Análise numérica do crescimento de trinca sob influência de nódulos de grafita submetida à flexão presente na raiz de dentes de engrenagem

Abstract

The austempered ductile iron presents many advantageous mechanical properties combined with competitive cost to be used as raw material for gears. In order to promote the consolidation of technical knowledge of this material, the aim of the current study is to investigate the influence of the graphite nodules (presented in the austempered matrix) in a crack located in the root of a spur gear tooth. Graphite nodules act as stress concentrators changing the stress field where they are located. Thus, 8,16, 32, 64 e 128 µm diameter nodules were placed at different distances from crack tip. The crack propagation angle (CPA) and the stress intensity factor (KI) were calculated using the finite element analysis software ABAQUS. The results show that there is a strong influence on KI and CPA when they are near to the crack tip. These values are approximately the same of the case with no nodules when the distances from the crack tip are bigger than 0.10 mm. Additionally, it is observed that the nodules act as stress concentrators with concentration capacity around 1.7 and 1.8, when the distance from the surface of the gear root is bigger than 0.10 mm. These values become higher when the nodules are close to the surface. It is also observed that the presence of different diameters nodules influence on the path of the crack propagation. The analyses with two different diameters, (32 e 64 µm) 0.025 mm distant from crack tip, show that for the bigger nodule the influence is greater.