The present EFM paper selected for discussion applies artificial intelligence (AI) to fatigue crack growth. The subject is on the outskirts of my competence. To say the least, I am on thin ice when it comes to AI, machine learning, neural networks and similar. Still, I get the feeling that the selected paper describes an interesting step forward. I am sure that it will, sooner or later, be a reliable tool for predicting closing and opening loads at fatigue crack growth. 

The paper is: “Combining artificial intelligence with different plasticity-induced crack closure criteria to determine opening and closing loads on a three-dimensional centre cracked specimen” by R. Baptista and V. Infante in Engineering Fracture Mechanics, vol. 312, 2024.

Several cases are calculated using 3D FE models with elastic-plastic modelling. The results are focusing on the plastic zone and the crack growth. The latter refers to a comparison with the Dugdale model for which the stress reaches a limiting stress level. When the level is reached, the connected elements are removed by node relaxation. The process is similar to a cohesive zone. 

Interestingly, the Dugdale model was already solved and published by Russians. The Russian scientists were the coworkers Leonov and Panasyuk and independent of the Barenblatt. The reason for it being called the Dugdale model is probably that the Russian results were not well known in the Western world. Barenblatt’s solution is a decohesive zone in which the cohesive stresses decrease with increasing distances between the cohesive zone boundaries. The solution by Leonov-Panasyuk and Dugdale is a special case of Barenblatt’s model. The special case is for an infinitesimally thin, perfectly plastic sheet in plane stress. Also, the cohesive zone is straight ahead of the crack tip. The comparison is mathematical, while Barenblatt’s solution is the more elaborate for a reason. It concerns the fracture processes that gradually decrease the load-carrying capacity, which brings us closer to the real world. A decohesive zone is a model of the fracture process region. It would be interesting to see results for a Barenblatt zone. Already in a Dugdale thin sheet that suffers from necking ahead of the crack tip, the limit load for separation decreases with the decreasing plate thickness in the neck. The ultimate displacement before the completed fracture should be around the same as the original sheet thickness.

https://imechanica.org/node/27498