A crescent-shaped mark running along the length of a gear tooth is called a beach mark and indicates shock load.

• A. Lack of lubrication
• B. Shock load
• C. Normal wear
• D. Heat damage

Answer: (B)

When a gear tooth experiences a sudden overload, the tooth is subjected to a high, instantaneous stress that causes rapid, localized deformation and damage at the root area. This abrupt event leaves a curved, crescent-shaped mark that runs along the length of the tooth—a beach mark—which records how the damage progressed under that shock load. This pattern is a hallmark of an overload situation rather than a slow, steady wear process.

Lack of lubrication tends to produce surface rubbing, scoring, and pitting from sliding contact and overheating, not a single crescent line that traces along the tooth. Normal wear shows gradual, relatively uniform material loss over many cycles rather than a distinct curved mark. Heat damage typically presents discoloration, surface softening, or glazing, not a recognizable beach mark.