For Spring 2011, the three teams are conducting the following failure analysis investigations:
Jeopardized Junk: Stem-Fracture of “Pressure Mushroom” Fasteners
Macroscopic examination of the pressure mushroom fasteners showed complete fracture of the stem from
the cap. Preliminary results also indicated that the failure occurred by a brittle fracture mode. At this point early in the FAI, it is suggested that factors associated with materials selection, heat treatment and hardening, and manufacturing processes need to be critically investigated. Multiple failures of the part have occurred in service resulting in line shutdown and productivity loss.
Epic Fail: Nucor-5160 T&P Round Steel Bars Fracture during Straightening Process
Vendor information purported that the 5140 T & P round steel bars subjected to torsion loading failed during a second stage straightening (S-S-S) process. Prior to the S-S-S process, the bar was hot- rolled and its diameter reduced by 4.6%. Routinely, the S-S-S process is considered a minimal-stress operation. However, preliminary findings suggest otherwise as surface hardening, roughness and cracking were observed in conjunction with internal residual stress induced cracking. The S-S-S processing procedures and materials selection are issues warranting further investigation.
Crack Crusaders: Deformation and Fracture of a Torsion Garage Door Opener Spring
A steel garage door spring failed prematurely under cyclic torsion loading. Macroscopic visual examination appeared to show that fracture of the spring was due to crack propagation to failure by fatigue crack growth initiating on the spring’s surface. The spring failed at 80% of life expectancy. As yet, the primary source responsible for the failure is undetermined. Though, preliminary findings suggest the introduction of surface defects, perhaps, during manufacturing. Possibly, corrosion issues related to environmental service conditions played a role in this failure.