/FAIL/COCKCROFT
Block Format Keyword A nonlinear stressstrain based failure criterion with linear damage accumulation.
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 viscoelastic and elastoplastic materials.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/FAIL/COCKCROFT/mat_ID/unit_ID  
C0  Alpha 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

fail_ID 
Definitions
Field  Contents  SI Unit Example 

mat_ID  Material
identifier. (Integer, maximum 10 digits) 

unit_ID  (Optional) Unit Identifier. (Integer, maximum 10 digits) 

C0  Cockcroft–Latham failure
criterion. 1
(Real) 
$\left[\text{Pa}\right]$ 
Alpha  Exponential moving average
filter on 1^{st} principal stress
${\sigma}_{\text{1}}$
. 4
(Real) 

fail_ID  (Optional) Failure criteria identifier.
(Integer, maximum 10 digits) 
Example
#RADIOSS STARTER
#12345678910
/UNIT/1
unit for mat
# MUNIT LUNIT TUNIT
Mg mm s
#12345678910
/MAT/PLAS_TAB/1/1
Steel
# RHO_I
7.8E9 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
#12345678910
/FAIL/COCKCROFT/1/1
# C0 Alpha
0.4
#12345678910
# 3. FUNCTIONS:
#12345678910
/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
#12345678910
#enddata
#12345678910
Comments
 This failure criterion is
defined based on the wellknown Cockcroft–Latham criterion.
(1) $$\underset{0}{\overset{{\overline{\epsilon}}_{f}}{\int}}\mathrm{max}({\sigma}_{1},0)\cdot d\overline{\epsilon}=C}0$$Where, ${\sigma}_{\text{1}}$
 First principal tension stress.
 $\overline{\epsilon}$
 The equivalent strain.
 No failure occurs in compression.
 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.
 An exponential moving
average filter is used for filtering the 1^{st} principal
stress.
(2) $${\sigma}_{f}\left(t\right)=\alpha \sigma \left(t\right)+\left(1\alpha \right)\sigma \left(t\text{\Delta}t\right)$$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.