The fatigue performance of the material is affected by both the material itself and external factors. 90% of the fatigue cracks of the material originate from the material surface or near the surface. The surface roughness of materials has become an external factor affecting the fatigue properties of materials. The test sample is taken from the engine body, and the standard test sample is obtained by machining. After machining, there are always some machining marks on the sample surface, which become the potential crack source. The surface roughness test mainly studies the effects of machined surface and sandpaper grinding after machining on the tensile compressive fatigue properties of gray cast iron.

The tensile compressive fatigue test material of gray cast iron with different surface roughness is low alloy HT250. The surface roughness value of the sample is detected by ols-3100 confocal microscope. Multiple areas are selected for detection to obtain the average value. The test machine is plg-100 high frequency fatigue test machine, with loading frequency of 130hz-140hz, stress ratio r = – 1, and loading force waveform of sine wave. A total of 8 samples were tested in this test, including 4 original samples and 4 sandpaper polished samples. Load all samples successively until the sample completes the cycle or fracture, and record the test data.