Materials Today Communications 38 (2024) 108343 Available online 10 February 2024 2352-4928/© 2024 Elsevier Ltd. All rights reserved. Experimentation on dynamic compressive response of bio-inspired helicoidal structured Basalt/Hemp/polyurethane rubber sandwich composites Darshan Gowda a , Vishwas Mahesh b , Vinyas Mahesh c, d, * , KS Ravishankar a a Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal, Mangaluru 575025, India b Department of Industrial Engineering and Management, Siddaganga Institute of Technology, Tumkur 572103, India c Department of Engineering, City, University of London, EC1V 0HB, United Kingdom d Department of Mechanical Engineering, National Institute of Technology Silchar, Assam 788010, India A R T I C L E INFO Keywords: Polyurethane rubber composite Dynamic compression test In-plane loading Through-plane loading Strain-rate parameters Damage analysis ABSTRACT In this article, to incorporate sustainability, enhance recyclability and achieve a good trade-off between the cost- weight-energy absorption performance, bioinspired helicoidal structured Basalt (B)/Hemp (H)/Polyurethane (PU) rubber hybrid composites are proposed, and their dynamic compressive response is experimentally inves- tigated using a split Hopkinson pressure bar (SHPB) setup. These composites’ high strain rate performance subjected to both in-plane and through-plane directions are studied. The strain rates ranging from 4254 to 10,750 s -1 are achieved by varying the striker bar’s input pressure. In addition, the performance of the bio- inspired helicoidal design is compared against the uniform monolithic and hybridised fibers laminated struc- tures. The experimental results suggest that the dynamic compressive properties of Basalt/Hemp-helicoidal (BH- helicoidal) laminates were on compar with that of B-laminates, achieving an almost 30% weight reduction. The optimised fiber orientation at a helical angle of 12 0 enhances interlaminar shear strength, mitigating buckling and delamination failures, thereby improving BH-helicoidal laminate’s structural integrity and dynamic compressive properties. Further, the through-plane dynamically loaded samples displayed better compressive properties due to increased stiffness than in-plane samples. The PU rubber matrix was thermally softened at higher strain rates, enhancing the flow stress. The strengthening mechanism of the proposed composites was evaluated through Cowper-Symonds, strain rate sensitivity, and thermal activation volume parameter. Macro- scopic and microscopic imaging was proposed to understand the damage behaviour of laminates as a function of loading direction. Overall, BH-helicoidal laminate is favoured for ballistic application due to its cost-effectiveness and sustainable design. 1. Introduction Fiber-reinforced polymer composites (FRPCs) are widely favoured in dynamic loading applications due to their superior mechanical proper- ties compared to metals. These applications encompass ballistic impact, aircraft, automobile accidents, naval structures, ship hulls, and civil construction, where FRPCs often serve as a lightweight core structure between intensified metallic sheets. While these composites excel in tensile and bending strength, their compressive strength is compara- tively lower, particularly under high strain rates [1–3]. Designing FRPCs with static properties for dynamic loading scenarios may result in overly conservative approaches, necessitating a comprehensive understanding of material behaviour under high-strain rate compressive loading. The Split Hopkinson Pressure Bar (SHPB) is vital for studying ma- terial responses under high compressive strain rates. Researchers have explored various materials, including synthetic and natural fibers, in hybrid forms within polymer matrices [1]. Equal importance is given to natural fibers for their strength, eco-friendliness, and cost-effectiveness [4]. Omar et al. [5] demonstrated superior compressive properties of jute composites at high strain rates. Researchers recommend combining synthetic fibres with natural fibres to balance cost-effectiveness and performance. Different stacking sequences like cross-ply, quasi-iso- tropic, inter-ply, and intra-ply configurations are explored for dynamic property evaluation. Bandaru et al. [6] suggest intra-ply laminates for protective structures, and bio-inspired helicoidal structures are * Corresponding author at: Department of Engineering, City, University of London, EC1V 0HB, United Kingdom. E-mail addresses: vinyas.mahesh@city.ac.uk, vinyas@mech.nits.ac.in (V. Mahesh). Contents lists available at ScienceDirect Materials Today Communications journal homepage: www.elsevier.com/locate/mtcomm https://doi.org/10.1016/j.mtcomm.2024.108343 Received 21 December 2023; Received in revised form 21 January 2024; Accepted 7 February 2024