Failure Analysis:Christmas Lights

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

Visual Examination

Contact removed by force

Contact easily removedOriginal failed contact

Corroded Contact

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

Fractography

Fracture surface of original failed contact

(600x)

Fracture surface of brass exemplar broken with overload (600x)

Conclusion• Stress Corrosion

Cracking (SCC)– Stress: bend– Corrosive

environment: Sulfur and Chlorine

• Solutions:- Coating/Electroplating- Socket design change- Annealing