塑性杆件加大变形，为何总是出错呢？

Iorifo

我现在算一根杆件的拉伸，
材料常数如下：
弹性：E＝1555E9;v=0.3
塑性： 屈服应力    屈服应变
           100E9         0
           200E9         0.2
           500E9         0.6
           1000E10     0.8
不知道这样定义塑性问题对不对？
加力计算总是出现如下的错误：
***WARNING: SOLVER PROBLEM.  ZERO PIVOT WHEN PROCESSING NODE 2 INSTANCE ROD-1
             D.O.F. 1
  Typically a zero pivot is associated with an overconstraint in the model.
However, ABAQUS was not able to indentify any chains of constraints that might
lead to an overconstraint at this node. This suggests that the model might be
in fact insufficiently constrained in this particular degree of freedom.
Please check the constraints used in this model.

***WARNING: Solver problem. Zero pivot when processing D.O.F. 1 of 1 nodes.
             The nodes have been identified in node set
             WarnNodeSolvProbZeroPiv_1_2_1_5_1.

***WARNING: THE SYSTEM MATRIX HAS 1 NEGATIVE EIGENVALUES.

     IN AN EIGENVALUE EXTRACTION STEP THE NUMBER OF NEGATIVE EIGENVALUES IS
     EQUAL TO THE NUMBER OF EIGENVALUES BELOW THE CURRENT SHIFT POINT.
     THIS MAY BE USED TO CHECK THAT EIGENVALUES HAVE NOT BEEN MISSED.
     NOTE: THE LANCZOS EIGENSOLVER APPLIES AN INTERNAL SHIFT WHICH WILL
     RESULT IN NEGATIVE EIGENVALUES.

     IN A DIRECT-SOLUTION STEADY-STATE DYNAMIC ANALYSIS, NEGATIVE
     EIGENVALUES ARE EXPECTED. A STATIC ANALYSIS CAN BE USED TO VERIFY THAT THE SYSTEM IS STABLE.

     IN OTHER CASES, NEGATIVE EIGENVALUES MEAN THAT THE SYSTEM MATRIX IS NOT
     POSITIVE DEFINITE:
     FOR EXAMPLE, A BIFURCATION (BUCKLING) LOAD MAY HAVE BEEN EXCEEDED.

     NEGATIVE EIGENVALUES MAY ALSO OCCUR IF QUADRATIC ELEMENTS ARE
     USED TO DEFINE CONTACT SURFACES.

***WARNING: THE STRAIN INCREMENT HAS EXCEEDED FIFTY TIMES THE STRAIN TO CAUSE
             FIRST YIELD AT 5 POINTS

***NOTE: THE RATE OF CONVERGENCE IS VERY SLOW.  THE INCREMENT WILL BE
          ATTEMPTED AGAIN WITH A TIME INCREMENT OF 1.23596E-03

***ERROR: TOO MANY ATTEMPTS MADE FOR THIS INCREMENT: ANALYSIS TERMINATED

     ANALYSIS SUMMARY:
     TOTAL OF          7  INCREMENTS
                      11  CUTBACKS IN AUTOMATIC INCREMENTATION
                     105  ITERATIONS
                     105  PASSES THROUGH THE EQUATION SOLVER OF WHICH
                     105  INVOLVE MATRIX DECOMPOSITION, INCLUDING
                       0  DECOMPOSITION(S) OF THE MASS MATRIX
                       1  REORDERING OF EQUATIONS TO MINIMIZE WAVEFRONT
                       0  ADDITIONAL RESIDUAL EVALUATIONS FOR LINE SEARCHES
                       0  ADDITIONAL OPERATOR EVALUATIONS FOR LINE SEARCHES
                       0  WARNING MESSAGES DURING USER INPUT PROCESSING
                     132  WARNING MESSAGES DURING ANALYSIS
                      85  ANALYSIS WARNINGS ARE NUMERICAL PROBLEM MESSAGES
                       4  ANALYSIS WARNINGS ARE NEGATIVE EIGENVALUE MESSAGES
                       1  ERROR MESSAGES

不知道到底出现了什么错误？请教大侠指点，谢谢！

st_knight

约束不够，造成发散！