Abstract
The traditional theory of ductile fracture has limitations for predicting crack generation during a cold shell nosing process. Various damage criteria are employed to explain fracture and failure in the nose part of a cold shell. In this study, differences in microstructure among fractured materials and analysis of their surfaces indicated the occurrence of brittle fractures. The degree of “plastic deformation-induced embrittlement” (PDIE) of plastically deformable materials affects the likelihood of brittle fractures; PDIE can also decrease the strength in tension due to the Bauschinger effect. Two indicators of brittle fracture are presented, i.e., the critical value of PDIE and the allowable tensile strength (which in turn depends on the degree of PDIE or embrittlement-effective strain). When the maximum principal stress is greater than the latter and the PDIE is greater than the former, our method determines the likelihood of brittle fracture. This approach was applied to an actual cold shell nosing process, and the predictions were in good quantitative agreement with the experimental results.
Highlights
Crack initiation and growth have been important issues in cold metal forming for many years [1,2]
Researchers have focused on ductile fracture, which can be understood based on damage criteria
= 0.30 and B = 0.05, ε B .Cr = 0.31 and B = 0.1, and ε B .Cr = 0.32 and B = 0.15, respecTherefore, we evaluated the occurrence of brittle fracture when the maximum principal tively
Summary
Crack initiation and growth have been important issues in cold metal forming for many years [1,2]. A number of damage models have been proposed [3,4,5,6,7,8,9,10,11,12,13,14] to understand crack generation and strain softening in metal forming [15,16,17]. Structural engineering [18,19] These models play major roles in predicting fracture phenomena occurring during metal forming and materials testing, and in mechanical structures. Damage models have been successfully applied to predict tensile strength even after the fracture point [15,17], as well as chevron cracking [15,16,20,21,22]. The predicted rate of decrease in tensile load was lower than in experimental tensile tests. The concordance between critical damage predictions and experimental results are path- and test dependent [1]
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