Computational analysis of submerged ultrasonic welding of carbon-fibre reinforced polyamide using multi-shape energy directors

This study investigates submerged ultrasonic welding (S-USW) of carbon-fiber-reinforced polyamide (CFRP) using rectangular, triangular, and semi-circular energy directors (EDs). A 3D finite element model in COMSOL Multiphysics simulated heat generation, stress, and displacement, validated through lap shear strength (LSS) tests. Rectangular EDs generated weld-zone temperatures up to 278 °C in air and 227 °C in water, with maximum LSS of 11.6 MPa. Triangular EDs reached lower peak temperatures (167 °C in S-USW) and weld strengths below 12 MPa despite faster melting. Semi-circular EDs achieved the most favorable outcomes, producing a uniform weld-zone temperature of ~227 °C and maximum LSS of 16.42 MPa under submerged conditions. Stress analysis confirmed reduced concentration compared to other geometries. These results demonstrate that semi-circular EDs enhance heat distribution, bond strength, and joint reliability in CFRP composites. The combined computational–experimental approach offers quantitative guidance for optimizing ultrasonic welding design and parameters.