Fatigue test of metal casting materials by lifting method

Lifting fatigue test is the most commonly used and accurate test method to detect the fatigue limit of metal materials or structures. On the basis of determining the fatigue strength by the conventional fatigue test method, or when the fatigue strength of the material or structure with a specified life cannot be measured directly by the test, the lifting method fatigue test is generally used to indirectly determine the fatigue strength.

The lifting method fatigue test is mainly used to determine the material fatigue strength limit or structural fatigue strength limit in the medium and long life zone. The required testing machine is generally tension compression fatigue testing machine. The machine parameters that the testing machine needs to meet are that the error of static load display value is less than or equal to ± 1%, the variation range of display value is less than or equal to ± 1%, the fluctuation of average load display value is less than or equal to ± 1% of the maximum allowable load, and the fluctuation of amplitude display value is less than or equal to ± 2% of the maximum allowable load. At the same time, the axis of the sample shall be in the same line with the axis of the fixture and the force application axis of the fatigue testing machine as far as possible to ensure accurate load transmission and avoid additional torque. For the same batch of samples, the test frequency shall be the same. If the test frequency is too different, the accuracy of the test results will be affected.

The lifting method generally takes whether the material breaks under the cycle times n = 10000000 times as the standard of whether the material is qualified or not. The lifting method fatigue test generally requires 13-16 valid data. According to the provisions of GB / t3075-2008 axial force control method for fatigue test of metal materials, the test samples are generally divided into circular section and rectangular section. The parallelism, coaxiality and perpendicularity of the samples are required to be less than or equal to 0.005d, and the average surface roughness Ra ≤ 0.2 μm。

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