Herry Purnomo, a doctoral student from the Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia (FTUI), has completed his postgraduate studies with a GPA of 3.88, earning the distinction of Cum Laude. He is officially the 119th doctoral graduate from the Department of Mechanical Engineering and the 599th from FTUI, as declared during the public doctoral promotion session held on Tuesday (June 17).
In his dissertation titled “Fabrication of Fiber-Reinforced Polymer Composites for 122 mm Diameter Rocket Motor Tubes,“ Herry addresses the structural efficiency challenges in Indonesia’s national rocket technology, which has long relied on heavy metals such as aluminium and steel. Through the filament winding fabrication method, he developed rocket motor tubes made from carbon fibre-reinforced polymer (CFRP) and hybrid aluminium–CFRP composites—materials that are lighter, stronger, and more resistant to thermomechanical loads.
“By applying various post-processing techniques such as shrink tape, compression moulding, and vacuum compression moulding, the fabricated composites successfully reduced void content to 2.33% and achieved a fibre volume fraction of up to 61.9%. Furthermore, the addition of MWCNT nanomaterials in the epoxy resin enhanced the elastic modulus to 101.7 GPa and the tensile strength to 1,415 MPa—approaching the theoretical predictions based on the rule of mixtures,” Herry explained in his presentation.
According to Herry, innovative testing approaches such as multiaxial testing using a Modified Arcan Fixture (MAF) and one-sided thermal loading simulations more accurately represent the actual working conditions of rocket motor tubes. The results show that CFRP usage can reduce structural tube weight by up to 75% compared to metal materials, significantly increasing the propellant-to-structure ratio, approaching the ideal 90:10 target.
In his remarks, the Chair of the Session, Prof. Dr Ir. Yanuar, M.Eng., M.Sc., expressed high appreciation for the research’s contribution to the development of national defence technology. “This dissertation not only provides technical solutions to the mass efficiency problems in rocket structures but also opens up great opportunities for Indonesia’s defence industry to achieve self-reliance through composite materials,” he stated.
The research also involved static testing of the MX-100 type rocket motor tube and thermal load simulations, which demonstrated the optimal performance of the hybrid CFRP–aluminium tube under operational conditions. From an economic standpoint, composite materials offer cost efficiency due to their lightweight and high specific strength, making them a strategic choice for future rocket design.
The public doctoral defence was led by Prof. Dr. Ir. Yanuar, M.Eng., M.Sc., as Chair of the Session; Prof. Dr. Ir. Tresna Priyana Soemardi, SE, M.Si., IPU., ASEAN Eng., as the Promoter; and Prof. Dr. Ir. Hendri DS Budiono, M.Eng., and Prof. Dr. Ir. Heri Budi Wibowo, M.T., as Co-Promoters. The examining committee included Prof. Dr. Ir. R. Danardono Agus Sumarsono, DEA, PE; Prof. Ir. Jamasri, Ph.D., IPU., ASEAN Eng.; Dr. Ir. Gatot Prayogo, M.Eng.; Dr.-Ing. Mohammad Adhitya, S.T., M.Sc.; and Jos Istiyanto, S.T., M.T., Ph.D.
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