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Fatigue crack growth rate experiments were performed on compact tension specimens of base plate and weldments of 5456-H116 aluminum and of base plate and the heat-affected zone (HAZ) of ASTM A710 Grade A steel. Stress ratios for the tests were 0.1 for both materials, with the aluminum weld also being tested at R = 0.5. Crack opening levels were determined for both the weld and the base plate in the aluminum material and for the A710 material in the as-welded and stress-relieved conditions. The fatigue crack growth rates of the welds and HAZ, when the total applied load was used, were significantly less than those of plate for both materials. Using the effective stress intensity, which accounts for crack closure and thus represents the actual stress intensity at the crack tip, results in a shift of the da/dN versus ΔK curves to a faster growth rate. Comparison of the curves shows that the fatigue crack growth rates of the aluminum weld material fall in the same scatter band of data as those for base plate and that, for the A710 material, the HAZ shifts to faster growth rates than the base plate does. This shift of data leads to more accurate estimates on fatigue life, based on the intrinsic properties of the material.
weldments, fatigue crack growth rates, crack closure, effective stress-intensity range, aluminum, steel
Materials engineer, David Taylor Research Center, Annapolis, MD