Abstract
The problem of crack propagation from internal defects in thermoplastic cylindrical bearing elements is addressed in this paper. The crack propagation in these elements takes place under mixed-mode conditions—i.e., all three possible loading modes (tensile opening mode I and shear opening modes II and III) of the crack are combined together. Moreover, their mutual relation changes during the rotation of the element. The dependency of the stress intensity factors on the crack length was described by general parametric equations. The model was then modified by adding a void to simulate the presence of a manufacturing defect. It was found that the influence of the void on the stress intensity factor values is quite high, but it fades with crack propagating further from the void. The effect of the friction between the crack faces was find negligible on stress intensity factor values. The results presented in this paper can be directly used for the calculation of bearing elements lifetime without complicated finite element simulations.
Highlights
It has become quite common nowadays to use thermoplastic materials for the production of cylindrical rollers in roller bearings or linear guidance parts
A parametrical numerical model was developed in order to simulate a growing crack inside a rolling cylinder under different conditions and to determine fracture mechanics parameters—the stress intensity factors
The second method was the determination of stress intensity factors directly from the deformation of the nodes was the determination of stress intensity factors directly from the deformation of the of the special crack tip elements [36]
Summary
It has become quite common nowadays to use thermoplastic materials for the production of cylindrical rollers in roller bearings or linear guidance parts. It is important to note that in the rolling contact fatigue the cracks grow under mixed-mode loading conditions, which means the shear modes II (in-plane shear) and III (out-of-plane shear) play a significant role in the crack propagation There is another mechanism of failure of the bearing elements—the crack propagates from an internal defect until it reaches a critical length and the bearing element breaks. An estimation of the total lifetime can be performed if the crack growth rate is known from experiments and the considered crack is accurately described by fracture parameters—see details in [23] This process is well established and used, e.g., for polyethylene (PE) pipes [23,24,25,26], or recently for polymer parts produced by additive manufacturing [27,28]. Attention was paid to the shape of the initial defect and the friction between crack faces, as they come into contact in some positions of the rolling cylinder
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