I recently have carried out the fracture analysis for center crack specimen via ABAQUS. I'm looking for the fracture parameters such as stress intensity factors (SIF) and J-integral.
Due to symmetry in geometry and loading conditions, only one quarter of the center crack specimen were simulated in my work.
I want to know the final result from which contour and which layer of element in thickness direction of specimen is correct?
I attached file the figures of crack and crack tip as well as result.
who can help me?
Hi Mohammad Nejati
Abaqus calculates J in the plane perpendicular to the crack front, if I have not mistaken.
In terms of which contour, you will need to compare the values obtained between all contours. Peak stresses will be around the crack tip, and reduced stresses as you move away from the tip. As the contour moves away from the crack tip, the increase would gradually be minimal and 'converges'. Typically this is considered the representative J for that particular plane. Alternatively you could take an average of a few J values from the 'converged' contours.
As J is calculated in a 2-D plane, it is also known that it could vary across the crack tip / crack front. In FEA, a crack tip is modelled as a straight line as a simple representation, a curved crack tip is often observed in reality. And depending on if any damage is modelled, pin-pointing to a single method to describe the 'accurate' J representation would be tricky.
However, assuming no damage is modelled in your case, most would agree with averaging the 'converged' J values across the crack front to be a representation of specimen J value. Depending on what you are investigating, you might want to pay some attention to the significance of the maximum and minim J calculated.
Just an off topic suggestion, for simplification purposes, perhaps modelling the specimen as a 2-D shell could make things easier? As long as the model is validated experimentally, and it simplifies the decision making process.
Hope this helps, and stay safe.
Regards,
Will
@ Wee Khor
Dear Wee Khor
Thank you for your explanation.
My problem is that from which row of elements in thickness direction of 3-D model I have to read J in ABAQUS? I showed in the picture previously. Which of them is correct?
Hi Mohammad Nejati
I believe there is no hard rule to which exact contour gives the exact J or K values for the respective loading. I've attached a few figures to illustrate the idea.
J is calculated from the contours around the specified crack tip (contour 3 and 13 are shown in the figure). The table shows J values from increment 7, step 0.35. To decide the representative J, it would be easier to comprehend on the next figure. J from Contour 1, 3, 7 and 13 are shown, and it shows that the increased contour (increasing contour area) gives increasing but converging values.
You could process the values by eliminating outliers, i.e. 5% difference from average, and average the remaining 'converged' contours for the representative J.
Hope this helps. PM if there are more questions.
Regards,
Will
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