Cap Screw Failure – Hydrogen Embrittlement
Specimen: ¾-inch Cap Screw from Automobile Suspension System
Background: A metallurgical failure analysis was conducted for a number of suspension cap screws. The cap screws had been zinc plated (galvanized), and had originated from an off-shore manufacturer.
Service Life: Mileage at the time of failure ranged from 30,000 to 50,000 miles.
Findings: The forensic engineering failure analysis of the cap screw found that the re-occurring under-head catastrophic failures were caused by hydrogen embrittlement originating most likely from a poor cleaning and galvanizing procedure during the manufacture of the cap screws.