Hi 

I am doing coupling pore fluid -deformation with rock permeability of very low . After bending the rock, pore pressure drops, after flatting the rock, pore pressure goes back to the initial state. I am just using linear elastic model with a Poisson ratio of 0.4 for all directions. I don't know why? I am very confusing, trying to figure out the mechanism .I checked the result, E3 is under compression of 65 microstrain, E1 is under tension of 40 microstrain, E2 is also under tension of 24.5 microstrain. So total volumetric strain is very small of 0.5 under tension. although this volumetric strain is under tension, but is almost equal to zero. I am wondering if there is a formula to relate volume change with input poisson ratio in 3D? if possion ratio is equal to 0.5, then it is compressible so volumetric strain will be zero. but why in my case, with possion ratio of 0.4, the volumetric strain is still very close zero. anyone can help me understand it? What result do I need to check? Thank you so much for your help. I appreciate it.