Official Answer
Answer
Edge tearing occurs during the coiling or stamping process if the tooling is dull or the material ductility is insufficient. These micro-cracks on the radial edge of the spring act as severe stress risers. Under cyclic loading, the stress intensity factor $K$ at the crack tip is defined by $K = Y \cdot \sigma \cdot \sqrt{\pi \cdot a}$, where $a$ is the crack depth. If $K$ exceeds the fracture toughness $K_{Ic}$ of the material (e.g., 17-7PH), the crack will propagate rapidly. Visual inspection at 10x magnification or fluorescent penetrant inspection (FPI) is required for high-criticality aerospace parts to ensure no edge defects are present.
