• Title, Summary, Keyword: Ductile Fracture

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Punching Fracture Experiments and Simulations of Unstiffened and Stiffened Panels for Ships and Offshore Structures

  • Park, Sung-Ju;Choung, Joonmo
    • Journal of Ocean Engineering and Technology
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    • v.34 no.3
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    • pp.155-166
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    • 2020
  • Ductile fracture prediction is critical for the reasonable damage extent assessment of ships and offshore structures subjected to accidental loads, such as ship collisions and groundings. A fracture model combining the Hosford-Coulomb ductile fracture model with the domain of solid-to-shell equivalence model (HC-SDDE), was used in fracture simulations based on shell elements for the punching fracture experiments of unstiffened and stiffened panels. The flow stress and ductile fracture characteristics of JIS G3131 SPHC steel were identified through tension tests for flat bar, notched tension bar, central hole tension bar, plane strain tension bar, and pure shear bar specimens. Punching fracture tests for unstiffened and stiffened panels are conducted to validate the presented HC-DSSE model. The calibrated fracture model is implemented in a user-defined material subroutine. The force-indentation curves and final damage extents obtained from the simulations are compared with experimental results. The HC-DSSE fracture model provides reasonable estimations in terms of force-indentation paths and residual damage extents.

Ductile Fracture in the Central Region of Circular Plate in Rotary Forging

  • Park, Seogou;Oh, Hung-Kuk
    • Transactions of Materials Processing
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    • v.5 no.4
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    • pp.337-342
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    • 1996
  • The present investigation is concerned with application of theory on fracture to the prediction of workability of materials in rotary forging with special reference to center crack. The validity of the theory on ductile fracture was examined by the experimental data. Then the workability of materials in rotary forging was determined.

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Modeling of a Ductile Fracture Criterion for Sheet Metal Considering Anisotropy (판재의 이방성을 고려한 연성파단모델 개발)

  • Park, N.;Huh, H.
    • Transactions of Materials Processing
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    • v.25 no.2
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    • pp.91-95
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    • 2016
  • This paper is concerned with modeling of a ductile fracture criterion for sheet metal considering anisotropy to predict the sudden fracture of advanced high strength steel (AHSS) sheets during complicated forming processes. The Lou−Huh ductile fracture criterion is modified using the Hill’s 48 anisotropic plastic potential instead of the von Mises isotropic plastic potential to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. To determine the coefficients of the model proposed, a two dimensional digital image correlation (2D-DIC) method is utilized to measure the strain histories on the surface of three different types of specimens during deformation. For the derivation of an anisotropic ductile fracture model, principal stresses (𝜎1,𝜎2, 𝜎3) are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress (𝜂𝐻, 𝐿,) based on the Hill’s 48 anisotropic plastic potential. The proposed anisotropic ductile fracture criterion was quantitatively evaluated according to various directions of the maximum principal stress. Fracture forming limit diagrams were also constructed to evaluate the forming limit in sheet metal forming of AHSS sheets over a wide range of loading conditions.

Bursting Failure Prediction in Tube Hydroforming Process (튜브 액압성형 공정에서의 터짐 현상 예측)

  • Kim, Jeong;Lei, Liping;Kang, Sung-Jong;Kang, Beom-Soo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.9 no.6
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    • pp.160-169
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    • 2001
  • To predict busting failure in tubular hydroforming, the criteria for ductile fracture proposed by Oyane is combined with the finite element method. From the histories of stress and strain in each element obtained from finite element analysis, the fracture initiation site is predicted by mean of the criterion. The prediction by the ductile fracture criterion is applied to three hydroforming processes such as a tee extrusion, an automobile rear axle housing and lower am. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by preforming processes. All the simulation results show the combination of the finite element analysis and the ductile fracture criteria is useful in the prediction of farming limit in hydroforming processes.

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Design of Hexagonal Fitting Nut Preform Considering Ductile Fracture (연성파괴를 고려한 6각 피팅너트 예비성형체 설계)

  • Park T. J.;Kim D. J.;Kim B. M.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.197-200
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    • 2001
  • In the multi-stage former, manufacture of hexagonal fitting nut was generated in a defective products about $70{\~}80\%$. Defective products reduced in a product stiffness and increased a product cost. Defects for manufacturing hexagonal fitting nut caused in a increase of ductile fracture value. So in the study, a preform designed to reduce ductile fracture value and designed preform verified through the finite element simulation. In conclusion, Ductile fracture value reduced if A round dimension of preform reduced and a part of opposition angle contributed in Plenty a volume.

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The Elasto-Plastic Finite Element Analysis of Ductile Fracture in Shape Rolling (형상압연시 연성파괴의 탄소성 유한요소해석)

  • 원영목;오규환
    • Transactions of Materials Processing
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    • v.5 no.1
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    • pp.72-80
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    • 1996
  • During the shape rolling process the influence of reduction ration and taper of shape roller on deformation and limit of ductile fracture such as free surface cracks developing in the workpiece has been studied. The deformation behaviours were analyzed by the 3-dimensional elasto-pastic finite element method and the conditions of ductile fracture were determined from 3-dimensional elasto-plastic finite element method and modified Cockrogt-Latham criterion. The deformed geometry and prediction of ductile fracture by 3-dimensional elasto-plastic finite element method are compared with experimental results The calcuated results are in good agreements with experimental data. The analysis used in the study was found to be effective in predicting the shape rolling process.

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Prediction of fracture in Hub-hole Expansion Process Using Ductile fracture Criteria (연성파괴기준을 이용한 허브홀 확장과정에서의 파단 예측)

  • Ko, Y. K.;Lee, J. S.;Huh, H.;Kim, H. K.;Park, S. H.
    • Transactions of Materials Processing
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    • v.14 no.7
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    • pp.601-606
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    • 2005
  • A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed for finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio are compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

Evaluation of the Ductile-Brittle Transition Behavior of fracture Toughness by Material Degradation (열화에 따른 파괴인성치의 연성-취성 천이거동 평가)

  • 석창성;김형익;김상필
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.5
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    • pp.140-147
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    • 2003
  • As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time at a high temperature, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sized specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.

The Evaluation of Ductile-Brittle Transition of Fracture Toughness by Material Degradation (재료열화에 따른 파괴인성치의 연성-취성 천이거동 평가)

  • Kim, Sang-Pil;Kim, Hyung-Ick;Seok, Chang-Sung
    • Proceedings of the KSME Conference
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    • pp.579-584
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    • 2001
  • As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life, and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sired specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.

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