Abstract
Two cracks, initiated from the opposite tips of a central notch inclined by 45°, were considered in cruciform specimens made of Ti6246. A static load was applied to a cruciform arm while a cyclic load was applied along the other arm. Fatigue propagation of cracked specimens was performed by means of Dual Boundary Element Method (DBEM) and Finite Element Method (FEM) codes. For crack path assessment, the Minimum Strain Energy Density (MSED) and the Maximum Tensile Stress (MTS) criteria were adopted in DBEM and FEM approaches, respectively. Moreover, the J and M integrals’ formulations were used to evaluate the SIFs along the crack fronts for DBEM and FEM codes, respectively. Crack-growth rates were predicted by using a Walker law, calibrated on mode I fracture experimental data. A good agreement between numerical and experimental crack paths was obtained.
Highlights
O ver the past few decades, many efforts have been made in the modeling and simulation of three-dimensional crack propagation problems
A crack-growth rate da / dNi was computed for each load case with the Eq 7, where da / dN is the crack-growth rate computed for any given crack front point and n is the number of load ranges in the spectrum
The agreement between crack-growth directions and crack-growth rates was very sound among Finite Element Method (FEM), Dual Boundary Element Method (DBEM) and experimental results
Summary
O ver the past few decades, many efforts have been made in the modeling and simulation of three-dimensional crack propagation problems. Several experimental tests were performed for different ratios between static and cyclic loads and the resulting crack paths and crack propagation rates were analyzed and compared with numerical results. Different ratios of HCF and LCF loading conditions were considered for the experimental tests, providing corresponding crack propagation directions. For some combinations of static and cyclic load magnitudes, load case “B” provided negative KI values, with no physical meaning since representative of mutual intersection of crack faces To circumvent this drawback, a nonlinear contact condition, with allowance for friction (friction coefficient = 0.3), was applied to the crack face elements for such load cases. The resulting KI values became negligible and the related KII and KIII decreased due to friction effects, with a corresponding impact on the Keq values and eventually on the final growth angle θ (Eq 5)
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