Failure Analysis Case Study on a Fractured Tailwheel Fork

Afailure analysis investigationwas conducted on a fractured aluminum tailwheel fork which failed moments after landing of a privately owned, 1955 twin-engine airplane. Non-destructive evaluation via dye-penetrant inspection revealed no discernible surface cracks. The chemical composition of the sand-cast component was identified via optical emission spectroscopy and is comparable to an aluminum sand-cast alloy, AA 712.0. Metallographic evaluation via optical microscopy and scanning electron microscopy revealed a high degree of porosity in the microstructure as well as the presence of deleterious intermetallic compounds within interdendritic regions. Macro-hardness testing produced hardness values which are noticeably higher than standard hardness values for 712.0. The primary fracture surfaces indicate evidence of mixed mode fracture, via intergranular cracking, cleaved intermetallic particles, and dimpled cellular regions in thematrix. The secondary fracture surface demonstrates similar features of intergranular fracture.