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Application of Ductile Fracture Criteria to Fracture Prediction of Punch-Stretch Tests
Yanshan Lou,Hoon Huh(허훈),Gihyun Bae(배기현),Younki Ko(고윤기),Seokbong Kim(김석봉) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
This paper applies various ductile fracture criteria into finite element analysis (FEA) to predict the fracture initiation of punch-stretch tests. Punch-stretch tests are carried out to construct forming limit diagrams (FLDs) of SPCC (Steel plated cold-rolled commercial quality). Limit dome heights (LDHs) are measured from the fractured specimens in punch-stretch tests. The limit strains in uniaxial tension, plane strain and equibiaxial tension conditions are measured in FLDs and utilized to evaluate the material constants in ductile fracture criteria. To implement ductile fracture criteria into FEA, user subroutines are developed for the commercial software ABAQUS/Explicit with the Hill48 yield function. Simulations are carried out to predict fracture initiation of punch-stretch tests by ductile fracture criteria. Fracture locations predicted by ductile fracture criteria are compared with fractured specimens in experiments. LDHs are measured from simulations and compared with experimental results. The comparison demonstrates that LDHs predicted by various ductile fracture criteria match the experimental results with higher accuracy for arc-shape specimens while the Lou-Huh criterion predicts more accurate LDHs than other ductile fracture criteria for square-shaped specimens.
Formability Prediction of Steel Sheets based on a Modified Oh Ductile Fracture Criterion
Yanshan Lou,Hoon Huh(허훈),Younki Ko 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
This paper modifies the Oh ductile fracture criterion by adding an exponent to the weight function. The modified Oh criterion is applied to predict forming limit diagrams (FLDs) of several steel sheets. Two material constants in the modified Oh criterion are evaluated by the experimental data of the materials. The mechanical properties of the materials are characterized by the Hollomon strain hardening law and the Yld89 yield function with the normal anisotropy. FLDs are predicted by the modified Oh criterion and several other famous ductile fracture criteria. FLDs predicted by ductile fracture criteria are compared with experimental data. The comparison demonstrates that FLDs predicted with the modified Oh criterion match the experimental data with higher accuracy than other ductile fracture criteria especially in the biaxial tension region.
루얀산(Yanshan Lou),박명준(Mingjun Piao),허훈(Hoon Huh) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
This paper is concerned with evaluation of various ductile fracture criteria in a general three dimensional (3D) stress state of stress triaxiality, the Lode parameter and the equivalent plastic strain to fracture. Evaluation is carried out by comparing fracture loci constructed by fracture criteria to experimental results of Al2024- T351. Comparison demonstrates that the Modified Mohr-Coulomb criterion and a newly proposed criterion provide sufficient predictability of fracture strain. Moreover, evaluation is emphasized on the predicted cut-off value for stress triaxiality. Evaluation suggests that the Cockcroft-Latham, Brozzo, Oh, KoHuh and the new criteria coupled a reasonable cut-off value for ductile materials.