Abstract
A computational model for determination of crack growth in a gear tooth root is presented. Two loading conditions are taken into account: (i) normal pulsating force acting at the highest point of the single tooth contact and (ii) the moving load along the tooth flank. In numerical analysis it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equation is then used for a further simulation of the fatigue crack growth. The functional relationship between the the stress intensity factor and crack length K = f(a), which is needed for determining the required number of loading cycles N for a crack propagation from the initial to the critical length, is obtained using a displacement correlation method in the framework of the FEM-method considering the effect of crack closure. The model is used for determining fatigue crack growth in a real gear made from case carburised and ground steel 14CiNiMo13-4, where the required material parameters were determined previously by appropriate test specimens. The results of the numerical analysis show that the prediction of crack propagation live and crack path in a gear tooth root are significantly different for both loading conditions considered.
Highlights
Two kinds of teeth damage can occur on gears under repeated loading due to fatigue; the pitting of gear teeth flanks and tooth breakage in the tooth root [1]
In this paper only the tooth breakage is addressed and the developed computational model is used for the calculation of tooth bending strength, i.e. the service life of gear tooth root
The standardised procedures are exclusively based on the experimental testing of the reference gears and they consider only the final stage of the fatigue process in the gear tooth root, i.e. the occurrence of final failure
Summary
Two kinds of teeth damage can occur on gears under repeated loading due to fatigue; the pitting of gear teeth flanks and tooth breakage in the tooth root [1]. The standardised procedures according to ISO-standards [1] are usually used for an approximate determination of load capacity of gear tooth root They are commonly based on the comparison of the maximum tooth-root stress with the permissible bending stress. Strojniški vestnik - Journal of Mechanical Engineering 57(2011) 579586 gear rotates This fact can be taken into account performing a quasi static numerical simulation in which the gear tooth engagement is broken down into multiple load steps and analyzed separately. In such a way, a more realistic stress cycle in the gear tooth root is obtained resulting in significantly more exact assessment of the crack propagation life, and in the entire fatigue life. An approach that accounts for fatigue crack closure effects is developed to propagate crack under nonproportional load
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