×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# How to specify material parameters at integr. points

 Forum Search FAQs Links MVPs

## How to specify material parameters at integr. points

(OP)
Hi there,

I come into a situation where I would like to specify different material parameters (Let's say in simple elastic case, the Young's modulus) for each integration point of the finite elements. By doing this I hope I can model materials of which the parameters are spatial variables, and therefore, cannot be treated as constants for an element. Does anyone know how to implement this in ABAQUS?

To split this question into more specific ones:
1. Does ABAQUS evaluate material properties at every integration points?
2. If yes, how to specify different properties for each integration points?
3. Is there a way to get stiffness matrices evaluated at the integration points? rather than the elemental stiffness matrix being the weighted sum of those matrices.
4. The last one is weird but actually helpful for me:
Will ABAQUS analysis proceed even if some material parameters do not make sense physically? In other words, how to let ABAQUS continue to analysis, without exiting itself due to fatal error warnings, when Young's modulus is negative?

### RE: How to specify material parameters at integr. points

The integration points are sample points used to obtain output, not to specify input. Variable 'materials' can be modelled, but it depends on what you need to do. If you explain what you're trying to do in more detail, we could offer some suggestions on which ABAQUS-specific material model to implement.

>1. Does ABAQUS evaluate material properties at every integration points?
Material props are not evaluated as such, but are given - and used by the constitutive model - on a element-by-element level. The integration points are used as 'sampling points' (see any numerical methods book on numerical integration methods under 'Gaussian Integration') in order to integrate the FE equations.

>2. If yes, how to specify different properties for each integration points?
See above.

>3. Is there a way to get stiffness matrices evaluated at the integration points? rather than the elemental stiffness matrix being the weighted sum of those matrices.
Integration points ARE used to obtain the stiffness of each element. The total stiffness (K) is the sum of all the elemental stiffnesses found as:

Ke = Integral [B]T [D] [B]

integrated over the domain, where D is a material constant matrix and B is a strain matrix.

>4. The last one is weird but actually helpful for me:
Will ABAQUS analysis proceed even if some material parameters do not make sense physically? In other words, how to let ABAQUS continue to analysis, without exiting itself due to fatal error warnings, when Young's modulus is negative?
I'm sure the modulus must have to be entered as positive. My thinking is that physically, a global negative modulus cannot exist, otherwise a local negative strain would produce a positive displacement and vice versa(!). It may be possible to have micro levels of negative modulus, but this isn't applicable at the global level.

Hope this helps,

-- drej --

### RE: How to specify material parameters at integr. points

Dear bigeyenemo

Your question is interesting and Drej's reply is very wise.
Apart from the negative elasticity, I'm afraid it's not possible to define but a single value for E & v for an element.
If the material properties vary spatially, why not refine your mesh and assign adjacent elements different Es and Poisson Ratios?

Dear drej: I couldn't really understand why a negative E means that a negative strain leads to a positive displacement. It is interesting for me to know why, since negative Poisson ratio is mathematically acceptable and I have actually seen synthetic materials with a negative Poisson ratio, but negative E signifies a violation from the fundamental laws of thermodynamics.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!