When working though y-axis layer shift issues I designed this model to excite my particular failure mode (basically circular shapes seemed more likely cause my printer to fail). Probably won't be effective in all failure scenarios, 'but something to try. For me it failed 100% of the time for what had been a frustratingly intermittent issue previously.

Suggest you align it so the smallest and central ellipses lie along the y-axis, turn the layer height down as far as possible (more layers = more chances to shift), use no top layers, thicker walls (I used 5), and line infill (at 0 and 135 degrees).

I also suggest using a brim to keep it on the build plate, it was really designed with that in mind.

Please leave a comment if it works for you. Pointers to other models that reliably fall would be welcome too.

2-20-18 - added a second y-axis test model (Y-Axis-Test_2.stl) I had attempted earlier at the request of a friend. This did NOT fail for me but might be something else to try. Suggest using, minimum layer height, linear infill along the y-axis (as shown in the image), no top or bottom layers, 2 copies, 1 at each end of the y-axis so the travel speed can be fully stimulated.