Advances in Science and Technology Vol. 171

Abstract: Assessment of structural responses to dynamic loads, such as impact, is essential because these loads can cause severe damage to infrastructure and pose risks to human lives. Important elements of structures, like bridge piers and building columns, are particularly vulnerable to impact loads from vehicle collisions or rockfalls. To address such critical loading, we conducted impact tests to analyze the responses of post-tensioned steel-reinforced concrete (RC) column sections under controlled impact loads. A large drop tower was used to accelerate a rigid cylindrical projectile with a flat nose, having a diameter of 100 mm, a length of 380 mm and a weight of 21.6 kg. Reaction forces were measured using load cells, while accelerometers captured high dynamic accelerations during impact. Both the reinforced concrete columns and the impactor were equipped with a speckle pattern, facilitating Digital Image Correlation (DIC) analysis. The DIC system was used to track the impactor velocity, to measure deflections, and to observe of the cracking patterns on the column surfaces. In total, six 200 mm × 300 mm × 1500 mm different column specimens were tested under two distinct impact velocities: 25 m/s and 33 m/s. The clear span was 1000 mm and the longitudinal and transverse reinforcement ratios were approximately 2 % and 0.7 %, respectively. Four columns were post-tensioned to two levels of 34 % and 67 % of their axial capacity and compared to two reference specimens with no axial force. This range of axial force was chosen to have a detailed evaluation of how different levels of post-tensioning influenced structural performance, specifically in terms of reaction force, lateral deflection and cracking patterns under impact loading. We observed that the mass of debris generated by the impact increased with impact velocity. In most cases, the debris mass also increased with a higher axial force ratio. This trend is likely due to the release of elastic energy stored within the post-tensioned specimen during the impact event, which intensified the dynamic response. Specifically, we noted a pronounced spalling of the concrete cover, primarily on the rear side of the impact, which led to the exposure of the reinforcement. The results of this study can serve as basis for analytical and numerical models and as guideline for testing additional parameters in similar specimens.

Abstract: Structural robustness is vital to prevent disproportionate damage in a progressive collapse of a structure. Current assessment methods in building structures, such as the notional removal of structural members, are unable to capture cascading effects from debris impact loading and chained hazard scenarios. Vehicular impact with penetration into the building volume is an example of a plausible chained hazard scenario. In this study, the adequacy of notional damage methods was assessed for vehicular impact loading on building structures and a comprehensive framework was developed to address key limitations in conventional design methods against vehicular impact. The conventional approaches have relied on prescriptive forces and simplified models and have over-looked important phenomena, such as variable vehicle stiffness and energy dissipation mechanisms. The use of the vehicular impact framework has been exemplified using a model for progressive collapse to assess the consequences of successive time-delayed column loss on the structural response from the penetration of a lorry. The time-delay of successive column loss from vehicular impact was determined by considering the kinetic energy and energy dissipation mechanisms. Higher initial velocities lead to higher post-impact velocities after the initial impact on a column and to a reduction in time between successive failures, thus heightening the likelihood of cascading failures in structural columns and progressive collapse. Progressive collapse simulations revealed that a building structure may have sufficient robustness to prevent progressive collapse when subjected to the loss of single columns. However, successive column losses triggered an extensive progressive collapse.

Abstract: Atomic Weopons Establishment (AWE) is tasked with substantiating the performance of numerous systems in diverse environments. Often this involves both experimental trials and numerical analysis undertaken in an integrated manner. One area in which this approach has been applied is the assessment of structural response to blast loading. Experimental testing is undertaken using blast tunnels/tubes to generate surrogate environments and obtain appropriate load profiles. AWE’s Air Blast Tunnel (ABT) – a unique facility for generating large-scale long duration blast waves – is commonly employed for this purpose. Modelling activities, including finite element analysis (FEA), hydrocode analysis and engineering calculations, are performed in conjunction with the trials to optimise their output. Data collected during the tests is subsequently exploited to facilitate model validation. Validated models are then used to study the true environments of interest. To complement the ABT and provide a facility in which new and novel test methods and technologies can be explored, the ‘Mini Air Blast Tunnel’ (MABT) was recently designed and constructed by AWE. One of the first applications of this facility was to support exploration of methods to engineer blast profiles and scale to larger tunnels; an area of ongoing interest. 18 shots were fired with various configurations of frangible section and/or tunnel blockage to study their effect on the blast profiles obtained. This study was accompanied by complementary analysis employing coupled Fluid-Structure Interaction (FSI). Pressure data recorded during the experimental trial were used to validate the model prior to it being exploited to consider further configurations that were not tested. The analysis revealed the influence of the thickness and strength of the frangible section on pressure-time histories within it, as well as the impact of blockage on increasing load on the test item in addition to the internal radial load applied to the tunnel structure. An overview of the trial and modelling activities will be provided whilst highlighting key similarities and differences between model and test results. The challenges and limitations encountered in the study and its potential future direction will also be discussed.

Abstract: The structural response of materials under dynamic impact loads is crucial in protective design, particularly in applications where energy absorption is a primary concern. This study presents a comprehensive experimental investigation into the energy storage potential of additively manufactured polymeric axial members subjected to high-speed and low-speed impact tests. These axial members were fabricated using additive manufacturing techniques, emphasizing optimizing their structural performance under deformation. The study focuses on assessing the performance of various internal infill geometries to enhance energy dissipation during impact loading. A series of tests was conducted to evaluate the members' capacity to absorb impact energy and to compare their performance under varied strain rates. The findings indicate that specific infill patterns significantly improve energy absorption capabilities, making them suitable for applications involving blast and impact-resistant designs. Furthermore, the results demonstrate that careful optimization of the internal structure of 3D-printed elements can effectively reduce the adverse effects of dynamic loads, making them a promising option for protective structures. The findings contribute to a broader understanding of material behavior at high strain rates, provide valuable guidance for designing lightweight, impact-resistant components, and provide new perspectives on utilizing innovative materials and manufacturing techniques to enhance structural resilience in demanding environments.

Abstract: The existing impact absorbing liner for a commercialized helmet, mostly made by expanded polystyrene (EPS) foam, do not fully prevent head and neck injuries, due to unable to withstand high impact during collisions. This paper proposes an innovative structure that enhance the impact absorbing abilities without neglecting the scratch resistance of a helmet liner. A sandwich structure using pyramidal lattice core, with vertical strut member was designed using SolidWorksTM software. The sandwich structure was fabricated using fused deposition modelling (FDM) with Polyamide-12 (nylon) filament for its heat and scratch resistance, and lastly filled with EPS foam through an EPS spray. Through observation, the printing result showed that no cracking and deformation issues during printing process. Finite element analysis (FEA) is then carried out using Ansys Workbench Software to test the designed sandwich structure model under a impact loading. The same testing was also conducted on a full EPS model to compare the impact absorbing behavior and efficiency of both structures. Under a simple collision with 10m/s hard surface, the results demonstrate that the new liner design absorbed impact more effectively, which reduces the force transferred to the rider’s head. Also, the sandwich structure model successfully dissipated the impact energy and spreaded to each lattice structure evenly, while the full EPS model only transmit the impact energy to the edge of model. However, further testing is needed to assess factors like weight, comfort, and cost before commercial implementation

Abstract: Sandwich panels are widely used in engineering applications due to their advantageous combination of lightweight and high strength. However, their long-term mechanical performance under repeated loading highly depends on the internal lattice structure. This study experimentally investigates the behavior of SLA-manufactured sandwich panels with different lattice geometries under cyclic loading conditions. Various lattice configurations were designed and subjected to repeated compressive loads while monitoring stress relaxation and mechanical deformation over time. The results demonstrate that lattice geometry significantly affects load-bearing capacity and energy dissipation. Notably, structures incorporating vertical support members exhibited higher energy absorption, whereas those without vertical supports, such as M4 and M5, showed improved resistance to stress relaxation over multiple cycles. Furthermore, while all specimens experienced load reductions after 25 cycles, the magnitude of these reductions varied based on the lattice configuration, with M3 exhibiting the highest load decay. These findings contribute to optimizing lattice-based sandwich structures for enhanced durability and mechanical efficiency in engineering applications.

Abstract: Recent research on the progressive collapse of buildings has mainly focused on load redistribution following member failure, commonly referred to as “re-distributional progressive collapse”. However, “impact-type progressive collapse” remains less explored. This mechanism, often triggered by dynamic events such as falling debris or fire scenarios, introduces complex interactions that are difficult to capture using traditional quasi-static models, leaving a significant gap in our understanding of how impact-type progressive collapses occur. This study aims to bridge that gap by investigating the impact forces generated between concrete bodies of various geometries through an experimental campaign. Spherical, semi-spherical, and cubic concrete samples were dropped onto a fiber-reinforced concrete plate from controlled heights. A high-speed camera captured the impact for detailed analysis, while parameters such as impactor mass and velocity, contact radius, and concrete compressive strength were systematically varied. Using advanced data processing techniques, namely Variational Mode Decomposition (VMD), results showed that a 73% increase in impact velocity led to a 75% rise in maximum contact force. Geometry had a significant influence, with spherical and semi-spherical specimens generating up to 64% higher forces than cubes of equal mass. In contrast, compressive strength had a minor effect, raising contact force by only 9% despite a 50% strength increase. High-speed camera footage confirmed more concentrated impacts for spherical shapes, while no notable differences were found between spherical and semi-spherical specimens of equal weight but different contact radii.

Abstract: Ultra-high molecular weight polyethylene (UHMWPE) laminate composites are widely used in impact-resistant structures due to their high specific strength and exceptional energy absorption capabilities. However, previous studies encountered challenges in characterizing the tensile properties of UHMWPE composites, including specimen slippage, stress concentrations, and failures outside the gauge length. This work presents the design and development of an interchangeable clamp for the tensile testing of UHMWPE composites. This clamp guarantees secure gripping and uniform load transfer across the UHMWPE specimens. The developed clamp can be used interchangeably in quasi-static and high-strain-rate devices, facilitating the evaluation of a broad range of strain rates. The tensile properties of two UHMWPE composites were subsequently assessed using this clamping system, with strain measured through three-dimensional digital image correlation (3D-DIC). The effectiveness of a 3D-DIC technique for measuring strain in the UHMWPE composite is demonstrated. The tests reveal that the designed clamp enables reliable measurements, with tensile strength values reaching approximately 1300 MPa. The measured tensile properties are useful for the input data of numerical simulations, providing valuable insights for developing highly efficient protective structures.

Abstract: The article summarizes the results of comprehensive theoretical and experimental studies of ice fracture under shock and explosive loads. Artificial ice and freshwater river ice were considered as objects of research. The results of full-scale underwater explosive tests are presented. Post-explosion analysis of the crushing of a 130-day ice sheet, including the morphology of destruction and diameter and state of the ice edge were obtained. The results of a five-layer ice target impacted by a low-velocity striker showed that a brittle fracture mechanism was dominant. A phenomenological model of ice destruction is briefly described. The model was a complex one of continuum mechanics and was based on fundamental conservation laws. The ice failure concept was based on a deterministic approach and the combined use of several failure criteria. The finite-element Lagrangian method contained a new method for isolating the discontinuity surfaces of materials. The calculations were carried out using the noncommercial software package Udar.Os.1. The impact of an ice cylinder on a rigid wall (aluminum plate) was simulated. Good agreement was obtained in terms of the morphology of the fracture and the velocity of the fracture wave. The contact surface algorithm was illustrated, which helped save computational time when modeling some problems of perforation and penetration, including the detonation process. In the numerical experiment, ice without phase transitions with averaged mechanical properties was considered. The impact response of the ice blocks to the shock and explosive load was simulated. The perforation of structures consisting of ice cubes and thin steel plates above and on them is simulated. Deep penetration of the steel sphere into an ice block and an ice block protected by a metal plate was simulated. Using numerical modeling, the location of explosive substances for the most effective fracture of thick ice was determined.