A COMPUTATIONAL MODEL FOR THE FATIGUE STUDY: Effects of overload, mean stress and plasticity on propagation

Rafael Luis Moresco¹; Eduardo Bittencourt¹; Guilherme Fiorin Fornel¹

¹ Universidade Federal do Rio Grande do Sul

doi:10.20906/CPS/CILAMCE2017-0323

Resumo

The fatigue crack growth is analyzed numerically using a finite element platform, where the fracture problem is treated discretely by cohesive interface elements. The studied cases are restricted to plane strain and only subjected to the normal opening between the surfaces of the crack. The separation of crack interfaces is described by the use of two models of irreversible cohesive zone, one with displacement to the origin and another with residual opening. The models have traction-separation relationships that do not follow a predefined path, being dependent on the evolution of the damage linked to the properties of the cohesive zone. Initially, basic uniaxial responses for the cohesive elements are shown, being these elements submitted to loads with different mean stresses. Then, model is applied in the analysis of the fatigue crack growth in a double cantilever beam, where the observed structure is formed by the union of two metal plates through a cohesive adhesive that directs the growth of the crack. Cases with single amplitude overload are computed to demonstrate the effects on the propagation. In addition, a transient fatigue analysis is performed through responses generated by the application of block loading sequences, which have variations in amplitudes and load ratio. The implemented computational model qualitatively reproduces the results presented in reference works for the analyzed problems.

Palavras-chave: cracks growth; cohesive zone model; transient fatigue