Fastener Failure Analysis

A fastener may experience either static loading or fatigue loading.  Static loading may be tension, shear, bending, or torsion.  These static loading conditions may occur in combination.  One example of fatigue loading is vibration. In addition to overload and fatigue, some other common reasons for fastener failures include environmental issues, manufacturing discrepancies, and improper use or incorrect installation.

Some common questions concerning fasteners are listed below:

•   How were the fasteners torqued?
•   In what order were fasteners tightened?
•   What is the best way to verify the torque on fasteners?
•   How does torque value vary over time?

Fatigue is one of the most common failure modes for threaded fasteners.  Fretting failures may result from small movements between adjacent surfaces.   Additionally, atmospheric corrosion, liquid immersion corrosion,  galvanic corrosion, crevice corrosion, stress corrosion cracking, and hydrogen damage may contribute to fastener failure.

Material selection, heat treatment, cutting or rolling threads, manufacturing, assembly, and design are some of the factors that effect fastener failures.  Failure analysis can determine the cause of the fastener failure and determine the primary or contributing causes of fastener failure.