مطالعه تاثير روش‌هاي كاليبراسيون بر دقت معيارهاي شكست نرم پديدار شناختي در فرايند شكل‌-دهي ورق‌هاي فلزي

Study of the Effect of Calibration Procedure on the Accuracy of the Phenomenological Ductile Fracture Criteria in Sheet Metal Forming

در اﯾﻦ ﻣﻘﺎﻟﻪ، ﺗﻌﯿﯿﻦ ﻟﺤﻈﻪ ﺷﮑﺴﺖ ﺗﻮﺳﻂ ﻣﻌﯿﺎرﻫﺎي ﺷﮑﺴﺖ ﻧﺮم و ﺗﺎﺛﯿﺮ ﺗﻮاﺑﻊ وزﻧﯽ آﺳﯿﺐ، روشﻫﺎ و آزﻣﻮنﻫﺎي ﮐﺎﻟﯿﺒﺮاﺳﯿﻮن، ﺑﺮ دﻗﺖ ﭘﯿﺶﺑﯿﻨﯽ ﻟﺤﻈﻪ ﺷﮑﺴﺖ ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺖ. ﺑﺮ اﺳﺎس ﺑﺮرﺳﯽﻫﺎي ﺣﺎﻟﺖ ﺗﻨﺶ، ﺳﻪ آزﻣﻮن ﮐﺎﻟﯿﺒﺮاﺳﯿﻮن ﮐﺸﺶ ﺗﮏ ﻣﺤﻮري، ﮐﺸﺶ ﮐﺮﻧﺶ ﺻﻔﺤﻪاي و ﮐﺸﺶ ﻧﻤﻮﻧﻪ داراي ﺗﻮرﻓﺘﮕﯽ ﺑﻪ ﻣﻨﻈﻮر ﺗﻌﯿﯿﻦ ﻣﻘﺎدﯾﺮ ﺑﺤﺮاﻧﯽ ﻣﻌﯿﺎرﻫﺎي ﺷﮑﺴﺖ ﺑﻪ ﮐﺎر ﮔﺮﻓﺘﻪ ﺷﺪﻧﺪ. ﺑﻪ ﻣﻨﻈﻮر ﺑﺮرﺳﯽ رﻓﺘﺎر ﺷﮑﺴﺖ در آﻟﻮﻣﯿﻨﯿﻮم آﻟﯿﺎژي 6061، ﻣﻌﯿﺎرﻫﺎي ﺷﮑﺴﺖ ﻧﺮم ﭘﺪﯾﺪارﺷﻨﺎﺧﺘﯽ آﯾﺎدا، راﯾﺲ-ﺗﺮﯾﺴﯽ و ﮐﻮﮐﺮاﻓﺖ-ﻟﺎﺗﻬﺎم ﻧﺮﻣﺎﻟﻪ، از ﻃﺮﯾﻖ روش ﺗﺮﮐﯿﺒﯽ ﺗﺠﺮﺑﯽ-ﺷﺒﯿﻪﺳﺎزي ﮐﺎﻟﯿﺒﺮه ﺷﺪﻧﺪ. ﻧﺮم اﻓﺰار اﺟﺰاي ﻣﺤﺪود اﺑﺎﮐﻮس ﺑﻪ ﻣﻨﻈﻮر ﺷﺒﯿﻪﺳﺎزي ﻓﺮاﯾﻨﺪ اﺳﺘﻔﺎده ﺷﺪ و ﻣﻌﯿﺎرﻫﺎي ﺷﮑﺴﺖ ﺗﻮﺳﻂ زﯾﺮﺑﺮﻧﺎﻣﻪ ﻣﻨﺎﺳﺐ ﺑﻪ ﺑﺮرﺳﯽﻫﺎي اﺟﺰاي ﻣﺤﺪود اﻋﻤﺎل ﺷﺪﻧﺪ. ﻣﻘﺎدﯾﺮ ﻧﯿﺮو-ﺟﺎﺑﺠﺎﯾﯽ و ﻃﻮل ﮐﻮرس ﺷﮑﺴﺖ در آزﻣﻮنﻫﺎي ﺗﺠﺮﺑﯽ، ﺑﻪ ﻣﻨﻈﻮر ﺻﺤﺖﺳﻨﺠﯽ ﻧﺘﺎﯾﺞ ﻋﺪدي و ﺑﺮرﺳﯽ دﻗﺖ ﻣﻌﯿﺎرﻫﺎ ﻣﻮرد اﺳﺘﻔﺎده ﻗﺮار ﮔﺮﻓﺘﻨﺪ. ﻣﻄﺎﺑﻖ ﺑﺎ ﻧﺘﺎﯾﺞ، روش ﮐﺎﻟﯿﺒﺮاﺳﯿﻮن ﺑﺮ ﻣﺒﻨﺎي ﺗﺎرﯾﺨﭽﻪ ﺣﺎﻟﺖ ﺗﻨﺶ در ﻣﻘﺎﯾﺴﻪ ﺑﺎ روش ﻣﻘﺪار ﻣﯿﺎﻧﮕﯿﻦ ﻧﺘﺎﯾﺞ دﻗﯿﻖﺗﺮي در ﭘﯿﺶﺑﯿﻨﯽ ﻟﺤﻈﻪ ﺷﮑﺴﺖ اراﺋﻪ ﻣﯽﻧﻤﺎﯾﺪ )3/4 درﺻﺪ ﮐﺎﻫﺶ در ﻣﯿﺎﻧﮕﯿﻦ ﺧﻄﺎي ﭘﯿﺶﺑﯿﻨﯽ ﺷﮑﺴﺖ(. در ﻣﯿﺎن ﺗﻤﺎﻣﯽ ﺣﺎﻟﺎت، ﻣﻌﯿﺎر ﮐﻮﮐﺮاﻓﺖ-ﻟﺎﺗﻬﺎم ﻧﺮﻣﺎﻟﻪ ﺗﺤﺖ ﮐﺎﻟﯿﺒﺮاﺳﯿﻮن ﺑﺎ آزﻣﻮن ﮐﺸﺶ ﮐﺮﻧﺶ ﺻﻔﺤه اي ﻣﻨﺎﺳﺐﺗﺮﯾﻦ ﻣﻌﯿﺎر و آزﻣﻮن ﮐﺎﻟﯿﺒﺮاﺳﯿﻮن ﺑﻪ ﻣﻨﻈﻮر ﭘﯿﺶﺑﯿﻨﯽ ﺷﮑﺴﺖ در ﻣﻘﺎدﯾﺮ ﻣﺜﺒﺖ ﭘﺎراﻣﺘﺮ ﺳﻪ ﻣﺤﻮري ﺗﻨﺶ ﻣﯽﺑﺎﺷﻨﺪ.

In this paper, determination of the fracture onset by the ductile fracture criteria was studied and the effect of damage function, calibration method, and calibration tests were investigated on the fracture prediction accuracy. Based on the stress state analysis, three different tension tests including the uniaxial, plane strain, and notched tension tests were conducted to determine the critical value of the ductile fracture criteria. In order to investigate the fracture behavior of AA6061-T6 aluminum alloy sheets, The Ayada, Rice-Tracey, and normalized Cockroft-Latham phenomenological ductile fracture criteria were calibrated through a hybrid experimental-numerical method. The finite element (FE) method were used to simulate the process and calibrated fracture criteria were implemented using an appropriate user subroutine. Experimental force-displacement curve and the fracture displacement were used to validated the numerical simulation and investigate the fracture prediction accuracy. According to the result, calibration method based on the history of the stress state lead to higher fracture prediction accuracy compared to average value method (3.4% decrease in average value of the fracture prediction error). Among all the possible condition, the normalized Cockroft-Latham fracture criteria with the plane strain tension test are the most suitable fracture criterion and calibration test to predict the fracture in the positive value of the stress triaxiality.