Experimental Investigation and Finite Element Analysis of Fatigue Crack Growth in Pipes Containing a Circumferential Semi-elliptical Crack Subjected to Bending |
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Authors: | A R Shahani M M Shodja A Shahhosseini |
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Institution: | (1) Department of Applied Mechanics, Faculty of Mechanical Engineering, K. N. Toosi University of Technology, P. O. Box 19395-1999, Tehran, Iran |
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Abstract: | In this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered.
Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region
must be done with great care. This may lead to an increase in the run time which makes it difficult to reach valid results
and conclusions. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this
method is used. Stress intensity factors in mode I condition are determined using three-dimensional finite element modeling
with 20 node iso-parametric brick elements in the ANSYS 9.0 standard code and the singular form of these finite elements at
the crack front. In order to estimate the analysis error, the structural parameter error in energy norm criterion was used.
Because of the advantages of non-dimensional analysis, this method is employed, and the stress intensity factors are normalized.
For the analysis of the fatigue crack growth, the Paris law is used. The propagation path of the surface flaw is obtained
from the diagram of aspect ratio versus relative crack depth. The fatigue crack growth analysis (the relative crack depth
against loading cycles diagram) of different initial crack aspect ratio under cyclic loading is also considered. Fatigue shape
development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material
constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed
experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending
loading tests are compared with the numerical results. The experimental results show good conformity with the finite element
results. |
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