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The response of polycrystalline nitinol with solely austenite structure was studied in three series of planar impact tests characterized by loading of the nitinol samples of 0.5–10 mm thickness by 1 mm thick aluminum impactor accelerated up to velocities of about 387, 429, and 567 m/s. In all the tests, the velocities of the free surfaces of the samples were monitored by a laser velocity interferometer. It was found that in all three test series, the amplitude of elastic precursor wave, being initially greater than 4 GPa, rapidly decays with the propagation distance down to ∼2.5 GPa, below which the decay is hindered by atomic clusters of the nanometer size. Based on the part of the velocity histories indicating the shock-induced austenite–martensite transformation, the initial, of about 2.5 × 103 s−1, and the maximum, up to 1 × 105 s−1, rates of the transformation were determined. As well, the impact stress slightly greater than 4 GPa was determined as that required for the onset of the B2 → B19′ transformation under shock loading. The unloading parts of the same velocity histories allowed a rough estimate of the fraction of the shock-transformed martensite and the elucidation of the virtually complete reversibility of the transformation. [ABSTRACT FROM AUTHOR]

The response of plane-parallel 2 mm thick samples of 47.3Ni-52.7Ti alloy was studied in two series of planar impact tests at temperatures between 300 and 473 K and between 473 and 318 K (heating to 473 K followed by cooling). In two additional series, the samples of 0.4–4 mm thickness were tested at 300 and 338 K (after preheating up to 473 K). In all the tests, the samples were loaded by 1 mm thick copper impactors having velocities equal to 314 ± 2 m/s. The velocity of the rear sample surface was continuously monitored by a laser Doppler velocimeter. It was shown that substantial, by an order of magnitude, variation of Hugoniot elastic limit σ H E L and compressive strength Y of the nitinol with temperature are caused by the martensite–austenite transformation and its reversal. The variation of the dynamic tensile (spall) strength σ s p of the nitinol along the heating–cooling path was found similar to that of σ H E L although the difference between σ s p values of austenite and martensite, ∼20%, is much more modest than in the case of σ H E L . The test series performed at constant temperatures with samples of different thicknesses allows one to conclude that the plastic deformation in shocked austenite is presumably realized by dislocation motion and multiplication controlled by phonon viscosity. In the shocked martensite, the plastic deformation mechanism at a stress lower than ∼0.3 GPa is likely a thermally activated combination of deformation twinning and slip of kinking dislocations. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the impact response of composite laminates made with conventional and bio-based epoxy resin. Drop tower impact tests were conducted at varying energy levels, including repeated low-energy impacts, to evaluate perforation resistance. The laminates' residual strength and damage tolerance were assessed using the Damage Index (DI) and by analysing the resonance frequency variations through the Impulse Excitation Technique (IET). The study demonstrates a strong correlation between the DI and the resonance frequencies of the specimens, suggesting that IET can effectively track damage progression in composite laminates. Bio-based resin laminates exhibited higher energy absorption at perforation and lower damage progression during repeated impacts due to the higher ductility of the resin. This method of using resonance frequencies to assess impact damage progression directly in composite laminates throughout the IET technique has not been previously reported in the literature. [ABSTRACT FROM AUTHOR]

This study investigates the impact of localization on a carbon fiber-reinforced polymer (CFRP) composite plate, considering the operating temperature of the composite structure. A multiplexed fiber Bragg grating (FBG) sensor, utilizing a cross-correlation-based impact localization algorithm, was employed for this purpose. This algorithm primarily depends on the shape of the impact response wavelength and is minimally affected by temperature variations. The study validates the effectiveness of the cross-correlation-based impact location detection technique with temperature compensation within the operational temperature range of composite structures. Results demonstrated that the algorithm successfully estimated the impact location for each of the 10 impact points at temperatures of −20, 0, 20, and 40 °C. Out of 40 impact points, 33 were accurately estimated under the given temperatures, with a total average error of 3.30 mm, which is significantly lower than the predefined grid size of 80 mm, equating to an error rate of 4.13%. Therefore, the cross-correlation-based impact localization algorithm has proven to be a promising tool for impact monitoring systems in composite structures under various temperature conditions. [ABSTRACT FROM AUTHOR]

Mailing campaigns are a way to keep longitudinal survey respondents engaged. While mailings usually include a survey answer request, sometimes respondents are contacted between-waves to update contact information or simply to keep respondent contact. Research on the actual impact of these between-wave contacts on response rates is scarce. This paper addresses three research questions: (1) Do between-wave campaigns impact response rate? (2) Does the addition of non-monetary incentives to between-wave campaigns further impact response rates? (3) Do between-wave campaigns also affect other members of the household? Following a one-year break between survey waves, we design a randomized survey experiment assigning respondents to five treatment conditions. Results show that keeping-in-touch mailings did not significantly increase the likelihood of an interview in the National Educational Panel Study for either children or their parents in general. However, when we focus on specific characteristics of the targets, significant differences are found. [ABSTRACT FROM AUTHOR]

Integrating scrap rubber particles as fillers into polymer matrix composites offers a cost effective and environmentally sustainable pathway to manage tyre waste through the creation of value-added products. This research explores the low-velocity impact (LVI) response and compression after impact (CAI) properties of rubberised foam-core glass fibre-reinforced epoxy (GFRE) sandwich composites. Syntactic foam cores integrated with rubber particles were manufactured using vacuum-assisted resin transfer moulding (VARTM). The compression properties of rubberised foam core, vital for resisting impact damage during LVI, were examined. Results show more than 40% reduction in compression strength and modulus of the syntactic foam upon the inclusion of 33 wt.% rubber particles. The LVI response and residual compression properties of rubberised foam-core composites were also evaluated. Rubberised foam cores caused a marginal reduction in the peak impact force and led to approximately 60% reduction in the delamination area. The pre-impact compression strength was unaffected by rubber particles within the core as the GFRE face sheets carried most of the compression load. Post-impact compression strength was slightly higher in rubberised foam-core composites due to reduced delamination. Digital Image Correlation (DIC) analysis tracking of the strain evolution during CAI experiments revealed the stress-raising effect of the impact damaged region. This study showcases sustainable scrap tyre management through the inclusion of rubber particles into foam-core composites without substantially reducing in-plane compression properties before or after low-velocity impact. [ABSTRACT FROM AUTHOR]

This study examined the flexural and impact responses of sandwich panels with honeycomb core and hybrid fiber-reinforced composite skins. The influence of laminate composition and thickness on these mechanical properties was investigated. Carbon, glass, and Kevlar fibers were employed in various combinations to fabricate the composite skins. The findings revealed a general trend of increasing flexural strength, modulus, and toughness with rising laminate thickness. However, the laminate configuration exerted a significant influence. Configurations with a higher carbon fiber content exhibited superior strength but reduced strain (ductility). Conversely, configurations incorporating glass or Kevlar fibers demonstrated enhanced ductility at the expense of strength. Overall, configurations utilizing dry carbon fabric skins achieved the highest flexural strength and toughness, while the combination of carbon and glass fibers offered a desirable compromise between strength and ductility. Regarding impact resistance, configurations with solely carbon fibers initially showed the best performance. However, configurations employing a combination of carbon and glass fibers exhibited a noteworthy increase in impact strength with increasing laminate thickness. This observation suggests that the inclusion of glass fibers alongside carbon fibers provides a well-balanced combination of strength and energy absorption capability. [ABSTRACT FROM AUTHOR]

The article "Mechanical testing of miniature carbon fiber reinforced polymer (CFRP) samples under digital light microscopy" explores the challenges of testing CFRP materials due to their composite nature and anisotropy. The study uses miniature sample testing and in situ mechanical testing techniques to understand the mechanical properties of CFRP at a micro-level. The research reveals insights into failure mechanisms specific to CFRP, such as delamination, matrix cracking, and fiber pull-out, providing a foundation for optimizing CFRP design and manufacturing for enhanced durability. The study was conducted by researchers from various institutions in Russia and published in the journal Fracture and Structural Integrity in 2025. [Extracted from the article]

This work aims to investigate the effect of a wide range of oblique impacts of the 7.62-mm-caliber projectile on the slim high-performance fiber-reinforced concrete (HPFRC) panels. The trajectory of the projectile, the depth of penetration, and the extent and type of plate damage are discussed in detail. The numerical models developed in commercially available software are also included in this work to support and supplement the experimental data. In the model, each fiber is modeled separately, leading to a more realistic prediction of the material behavior. The analyses identified four basic scenarios for projectile impact: total plate perforation by the projectile core, core penetration combined with or without rear HPFRC material detachment, and ricochet. The results show that the numerical model can effectively and accurately predict the impact response and damage morphologies of the slim HPFRC panel. [ABSTRACT FROM AUTHOR]

A novelty FG honeycomb-reinforced laminate (FGHRL) with viscoelastic material is constructed for an industrial exoskeleton. The study examines how FGHRL dissipates energy under hygrothermal conditions. Low-velocity impacts on the exoskeleton's load-bearing structure are simulated using a spherical object. Parameters for the FGHRL, made of a two-phase material, are estimated using the Halpin-Tsai model and macroscopically uniform theory. In-plane deformations are determined using Reddy's HSDT, while the impact response is evaluated with Newmark-β and Wilson-θ methods. Energy dissipation properties are calculated using the energy balance model, validated through CUF-based FEM and LS-DYNA explicit solution, and factors influencing energy dissipation are investigated. [ABSTRACT FROM AUTHOR]

In this study, the impact response of sandwich composites with four different metal reinforcement weight ratios (0%, 3%, 5%, and 10%) under single and repeated low-velocity impact loads was investigated. The permanent deflection did not occur at the energy level of 10 J, but it occurred at higher energy levels. Increasing the temperature has a significant effect on the repeated impact strength of the sandwich composites with metal reinforcement, similar to the sandwich composites without metal waste reinforcement. The low-velocity impact test results indicated that the number of impacts causing full perforation decreased as the impact energy levels increased. [ABSTRACT FROM AUTHOR]

Asymmetric sandwich panels (ASPs) with tapered transitions are effective configurations for connecting them with other structural elements. However, fiber reinforced composite panels are susceptible to impact events and thus it is imperative to gain a comprehensive understanding of the impact failure mechanisms of ASPs. This article investigates the failure mechanisms of ASPs subjected to low-velocity impacts experimentally and numerically. Low-velocity impact tests are conducted at two energy levels to induce barely visible impact damage (BVID) and visible impact damage (VID). A non-linear finite element (FE) model is developed to elucidate the damage behavior and failure mechanisms of ASPs. The numerical results are compared with experimental data to validate the FE model. Additionally, a parametric study is undertaken to explore the failure mechanisms of ASPs subjected to penetration. This study also investigates the influence of impactor diameter, impactor angle, foam core thickness, face sheet stacking sequence, and face sheet thickness on impact response through numerical simulations. The reported results hold potential significance for safety design ASPs. [ABSTRACT FROM AUTHOR]

Numerical simulation is significant for investigating impact performance of functionally graded SiCp/Al6061 composite plate. Existing numerical studies rely on stress–strain characteristics derived from theoretical models which hardly consider damage softening and porosity effect. In this work, an effective modeling method is developed to generate geometric models of representative volume elements (RVEs) of SiCp/Al6061 composites. It avoids the limitations of traditional methods in generating RVEs with high ceramic content. Finite element (FE) models for uniaxial compression of RVEs are established with consideration of elastoplastic behaviors of constituent materials and interfacial damage. Stress–strain curves of SiCp/Al6061 composites are obtained from FE simulation results by a homogenization method. The stress–strain curves can reproduce the damage softening, and the predicted elastic moduli agree well with those estimated by Mori–Tanaka theory. Low-velocity impacts of a functionally graded SiCp/Al6061 composite plate are simulated using the stress–strain curves. The simulation results are close to those using stress–strain curves obtained by a theoretical method, however, overestimate contact forces in comparison with experimental results. Novel porous RVE FE models are further developed to consider the porosity effect. The models give an improved prediction for stress–strain characteristics of the composites and low-velocity impact response of the functionally graded composite plate. [ABSTRACT FROM AUTHOR]

Impact problems have always been a field of interest for researchers because of their wide application in industries, especially in producing protective structures in defence. In the present study, finite element analysis is used to analyze the ballistic performance of monolithic and double-layered plates against cylindrical projectile with different nose shapes, viz. trapezoidal and flat-nosed, using a dynamic temperature displacement explicit analysis in the commercial finite element software ABAQUS. Further, the study compares the ballistic resistance (BR) of plates with different thicknesses (6, 10, and 12 mm) against the same configuration of projectiles. The Johnson–Cook (JC) constitutive strength and damage model characterizes the target and projectile material behavior. Mie–Grüneisen equation of state describes the material behavior of projectile and target under high pressure. The impact response of the target is compared in terms of plate deformation, ballistic limit velocity, and failure pattern of targets during impact. The monolithic plate has 2.42% higher impact resistance than the double-layered plate for the trapezoidal-nosed projectile, while for a flat-nosed projectile, double-layered plates have 9.42% higher BR than the monolithic plates. Moreover, the BR of plates (6, 10, and 12 mm) for flat-nosed projectiles is found to be 7.94, 5.56, and 4.59% higher than trapezoidal-nosed projectiles. [ABSTRACT FROM AUTHOR]

ABSTRACT Molecular dynamics (MD) and the material point method (MPM) are both particle methods in spatial discretization. Molecular dynamics is a discrete particle method that is widely applied to predict fundamental physical properties and dynamic materials behaviors at nanoscale. The MPM is a continuum‐based particle method that was proposed about three decades ago to simulate large‐deformation problems involving multiphase interaction and failure evolution beyond the nanoscale. However, it is still a challenging task to validate MD responses against the experimental data due to the spatial limitation in impact and/or shock tests. The objective of this investigation is therefore to compare the MPM and MD solutions for the impact responses of porous solids at nanoscale. Since the governing equations for MD and explicit MPM are similar in temporal domain with different spatial discretization schemes, the MPM solutions could be verified against the MD ones, and the MD solutions might then be indirectly validated against the MPM ones as validated beyond the nanoscale. Since both MD forcing functions and MPM constitutive modeling are well‐formulated for metallic solids, we report a comprehensive comparative study of 40×40×40nm$40\ \times \ 40\ \times \ 40\ {\mathrm{nm}}$ porous and non‐porous gold cubic targets impacted by full density non‐porous gold cubic flyers using the MPM and MD, respectively. The overall deformation patterns and particle‐velocity histories are demonstrated and analyzed, as obtained with the two particle methods. It appears that the MD and MPM solutions are consistent in capturing the physical responses, which shows the potential of using the MPM for multiscale simulations of extreme events involving porous solids, such as underground penetration and space exploration. In addition, MD solutions might be indirectly validated against the MPM ones for evaluating geological responses to extreme loadings, which provides an alternative route for multiscale verification and validation. [ABSTRACT FROM AUTHOR]

AbstractThis study investigates the impact response of bio-inspired helicoidal laminated composite plates under soft body impacts using the SPH methodology in ABAQUS. Impacts at velocities of 50 m/s, 100 m/s, and 200 m/s are analyzed for different helicoidal schemes. The model is validated against existing literature, and damage is evaluated using the Hashin failure model. Helicoidal laminates exhibit less damage than cross-ply and quasi-isotropic laminates. Damage increases with impact velocity, becoming severe at 200 m/s, with significant vibrations. The study highlights the superior performance of helicoidal laminates under high-velocity impacts. [ABSTRACT FROM AUTHOR]

Advances in the development of additive manufacturing materials (AM) and the low availability of studies on the impact response of AM specimens are the main reasons for this paper. Therefore, the influence of building orientation (vertical and horizontal) and the angle of the raster (15°/−75°, 30°/−60°, 45°/−45°, and 0°/90°) on the tensile and impact strength of AM specimens was investigated. The polylactic acid (PLA)-PolyMax, Mediflex and acrylonitrile-butadiene-styrene (ABS) filaments were chosen to provide a comprehensive characterization of AM materials with versatile mechanical properties. The experimental results of this study show that the tensile strength and toughness of PolyMax PLA specimens are comparable to ABS specimens, while Mediflex samples are characterized by their higher toughness, but lower impact force needed to break the samples. The Mediflex Charpy fracture surfaces exhibit a ductile character compared to those of brittle ABS and PLA. Furthermore, fracture surface morphology shows the allocation of voids, which helps us to understand differences in mechanical properties, and allows one to properly interpret the results of the geometrical accuracy of AM specimens with various printing settings. [ABSTRACT FROM AUTHOR]

Numerical simulation has great potential to provide a more comprehensive understanding of human impact response to injury mechanisms. Finite Element (FE) models are used as a tool to study human injuries in greater detail, for example, the THUMS (Total Human Model Safety of TOYOTA) model, which is widely used as a reliable human model in different fields to predict human injuries such as fractures, internal organ damage, and brain tissue injuries. However, no available FE model can be used to simulate human‐robot collisions based on standards ISO/TS 15066 and the biomechanical characteristics of human soft tissues in vivo. The authors have developed a head model based on the structures (dimensions and anatomy) of the THUMS head model, specifically designed to simulate impact loads on the masticatory muscles. Based on medical imaging (MRI) data, the soft tissues at the location of the masticatory muscles in the THUMS head are transformed from monolayer to multilayer, that is, a composite geometry of skin‐fat‐muscle each with its own material model and parameters. The model was optimized and validated using the experimental data from the Fraunhofer IFF subjects study, which determined biomechanical thresholds for specific body locations in ISO/TS 15066 under dynamic collisions. [ABSTRACT FROM AUTHOR]

This study analyzes the impact mechanical response of sandwich structures with foam and wood cores through experimental and numerical methods. The aim is to determine whether a sustainable core material, such as cork wood, can serve as a reliable alternative to the commonly used Polystyrene (PS) foam core in sandwich structures. Impact experiments were conducted at varying energy levels using an INSTRON CEAST 9350 drop tower, demonstrating the superiority of sandwich structures compared to single-material alternatives. Numerical models were developed in ABAQUS, where glass fiber reinforced polymer (GFRP) composite panels were represented using solid element C3D8R and the 3D Hashin failure criteria, which were incorporated via the user subroutine VUMAT. The results indicate that the contact force of the sandwich structure with a wood core surpassed that of the foam core counterpart. In both sandwich structures, damage initially occurred at the impact point on the surface, leading to plastic deformation and damage within the core, while the composite panel on the rear surface ultimately failed. These findings provide valuable insights for designers, enabling parametric studies to select appropriate core materials that enhance the impact resistance of sandwich structures. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Nanchang University (Engineering & Technology) is the property of Nanchang University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Several composite sleeper technologies have been developed, possibly allowing the railway sector to replace wood and concrete sleepers. Although high-magnitude impact loads can occur on the railway track and sleepers due to wheel/rail abnormalities or train derailment, the behaviour of these sleepers under impact loading has not yet been well understood. In this paper, a high-energy drop hammer facility was utilized to investigate the impact behaviour of a polymeric composite rail sleeper made of high-density polyethylene (HDPE) and unidirectional glass fibre reinforced plastic (GFRP). Quasi-static tests and high strain rate tests were conducted on the materials at room and low/high temperatures to gain more insight into the effects of the temperature and strain rate on the mechanical properties of the HDPE and GFRP made of virgin resin. The results suggest that both materials exhibit strong viscoelastic plasticity, temperature softening, and strain rate-hardening effects. High strain rate and low temperature made the GFRP material extremely brittle and prone to develop cracks. Due to the temperature and strain rate dependency of the thermoplastic materials of the sleepers, in addition to impact tests at room temperature (~23°C), impact tests were also performed at low temperatures (~ minus 30°C) on the sleepers. The findings suggest that low-temperature impact assessment should be considered for all polymeric sleepers (to be installed in regions having extremely low temperatures) since these low temperatures affect the ductility of polymers, decreasing the ultimate impact load-bearing capacity of composite sleepers. [ABSTRACT FROM AUTHOR]

Chest injuries are commonly encountered in traffic accidents, with ribs playing a crucial role in chest impact response. This study focuses on the damping performance of ribs and its influence on chest response during collisions. Employing mechanical bionics principles, the mechanical equivalence of ribs under collision impact was determined. Consequently, a rib impact dynamic model based on equivalent damping theory was developed. This model was integrated with a rib drop hammer impact test system, yielding a numerical solution for the equivalent damping ratio of the rib, quantified as 0.085. Additionally, to validate the accuracy of the rib impact dynamics model, a verification method based on the half-power bandwidth method was proposed. Through the implementation of the rib force hammer impact test, the equivalent damping ratio was determined to be 0.093, showing an 8.6% deviation from the result of the impact dynamics model. These findings not only confirm the validity of the rib equivalent damping theory within the impact dynamics model but also provide theoretical support for the design and improvement of dummy ribs and, potentially, the overall development of crash test dummies. [ABSTRACT FROM AUTHOR]

Ti matrix composites (TMCs) are promising structural materials that meet the increasing demands for light weight the automobile and aircraft industries. However, the room temperature brittleness in the traditionally homogeneous reinforcement distribution of TMCs limits their application in high-strain-rate impact environments. In the present study, novel bilayer TMCs with hierarchical microstructures were designed by the laminated combination of graphene nanoplatelet (GNPs) reinforced TC4 (Ti-6Al-4V) composites (GNPs/TC4) and a monolithic TC4. Meanwhile, the configuration of the microstructure, impact performance V50, and deformation modes of the bilayered TC4-(GNPs/TC4) plate was investigated. The plates were fabricated via field-assisted sintering technology (FAST). It turned out that the TC4-(GNPs/TC4) plate with a 7.5 mm thickness against a 7.62 mm projectile exhibited greater impact performance (V50~825 m/s) compared to the TC4 and GNPs/TC4 single-layer plates. The plate failure modes were dependent on the microstructure while the failure behaviors seemed to be influenced by the hierarchical configuration. This work provided a new strategy for utilizing TMCs in the field of high-strain-rate impact environments. [ABSTRACT FROM AUTHOR]

This paper investigates the low-velocity impact response and damage behavior of glass fiber reinforced polymer (GFRP) hollow ribbed emergency pipes of our design under different impact heights. Drop hammer impact tests with impact velocities of 8.41 m/s, 8.97 m/s, and 9.50 m/s were conducted using an impact platform. A progressive damage model for low-velocity impact was developed using Abaqus/Explicit finite element software. The model used the three-dimensional Hashin damage initiation criteria and a damage evolution model based on the equivalent strain method to simulate the initiation and evolution of intralaminar damage in the pipe ring. A cohesive zone model (CZM) based on a bilinear traction-separation law was used to simulate delamination. The results show that the pipe rings experienced fiber or matrix fractures and delamination damage during the impact process. Additionally, the pipe ring specimens underwent bending vibrations under the impact load, leading to fluctuating contact forces at all three impact heights. Analysis of the simulation results reveals that the primary damage modes in the GFRP hollow ribbed emergency pipe are fiber tension damage, matrix tension damage, and fiber compression damage, with delamination occurring mainly in the impact area and the interface area on both sides of the rib. [ABSTRACT FROM AUTHOR]

This study presents a novel hybrid‐sandwich composite structure, customized for nose radomes applications, incorporating a foam core and distinct opposite face sheets composed of Kevlar and S‐Glass materials. Addressing in‐phase electromagnetic properties, UV protection and low velocity impact responses in our previously published work, this paper empirically and numerically investigates the damage tolerance response of the proposed structures through compression after impact (CAI) testing. The low velocity impacts (LVIs) on S‐Glass face sheets exhibited unique energy dispersion and absorption mechanisms, resulting in variations in indent damage depths and widths across all impact energy levels as compared with LVIs on Kevlar face sheets. After experimentally assessing the CAI behavior, a FE model is developed to predict CAI behavior, which closely aligned with experimental findings. This study, unprecedented in existing literature, proposes hybrid sandwich structures for nose radome aerospace applications, with superior specific impact and residual strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes. Highlights: Innovative composites with superior low velocity impact response, tested for compression after impact performance.Designed for nose radomes found suitable for other impact prone applications.Experimental and numerical modeling showed comparable results.Major differences observed in damage mechanics, resistance, and tolerances. [ABSTRACT FROM AUTHOR]

In this study, we address the challenge of hidden damages in FRP composites, such as delamination, matrix cracking, and fibre breakage resulting from transverse low-velocity impact (LVI)—damages often elusive on the surface. Our methodology operates at the meso-scale, depicting laminates as stacked homogenized plies incorporating interfaces. To capture the mechanical behaviour and damages, we extend an existing nonlinear mean-field debonding model (NMFDM), accommodating asymmetric matrix plasticity (AAMP), fibre–matrix interface debonding failure, and in-plane progressive failure. In a key enhancement, we introduce a strain rate term to the AAMP model, addressing strain rate effects associated with LVI loading. Additionally, we incorporate a novel strain-driven 3D failure criteria, offering a more precise assessment of progressive failure subjected to LVI loading. The interfaces between plies are modelled using surface-based cohesive behaviour to capture interaction phenomena. To validate the developed NMFDM, we conduct impact simulations at various energies on a UD composite laminate consisting of AS4/8552 carbon fibre and epoxy matrix. These simulations showcase the predictive capability and accuracy of the NMFDM in capturing the intricate behaviour and damage progression of UD composites subjected to LVI. [ABSTRACT FROM AUTHOR]

Current reports on accidents in urban areas reveal the devastation of boundary walls and the consequent risks to human lives and property damage. The present study proposes to mitigate such risks through the development and application of a robust and shock-absorbent composite wall system to replace the normal concrete wall system. The paper adopted a comprehensive Finite Element (FE) study using ABAQUS and used the three-dimensional validated model to initially evaluate the selected four different innovative wall systems (Polypropylene fibre-reinforced composite, ECC-Concrete, ECC-Rubberised concrete, and Rubberised concrete-Concrete composite walls) to evaluate their structural performances under lateral impact and blast loads. The most suitable composition of the wall system is identified after comparing the impact resistance, blast resistance, and the energy absorption capacity of all the selected wall structures. Then, an optimisation study on the best-performed composite is conducted to propose the most appropriate geometric parameters for the composite wall. ECC-Rubberised concrete composite wall shows the least deflection at the selected magnitudes of impact loads and blast loads compared to the other walls. The energy absorption capacity of the ECC-Rubberised concrete composite wall is the highest among all the walls including the normal concrete wall. [ABSTRACT FROM AUTHOR]

The all-CFRP sandwich structure with ultralight honeycomb is designed and manufactured by stretching process. Two scenarios, including global and local impact, are considered to reveal the characteristics of impact resistance. The effects of different impact energies and core densities on energy absorption and failure mechanism are thoroughly discussed. Meanwhile, the post-impact residual compressive strength is carried out to evaluate the influence of impact on structural strength and stability. The results show that under the global impact, the impact resistance is related to core density, and the energy absorption is mainly from honeycomb core. While under the local impact, as the impact energy increases, the failure mechanism of the structure changes from core crushing to penetration. The research provides a guidance for low-velocity impact performance and structural optimization design of sandwich structures. [ABSTRACT FROM AUTHOR]

Subcritical damage in sandwich panels refers to damage that occurs in the skins or core of the panel due to loading below the ultimate strength of the materials, and it can reduce the strength and durability of sandwich panels, leading to premature and unpredicted failure. In this work, a computational tool was developed for designing sandwich structures and optimizing their subcritical impact response. The model was validated experimentally on sandwich panels comprising an aluminium honeycomb core with carbon fiber reinforced epoxy skins. The study investigates subcritical damage in aluminium honeycomb and CFRP sandwich panels through mechanical experiments and finite element simulations. A novel computational tool was developed to optimize the impact response of these structures. Experimental validation was performed using standardized tests, and numerical simulations were conducted using Abaqus. Key findings indicate that the developed tool accurately predicts damage and stiffness reduction, offering significant potential for optimizing sandwich panel designs. [ABSTRACT FROM AUTHOR]

This study investigated the low-velocity impact response of titanium-based carbon-fibre/epoxy laminate (TI-CF FML). A comprehensive experimental study was carried out with impact energies ranging from 16.9 J to 91.9 J. Finite element analysis, performed using ABAQUS, was employed to elucidate the failure mechanisms of the laminate. Three distinct damage modes were identified based on the impact energy levels. The energy absorption characteristics of the TI-CF FML were analysed, revealing that maximum energy absorption is achieved and remains constant after penetration occurs. The relationship between impact force and displacement was also explored, showing that the laminate can withstand a peak force of 13.1 kN. The research on the impact resistance, damage mechanisms and energy absorption capacity of TI-CF FML provides an in-depth understanding of the impact behaviour of the laminate and its suitability for various industrial applications. [ABSTRACT FROM AUTHOR]

Previous studies on the dynamic problems of magneto-electro-elastic (MEE) beams mainly focused on the buckling and free vibration, no literature paid attention to the low-velocity impact response problem. More importantly, no one conducted the investigation on the nonlinear low-velocity impact of MEE beams with considering the effect of initial geometric imperfection. To fill this gap, this article aims to study the low-velocity impact problem of MEE beams with initial geometric imperfection. Firstly, the nonlinear Hertz contact law is used to describe the displacement and contact force of the MEE beam, and the initial conditions for the beam and impactor are given. Subsequently, considering the multiple coupling effect, the dynamic model is established through Hamilton's principle. Taking the simply-supported boundary condition into account, the Galerkin principle is utilized to reduce the dimensionality, resulting in a nonlinear equation regarding contact time, lateral central displacement and contact force. Meanwhile, two comparative analyses are conducted to confirm the rationality of the present work. Finally, the Runge–Kutta method is employed to solve the low-velocity impact response, in which the effects of electric potential, magnetic potential, initial geometric imperfection, temperature rise, prestress, damping coefficient, the radius and velocity of the impactor as well as the geometric dimension of the beam are discussed. [ABSTRACT FROM AUTHOR]

In conventional double-hulled submarines, the connecting structures that facilitate the linkage between the two hulls are crucial for load transmission. This paper aims to elucidate the effect of these connecting structures on resistance to shock waves generated by underwater explosions. Firstly, a self-developed numerical solver is built for the one-dimensional water-filled elastically connected double-layer plate model. The shock wave propagation characteristics, shock response of structure, water cavitation, and impact loads transmitted through the gap water and the connecting structures are analyzed quantitatively. The results reveal that the majority of the shock impulse is transmitted by the gap water if the equivalent stiffness of the connecting structures is much less than that of the gap water. Then, a three-dimensional model of the double-hulled, water-filled cylindrical shell is constructed in Abaqus/Explicit, utilizing the acoustic-structural coupling methodology. The analysis focuses on the influence of the thickness and density distribution of the connecting structures on the system's shock response. The results indicate that a densely arranged connecting structure results in a wavy deformation of the outer hull and a notable reduction in both the impact response and strain energy of the inner hull. When the stiffness of the densely arranged connecting structure is comparatively low, the internal energy and plastic energy of the inner hull are decreased by 16.5% and 24.1%, respectively. The findings of this research are useful for assessing shock resistance and for the design of connecting structures within conventional double-hulled submarines. [ABSTRACT FROM AUTHOR]

Based on numerical modelling, this study investigates asymmetric semicylindrical composite laminate shells' damage characteristics under low-velocity impact loads. For this purpose, several asymmetric stacking sequences were subjected to low-velocity impact and the results were analysed in terms of force, displacement, contact time, and absorbed energy. It is concluded that the maximum impact force decreases with an increase in the number of layers oriented at 0°, particularly in the upper half of the laminate. The laminates with a 45° orientation in the upper layers present the lowest displacement values, whereas the laminates with the upper layers oriented at 0° exhibit longer contact times. It is also observed that intralaminar damage is responsible for almost half of the total impact energy, followed by delaminations and friction. Stacking sequences with upper layers at 45° exhibit slightly higher energy dissipation due to intralaminar damage (fibre failure) and interlaminar damage (delamination).

Auxetic metamaterials, known for their unusual properties, are being explored as cores for sandwich structures to improve impact resistance. This study investigated the low-velocity impact response of sandwich panels with various core designs using finite element method (FEM) and experiments on 3D-printed specimens. These cores include pure honeycomb, pure auxetic, and gradient variations with controlled gradients of Poisson's ratio, transitioning from negative to positive (NTP), positive to negative (PTN), negative-to-positive-to-negative (NTPTN), and positive-to-negative-to-positive (PTNTP). These gradients were achieved by adjusting the unit cell angle within the core. Under quasi-static indentation, the gradient PTN design improved energy absorption by 26% compared to the honeycomb structure, while the gradient NTP structure showed a 9% improvement over the auxetic core. As for the impact tests, the gradient NTP and PTN structures significantly enhanced the indentation resistance of auxetic and honeycomb structures by 21.3% and 6.5%, respectively. Interestingly, while the optimal core for peak energy absorption varied with impact velocity, gradient structures generally provided superior energy absorption, particularly at lower velocities. FEM results at initial impact velocities of 10, 15, 20 m/s confirmed that structures having negative Poisson's ratio at their top layer exhibited the lowest penetration depth. Additionally, gradient structures, particularly NTP and NTPTN, demonstrated superior energy absorption capability compared to purely auxetic or honeycomb structures, especially at lower velocities. The study highlights the benefits of utilizing gradient auxetic metamaterial cores in high-performance sandwich structures for impact resistance applications. These structures showed minimal localized damage, reduced densification risk due to uniform crushing, and lower penetration depth. [ABSTRACT FROM AUTHOR]

This research explores the Low-Velocity Impact behavior of thermoplastic composite sandwich panels with 100% recycled Polyethylene Terephthalate (PET) foam sourced from post-consumer plastic water bottles. Being recognized as a reliable technique, hybridization using stainless-steel mesh layers was employed to reinforce the panels' composite facesheets of sandwich panels accessible for modular housing, cold storage rooms and cargo trucks. Adequate impregnation of the reinforcement metallic mesh layer alongside proper skin-to-core adhesion was accomplished by optimizing a two-phase compression molding method. The effect of hybridization on impact response of sandwich panels with two different PET foam core thicknesses, and stacking sequence were evaluated. It was revealed that reinforcing the impacted surface of the composite sandwich panels significantly increased the perforation threshold. Moreover, analyzing the post-impact section view of the samples indicated that hybridization modified the damage propagation response of the PET foam core sandwich composites, through which the energy absorption capacity was improved. [ABSTRACT FROM AUTHOR]

The impact effects of falling rocks on sand–reinforced concrete slab composite protective structures involve several factors. Among them, the existing codes are unable to consider the effect of rockfall shape and the angle of contact between the rockfall and the object on the impact force as well as the depth of penetration. Based on extensive field investigation, this paper proposes a shape factor to simplify the rockfall into an ellipsoid and determines the shape and dimensions of the rockfall by three-dimensional axis length. Besides, a coupled SPH-FEM numerical calculation model is established and validated through comparison with a large-scale outdoor test of a rockfall impact protection structure. Finally, the effects of rockfall shape and impact angle on the symbolic parameters including impact force, impulse and energy in the impact process are revealed. The findings indicate that the maximum force and displacement of the midpoint of the bottom of the reinforced concrete slab have relative errors within 5.0 % when compared to the model test, confirming the precision of the models discussed in this paper. For the same rockfall, the peak force decreases with the impact angle increasing; taking the same volume of spherical rockfall as the reference, under the same rockfall pattern, the peak impact force and impulse amplification factor decreases with the increase in contact attitude angle. Additionally, the scaling effect becomes more pronounced when the shape factor of the rockfall is smaller; under the same shape factor, the impact depth of the cushion layer is the smallest when the attitude angle is 45°, and the maximum when the impact angle is 90°; the SPH-FEM coupling algorithm could reasonably reproduce the pit-forming process of sand and soil, and it is very effective in simulating the flow effect of soil particles under impact.

This study deals with the development of interlayer hybrid composites with improved low-velocity impact response. In the composites produced using the hand lay-up technique, glass, carbon, and Kevlar woven fabrics were used as reinforcement materials and epoxy resin was used as the matrix material. Shear thickening fluid (STF) was impregnated into the fabric for enhancing their performance. The effect of hybridization with different stacking sequences and the impregnation of STF on the peak load, deflection at peak load, energy absorption, impact strength, and damage degree were investigated. All samples were subjected to 3.12 m/s and 4.42 m/s impact velocities using a drop-weight impact tester applying 200J and 400J impact energy levels, respectively. The results revealed that in samples containing neat fabrics, the performances of the pure Kevlar samples were much better in comparison to hybrid samples, especially under high impact energy. However, STF significantly improved the impact strength and energy absorption (up to 30 times) of all samples, including hybrid ones. On the other hand, as the impact energy increased, the use of a Kevlar reinforced plate on the impact surface was crucial, providing higher energy absorption, and no perforation was observed since most of the energy was required to initiate the damage. In the samples with Kevlar in the intermediate layer, however, the majority of the impact energy caused propagation and expansion of the damage. According to the findings, up to 50% cost savings were achieved in STF-impregnated hybrid samples containing Kevlar. [ABSTRACT FROM AUTHOR]

This study analyzes the low-velocity impact response of cantilever sandwich beams with foam cores and carbon nanotube (CNT) reinforced facesheets. Using the fifth-order shear and normal deformation theory, we explore three CNT distribution types through the thickness of the facesheets: uniformly distributed UD, functionally graded-V FG-V, and functionally graded-Λ FG- Λ. The contact force during impact is calculated according to Hertz contact law. Our findings indicate that the FG-V distribution offers the highest contact stiffness, resulting in reduced deflection compared to UD and FG- Λ distributions. Additionally, an increase in the core-to-face thickness ratio leads to decreased deflection and increased contact force, attributed to enhanced beam stiffness. The volumetric fraction of CNTs also plays a critical role, increased CNT content raises beam stiffness, decreasing deflection and enhancing contact force. Furthermore, the impactor's initial velocity directly influences the deflection and contact force, with higher velocities leading to greater deflections due to increased kinetic energy. This comprehensive analysis underscores the significant effects of CNT distribution, volumetric fraction, and geometrical parameters on the dynamic response of sandwich beams under impact conditions. [ABSTRACT FROM AUTHOR]

To investigate the enhancement mechanism of polyurea elastomeric coating on the anti-impact of unidirectional graded auxetic honeycomb sandwich panels. With the help of LS-DYNA finite element analysis software, the dynamic response of the sandwich panel to a cylindrical impact is simulated numerically. The influence of polyurea coating by the method of outline volume analysis position on its anti-impact is first analyzed. On this basis, the effects of impact velocity, impact angle of the cylinder, coating thickness, and coating area of polyurea elastomer on the sandwich panel are further discussed by the method of outline volume analysis. Finally, the polyurea thickness on both sides of the coated polyurea sandwich panel (type C) on both sides is optimized. The results show that the coating of polyurea elastomer can effectively enhance the impact protection performance of sandwich panels. By comparison with sandwich panel of uncoated structure (Type O), type C achieves the best anti-impact, and the maximum post deflection (Defl) is reduced by 61.6%. The increase in impact velocity and the decrease in impact angle will increase the maximum deflection of the sandwich panel if other variables remain constant. When the cylinder impact speed is certain, preference is given to sandwich panels that are thicker, larger, and have polyurea sprayed on both sides. The optimization by the response surface method shows that the sandwich panel with the best anti-impact may be obtained when the polyurea thickness ratio of the impact side to the back side is 1.3:0.7. [ABSTRACT FROM AUTHOR]

The assessment of energy absorption behavior has a vital role in determining suitability of lightweight composites for impact protection applications. This study focuses on evaluating the energy absorption characteristics of cenosphere reinforced epoxy syntactic foam core and jute epoxy facesheet sandwich composite subjected to low velocity impact. The syntactic foam is composed of lightweight cenospheres embedded within an epoxy matrix, resulting in a high‐strength and lightweight composite material. Low velocity impact tests were conducted using a drop tower apparatus to simulate realistic impact conditions. The impact force, energy absorption and damage mitigation of the syntactic foam specimens with varied weight percentage of Cenosphere (0%, 10%, 20% and 30%) were measured and analyzed to assess the energy absorption behavior. The gradation revealed that the weight of top layer when compared to bottom layer is 50.49%, 70.23% and 95.74% less in syntactic foam core with 10, 20 and 30 wt% Cenosphere respectively, indicating gradation. The study demonstrates that the addition of Cenosphere up to 20 wt% enhances the energy absorption capacity of the sandwich composites by 59.37%–93.44% compared to sandwich without Cenosphere reinforced core. However, beyond this threshold, a decline in energy absorption is observed when subjected to low‐velocity impact (LVI). Fractography analysis demonstrates that the incorporation of Cenosphere induces a rough fracture surface with deep river‐like topography, indicative of greater energy absorption during impact loading. This substantiates the conclusion that Cenosphere‐reinforced syntactic foams exhibit enhanced impact resistance, making them promising materials for structures subjected to low‐velocity impact events. Highlights: Development of functionally graded core sandwich composite for low velocity impact applications.Assessing the performance of developed composites under low velocity impact loading.Determining the optimal weight percentage of cenospshere in functionally graded core.Studying the fractography of developed sandwich composites.Corelation between experimental and finite element studies. [ABSTRACT FROM AUTHOR]

Considering the nonlinearity of shear in the mechanics of composite materials, the increase of shear strength when the substrate interface is compressed, and the shear of the matrix itself, the Chang–Chang criterion is improved. The improved Chang–Chang criterion was used to establish a progressive damage model of low‐velocity impact of composites. The low‐velocity impact process of T700/EM134 composite laminates in the energy range from 5 to 10 J was compared by physical tests and finite element simulations, and the calculated impact response curves and material damage were in good agreement with the test results, which proved that the model of the improved criterion was suitable for the damage prediction of low‐velocity impact of composite laminates. Highlight: Consider various situations in composite material shearing.Improved based on the Chang–Chang criterion.Establishing a progressive damage model for low‐speed impacts.Comparison through physical experiments and finite element simulation.Prove that the improved criterion model is suitable for damage prediction. [ABSTRACT FROM AUTHOR]

In previous earthquakes, a significant number of adjacent buildings in a series have been damaged due to collisions. Pounding between adjacent structures in a series causes them to inflict multiple blows on one another, which is a complex type of collision. Previous studies have produced inconsistent or conflicting research conclusions due to various parameters of buildings and excitation. It is challenging to determine a universal law of collision reactions between adjacent buildings in a row. To address the complexity of these parameters, the dimensional analysis method is used. This work establishes a mathematical model for the dimensionless collision response of adjacent structures in a row. The layout of the structures is considered through three different configurations, and the effects of unilateral and bilateral collisions are compared. The analysis also considers the impacts of the frequency ratio, mass ratio and gap size of the oscillators. According to the impact of pounding, the displacement and velocity responses of the outer structures with low mass and stiffness can be divided into multiple spectral regions based on the frequency ratio of the structure and excitation. The effects of the mass ratio and frequency ratio on the responses of the outer flexible structures are correlated with the spectral regions. The results indicate that placing a structure with a small mass and stiffness outside is dangerous, since it causes a much larger pounding force and displacement of the outer structure. Compared with the unilateral impact response, the bilateral impact response induces a smaller displacement of the middle structure with a slight mass and stiffness. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data. [ABSTRACT FROM AUTHOR]