Propagation analysis of root crack of spur gear

According to the statistics of scholars, most of the mechanical component failures belong to fatigue failure, accounting for 50% – 90%. Especially with the development of mechanical system to large-scale, integrated, complex, high temperature, corrosion and other working environments, the factors affecting fatigue failure can not be fully considered, which brings many difficulties to the research of fatigue failure. The economic loss caused by fatigue fracture in industry is immeasurable, so there are more and more studies on the fatigue characteristics of components. With the development of damage mechanics and fracture mechanics, great progress has been made in the research of fatigue fracture. The main contents are the research on the mechanism of fatigue crack initiation and crack propagation and the prediction of fatigue life of spur gears.

In the mechanical transmission system, spur gear is the most widely used transmission part. The main function of spur gear is to transmit motion, load and change the direction of motion. Therefore, the failure of gears has a fatal impact on the mechanical transmission system. The failure form of spur gears is shown in the figure.

Tooth surface pitting, tooth surface gluing and tooth surface wear belong to contact fatigue failure, while tooth root fracture belongs to bending fatigue failure. Among them, fracture along tooth root is the most serious and common failure form. The causes of tooth fracture are very complex: under the comprehensive influence of the section mutation of the excessive part of the tooth root, the machining trace and the stress concentration caused by the size change, the tooth root is very easy to initiate fatigue cracks, and then the root fracture failure occurs. In the process of studying the fatigue crack mechanism, scholars found that under the action of cyclic load, the micro crack further expands under the action of cyclic load, and the ultimate root fracture failure accounts for 32.8% of the failure of spur gear. Therefore, the failure analysis of spur gear has important guiding significance for the design of spur gear. Analyzing the fatigue fracture of gear teeth, studying the characteristics of fatigue cracks and predicting fatigue life are important contents of fatigue fracture; Only when we have a clear understanding of the mechanism of fatigue crack, can we optimize the design and anti fracture design of spur gear, so as to improve the working performance and prolong its working life.

With the development of computer technology, more and more software tools are used to study the fatigue cracks of spur gears. The large general software ANSYS has a special module for calculating the fracture parameters at the crack tip, and also has the analysis function of fatigue life at a certain position. ANSYS APDL can be used to write a program to simulate the crack propagation process and calculate the crack fracture parameters, and more accurate results can be obtained. MSC. Fatigue is a professional software for analyzing the fatigue life of spur gears. It can consider the influence of surface roughness and other parameters on the contact fatigue life. ANSYS Workbench can also analyze the fatigue life of spur gears and give the life distribution cloud diagram and the safety factor cloud diagram under the design life, making the results more intuitive. FRANC2D and FRANC3D are professional software for simulating crack propagation. Most scholars use this software in plane crack and three-dimensional crack propagation analysis; The advantage of the software is that there are different fracture criteria to choose from, and the geometry and size of the initial crack can be set according to the actual needs. After embedding the initial crack, the crack propagation can be automatically determined according to the parameters of the initial crack and the automatic grid division in the fracture process can be realized, This avoids the error caused by artificially specifying crack propagation parameters when programming with ANSYS APDL.

In the research of fatigue crack, the actual working environment and working conditions must be considered as much as possible, so that the research results have greater value and significance for practical application.

Combined with the actual meshing situation of spur gear, the modeling and static analysis program is compiled by using ANSYS APDL. Considering the uneven distribution of load in tooth direction caused by installation and manufacturing error during spur gear transmission, two different distributed loads are applied on the contact line of tooth top, and the effects of the two loads on the fracture parameters of tooth root are analyzed and obtained; The crack propagation characteristics and crack propagation life under two loads are studied by using FRANC3D software, in order to make the results as close as possible to the actual situation. Because the factors leading to the root crack are very complex, the location of the initial crack has great uncertainty. In order to study the effects of different distributed loads on the crack characteristics and crack propagation life, the location of the initial crack on the root is kept unchanged in this paper.

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