/FAIL/COCKCROFT

Is compatible with shells and solids. Fracture occurs when the accumulated equivalent strain modified by maximum principal tensile stress reaches a critical value. Is compatible with visco-elastic and elasto-plastic materials.

Format

Definitions

Example

#RADIOSS STARTER
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/UNIT/1
unit for mat
#              MUNIT               LUNIT               TUNIT
                  Mg                  mm                   s
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/MAT/PLAS_TAB/1/1
Steel
#              RHO_I
              7.8E-9                   0
#                  E                  Nu           Eps_p_max               Eps_t               Eps_m
              210000                  .3                   0                   0                   0
#  N_funct  F_smooth              C_hard               F_cut               Eps_f                  VP
         1         0                   0                   0                   0                   0
#  fct_IDp              Fscale   Fct_IDE                EInf                  CE
         0                   0         0                   0                   0
# func_ID1  func_ID2  func_ID3  func_ID4  func_ID5
         1
#           Fscale_1            Fscale_2            Fscale_3            Fscale_4            Fscale_5
                   1
#          Eps_dot_1           Eps_dot_2           Eps_dot_3           Eps_dot_4           Eps_dot_5
                   0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FAIL/COCKCROFT/1/1
#                 C0               Alpha
                 0.4
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#-  3. FUNCTIONS:
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/1
function_36
#                  X                   Y
                0.00              270.00
                0.01              298.39
                0.02              313.04
                0.03              324.89
                0.04              335.23
                0.05              344.58
                0.06              353.20
                0.07              361.26
                0.08              368.87
                0.09              376.11
                0.10              383.03
                0.20              441.33
                0.30              488.52
                0.40              529.69
                0.50              566.89
                0.60              601.21
                0.70              633.30
                0.80              663.61
                0.90              692.43
                1.00              720.00
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#enddata
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

Comments

1. This failure criterion is defined based on the well-known Cockcroft–Latham criterion.(1)
   $${\displaystyle \underset{0}{\overset{{\overline{\epsilon }}_f}{\int }}\max ({\sigma }_1,0)\cdot d\overline{\epsilon }=C}0$$
   Where,

   ${\sigma }_{\text{1}}$

   First principal tension stress.

   $\overline{\epsilon }$

   The equivalent strain.

2. No failure occurs in compression.
3. When this failure is used with /MAT/LAW1, only N=1 (membrane) is supported. It does not work when N=0 global integration is used.
4. An exponential moving average filter is used for filtering the 1^st principal stress.(2)
   $${\sigma }_f\left(t\right)=\alpha \sigma \left(t\right)+\left(1-\alpha \right)\sigma \left(t-\text{Δ}t\right)$$
   Where,

   ${\sigma }_f$

   Filtered stress.

   $\alpha$

   Degree of weighting decrease, a constant smoothing factor between 0 and 1. A higher $\alpha$ value discounts previous values faster, which means the stress is less filtered.