Reinforced ConcreteComposites

CohesiveSpringsContact

Modeling in ABAQUS

Weidong Wu

Department of Civil EngineeringThe University of Mississippi

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In order to use ABAQUS

• FEA background

• Know what you will model

Create your model correctly

• Always refer to the manual whenever you are not sure

• Solve difficulties through .dat .msg .sta files

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How to model composites

• Two ways:

-Composite shell sections when your model is simple

-Composites layup Real-world application, may handle large

number of plies

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Composites Modeling

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Composite shell sections

• Composed of layers made of different materials in different orientations.

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Define composite shell in CAE

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Composites layup

Ply orientation

The orientation of each ply

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Define composite layup in CAE

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• In Preparation…

How to model RC

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Cohesive Modeling

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Applications

Modeling adhesives, bonded interfaces, and gaskets

Constitutive response types Continuum based

A traction-separation description of the interface

A uniaxial stress state-gasket /small adhesive patches

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Creating a cohesive layer

You should define the geometric region that represents the cohesive layer as a SOLID, even if the thickness of the layer is close to zero

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Creating a cohesive layer

If thickness is less than10–4 , specify it

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Cohesive Elements

• COH2D4

• COH3D6

• COH3D8

8-node three-dimensional

cohesive element

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Define Interaction

• Cohesive zone should have more refined mesh

In most applications it is appropriate to have both faces of the cohesive elements tied to neighboring components

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• If you want to model the cohesive layer using a mesh that is finer than the adjacent bulk material mesh, the cohesive layer should be generated as a separate mesh and tied to the bulk material using tie constraints

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Continuum-based modeling A glue-like material has a finite thickness Using conventional material models When used with conventional material models, cohesive

elements use true stress and strain measures The cohesive layer is subjected to only through-

thickness strain, and two transverse shear strain components

All standard output variables in ABAQUS are available for cohesive elements that are used with conventional material models

* COHESIVE SECTION, RESPONSE=CONTINUUM Modeling of damage with cohesive elements can be

carried out only in Abaqus/Explicit

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Modeling of damage with cohesive elements

Progressive damage and failure for

-Ductile metals

-Fiber-reinforced composites

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Traction-separation-based modeling

The intermediate glue material is very thin and may be considered to be of zero thickness

Model the delamination at interfaces in composites Cohesive behavior defined directly in terms of a traction-

separation law

t-The nominal traction stress vector k-is the stiffness that relates the nominal stress S to the displacement

When used with a material model that is based on a traction-separation description, cohesive elements use nominal stress and strain measures

COHESIVE SECTION, RESPONSE=TRACTION SEPARATION

PL S

AE K

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A uniaxial stress state-gasket modeling

Fully nonlinear (can be used with finite strains and rotations);

Can have mass in a dynamic analysisAvailable in both ABAQUS/Standard and

ABAQUS/Explicit

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Contact Modeling In Preparation…

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Introduction

Surface based or contact element basedInteraction between surfaces -Normal -Tangential: sliding frictionContact Property: to define contact

interaction models: -Normal hard -Tangential: finite or small sliding

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Master and slave surface

• Only the master surface can penetrate the slave surface

• the slave surface should be the more finely meshed surface

• if the mesh densities are similar, the slave surface should be the surface with the softer underlying material

• Element selectionit is better, in general, to use first-order elements for those parts of a model that will form a slave surface

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• If you choose the Finite sliding formulation and the Surface to surface discretization method, the contact interaction property that you select cannot specify a “hard” contact pressure-overclosure relationship

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What You May Always Need to Know

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Job Execution Control

• Abaqus Job suspend, resume, and terminate

• abaqus {suspend | resume | terminate} job=job-name

abaqus terminate job=input_file 

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Automatic stabilization of unstable static problems

• Nonlinear static problems can be unstable

• Causes: geometrical nature, such as buckling,

material nature, such as material softening

Rigid body motion

• Solution: automatic addition of volume-proportional damping

to the model to obtain a smooth motion

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How to decide the damping factor

• Automatic stabilization of static problems with a constant damping factor

1. Based on the dissipated energy fraction,default=0.0002

2. Directly specifying the damping factor

3. Propagating the damping factors from the immediately preceding

general step into the current step

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Common Difficulties

• Warning message: Zero pivot and numerical singularity

Causes: 1. Nodes may be overconstrained in a model

2. The model might be insufficiently constrained, rigid body motion occurs.

• TOO MANY ATTEMPTS MADE FOR THIS INCREMENT

• Causes: so many reasons 1.Cannot reach convergence