In order to study the problem of fatigue crack propagation and fatigue life of low-speed and heavy-duty gear, a low-speed and heavy-duty gear close to the engineering practice is designed, and the bending fatigue test is carried out on the bending fatigue testing machine, so as to obtain accurate and real data, and obtain the fatigue limit value of the bending fatigue strength of the low-speed and heavy-duty gear.
In the process of bending fatigue test, because the bending stress of the gear is mainly loaded by the fatigue testing machine, it is necessary to fix the gear on the worktable; Because the impact of the gear is very large in the test process, it has higher requirements for the fixture to fix the gear on the test bench
1) Ensure enough ability to resist deformation and support the test gear reliably during the test;
2) Ensure that the load can accurately act on the tooth surface near the gear addendum circle, and ensure that the load action position is accurate;
3) The load line acting on the tooth must be tangent to the base circle of the test gear;
4) The uniform distribution of load must be ensured along the direction of gear tooth width.
GB / T 14230-1993 specifies two kinds of special fixtures for gear bending fatigue test: single tooth loading and double tooth loading. Single tooth loading is adopted in this test, and the fixed form of gear is shown in Figure.
The lower plane of the fixture is in close agreement with the working plane of the bending fatigue testing machine. The fixture itself not only fixed the gear, but also limited the rotation and axial movement of the gear. The fixture is fixed with the worktable by bolts, so that the force of the lower working plane can be stably transmitted to the fixture of the worktable. For the rotation of the gear, first use a shaft to fit with the shaft hole of the gear to fix the position of the gear, and then use a down pressure head to hold one tooth of the gear, so as to limit the rotation of the gear. In order to prevent the axial movement of the gear, a pair of high strength bolts are used to fasten the side of the gear. The center line of the lower pressure head of the fixture is perpendicular to the plane of the worktable; Because of the special fixing condition of the upper ram, the center line of the upper ram is perpendicular to the plane of the worktable automatically; And ensure that the axis of the upper and lower indenter coincides, so that the transmitted force can be closed.