Abstract
Often material failures involve a synergy of mechanisms, environmental stressors, design constraints and loading scenarios, that work in congress to cause an unpredicted fracture or acceleration of degradation leading to failure. This work covers a root cause case study analyzing the combined influence of various factors resulting in the delayed cracking of welded transmission gear assemblies. The gear assembly was comprised of a single ring gear electron-beam (e-beam) welded around its interior circumference onto a mated shaft. Both components were composed of a proprietary high strength steel. Mated surfaces were cleaned prior to assembly. The surface-tempered, low-vacuum e-beam weld was ultrasonically inspected after assembly, and in all cases no solidification cracks were detected in the failed components. The delayed crack feature was seemingly presenting itself at random with no correlation to time of production, lot of material, or process change. A combination of metallurgical events, storage conditions and orientation control of part grabbers ultimately led to the delayed cracking phenomenon.
