Single point fatigue test method for metal casting materials

Single point fatigue test is applicable to the service of metal components under rotating bending load at room temperature, high temperature or corrosive air. The single point fatigue test method is generally used to approximately determine the fatigue curve and roughly estimate the fatigue limit when the number of samples is limited and the requirements for test results are not high. The fatigue testing machine required for the test is generally bending fatigue testing machine and tension compression testing machine. The machine parameters that the testing machine should meet are that the bending load fluctuation value is less than or equal to ± 1% of the full load of the testing machine. The test loading frequency should comprehensively consider the sample material and testing machine to avoid vibration of the sample and affect the test results. The test results obtained by different types of samples are different, so the samples used in the same batch of tests shall have the same diameter, shape and dimensional tolerance. According to the rotating bending method for fatigue testing of metallic materials (GB / t4337-2008), the test parts of single point fatigue test specimens are divided into cylindrical, conical and funnel-shaped.

Single point fatigue test generally requires 8-10 samples. The minimum section diameter D of the sample is generally 6, 7, 8 and 9.5mm, and the deviation is less than 0.005d. Among them, the parallelism of the test part of the cylindrical sample shall be within 0.05mm, the transition arc radius shall not be less than 3D, and the arc radius of the funnel-shaped sample shall not be less than 5D.

During the single point fatigue test, the applied load p needs to be calculated first, which can be calculated from the maximum bending normal stress of the minimum diameter section of the sample according to the following formula:

Where, taking the loading coefficient k = π d3min / 16a, P = k can be obtained σ。 The K value can be calculated in advance according to the sleeve length dimension a of the testing machine and the minimum diameter Dmin of the sample, and made into a table. Stress in specimen σ After determination, the load p to be applied can be calculated. After the load calculation, the samples can be tested one by one according to the test requirements. The stress level is generally level 4, and the control accuracy needs to be met.

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