Failure investigation on the cracked crawler pad link

An in-service failure of traveling gear crawler pad occurred on dredger. Inspection revealed cracking of two links that connect individual pads together. Intergranular brittle fracture occurred on the links and a significant amount of chain-like and rod-like AlN inclusions were found on the intergranular fracture surfaces. Examination of mechanical properties indicates that the plasticity and impact toughness of link material are considerably lower than the specified values, indicating the brittle nature of link material. The presence of intergranular AlN inclusions resulting from considerably excessive aluminum content in link material is responsible for the brittle nature of link material. The presence of shrinkage cavities facilitated the cracking process.