزیت و</span> <span dir="RTL">همچنین</span> <span dir="RTL">نمونه</span> <span dir="RTL">های</span> <span dir="RTL">بتنی</span> <span dir="RTL">آزمایش</span> <span dir="RTL">خمش</span> <span dir="RTL">سه نقطه‌ای</span> <span dir="RTL">برای</span> <span dir="RTL">تعیین</span> <span dir="RTL">چقرمگی</span> <span dir="RTL">شکست</span> <span dir="RTL">حالت</span> </span></span><span>I </span><span lang="AR-SA" dir="RTL">انجام</span><span lang="AR-SA"> <span dir="RTL">گرفته</span> <span dir="RTL">است</span></span><span>. <span lang="AR-SA" dir="RTL">برای</span><span lang="AR-SA"> <span dir="RTL">شناخت ترکیب</span> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">مطالعات</span> <span dir="RTL">سنگ شناسی</span> <span dir="RTL">و</span> <span dir="RTL">تحلیل</span> <span dir="RTL">پراش</span> <span dir="RTL">اشعه</span> <span dir="RTL">ایکس</span></span>( </span><span>XRD </span><span>) <span lang="AR-SA" dir="RTL">نیز</span><span lang="AR-SA"> <span dir="RTL">انجام</span> <span dir="RTL">شده</span> <span dir="RTL">است</span></span>. <span lang="AR-SA" dir="RTL">نمونه‌ها</span><span lang="AR-SA"> <span dir="RTL">1،</span> <span dir="RTL">5</span> <span dir="RTL">و</span> <span dir="RTL">10</span> <span dir="RTL">سیکل</span> <span dir="RTL">تا 700</span> <span dir="RTL">درجه</span> <span dir="RTL">سانتیگراد</span> <span dir="RTL">گرم</span> <span dir="RTL">و</span> <span dir="RTL">سپس</span> <span dir="RTL">سرد</span> <span dir="RTL">شده‌اند</span></span>. <span lang="AR-SA" dir="RTL">بر</span><span lang="AR-SA"> <span dir="RTL">روی</span> <span dir="RTL">نمونه‌ها</span> <span dir="RTL">در</span> <span dir="RTL">دمای</span> <span dir="RTL">محیط</span></span>) <span lang="AR-SA" dir="RTL">25</span><span lang="AR-SA"> <span dir="RTL">درجه</span> <span dir="RTL">سانتیگراد</span></span>(<span lang="AR-SA" dir="RTL">،</span><span lang="AR-SA"> <span dir="RTL">یک</span> <span dir="RTL">سری</span> <span dir="RTL">آزمایش</span> <span dir="RTL">نیز انجام</span> <span dir="RTL">شده</span> <span dir="RTL">است</span></span>. <span lang="AR-SA" dir="RTL">سرعت</span><span lang="AR-SA"> <span dir="RTL">افزایش</span> <span dir="RTL">دما</span> <span dir="RTL">برای</span> <span dir="RTL">نمونه‌ها</span> <span dir="RTL">در</span> <span dir="RTL">کوره</span> <span dir="RTL">الکتریکی،</span> <span dir="RTL">15</span> <span dir="RTL">درجه</span> <span dir="RTL">سانتیگراد</span> <span dir="RTL">بر</span> <span dir="RTL">دقیقه</span> <span dir="RTL">و</span> <span dir="RTL">متناسب</span> <span dir="RTL">با</span> <span dir="RTL">افزایش</span> <span dir="RTL">دما</span> <span dir="RTL">در فرآیند</span> <span dir="RTL">آتش سوزی</span> <span dir="RTL">در</span> <span dir="RTL">نظر</span> <span dir="RTL">گرفته</span> <span dir="RTL">شده</span> <span dir="RTL">است</span></span>. <span lang="AR-SA" dir="RTL">چقرمگی</span><span lang="AR-SA"> <span dir="RTL">شکست</span> <span dir="RTL">برای</span> <span dir="RTL">نمونه</span> <span dir="RTL">سنگ</span> <span dir="RTL">آندزیت،</span> <span dir="RTL">ماسه سنگ</span> <span dir="RTL">و</span> <span dir="RTL">سنگ</span> <span dir="RTL">آهک</span> <span dir="RTL">تحت</span> <span dir="RTL">شرایط سیکلی</span> <span dir="RTL">کاهش</span> <span dir="RTL">می‌یابد</span></span>. <span lang="AR-SA" dir="RTL">به</span><span lang="AR-SA"> <span dir="RTL">این</span> <span dir="RTL">صورت</span> <span dir="RTL">که،</span> <span dir="RTL">بعد</span> <span dir="RTL">از</span> <span dir="RTL">اعمال</span> <span dir="RTL">سیکل‌های</span> <span dir="RTL">گرم</span> <span dir="RTL">شدن</span> <span dir="RTL">و</span> <span dir="RTL">سرد</span> <span dir="RTL">شدن،</span> <span dir="RTL">میکروترک‌ها</span> <span dir="RTL">در</span> <span dir="RTL">نمونه</span> <span dir="RTL">سنگ‌ها گسترش</span> <span dir="RTL">می‌یابد</span> <span dir="RTL">که</span> <span dir="RTL">این</span> <span dir="RTL">باعث</span> <span dir="RTL">افزایش</span> <span dir="RTL">تخلخل</span> <span dir="RTL">مؤثر</span> <span dir="RTL">و</span> <span dir="RTL">کاهش</span> <span dir="RTL">سرعت</span> <span dir="RTL">امواج</span> </span></span><span>P </span><span lang="AR-SA" dir="RTL">در</span><span lang="AR-SA"> <span dir="RTL">نمونه</span> <span dir="RTL">سنگ‌ها</span> <span dir="RTL">می‌گردد.</span></span> https://ceej.aut.ac.ir/article_1965_fb0ba26b961c295db998ff3bb7defe5e.pdf