Advances in Science and Technology Vol. 171

Abstract: Fiber-reinforced polymers (FRP) bars have gained widespread recognition as a viable alternative to steel reinforcement in concrete structures over the past decades due to their advantages in corrosion resistance, durability, and lightweight properties. However, existing research and current design codes do not adequately address the dynamic compressive response of FRP bars under high-impact loading conditions. This gap in knowledge presents a significant challenge in accurately predicting the response of FRP-reinforced structures under extreme loading events. Therefore, it is essential to investigate the response of FRP bars under dynamic loading conditions across a range of strain rates to improve design codes and ensure the reliability and safety of structures subjected to such conditions. This study presents an experimental program conducted on basalt FRP (BFRP) bars subjected to dynamic testing using the Split Hopkinson Pressure Bar (SHPB) apparatus. The 12-mm BFRP bars are subjected to impact loading at high strain rates ranging from 345 to 1300 s^-1. These varying strain rates are achieved by adjusting the pressure of the impact bar. A high-speed camera is employed to capture the failure mechanisms and provide visualization of the deformations during loading. The study focuses on evaluating the stress-strain relationship and failure modes of the tested BFRP bars under various loading rates. The results revealed that at higher strain rates of ∼1300 s^-1, BFRP bars lost 40% of its compressive strength when compared to its quasi-static strength (tested at 3.5 x 10^-4 s^-1). At lower strain rates (∼345 s^-1), 20% of the quasi-static strength is lost. At intermediate strain rates (∼590-740 s^-1), one sample showed a strength reduction of 26%, while another sample showed a strength gain of 10%. This proves that BFRP bars are highly strain-rate dependent. Additionally, the results show relatively significant variation in the behavior of the samples at similar strain rates, indicating microstructural differences between them.

Abstract: The newly developed hybrid FRP-concrete-steel double-skin tubular column (DSTC) integrates both high corrosion resistance and load-bearing capacity, enabling its potential for applications in high-temperature, high-humidity, and highly corrosive island environments, compared to traditional reinforced concrete or steel columns. However, from the perspective of multi-hazard mitigation, existing research on DSTC columns has predominantly focused on their static and seismic performance, while studies on the behavior of DSTCs under near-field blast load are scarce. In this paper, three glass fiber reinforced polymer (GFRP)-concrete-steel double-skin tubular columns (GFRP-DSTCs) were fabricated and tested under near-field explosion with same TNT equivalent but different scaled distances (ranging from 0.368 m/kg^1/3 to 0.240 m/kg^1/3). The GFRP tube was made through filament-wound technique and vinyl ester resins, and the glass fibers were oriented at ±80º with respect to the longitudinal axis of the column. The GFRP-DSTCs were installed in a field with bottom end fixed and top end simply supported. The results show that under near-field blast load, the damage to GFRP-DSTCs were concentrated in the region close the charge, where material failure and localized deformation were observed. When the scaled distance was 0.368 m/kg^1/3, the specimens showed only localized inward bending, with the surface of the GFRP tube on the blast-facing surface subjected to the impact of detonation products, resulting in a roughened surface. Additionally, the localized surface turned black due to the explosion fireball and numerous circumferential cracks developed on the other area. While the scaled distance was 0.301 m/kg^1/3, the specimen exhibited significant localized rupture of the GFRP tube at the blast-facing surface, accompanied by lamination along the thickness direction of the tube, and the concrete at the blast-facing surface was extensively crushed. As the scaled distance further decreased to 0.240 m/kg^1/3, the concrete crushing zone extended from the blast-facing surface to the entire side surface with the inner steel tube exposed and bent.

Abstract: In current days, sandwich structures have become popular due to their flexibility with design requirements and excellent performance under extreme loads, such as blast. There are different strategies for enhancing the blast resistance of such sandwich structures. Including an additional layer of polyurea and stiffeners are widely used techniques that may enhance the performance of the panels under high-rate loadings. In this study, the effects of polyurea and stiffeners on the protection of a steel and aluminum foam sandwich panels is studied. Effective configuration of the panels with both polyurea and stiffeners are investigated. Here, different configuration cases of the sandwich panels: (a) panel without polyurea and stiffeners, (b) with polyurea applied on the rear face, (c) with stiffeners applied on the rear face, and (d) with stiffeners and polyurea on the rear face are investigated and compared. The finite element models of sandwich panels are developed, where steel facesheets, steel stiffeners, and polyurea are modeled with shell elements, and aluminum foam core is modeled with solid elements. Elastic-plastic, crushing foam, and hyperelastic material behaviors are implemented for steel, aluminum, and polyurea layers of the sandwich panels, respectively. The performance of the different configurations of the panels are compared in terms of the response quantities, i.e., deformation, equivalent von-Mises stresses, and energy absorption. Moreover, the damage patterns with fragmentation effect are depicted for all the considered sandwich panels. The results of the study show that both polyurea and stiffeners are the most effective configurations in protecting the sandwich structures; however, with the same thickness of polyurea and stiffener, the stiffeners show better performance than polyurea against blast load. Furthermore, it is observed that the deflection values across the configurations follow a logarithmic decay pattern.

Abstract: The present study investigates the response of precast concrete sandwich wall panels under blast load incorporating varying degrees of composite action. The percentage of composite action quantifies a panel’s composite behavior relative to a fully composite assumption, with 0% indicating a fully non-composite panel and 100% indicating a fully composite panel. For this study, the precast panel is modeled as an equivalent single degree of freedom (SDOF) system using the transformation factors. The panel is subjected to a range of blast load while the degree of composite action is varied from 0% to 100%. The response of the panels is evaluated in terms of support rotation, ductility, and support reactions. The effect of degree of composite action on the response of the panel is investigated for a range of blast impulses. The threshold blast impulse value is determined for each partial composite panel considering the moderate level of damage of the panel as per ASCE 59-11 and plastic response of the panel. Further, a range of optimum degree of composite action is identified while trading-off between support rotation and support reaction. The effect of panel span and section moment capacity on the optimum degree of composite action is investigated. It is observed that span length affects the optimum degree of composite action although moment capacity is not influential.

Abstract: An explosion generates a supersonic shock wave, causing a significant impact on human lives and properties. The consequences of the rising blast incidents result in massive loss of lives and economic loss due to the collapse of structures. The reinforced concrete columns, a critical structural member highly vulnerable to explosions, must be investigated. Ultra high performance concrete (UHPC) shows high compressive and tensile strength, making it suitable for use in high-strain-rate loading like contact explosion. This study evaluates the damage due to contact explosion on UHPC columns with different lengths to diameters (L/D) ratios of cylindrical-shaped TNT and stirrup types using the finite element (FE) model in LS-DYNA. The model is validated with the experimental data available in the literature. The detonation and propagation of blast waves are simulated by explicitly modeling the explosive and surrounding air using a multi-material Arbitrary Lagrangian-Eulerian (MMALE) formulation. Subsequent displacement control, a quasi-static load is applied to estimate the residual load-carrying capacity. The results indicate that the utilization of UHPC effectively reduces the local damage in the column and retains higher residual capacity than normal-strength concrete (NSC). Furthermore, the L/D ratio of TNT and stirrup configuration play important roles in determining the extent of damage and the residual capacity, highlighting the need to carefully consider these factors in designing columns subjected to contact explosions.

Abstract: Recently, ceramics and metal-armed structures have been replaced by ceramics combined with ultra-high molecular weight polyethylene (UHMWPE) composite laminated structures for NIJ level III and level IV body armor applications. This shift is due to the superior specific energy absorption capabilities of the ceramics/UHMWPE composites compared to traditional ceramics and metal armor; however, it comes at a higher cost. Manufacturing body armor that offers higher specific energy absorption at a lower cost is challenging. As the thickness of UHMWPE increases, both the specific energy absorption and the overall cost of the body armor increase. Additionally, there is limited experimental data to evaluate the thickness of ceramics and UHMWPE to explore the performance of NIJ level III body armor, indicating that further research is needed. In this study, six different types of ballistic plate configurations were manufactured. Following that, high velocity impact tests were conducted to investigate the effects of front and back layer thicknesses of UHMWPE (Type 1 to Type 3 plates), the effects of foam material (Type 4 plate), and the effects of different thicknesses of boron carbide (B₄C) ceramic strike face (Type 5 and Type 6 plates) on the back face signature (BFS) of the ballistic plate. It was found that the BFS of Type 5 and Type 6 ballistic plate configurations is lower by 12% and 8.5%, respectively, compared with that of the Type 4 UHMWPE/polyvinyl chloride low-density foam ballistic plate. However, the Type 5 option is cost-effective and easy to manufacture, making it the preferred choice over the Type 6 variant.

Abstract: This study evaluates the performance of a ballistic helmet made from carbon nanotube reinforced Ultra-High Molecular Weight Polyethylene composites, based on experiments conducted at the Blast Impact Simulation and Testing Laboratory, Visvesvaraya National Institute of Technology (VNIT), Nagpur, India. Authors have carried out simulations using LS-Dyna^® to understand and predict the behavior of carbon nanotube reinforced ultra-high molecular weight polyethylene composite under ballistic impact conditions. The authors have validated the Finite Element model against experimental tests using a high-pressure gas gun at VNIT, Nagpur, India, with a single impact from an ogive-shaped hardened steel projectile at an impact velocity of 573 m/s. Results showed that carbon nanotube reinforcement enhanced the composite's mechanical properties, improving its ability to absorb energy and ballistic penetration resistance. The study highlights the potential of the said composites for ballistic protection, offering a balance of lightweight material and high-impact resistance. Further, it emphasizes the importance of combining simulations with experimental tests to predict material performance and suggests further optimization for enhanced protection. This research contributes to developing advanced military, law enforcement, and civilian protective gear materials.

Abstract: This research investigates the penetration characteristics of single-nose blunt and double-nose blunt-blunt projectiles impacting thin aluminum plates using numerical analysis in ABAQUS. Finite element simulations model a 29.7g projectile impacting a 0.82mm thick aluminum plate at velocities ranging from 40 to 100 m/s. Results reveal distinct failure mechanisms, deformation profiles, and energy absorption behaviors influenced by projectile geometry. The blunt-blunt projectile exhibits a lower ballistic limit and two-plug failure, while the blunt projectile requires higher velocity for penetration, resulting in a single plug. The blunt-blunt projectile penetrates more efficiently, while the blunt projectile dissipates more energy at lower velocities. Analysis of residual velocity, impact duration, and deformation highlights the importance of projectile nose geometry in penetration performance. These insights contribute to the advancement of impact-resistant materials and structural designs for enhanced ballistic protection.

Abstract: Concrete is a widely used material for construction, playing a crucial role in infrastructural design. Recently, with the increase in threats and protection requirements, developments and investigations are continually needed in concrete for impact-resistant applications. This study investigates the ballistic performance of sixteen concrete formulations subjected to high-velocity impact using a 12.7×99 mm armour-piercing projectile fired from a single-stage gas gun at an impact velocity of 850 m/s. The experimental campaign evaluated depth of penetration (DOP), mass loss, and failure across different concrete formulations under the same test conditions. Concrete types included ordinary concrete (OC), steel- and basalt-fibre-reinforced mixes, ultra-high-performance concrete (UHPC), basalt fibre reinforced concrete (BFRC), rubber aggregate concretes (RSC), and cement-modified variants. Qualitative analysis, high-speed camera sequences, and three-dimensional (3D) scanning were employed to assess the penetration response of each configuration. Results show that UHPC formulations exhibited the best ballistic resistance, with DOP values reduced by nearly 50% compared to ordinary concrete. Steel-fibre-reinforced concretes showed a fibre-dosage-dependent improvement in DOP and material retention, with SF160 emerging as the most balanced solution. In contrast, rubber-modified mixes demonstrated higher DOP but effectively limited surface scabbing. These findings highlight the importance of material composition in optimising ballistic performance and guide the selection of concrete systems for infrastructure protection applications.

Abstract: Metamaterials have emerged as promising candidates for protective structures due to their lightweight design and energy absorption capabilities. While various lattice-based architectures have been explored, further research is needed to optimize their dynamic response and computational modeling. Recent studies highlight the superior strength-to-weight ratios of lattice metamaterials over traditional foams, yet challenges remain in balancing predictive accuracy and computational efficiency.This study introduces novel computational frameworks for the design and analysis of deterministic, hybrid, and stochastic lattice architectures. Using finite element models, different unit cell configurations are evaluated under dynamic loading, comparing beam-based models for efficiency with 3D solid models for accuracy. A comparative assessment with foam materials further examines energy absorption performance.The framework developed in this study provides a versatile tool for the automatic generation and analysis of lattice structures. Moreover, this study provides critical insights into lattice topology, computational trade-offs, and impact resistance.