Modeling adhesive joints and bonded interfaces

You can model:

• Adhesive joints – two components connected by a glue-like material that has a finite thickness.

• Fracture at bonded interfaces – crack propagation in glue material that is very thin and for all practical purposes may be considered to be of zero thickness.

• Gaskets (limited capability) – seal between two components. No specialized gasket behavior (typically defined in terms of pressure versus closure) is available. If you want to model special gasket behavior, use special-purpose gasket elements as described in Gaskets.

For more information, see About Cohesive Elements.

The two main approaches that you can use to include cohesive elements in your model are

• embedding one or more layers of cohesive elements in the mesh of an existing model; or

• creating the analysis model using the geometry and mesh tools.

You can model the connection at the interface between the cohesive layer and the surrounding bulk material by sharing nodes or by defining a tie constraint. The tie-constraint approach allows you to model the cohesive layer using a finer discretization than that of the bulk material and may be more desirable in certain modeling situations. For more information, see Defining tie constraints between the cohesive layer and the surrounding bulk material.

Like gasket elements, cohesive elements have an orientation associated with them. This orientation defines the thickness direction of the elements, and it should be consistent throughout the cohesive layer. Swept or offset meshing techniques should be used to generate the mesh in the cohesive layer because these tools produce meshes that are oriented consistently. You can also use the bottom-up sweep meshing method, but you must sweep in the direction of the element thickness to maintain the correct orientation. You should create a single layer of solid elements to model the cohesive region. The use of more than one layer through the thickness could produce unreliable results and is not recommended. You can generate the mesh in the surrounding bulk material using any of the mesh tools because these elements do not need to be oriented.

The general procedure for modeling adhesive joints and bonded interfaces involves the following steps:

1. Create a model, and assign a cohesive element type to the cohesive region in the Mesh module using one of the following approaches:

   • Embedding cohesive elements in an existing three-dimensional mesh

   • Creating a model with cohesive elements using geometry and mesh tools

2. In the Property module, define a material and a cohesive section that refers to the material, and assign the cohesive section to the cohesive region. See Assigning cohesive modeling data for more information.

3. To model progressive damage and failure of cohesive layers as discussed in Defining the Constitutive Response of Cohesive Elements Using a Traction-Separation Description, include the desired damage initiation and damage evolution information in the material definition (select MechanicalDamage for Traction Separation Lawsdamage type). For more information, see Defining damage.