• Fatigue strength of bars subject to cyclic bending load.
  • Influence of different curvature radii and surface finish on fatigue strength.
  • Preparation of a stress-number (S-N) diagram.


  • Benchtop unit for fatigue strength testing.
  • 3 cylindrical specimens made of steel, Ck35.
  • Special shape specimens for demonstrating the influence of notching and surface finish.
  • Recording of a stress-number (S-N) diagram.
  • Adjustment using threaded spindle with hand wheel.
  • Loading via moveable plain bearing.
  • Automatic shut down on specimen fracture by stop switch integrated into the bearing.
  • Electronic load cycle and revolutions counter with 8-digit digital display.
  • Contact less inductive speed sensor.

This apparatus explains the effects of fatigue. A simple cantilever specimen rotates at fixed/variable speed, including a sinusoidal variation of bending stress the equipment demonstration and experimentally confirm basic engineering principles.

Using this benchtop unit, the basic principles of fatigue testing can be conveyed. A rotating metal test bar, clamped at one end, is loaded using a spring balance with a point force. This results in a cyclic bending load on the cylindrical specimen. The amplitude of the cyclic loading can be continuously adjusted using a threaded spindle with hand wheel.

After a certain number of load cycles, the specimen breaks as a result of material fatigue. In this case the machine is shut down automatically by the stop switch. The number of load cycles is counted by an electrical counter and displayed digitally. This can also be used for measuring the speed. Different shape specimens enable the influence of notching and surface finish on fatigue strength to be demonstrated.