فهرس المقالات Crack Propagation

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  1 - Microstructural Investigations and Fracture Analysis of a Multi-Layer Al Panel of a Crashed Aircraft
  H.R. Faridi A. Momeni M. Mohammadpour V. Sarfarazi
  In this paper, the failure analysis was performed on a crashed airplane trunk sample. Received sample was composed of five different layers; Al 2024 as outer layer, a nearly pure Al clad, an anodized layer, an isolating material and the alloy 413 as interior layer. Macr أکثر

  In this paper, the failure analysis was performed on a crashed airplane trunk sample. Received sample was composed of five different layers; Al 2024 as outer layer, a nearly pure Al clad, an anodized layer, an isolating material and the alloy 413 as interior layer. Macro and micro-cracks in the sample were mostly initiated from the areas close to or around the rivets. These cracks initiated in anodized layer, got through the cladding and entered into the outer Al 2024. Few corrosion sites similar to crevice were also observed behind the rivets and between isolating and cladding layers. It was found that the crevice corrosion and fatigue were responsible to form micro-cracks at these sites. Microstructural observations of Al 2024 layer showed that the micro-cracks were mostly initiated form inside out then they progressed through the interfaces of second phase particles and the matrix. It was found that larger particles were in favor of crack propagation along their interfaces. Second phase large particles are attributed to over-aging of trunk sample which was subjected to excessive heat from the engines. تفاصيل المقالة
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  2 - Evaluating the Effects of Overload and Welding Residual Stress in Fatigue Crack Propagation
  Ali Moarefzadeh Shahram Shahrooi Mehdi Jalali Azizpour
  In this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as fun أکثر

  In this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as function depending on SIFs resulted by external load, weld residual stress and overload. Weight function is applied to calculate SIF resulted by weld residual stress. Also, a method is introduced to determine overload SIF and overload stress ratio. Then fatigue crack propagation equation is modified for our purpose. In other words, a simple and efficient method is presented in this paper for predicting fatigue crack propagation rate in welded joints when the overload is happen. Finally for evaluating this modified equation, experimental methods are applied. Test samples were M(T) geometry made of aluminum alloy with a longitudinal weld by the Gas Tungsten arc welding process. Modified equation has a good agreement with the experimental model presented in this field. تفاصيل المقالة
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  3 - Geometrical Optimization of the Cast Iron Bullion Moulds Based on Fracture Mechanics
  A Niknejad M Karami Khorramabadi M.J Sheikhpoor S.A Samieh Zargar
  In this paper, the causes of the crack initiation in cast iron bullion moulds in Meybod Steel Corporation are investigated and then some new geometrical models are presented to replace the current moulds. Finally, among the new presented models and according to the life أکثر

  In this paper, the causes of the crack initiation in cast iron bullion moulds in Meybod Steel Corporation are investigated and then some new geometrical models are presented to replace the current moulds. Finally, among the new presented models and according to the life assessment, the best model is selected and suggested as the replaced one. For this purpose, the three recommended moulds were modeled and analyzed by ANSYS software. First, a thermal analysis and then a thermo-mechanical coupled field analysis were performed on each three model. The results of the analysis are used to determine the critical zone. The critical zone is selected on the symmetric axis of the inner surface of the mould. By comparing the principle stress contours and temperature distribution contours of three models, one of the suggested models was selected as optimized geometrical model. Then, the crack modeling and the life assessment on the optimized model were implemented and the total life of the model was calculated. Comparison of the life of the optimized and the initial models shows an increase in the life of the suggested model. The results are verified with the experiments. تفاصيل المقالة
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  4 - طراحی و ساخت مجموعه سازه آزمایش پدیده رشد سریع ترک جهت کاربرد در اندازه‌گیری سرعت رشد نوک ترک در لوله‌های خطوط انتقال‌
  سید محمود مدنی محمد رضا فروزان علیرضا صالحیان
  لوله‌ها در فرآیند ساخت و عملکرد، ناشی از عواملی از قبیل خستگی و خوردگی در معرض ایجاد ریز ترک‌هایی در سطوح داخلی و خارجی لوله قرار دارند. در این حالت، ترک با سرعت بسیار زیادی به موازات محور لوله رشد خواهد نمود. در این تحقیق که برای اولین بار در کشور صورت گرفته، به طراحی أکثر

  لوله‌ها در فرآیند ساخت و عملکرد، ناشی از عواملی از قبیل خستگی و خوردگی در معرض ایجاد ریز ترک‌هایی در سطوح داخلی و خارجی لوله قرار دارند. در این حالت، ترک با سرعت بسیار زیادی به موازات محور لوله رشد خواهد نمود. در این تحقیق که برای اولین بار در کشور صورت گرفته، به طراحی و ساخت مجموعه سازه آزمایش با هدف اندازه‌گیری سرعت رشد نوک ترک با استفاده از دو روش دوربین‌‌‌سرعت‌بالا و دستگاه زمان‌سنج‌سیمی در لوله های بدون درز آلومینیمی از سری 6063-T5 پرداخته شده است. نتایج بدست آمده از آزمایش با این مجموعه سازه عیارت است از: فشار ترکیدگی برای نمونه‌های با عمق ترک 8/0، 0/1 و 2/1 به ترتیب برابر 70، 65 و 58 بار و سرعت‌‌های بدست آمده با کمک دوربین‌‌سرعت‌بالا و دستگاه زمان‌سنج سیمی در محدوده 120 تا 132 و 120 تا 126 متر بر ثانیه ثبت شد. نتایج کیفی بدست آمده در این تحقیق تطابق مناسبی با دیگر تحقیقات ارائه شده در دیگر منابع علمی دارد. تفاصيل المقالة
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  5 - Investigating the Effect of Residual Stress on Fatigue Crack Propagation by Modified J-integral and Experimental Method
  Ali Moarrefzadeh Shahram Shahrooi
  This paper is introduced new method for predicting of fatigue crack propagation (FCP) in residual stress (RS) field due to welding. If there is stress in the material and is subjected to loading, the effects of loading and RS must be considered simultaneously. For this أکثر

  This paper is introduced new method for predicting of fatigue crack propagation (FCP) in residual stress (RS) field due to welding. If there is stress in the material and is subjected to loading, the effects of loading and RS must be considered simultaneously. For this purpose, stress intensity factor (SIF) in liner elastic fracture mechanics (LEFM) approach and J-integral in elastic-plastic fracture mechanics (EPFM) approach are used. The superposition principle based on LEFM is used to consider the RS effects on the cycle ratio and SIF. To achieve more appropriate results based on EPFM, the J-integral is modified to consider the simultaneous effects of RS and external loading. Finally, the FCP equations are modified to consider into calculation the simultaneous influences of RS and cyclic loading. Results from FCP equation based on J-integral are in good agreement with experimental results. The obtained results show that the MLPG method is suitable for calculating the residual stress and the modified J-integral method is the best method for predicting FCP in the RS field caused by welding. تفاصيل المقالة
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  6 - بررسی تاثیرچسبندگی-لغزش برترک خوردگی صفحه ی بتن آرمه با استفاده ازمدل شبکه ای
  حمید شجاعی فر مسعود فرزام
  چکیده: دراین مقاله سه مدل چسبندگی-لغزش(Farra,Harajli,CEB-FIP) که برمبنای نتایج مطالعات تجربی قبلی بدست آمده اند، مطالعه می شوند تا اثر چسبندگی-لغزش در فاصله ی ترک و نحوه ی انتشار ترک صفحه ی بتن آرمه بررسی شود. برای این منظور، یک صفحه ی بتن آرمه با استفاده از مدل عددی أکثر

  چکیده: دراین مقاله سه مدل چسبندگی-لغزش(Farra,Harajli,CEB-FIP) که برمبنای نتایج مطالعات تجربی قبلی بدست آمده اند، مطالعه می شوند تا اثر چسبندگی-لغزش در فاصله ی ترک و نحوه ی انتشار ترک صفحه ی بتن آرمه بررسی شود. برای این منظور، یک صفحه ی بتن آرمه با استفاده از مدل عددی شبکه ای توسط نرم افزار ABAQUS مدل سازی شده است و روند ترک خوردگی توسط خرابی عضوهای میله ای بتن نشان داده شده است. مدل های شبکه ای بر اساس معیار ترک خوردگی توسعه یافته و با بکارگیری اصول مکانیک شکست در ارزیابی ترک خوردگی اعضا بتن آرمه بکار رفته اند. بتن وفولاد با یک مدل برهم کنش دهنده (Bond-Link) و با در نظر گرفتن اثر چسبندگی-لغزش با یکدیگر ترکیب شده اند تا رفتار مصالح ترکیبی بتن آرمه را توصیف کنند. نتایج تحلیل ها نشان داده‌اند که مدل های چسبندگی-لغزش تاثیر مهمی در فاصله ی ترک، عرض ترک، نحوه ی انتشار ترک و موضع شدگی خرابی دارند. تفاصيل المقالة
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  7 - Application of image-processing to crack propagation process identification in concrete under fatigue phenomenon
  Mohsen Heydari Mofrad Yasin Hoseini-Azar
  Concrete is the most important material in geotechnical projects and constructions which that due to the cyclical loading and fatigues were always under failures. The fatigue is natural events were occurred in under cyclical loaded materials which causes very complex fa أکثر

  Concrete is the most important material in geotechnical projects and constructions which that due to the cyclical loading and fatigues were always under failures. The fatigue is natural events were occurred in under cyclical loaded materials which causes very complex failures in under low stress and in elastic behavior. Although the concrete behavior and changes under axial loading are studied, but failure mechanism of fatigue and crack propagation on concrete (as the main factor to failure) is on obscurity. The investigation of crack propagation process from the beginning to failure under cyclic axial loading can be identified the fatigue mechanism. This study tired to monitoring and modeling the crack propagation mechanism under the cyclic uniaxial compressive strength (UCS ) in axial loading of concrete specimens which help to understands of crack propagation and developed path in the body. For this purpose, the concrete specimens are tested by UCS , take photos repetitively (in 5 loading-unloading cycles) and used the image-processing techniques (IPT) for crack detection, propagation and simulation of the failure in concrete. The simulation results shown the IPT is good performance to crack propagation detections and propagation process is perfectly simulated by IPT. تفاصيل المقالة
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  8 - Propagation of Crack in Linear Elastic Materials Considering Crack Path Correction Factor
  مهدی پورمحمود
  Modelling of crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics أکثر

  Modelling of crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics. Crack growth process is simulated by an incremental crack-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor. In this paper, a procedure to correct the direction of crack propagation in the analysis of finite element is peresented to ensure that a unique final crack path is achieved for different analysis of a problem by using different increments of crack. For each increment of crack extension, finite element method is applied to perform a single region stress analysis of the cracked structure. Results of this incremental crack extension analysis are presented for several geometries. تفاصيل المقالة
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  9 - Propagation of Crack in Linear Elastic Materials with Considering Crack Path Correction Factor
  مهران مرادی مهدی پورمحمود
  Modeling of crack propagation by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture me أکثر

  Modeling of crack propagation by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics. Crack - growth process is simulated by an incremental crack-extension analysis based on the maximum principal stress criterion which is expressed in terms of the stress intensity factor. In this paper a procedure is employed to correct direction of crack propagation to ensure that a unique final crack path is achieved for different analysis of a problem by using different increments of crack. For each increment of crack extension, finite element method is applied to perform a single - region stress analysis of the cracked structure. Results of this incremental crack – extension analysis are presented for several geometries. تفاصيل المقالة