Minkook Kim

Basalt fiber‐reinforced polymer (BFRP) composites are gaining attention as sustainable alternatives to conventional fiber‐reinforced polymers owing to their favorable mechanical properties and environmental advantages. However, their structural performance under dynamic loading remains insufficiently explored, particularly in geometrically complex configurations, due to the inherently low interlaminar strength of BFRPs. In this study, the dynamic impact behavior of a hat‐shaped BFRP composite structure was investigated using experimental testing and finite element analysis (FEA). A previously developed cellulose nanocrystal (CNC) surface treatment technique was applied to the BFRP to improve interfacial bonding and damage tolerance. This approach resulted in an increased energy absorption capacity and resistance to delamination compared with those of the unmodified BFRPs. Furthermore, the influence of span length (80, 140, and 200 mm) on failure mechanisms and energy absorption was analyzed. The results revealed a clear transition in failure modes from shear‐induced brittle failure at shorter spans to tensile‐dominated progressive failure at longer spans. The numerical analyses strongly agreed with the experimental results. This work provides novel insights into the span‐dependent and crashworthiness of BFRP composites and demonstrates their potential for use in lightweight and energy‐absorbing structures.

Three-dimensional printing is a highly promising manufacturing technology that enables easy production of complex shapes. Composite lattice structures are highly efficient, having the advantages of fiber-reinforced composites and the excellent structural performance of lattice configurations. Highly efficient structures can be developed by combining the benefits of 3D printing and composite lattice structures. This study examined the effect of printing path and axial angle in joint areas on the compressive strength of composite lattice unit cells fabricated via continuous fiber 3D printing. Compression tests were conducted to analyze deformation, failure modes, and causes of failure. A finite element model was used to analyze buckling behavior and establish design criteria. Results showed that the printing path significantly influenced failure mode and strength, while a fabrication method without a defect at the joint was important for improving structural performance. Finally, design criteria, in terms of the knockdown factor and in-plane bifurcation buckling behavior, were developed based on experimental and numerical results.

Despite the exceptional mechanical properties of epoxy‐based carbon fiber‐reinforced plastic (CFRP), its commercial potential is limited due to high production costs and manufacturing difficulties. As a promising alternative, thermoplastic‐based CFRP (CFRTP) offers simpler manufacturing, lower cost, and recyclability. This study presents a strategy to overcome challenges for CFRTP manufacturing by using a low molecular weight (MW) thermoplastic that forms high‐MW assemblies via dynamic molecular interactions. A quadruple hydrogen‐bonding unit (UPy)‐end functional polyamide (PA‐UPy) was synthesized by simple solid‐state melt reaction of powdered mixture of PA12 and UPy‐containing isocyanate. An increase in tensile properties was observed with an increase in crystallinity by the adoption of UPy moiety. The adoption of PA‐UPy in CFRTP, prepared by simply stacking the powder and CF fabric followed by hot pressing, enhanced the composite's tensile and interlaminar properties. Therefore, this process is proposed as a simple and effective method to improve the mechanical properties of CFRTP. Highlights: Synthesis of PA‐UPy achieved via solid‐state melt reaction of PA and UPy. PA supramolecular structure boosts tensile strength and modulus of films and CFRTP. UPy‐NCO doubles the interlaminar shear strength of PA‐UPy‐based CFRTP.

Adhesive bonding is a suitable joining method to satisfy the increasing industrial demand for carbon fiber-reinforced polymers without the need for a machining process. However, thermoplastic-based carbon fiber-reinforced polymers have small adhesive strength with structural thermoset adhesives. In this study, an ultraviolet irradiation surface treatment was developed to improve the adhesive bonding strength for polyamide-based carbon fiber-reinforced polymer. The type of ultraviolet wavelength, irradiation distance and irradiation time were optimized. Surface treatment with simultaneous UV irradiation of 185 nm and 254 nm wavelength generated unbound N-H stretching that was capable of chemical bonding with epoxy adhesives through a photo-scission reaction of the amide bond of polyamide matrix. Therefore, ultraviolet irradiation treatment improved the wettability and functional groups of the polyamide-based carbon fiber-reinforced polymers for adhesive bonding. As a result, the adhesive strength of the polyamide-based carbon fiber-reinforced polymers was increased by more than 230%.