Simulation of ductile crack growth using computational cells: Numerical aspects

Arne S. Gullerud, Xiaosheng Gao, Robert H. Dodds, R. Haj-Ali

Research output: Contribution to journalArticlepeer-review


This study explores key computational issues that affect analyses employing the computational cell methodology to predict crack growth in ductile metals caused by void growth and coalescence. These issues - computational load step size, procedures to remove cells with high porosity from the analysis, and the porosity for cell deletion - can adversely affect predicted crack growth resistance (R) curves and/or hinder convergence of both local constitutive and global iterative computations. Strain increments generated by large computational load steps introduce errors in the predicted peak stress of computational cells and prevent convergence of stress updates for the Gurson-Tvergaard constitutive model. An adaptive load control algorithm, which limits the maximum porosity over a load step, eliminates this problem. The delayed release of remaining forces in newly deleted cells elements elevates the stress triaxiality and thus artificially accelerates the rate of crack extension. The release of cell forces using a traction-separation model minimizes this effect while maintaining good numerical convergence of the solutions. Crack growth analyses for a moderate strength steel demonstrate that critical porosity values (fE) between 0.1 and 0.2 show almost no effect on predicted R-curves, while both larger and smaller values lead to low J-Δa curves. Finally, a parametric study indicates that specimens of low-hardening materials and specimens with high crack-front constraint show a stronger influence of large computational load steps and the delayed release of cell forces. Use of the adaptive load control algorithm and the traction-separation model with the controlling parameters described here, minimize numerical effects on predicted R-curves.

Original languageEnglish
Pages (from-to)65-92
Number of pages28
JournalEngineering Fracture Mechanics
Issue number1
StatePublished - 1 May 2000
Externally publishedYes


  • Cell elements
  • Crack growth
  • Damage mechanics
  • Finite elements
  • Fracture specimens


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