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ABAQUS - Stress Intensity Factor for Single Radial Crack in Thick Walled Cylinder

Submitted by IanLau on
research
ABAQUS
crack-tip stress intensity factor
contour integrals
thick walled cylinder
stress intensity factor

Hi,

I am trying to analyze the stress intensity factor (SIF) using contour integral of a 2D thick walled cylinder under plane stress with different wall ratios under internal pressure loading only and a single radial crack of varying length in Abaqus.

The wall ratio (inner & outer radius) I am interested in modelling is of ratio 6 (i.e. for inner radius of 1, outer radius is 6).

I have modelled ratios from 1-6 with crack length varying from 0.1-0.9 of the wall thickness. (i.e. for ratio 3, the wall thickness is 2, hence the crack varies from 0.1-0.9 x 2).

What I have discovered:

  • for ratios (<5) the SIF at the crack tip monotonically increases as crack extends from 0.1-0.9 of the wall thickness.
  • for ratios (>5) the SIF at the crack tip decreases as crack length extends from 0.1-0.6, and increases later on from crack length 0.7-0.9.
  • the stress distribution for ratio (<5), the max stress always occur at the crack tip leading to the increase in SIF as crack extends.
  • the stress distribution for ratio (>5), the max stress do not always occur at the crack tip but at the sometimes at the inner wall leading to a decrease in SIF but later on occurring at the crack tip as crack extends.

I have compared my results obtain with published literature for ratios (1-3) and are in good agreement (less than 2%). But there is no published data for ratios (>3) and I require the results for larger ratios.

I believe thre isn't any issue with my modelling procedure since I obtained results that are in good agreement for ratios (1-3) but however, I cannot explain why the issue of maximum stress not occurring at the crack tip for larger ratios. I applied a triangular mesh at the crack front converging at the crack tip and quad mesh on the remaining geometry.

So my questions are:

  1. Has anyone ever encountered a situation where SIF decreases with increasing crack length even though all other parameters remained the same?
  2. Is a decrease in SIF unreasonable? Because, in theory it should increase with crack length when stress remain constant.
  3. Why is the max stress not always occurring at the crack tip in the modelled and instead on the inner wall surface for ratios (>5).

Any advice/input/recommendation would be greatly appreciated. I can upload my model if required and can also be contacted through email at ianlau11 [at] gmail.com

Kind regards,

Ian