Are all 3D-Cracks mix-mode cracks?

I followed this blog with interest for several weeks before I decide to ask my first question. As a newcomer in fracture mechanics, I got confused with a FE-Analysis several days ago, which calcultes the J-Integral of a 3D-crack. Ich transferred the J-Integral calculated using FEM (ADINA) to K (stress intensity factor) and found that the calculated FE-Value is 50% greater than the value acording to the IWM-Methode, which is developed to calculate the K-factors für crack in cylinders.

After checking the stress status on the crack front, I found that the schearing stress Sigma(xy) is 15% of the external loading. So I think, this is a mix-mode crack and the J-Integral is the summer of K1,K2 and K3. The Question is: Is my consideriton right? Is there any other reasons? Are all 3D-Cracks mix-mode cracks?