Rest line

Fatigue fracture of a cast aluminum - pedal arm
Light: the brittle or violent rupture
dark: the fatigue fracture with snap lines

Latch lines are the macroscopic characteristic of a fatigue fracture , they reveal the cyclical crack growth on the fracture surface. They arise from corrosion at the end of the crack in the event of a long-term change in the mean voltage. This often changes when there is a change in the operating status, for example a plant shutdown overnight or a reversal of the direction of rotation. Depending on the material and environmental conditions, it takes between 30 minutes and a few days to create a visible stop line. If the operating conditions are recorded, the starting point of the crack can be estimated with the aid of the snap lines.

Another broken aluminum crank arm of a bicycle with clamshaped locking lines and brittle fracture or deformation fracture on the remaining surface.

In the event of a vibration break, stop lines do not necessarily have to be recognizable. These only arise if there was not only a single-stage exposure.

Web links

• Technical reliability + damage analysis (accessed on October 14, 2019)
• Bolt "saves" the course of damage (accessed on October 14, 2019)
• Proceedings of the 1st Pforzheim Materials Day (accessed on October 14, 2019)