Materials/Failure

You get data for LAW24 from the following tests:

• Get density by weighing a specimen
• Get Young's modulus with a cylinder compression test
• Poisson coefficient (usually assumed to be near 0.2)
• Get ‘fc’ from Compression strength (using cube compression test)

With the following additional tests, material LAW24 will be more accurate (in fact, providing data fits the failure envelope):

• Get ‘ft’ from tensile test:

  ‘ft’ is direct tensile strength. This test provides ‘ft/fc’ value for LAW24.

• Get couple of (ft,Ht) from Splitting tensile test:

  ‘Fst’ is splitting tensile strength in Splitting tensile test. Assume that Fst=ft., then you need to model this test to fit limit strength (ft) by validating ‘Ht’ value. This test should be with very slow velocity, so use HA8 solid property for in Splitting tensile test.

• Get ‘fb’ from Biaxial test and get (f2,s0) from confined test.

WARNING ID: 519
** WARNING IN SANDWICH SHELL INITIALIZATION
SHELL (ID=…) MASS (TYPE NUMBER …) 
SUM OF LAYER MASS DIFFER FROM TOTAL
WARNING ID: 520
** WARNING IN SANDWICH SHELL INITIALIZATION 
SHELL (ID=…) INERTIA (TYPE NUMBER …)
POTENTIAL INSTABILITY DUE TO LAYER INERTIA DISTRIBUTION

Indeed, mass me and inertia I of the element which will be distributed to the nodes of the shell are correctly computed from the characteristics of each layer:(1)

$$m_e=\left({\displaystyle \sum _{j=1,N}{p}_j{t}_j}\right)S$$

Where,

$S$

Area of shell element

$N$

Number of layers

$p_j$

Density of layer $j$

$t_j$

Thickness of layer $j$

$I={\displaystyle \sum _{j=1,N}{p}_j{t}_j}S\left(\frac{S+t_j{}^2}{12}+z_j{}^2\right)$

$z_j$

Distance to the middle plane of the shell element

The possible messages in case of failure criteria for shell elements using LAW25 are:

FAILURE-1

Criteria ${\epsilon }_{m1}$ for maximum tensile strain in first direction has been reached

FAILURE-2

Criteria ${\epsilon }_{m2}$ for maximum tensile strain in second direction has been reached

FAILURE-P

Criteria ${\text{W}}_p^{\max }$ (maximum plastic work for failure) has been reached

When the element is deleted (it depends on the failure of its different layers and on the flag I_off - Total Element Failure Criteria - into the global material associated to the PART), the following message is written:

RUPTURE OF SHELL ELEMENT …

If number of integration points N=0 in /PROP/SHELL, then global integration approach is used.

• Global integration (N=0) is only compatible with Material Laws 1, 2, 22, 36, 43 and 60.
• Failure models are not available with global integration for shells.
• Global integration is not compatible with saving stresses to state files using /STATE/DT which creates /INISHE and /INISH3N.

Workaround: Use material LAW2 with integration point and a huge value for the yield stress. As of V51, material LAW1 for shells uses global formulation, except if one integration point is asked for in the property, then a membrane only behavior occurs.