Fatigue crack growth characteristics of additive-manufactured aluminum alloys based on the effective stress intensity factor range

In this study, the relationship between the crack growth rate and the effective stress intensity factor range of additive-manufactured aluminum alloy was evaluated. Fatigue crack growth tests were conducted for the as-built, artificial aging, and T6 heat-treated materials. Crack closure was measured, and the essential fatigue crack growth characteristics were evaluated by examining the effective stress intensity factor range. Based on the experimental results, the effects of the heat treatment and building direction on essential fatigue crack growth characteristics were investigated. For the as-built material, Si precipitated with a fine cell structure. Cracks propagated linearly within the cell, and the curve of the crack path was small because of the fine cellular structure. Therefore, the surface roughness of the fracture surface was small, and roughness-induced crack closure was also small. Crack growth resistance did not appear to be affected by the cellular Si structure. For the T6 material, Si precipitated with a spherical particle shape, and the crack path was curved by this Si particle. Therefore, the crack growth rate was lower in the T6 material than in the as-built material in the crack growth rate-effective stress intensity factor relationship. In addition, the surface roughness of the fracture surface was increased by the curve of the crack path. In the crack growth rate-stress intensity factor relationship, the crack growth rate of T6 samples was slower than that of as-built samples because of the increasing crack closure and crack growth resistance. Moreover, the building direction did not affect the essential fatigue crack growth characteristics.