Hourglass (maybe?) problem
Hello everyone! Im trying to model the mechanical behaviour of a battery cell, considering all of its components (separators, active materials on collectors ecc.). The layer are extremely thin as you can check in the model; i used solid elements with ELFORM=1 for all the parts; i used CRUSHABLE FOAM MATERIAL to model separators and active materials coating the collectors, MAT PLASTIC KINEMATICS to model the aluminum and copper collectors. Furthermore i used the ADD_EROSION to consider the failure of the separators (when a certain number of elements of the separators reach a certain value of strain the simulation terminates). I used ERODING SURFACE TO SURFACE for the contacts among separators and the parts close to them, while i used AUTOMATIC SURFACE TO SURFACE to model the contact between the parts without erosion; in both case i used SOFT=2 SNLOG=1. In control cards i set ERODE=1, ESOERT=3. Now ill explain my problem: as you can see in the picture it seems that some hourglass modes starts at a certain time (i used Hourglass 6 and QH=0.1) but when i check the hourglass energy in GLSTAT i've got that it is a lot smaller than internal energy so i dont understand why this happens! Another Strange thing is related to the fact that the energy ratio is different from 1 as you can see in the picture. What can be the problem? Thank you a lot in advance and greetings from italy!
Ill leave here some pics to understand better the problem