Design and Validation of PEEK-Based Curved Lap Joints for Ultrasonic Welding in On-Orbit Rapid Construction of Truss Structures

Abstract To address uneven energy distribution and insufficient melting in vacuum ultrasonic welding of polyetheretherketone (PEEK) joints for on-orbit construction, this study proposes a segmented “Once clamping, Twice welding” strategy. By modeling ultrasonic heating and heat conduction, the mechanism of geometric control on melting was revealed. A triangular energy director (tip angle 50 deg, spacing 2 mm) was designed, achieving a peak heating rate of 744.93 °C/s—3.2 times higher than semicircular or rectangular designs. Vacuum experiments with high-speed infrared and imaging monitoring showed that the segmented process (1.5 s near-field → 30 s cooling → 1.5 s far-field) overcame energy attenuation issues. This resulted in a uniform fusion ratio of 91.7% and a joint tensile strength of 76.5 MPa (85.4% of base PEEK), surpassing the 48.6 MPa from conventional single welding by 57.4%. The method resolves key energy distribution challenges in multilayer curved joints, supporting the rapid construction of large-scale space infrastructure.