Dissertação
Análise de propagação de trincas por fadiga em uma viga da estrutura de um forno de reaquecimento
Fecha
2016-09-16Autor
Leonardo Carneiro Vianna Schettini
Institución
Resumen
Fatigue crack is one of main problems in mechanical components and metallic structures. In
this work fatigue cracks are analyzed in one of beams that is in charge of translation
movement of the billet inside the reheating furnace, in order to support the plans of inspection
and maintenance. The study is based on fracture mechanics, applying concepts about crack
propagation on mechanical components submitted to fatigue. The methodology consists in the
global-local analysis strategy to calculate the crack propagation and the life under fatigue
which was divided in three steps. The first one corresponds to the global linear elastic analysis
of the beam, considering absence of cracks, using the numerical finite elements method
(FEM) by SOLIDWORKS software. This step enables the establishment of critical regions
considering the work to be done and, therefore, most susceptible to cracks. In the second step,
two different cracks are inserted in the global model obtained in the first step. Crack position
is defined by the reality of the failures observed in the translation beam, this enables the threedimensional simulation model to be closer to reality. From these models, displacements are
obtained from maximum and minimum loads. At the end, the third step corresponds to the
modeling using boundary element method (BEM) to analyze cracks in three-dimensional
bodies, applying FRANC3D software. The displacements found in the second step are applied
as contour conditions in the local models created on FRANC3D. Results of this third step can
be used to refine global analysis of the second step, in a continuous process of refining
analysis. Results of a tensioned plate are presented, similarly to the model proposed by
BORGES (2010). It was observed that the values obtained with numerical methods were
similar to the ones obtained using the fundamentals of fracture mechanics, validating the
proposed methodology. The local models, presenting different cracks, of a plate taken from
the translation beam and of a piece of the translation beam, exposed to a cyclic loading, have
proven feasible to estimate crack propagation on mechanical components, based on
fundamentals of fracture mechanics. In order to calculate the life under fatigue defined by
NBR-8800, the results obtained are consistent when compared to the results coming from the
local models.