Warning messages related to negative eigen values while using Abaqus Standard
I am working on simulation of necking in a uniaxial tension test using sheet specimens of 1 mm sheet thickness. I have given stress strain data upto a plastic strain of 1 , I am using 4 elements in the thickness direction of the sheet.My job is able to complete but with lot of warning messages as follows:
1) The strain increment has exceeded fifty times the strain to cause first yield at 286 points
2) The system matrix has 174 negative eigenvalues.
3) The strain increment is so large that the program will not attempt the plasticity calculation at 15 points
Can anyone please explain the reason for this kind of warning messages and how to resolve them. Is there any effect of these messages in the accuracy of the solution?
Thanks in advance.