Effects of Control Modes and Process Parameters on Interfacial Evolution and Mechanical Performance in Ultrasonic Welding of Woven GF / PPS Composites

Ultrasonic welding of eight‐harness satin woven glass‐fiber‐reinforced polyphenylene sulfide (GF/PPS) composites was investigated by comparing time‐, energy‐, and displacement‐controlled modes and examining the coupled effects of vibration amplitude, welding force, and normalized sonotrode travel. Lap‐shear testing, power–time analysis, metallography, micro‐computed tomography (micro‐CT), and scanning electron microscopy (SEM) were combined to investigate process–structure–property relationships. Nine representative SEM fracture fields were quantitatively classified into Pore/void, Residual resin, and Broken fibers regions. Their projected area fractions were related to mean lap‐shear strength (LSS) alongside micro‐CT‐derived internal porosity. Joint strength depended on the combined welding parameters, reaching 21.17 ± 0.66 MPa for the strongest investigated 90° condition. At matched normalized travel, lower representative internal porosity was consistently associated with higher LSS. Greater areas of fiber‐fracture features and smaller pore/void regions on the fracture surfaces also corresponded to improved joint performance, reflecting changes in the involvement of adjacent fiber‐reinforced regions during failure. These findings clarify interfacial consolidation, defect evolution, and fracture behavior and provide a basis for subsequent process‐window optimization and quantitative weld‐quality assessment of woven GF/PPS composites.