Semester of Graduation
Fall 2025
Degree
Master of Science (MS)
Department
Mechanical and Industrial Engineering
Document Type
Thesis
Abstract
Interest in the repair and reuse of thermoplastic composites (TPCs) is growing, especially for lightweight space/lunar structures. Ultrasonic welding (USW) is a promising joining technique by which vibration is applied to create heat. An energy director (ED) is used at the joint interface to concentrate heat generation to the desired surface. This work explores the effect of dissimilar ED materials on the disassembly repair of TPCs using USW, to potentially tailor weld properties for specific applications. Single lap joints were created using carbon fiber (CF)/polyether ether ketone (PEEK) adherends with PEEK, polyphenylene sulfide (PPS), polyetherimide (PEI), and low melt polyaryletherketone (LM-PAEK) as EDs. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and degree of healing tests were performed on all ED materials. PPS showed the least compatibility due to the large difference between its melting temperature (281.9°C) and the PEEK TPC matrix (345.0°C). Regular welds used PEEK and PEI EDs welded at 1000 N and PEI and PPS EDs welded at 500 N; these samples all initially had 40% travel (the sonotrode moved 40% of the ED’s thickness downwards). Low travel welds used PEEK, PEI, and LM-PAEK EDs welded with 20% travel and 750-800 N of welding force. Regardless of the initial weld parameters, significant interlaminar fracture occurred upon disassembly. PEEK (1000 N) and PEI (1000 N) had comparable LSSs (29.4 MPa and 30.1 MPa) to the low travel PEEK and PEI samples (31.3 MPa and 28.0 MPa). Samples were rewelded for two repair cycles, but LSS recovery was low due to the poor joint surface contact from the damaged interfaces. LSS recovery typically varied between 25% and 50% for both repairs. However, low travel welds were only repaired once because the 20% travel could not overcome the damage incurred after the first repair. The LM-PAEK samples could not be repaired at all, likely due to reduced material compatibility.
Date
10-23-2025
Recommended Citation
Friedman, Emily Nicole, "ENABLING ASSEMBLY AND REPAIR OF DISSIMILAR THERMOPLASTIC COMPOSITES FOR SPACE APPLICATIONS VIA ULTRASONIC WELDING" (2025). LSU Master's Theses. 6251.
https://repository.lsu.edu/gradschool_theses/6251
Committee Chair
Genevieve Palardy