Influence of different load models on gear crack path shapes and fatigue lives

Abstract

A B S T R A C T A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period.The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth. a = crack size a 2 = crack-initiation size b 0i = shear fatigue strength exponent b i = axial fatigue strength exponent C = material parameter of Paris equation c 0i = shear fatigue ductility exponent c i = axial fatigue ductility exponent C sur = surface finish correction factor d s = shear damage parameter d t = tensile damage parameter E = elastic modulus FP = final contact point F j = force acting on the gear for jth load case G = shear modulus g = transition function HPSTC = highest point of the single tooth contact i = gear ratio IP = initial contact point K = cyclic strength coefficient k = empirical material constant K c = stress intensity factor critical value K cl = stress intensity factor when closure occurs K I = mode I stress intensity factor

Multiscale modeling and simulation of rolling contact fatigue

“…The stress loading cycle is calculated using the critical plane damage method [72] based upon the analysis of stresses or strains as they experienced at a particular plane of the material. Calculating the stress loading cycle at the critical plane is essential for analyzing the rolling contact fatigue life because the critical plane is experienced the most extreme damage and is most likely for the fatigue crack to initiate [73]. The emergence of different fracture modes generally depends on the material type, strain amplitude and state of stresses.…”

“…The emergence of different fracture modes generally depends on the material type, strain amplitude and state of stresses. If the tensile stress is the dominant stress in the material, the following tensile-based damage model will be used to predict the fatigue life [73]:…”

“…If the shear stress is the dominant stress in the material, the following shear-based damage model will be used to predict the fatigue crack initiation life of the material [73]:…”

“…Shear subsurface stresses due to contact loading cause a substantial dislocation motion, which can initiate fatigue cracking [73,76]. Sraml et.…”

“…Podrug et. al [73] presented a computational model for finding fatigue lives of gears under moving bending loads. They modeled twodimensional crack propagation and also studied the effects of a moving load on the fatigue life of a gear.…”