Reinforced ConcreteCompositesCohesiveSpringsContact Modeling in ABAQUS

Weidong Wu

Department of Civil EngineeringThe University of Mississippi

In order to use ABAQUSFEA backgroundKnow what you will model Create your model correctlyAlways refer to the manual whenever you are not sureSolve difficulties through .dat .msg .sta files

How to model compositesTwo ways: -Composite shell sections when your model is simple -Composites layup Real-world application, may handle large number of plies

Composites Modeling

Composite shell sectionsComposed of layers made of different materials in different orientations.

Define composite shell in CAE

Composites layupPly orientation The orientation of each ply

Define composite layup in CAE

How to model RCIn Preparation

Cohesive Modeling

ApplicationsModeling 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

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

Creating a cohesive layerIf thickness is less than104 , specify it

Cohesive ElementsCOH2D4 COH3D6 COH3D8 8-node three-dimensional cohesive element

Define InteractionCohesive zone should have more refined meshIn most applications it is appropriate to have both faces of the cohesive elements tied to neighboring components

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

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

Modeling of damage with cohesive elements Progressive damage and failure for -Ductile metals -Fiber-reinforced composites

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

A uniaxial stress state-gasket modelingFully nonlinear (can be used with finite strains and rotations);Can have mass in a dynamic analysisAvailable in both ABAQUS/Standard and ABAQUS/Explicit

Contact Modeling In Preparation

IntroductionSurface based or contact element basedInteraction between surfaces -Normal -Tangential: sliding frictionContact Property: to define contact interaction models: -Normal hard -Tangential: finite or small sliding

Master and slave surfaceOnly the master surface can penetrate the slave surface the slave surface should be the more finely meshed surfaceif the mesh densities are similar, the slave surface should be the surface with the softer underlying materialElement selection it is better, in general, to use first-order elements for those parts of a model that will form a slave surface

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

What You May Always Need to Know

Job Execution ControlAbaqus Job suspend, resume, and terminate abaqus {suspend | resume | terminate} job=job-name abaqus terminate job=input_file

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

How to decide the damping factorAutomatic 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

Common DifficultiesWarning 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 INCREMENTCauses: so many reasons 1.Cannot reach convergence