Checking for breach...
 

Checking for breach and spall  

 

saberman12
(@saberman12)
Active Member
Joined: 4 months ago
Posts: 12
November 1, 2019 7:25 am  

Hi, I am trying to look for any breach and spall in my model after it has been subjected to a blast loading in LS-Dyna. I have seen people using either the erosion method of erasing the element when the element fails as the spall or the effective plastic strain method, where the element is considered failed(spall) when the strain passes certain value. I am working with the latter method. However, I am unable to understand why the element is considered spall when it crosses the effective plastic strain value(e.g 1.95) and why is this value chosen.


Quote
Negative Volume
(@negativevolume)
Estimable Member Admin
Joined: 10 months ago
Posts: 120
November 10, 2019 4:56 pm  

@saberman12

I'm not familiar with spall but am familiar with strain-based fracture/element deletion. Generally, you find a strain value where a certain material is prone to fracture and tell the elements to delete when they cross that strain value in simulation. You also need to be careful what type of strain that you find in the literature (effective plastic vs first principle vs von mises) because you will need to make sure that you define this in the card that you will be using. 

For example *Mat_Add_Erosion allows you to add erosion (eg fracture or deterioration) to specific materials that you have in your model. It has the following options:

  • MXPRES:=Maximum pressure at failure
  • MXEPS:=Maximum principal strain at failure
  • EFFEPS:=Maximum effective strain at failure
  • VOLEPS:=Volumetric strain at failure

So given that you have an effective plastic strain to use, you may have to convert that value to one of the available types of strain. You can also define the damage model that will be applied using:

DMGTYP:=For GISSMO damage type the following applies.
EQ.0: Damage is accumulated, no coupling to flow stress, no failure.
EQ.1: Damage is accumulated, element failure occurs for D=1. Coupling of damage to flow stress depending on parameters, see remarks below.
For IDAM.LT.0 the following applies.
EQ.0: No action is taken
EQ.1: Damage history is initiated based on values of initial plastic strains and initial strain tensor, this is to be used in multistage analyses when damage history is unavailable from previous steps. This relies on having a zero initial stress and a non-zero initial strain state

I know that is a lot, so let me know if this helped or not. 


ReplyQuote
Share: