نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشیار، مهندسی مکانیک، دانشگاه سمنان، سمنان.

2 کارشناس ارشد، مهندسی هوافضا، دانشگاه سمنان، سمنا ن.

چکیده

در این مقاله، به بررسی اثرات نرخ بارگذاری بر رفتار خستگی کم‌چرخه در کامپوزیت‌های تقویت‌شده با الیاف کربن پرداخته شده است. ابتدا، قطعات کامپوزیتی سوراخ‌دار، تحت بارگذاری کششی در دو فرکانس اعمال بار مختلف قرار گرفته شده تا دامنه مورد استفاده در آزمون خستگی کم‌چرخه بدست آید. سپس نمونه‌ها تحت بارگذاری خستگی در سه مقدار جابجایی و پنج فرکانس بارگذاری قرار گرفتند و تاثیر آن‌ها در مقدار بیشینه و کمینه تنش در هر سیکل، عمر خستگی و مقادیر تنش دامنه و میانگین محاسبه و در انتها، تصاویر سطح شکست و تصاویر میکروسکوپ الکترونی روبشی ارائه شدند. نتایج نشان داد که با افزایش نرخ بارگذاری کششی مقدار بیشینه تنش، به دلیل تمایل بیشتر ماده به رفتار ترد، افزایش پیدا می‌کند. همچنین بیشینه تنش در جابجایی ثابت و فرکانس‌های بارگذاری مختلف مقدار کمی با افزایش همراه بوده ولی در فرکانس ثابت و جابجایی‌های متفاوت بسیار افزایش یافت. عمر خستگی نیز در جابجایی ثابت با افزایش فرکانس بارگذاری روندی افزایشی و در فرکانس بارگذاری ثابت با افزایش جابجایی روندی کاهشی داشت. به کمک تحلیل حساسیت مشخص شد که تغییر فرکانس بارگذاری در جابجایی ثابت همچنین تغییر جابجایی در فرکانس 1-5 هرتز تاثیری در مقدار تنش بیشینه نداشته ولی در فرکانس‌های 10-20 هرتز تاثیرگذار است. رفتار سیکلیک ماده نشان داد که تنش بیشینه در طول سیکل‌های بارگذاری، به دلیل تجمیع آسیب، کاهش می‌یابد و سفتی کامپوزیت کاهش می‌یابد. مکانیزم‌های آسیب با تغییر فرکانس بارگذاری، تغییر کرده و درصد شکست الیاف با افزایش فرکانس بارگذاری، افزایش یافت.

کلیدواژه‌ها

عنوان مقاله [English]

Study of cyclic behavior, displacement-controlled low-cycle fatigue lifetime and failure in open-hole polymer-matrix composite reinforced by carbon fibers under various loading rates and amplitudes

نویسندگان [English]

  • Mohammad Azadi 1
  • Mohammad Dorfaki 2

1 Faculty of Mechanical Engineering, Semnan University, Semnan, Iran.

2 Faculty of Mechanical Engineering, Semnan University, Semnan, Iran.

چکیده [English]

In this article, effects of the loading rate on low-cycle fatigue behaviors in carbon fiber reinforced composites have been investigated. Firstly, open-hole composite specimens were exposed to two different tensile loading rates to achieve displacements in low-cycle fatigue tests. Then, samples were subjected to cyclic loading, in three displacements and five loading frequencies. Fracture surfaces and scanning electron microscopy images were also shown. Obtained results indicated that increasing the rate enhanced the maximum stress due to the material tend to the brittle behavior. The maximum stress in different frequencies had a small enhancement; however, it enhanced at various displacements. The lifetime had a decreasing trend in a constant displacement, with increasing the frequency and increased in a constant frequency, with increasing the displacement. By analyzing the sensitivity, the change in the loading frequency (at constant displacements) and the displacement (frequencies: 1-5 Hz) were not effective on the maximum stress. However, under 10-20 Hz, it was effective on the maximum stress. The material cyclic behavior demonstrated that the maximum stress decreased during loading cycles due to the damage accumulation and the composite stiffness reduced. The failure mechanisms changed by changing the frequency and the percentage of the fiber breakage increased by increasing the loading frequency.

کلیدواژه‌ها [English]

  • Polymer matrix composite
  • Carbon fibers
  • Low-cycle fatigue
  • Displacement rate
  • Displacement amplitude
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