Generally speaking, stress corrosion, metal fatigue, and explosion due to excessive internal pressure are the three major factors that lead to notch cracking of easy-to-pull covers. We can judge its type by further examining the specific morphology and surface characteristics of the nicked cracked section through an optical microscope.
Stress corrosion section: scallop or fan shape. As shown in Figure 5, the typical stress corrosion metal cross-section morphology is scallop or fan shape
The section shape produced by stress corrosion is scallop or fan shape.
Metal fatigue section: streaks. As shown in Fig. 6, the typical shape of the metal fatigue section is streak.
The cross-sectional shape caused by metal fatigue is streak-like.
Excessive internal pressure and burst section: ductile cup-shaped and cone-shaped grain. As shown in Fig. 7, the typical shape of the metal section that burst due to excessive internal pressure is the ductile cup and conical grain.
The shape of the metal section that exploded due to excessive internal pressure is a ductile cup-shaped and conical-shaped grain.
