Browsing by Author "Koc, Bahattin"

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Citation - WoS: 3
Citation - Scopus: 3
4D Printing of Reusable Mechanical Metamaterial Energy Absorber, Experimental and Numerical Investigation
(Iop Publishing Ltd, 2025) Fallah, Ali; Saleem, Qandeel; Scalet, Giulia; Koc, Bahattin
This study investigates the compression behavior, energy absorption, shape memory properties, and reusability of 4D-printed smart mechanical metamaterials. Four structural configurations, i.e. honeycomb, re-entrant, and two modified re-entrant designs were developed to assess microstructure effects. Samples were fabricated using Polylactic Acid (PLA), a widely used shape memory polymer (SMP) in 4D printing, and polyethylene terephthalate glycol (PETG), an emerging SMP with demonstrated shape memory performance in recent studies. Cold-programming-induced shape recovery was evaluated at room temperature, simulating real-world conditions. Finite element simulations of compression and shape memory cycles matched experimental results well. Auxetic samples with negative Poisson's ratios showed superior energy absorption. However, only PETG demonstrated sufficient reusability, while PLA proved unsuitable for reusable designs. The PETG-3 modified re-entrant structure exhibited the best performance, with high energy absorption, delayed densification onset, and shape recovery and reusability factors of 0.95 and 0.96, respectively. Findings highlight the importance of considering both shape recovery and reusability when designing smart structures to address industrial challenges.
Citation - WoS: 1
Citation - Scopus: 1
4D-Printed Continuous Fiber-Reinforced PLA/TPU Auxetic Composites: Mechanical Performance, Energy Absorption, Shape Recovery, and Reusability Evaluation
(SpringerNature, 2025) Alkan, Atakan; Ranjbar Aghjehkohal, Amin; Fallah, Ali; Koc, Bahattin
This study explores the mechanical performance, energy absorption, shape recovery, and reusability of 4D-printed continuous carbon fiber-reinforced auxetic composite structures based on PLA/TPU blends, designed for load-bearing applications. PLA-TPU mixtures with different TPU content were developed to optimize the balance between flexibility and strength, with carbon fibers incorporated to enhance the mechanical properties of the resulting composites. Thermo-mechanical characterization of the blends was conducted, followed by a detailed evaluation of the structures' mechanical behavior and energy absorption capacity under room temperature conditions, simulating practical industrial scenarios. The shape recovery performance of these composite structures was also investigated. To assess reusability, the programming-recovery cycle was repeated five times, analyzing the retention of mechanical properties and shape recovery over multiple cycles to determine durability. Results revealed that TPU integration provided sufficient flexibility for cold programming, while carbon fiber reinforcement significantly enhanced stiffness and strength. The 4D-printed composites exhibited consistent shape recovery and maintained mechanical integrity after five cycles, confirming their reusability. These findings demonstrate the potential of 4D-printed PLA/TPU-based carbon fiber-reinforced composites as smart, durable materials for load-bearing applications in industries such as biomedical engineering, automotive, and aerospace.