Brittle Fracture of a Die-Cast Aluminum Camlock Coupler in a Hydraulic Hose Assembly

A mechanical failure involving a camlock coupler in a hydraulic hose assembly was investigated following an incident associated with a hose, pipe adapter, and fire hose nozzle assembly. The failure involved separation of fragments from the female camlock fitting used to connect the hose assembly to a Viper fire hose nozzle through a quick-connect coupling system. A comprehensive metallurgical failure analysis was performed to determine the fracture mechanism and contributing factors.

The investigation included visual examination, low-magnification inspection, metallographic analysis, and scanning electron microscopy (SEM) fractography. Macroscopic examination revealed multiple cracks on the camlock fitting, including longitudinal and circumferential cracking near the locking arm contact regions. Fracture surfaces were examined to identify crack initiation locations and propagation characteristics.

Fractographic analysis showed that fracture initiated at localized contact points where the locking arms applied load to the outer diameter of the male camlock component. The cracks propagated rapidly through the component once initiated. SEM examination revealed predominantly transgranular cleavage features with minimal plastic deformation, indicating a brittle fracture mechanism. Metallographic observations also showed that the fitting was manufactured from a porous die-cast aluminum-silicon alloy with limited ductility, which reduced the component’s tolerance to localized overstress.

The results indicate that the failure was caused by brittle fracture initiated by localized overstressing at the camlock locking arm contact regions. The inherent porosity and low fracture toughness associated with the die-cast aluminum alloy further reduced the structural integrity of the fitting, allowing rapid crack propagation once fracture initiated.

This case highlights the susceptibility of die-cast aluminum couplers to brittle fracture when subjected to concentrated loads and emphasizes the importance of material selection, inspection, and design considerations in quick-connect coupling systems used in pressurized hose assemblies.