# OOF: Finite Element Analysis of Microstructures

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##

valeria

This element was contributed by Valeria Cannillo.
It is designed to fail (i.e. mutate) following the Weibull law:

A failure probability is computed in every element from Eq. (4.2), using the maximum principal stress as . Each element has an area that is used to determine the volume in Eq. (4.2) through the characteristic element thickness.

Each element is then randomly assigned a *test* probability
from a uniform distribution in the interval . The
element fractures if

The process of mutation is similar to that for the damage element (Section 4.5.10):

1. if Eq. (4.3) is favorable for cracking, the direction of the maximum principle stress is found

2. Modification of the stiffness matrix proceeds as in the damage element

### Parameters

*orientation*- As with the damage element. this is meaningless.
*thermoelastic coefficients*- All thermoelastic coefficients for a undamaged
element are isotropic.
*weibull_m*- The Weibull parameter . [dimensionless]
*weibull_s0*- The Weibull parameter
. [stress]
*weibull_a0*- The reference area (related to the reference volume
through the characteristic element thickness) [area]
*knockdown1*- The factor which multiplies the rotated stiffness matrix's Czzz z
component during a mutation. This should be a small number, if the
element is really to be ``cracked''. [dimensionless]
*knockdown2*- The factor which multiplies the rotated stiffness matrix's remaining
Cijkl components for at least one of ijkl=z during a
mutation. [dimensionless]
*only_once*- If true, an element which has been damaged during one mutate command
will not be damaged further on subsequent mutate commands. If false,
the knockdown factors may be applied multiple times. Default:
`false`

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