Crack extensions in arc-shaped specimens of hydrogen-charged and as-received conventionally forged (CF) 21-6-9 austenitic stainless steels are investigated by two-dimensional finite element analyses with the cohesive zone model. The material constitutive relation is first obtained from fitting the experimental tensile stress-strain data by conducting an axisymmetric finite element analysis of a round bar tensile specimen of the as-received CF steel. The material constitutive relation for the hydrogen-charged CF steel is estimated based on the experimental tensile stress-strain data of the as-received CF steel and the hydrogen-charged high-energy-rate-forged (HERF) 21-6-9 stainless steel. The cohesive zone model with the exponential traction-separation law is then adopted to simulate crack extensions in arc-shaped specimens of the hydrogen-charged and as-received CF steels. The cohesive strength of the cohesive zone model is calibrated to match the experimental load-displacement curve with the cohesive energy determined by the J-integral at the maximum load of the arc-shaped specimen. The computational results showed that the numerical predictions of the load-displacement and crack extension-displacement curves for the hydrogen-charged and as-received CF steel specimens are compared reasonably well with the experimental data.
The crack extension in a compact tension specimen of hydrided irradiated Zr-2.5Nb material is investigated by a two-dimensional plane stress finite element analysis. The stress-strain relation of the Zr-2.5Nb material for the finite element analysis is obtained from fitting the experimental tensile stress-strain curve of the irradiated Zr-2.5Nb material without hydrides by a three-dimensional finite element analysis. The calibration of the cohesive zone model with a trapezoidal traction-separation law is based on fitting the load-displacement-crack extension experimental data of a compact tension specimen of hydrided irradiated Zr-2.5Nb material. The general trends of the load-displacement, crack extension-displacement, and load-crack extension curves obtained from the finite element analysis based on the calibrated cohesive zone model are in agreement with the experimental data.
Separation work rate as a function of the crack extension in a thin curved compact tension (CCT) specimen of Zr-2.5Nb pressure tube material is investigated by three-dimensional finite element analyses with the finite step nodal release method. The straight crack front for the crack extension is assumed. The crack extension is simulated by releasing the nodal points ahead of the initial straight fatigue crack front in the CCT specimen. The crack extension follows the available experimental crack extension-displacement data. The computational results show that the plastic zone size and shape change along the crack front as the crack extension increases. The computational results also show that the separation work rate is a function of the crack extension and is similar to the experimental J-R curve. The computational results suggest that in a two-dimensional finite element analysis of the crack extension in the thin CCT specimen with the cohesive energy approach, the cohesive energy can vary to account for the change of the constraint conditions along the crack front as the plastic zone size increases with the crack extension.
<div class="section abstract"><div class="htmlview paragraph">Finite element (FE) analyses of macroscopic stress-strain relations and failure modes for tensile tests of additively manufactured (AM) AlSi10Mg in different loading directions with respect to the building direction are conducted with consideration of melt pool (MP) microstructures and pores. The material constitutive relations in different orientations of AM AlSi10Mg are first obtained from fitting the experimental tensile engineering stress-strain curves by conducting axisymmetric FE analyses of round bar tensile specimens. Four representative volume elements (RVEs) with MP microstructures with and without pores are identified and selected based on the micrographs of the longitudinal cross-sections of the vertical and horizontal tensile specimens. Two-dimensional plane stress elastic-plastic FE analyses of the RVEs subjected to uniaxial tension are then conducted. The true stress-plastic strain curves for MPs and melt pool boundaries (MPBs) are obtained in scale with those of the tensile tests based on the microhardness values. The simulation engineering stress-strain curves of the RVEs are in good agreement with the experimental data. The simulation results indicate that the plastic deformation is initiated at the soft MPBs and near the material defects of pores, grows along MPBs in the vertical specimens or across MPs in the horizontal specimens as the macroscopic strain increases, and finally possible fracture paths connecting the regions with large plastic strains are identified. The identified failure modes are in good agreement with those from experiments. The simulation results also indicate that the MP microstructures and pores play important roles in the failure modes and anisotropy of ductility of AM AlSi10Mg.</div></div>
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