Modeling Wear in Ansys Mechanical

Wear refers to the gradual removal of material from a surface due to mechanical contact. In practical engineering systems like bearings, gears, fasteners, and seals, wear can influence long-term durability and lead to performance degradation. Ansys Mechanical enables users to simulate this phenomenon using empirical wear models. Chief among them is the Archard wear model.

In this blog, we’ll explore how wear is modeled in Ansys, how to implement the Archard model, the use of APDL commands, postprocessing strategies, and meshing guidelines.

What Is Wear in Finite Element Analysis?

In FEA, wear is modeled by shifting nodes on contact surfaces to replicate material erosion. The simulation iteratively updates geometry and recalculates equilibrium after each update, making the process nonlinear.

Ansys handles wear at the continuum scale using empirical laws that relate pressure, relative motion, and material resistance to surface loss.

Supported Contact Elements

Wear modeling is only available for the following contact element types:

• CONTA173
• CONTA174
• CONTA175

To activate wear, a material definition with the TB,WEAR model is applied to these contact elements.

Wear Modeling Options

There are two types of wear models:

1. Archard Wear Model (native)

2. User-Defined Wear Model (custom via USERWEAR)

This article focuses on the Archard method.

Archard Wear Model Explained

The Archard model approximates wear rate using the relationship:

Where:

• K = Wear coefficient

• H = Hardness of material

• P = Contact pressure

• v = Relative sliding velocity

• m = Pressure exponent

• n = Velocity exponent

By default, the wear vector points opposite the contact normal, though this can be changed using directional inputs.

APDL Setup: Defining Wear Using TB,WEAR and TBDATA

To activate wear modeling in Ansys Mechanical, a dedicated material model must be defined using the TB,WEAR command. This command, combined with TBDATA, allows users to input wear-related material constants that control how wear is calculated and applied across contact surfaces.

The basic Syntax for implementing the Archard Wear Model is:

• The ARCD keyword activates the built-in Archard model.

• The material ID (1 in this case) must correspond to a contact element set (e.g.,CONTA172, CONTA174 or CONTA175).

Additional Archard wear constants are defined as follows:

• The Archard equation implemented in Ansys is generalized, meaning that pressure and velocity dependencies are tunable via m and n.

• Omitting C5-C8 uses the default direction (opposite to contact normal).

   

Estimating Material Hardness

In plasticity-based material models like TB,BISO, C2 (hardness) can be estimated automatically from the current yield stress:

Conditions:

• • Applicable only if underlying elements are: PLANE182, PLANE183, SOLID185, SOLID186, SOLID187 or SOLID285

  • No wear will occur in the first substep because prior yield data is not yet available.

Understanding C5: Behavior Flags for Wear Application

The fifth constant, C5, alters how the wear increment is calculated and applied. Each option is suited to a different modeling scenario:

• Use C5 = 1 for smoother wear behavior on asymmetric contact between dissimilar meshes.

• Use C5 = 10 or 11 to ensure uniform wear distribution across interfaces.

• Use C5 = -99 to debug or study wear trends without affecting convergence or geometry.

Advanced Use: Directional Wear Control

If wear must be applied in a direction other than opposite the contact normal, use direction cosines:

This is useful when:

• Wear is induced by rotational contact

• Oblique sliding dominates material removal

• Experimental calibration justifies a directional bias

Ensure that (nx, ny, nz) represent a unit vector in global coordinates.

Time- and Temperature-Dependent Wear

Use TBFIELD or TBTEMP to define time- or temperature-varying wear coefficients.

Time Dependence:

Use this for applications like fretting or fatigue where wear evolves slowly over time.

Temperature Dependence:

Apply this in cases where sliding friction causes localized heating and temperature affects material resistance.

Accelerating Wear Simulation

While wear analysis in Ansys is inherently nonlinear and iterative, automation techniques can significantly improve efficiency, especially for long-duration simulations. Ansys offers two primary methods for accelerating and controlling wear progression: automatic wear scaling (AUTS) and cycle-by-cycle wear scaling (CBCS). These approaches allow the simulation to represent extended physical timeframes without requiring excessive substeps, enabling engineers to efficiently evaluate long-term wear behavior under steady or cyclic loading. Both methods can be customized to balance speed and accuracy depending on the application's requirements.

Automatic Scaling (AUTS)

Scales wear at every substep based on contact penetration depth.

Cycle-by-Cycle Scaling (CBCS)

Updates wear only at the end of load cycles. Ideal for periodic loads.

AUTS is generally smoother; use CBCS only when cycles are clearly defined.

Geometry Update and Equilibrium

At each substep, once convergence is met, wear increments shift surface nodes. This temporarily disrupts equilibrium, which is resolved through additional iterations. Small timesteps are advised to avoid issues like unexpected contact separation.

Mesh Considerations During Wear

Wear modeling alters surface geometry and may distort underlying solid elements. To manage mesh integrity:

• Use rezoning or nonlinear adaptivity (NLADAPTIVE)

• Enable morphing for tet/brick elements

• Avoid mixed meshes in contact regions

Example: NLADAPTIVE Setup

Explanation of Parameters:

• contwearel: Component name containing the contact elements undergoing wear

• add: Adds a new criterion for triggering adaptive remeshing

• contact: Type of criterion to evaluate (based on contact conditions)

• wear: Subtype specifying that wear is the criterion of interest

• 0.75: Threshold; triggers remeshing when 75% of material is worn

• on: Activates the adaptive process

• 5: Frequency; the program checks the wear criterion every 5 substeps

• 1,7: Start and end time between which this adaptivity rule is active

Postprocessing Wear Data

Extracting Results:

• NMISC: Total wear vector per node

• NLHIST: Wear volume tracking and auto-stop criteria

Visualization:

• View wear displacement in .rst file

• Plot worn vs. unworn geometries

• Analyze trends in contact pressure or surface damage

USERWEAR Subroutine: When Customization Is Needed

For highly specific wear models, implement the USERWEAR routine.

Input variables include:

• Slip, stress, and temperature

• Contact node coordinates

• Material constants (from TBDATA)

Define output:

• WearInc = Wear increment per substep

• WearDir = Optional vector direction

Ideal for applications requiring custom physics or highly nonlinear wear behavior.

Final Thoughts

Ansys Mechanical offers robust wear modeling capabilities, particularly through the Archard model. With careful consideration of wear direction, scaling, and element distortion, engineers can simulate realistic material degradation over time.

To summarize:

• Use Archard for general cases, USERWEAR for custom needs

• Apply scaling for efficiency

• Protect mesh quality with rezoning or adaptivity

• Postprocess wear effects to inform design improvements

By integrating these tools, engineers can confidently predict wear performance and make data-driven design choices.