Development of flaw acceptance criteria and quality control measures for highly skewed propeller blades

Highly skewed propellers (HSPs), with skew angles over 25 degrees, are widely used to improve propulsion efficiency and reduce noise. However, their unique geometry can negatively impact fatigue performance, especially in nickel-aluminum-bronze (NAB) blades prone to casting flaws. This study re-evaluated current quality control standards, focusing on the risk of thermal embrittlement from post-weld heat treatment (PWHT), which may lower fatigue resistance in repair welds. As an alternative, shot peening was proposed and optimized to enhance fatigue life while meeting quality standards. Additionally, a new flaw evaluation algorithm was developed to visualize the stress intensity factor range (ΔK) and identify severity zones based on the fatigue crack growth threshold (ΔK_th). Flaws inside the severity zone undergo fatigue crack growth analysis, while those outside may not require repair. This method enables a more efficient, quantitative assessment of flaw acceptability, improving both the reliability and quality control of HSP blades.