Abstract
A comparison between the three-dimensional experimental and numerical displacement fields surrounding a notch/crack in a ductile 4340 steel tested in three-point bending is presented. Excellent agreement between computed and measured deformations exists at load levels below 50 to 75 percent of ultimate loads. Experimentally determined crack tunnel profiles are included in the finite element model through nodal release; the evidence of the crack tunnel appears in the displacements at the surface. It is shown that surface measurements of unloading reveal specimen-internal failure initiation in the form of tunneling. Out-of-plane deformations deviate from analytical values earlier than in-plane values; this observation compromises the accuracy with which predictions of in-plane crack tip variables can be made when they are based on measured out-of-plane deformations (caustics, gradient sensing) once significant plasticity arises. Comparison is made between J-integral values calculated from the external boundary conditions and from a domain integral. The tunneling tests provide a method of estimating a critical value of J. The stress intensity factor governs the deformation in the elastic regime, but, because of the finite notch- tip radius underlying the experimental configuration, the HRR field does not describe the deformation well under plastic conditions. Comparison of numerical simulations with and without tunneling provide insight into criteria that could be used to implement an implicit crack propagation scheme into the numerical model.
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Schultheisz, C., Pfaff, R. & Knauss, W. An Experimental/Analytical Compression of Three-Dimentional Deformations at the Tip of a Crack in a Plastically deforming Plate III: Material Characterization and finite element analysis. International Journal of Fracture 90, 47–81 (1998). https://doi.org/10.1023/A:1007455804995
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DOI: https://doi.org/10.1023/A:1007455804995