This research is to test the fatigue endurance of the material by using end bending of specimen. The testing material is S45C steel and forming to the standard size for testing. The specimens with a diameter of 8 mm required a different bending moment. It was found that the large bending moment affects the fatigue of the specimen. The specimen quickly damaged due to the high bending stress and there were a small number of load cycles. If the bending moment acting on the specimen was reduced to the bending stress decreased and the number of load cycles increasing. It was shown that the bending stress and the magnitude of the bending moment affected the fatigue of the material. Also the appearance of damage marks of the specimen will have a flaw around the fracture surface. Then the flaw will be enlarged until the specimen will be damaged by fracture.

The fatigue testing machine that uses the force of torsion is invented to be a compact machine that uses the torsion as the force in the test. From the tests it achieved the highest of 200 newton meters using pneumatics to test the metal materials i.e. the steel S45C molded in accordance with the JIS Z 2274 standard. To find out the capacity of the fatigue testing machine that uses the force of torsion with 8 mm 10 mm and 12 mm diameter test pieces the machine was tested with different levels of the force of torsion and the percentage of the deviation of the tests did not exceed the limit of + 10 percent. This research could reduce the cost of the procurement of the fatigue testing machine that uses the force of torsion and could be used in the instruction in the department of mechanical engineering faculty of engineering Rajamangala University of Technology Phra Nakhon in the future.