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Tooth surface contact stress The gear tooth surface contact stress varies with the gear entering different meshing stages and instantaneous coincidence. Taking 4 different nodes of the tooth surface, the contact stress changes as shown. It shows the variation of the maximum contact stress of the tooth surface in the whole process of the intermediate tooth contact: the contact stress of the gear in the first half of the meshing is large, the maximum contact stress is 1570MPa, and the average value is about 1500MPa; when it enters the 3 tooth meshing, the tooth surface contact stress will be Decrease, the average contact stress in the second half is about 1300 MPa. Therefore, the fatigue failure of the tooth surface contact of the helical gear mainly occurs in the first half of the gear tooth engagement. This conclusion should be obtained from the damage area of ​​the contact fatigue damage gear. verification.
The driving gear tooth surface contact stress numbers 2, 3 respectively indicate that the gear is in the 2-tooth meshing or 3-tooth meshing state, and the following is the same as the maximum value of the incremental contact stress per incremental step of the driving gear meshing process. 2.2 Root bending strength The driving gear intermediate tooth The law that the maximum value of the root bending stress varies with the meshing process is as shown. The gear teeth just enter the meshing and the stress on the root of the first 1/3 segment is small; as the meshing process progresses, the maximum stress of the tooth root gradually increases along the tooth width, so the bending fatigue damage of the gear teeth will mainly occur along the tooth width. The rear 2/3 area of ​​the direction; the maximum Mises stress value of the root side of the tooth root is 395 MPa, and the Mises stress and the maximum principal stress change curve at this point are as shown. The pressure side Mises stress and the minimum principal stress curve are shown as shown. The maximum value of Mises stress is 250 MPa, which is smaller than the stress value of the tension side. Therefore, the bending fatigue failure will mainly occur on the tension side of the root.
The maximum value of the root stress of the driving gear intermediate tooth meshing process. The driving gear passive gear computer aided engineering. The maximum gear point bending stress and the maximum principal stress curve of the active gear tooth root in 2006. Stress curve 2.3 Root bending fatigue life The MSCFatigue fatigue analysis software is used to calculate the bending fatigue life of the driving gear. The gear material is 17Cr2Ni2AH and the UTS is 1100MPa. The material SN curve is used to input the material characteristic curve into the program; The root maximum stress node node84905 is the object, and the stress curve of the node is normalized. As the input load, the Goodman method is selected to correct the average tensile stress SN curve. The theoretical fatigue damage model used in MSCFatigue is to process multiple axes. The six multi-axis component stresses defined by the stress, and thus the stress tensor, can be combined into a single-axis or combined value for each node of each time step in the fatigue calculation, using the Max.Abs.Principle method. In addition, stress concentration will occur at the chamfer of the tooth when the tooth is loaded, and the size, surface processing and treatment state of the gear will have a great influence on its life. Through the simulation calculation of the solid model, the median life of the driving gear is 5.64E7 (the number of meshing), for example.
17Cr2Ni2AH material SN curve active gear tooth root maximum stress point Node84905 median life If we define the safety life factor parts actual life safety life factor part design life According to the design requirements, the gearbox input end of the constant mesh gear pair drive gear design life is 1.91E7 ( The number of engagements), so the safe life factor of the gear is available.
Conclusion (1) Using MSCMarc to simulate the cylindrical helical gear, the contact stress of the tooth surface and the bending stress of the root are obtained. The contact fatigue failure of the cylindrical helical gear tooth surface mainly occurs in the first half of the gear tooth meshing; the tooth bending fatigue failure will mainly occur in the rear 2/3 area along the tooth width direction; (2) Apply the MSCFatigue fatigue analysis software to the active The gear bending fatigue life is calculated and the safety life factor is 2.95, which fully meets the design requirements and has room for further optimization.