Failure Analysis: Christmas Lights

1
Failure AnalysisChristmas Lights
2
Case Description Hypotheses

• Fracture of the bent brass contact piece in
  various light bulb sockets
• The unbent contact never failed
• Brass composition from EDS
• Copper 70
• Zinc 30
• Possible causes
• Overload
• Fatigue
• Corrosion

3
Visual Examination
Original failed contact
Contact easily removed
Contact removed by force
Corroded Contact
4
Metallography(Longitudinal Sections)
Section of original broken part at fracture
surface
Close-up of crack
Slip lines on unfractured sample at bend
Slip lines on original fractured sample
5
Fractography
Fracture surface of original failed contact (600x)
Fracture surface of brass exemplar broken with
overload (600x)
6
Conclusion

• Stress Corrosion Cracking (SCC)
• Stress bend
• Corrosive environment Sulfur and Chlorine
• Solutions
• - Coating/Electroplating
• Socket design change
• Annealing