اﻧﺘﺨﺎب ﻣﻌﯿﺎر ﺷﮑﺴﺖ ﻧﺮم ﻣﻨﺎﺳﺐ ﺟﻬﺖ ﭘﯿﺶ ﺑﯿﻨﯽ ﺷﮑﺴﺖ در ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﺎﻃﻊ داراي ﺗﺎﺧﻮردگي

Selection of Appropriate Ductile Fracture Criterion to Predict Failure of Folded Cross Section Profiles in Reshaping Process

ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻏﻠﺘﮑﯽ ﺳﺮد ﯾﮑﯽ از روش ﻫﺎي ﭘﺮﮐﺎرﺑﺮد در ﺗﻮﻟﯿﺪ ﻟﻮﻟﻪ و ﭘﺮوﻓﯿﻞ ﻫﺎي ﻓﻠﺰي ﻣﯽ ﺑﺎﺷﺪ. ﺑﺎوﺟﻮد ﻣﺰاﯾﺎي ﻓﺮاوان اﯾﻦ روش، ﭘﺮوﻓﯿﻞ ﻫﺎي ﻓﻠﺰي داراي ﺗﺎﺧﻮردﮔﯽ ﺑﺎ ﻗﺎﺑﻠﯿﺖ ﺷﮑﻞ دﻫﯽ ﭘﺎﯾﯿﻦ ﻣﺎﻧﻨﺪ ﭘﺮوﻓﯿﻞ ﻫﺎي آﻟﻮﻣﯿﻨﯿﻮﻣﯽ، در ﻫﻨﮕﺎم ﺗﻮﻟﯿﺪ دﭼﺎر ﭘﺪﯾﺪه ﺷﮑﺴﺖ ﻣﯽ ﺷﻮﻧﺪ. ﻃﺮاﺣﯽ ﻣﻨﺎﺳﺐ ﺧﻂ ﺗﻮﻟﯿﺪ و اﻟﮕﻮي ﮔﻞ ﻣﯽ ﺗﻮاﻧﺪ در ﭘﯿﺸﮕﯿﺮي از اﯾﻦ ﻋﯿﺐ ﻣﺆﺛﺮ ﺑﺎﺷﺪ. در اﯾﻦ ﺗﺤﻘﯿﻖ، ﺑﻪ ﺑﺮرﺳﯽ و ﻣﻘﺎﯾﺴﻪ ﺳﻪ ﻣﻌﯿﺎر ﺷﮑﺴﺖ ﻧﺮم ﺑﺮوزو، آﯾﺎدا و راﯾﺲ-ﺗﺮﯾﺴﯽ ﺑﺮاي ﭘﯿﺶ ﺑﯿﻨﯽ ﭘﺪﯾﺪه ﺷﮑﺴﺖ در ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﻄﻊ ﺗﺎﺧﻮرده ﭘﺮداﺧﺘﻪ ﺷﺪه اﺳﺖ. ﺑﻪ اﯾﻦ ﻣﻨﻈﻮر ﺷﺒﯿﻪ ﺳﺎزي اﺟﺰاي ﻣﺤﺪود ﺗﻮﺳﻂ ﻧﺮم اﻓﺰار آﺑﺎﮐﻮس ﺑﺎ در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﻣﻌﯿﺎر ﺷﮑﺴﺖ اﻧﺠﺎم ﺷﺪ. ﺑﺮاي اﻋﺘﺒﺎرﺳﻨﺠﯽ ﻧﺘﺎﯾﺞ از آزﻣﺎﯾﺶ ﺗﺠﺮﺑﯽ و ﺷﺒﯿﻪ ﺳﺎزي اﺟﺰاي ﻣﺤﺪود ﻟﻪ ﮐﺮدن ﻟﻮﻟﻪ اﺳﺘﻔﺎده ﺷﺪ. ﻧﺘﺎﯾﺞ آزﻣﺎﯾﺶ ﻟﻪ ﮐﺮدن ﻟﻮﻟﻪ ﻧﺸﺎن دﻫﻨﺪه دﻗﺖ ﺑﺎﻻﺗﺮ ﻣﻌﯿﺎر ﺑﺮوزو ﻧﺴﺒﺖ ﺑﻪ دو ﻣﻌﯿﺎر دﯾﮕﺮ ﻣﯽ ﺑﺎﺷﺪ. ﺳﭙﺲ ﺑﺎ اﺳﺘﻔﺎده از ﺳﺎﺑﺮوﺗﯿﻦ ﻧﻮﺷﺘﻪ ﺷﺪه ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﻄﻊ ﻓﻮﻻدي داراي ﺗﺎﺧﻮردﮔﯽ ﺷﺒﯿﻪ ﺳﺎزي و ﻧﺘﺎﯾﺞ آن ﺑﺎ ﻧﻤﻮﻧﻪ ﺗﺠﺮﺑﯽ ﻣﻘﺎﯾﺴﻪ ﺷﺪ. در ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﻄﻊ ﻓﻮﻻدي ﺗﺎﺧﻮرده ﻫﻤﺎﻧﻨﺪ آزﻣﺎﯾﺶ ﺗﺠﺮﺑﯽ ﺷﮑﺴﺘﯽ ﻣﺸﺎﻫﺪه ﻧﺸﺪه اﺳﺖ. در ﺷﺒﯿﻪ ﺳﺎزي ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﻄﻊ آﻟﻮﻣﯿﻨﯿﻮﻣﯽ داراي ﺗﺎﺧﻮردﮔﯽ ﻫﺮ ﯾﮏ از ﻣﻌﯿﺎرﻫﺎي ﺑﺮوزو، راﯾﺲ-ﺗﺮﯾﺴﯽ و آﯾﺎدا ﺑﻪ ﺗﺮﺗﯿﺐ ﻃﻮل ﺷﮑﺴﺖ 10/92، 16/05 و 20/58 ﻣﯿﻠﯽ ﻣﺘﺮ را ﭘﯿﺶ ﺑﯿﻨﯽ ﻣﯽ ﮐﻨﻨﺪ. در ﻧﺘﯿﺠﻪ ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ ﺻﺤﺖ ﺑﺎﻻﺗﺮ ﻣﻌﯿﺎر ﺑﺮوزو در ﭘﯿﺶ ﺑﯿﻨﯽ ﺷﮑﺴﺖ در آزﻣﺎﯾﺶ ﻟﻪ ﮐﺮدن ﻟﻮﻟﻪ، ﻃﻮل ﺷﮑﺴﺖ ﺣﺎﺻﻞ از اﯾﻦ ﻣﻌﯿﺎر در ﻓﺮاﯾﻨﺪ ﺷﮑﻞ دﻫﯽ ﻣﺠﺪد ﻣﻘﻄﻊ آﻟﻮﻣﯿﻨﯿﻮﻣﯽ داراي ﺗﺎﺧﻮردﮔﯽ ﺑﻪ ﻋﻨﻮان ﻣﻘﺪار ﻗﺎﺑﻞ اﻋﺘﻤﺎد اﻧﺘﺨﺎب ﺷﺪ.

The cold roll forming process is one of the most widely used methods in the production of metal profiles. This method, despite its many advantages for producing folded cross section profiles, the fracture has happened for low-formability metals such as aluminum. Proper design of the line and flower pattern can be effective in preventing this defect. In this paper, three ductile fracture criteria of Brozzo, Ayada and Rice-Tracy are compared to predict the fracture initiation in the reshaping process of the folded cross section. For this purpose, finite element method was performed by Abaqus software considering the fracture criterion. Experimental tests and simulations of the tube flattening were used to verify the results. The results of the tube flattening test show that Brozzo’s accuracy should be higher according to the other two criteria. Then,by using the written subroutine the process of forming the folded steel cross section has been simulated and compared with the experimental results. No fracture in the experimental process of forming the folded steel cross section was observed. According to the simulation results of the folded aluminum cross-section process, each of the Brozzo, Rice-Tracy and Ayada criteria predict the failure lengths of 10.9, 16.1 and 20.6 mm, respectively. Therefore, according to the higher accuracy of the Brozzo criterion in predicting failure in the tube flattening test, the fracture length of this criterion in the process of reshaping of the folded aluminum cross section was selected as a reliable value.