Introduction

Cold spray (CS) is a solid-state coating and additive manufacturing process where fine metal or polymer particles are accelerated to high velocities (300–1200 m/s) using a supersonic gas jet (typically air, nitrogen, or helium) and directed toward a substrate. Upon impact, these particles deform plastically and bond to the surface without melting. This unique characteristic makes cold spray ideal for temperature-sensitive materials like ABS (Acrylonitrile Butadiene Styrene), a common thermoplastic used in automotive and consumer electronics.

To understand and optimize particle impact dynamics during cold spray, numerical simulation methods are used. One of the most accurate techniques for such high-speed, large-deformation interactions is the Coupled Eulerian-Lagrangian (CEL) method.

Explanation of the CEL Method for Cold Spray Analysis

1. Why Use CEL?

Traditional simulation methods like the Lagrangian approach often struggle with mesh distortion when modeling large deformation events, such as high-speed particle impacts. The Eulerian method, on the other hand, handles large deformations well but isn’t ideal for tracking solid materials.

The CEL method combines the strengths of both:

• Lagrangian domain: For the impacting ABS particle (material follows the mesh).
• Eulerian domain: For the gas jet and sometimes the substrate (mesh is fixed, material flows through it).

This makes CEL ideal for simulating:

• High-velocity impact.
• Thermomechanical interactions.
• Material flow, deformation, and potential bonding behavior.

Cold Spray of ABS: Key Simulation Aspects with CEL

2. Material Behavior of ABS

• ABS is a thermoplastic polymer with complex, rate-dependent behavior.
• In CEL, ABS is modeled with:
  • A viscoelastic-plastic constitutive model.
  • Temperature-dependent properties (important due to adiabatic heating on impact).
  • Optional damage models to predict fracture or failure.

3. Simulation Steps

1. Pre-processing:
   • Define geometry: a spherical ABS particle and a flat substrate.
   • Assign material properties (density, yield strength, heat capacity, etc.).
   • Mesh: fine for particle; coarser for substrate or Eulerian domain.
2. Boundary and initial conditions:
   • Initial velocity of the particle (from 300–1000 m/s).
   • Ambient temperature and gas properties (if modeled).
3. Contact interaction:
   • Define particle-substrate interaction with friction and thermal conduction.
4. Run CEL simulation: Track deformation, velocity changes, and temperature evolution.

4. Analysis Outcomes

• Particle deformation: How the ABS particle flattens or splashes.
• Temperature rise: Due to plastic work and friction.
• Bonding behavior: Indirectly inferred from contact duration, pressure, and temperature.
• Residual stress and potential defects.

Cold spray analysis of ABS particles using the CEL method provides deep insights into the deformation and bonding mechanisms during impact. This simulation approach is particularly useful for optimizing spray parameters (e.g., velocity, particle size) and understanding failure modes (e.g., rebounding or fragmentation). The CEL method’s ability to handle complex material behavior and high deformation makes it a valuable tool in developing polymer-based cold spray technologies.