Fatigue Damage Identification And Analysis Based On The Hammer Excitation Method

Fatigue failure is still one of the most important failure forms of mechanical components. To ensure the reliable and effective operation of the equipment and avoid the occurrence of malignant accidents, it is necessary to study the fatigue of the mechanical components.40Cr is one of the widely used steel in mechanical industry. In engineering, it is often used in the design of gear and shaft, and it is almost always under the action of alternating stress in the work, and fatigue breakdown are the main causes of its failure. The test method of hammering excitation is simple and easy to operate, and it has been used by many scholars to identify the structural identification and has achieved some results. This thesis attempts to take the 40Cr steel as the research object and studies the fatigue damage identification and life-estimation of 40Cr specimen based on the hammer excitation. The thesis mainly contains the following context.1. In order to produce different cycle times of 40Cr specimens, fatigue test was carried out on a group of the same size with U-shaped notch 40Cr round bar specimen with tension torsion complex load. This is also to provide a specimen to the test after.2. In this thesis, the hammer excitation method is investigated in detail, and the various factors affecting the test result are summarized, and on the thesis of the specific 40Cr test pieces to choose the appropriate method. Before the modal parameters of the 40Cr specimen were tested by the specific impulse hammer test, the modal analysis of the 40Cr specimens was carried out firstly by using ANSYS to provide the reference basis for the impulse hammer test.3. The modal parameters of 40Cr specimens with different fatigue cycle times were measured by pulse hammering test. The relationship between the modal parameters and the damage degree of the test piece is analyzed.The characteristics of hysteresis loop in the fatigue test are observed, and the 40Cr steel is found as a cyclic softening material. By ANSYS analysis, the first two order bending modes of the 40Cr specimens are obtained, which are respectively 1893.7Hz and 6541.7Hz. At the same time, the mean values of the first two order bending modes of the 40Cr specimens are 1873.59Hz and 6545.33Hz, which are measured by the impulse hammer test. The average relative error between the measured value and the theoretical value is 1.06% and 0.06% respectively, which indicates that the test method and the results are reliable. Finally, by comparing the relationship between the different fatigue damage degree and the modal parameters of 40Cr specimens, it is found that the fatigue damage degree of 40Cr specimen can be identified by the first modal frequency. When the fatigue damage of the 40Cr specimen is increased, the first mode frequency of the specimen decreases sharply.