Altair RISE

A program to recognize and reward our most engaged community members

Nominate Yourself Now!

LAW36 failure strain parameters?

Altair Forum User

I am trying to understand the various parameters for LAW36.

1. EPS_p_max

2. EPS_t1 - Maximum tensile failure strain (EPSt in reference guide)

3. EPS_t2 - Maximum tensile failure damage (EPSm in reference guide)

4. Epsilon_F - Tensile strain for element deletion (EPSf in reference guide)

What I understand about these is :

1. EPS_p_max - Plastic Strain beyond this will cause element deletion

2. EPS_t1 - Strain beyond which the line connecting t1 and t2 will be used

3. EPS_t2 - Strain beyond which the element will be separated from the connected elements

4. Epsilon_F - Strain beyond which element will be deleted

If my understanding is correct then what is the point of having Epsilon_F? We already have EPS_p_max to determine the element deletion strain.

<?xml version="1.0" encoding="UTF-8"?>

Find more posts tagged with

English

Radioss

Accepted answers

All comments

Altair Forum User

This option is to use the failure criteria based on the maximum principal strain. When the principal strain of the model reaches Eps_f value (maximum tensile failure strain), the element is deleted.

Altair Forum User

Can you please tell me the difference between the 4 fields I listed in the question. The reference guide has no meaningful explaination. I am observing that element gets deleted at EPS_p_max itself so no chance to reach till Eps_f. Why have 2 fields to do the same thing?

Altair Forum User

This material model provides an elastic-plastic material option that allows stress vs. strain curve input and strain rate dependency. Failure is based on effective plastic strain or the major principal in-plane strain component.

For EPS_t is the tensile failure strain at which stress starts to reduce.

For EPS_m, when the principal strain is more than EPS_m the stress is reduced to 0,but the element is not deleted.

For EPS_f, failure criteria based on the maximum principal strain. The element is deleted once when the principal strain of the model reaches Eps_f value.

If you are able to update these values, the failure can be defined with the principal in-plane strain components. And this material behavior is typically shown in the graph.

Altair Forum User

Great, this is helpful. So what is the state after it reaches EPS_m? Lets say I make the EPS_f or EPS_p_max far enough so that it would never be reached. So how is the behaviour defined for elements after they reach EPS_m? Are they rigid? Are no longer straining? If they are straining and yet maintain zero stress, that means they are not absorbing any energy. Please can you elaborate this state as it may be exactly what I am looking for.

Altair Forum User

From the graph, which shows the material behavior, the stress will be reduced to zero and it will continue to strain till it reaches the EPS_f where the element failure will happen.

Nothing more is provided in the documentation also.

Please search on Elastic Plastic Piecewise Linear Material model if you want to explore more on this material characteristics.

Altair Forum User

Alright Thank You George.

Mr_Ty

EPS_m and EPS_p_max are a value, right?

Simon Križnik

@tranty

these parameters require strain value input:

EPS_p_max is Failure plastic strain

EPS_m is Maximum tensile failure strain at which the stress in element is set to zero.