curved crack

The word "extreme" seems to be "trending" a lot these days, see the recent discussions on the new journal Extreme Mechanics Letters.

My collaborator Ruben Sevilla at Swansea and I were interested in very curved crack paths that develop in nature and have been replicated experimentally in thin films attached to elastic substrates.

I am trying to develop a model in ABAQUS and perform crack analysis using FRANC3D. I am having a problem right at the beginning.

I am able to create the model in ABAQUS and write the .inp file. I open this file in FRANC3D and am trying to insert a curved crack. I repeat a 'curved crack'. The crack is not planar. When I try to define the crack front using 'user defined points', the software is approximating all the points I enter to a best-fit 'plane'. So it is generating a planar crack when i wanta curved crack.