شبيه سازي سه بعدي و بررسي تاثير دما در ترك هاي شبه بيضوي محوري و محيطي در مخازن استوانه اي

3D Simulation and effect of temperature on crack elliptically axial and cirumferential in the cylindrical vessels

در ﻃﻮل ﻣﺪت ﻋﻤﺮ ﯾﮏ ﻣﺨﺰن، اﯾﺠﺎد ﻣﻌﺎﯾﺒﯽ ﻫﻤﭽﻮن ﺗﺮكﻫﺎ اﻣﺮي اﺟﺘﻨﺎبﻧﺎﭘﺬﯾﺮ اﺳﺖ ﮐﻪ ﺑﻪدﻻﯾﻠﯽ ﻧﻈﯿﺮ ﺧﻮردﮔﯽ ﯾﺎ ﺑﺎرﮔﺬاري ﺧﺴﺘﮕﯽ و... ﺑﻪ وﺟﻮد ﻣﯽآﯾﻨﺪ. ﯾﮑﯽ از اﻧﻮاع ﻋﻤﺪة ﺗﺮكﻫﺎي اﯾﺠﺎدﺷﺪه، ﺗﺮكﻫﺎي ﺷﺒﻪﺑﯿﻀﻮي ﻫﺴﺘﻨﺪ. ﻫﺪف از اﯾﻦ ﺗﺤﻘﯿﻖ، ﺑﺮرﺳﯽ اﯾﻦ ﻧﻮع از ﺗﺮكﻫﺎ در ﯾﮏ ﻣﺪل ﻣﺨﺰن اﺳﺘﻮاﻧﻪاي از ﺟﻨﺲ اﺳﺘﯿﻞ ﺑﺎ اﺳﺘﺎﻧﺪارد ASME و ﺗﺄﺛﯿﺮات ﺗﺮﻣﻮﻣﮑﺎﻧﯿﮑﯽ آن اﺳﺖ. ﺑﺮاي ﺷﺒﯿﻪﺳﺎزي ﺗﺮك از دو ﻧﺴﺒﺖ a/c و a/t ﮐﻪ ﻣﻌﺮف اﺑﻌﺎد ﺗﺮك ﻫﺴﺘﻨﺪ، اﺳﺘﻔﺎده ﺷﺪه اﺳﺖ. در اﯾﻨﺠﺎ ﺑﺮاي ﺑﻪدﺳﺖآوردن ﺿﺮاﯾﺐ ﺷﺪت ﺗﻨﺶ از ﺷﺒﯿﻪﺳﺎزي ﺗﺮك و ﻣﺨﺰن در ﻧﺮماﻓﺰار اﻟﻤﺎن ﻣﺤﺪود ANSYS، در ﻣﺤﯿﻂ workbench اﺳﺘﻔﺎده ﺷﺪه اﺳﺖ. ﺑﺮاي ﻣﺤﺎﺳﺒﮥ ﺿﺮاﯾﺐ ﺷﺪت ﺗﻨﺶ در ﻧﻘﺎط ﻣﺨﺘﻠﻒ واﻗﻊ ﺑﺮ ﺟﺒﻬﮥ ﺗﺮك ﻣﺨﺘﺼﺎت ﻣﻮﺿﻌﯽ اﯾﺠﺎد ﺷﺪ و ﺑﺮ اﺳﺎس ﮐﺎﻧﺘﻮرﻫﺎي ﻣﺨﺘﻠﻒ در ﻧﻮدﻫﺎي اﻃﺮاف ﻧﻮك ﺗﺮك ﯾﺎ ﻣﯿﺰان ﺑﺎزﺷﺪﮔﯽ در ﺻﻔﺤﮥ ﺗﺮك ﻣﻘﺎدﯾﺮ ﺿﺮاﯾﺐ ﺷﺪت ﺗﻨﺶ را ﺑﺮ اﺳﺎس ﻣﻌﯿﺎر ﻣﺪﻧﻈﺮ ﻣﺤﺎﺳﺒﻪ ﺷﺪ. ﺑﺎ اﺳﺘﻔﺎده از ﻣﻘﺎدﯾﺮ ﺿﺮاﯾﺐ ﺷﺪت ﺗﻨﺶ ﺑﻪدﺳﺖآﻣﺪه در اﺑﻌﺎد ﻣﺸﺨﺺ ﻣﺨﺰن و ﺗﺮك و ﻫﻤﭽﻨﯿﻦ ﺷﺮاﯾﻂ ﺑﺎرﮔﺬاري و ﺟﻨﺲ ﻣﺨﺰن، ﻧﻘﺎط ﺑﺤﺮاﻧﯽ ﺗﺮك ﻣﺸﺨﺺ ﺷﺪ. ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ ﻧﺘﺎﯾﺞ ﺑﻪدﺳﺖآﻣﺪه از ﻣﺮاﺣﻞ ﻗﺒﻞ و ﺑﺎ ﮐﻤﮏ ﻣﻌﺎدﻟﮥ ﭘﺎرﯾﺲ، ﻋﻤﺮ ﻣﺨﺰن و ﺗﻌﺪاد ﺳﯿﮑﻞ ﺑﺎرﮔﺬاري ﻣﺸﺨﺺ ﺷﺪ و در ﻧﻬﺎﯾﺖ ﻧﺘﺎﯾﺞ ﺑﻪدﺳﺖآﻣﺪه از ﺿﺮﯾﺐ ﺷﺪت ﺗﻨﺶ ﺑﺎ ﻧﺘﺎﯾﺞ ﺿﺮﯾﺐ ﺷﺪت ﺗﻨﺶ ﺑﺮ اﺛﺮ اﺧﺘﻼف دﻣﺎي ﺟﺪارة ﻣﺨﺰن ﻣﻘﺎﯾﺴﻪ ﺷﺪ.

During the life of a reservoir, defects such as cracks are inevitable due to reasons such as corrosion or fatigue loading, and so on. One of the most common types of cracks is the half-elliptic cracks. The purpose of this study is to investigate this type of cracks in the ASME standard steel cylinder tank model and its thermomechanical effects. In order to simulate the cracks, two a/c and a/t ratios representing the dimensions of the cracks are used. Here, in order to obtain stress intensity coefficients from the crack and tank simulation in the ANSYS finite element software, the workbench environment has been used. In order to calculate the stress intensity coefficients, it was necessary to create local coordinates in different points on the crack front and calculate the stress intensity coefficients based on the different contours in the nodes around the crack tip or the crack opening in the crack front, based on the desired criterion. Regarding to the values of the stress intensity coefficients obtained from the specific dimensions of cracks in the reservoir, as well as the loading conditions and the shape of the reservoir, we can determine the criticality of the crack. According to the results obtained from the previous steps and with the help of the Paris equation, the reservoir life and the number of loading cycles were determined. Finally, the results of the stress coefficient were compared with the results of the stress intensity factor due to the difference in the temperature of the reservoir wall.