Before the formal bending fatigue test, the load level of the test needs to be determined. Pick two from the processed test pieces for static strength test. According to the static strength test, the maximum load level is 32KN. Five load levels are selected for this bending fatigue test, namely 25kn, 22kn, 19kn, 16kn and 13kn. Number the test gear and the teeth on the gear with numbers 01-20 respectively. The test adopts single tooth loading, the load is applied to the test tooth through the upper indenter, and the tooth supported by the support block is separated from the test tooth by two teeth. During the test, it must be ensured that the vertical line of the overload load point is tangent to the base circle of the gear. The state of the test gear fixed on the test bench is shown in Figure 1.
The loading waveform of the test is sine wave, the loading stress ratio r = 0.1, and the loading mode is pressure fatigue one-way tooth loading (two gears are separated between two test teeth). The test is divided into 5 groups, and 8 test points are taken in each group. The specific conditions are as follows: 8 test points for 25kn test and 8 test points for 22kn test; Conduct 19kn test and take 8 test points; Conduct 16kn test and take 8 test points; Conduct 13kn test and take 8 test points.
During the test, check the condition of pressure teeth every 30 minutes, and record the maximum load, minimum load, cycle times, etc. The occurrence of gear fatigue is judged by the crack, frequency and load measured in the test. When the measured crack, frequency and load drop is greater than 5% of the initial value, it can be considered that a crack occurs.
When the number of cycles exceeds 1000000 times and the gear still does not have fatigue failure, judge that the test point is an out of range point, stop loading it, and replace the next test tooth to continue the test.
To verify the probability distribution of test points, it is required that the test points of corresponding 5 stress levels must meet the normal distribution. If the test points do not meet the normal distribution, in order to meet the requirements, further tests must be carried out to obtain supplementary points.
The state of the test gear tooth after breaking is shown in Figure 2. Single tooth fatigue life data of 10 gears under 5 load levels.