About Mechanical Contact Properties

Defining the Contact Pressure-Overclosure Relationship

The default contact pressure-overclosure relationship used by Abaqus is referred to as the “hard” contact model. Hard contact implies that:

the surfaces transmit no contact pressure unless the nodes of the secondary surface contact the main surface;
no penetration is allowed at each constraint location (depending on the constraint enforcement method used, this condition will either be strictly satisfied or approximated);
there is no limit to the magnitude of contact pressure that can be transmitted when the surfaces are in contact.

You can define a nondefault pressure-overclosure relationship for a surface interaction. The various pressure-overclosure relationships available in Abaqus are discussed in Contact Pressure-Overclosure Relationships, and the constraint methods available to enforce these relationships are discussed in Contact Constraint Enforcement Methods in Abaqus/Standard.

Defining a Friction Model

By default, Abaqus assumes that contact between surfaces is frictionless. You can include a friction model as part of a surface interaction definition.

Details of the various friction models available in Abaqus are discussed in Frictional Behavior.

Defining Contact Cohesive Behavior

You can define contact cohesive behavior to model delamination of initially bonded surfaces or to model “sticky” contact between parts that are initially separated but bond on coming into contact, with the possibility that the bond may undergo progressive damage and fail.

Contact cohesive behavior is modeled within the general contact framework in Abaqus/Explicit and within the general contact or contact pair framework in Abaqus/Standard. Details of the contact cohesive behavior model are discussed in Contact Cohesive Behavior.

Defining a Surface Interaction Model with Damping between the Surfaces

You can define damping forces to oppose the relative motion between the interacting surfaces.

In Abaqus/Standard the specified contact damping affects the motion in the normal direction only, whereas in Abaqus/Explicit contact damping can affect both the relative tangential motion and the motion normal to the surfaces.

The details of the contact damping model are discussed in Contact Damping.

Defining Contact Blockage in Abaqus/Explicit

In Abaqus/Explicit you can control the combination of surfaces that can cause blockage of flow out of a surface-based fluid cavity. The details of contact blockage are discussed in Contact Blockage.

User-Defined Interfacial Constitutive Behavior

Instead of choosing one or some combination of the various interfacial behavior models that are available in Abaqus, you can define any special or proprietary interfacial constitutive behavior through a user subroutine. In Abaqus/Standard you can use the subroutine UINTER; whereas in Abaqus/Explicit you can use VUINTER if you are using the contact pair algorithm and VUINTERACTION if you are using the general contact algorithm.

In Abaqus/Explicit a penalty enforcement of the contact constraint must be used for interacting surfaces whose interfacial behavior is governed by VUINTER or VUINTERACTION.

Details of the definition of a user-defined interfacial constitutive behavior are discussed in User-Defined Interfacial Constitutive Behavior.

Defining a Pressure Penetration Load in Abaqus/Standard

You can define pressure penetration loads to simulate the penetration of fluid between two contacting surfaces in Abaqus/Standard. The details of the pressure penetration model are discussed in Fluid Pressure Penetration Loads.

Defining CZone Crush Characteristics in Abaqus/Explicit

The CZone capability in Abaqus/Explicit integrates material, element, and contact modeling aspects to simulate crushing of laminated composites. This capability is discussed in CZone Analysis.

Defining the Interaction of Debonded Surfaces in Abaqus/Standard

You can allow two initially bonded surfaces to debond in Abaqus/Standard, as discussed in Crack Propagation Analysis. The details of the contact interaction model after debonding are discussed in Interaction of Debonded Surfaces.

Dependence of Contact Properties on Rates of Relative Motion

For cases in which contact properties depend on rates of relative motion, Abaqus/Explicit uses a filtered rate of relative motion to compute the corresponding contact property, as discussed in Filtering Rates of Relative Motion. If dependence of a contact property is based on interpolation of tabular data, Abaqus/Explicit uses logarithmic interpolation of rates of relative motion by default and linear interpolation with respect to other independent variables, as discussed in Interpolating Tabular Data with Respect to Rates of Relative Motion. Abaqus/Standard does not filter rates of relative motion and uses linear interpolation of all tabular data.

Filtering Rates of Relative Motion

Certain contact properties depend on slip rate or rate of separation. Abaqus/Explicit filters these rate measures to minimize the effects of high frequency noise; whereas Abaqus/Standard does not filter the rate measures. The formula used in Abaqus/Explicit to filter slip rate or rate of separation is

{\dot{\bar{δ}}}_{c u r r} = ω \frac{Δ δ}{Δ t} + (1 - ω) {\dot{\bar{δ}}}_{p r e v} .

Here, $Δ δ$ is the increment change in slip or equivalent separation over the time increment $Δ t,$ , and ${\dot{\bar{δ}}}_{c u r r}$ and ${\dot{\bar{δ}}}_{p r e v}$ are current and previous filtered values, respectively, of the equivalent rate of separation or rate of slip at a node. The factor $ω, (0 < ω \leq 1),$ facilitates filtering high-frequency oscillations associated with rate-dependent behavior. The default value of $ω$ is 0.9. A value of $ω = 1$ provides no filtering effect.

For discussion of the dependence of th friction coefficient on slip rate for both tabular dependence and for exponential decay friction behavior, see Frictional Behavior. For discussion of the dependence of cohesive damage initiation and evolution parameters on the effective rate of separation, see Contact Cohesive Behavior.

Input File Usage

Use the following option to define a constant filter factor:

SURFACE INTERACTION, RATE FACTOR= $ω$

Abaqus/CAE Usage

Defining a constant filter factor is not supported in Abaqus/CAE.

Interpolating Tabular Data with Respect to Rates of Relative Motion

Interpolation associated with tabular dependence of friction coefficients and cohesive damage parameters in Abaqus/Explicit can be logarithmic or linear with respect to rate dependencies. Abaqus/Standard always uses linear interpolation for tabular dependence.

The formula for logarithmic interpolation to determine the value of a given parameter $ρ$ for a filtered slip/separation rate ${\dot{\bar{δ}}}_{c u r r}$ from neighboring data points $({\dot{δ}}_{1}, ρ_{1})$ and $({\dot{δ}}_{2}, ρ_{2})$ is

ρ = ρ_{1} + \frac{\ln (\frac{{\dot{\bar{δ}}}_{c u r r}}{{\dot{δ}}_{1}})}{\ln (\frac{{\dot{δ}}_{2}}{{\dot{δ}}_{1}})} (ρ_{2} - ρ_{1}) .

The formula for linear interpolation is

ρ = ρ_{1} + \frac{({\dot{\bar{δ}}}_{c u r r} {\dot{- δ}}_{1})}{({\dot{δ}}_{2} - {\dot{δ}}_{1})} (ρ_{2} - ρ_{1}) .

Tabular data as a function of slip/separation rate is often provided at evenly spaced intervals on a logarithmic scale. Consider logarithmic and linear interpolation schemes for ${\dot{\bar{δ}}}_{c u r r} = 3$ between data points at ${\dot{δ}}_{1} = 1$ and ${\dot{δ}}_{2} = 10.$ . Logarithmic interpolation gives $ρ$ approximately halfway between $ρ_{1}$ and $ρ_{2}$ ; whereas linear interpolation gives $ρ$ approximately 22% of the way between $ρ_{1}$ and $ρ_{2}$ .

Abaqus/Explicit internally converts (or “regularizes”) tabular dependencies to equally spaced intervals of independent variables to efficiently determine which data points to interpolate between. With logarithmic interpolation, these intervals are equally spaced on a logarithmic scale, often resulting in dramatically fewer intervals when data you provide is orders of magnitude over the slip/separation rates. Abaqus/Standard does not regularize tabular data.