Abstract:

At present, the calculation methods of bending stress is still lack for the racks that module are more than 50 mm. In order to improve the calculation accuracy of big module rack tooth root stress, the method of the broken-line section is modified based on the fatigue crack growth path at tooth root, a new broken-line section model to calculate the tooth root stress is established, and a stress permeability factor is first introduced to identify the width of broken-line. The calculation formulas of root bending stress and root compression stress are derived by integral-iterative method. The factors that influence the calculation accuracy of the new broken-line section are analyzed, and the calculation methods of the angle of broken-line section, stress permeability factor and bending arm are studied. The stress calculated by the new method is almost equal to the numerical solution of FEM at every point on the broken-line section. The bending stresses of rack root are tested on the bedstand designed for Three Gorges shiplift rack. Based on the test data, the relationship between torque and root stress is built up by the Gauss-Newton method, and also the root stresses at the nominal torque are obtained. Then the contrastive analyses of test value, analytic value and numerical value are completed. The results show that the relative error calculated by the new method is less than 5%, the analytic solutions are more closer to the test data. Therefore the broken-line section method proposed can be used in the tooth root stress calculation of tooth root stress.

Key words: broken-line section method, stress permeability factor, stress test, tooth root stress, rack with rough module