Load effects on macroscopic scale fatigue crack growth path in 2324-T39 aluminium alloy thin plates

• Fatigue crack tends to propagate along the L-direction.
• No remarkable crack branching was observed under CA loading condition.
• Significant crack branching appeared in VA loading condition.
• The underloads following the peak load result in further retardation.

In the present paper, an experimental study is accomplished to characterise the load effects, including K-level, stress ratio, overloads and underloads, on fatigue crack growth path in aluminium alloy 2324-T39 thin plates under constant amplitude (CA) and simple variable amplitude (VA) loading conditions. Crack growth in L–T and T–L oriented specimens is also examined. The test results indicate that the crack path in the L–T oriented specimens under CA loading is remarkably meandering, but no significant crack branching is observed, compared with T–L oriented specimens; tension overloads produce macroscopic crack branching, and the K-level seems to be the principal factor on crack path deviation.